Research at the Institute of Chemistry (IfC)

This page provides an overview of research activities at the Institute of Chemistry. Our institute plays a leading role in different large collaborative research initiatives that are currently underway. Several researchers at our institute contribute as principal investigators (PI's) to collaborative third party-funded research projects, that are not centred at IfC. Thematically, research at our institute is focused on four areas of research. We have an excellent research infrastructure at our hands to pursue timely projects that are documented in numerous publications. We are connected to several non-university research institutes in the Berlin-Brandenburg area through joint appointments, professorships and lectureships.

DFG-Sonderforschungsbereich 1636 Elementary processes of light-driven reactions at nanoscale metals Research groups from the IfC and the Institute of Physics and Astronomy, with participation of PIs from neighbouring institutions, investigate light-driven processes at nanoscale metals with the aim to develop a comprehensive, fundamental understanding of the underlying elementary processes and to establish novel synthetic methods.

Contact at IfC: Prof. Dr. Ilko Bald For further information: https://www.uni-potsdam.de/en/elephant

Evolving polyesters Research Groups from IfC and University of Halle aim at a combination of fundamental and applied research to develop new and improved application perspectives for polyester materials in actual use (one of the most important classes of thermoplastic polymers) as well as new materials and new chemical approaches. The initiative brings together Chemistry, Engineering and biological/environmental sciences.

Contact at IfC: Prof. Dr. Alexander Böker

Subprojects in collaborative research projects

Researchers from our institute regularly contribute to collaborative research projects as principal investigators. This is a selection of subprojects headed by IfC-researchers:
 

Funding source	Program/type of collaborative project	Title of subproject	Duration of project	PIs from IfC-UP
BMBF	InnoProfile Transfer	ALS ComBi Angewandte Lasersensorik in komplexen Biosystemen	10/2012 – 09/2017	Prof. Dr. Hans-Gerd Löhmansröben
BMBF	BonaRes (Modul A, Phase 3)	I4S – Integriertes System zum ortsspezifischen Management der Bodenfruchtbarkeit, Teilprojekt H: Mobile Elementanalytik mittels Laser-induzierter Breakdownspektroskopie	2022 - 2025	apl. Prof. M. Kumke / Dr. T. Beitz
BMBF	Spitzenforschung und Innovation in den neuen Ländern: Impulszentrum für Integrierte Bioanalytik - das Taschentuch¬labor.	Projects 4.3 New Monomers and coupling units, 5.1 Responsive Hydrogels, and 7.1 Chromophore-Functionalized Hydrogel-Forming Polymers	2009-2014	Prof. Dr. André Laschewsky
BMBF	Zukunftstechnologien für die industrielle Bioökonomie: Schwerpunkt Biohybride Technologien	PepTight – Lasst die Biologie ran – Peptide umgarnden entscheidende Rohstoffe: die „natürliche Trennung von Lanthaniden“	2021 - 2024	apl. Prof. M. Kumke, Prof. H. Möller, Prof. A. Böker
BMBF	Verbundvorhaben GET H2 TransHyDE	Luftgestützte Wasserstoffferndetektion	2021 - 2025	apl. Prof. M. Kumke
BMBF	Qualitätsoffensive Lehrerbildung – PSI Potsdam (ZeLB-UP)	Development of competences of teachers in the context of learning individually, use of experiments and new media	06/2015 - 12/2018	Apl. Prof. Dr. B. Duvinage
BMBF	Batterie 2020: FestPoLiS	Herstellung von Hybridpolymerelektrolyten mit kinetisch optimierter Kathode	2023-2025	Prof. Dr. Yan Lu
BMBF	Batterie 2020: SkaLiS	Skalierbare Synthese funktioneller poröser Kathodenmaterialien für Lithium/Schwefel-Pouchzellen	2021-2024	Prof. Dr. Yan Lu
BMBF	OptiPBR: Optische Softsensorik von Algenkultivierungen in großskaligen Photobioreaktioren	Erkennung von mikrobiellen Belastungen und Prozessverfolgung mittels optischer Sensorik und Entwicklung einer Sensorplattform	01/2022 - 12/2024	Prof. Dr. Ilko Bald
BMBF	Unternehmen Region – Meta-ZIK: Optische Zellsensorik und -manipulation (OptiZeD, mit B CUBE Dresden)	Smarte optische Fasern durch Integration von Nanomaterialien	08/2019 - 12/2022	Dr. Claudia Pacholski, Prof. Dr. Ilko Bald
BMBF	Qualitätsoffensive Lehrerbildung – PSI Potsdam (ZeLB-UP)	Development, use and evaluation of materials for hetereogeneous learning groups	01/2019 - 12/2023	PD Dr. J. Hermanns
BMBF	Qualitätsoffensive Lehrerbildung – PSI Potsdam (ZeLB-UP)	Development, use and evaluation of materials and concepts for teaching organic chemistry at university	01/2019 - 12/2023	PD Dr. J. Hermanns
BMWi	AiF - Industrielle Gemeinschaftsforschung	Herstellung, Skalierung und Charakterisierung von Perowskit-Nanopartikeln für die Konstruktion	2021 - 2023	apl. Prof. M. Kumke
BMWi	BMWi-Förderkonzept “Forschung zur Entsorgung radioaktiver Abfälle“	Geochemisch Radionuklidrückhaltung an Zementalterationsphasen – Phase II	2020 - 2023	apl. Prof. M. Kumke
BMWi	AiF-ZIM Förderprogramm – Projektform FuE-Kooperationsprojekte	Entwicklung eines erstmals kovalent gebundenen polymeren und umweltfreundlichen TopCoatings als Schutzschicht für Zinkoberflächen	2016-2019	Prof. Dr. Helmut Schlaad
BMWi/BMBF	SUGAR (Submarine Gashydrate Ressourcen)	SUGAR III: SEDIMENTPARAMETER: Bau einer seismischen Tomografie für den Reservoirsimulator zur Bestimmung der Abhängigkeiten der Wellengeschwindigkeit	2008 - 2018	Apl. Prof. Dr. J. Schicks
BMWi/BMBF	SUGAR (Submarine Gashydrate Ressourcen)	SUGAR II: Optimierung von Verfahren zum Abbau natürlicher Hydratlagerstätten basierend auf Experimenten und numerischen Simulationen	2008 - 2018	Apl. Prof. Dr. J. Schicks
BMWi/BMBF	SUGAR (Submarine Gashydrate Ressourcen)	SUGAR I: Entwicklung einer Simulationsplattform sowie eines Reaktors (im Labormaßstab) zur thermischen Hydratzersetzung	2008 - 2018	Apl. Prof. Dr. J. Schicks
DESY Hamburg	Centre for Molecular Water Science (CMWS)	Projekt im Early Science Program, Pillar 5: The Role of Water in Different Types of Hydrogels: How is Water Determining Functionality?		JProf. Dr. H. Müller-Werkmeister (Pillar spokesperson P5 „Water in the Molecular Life Sciences”)
DFG	Joint DFG-NSFC research project	Hybrid nanostructures based on protein-assembly driven by carbohydrate-protein interactions	2019-2022	Prof. Dr. Yan Lu
DFG	RTG “Bioactive Peptides” (TU Berlin)	Characterization of peptide structure and conformational dynamics by NMR spectroscopy	Since 2019	Prof. Dr. H. Möller
DFG	GRK 2482 MODISC (HHU Düsseldorf): Modulation of Intersystem Crossing	Project D: Science Education and outreach	10/2019-09/2023	Prof. Dr. Amitabh Banerji
DFG	FOR 5538 (with MPI and OVGU Magdeburg, LIKAT and University of Rostock): IMPD4Cat (Multistep Catalytic Production Systems for Fine Chemistry by Integrated Molecular, Material and Process Design)	Optimization of earth-abundant metal-catalyzed oxidation reactions relevant for the synthesis of amino acids (metal-based oxidation reactions)	2023-2027	Prof. Dr. Nora Kulak
DFG		Untersuchung von reaktiven Sauerstoffspezies auf der Nanometer-Skala – Kombination von DNA-Origamis und Ceria-Nanopartikeln	2021 - 2024	apl. Prof. M. Kumke / Prof. I. Bald
DFG	Graduiertenschule, Exzellenzinitiative Bund/Länder	SALSA School of Analytical Science Adlershof GSC 1013/1	11/12 – 10/19	Prof. Dr. Ilko Bald, Prof. Dr. Heiko Möller, Prof. Dr. Hans-Gerd Löhmansröben
DFG	Forschungsgruppe	InChem FOR 2177	01/18 – 08/22	Prof. Dr. Hans-Gerd Löhmansröben
DFG	SPP 2248 “Polymer-based batteries”	Electrochemical Construction of Functional Conducting Polymers as Free-Standing Cathode for Li-S Batteries: Synthesis, Operando Analysis, and Simulation	2021-2023	Prof. Dr. Yan Lu
DFG	IUPAC International Pilot Call “Novel Polymer Synthesis and New Supramolecular Polymer Assemblies”	Synthesis and properties of glycopolypeptide biohybrid materials	2011-2014	Prof. Dr. Helmut Schlaad
DFG	SPP 1708 (Materials Synthesis near Room Temperature)	ILPIN: Ionic Liquid Precursors for Multicomponent Inorganic Nanomaterials	2014 - 2020	Prof. Dr. Andreas Taubert; Prof. Dr. Peter Saalfrank
DFG	SPP 1569 (Generation of Multifunctional Inorganic Materials by Molecular Bionics)	SpiderMAEN: Recombinant Spider Silk-based Hybrid Materials for Advanced Energy Technology	2012 - 2019	Prof. Dr. Andreas Taubert
DFG	Priority Program SPP 1259 Smart Hydrogels	Project "Structure and Kinetiks of Stimuli-responsive, Thin Hydrogel Films Made of Amphiphilic Block Copolymers"	2006-2013	Prof. Dr. André Laschewsky
DFG	GRK 1582 (FU and HU Berlin): Fluorine as a key element	Fluorinated and perfluoroalkylated pyrrole- and pyridine ligand systems and their bioactive Cu(II) complexes	2012-2018	Prof. Dr. Nora Kulak
DFG / Excellence Initiative	SALSA – School of Analytical Sciences Adlershof (HU Berlin)	Biophysical Characterization of Small-molecule binding to Ceramide Transfer Protein	2017-2020	Prof. Dr. H. Möller, UP Prof. Dr. C. Arenz, HU Berlin
DFG / Excellence Initiative	SALSA – School of Analytical Sciences Adlershof (HU Berlin)	3D Structure of the Biomarker Hepcidin-25 in its Native State – From improved diagnostic antibodies to receptor binding	2015-2018	Prof. Dr. H. Möller, UP Prof. Dr. M. Weller, BAM
DFG EXC 2008/1-390540038	Exzellenzcluster EXC 2008/1-390540038 (TU Berlin): Unifying Systems in Catalysis	Project, unit D: Properties, Reactivity and Dynamics of Excited Molecules and their Role in Photocatalysis Project, unit D: Challenging Photo(electro)cata-lytic Reactions on Layered, Porous Materials: A Computational Approach	2019-2022 2023-2025	Prof. Dr. Peter Saalfrank
DFG EXC 314	Exzellenzcluster EXC 314 (TU Berlin): Unifying Concepts in Catalysis	Project B4: Structure and Dynamics of Chromophores in Proteins	(2008-2012) 2017-2018	Prof. Dr. Peter Saalfrank
DFG-Exzellenzcluster	EXC 2008/1-390540038 (TU Berlin): Unifying Systems in Catalysis	Projekt im Bereich D, Ultrafast spectroscopy and structural dynamics studies to follow energy transport in COFs for photocatalysis	2023-2025	JProf. Dr. H. Müller-Werkmeister
DFG-Exzellenzcluster	EXC 2008/1-390540038 (TU Berlin): Unifying Systems in Catalysis	Projekt im Bereich E, Ultrafast spectroscopy of exotic rhodopsins and other membrane proteins	2023-2025	JProf. Dr. H. Müller-Werkmeister
DFG-Exzellenzcluster	EXC 2008/1-390540038 (TU Berlin): Unifying Systems in Catalysis	Projekt im Bereich E, Dynamic characterization of membrane proteins by ultrafast IR and VIS spectroscopy and time-resolved serial crystallography	2020-2022	JProf. Dr. H. Müller-Werkmeister
DFG-FOR 1282	FOR 1282 (TU Berlin): Controlling the Electronic Structures of Semiconductor Nanoparticles by Doping and Hybrid Formation	Project K: Excited State Properties and Spectroscopy of Semiconductor Nanoparticles	2013-2017	Prof. Dr. Peter Saalfrank, Dr. Dominik Kröner
DFG-SFB 1109	SFB 1109 (HU Berlin): Understanding of Metal Oxide / Water Systems at the Molecular Scale	Project B01: Understanding Water Structure and Reactivity at Aluminium Oxide Surfaces Using Nonlinear Vibrational Spectroscopy and Theory	2014-2019	Prof. Dr. Peter Saalfrank, Dr. R.K. Campen
DFG-SFB 658	SFB 658 (FU Berlin): Elementarprozesse in molekularen Schaltern an Oberflächen	Project C2: Quantentheorie licht- und elektronengetriebener molekularer Schalter an Oberflächen	(2005-2009) 2009-2013 2013-2017	Prof. Dr. Peter Saalfrank, Prof. Dr. Tillmann Klamroth
EC	EURAD	Cement-Organics-Radionuclide-Interactions	2019 - 2023	apl. Prof. M. Kumke
EU	H2020 -NMBP-TO-IND-2018-2020: Foundations for Tomorrow’s Industry	NanoPAT – Process Analytical Technologies for Industrial Nanoparticle Production	06/2020 – 05/2024	Prof. Dr. Ilko Bald
EU (Horizon 2020)-ACCIÓ	TecnicoSpring Industry call 2021	COMBILOOP: Composite Materials made from Biobased Limonene Polycarbonates	2022-2024	Prof. Dr. Helmut Schlaad Prof. Arjan Kleij, ICIQ, Tarragona, Spain
Fraunhofer IAP und UP	Leistungszentrum “Integration biologischer und physikalisch-chemischer Materialfunktionen”	Sortase-basierte Protein-Polymer und Protein-Nanopartikel-Konjugate: Charakterisierung von 3D-Struktur, Dynamik und Interaktion mittels NMR-Spektroskopie	Since 2020	Prof. Dr. H. Möller, UP; Dr. U. Glebe / Prof. Dr. A. Böker, IAP
Fraunhofer-Gesellschaft	Fraunhofer Cluster of Excellence	Circular Plastics Economy (https://www.ccpe.fraunhofer.de/)		Prof. Dr. Alexander Böker
Fraunhofer-Gesellschaft	Fraunhofer Cluster of Excellence	Programmable Materials (https://cpm.fraunhofer.de/)		Prof. Dr. Alexander Böker
Helmholtz	Helmholtz Graduate School MacroBio	Metal complexes as protease mimics	2016-2019	Prof. Dr. Nora Kulak
MPG	IMPRS Graduiertenschule „Multiscale Biosystems“ (MPI KG)	GPI-anchored proteins – From bioorganic chemistry to biophysics	Since 2019	Dr. R. Dimova, MPI KG Prof. Dr. H. Möller, UP
MPG	IMPRS Graduiertenschule „Multiscale Biosystems“ (MPI KG)	Fighting Protozoan Parasites Using Novel Carbohydrates Binding Nanobodies	Since 2019	Prof. Dr. H. Möller, UP Dr. O. Moscovitz, MPI KG
SICPA SA	FuE-Projekt	Laser-based IMS for highly reproducible marker detection	2022 - 2024	apl. Prof. M. Kumke / Dr. T. Beitz

J. Ameixa, I. Bald Unraveling the Complexity of DNA Radiation Damage Using DNA Nanotechnology Acc. Chem. Res. 2024, 57, 1608-1619 DOI: 10.1021/acs.accounts.4c00121AbstractRadiation cancer therapies use different ionizing radiation qualities that damage DNA molecules in tumor cells by a yet not completely understood plethora of mechanisms and processes. While the direct action of the radiation is significant, the byproducts of the water radiolysis, mainly secondary low-energy electrons (LEEs, <20 eV) and reactive oxygen species (ROS), can also efficiently cause DNA damage, in terms of DNA strand breakage or DNA interstrand cross-linking. As a result, these types of DNA damage evolve into mutations hindering DNA replication, leading to cancer cell death. Concomitant chemo-radiotherapy explores the addition of radiosensitizing therapeutics commonly targeting DNA, such as platinum derivatives and halogenated nucleosides, to enhance the harmful effects of ionizing radiation on the DNA molecule. Further complicating the landscape of DNA damage are secondary structures such as G-quadruplexes occurring in telomeric DNA. These structures protect DNA from radiation damage, rendering them as promising targets for new and more selective cancer radiation treatments, rather than targeting linear DNA. However, despite extensive research, there is no single paradigm approach to understanding the mysterious way in which ionizing radiation causes DNA damage. This is due to the multidisciplinary nature of the field of research, which deals with multiple levels of biological organization, from the molecular building blocks of life toward cells and organisms, as well as with complex multiscale radiation-induced effects. Also, intrinsic DNA features, such as DNA topology and specific oligonucleotide sequences, strongly influence its response to damage from ionizing radiation. In this Account, we present our studies focused on the absolute quantification of photon- and low-energy electron-induced DNA damage in strategically selected target DNA sequences. Our methodology involves using DNA origami nanostructures, specifically the Rothemund triangle, as a platform to expose DNA sequences to either low-energy electrons or vacuum-ultraviolet (VUV, <15 eV) photons and subsequent atomic force microscopy (AFM) analysis. Through this approach, the effects of the DNA sequence, incorporation of halogenated radiosensitizers, DNA topology, and the radiation quality on radiation-induced DNA strand breakage have been systematically assessed and correlated with fundamental photon- and electron-driven mechanisms underlying DNA radiation damage. At lower energies, these mechanisms include dissociative electron attachment (DEA), where electrons attach to DNA molecules causing strand breaks, and dissociative photoexcitation of DNA. Additionally, further dissociative processes such as photoionization and electron impact contribute to the complex cascade of DNA damage events induced by ionizing radiation. We expect that emerging DNA origami-based approaches will lead to a paradigm shift in research fields associated with DNA damage and suggest future directions, which can foster the development of technological applications in nanomedicine, e.g., optimized cancer treatments or the molecular design of optimized radiosensitizing therapeutics.
A. Mostafa, Y. Kanehira, K. Tapio, I. Bald From Bulk to Single Molecules: Surface-Enhanced Raman Scattering of Cytochrome C Using Plasmonic DNA Origami Nanoantennas Nano Lett. 2024, 24, 6916-6923 DOI: 10.1021/acs.nanolett.4c00834AbstractCytochrome C, an evolutionarily conserved protein, plays pivotal roles in cellular respiration and apoptosis. Understanding its molecular intricacies is essential for both academic inquiry and potential biomedical applications. This study introduces an advanced single-molecule surface-enhanced Raman scattering (SM-SERS) system based on DNA origami nanoantennas (DONAs), optimized to provide unparalleled insights into protein structure and interactions. Our system effectively detects shifts in the Amide III band, thereby elucidating protein dynamics and conformational changes. Additionally, the system permits concurrent observations of oxidation processes and Amide bands, offering an integrated view of protein structural and chemical modifications. Notably, our approach diverges from traditional SM-SERS techniques by de-emphasizing resonance conditions for SERS excitation, aiming to mitigate challenges like peak oversaturation. Our findings underscore the capability of our DONAs to illuminate single-molecule behaviors, even within aggregate systems, providing clarity on molecular interactions and behaviors.
A. Dutta, M. Oncak, F. Izadi, E. Arthur-Baidoo, J. Ameixa, S. Denifl, I. Bald Plasmon-driven chemical transformation of a secondary amide probed by surface enhanced Raman scattering Commun. Chem. 2024, 7, 188 DOI: 10.1038/s42004-024-01276-2AbstractPlasmon-driven chemical conversion is gaining burgeoning interest in the field of heterogeneous catalysis. Herein, we study the reactivity of N-methyl-4-sulfanylbenzamide (NMSB) at nanocavities of gold and silver nanoparticle aggregates under plasmonic excitation to gain understanding of the respective reaction mechanism. NMSB is a secondary amide, which is a frequent binding motive found in peptides and a common coupling product of organic molecules and biomolecules. Surface-enhanced Raman scattering (SERS) is used as a two-in-one in-situ spectroscopic tool to initiate the molecular transformation process and simultaneously monitor and analyze the reaction products. Supported by dissociative electron attachment (DEA) studies with the gas phase molecule, a hot electron-mediated conversion of NMSB to p-mercaptobenzamide and p-mercaptobenzonitrile is proposed at the plasmonic nanocavities. The reaction rate showed negligible dependence on the external temperature, ruling out the dominant role of heat in the chemical transformation at the plasmonic interface. This is reflected in the absence of a superlinear relationship between the reaction rate constant and the laser power density, and DEA and SERS studies indicate a hot-electron mediated pathway. We conclude that the overall reaction rate is limited by the availability of energetic hot electrons to the NMSB molecule.
Y. Kanehira, S. Kogikoski Jr., E. Titov, K. Tapio, I. Bald Watching a Single Enzyme at Work Using Single-Molecule Surface-Enhanced Raman Scattering and DNA Origami-Based Plasmonic Antennas ACS Nano 2024, 18, 20191-20200 DOI: 10.1021/acsnano.4c03384AbstractThe detection of a single-enzyme catalytic reaction by surfaced-enhanced Raman scattering (SERS) is presented by utilizing DNA origami-based plasmonic antennas. A single horseradish peroxidase (HRP) was accommodated on a DNA origami nanofork plasmonic antenna (DONA) containing gold nanoparticles, enabling the tracing of single-molecule SERS signals during the peroxide reduction reaction. This allows monitoring of the structure of a single enzymatic catalytic center and products under suitable liquid conditions. Herein, we demonstrate the chemical changes of HRP and the appearance of tetramethylbenzidine (TMB), which works as a hydrogen donor before and after the catalytic reaction. The results show that the iron in HRP adopts Fe4+ and low spin states with the introduction of H2O2, indicating compound-I formation. Density functional theory (DFT) calculations were performed for later catalytic steps to rationalize the experimental Raman/SERS spectra. The presented data provide several possibilities for tracking single biomolecules in situ during a chemical reaction and further developing plasmon-enhanced biocatalysis.\r\n
P. Wessig, P. Schmidt, D. Badetko, E.Sperlich, A. Kelling Total synthesis of Comfreyn A and structural analogues via two photochemical key steps Photochem. Photobiol. Sci. 2024, 23, 1485-1495 DOI: 10.1007/s43630-024-00607-5AbstractIn this work the influence of o-fluorine substituents on the photo-dehydro-Diels–Alder (PDDA) reaction was investigated and the findings of this study were applied to the total synthesis of natural products. The reactant molecules consisted of two alkyl arylpropiolates, connected by a suberic acid tether and bearing fluorine substituents in each of the o-positions. While quantum chemical calculations suggested that a fluorine substituent prevents an attack of the adjacent carbon atom in the second C–C bond forming step of the PDDA reaction, this attack took place nevertheless. The subsequent fluoride elimination, assisted by protic solvents or trialkylsilanes, resulted in an "Umpolung" of the 4-position of the cycloallene intermediate enabling the introduction of nucleophiles at this position. The nucleophilic replacement of the second fluorine substituent could also be triggered photochemically. After removal of the tether, the two arene moieties stand nearly perpendicular to each other and a selective excitation of the naphthalene moiety was possible. This led to an intramolecular photoinduced electron transfer (PET) followed by a nucleophilic replacement of the fluoride according to a SR+N1Ar* mechanism. The formed phenolic hydroxyl group underwent spontaneous lactonization with the adjacent ester group. Based on these results, the first total synthesis of the lignan Comfreyn A and some structural analogues were developed.
D. Vasquez Munoz, F. Rohne, I. Meier, C. Braksch, N. Lomadze, A. Heraji Esfahani, A. Nitschke, A. Taubert, S. Santer, M. Hartlieb, M. Bekir Separation of surface grafted microparticles via light and temperature Small 2024, DOI: 10.1002/smsc.202400146AbstractSeparation of equally sized particles distinguished solely by interfacial properties remains a highly challenging task. Herein, a particle fractioning method is proposed, which is suitable to differentiate between polymer-grafted microparticles that are equal in size. The separation relies on the combination of a pressure driven microfluidic flow, together with simultaneous light illumination and temperature control. Heating the solution forces thermo-responsive surface grafts to undergo a volume phase transition and therefore locally changing the interfacial properties of the microparticles. Light illumination induces the phoretic/osmotic activity of the microparticles and lifts them into a higher plane, where hovering particles experience a different shear stress proportional to the height. The light-induced hovering height depends on the interfacial properties, and this complex interaction leads to different movements of the microparticles as a function of their surface grafting. The concepts are visualized in experimental studies, where the complex physical principle provides a simple method for fractioning a binary mixture with at least one thermo-responsive polymer graft.
A. Alsawaf, A.-C. Lehnen, O. Dolynchuk, A. M. Bapolisi, C. Beresowski, A. Böker, I. Bald, M. Hartlieb Antibacterial Nanoplatelets via Crystallization-Driven Self-Assembly of Poly(L-lactide)-based Block Copolymers Biomacromolecules 2024, DOI: 10.1021/acs.biomac.4c00767AbstractMembrane-active antimicrobial materials are promising substances to fight antimicrobial resistance. Herein, crystallization-driven self-assembly (CDSA) is employed for the preparation of nanoparticles with different morphologies, and their bioactivity is explored. Block copolymers (BCPs) featuring a crystallizable and antimicrobial block were synthesized using a combination of ring-opening and photoiniferter RAFT polymerizations. Subsequently formed nanostructures formed by CDSA could not be deprotected without degradation of the structures. CDSA of deprotected BCPs yielded 2D diamond-shaped nanoplatelets in MeOH, while spherical nanostructures were observed for assembly in water. Platelets exhibited improved antibacterial capabilities against two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) compared to their spherical counterparts. The absence of hemolytic activity leads to the excellent selectivity of platelets. A mechanism based on membrane permeabilization was confirmed via dye-leakage assays. This study emphasized the impact of the shape of nanostructures on their interaction with bacterial cells and how a controlled assembly can improve bioactivity.
Bekir, M.; Gurke, J.; Reifarth, M. Photoswitchable Surfactants–Are there Alternatives to Azobenzene-Based Systems? ChemSystemsChem 2024, DOI: 10.1002/syst.202400026AbstractOwing to their property to alter their surface-activity upon the irradiation with light, \r\nphotoswitchable surfactants have gained tremendous interest in colloidal science. Their mere addition to a colloidal system allows, e. g., to obtain control over polyelectrolytes, micro- and nanoscale particles or emulsions. Most literature examples focus on azobenzene-based, or related, systems, which employ a photoisomerization reaction for switching, Other structures, such as spiropyrans, play a subordinate role, although they have gained increasing attention over the past few years. In this perspective article, we want to provide an overview about existing systems of photoswitchable surfactants. We address the issue that alternative photoswitches are given less attention, and what benefits surfactants could possess that are based on said switchable units. With our contribution, we want to broaden the view on stimuli-responsive surfactants - and to provide a guideline for the design of novel structures.
Aiyedun, P. O.; Sonibare, M. A.; Ajiboye, C. O.; Gueye, B.; Paliwal, R.; Albach, D. C.; Nchiozem-Ngnitedem, V.-A.; Schmidt, B. Phytoecdysteroids from Dioscorea dumetorum (Kunth) Pax. And their antioxidant and antidiabetic activities Fitoterapia 2024, 177, 106103 DOI: 10.1016/j.fitote.2024.106103AbstractDioscorea dumetorum, also known as yam, is an important crop species in West Africa. In a phytochemical investigation four previously described and two new natural products were isolated from tubers and peels of D. dumetorum. In an international collaborative project the structure elucidation of the secondary plant metabolites was accomplished by spectroscopic means, and the antidiabetic and antioxidant activity of D. dumetorum could be rationalized by testing the isolated natural products in a glucosidase inhibitory assay and a DPPH. scavenging assay.
D. Skoulas, O. M. Ojo, A. Thalhammer, Z. Kochovski, H. Schlaad Solution Behavior of Glyco-Copoly(L-Glutamic Acid)s in Dilute Saline Solution Biomacromolecules 2024, 25, 3724–3730 DOI: 10.1021/acs.biomac.4c00288AbstractA small series of copoly(α,L-glutamic acid/DL-allylglycine)s with the same chain length and allylglycine content (~10 mol %) but different spatial distribution of allylglycine units was synthesized and subsequently glycosylated via thiol-ene chemistry. Dilute aqueous copolypeptide solutions (0.1 wt %, physiological saline) were analyzed by circular dichroism spectroscopy, dynamic light scattering, and cryogenic transmission electron microscopy. The copolypeptides adopted a random coil or α-helix conformation, depending on solution pH, and the glycosylated residues either distorted or enhanced the folding into an α-helix depending on their location and spatial distribution along the chain. However, regardless of their secondary structure and degree of charging, all partially glycosylated copolypeptides self-assembled into 3D spherical structures, supposedly driven by a hydrophilic effect promoting microphase separation into glucose-rich and glutamate-rich domains.\r\n
M. Szomek, V. Akkerman, L. Lauritsen, H.-L. Walther, A. Dupont Juhl, K. Thaysen, J. M. Egebjerg, D. F. Covey, M. Lehmann, P. Wessig, A. J. Foster, B. Poolman, S. Werner, G. Schneider, P. Müller, D. Wüstner Ergosterol promotes aggregation of natamycin in the yeast plasma membrane Biophys. Biochem. Acta (BBA) - Biomembranes 2024, 2024, 184350 DOI: 10.1016/j.bbamem.2024.184350AbstractPolyene macrolides are antifungal substances, which interact with cells in a sterol-dependent manner. While being widely used, their mode of action is poorly understood. Here, we employ ultraviolet-sensitive (UV) microscopy to show that the antifungal polyene natamycin binds to the yeast plasma membrane (PM) and causes permeation of propidium iodide into cells. Right before membrane permeability became compromised, we observed clustering of natamycin in the PM that was independent of PM protein domains. Aggregation of natamycin was paralleled by cell deformation and membrane blebbing as revealed by soft X-ray microscopy. Substituting ergosterol for cholesterol decreased natamycin binding and caused a reduced clustering of natamycin in the PM. Blocking of ergosterol synthesis necessitates sterol import via the ABC transporters Aus1/Pdr11 to ensure natamycin binding. Quantitative imaging of dehydroergosterol (DHE) and cholestatrienol (CTL), two analogues of ergosterol and cholesterol, respectively, revealed a largely homogeneous lateral sterol distribution in the PM, ruling out that natamycin binds to pre-assembled sterol domains. Depletion of sphingolipids using myriocin increased natamycin binding to yeast cells, likely by increasing the ergosterol fraction in the outer PM leaflet. Importantly, binding and membrane aggregation of natamycin was paralleled by a decrease of the dipole potential in the PM, and this effect was enhanced in the presence of myriocin. We conclude that ergosterol promotes binding and aggregation of natamycin in the yeast PM, which can be synergistically enhanced by inhibitors of sphingolipid synthesis.
C. Gallizioli, D. Battke, H. Schlaad, P. Deglmann, A. J. Plajer Ring-opening terpolymerization of elemental sulfur waste with propylene oxide and carbon disulfide via lithium catalysis Angew. Chem. Int. Ed. 2024, 63, e202319810 DOI: 10.1002/anie.202319810AbstractElemental sulfur, a waste product of the oil refinement process, represents a promising raw material for the synthesis of degradable polymers. We show that simple lithium alkoxides facilitate the polymerisation of elemental sulfur S8 with industrially relevant propylene oxide (PO) and CS2 (a base chemical sourced from waste S8 itself) to give poly(monothiocarbonate-alt-Sx) in which x can be controlled by the amount of supplied sulfur. The in situ generation of thiolate intermediates obtained by a rearrangement, which follows CS2 and PO incorporation, allows to combine S8 and epoxides into one polymer sequence that would otherwise not be possible. Mechanistic investigations reveal that alkyl oligosulfide intermediates from S8 ring opening and sulfur chain length equilibration represent the better nucleophiles for inserting the next PO if compared to the trithiocarbonates obtained from the competing CS2 addition, which causes the sequence selectivity. The polymers can be crosslinked in situ with multifunctional thiols to yield reprocessable and degradable networks. Our report demonstrates how mechanistic understanding allows to combine intrinsically incompatible building blocks for sulfur waste utilisation.
Karthäuser, J. F.; Kopecz, R.; Schönemann, E.; Martínez Guajardo, A.; Laschewsky, A.; Rosenhahn, A. Spacer Effects in Sulfo- and Sulfabetaine Polymers on Their Resistance against Proteins and Pathogenic Bacteria Adv. Mater. Interfaces 2024, 11, [2300873] DOI: 10.1002/admi.202300873AbstractA set of of zwitterioniic methacrylates sulfobetaine is copolymerized with a benzophenone-bearing photocrosslinker. The nature of the anionic group, the side chain spacer between backbone+betaine moieties, and the intercharge spacers between cationic and anionic groups are varied systematically. After photo X-linking by near UV irradiation, the fouling resistance of spin-coated polymer films vs. a set of proteins and pathogenic bacteria is compared. The results corroborate previous findings that even minor molecular changes can strongly affect low-fouling performance of polyzwitterions
D. Keller, J. Hermanns Development of a self-test for undergraduate chemistry students: how do students solve tasks on basic content knowledge? Chemistry Teacher International 2024, 6, 65-75 DOI: https://doi.org/10.1515/cti-2023-0068AbstractIn this paper we describe the development of a self-test on content knowledge as one element of a digital learning environment. The self-test on prior knowledge consists of tasks in the categories Periodic Table of Elements, chemical bonding, chemical formulas, and chemical reactions (reaction equations and reaction mechanisms). For the study, tasks from all topics have been used in a paper-pencil multiple-choice and multiple response test on the task at hand and an accompanying questionnaire with closed and open items. The results of the study show that the students rated the tasks as suitable. Comments for improving the tasks regarding the wording or the design were implemented. Because of students’ lack of understanding regarding some of the technical terms, a glossary and games will be added to the digital learning environment. Many students overestimated their knowledge and their competences, therefore the self-test in the learning environment will include feedback to ensure that the students can improve their content knowledge and its application.
Tobias Pausch, Tim David, Dr. Tom Fleck-Kunde, Hendrik Pols, Dr. Johannes Gurke, Dr. Bernd M. Schmidt Multifold Post-Modification of Macrocycles and Cages by Isocyanate-Induced Azadefluorination Cyclisation Angewandte Chemie International Edition 2024, 63DOI: AbstractWe present the multiple post-modification of organic macrocycles and cages, introducing functional groups into two- and three-dimensional supramolecular scaffolds bearing fluorine substituents, which opens up new possibilities in multi-step supramolecular chemistry employing the vast chemical space of readily available isocyanates. The mechanism and scope of the reaction that proceeds after isocyanate addition to the benzylamine motif via an azadefluorination cyclisation (ADFC) were investigated using DFT calculations, and a series of aromatic isocyanates with different electronic properties were tested. The compounds show excellent chemical stability and were fully characterised. They can be used for subsequent cross-coupling reactions, and ADFC can be used directly to generate cross-linked membranes from macrocycles or cages when using ditopic isocyanates. Single-crystal X-ray (SC-XRD) analysis shows the proof of the formation of the desired supramolecular entity together with the connectivity predicted by calculations and from 19F NMR shifts, allowing the late-stage functionalisation of self-assembled macrocycles and cages by ADFC.
Tobias E. Naegele, Johannes Gurke, Etienne Rognin, Niamh Willis-Fox, Anthony Dennis, Xudong Tao, Ronan Daly, Ulrich F. Keyser, George G. Malliaras Redox Flow Iontophoresis for Continuous Drug Delivery Advanced Materials Technologies 2024 2024, 9DOI: https://doi.org/10.1002/admt.202301641AbstractDrug delivery into the brain and spinal cord is fundamentally limited by the blood-brain barrier which impedes the use of the vast majority of drugs. Implants based on iontophoresis use an applied voltage to deliver charged drug molecules, allowing solvent-free delivery directly into the site of interest and overcoming issues associated with systemic exposure to the drug. However, during continuous delivery over long periods, electrochemical reactions occur at the electrodes leading to corrosive gas formation. Here, the concept of redox flow iontophoresis is presented, where a redox mediator solution is used to control electrode reactions and sustain continuous delivery for theoretically unlimited duration. As a proof-of-concept, a redox flow iontophoresis-based brain implant that can continuously deliver the cancer drug doxorubicin at stable rates exceeding 2 nmol min-1 is demonstrated. This new concept enables the continuous delivery of various potent drugs into the brain and spinal cord and therefore has the potential to improve treatment options for various diseases.
N. Pallab,S. Reinicke, J. Gurke, R. Rihm, S. Kogikoski Jr., M. Hartlieb, M. Reifarth Polymer-assisted microcontact printing: Using a tailor-made polydimethylsiloxane (PDMS) stamp for precise patterning of rough surfaces Polym. Chem. 2024, 15, 853-867 DOI: 10.1039/D3PY01036HAbstractRough, capillary-active surfaces remain demanding substrates for microcontact printing (μCP), as the diffusive mobility of the ink thereon drastically limits the printing resolution. To reduce ink smearing, we developed polymer-supported μCP, which includes a stamp with a polymer brush-decorated surface. The ink molecules are thereby bound to the stamp-bound brush matrix, from where they may be transferred to the substrate, which exclusively occurs during the contact of both interfaces. Conventionally, Sylgard 184-based polydimethylsiloxane (PDMS) stamps are used for μCP. The material\'s surface must be functionalized in a multi-step procedure for the protocol. In addition, Sylgard comes along with the drawback of a persistent leakage of oligomeric PDMS (oPDMS), which can contaminate the substrate. To circumvent these problems, we developed a novel stamp material that (i) enables a straightforward polymer grafting and (ii) shows a low tendency for oPDMS leakage. We prepared the stamp with a commercially available amino-functionalized PDMS prepolymer and a polymeric crosslinker that can be used for a controlled photoiniferter reversible addition and fragmentation chain transfer (PI-RAFT) polymerization. The prepared stamp shows elastic properties in the relevant strain region, is compatible with brush formation, and has been demonstrated to be suitable for transferring precise patterns on rough capillary-active oxide surfaces.
A.-C. Lehnen, S. Kogikoski Jr., T. Stensitzki, A. AlSawaf, A. Bapolisi, M. Wolff, J. De Breuck, H. Müller-Werkmeister, S. Chiantia, I. Bald, M. N. Leiske, M. Hartlieb Anisotropy in Antimicrobial Bottle Brush Copolymers and its Influence on Biological Activity Adv. Funct. Mater. 2024, 34, 2312651 DOI: 10.1002/adfm.202312651AbstractAntimicrobial polymers are a promising alternative to conventional antibiotics in the fight against antimicrobial resistance. Cationic bottle brush copolymers have shown to be superior to linear topologies in previous studies. Herein, the aspect ratio of such polymers is varied creating differently shaped confined unimolecular structures with varying degrees of side chain mobility. Using reversible addition-fragmentation chain-transfer (RAFT) polymerization, bottle brushes are produced in a one-pot procedure. The morphology is confirmed by atomic force microscopy. The hydrophobicity, as determined via high performance-liquid chromatography (HPLC) analysis, is drastically influenced by the topology. Using Fourier-transform infrared (FTIR) spectroscopy, it is found that polymers with a high side chain mobility and increased global hydrophilicity, are less hydrated, and have stronger intramolecular hydrogen bonds. A phase segregated morphology leading to unimolecular micellization is assumed. Biological tests reveal increased antimicrobial activity for such segregated polymers. Their excellent hemocompatibility results in highly selective antimicrobial polymers whose adaptability seems to be a key feature in their excellent performance. This study highlights the tremendous importance of structural control in antimicrobial polymers.
T. Skorjanc,* J. Heinrich, D. Makuc, N. Kulak, M. Valant Sustained delivery of Cu(II)-based DNA intercalators by nanometer-sized cyclodextrin-based porous polymers ACS Appl. Nano Mater 2023, 6, 21162-21168 DOI: https://doi.org/10.1021/acsanm.3c04219AbstractDNA intercalators are small molecules that insert between adjacent DNA base pairs and thus disturb DNA replication and transcription, which can lead to cell death. Certain metal complexes are excellent DNA intercalators and have shown promise in chemotherapy. Here, a cyclodextrin porous polymer was prepared, characterized, exfoliated to form nanometer-sized particles and used as a delivery vehicle for metal-free and Cu(II)-metalated anthraquinone-based DNA intercalators with a goal of minimizing side effects of the highly toxic DNA intercalators. NMR experiments, including DOSY NMR, have shown the interaction between the cyclodextrin building block and the studied DNA intercalators. Porous nature of the delivery vehicle provided ample surface area for interaction with the drug candidates, resulting in encapsulation rates of up to 56%. Sustained cargo release from the polymer was achieved over 8 days, and time-dependent cytotoxicity was observed. Furthermore, optical microscopy images indicated delivery vehicle internalization as well as disturbed cellular morphology within 24 h of incubation. We anticipate that this study will stimulate further interest in the development of polymeric delivery systems for metal complexes.
M. Scaccaglia, S. Pinelli, L. Manini, B. Ghezzi, M. Nicastro, J. Heinrich, N. Kulak, P. Mozzoni, G. Pelosi, F. Bisceglie Gold(III) Complexes with Thiosemicarbazone Ligands: Insights into Their Cytotoxic Effects on Lung Cancer Cells J. Inorg. Biochem. 2024, 251, 112438 DOI: https://doi.org/10.1016/j.jinorgbio.2023.112438AbstractCancer continues to pose a global threat, underscoring the urgent need for more effective and safer treatment options. Gold-based compounds have recently emerged as promising candidates due to their diverse range of biological activities. In this study, three gold(III) complexes derived from thiosemicarbazone ligands have been synthesized, fully characterized, including their X-ray crystal structures. We conducted initial mode-of-action studies on DNA and BSA, followed by a comprehensive investigation into the cytotoxic effects of these novel gold(III) complexes on lung cancer cells (A549, H2052, and H28). The results demonstrated a concentration-dependent cytotoxic response, with H28 cells exhibiting the highest sensitivity to the treatment. Furthermore, the analysis of the cell cycle revealed that these compounds induce cell cycle arrest and promote apoptosis as a response to treatment. We also observed distinct morphological changes and increased oxidative stress, contributing significantly to cell death. Notably, these complexes exhibited the ability to suppress interleukin-6 production in mesothelioma cell lines, and this highlights their anti-inflammatory potential. To gain an initial understanding of cytotoxicity on healthy cells, hemolysis tests were conducted against human blood cells, with no evidence of hemolysis. Furthermore, a toxicity assessment through the in vivo Galleria mellonella model underscored the absence of detectable toxicity. These findings prove that these complexes are promising novel therapeutic agents for lung cancer.
R. Steinbrecher, P.r. Zhang, C. M. Papadakis, P. Müller-Buschbaum, A. Taubert, A. Laschewsky Boosting the Photo-switchability of Double-responsive Water-soluble Polymers by Incorporating Arylazopyrazole Dyes Chem. Commun. 2024, 60, 1747-1750 DOI: 10.1039/d3cc06178gAbstractA series of dual thermo- and light-responsive, water-soluble polymers is prepared by copolymerizing N,N-dimethylacrylamide with a functionalized acrylamide bearing an azodye of the new family of arylazopyrazoles (AAP). Its light-induced trans-cis photo isomerization provides an exceptionally effective photo-switch, which can reversibly shift the LCST-type phase transition temperatures of the copolymers by up to 25 K. The spectral separation of the main \r\nabsorption bands of the trans- and cis-states of the azodye in the near UV-Vis range is sufficient for transforming the majority of the AAP chromophore into the cis-isomer in the photo stationary state (>85 %),\r\n thereby modulating effectively the overall hydrophilicity. The polymers change their LCSTs in aqueous solution depending on the content of azodye in a non-monotonous way. Substantial changes of the cloud point are achieved for moderate AAP contents, with outstanding shifts of nearly 25 K for the copolymers bearing 7-9 mol % of azodye. Moreover, the lifetime of the cis-state is advantageously long (τ½= 19 h at 40 °C) compared to previously reported azobenzene-functionalized photo-responsive polymers, thus enabling the switching between bi-stable states.
C. P. Braksch, A.-C. Lehnen, A. M. Bapolisi, J. Gurke, J. De Breuck, M. N. Leiske, M. Hartlieb Staphylococcus aureus selective antimicrobial polymers based on an arginine-derived monomer J. Polym. Sci. 2024, 62, 132-145 DOI: 10.1002/pol.20230591AbstractThe continuous spread of resistance genes among bacterial populations, in particular in hospital setting, threatens the advances of our medical systems and already costs more than 1 million lives per year. Antimicrobial polymers (APs) are a promising type of materials to counteract these developments, as they are non-susceptible toward resistance development, and even target resistant bacteria. We herein show the synthesis of an arginine-containing monomer and its polymerization via photo-induced reversible addition-fragmentation chain-transfer polymerization. The synthesis is straightforward, and the macromolecules possess two charged functions (i.e., guanidinium and ammonium) per repeating unit after deprotection. Assessment of the biological activity reveals that polymers inhibit the growth of methicillin-resistant Staphylococcus aureus (MRSA) while being relatively inactive against\r\ntested Gram-negative strains. Surprisingly, among the tested polymers, the homopolymer of the arginine-derived monomer is the best-performing material, even though it possesses no notable hydrophobic units. Toxicity tests against red blood cells and other mammalian cells show a good biocompatibility of polymers, leading to an overall excellent selectivity. Using membrane models, the mechanism of action was found to be membrane disruption. The good selectivity of the herein presented polymer for MRSA makes them promising materials for the development of therapeutic agents against such infections.
A. Alsawaf, Y. Kanehira, A. M. Bapolisi, I. Bald, M. Hartlieb PLLA-Based Block Copolymers via Raft Polymerization—Impact of the Synthetic Route and Activation Mechanism Macromol. Chem. Phys. 2023, 224, 2300274 DOI: 10.1002/macp.202300274AbstractDesigning supramolecular structures with well-defined dimensions and diverse morphologies via the self-assembly of block copolymers is renowned. Specifically, the design of 1D fiber nanostructures is extensively emphasized, due to their unique properties in many areas, such as microelectronics, photonics, and particularly in the biomedical field. Herein, amphiphilic diblock copolymers of P(l-lactide)-b-P(N-t-butoxy-carbonyl-N’-acryloyl-1,2-diaminoethane)-co-P(N-isopropylacrylamide) PLLAn-b-P(BocAEAm)m-co- P(NiPAAm)l– are developed. Two synthetic strategies are investigated to equip PLLA with a chain transfer agent (CTA), either by Steglich esterification of PLLA-OH or via the ring-opening polymerization of l-lactide using a CTA containing a hydroxyl functional group. The second strategy proves to be superior in terms of degree of functionalization. The corona-forming blocks, with degrees of polymerization of 200 and above are achieved in good definition by photo-iniferter RAFT polymerization (Ð < 1.25), while a Ð of 1.75 is obtained by conventional RAFT polymerization. The self-assembly of the developed system leads to the formation of nanofibers with a height of 11 nm and a length of ≈ 300 nm, which is determined by atomic force microscopy (AFM). These fibers are the basis for new antimicrobial nanomaterials after deprotection, as the subject of upcoming work.
Yuya Kanehira, Kosti Tapio, Gino Wegner, Sergio Kogikoski Jr., Sibylle Rüstig, Claudia Prietzel, Kurt Busch, and Ilko Bald The Effect of Nanoparticle Composition on the Surface-Enhanced Raman Scattering Performance of Plasmonic DNA Origami Nanoantennas ACS Nano 2023, 17, 21227–21239 DOI: 10.1021/acsnano.3c05464AbstractA versatile generation of plasmonic nanoparticle dimers for surface-enhanced Raman scattering (SERS) is presented by combining a DNA origami nanofork and spherical and nonspherical Au or Ag nanoparticles. Combining different nanoparticle species with a DNA origami nanofork to form DNA origami nanoantennas (DONAs), the plasmonic nanoparticle dimers can be optimized for a specific excitation wavelength in SERS. The preparation of such nanoparticle dimers is robust enough to enable the characterization of SERS intensities and SERS enhancement factors of dye-modified DONAs on a single dimer level by measuring in total several thousands of dimers from five different dimer designs, each functionalized with three different Raman reporter molecules and measured at four different excitation wavelengths. Based on these data, SERS enhancement factor (EF) distributions have been determined for each dimer design and excitation wavelengths. The structures and measurement conditions with the highest EFs are suitable for single-molecule SERS (SM-SERS), which is realized by placing single dye molecules into hot spots. We demonstrate that the probability of placing single molecules in a strongly enhancing hot spot for SM-SERS can be increased by using anisotropic nanoparticles with several sharp edges, such as nanoflowers. Combining a Ag nanoparticle with a Au particle in one dimer structure allows for a broadband excitation covering almost the whole visible range. The most versatile plasmonic dimer structure for SERS combines a spherical Ag nanoparticle with a Au nanoflower. Employing the discontinuous Galerkin time domain method, we numerically investigate the bare, symmetric dimers with respect to spectral and near-field properties, showing that, indeed, the nanoflowers induce multiple hot spots located at the edges which surpass the intensity of the spherical dimers, indicating the possibility for SM-SERS. The presented DONA structures and SERS data provide a robust basis for applying such designs as versatile SERS tags and as substrates for SM-SERS measurements.
J. Hermanns*, A. Bresler and H. Kunold Students\' learning and application of basic concepts in the course \"Organic Chemistry I for preservice chemistry teachers\" J. Chem. Educ. 2023, 100 (11), 4249-4260 DOI: 10.1021/acs.jchemed.3c00108AbstractIn their second year at university, preservice chemistry teachers are confronted with organic chemistry. Because it is known that students often struggle with the subject, a new course design was developed, used, and evaluated for this study. To ensure meaningful learning, the students had many opportunities to actively participate in the course (due to the COVID pandemic via Zoom). Many partner and group work phases were used for solving and discussing tasks in organic chemistry. The application of basic and advanced skills was practiced explicitly as well as implicitly. The interaction among the students during the course, the use of basic concepts in the course design, and the learning outcomes of the written exam were analyzed in detail. Students’ interaction was best in the partner group phases. Here, the students participated equally. All concepts, such as the concepts of nucleophilicity and electrophilicity, for example, were employed during the course, explicitly and implicitly. However, the analysis of the written exam showed that the students were more successful if they had to apply basic skills. The more complex the task was, the less the application of basic skills could be observed. Whether or not the students applied those skills but did not write them down remains unclear, although the results hint that they did not. In the future, the application of basic and advanced skills should be made more transparent.
Y. Mai-Linde, T. Linker Simple Synthesis of 1,2-Dideoxy-2-Vinyl Carbohydrates by Tin-Free Radical Reactions of Xanthates Chem. Eur. J. 2023, , e202302118 DOI: 10.1002/chem.202302118AbstractVinyl-substituted carbohydrates have been synthesized from glycals derived from hexoses and pentoses. Key step is the radical reaction of xanthates in the presence of triethylborane, a non-toxic reagent. The mechanism has been investigated by isolation of various side products, which speak for a reversibility of the cyclopropylmethyl radical ring-opening. Compared to reactions with tributyltin hydride, higher regioselectivities in favor of the 2-vinyl-substituted sugars have been obtained. Yields are slightly lower with triethylborane, but all products have been isolated in analytically pure form. The new reaction is applicable to benzyl- and silyl-protected carbohydrates, which makes free sugars accessible as well. Overall, more than 15 1,2- dideoxy-2-vinyl carbohydrates have been synthesized from simple precursors in only few steps.
W. Fudickar, M. Metz, T. Krüger-Braunert, A. Kelling, E. Sperlich, P. Wessig, T. Linker Photochemistry of β-γ-Unsaturated Spirolactones Photochem 2023, 3, 408-426 DOI: 10.3390/photochem3040025Abstractβ-γ-unsaturated spirolactones are easily available by Birch reduction. We describe their photochemistry in the presence of or without carbonyl compounds. The spirolactones show a distinct absorption band at 230 nm, which is not present in other cyclohexadienes. We explain this behavior by an interaction of the double bonds with the carbonyl group through space, further proven by TDDFT calculations. This allows their direct excitation with UV-C light. Interestingly, we obtain only products of an oxa-di-π-methane rearrangement, hitherto unknown for lactones. This speaks for a reaction pathway starting from singlet states, confirmed by calculated relative energies of biradical intermediates. Although polymerization is the main side reaction, we were able to isolate tricyclic lactones in moderate yields in a pure form. In the presence of benzaldehyde or benzophenone, Excitation with UV-B light was possible, leading to H-atom abstraction in the allylic position and\r\nformation of alcohols. With an electron-rich double bond, the Paternó–Büchi products were isolated as well. The different diastereomers were separated by column chromatography or HPLC. Their relative configurations were determined using NOESY measurements or X-ray structure analysis. Overall, β-γ-unsaturated spirolactones show a remarkably different photochemistry compared to other cyclohexadienes, affording new products in only a few steps.
D. Keller, J. Hermanns The digital task navigator as scaffold for supporting higher education students while solving tasks in organic chemistry J. Chem. Educ. 2023, 100(10), 3818-3824 DOI: 10.1021/acs.jchemed.2c00518AbstractScaffolds can be seen as a suitable tool to support students learning chemistry. Digital task navigators, written scaffolds that support students solving tasks in organic chemistry, were developed, used, and evaluated for this study. A paper task navigator was further developed into a digital task navigator, which included links to explanations of special terms that were unknown to the students. The students could use the links to find these explanations if they needed them. Four newly designed digital task navigators were evaluated using questionnaires. The students rated this newly developed digital scaffold quite highly. Students who used the links to the explanations felt these were also helpful. The results of the students’ ratings can be used to design additional digital task navigators for other topics, as well as to develop this scaffold further.
A.-C. Lehnen, S. Hanke, M. Schneider, C. M. L. Radelof, J. Perestrelo, S. Reinicke, M. Reifarth, A. Taubert, K. M. Arndt, M. Hartlieb, Modification of 3D-printed PLA structures using Photo-iniferter RAFT Polymerization: Toward on-demand antimicrobial water filters Macro. Rapid Commun. 2023, , 2300408 DOI: 10.1002/marc.202300408AbstractWater filtration is an important application to ensure the accessibility of clean drinking water. As requirements and contaminants vary on a local level, adjustable filter devices and their evaluation with contaminants are required. Within this work, modular filter devices are designed featuring an adjustable surface functionalization. For this purpose, 3D-printed structures are created consisting of bio-based poly(lactic acid) (PLA) that are manufactured by extrusion printing. The surface of PLA is activated with amino groups that are used to install xanthates as chain transfer agents. Subsequently, photo-iniferter (PI) polymerization is used to create cationic polymer brushes on the surface of PLA substrates. Multiple surface characterization techniques are employed to prove successful growth of polymer brushes on PLA. After initial optimization studies on flat surfaces, filter devices are printed, functionalized, and used to remove bacteria from contaminated water. Significant reduction of the number of microorganisms is detected after filtration (single filtration or cycling) and contaminating organism can also be removed from freshwater samples by simple incubation with a 3D-printed filter. The herein developed setup for producing functional filter devices and probing their performance in affinity filtration is a useful platform technology, enabling the rapid testing of polymer brushes for such applications.
P. Akarsu, S. Reinicke, A.-C. Lehnen, M. Bekir, A. Böker, M. Hartlieb, M. Reifarth Fabrication of Patchy Silica Microspheres with Tailor-made Functionality using Photo-Iniferter (PI)-RAFT Polymerization Small 2023, , 2301761 DOI: 10.1002/smll.202301761AbstractTheir inherent directional information renders patchy particles interesting building blocks for advanced applications in materials science. In this study, a feasible method to fabricate patchy silicon dioxide microspheres is demonstrated, which they are able to equip with tailor-made polymeric materials as patches. Their fabrication method relies on a solid-state supported microcontact printing (µCP) routine optimized for the transfer of functional groups to capillary-active substrates, which is used to introduce amino functionalities as patches to a monolayer of particles. Acting as anchor groups for polymerization, photo-iniferter reversible addition-fragmentation chain-transfer (RAFT) is used to graft polymer from the patch areas. Accordingly, particles with poly(N-acryloyl morpholine), poly(N-isopropyl acrylamide), and poly(n-butyl acrylate) are prepared as representative acrylic acid-derived functional patch materials. To facilitate their handling in water, a passivation strategy of the particles for aqueous systems is introduced. The protocol introduced here, therefore, promises a vast degree of freedom in engineering the surface properties of highly functional patchy particles. This feature is unmatched by other techniques to fabricate anisotropic colloids. The method, thus, can be considered a platform technology, culminating in the fabrication of particles that possess locally precisely formed patches on particles at a low µm scale with a high material functionality.
V. Akkerman, H. A. Scheidt, P. Reinholdt, M. Bashawat, M. Szomek, M. Lehmann, P. Wessig, D. F. Covey, J. Kongsted, P. Müller, D. Wüstner Natamycin interferes with ergosterol-dependent lipid phases in model membranes BBA Advances 2023, 4, 100102 DOI: 10.1016/j.bbadva.2023.100102AbstractNatamycin is an antifungal polyene macrolide that is used as a food preservative but also to treat fungal keratitis and other yeast infections. In contrast to other polyene antimycotics, natamycin does not form ion pores in the plasma membrane, but its mode of action is poorly understood. Using nuclear magnetic resonance (NMR) spectroscopy of deuterated sterols, we find that natamycin slows the mobility of ergosterol and cholesterol in liquid-ordered (Lo) membranes to a similar extent. This is supported by molecular dynamics (MD) simulations, which additionally reveal a strong impact of natamycin dimers on sterol dynamics and water permeability. Interference with sterol-dependent lipid packing is also reflected in a natamycin-mediated increase in membrane accessibility for dithionite, particularly in bilayers containing ergosterol. NMR experiments with deuterated\\r\\nsphingomyelin (SM) in sterol-containing membranes reveal that natamycin reduces phase separation and increases lipid exchange in bilayers with ergosterol. In ternary lipid mixtures containing monounsaturated phosphatidylcholine, saturated SM, and either ergosterol or cholesterol, natamycin interferes with phase separation\\r\\ninto Lo and liquid-disordered (Ld) domains, as shown by NMR spectroscopy. Employing the intrinsic fluorescence of natamycin in ultraviolet-sensitive microscopy, we can visualize the binding of natamycin to giant unilamellar\\r\\nvesicles (GUVs) and find that it has the highest affinity for the Lo phase in GUVs containing ergosterol. Our results suggest that natamycin specifically interacts with the sterol-induced ordered phase, in which it disrupts lipid packing and increases solvent accessibility. This property is particularly pronounced in ergosterol con-taining membranes, which could underlie the selective antifungal activity of natamycin
C. Henschel, D. Schanzenbach, A. Laschewsky, C.-H. Ko, C. M. Papadakis, P. Müller-Buschbaum Thermoresponsive and Co-nonsolvency Behavior of Poly(N-vinyl isobutyramide) and Poly(N-isopropyl methacrylamide) as Poly(N-isopropyl acrylamide) Analogs in Aqueous Media Colloid Polym. Sci. 2023, 301, 703-720 DOI: 10.1007/s00396-023-05083-4AbstractLarge sets of poly(N-vinyl isobutyramide), pNVIBAm, and poly(N-isopropyl methacrylamide), pNIPMAm are synthesized. The thermo- and solvent-responsive behaviors of these nonionic polymers in aqueous solution are studied for molar masses ranging from about 20 to 150 kg/mol. Both pNVIBAm and pNIPMAm show a lower critical solution temperature (LCST) of the rare so-called type II, in analogy to their well-studied analogue poly(N-isopropyl acrylamide) pNIPAm. Also, both polymers exhibit co-nonsolvency behavior in mixtures of water with several co-solvents, comprising lower alcohols as well as a number of polar aprotic solvents. Cloud points of the aqueous solutions are a few degrees higher than for pNIPAm, increasing as pNIPAm < pNVIBAm < pNIPMAm, while the co-nonsolvency behavior becomes less pronounced simultaneously. Exceptionally, pNIPMAm does not show co-nonsolvency in mixtures of water and DMF.
C. Gäbert, D. Hicke, L. Mayerhofer, M. Hartlieb, S. Reinicke Light-Dependent RAFT Polymerization of Spiropyran Acrylates Macro. Rapid Comm. 2023, , 202300108 DOI: 10.1002/marc.202300108AbstractLight-mediated polymerization techniques offer distinct advantages over polymerization reactions fueled by thermal energy, such as high spatial and temporal control as well as the possibility to work under mild reaction conditions. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a highly versatile radical polymerization method that can be utilized to control a variety of monomers and produce a vast number of complex macromolecular structures. The use of light to drive a RAFT-polymerization is possible via multiple routes. Besides the use of photo-initiators, or photo-catalysts, the direct activation of the chain transfer agent controlling the RAFT process in a photo-iniferter (PI) process is an elegant way to initiate and control polymerization reactions. Within this review, PI-RAFT polymerization and its advantages over the conventional RAFT process are\r\ndiscussed in detail.
Pablo Wessig, Max Lehmann [1,3]-Dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes – Synthesis, Properties and Applications Synthesis 2023, 55, 1824-1833 DOI: 10.1055/s-0042-1751428AbstractIn this review we give an overview of the syntheses and photophysical properties of the new class of fluorescent dyes based on a [1,3]-dioxolo[4.5-f]benzodioxole core and their derivatives. Starting from commercially available reactants (e.g. sesamol, 1,2,4,5-tetrachlorobenzene) the core units can be prepared in a simple manner. Then, the benzene core can be derivatized via lithiation and their photophysical properties can be adjusted as desired. The obtained fluorophores have an absorption range of 403 - 520 nm and an emission range of 495 - 665 nm. This class of fluorescent dyes is also characterized by a long fluorescence lifetime, a high stability towards photobleaching, large Stokes shifts and small size. Thus, the DBD dyes are optimally suited for optical sensing.
Peixi Wang, Christina Geiger, Julija Reitenbach, Apostolos Vagias, Lucas P. Kreuzer, Suzhe Liang, Robert Cubitt, Viet Hildebrand, André Laschewsky, Christine M. Papadakis, and Peter Müller-Buschbaum KCl-Modulated Hydration and Subsequent Thermoresponsive Behavior of Poly(sulfobetaine)-Based Diblock Copolymer Thin Films Macromolecules 2023, 56, 4087-4099 DOI: 10.1021/acs.macromol.3c00484AbstractDouble thermoresponsive diblock copolymer (DBC) are made from a short zwitterionic polymer block (PSBP with UCST) and a long non-ionic block (PNIPMAM with LCST). The KCl-modulated swelling of spin-coated thin films in D2O atmosphere and the subsequent responsive behavior are studied via spectral reflectance (SR), in situ time-of-flight neutron reflectometry (ToF-NR), and Fourier-transform infrared (FTIR) spectroscopy. The addition of KCl to the DBC thin films strongly increases the swelling ratio and D2O content during vapor treatment with D2O, with two observable separate volume phase transition temperatures (VPTTs). The macroscopic and mesoscopic D2O absorption and desorption are correlated with the changes of the hydration and de-hydration of the different hydrophilic groups (amide, ammonium & sulfonate) by the added KCl.
Vivien Meggyes, Amitabh Banerji Chemiedidaktik: Wasserstofftechnik in der Plastikbox Nachr. d. Chemie 2023, 71, 15-18 DOI: 10.1002/nadc.20234134091AbstractAus Alltagsmaterialien können Schüler:innen eine Mini-Zelle zur Wasserelektrolyse und eine Brennstoffzelle selbst bauen und so deren Prinzipien kennen lernen. Solche und weitere Experimente entwickeln Wissenschaftler:innen im Projekt „TeacH2 Tomorrow: low-cost Wasserstofftechnologien“.
Nchiozem-Ngnitedem, V.-A.; Sperlich, E.; Matieta, V. Y.; Ngnouzouba Kuete, J. R.; Kuete, V.; Omer, E. A.; Efferth, T.; Schmidt, B. Synthesis and Bioactivity of Isoflavones from Ficus carica and Some Non-Natural Analogues. J. Nat. Prod. 2023, 86, 1520 DOI: 10.1021/acs.jnatprod.3c00219AbstractIn an international joint research project, isoflavones from the fruits of Ficus carica, the common fig tree, were synthesized through a Suzuki-coupling approach and tested for their antibacterial activity against various Gram-positive and Gram-negative bacterial strains. In combination with an efflux pump inhibitor an up to 128-folde increase of the antibiotic activity was observed.
P. Gasse, T. Stensitzki, Y. Mai-Linde, T. Linker, H. M. Müller-Werkmeister 2D-IR spectroscopy of carbohydrates: Characterization of thiocyanate-labeled β-glucose in CHCl3 and H2O J. Chem. Phys. 2023, 158, 145101 DOI: 10.1063/5.0139166Abstract2D-IR spectroscopy of carbohydrates has been realized for the first time. Using a chemical synthesis scheme to incorporate -SCN at C2 position of glucose allows a detailed study of the molecular dynamics on the picosecond scale and opens possibilities for applications of 2D-IR spectroscopy to problems in glycobiology.
D. Keller, J. Hermanns How do students apply the octet rule and how do they justify this application? Chemistry Teacher International 2023, 5, 61-74 DOI: 10.1515/cti-2022-0023AbstractIn this paper we describe an intervention study on the application of the octet rule. This study was conducted at a German University with students in their first- and second undergraduate year. As repeatedly observed by us before, the evaluation of the study confirmed that the students have difficulties with the application of the octet rule in general, but above all for charged molecules. After an intervention, which consisted of a detailed checklist for the application of the octet rule and training opportunities, the students’ competences increased, especially for the tasks which included charged molecules. Students’ explanations were not as good as expected; the linguistic quality did not increase significantly from pre- to post-test. This is not surprising, because the training of argumentation skills was not part of the intervention. The intended goal, training the application of the octet rule, has been achieved
N. Lüdecke, M. Bekir, S. Eickelmann, M. Hartlieb, H. Schlaad Toward Protein-Repellent Surface Coatings from Catechol-containing Cationic Poly(2-ethyl-2-oxazoline) ACS Appl. Mater. Interfaces 2023, 15, 19582-19592 DOI: 10.1021/acsami.2c22518AbstractInspired by mussel proteins that enable surface binding in harsh marine environments, we envisioned a platform of protein-repellent macromolecules based on poly(2-ethyl-2-oxazoline) carrying catechol and cationic functional groups. To facilitate surface attachment, catechol units were installed by copolymerizing a functional comonomer, i.e., 2-(3,4-dimethoxyphenyl)-2-oxazoline, in a gradient fashion. Cationic units were introduced by partial acidic hydrolysis. Surface affinity of these polymers was probed using a Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D), and it was found that polymers with catechol units had a strong tendency to form surface-bound layers on different substrates, i.e., gold, iron, borosilicate, and polystyrene. While the neutral catechol-containing polymers showed strong, but uncontrolled binding, the ones with additional cationic units were able to form defined and durable polymer films. These coatings were able to prevent the attachment of different model proteins, i.e., bovine serum albumin (BSA), fibrinogen (FI), or lysozyme (LYZ). The herein introduced platform offers a straightforward access to non-fouling surface coatings using a biomimetic approach.
E. Khechine, S. Noack, H. Schlaad, J. Xu, G. Reiter, R. Reiter Reversible dehydration-hydration of poly(ethylene glycol) in Langmuir monolayers of a diblock copolymer inferred from changes in filament curvature Langmuir 2023, 39, 2710-2718 DOI: 10.1021/acs.langmuir.2c03179AbstractWe investigated changes in the hydration state of poly(ethylene glycol) (PEG) through morphological changes in Langmuir monolayers of a PEG-poly(L-lactide) (PLLA) (PEG-b-PLLA) diblock copolymer. When the PEG blocks were hydrated, we observed a remarkable morphology of bundles of ring-like filaments, arranged concentrically, yielding densely packed disk-like objects with a hollow center. We attribute the uniform curvature of these filaments to a strong mismatch between the molecular volumes occupied by PLLA blocks and hydrated PEG blocks. Under the constraint that each hydrated PEG block is attached to a hydrophobic PLLA block anchored to the air–water interface, this mismatch of molecular volumes caused strong repulsion within the PEG layer, in particular when the PLLA blocks packed tightly. Induced by a transition in the ordering of the PLLA blocks, the PEG blocks lost their hydration shell and packed into a dense polymer brush, accompanied by a reduction of the pressure within the PEG layer. During this packing process, the curvature of the filaments was eliminated and the ring-like filaments fractured into small linear pieces. Upon compression, the linear pieces coalesced and formed long filaments aligned in parallel. Importantly, upon expansion of the Langmuir film, these changes in morphology were reversible, and the PEG blocks could be rehydrated and bundles of concentrically arranged ring-like filaments were reformed. We conclude that the change in curvature of the filaments provides a means for distinguishing between the hydrated and dehydrated states of PEG.
Kwesiga, G.; Greese, J.; Kelling, A.; Sperlich, E.; Schmidt, B. The Suzuki–Miyaura Cross-Coupling–Claisen Rearrangement–Cross-Metathesis Approach to Prenylated Isoflavones J. Org. Chem. 2023, 88, 1649-1664 DOI: 10.1021/acs.joc.2c02698AbstractPrenylated isoflavones, originally isolated from the East African medicinal plants of the genera Erythrina and Millettia, have been synthesized through a Suzuki-Miyaura cross coupling strategy, in combination with a Claisen-rearrangement/cross metathesis sequence for installing the prenyl substituent. Isoflavones belong to the large group of plant polyphenols and show a wide range of bioactivities, e.g. estrogenic activity, anti-inflammatory and antimicrobial activity.
J. Reitenbach, C. Geiger, P. Wang, A. Vagias, R. Cubitt, D. Schanzenbach, A. Laschewsky, C. M. Papadakis, P. Müller-Buschbaum Effect of Magnesium Salts with Chaotropic Anions on the Swelling Behavior of PNIPMAM Thin Films Macromolecules 2023, 56, 567-577 DOI: 10.1021/acs.macromol.2c02282AbstractThe stimuli-responsive polymer poly(N-isopropyl methacrylamide) (PNIPMAm) exhibits in thin film geometry a volume-phase transition upon temperature increase in water vapor. In view of potential uses in nanodevices, we investigated the swelling behavior of PNIPMAm thin films containing magnesium salts in water vapor. Extent, kinetics of swelling, and water content were studied by in situ time-of-flight neutron reflectometry (ToF-NR). Additionally, the local solvation of the specific functional groups was probed by in situ Fourier-transform infrared (FTIR). Furthermore, the temporal sequence of solvation events was elucidated via two-dimensional FTIR correlation analysis. We show that the addition of Mg(ClO₄)₂ and in particular of Mg(NO₃)₂ enhances the response of PNIPMAM substantially, and thus, the responsiveness of switches and sensors based such thin films.
P. Wessig, D. Badetko, L. Wichterich, E. Sperlich, A. Kelling Total Synthesis of Arylnaphthalene Lignans via a Photochemical Key Step Eur. J. Org. Chem. 2023, 26, e202201234 DOI: 10.1002/ejoc.202201234AbstractThe total syntheses of three arylnaphthalene lignans (ANLs) were developed: Vitrofolal E (1), Noralashinol (2), and Ternifoliuslignan E (3). These natural products have in common a missing substituent in 2-position of the naphthalene moiety (2H-ANLs). The key step of these syntheses is a regioselective intramolecular Photo-Dehydro-Diels-Alder (PDDA) reaction with (1,7)naphthalenophanes as primary products. A further improvement of the photochemical step was achieved by triplet sensitization with xanthone, allowing the use of more efficient UVA lamps. It should be noted that this work is a continuation of a previous publication about the total synthesis of lignans using the PDDA reaction.
A. Prause, M. Hechenbichler, R. Schmidt, M. Simon, S. Prévost, L. Cavalcanti, Y. Talmon, A. Laschewsky, M. Gradzielski Rheological Control of Aqueous Dispersions by Thermo-responsive BAB* Copolymers of Different Architectures. Macromolecules 2023, 56, 104-121 DOI: 10.1021/acs.macromol.2c01965 AbstractWe synthesized libraries of amphiphilic copolymers with BAB*-, B2AB*-, and B(AB*)2-type polymer architectures from various N-substituted polyacrylamides, varying their structures systematically. Here, ‘A’ stands for a long permanently hydrophilic block, ‘B’ is a permanently hydrophobic end group (\\\"sticker)\\\", and ‘B*’ indicates a relatively short thermo-responsive block. These ternary amphiphilic block polymers undergo temperature-dependent self-assembly in aqueous solution and are shown to act as “smart” copolymer thickener. They enable the control of the solutions\\\' rheological properties, and in particular, they allow for maintaining and even increasing the viscosity at elevated temperatures. The thermally-induced macroscopic rheological changes can be correlated with with the mesoscopic organization of the respective systems, as characterized by light scattering (SLS and DLS), small-angle neutron scattering (SANS), and fluorescent probe studies.
A.-C. Lehnen, J. Gurke, A. M. Bapolisi, M. Reifarth, M. Bekir, M. Hartlieb Xanthate-supported photo-iniferter (XPI)-RAFT polymerization: facile and\r\nrapid access to complex macromolecules. Chem. Sci. 2023, 14, 593-603 DOI: 10.1039/D2SC05197DAbstractXanthate-supported photo-iniferter (XPI)-reversible addition–fragmentation chain-transfer (RAFT) polymerization is introduced as a fast and versatile photo-polymerization strategy. Small amounts of xanthate are added to conventional RAFT polymerizations to act as a photo-iniferter under light irradiation. Radical exchange is facilitated by the main CTA ensuring control over the molecular weight distribution, while xanthate enables an efficient photo-(re)activation. The photo-active moiety is thus introduced into the polymer as an end group, which makes chain extension of the produced polymers possible directly by irradiation. This is in sharp contrast to conventional photo-initiators, or photo electron transfer (PET)-RAFT polymerizations, where radical generation depends on the added small molecules. In contrast to regular photo-iniferter-RAFT polymerization, photo-activation is decoupled from polymerization control, rendering XPI-RAFT an elegant tool for the fabrication of defined and complex macromolecules. The method is oxygen tolerant and robust and was used to perform screenings in a well-plate format, and it was even possible to produce multiblock copolymers in a coffee mug under open-to-air conditions. XPI-RAFT does not rely on highly specialized equipment and qualifies as a universal tool for the straightforward synthesis of complex macromolecules. The method is user-friendly and broadens the scope of what can be achieved with photo-polymerization techniques.
A. Choudhury, J. A. DeVine, S. Sinha, J. A. Lau, A. Kandratsenka, D. Schwarzer, P. Saalfrank, A. M. Wodtke Condensed Phase Isomerization Through Tunneling Gateways Nature 2022, 612, 691-696 DOI: 10.1038/s41586-022-05451-0AbstractQuantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave. Usually, lighter particles tunnel more efficiently than heavier ones. In this work, experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface, show nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed.
R. Schürmann, A. Dutta, K. Ebel, K. Tapio, A. R. Milosavljevic, I. Bald Plasmonic reactivity of halogen thiophenols on gold nanoparticles studied by SERS and XPS J. Chem. Phys. 2022, 157, 084708 DOI: 10.1063/5.0098110AbstractLocalized surface plasmon resonances on noble metal nanoparticles (NPs) can efficiently drive reactions of adsorbed ligand molecules and provide versatile opportunities in chemical synthesis. The driving forces of these reactions are typically elevated temperatures, hot charge carriers, or enhanced electric fields. In the present work, dehalogenation of halogenated thiophenols on the surface of AuNPs has been studied by surface enhanced Raman scattering (SERS) as a function of the photon energy to track the kinetics and identify reaction products. Reaction rates are found to be surprisingly similar for different halothiophenols studied here, although the bond dissociation energies of the C–X bonds differ significantly. Complementary information about the electronic properties at the AuNP surface, namely, work-function and valence band states, has been determined by x-ray photoelectron spectroscopy of isolated AuNPs in the gas-phase. In this way, it is revealed how the electronic properties are altered by the adsorption of the ligand molecules, and we conclude that the reaction rates are mainly determined by the plasmonic properties of the AuNPs. SERS spectra reveal differences in the reaction product formation for different halogen species, and, on this basis, the possible reaction mechanisms are discussed to approach an understanding of opportunities and limitations in the design of catalytical systems with plasmonic NPs.
A. Dutta, K. Tapio, A. Suma, A. Mostafa, Y. Kanehira, V. Carnevale, G. Bussi, I. Bald Molecular States and Spin Crossover of Hemin Studied by DNA Origami Enabled Single-Molecule Surface-Enhanced Raman Scattering Nanoscale 2022, 14, 16467-16478 DOI: 10.1039/d2nr03664aAbstractUsing hot charge carriers far from a plasmonic nanoparticle surface is very attractive for many applications in catalysis and nanomedicine and will lead to a better understanding of plasmon-induced processes, such as hot-chargecarrier- or heat-driven chemical reactions. Herein we show that DNA is able to transfer hot electrons generated by a silver nanoparticle over several nanometers to drive a chemical reaction in a molecule nonadsorbed on the surface. For this we use 8-bromo-adenosine introduced in different positions within a double-stranded DNA oligonucleotide. The DNA is also used to assemble the nanoparticles into nanoparticles ensembles enabling the use of surface-enhanced Raman scattering to track the decomposition reaction. To prove the DNA-mediated transfer, the probe molecule was insulated from the source of charge carriers, which hindered the reaction. The results indicate that DNA can be used to study the transfer of hot electrons and the mechanisms of advanced plasmonic catalysts.
J. Hermanns, D. Keller How do students reason when they have to describe the "what" and "why" of a given reaction mechanism? N. Graulich and G. Shultz: Student Reasoning in Organic Chemistry - Research Advances and Evidence-based Instructional Practices, Royal Society of Chemistry, GB. 2022, , 125-140 DOI: AbstractMechanistic reasoning of students has been the focus of research in recent years. To initiate and research this reasoning, students were asked to explain mechanistic steps for mechanisms in organic chemistry formerly unknown to them with their own words. The mechanisms were divided in their singular steps and captions for each mechanistic step were written by the students resulting in mechanism comics. Those mechanism comics were qualitatively evaluated. The coding process included three rounds. The written captions were assigned as descriptive or causal, were assigned as “activities” or “properties of entities” and in the last round were analyzed to decide whether those were technically correct, partially correct or not correct. The analysis shows that the students’ reasoning mostly was descriptive; they described “what” happened in the mechanistic steps and less “why”. The students mostly described “how” the particles interacted. Because the mechanism comics do not need much time and effort, they are a suitable instrument for learning the design of reaction mechanisms and for getting insights in the quality of students’ mechanistic reasoning.
Sand, P.; Schmidt, B. Orthogonal Arylation of a Diene-Sulfonamide using Cationic Transition Metal Catalysts. Eur. J. Org. Chem. 2022, , e202201336 DOI: https://doi.org/10.1002/ejoc.202201336AbstractThe regioselectivity of two mechanistically distinct alkenylation reactions catalyzed by in situ-formed cationic transition metal complexes was studied using N-allyl-N-phenylethenesulfonamide as a model compound. Orthogonal selectivity was observed for the Ru-catalyzed C-H-activating alkenylation with acetanilides, which occurs preferentially at the electron deficient double bond, and for a Pd-catalyzed Heck-type coupling with arene diazonium salts, which occurs preferentially at the more electron rich double bond of the N-allyl substituent.
A.-C. Lehnen, A. M. Bapolisi, M. Krass, A. AlSawaf, J. A. M. Kurki, S. Kersting, H. Fuchs, M. Hartlieb Shape matters: Highly selective Antimicrobial Bottle Brush copolymers via a\r\none-pot RAFT polymerization approach Biomacromolecules 2022, 23, 5350-5360 DOI: 10.1021/acs.biomac.2c01187AbstractThe one-pot synthesis of antimicrobial bottle brush copolymers is presented. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is used for the production of the polymeric backbone, as well as for the grafts, which were installed using a grafting-from approach. A combination of N-isopropyl acrylamide and a Boc-protected primary amine-containing acrylamide was used in different compositions. After deprotection, polymers featuring different charge densities were obtained in both linear and bottle brush topologies. Antimicrobial activity was tested against three clinically relevant bacterial strains, and growth inhibition was significantly increased for bottle brush copolymers. Blood compatibility investigations revealed strong hemagglutination for linear copolymers and pronounced hemolysis for bottle brush copolymers. However, one bottle brush copolymer with a 50% charge density revealed strong antibacterial activity and negligible in vitro blood toxicity (regarding hemolysis and hemagglutination tests) resulting in selectivity values as high as 320. Membrane models were used to probe the mechanism of shown polymers that was found to be based on membrane disruption. The trends from bioassays are accurately reflected in model systems indicating that differences in lipid composition might be responsible for selectivity. However, bottle brush copolymers were found to possess increased cytotoxicity against human embryonic kidney (HEK) cells compared with linear analogues. The introduced synthetic platform enables screening of further, previously inaccessible parameters associated with the bottle brush topology, paving the way to further improve their activity profiles.
J. Yang, S. Ghosh, A. Acharija, Ch. Penschke, Y. Tstsui, J. Rabeah, T. Wang, S.Y. Djoko, J. Roeser, M.-y. Ye, S. Li, C. Li., R. Schomäcker, R. Van De Krol, S. Sekl, P. Saalfrank und A. Thomas Constitutional Isomerism of the Linkages in Donor-acceptor\r\nCovalent Organic Frameworks and Its Impact on Photocatalysis Nature Commun. 2022, 13, 1-10 DOI: 10.1038/s41467-022-33875-9AbstractIn this work, the effect of constitutional isomerism in covalent organic\r\nframeworks (COFs) of the donor-acceptor type and its impact on\r\nphotocatalysis are studied. Seemingly small differences in their constitution, can cause\r\nsubstantial differences in the peformance of these photocatalysts which\r\nare analyzed by experiment and theory.\r\n
Eric W. Fischer, Peter Saalfrank Cavity-Induced Non-Adiabatic Dynamics and Spectroscopy of Molecular Rovibrational Polaritons Studied by Multi-Mode Quantum Models. J. Chem. Phys. 2022, 157, 1-13 DOI: 10.1063/5.0098006AbstractMatter-light hybrid states, so-called polaritons, play an increasing role\r\nin chemistry, e.g., in spectroscopy and reaction dynamics. Here\r\nwe study theoretically the quantum dynamics and spectroscopy of\r\nrovibrational polaritons formed in a model system composed of a single\r\nrovibrating diatomic molecule, which interacts with two degenerate,\r\northogonally polarized modes of an optical Fabry–Pérot cavity. We identify\r\nthree-state vibro-polaritonic conical intersections (VPCIs) between singly\r\nexcited vibro-polaritonic states. The non-trivial VPCI topology\r\nmanifests as pronounced multi-peak progression in the spectral region of\r\nthe upper vibrational polariton, which is traced back to the emergence of\r\nrovibro-polaritonic light–matter hybrid states.
M. Hechenbichler, A. Prause, M. Gradzielski, A. Laschewsky Thermo-responsive Self-assembly of Two-fold Fluorescently Labelled Block Copolymers in Aqueous Solution and Microemulsions Langmuir 2022, 38, 5166-5182 DOI: 10.1021/acs.langmuir.1c02318AbstractA nonionic double hydrophilic linear block copolymer with a permanently hydrophilic and a thermo-responsive block (showing an LCST transition) is prepared by reversible addition fragmentation chain transfer (RAFT) polymerization of acrylamides. By virtue of a specifically designed chain transfer agent, the polymer is functionalized with two complementary fluorescent dyes as end groups which are suited for Förster resonance energy transfer (FRET). The temperature-dependent self-assembly of the two-fold fluorescently labelled copolymer is studied in pure aqueous solution as well as in an o/w microemulsion, and compared to the behaviors of the analogously labelled homopolymers. The results show that the block copolymer behaves as polymeric surfactant at low temperatures, with one relatively small hydrophobic end block and an extended hydrophilic chain forming ‘hairy micelles’. In contrast, when heated above the phase transition temperature of the responsive block, the copolymer behaves as an associative telechelic with two different hydrophobic end blocks that do not mix. In consequence, large dynamic aggregates are formed instead of a network of bridged ‘flower micelles’. These are connected alternatingly by the original micellar cores and by clusters of the collapsed polymer blocks. This behavior is even more favored in the w/o microemulsion than in pure aqueous solution, as the microemulsion droplets constitute an attractive anchoring point for the hydrophobic dodecyl sticker, but not for the collapsed polymer chains.
A. Prause, M. Hechenbichler, B. von Lospichl, A. Feoktystov, R. Schweins, N. Mahmoudi, A. Laschewsky, M. Gradzielski Aggregation behavior of non-symmetrically end-capped thermo-responsive block polymers in aqueous solution: between polymer coil and micellar state Macromolecules 2022, 55, 5849-5863 DOI: 10.1021/acs.macromol.2c00878AbstractA library of novel amphiphilic BAB* copolymers is synthesized, with ‘A’ being a long permanently hydrophilic block of poly(N,N dimethylacrylamide) (pDMAm), ‘B’ a permanently hydrophobic end group, and ‘B*’ a thermo-responsive block. While keeping blocks A and B constant in the study, the chemical structure of the responsive B* block was varied, employing poly(N n propylacrylamide), poly(N isopropylacrylamide), poly(N,N diethylacrylamide) and poly(N acryloylpyrrolidine) (pNAP). All these polyacrylamides show distinct lower critical solution temperature (LCST) behavior with differing transition temperatures. The self-assembly of the various amphiphilic copolymers in aqueous solution was studied as a function of concentration and temperature and of the systematically varied lengths of the B* blocks, using complementary scattering methods (SLS, DLS, SANS). The heating above the phase transition temperature of the responsive B* blocks induces the formation of well-structured, ordered aggregates. The aggregation can be controlled by choice and length of the TR block
L. Schardt, A. Martínez Guajardo, J. Koc, J. L. Clarke, J. A. Finlay, A. S. Clare, H. Gardner, G.W. Swain, K. Hunsucker, A. Laschewsky, A. Rosenhahn Low fouling polysulfobetaines with variable hydrophobic content Macromol. Rapid Commun. 2022, 43, [2100589] DOI: 10.1002/marc.202100589AbstractCoatings of amphiphilic polymers combining hydrophilic zwitterionic groups with hydrophobic elements seem a promising strategy to decrease biofouling. To better understand the impact of the hydrophobic component in such coatings on the interfacial molecular reorganization dynamics and the fouling resistance, we prepared a series of poly(sulfobetaine methacrylate)s with increasing contents of hydrophobic comonomer butylmethacylate. Biofouling is assessed in laboratory assays with a set of model foulants of different sizes, including proteins, a diatom and a green algae. The fouling behaviors of the photo-crosslinked coatings are compared to those of the underlying homopolymers. While all zwitterionic coatings strongly reduce biofouling, the amphiphilic copolymers revealed the best fouling resistance. In preliminary field tests in the ocean, the reduced susceptibility to silt incorporation of the copolymers, compared to the highly swollen polyzwitterion homopolymer, likely contributes to their higher fouling resistance.\r\n\r\n
J. F. Karthäuser, J. Koc, E. Schönemann, R. Wanka, N. Aldred, A. S. Clare, A. Rosenhahn, A. Laschewsky Optimizing Fouling Resistance of Poly(sulfabetaine)s through Backbone and Charge Separation Adv. Mater. Interfaces 2022, 9, [2200677] DOI: 10.1002/admi.202200677AbstractAs set of systematically varied poly(sulfabetaine methacrylate)s, i.e. combining ammonium and sulfate moieties within the constitutional repeat unit, is studied as a new class of zwitterionic polymers. Photo-crosslinked films are prepared and explored as potential coatings against marine biofouling studying several types of typical foulant organisms (bateria, diatoms, barnacles). We investigate in particular the effect of the spacer groups that separate the cationic ammonium from the anionic sulfate groups, as well as those separating the zwitterionic group from the polymer backbone. All polymers compare well with the standard poly(sulfobetaine methacrylate) polySPE that serves as benchmark for an effective low-fouling material. Though overall, the highest fouling-resistance is found for polymers having the shorter ethylene spacers, both spacer types, intercharge or betaine-to-backbone, control which particular organism is most effectively prevented from fouling.
J. Hermanns*, L. Zöllner, C. Filschke Newly designed laboratory course for pre-service chemistry teachers: Do the students rate their practical skills as relevant for their future profession? J. Chem. Educ. 2022, 99, 3713-3722 DOI: 10.1021/acs.jchemed.2c00618AbstractThe laboratory course in organic chemistry for preservice chemistry teachers has been designed anew. For the course, only two weeks (eight hours a day) are available. Therefore, we wanted to use this time effectively, which led to the following main goals: the students should achieve practical skills, understand the practical procedures they had to conduct, and apply those well-founded to new problems. Besides this, the students should get to know procedures and experiments for their future profession. The design of the course focusses on the concept of “school-related content knowledge” that was applied and adapted for planning this laboratory course. The new course has been evaluated using the results of two questionnaires as well as the content of the reflection tasks that were part of the students’ laboratory journals. The students are very content with this newly designed course and are of the opinion that they developed practical skills, and that they are able to apply those skills for new experiments. They also rate those skills as useful for their future profession as a chemistry teacher.
P. Gurnani, C. Sanchez-Cano, H. Xandri-Monje, J. Zhang, S. Ellacott, E. Mansfield, M. Hartlieb, R. Dallmann, S. Perrier Probing the effect of rigidity on the cellular uptake of core-shell nanoparticles: Stiffness effects are size dependent Small 2022, 18, 2203070 DOI: 10.1002/smll.202203070AbstractNanoparticles are well established vectors for the delivery of a wide range of biomedically relevant cargoes. Numerous studies have investigated the impact of size, shape, charge, and surface functionality of nanoparticles on mammalian cellular uptake. Rigidity has been studied to a far lesser extent, and its effects are still unclear. Here, the importance of this property, and its interplay with particle size, is systematically explored using a library of core-shell spherical PEGylated nanoparticles synthesized by RAFT emulsion polymerization. Rigidity of these particles is controlled by altering the intrinsic glass transition temperature of their constituting polymers. Three polymeric core rigidities are tested: hard, medium, and soft using two particle sizes, 50 and 100 nm diameters. Cellular uptake studies indicate that softer particles are taken up faster and threefold more than harder nanoparticles with the larger 100 nm particles. In addition, the study indicates major differences in the cellular uptake pathway, with harder particles being internalized through clathrin- and caveolae-mediated endocytosis as well as macropinocytosis, while softer particles are taken up bycaveolae- and non-receptormediated endocytosis. However, 50 nm derivatives do not show any appreciable differences in uptake efficiency, suggesting that rigidity as a parameter in the biological regime may be size dependent.
A. M. Bapolisi, P. Kielb, M. Bekir, A.-C. Lehnen, C. Radon, S. Laroque, P. Wendler, H. M. Müller-Werkmeister, M. Hartlieb Antimicrobial Polymers of Linear and Bottlebrush Architecture: Probing the Membrane Interaction and Physicochemical Properties Macro. Rapid Comm. 2022, 43, 2200288 DOI: 10.1002/marc.202200288AbstractPolymeric antimicrobial peptide mimics are a promising alternative for the future management of the daunting problems associated with antimicrobial resistance. However, the development of successful antimicrobial polymers (APs) requires careful control of factors such as amphiphilic balance, molecular weight, dispersity, sequence, and architecture. While most of the earlier developed APs focus on random linear copolymers, the development of APs with advanced architectures proves to be more potent. It is recently developed multivalent bottlebrush APs with improved antibacterial and hemocompatibility profiles, outperforming their linear counterparts. Understanding the rationale behind the outstanding biological activity of these newly developed antimicrobials is vital to further improving their performance. This work investigates the physicochemical properties governing the differences in activity between linear and bottlebrush architectures using various spectroscopic and microscopic techniques. Linear copolymers are more solvated, thermo-responsive, and possess facial amphiphilicity resulting in random aggregations when interacting with liposomes mimicking Escheria coli membranes. The bottlebrush copolymers adopt a more stable secondary conformation in aqueous solution in comparison to linear copolymers, conferring rapid and more specific binding mechanism to membranes. The advantageous physicochemical properties of the bottlebrush topology seem to be a determinant factor in the activity of these promising APs.
J. Hermanns, H. Kunold Mechanism comics as a task in a written exam in organic chemistry for pre-service chemistry teachers Chemistry Teacher International 2022, 4, 259-269 DOI: 10.1515/cti-2021-0035AbstractIn this paper we describe and evaluate a study on the use of mechanism comics as solution to a task in a written exam for the course “organic chemistry I for pre-service chemistry teachers”. The students had to design a reaction mechanism for a reaction that was unknown to them and to write captions for every step to explain all steps of their reaction mechanism. The students’ work was evaluated using the method of qualitative content analysis in four rounds by both authors. The majority of the captions was coded as “descriptive” and only the minority as “causal”. Therefore, the students mostly describe “what” happens, but seldom “why” this happens. Implicit electron movement is also described more often than explicit electron movement. The majority of the captions were technically correct. Summarizing, the students are capable of designing and describing a reaction mechanism for a formerly unknown reaction. The quality of their reasoning could be improved. In the new course, the quality of the mechanistic reasoning and then especially the explanations of “why” mechanistic steps occur will be in a much clearer focus.
P. Wessig, D. Badetko, M. Koebe Triplet Sensitized Photo-Dehydro-Diels-Alder Reaction ChemistrySelect 2022, 7, e202202648 DOI: 10.1002/slct.202202648AbstractWe report on the triplet sensitization of the intramolecular Photo-Dehydro-Diels-Alder (PDDA) reaction of two diaryl suberates bearing methyl propiolate chromophors. Compared with the non-sensitized irradiation, considerably increased yields could be observed. Moreover, it is possible to use the more efficient UVA lamps instead of UVB lamps. Among three investigated sensitizers (xanthone, benzophenone, thioxanthone) xanthone gave the best results.
U. Tritschler, J. M. Delgado López, T. R. Umbach, A. E. S. Van Driessche, H. Schlaad, H. Cölfen, M. Kellermeier Oriented attachment and aggregation as a viable pathway to self-assembled organic/inorganic hybrid materials CrystEngComm 2022, 24, 6320-6329 DOI: 10.1039/d2ce00447jAbstractOrganic–inorganic composite materials with tailored properties can be designed in the lab through bio-inspired approaches. In this context, we exploited the particle-based crystallisation process of calcium sulfate, a technologically important mineral, to hybridise inorganic and organic matter. We identified and synthesised an organic polymer showing strong affinity to bind to the surfaces of mineral precursors as well as intrinsic tendency to self-organise. Subsequently, polymer-coated building units were allowed to self-assemble via oriented attachment, aggregation and phase transformation, which produced ordered superstructures where the organic polymer is intercalated between the subunits and surrounds the hybrid core as a shell. This specific architecture across multiple length scales leads to unique mechanical properties, comparable to those of natural biominerals. Thus, our results devise a straightforward pathway to prepare organic–inorganic hybrid structures via bottom-up self-assembly processes innate to the crystallisation of the inorganic phase. This approach can likely be transferred to other inorganic minerals, affording next-generation materials for applications in the construction sector, biomedicine and beyond.
Eric Sperlich, Alexandra Kelling, George Kwesiga, Bernd Schmidt Intermolecular interactions in the solid-state structures of isoflavones: the relationship between supramolecular structure, torsion angle, and macroscopic properties CrystEngComm 2022, DOI: 10.1039/D2CE00169AAbstractThe molecular structures of three closely related isoflavones have been determined by single crystal X-ray diffraction and have been analysed by geometry matching with the CSD, Hirshfeld surface analysis and analysis of stacking interactions with the Aromatic Analyser program (CSD). The formation of the supramolecular structure by non-covalent interactions was studied and substantial differences in the macroscopic properties e.g., the solubility, were correlated with hydrogen bonding and π-stacking interactions. Moreover, a correlation between the supramolecular structure, the torsion angle (between benzopyran group and aryl group), and macroscopic properties was determined in the three compounds.
T. G. Floyd, J. Song, A. Hapeshi, S. Laroque, M. Hartlieb, S. Perrier Bottlebrush Copolymers for Gene Delivery: Influence of Architecture, Charge Density, and Backbone Length on Transfection Efficiency J. Mater. Chem. B 2022, 10, 3696-3704 DOI: 10.1039/D2TB00490AAbstractThe influence of polymer architecture of polycations on their ability to transfect mammalian cells is probed. Polymer bottle brushes with grafts made from partially hydrolysed poly(2-ethyl-2-oxazoline) are used while varying the length of the polymer backbone as well as the degree of hydrolysis (cationic charge content). Polyplex formation is investigated via gel electrophoresis, dye-displacement and dynamic light scattering. Bottle brushes show a superior ability to complex pDNA when compared to linear copolymers. Also, nucleic acid release was found to be improved by a graft architecture. Polyplexes based on bottle brush copolymers showed an elongated shape in transmission electron microscopy images. The cytotoxicity against mammalian cells is drastically reduced when a graft architecture is used instead of linear copolymers. Moreover, the best-performing bottle brush copolymer showed a transfection ability comparable with that of linear poly(ethylenimine), the gold standard of polymeric transfection agents, which is used as positive control. In combination with their markedly lowered cytotoxicity, cationic bottle brush copolymers are therefore shown to be a highly promising class of gene delivery vectors.
M. Reifarth, M. Bekir, A. M. Bapolisi, E. Titov, F. Nußhardt, J. Nowaczyk, D. Grigoriev, A. Sharma, P. Saalfrank, S. Santer, M. Hartlieb, A. Böker A Dual pH- and Light-Responsive Spiropyran-Based Surfactant: Investigations on Its Switching Behavior and Remote Control over Emulsion Stability Angw. Chem. Int. Ed. 2022, 61, e202114687 DOI: 10.1002/anie.202114687AbstractA cationic surfactant containing a spiropyran unit is prepared exhibiting a dual-responsive adjustability of its surface-active characteristics. The switching mechanism of the system relies on the reversible conversion of the non-ionic spiropyran (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH-dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli-responsive behavior enables remote-control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH-dependent manipulation of oil-in-water emulsions.
P. Wessig, D. Badetko, M. Czarnecki, L. Wichterich, P. Schmidt, C. Brudy, E. Sperlich, A. Kelling Studies toward the Total Synthesis of Arylnaphthalene Lignans via a\r\nPhoto-Dehydro-Diels-Alder (PDDA) Reaction J. Org. Chem. 2022, 87, 5904-5915 DOI: 10.1021/acs.joc.2c00195AbstractAn efficient method for the preparation of arylnaphthalene lignans (ANLs) was developed, which is based on the Photo-Dehydro-DIELS-ALDER (PDDA) reaction. While intermolecular PDDA reactions turned out to be inefficient, the intramolecular variant using suberic acid as tether linking two aryl propiolic esters smoothly provided naphthalenophanes. The irradiations were performed with a previously developed annular continuous-flow reactor and UVB lamps. In this way, the natural products Alashinol D, Taiwanin C, und an unnamed ANL could be prepared.
J. Hermanns, D. Keller The development, use and evaluation of digital games and quizzes in an introductory course on organic chemistry for preservice chemistry teachers J. Chem. Educ. 2022, 99, 1715-1724 DOI: 10.1021/acs.jchemed.2c00058AbstractDue to the COVID pandemic the introductory course on organic chemistry was developed and conducted as an online course. To ensure methodical variety in this course, educational games and quizzes have been developed, used and evaluated. The attendance of the course, and therefore also the use of the quizzes and games was voluntary. The quizzes’ main goal was to give the students the opportunity to check whether they memorized the knowledge needed in the course. Another goal was to make transparent which knowledge the students should rote memorize. The evaluation shows that the students had not internalized all knowledge which they should apply in several tasks on organic chemistry. They answered multi-select questions in general less well than single-select questions. The games should combine fun with learning. The evaluation of the games shows that the students rated them very well. The students used those games again for their exam preparation as the monitoring of accessing the games showed. Students’ experiences with using electronic devices in general or for quizzes and games have also been evaluated because their experience could influence the students’ assessment of the quizzes and games used in our study. However, the students used electronic devices regularly and should therefore be technically competent to use our quizzes and games. The evaluation showed that the use of digital games for learning purposes is neither at school nor at university very common, although the students had worked with such tools before. The students are also very interested in using and developing such digital games for their own study, but also for their future work at school.
J. Hermanns, I. Glowinski Who prefers online teaching and learning? The relevance of students\' personal characteristics and learning strategies Progress in Science Education 2022, 5, 35-47 DOI: 10.25321/prise.2022.1320AbstractStudents’ learning is influenced by students’ personal characteristics and learning strategies. There are learning-oriented and grade-oriented students. To predict study outcome, the “big five personality characteristics” can be used. Those are extraversion, agreeableness, conscientiousness, emotional stability and autonomy as well as personal orientations on learning and students’ study approach. Other personality characteristics are for example motivation or students’ self-concept. Three learning strategies have been mentioned in the literature: cognitive, metacognitive and resource management learning strategies. Learning strategies can be defined as the learning behaviour and the attitudes behind this behaviour. For online teaching in courses on STEM subjects, an online questionnaire was developed, used and evaluated. The study focusses on relationships associated with students’ preference for online teaching and a preference for classroom learning. The relationships between the students’ personal characteristics and attitudes and their general learning strategies towards online learning have been evaluated. Enthusiasm and study satisfaction show a large correlation with their appreciation of online provided as learning resources during the online term. However, these personal characteristics of students show only small correlations with the preference for online learning and classroom learning. Positive correlations for online learning show negative for classroom learning. The relevant learning strategies (“effort”, “general time management”, “literature use”, “learning environment” and ”control”) correlate mostly signficantly but always negatively in a small range with a preference for classroom learning. Poorly developed general learning strategies could let students prefer the less self-regulated learning. However, for predicting a preference for online learning, general learning strategies seem to have a limited value. The successful mastering of the requirements during the online term seems to be more relevant, independent from the expression of general learning strategies.
A.-C. Lehnen, J. A. M. Kurki, M. Hartlieb The difference between photo-iniferter and conventional RAFT polymerization: high livingness enables the straightforward synthesis of multiblock copolymers Polym. Chem. 2022, 13, 1537-1546 DOI: 10.1039/D1PY01530CAbstractPhoto-iniferter (PI)-RAFT polymerization, the direct activation of chain transfer agents via light, is a fascinating polymerization technique, as it overcomes some restriction of conventional RAFT polymerization. As such, we elucidated the role of reversible deactivation in this context using a monomer-CTA pair with low chain transfer capabilities. Tests with varying targeted degrees of polymerization (DP) or monomer concentrations revealed no significant improvement of polymerization control using the PI-process. Control can however be achieved via slow monomer addition, increasing the number of activation/deactivation events per monomer addition....
Lood, K.; Tikk, T.; Krüger, M.; Schmidt, B. Methylene Capping Facilitates Cross-Metathesis Reactions of Enals: A Short Synthesis of 7-Methoxywutaifuranal from the Xylochemical Isoeugenol J. Org. Chem. 2022, 87, 3079-3088 DOI: 10.1021/acs.joc.1c02851AbstractXylochemicals are chemicals derived from wood-based renewables, e. g. lignin. A number of naturally occurring isopropenylbenzenes, e. g. isoeugenol, trans-anethole and α-asarone, were found to be effective substrates for olefin cross metathesis reactions with crotonaldehyde to furnish valuable oxygenated cinnamaldehydes. Surprisingly, the cross metathesis reactions proceed more efficiently with crotonaldehyde than with the sterically less hindered acrolein, which we attribute to methylene capping of the propagating catalytically active Ru-carbene species. The method was applied to the synthesis of the natural product 7-methoxywutaifuranal, which was synthesized through a one-pot RCM-CM-sequence.
Fudickar, W.; Roder, P.; Listek, M.; Hanack, K.; Linker, T. Pyridinium Alkynylanthracenes as Sensitizers for Photodynamic Therapy Photochem Photobiol. 2022, 98, 193-201 DOI: 10.1111/php.13554AbstractPhotodynamic therapy (PDT) is a mild but effective method to treat certain types of cancer upon irradiation with visible light. Here, three isomeric methylpyridinium alkynylanthracenes 1o-p were evaluated as sensitizers for PDT. Upon irradiation with blue or green light,all three compounds show the ability to initiate strand breaks of plasmid DNA. The mayor species responsible for cleavage is singlet oxygen (1O2) as confirmed by scavenging reagents. Only isomers 1m and 1p can be incorporated into HeLa cells, whereas isomer 1o cannot permeate through the membrane. While isomer 1m targets the cell nucleus, isomer 1p assembles in the cellular cytoplasm and impacts the cellular integrity. This is in accordance with a moderate toxicity of 1p in the dark, whereas 1m exhibits no dark toxicity. Both isomers are suitable as PDT reagents, with a CC50 of 3 μm and 75 nm, for 1p and 1m, respectively. Thus, derivative 1m, which can be easily synthesized, becomes an interesting candidate for cancer therapy.
Fudickar, W.; Metz, M.; Mai-Linde, Y.; Krüger, T.; Kelling, A.; Sperlich, E.; Linker, T. Influence of Functional Groups on the Ene Reaction of Singlet Oxygen with 1,4-Cyclohexadienes Photochem Photobiol. 2021, 97, 1289–1297 DOI: 10.1111/php.13422AbstractThe photooxygenation of 1,4-cyclohexadienes has been studied with a special focus on regio- and stereoselectivities. In all examples, only the methyl-substituted double bond undergoes an ene reaction with singlet oxygen, to afford hydroperoxides in moderate to good yields. We explain the high regioselectivities by a "large-group effect" of the adjacent quaternary stereocenter. Nitriles decrease the reactivity of singlet oxygen, presumably by quenching, but can stabilize proposed per-epoxide intermediates by polar interactions resulting in different stereoselectivities. Spiro lactams and lactones show an interesting effect on regio- and stereoselectivities of the ene reactions. Thus, singlet oxygen attacks the double bond preferentially anti to the carbonyl group, affording only one regioisomeric hydroperoxide. If the reaction occurs from the opposite face, the other regioisomer is exclusively formed by severe electrostatic repulsion in a perepoxide intermediate. We explain this unusual behavior by the fixed geometry of spiro compounds and call it a "spiro effect" in singlet oxygen ene reactions.
R. R. Raju, J. Koetz Pickering Janus emulsions stabilized with gold nanoparticles Langmuir 2022, 38, 147-155 DOI: 10.1021/acs.langmuir.1c02256AbstractWe report a modified approach to batch scale preparation of completely engulfed core-shell emulsions or partially engulfed Janus emulsions with colorful optical properties, containing water, olive oil and silicone oil. In situ reduction of gold chloride, forming gold nanoparticles (AuNPs) at the olive oil interface in absence or presence of chitosan, leads to the formation of compartmentalized olive-silicone oil emulsion droplets in water. In absence of additional reducing components, time-dependent morphological transformations from partial engulfment to complete engulfment were observed. Similar experiments in presence of chitosan or pre-synthesized AuNPs show an opposite time-dependent trend of transformation of core-shell structures into partially engulfed ones. This behavior can be understood by a time-dependent rearrangement of the AuNPs at the interface and changes of the interfacial tension. The Pickering effect of AuNPs at oil-water and oil-oil interfaces bring not only color effects to individual micro-droplets, which are of special relevance for the preparation of new optical elements, but also a surprising self-assembly of droplets.
M. Hartlieb Photo-Iniferter RAFT Polymerization. Macromol. Rapid Commun. 2022, 43, 2100514 DOI: 10.1002/marc.202100514AbstractLight-mediated polymerization techniques offer distinct advantages over polymerization reactions fueled by thermal energy, such as high spatial and temporal control as well as the possibility to work under mild reaction conditions. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a highly versatile radical polymerization method that can be utilized to control a variety of monomers and produce a vast number of complex macromolecular structures. The use of light to drive a RAFT-polymerization is possible via multiple routes. Besides the use of photo-initiators, or photo-catalysts, the direct activation of the chain transfer agent controlling the RAFT process in a photo-iniferter (PI) process is an elegant way to initiate and control polymerization reactions. Within this review, PI-RAFT polymerization and its advantages over the conventional RAFT process are discussed in detail.
P. Wessig, S. Krebs N-Aroylsulfonamide-Photofragmentation (ASAP) - A versatile route to biaryls Eur. J. Org. Chem. 2021, , 6367-6374 DOI: 10.1002/ejoc.202100955AbstractThe photochemical fragmentation of N-aroylsulfonamides 9 (ASAP) is a powerful method for the preparation of various biaryls. Compounds 9 are easily accessible in two steps from amines by treatment with arenesulfonyl chlorides and aroyl chlorides. Many of these compounds were prepared for the first time. The irradiation takes place in a previously developed continuous-flow reactor using inexpensive UVB or UVC fluorescent lamps. Isocyanates and sulphur dioxide are formed as the only by-products. The ASAP tolerates a variety of functional groups and is even suited for the preparation of phenylnaphthalenes and terphenyls. The mechanism of the ASAP was elucidated by interaction of photophysical and quantumchemical (DFT) methods and revealed a spirocyclic biradical as key intermediate.
T. Krüger, A. Bramborg, A. Kelling, E. Sperlich, T. Linker Birch Reduction of Arenes as an Easy Entry to γ-Spirolactones Eur. J. Org. Chem. 2021, , 6383-6391 DOI: 10.1002/ejoc.202101018AbstractA convenient method for the synthesis of γ-spirolactones in only 2–3 steps is described. Birch reduction of inexpensive and commercially available aromatic carboxylic acids in the presence of ethyleneoxide affords hydroxyacids, which undergo direct lactonization during work-up. Suitable precursors are methyl-substituted benzoic acids, naphthoic, and dicarboxylic acids. Subsequent hydrogenation proceeds smoothly with Pd/C as catalyst and saturated γ-spirolactones are isolated in excellent yields and stereoselectivities. Thus, up to 3 new stereogenic centers can be constructed as sole diastereomers from achiral benzoic acids. Furthermore, it is possible to control the degree of saturation with \r\nRaney nickel or Wilkinson\'s catalyst to obtain products with 1 double bond. Overall, more than 30 new γ-spirolactones have been synthesized in analytically pure form.
R. R. Raju, J. Koetz Inner Rotation of Pickering Janus Emulsions Nanomaterials 2021, 11, 3312 DOI: 10.3390/nano11123312AbstractJanus droplets were prepared by vortex mixing of 3 non-mixable liquids, i.e. olive oil, silicone oil and water in presence of gold nanoparticles (AuNPs) in the aqueous phase and magnetite nanoparticles (MNPs) in olive oil. The resulting Pickering emulsions were stabilized by a red colored AuNP layer at the olive oil/water interface and MNPs at the oil/oil interface. The core-shell droplets can be stimulated by an external magnetic field. Surprisingly, an inner rotation of the silicon droplet is observed, when MNPs are fixed at the inner silicon droplet interface. This is a first example of a controlled movement of the inner part of complex double emulsions by magnetic manipulations via interfacially confined magnetic nanoparticles.
P. Akarsu, R. Grobe, J. Nowaczyk, M. Hartlieb, S. Reinicke, A. Böker, M. Sperling, M. Reifarth Solid-Phase Microcontact Printing for Precise Patterning of Rough Surfaces: Using Polymer-Tethered Elastomeric Stamps for the Transfer of Reactive Silanes Appl. Polym. Mater. 2021, 3, 2420-2431 DOI: Abstract
T. G. Floyd, S. Häkkinen, S. C. L. Hall, R. M. Dalgliesh, A.-C. Lehnen, M. Hartlieb, S. Perrier Cationic Bottlebrush Copolymers from Partially Hydrolyzed 2 Poly(oxazoline)s. Macromolecules 2021, 54, 9461-9473 DOI: 10.1021/acs.macromol.1c01458AbstractCationically charged bottlebrush copolymers were produced by hydrolysis of poly(2-ethyl-2-oxazoline) (PEtOx). The cationic ring-opening polymerization of EtOx was initiated using a styrene derivative to produce PEtOx macromonomers with two different lengths. After detailed characterization, these macromonomers were polymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization in a grafting-through process. The length of the bottlebrush backbone was varied, and it was found that a good control over the polymerization could be retained up to backbone DP 50. Hydrolysis of PEtOx repeating units under acidic conditions afforded cationic bottlebrushes, with a defined charge content that could be adjusted by changing the hydrolysis reaction time. Bottlebrush copolymers were analyzed in detail using size-exclusion chromatography, small-angle neutron scattering, and atomic force microscopy indicating a cylindrical topology and an increasing flexibility with increasing chain length.
Jolanda Hermanns, David Keller How Do Preservice Chemistry Teachers Rate Tasks Following the Construct of School-Related Content Knowledge in a Concept-Orientated Course on Organic Chemistry? J. Chem. Educ. 2021, 98, 3442-3449 DOI: 10.1021/acs.jchemed.1c00593AbstractIn this paper, we describe a study on tasks following the construct of school-related content knowledge. We know from previous studies that such tasks were rated by the preservice chemistry teachers as important for their future profession. Those studies were conducted in a traditional course on organic chemistry which was organized around chemical families. Therefore, we used and evaluated the tasks again in a new course on organic chemistry which is organized around basic concepts in organic chemistry. The results of this evaluation show that the students rate the tasks equally well but use other arguments for their rating. They do not focus only on the content of the tasks and whether this content belongs to the school curriculum or not. The students of the conceptual course rated the content more often (95%) as important for their future profession compared with the students in the traditional course (57%). Both groups of students rated the importance of the nature of the task the same way.
Sand, P.; Schmidt, B. Ruthenium-Catalyzed Sulfoalkenylation of Acetanilides and Dual-Use of the Catalyst Directing Group Eur. J. Org. Chem. 2021, , 5497-5506 DOI: 10.1002/ejoc.202101216AbstractRu-Catalysis enables to overcome limitations of Pd-catalyzed C-H-alkenylations using sulfonamides. A dual use concept is presented for the catalyst directing group, the acetamide substituent, which can be removed traceless by deacetylation-diazotation-coupling sequence, or by incorporation into the pyrrolo[2,3-c]quinoline skeleton.
W. Fudickar, M. Bauch, H. Ihmels, T. Linker DNA-Triggered Enhancement of Singlet Oxygen Production by Pyridinium Alkynylanthracenes Chem. Eur. J. 2021, 27, 13591–13604 DOI: 10.1002/chem.202101918AbstractThere is an ongoing interest in 1O2 sensitizers, whose activity is selectively controlled by their interaction with DNA. To this end, we synthesized three isomeric pyridinium alkynylanthracenes 2o-p and a water-soluble trapping reagent for 1O2. In water and in the absence of DNA, these dyes show a poor efficiency to sensitize the photooxygenation of the trapping reagent as they decompose due to electron transfer processes. In contrast, in the presence of DNA 1O2 is generated from the excited DNA-bound ligand. The interactions of 2o-p with DNA were investigated by thermal DNA melting studies, UV/vis and fluorescence spectroscopy, and linear and circular dichroism spectroscopy. Our studies revealed an intercalative binding with an orientation of the long pyridyl-alkynyl axis parallel to the main axis of the DNA base pairs. In the presence of poly(dA:dT), all three isomers show an enhanced formation of singlet oxygen, as indicated by the reaction of the latter with the trapping reagent. With green light irradiation of isomer 2o in poly(dA:dT), the conversion rate of the trapping reagent is enhanced by a factor >10. The formation of 1O2 was confirmed by control experiments under\r\nanaerobic conditions, in deuterated solvents, or by addition of 1O2 quenchers. When bound to poly(dG:dC), the opposite effect was observed only for isomers 2o and 2m, namely the trapping reagent reacted significantly slower. Overall, we showed that pyridinium alkynylanthracenes are very useful intercalators, that exhibit an enhanced photochemical 1O2 generation in the DNA-bound state.
T. Krüger, T. Linker Synthesis of γ-Spirolactams by Birch Reduction of Arenes Eur. J. Org. Chem. 2021, , 1585-1591 DOI: 10.1002/ejoc.202100056AbstractA convenient method for the synthesis of γ-spirolactams in only three steps is described. Birch reduction of inexpensive and commercially available aromatic carboxylic acids in the presence of chloroacetonitrile affords nitriles in moderate to good yields. Suitable precursors are methyl-substituted benzoic acids, naphthoic, and anthroic acid. Subsequent catalytic hydrogenation proceeds smoothly with PtO2 or Raney Ni as catalysts and lactams are isolated in excellent yields and stereoselectivities. Thus, up to 3 new stereogenic centers can be constructed as sole diastereomers from achiral benzoic acids. Furthermore, it is possible to control the degree of saturation at different pressures, affording products with 0, 1, or 2 double bonds. Overall, more than 15 new γ-spirolactams have been synthesized in analytically pure form.
N. Lüdecke, H. Schlaad Inspired by mussel adhesive protein: Hydrophilic cationic copoly(2-oxazoline)s carrying catecholic side chains Polym. Chem. 2021, 12, 5310-5319 DOI: 10.1039/d1py00679gAbstractA set of new functionalized poly(2-oxazoline) homopolymers and copolymers carrying protected catecholic side chains were prepared by microwave-assisted cationic ring-opening (co)polymerization. The copolymerizations of 2-ethyl-2-oxazoline with either 2-(3,4-dimethoxyphenyl)-, 2-(3,4-dimethoxybenzyl)-, or 2-(3,4-dimethoxycinnamyl)-2-oxazoline (comonomer ratio 90 : 10) produced gradient or random copolymers with narrow molar mass distributions. During the copolymerization with the 2-(3,4-dimethoxycinnamyl)-2-oxazoline, however, chain coupling reactions occurred at monomer conversions of >50%, supposedly via Michael-type addition of intermediately formed ketene N,O-acetal end groups to 3,4-dimethoxycinnamyl amide side chains. A poly[(2-ethyl-2-oxazoline)-grad-(2-(3,4-dimethoxyphenyl)-2-oxazoline)] was examplarily subjected to partial demethylation and acidic hydrolysis to give a hydrophilic copolymer carrying both catecholic and cationic units, which is designed as a bioinspired adhesive copolymer mimicking mussel adhesive protein.
R. F. Martín, A. F. Thünemann, J. M. Stockmann, J. Radnik, J. Koetz From nanoparticle heteroclusters to filament networks by self-assembly at the water-oil interface of reverse microemulsions Langmuir 2021, 37, 8876-8885 DOI: 10.1021/acs.langmuir.1c01348AbstractSurface self-assembly of spherical nanoparticles of sizes below 10 nm into hierarchical heterostructures is under arising development despite the inherent difficulties to obtain complex ordering patterns in larger scale. Due to template-mediated interactions between oil-dispersible superparamagnetic nanoparticles (MNPs) and polyethyleneimine-stabilized gold nanoparticles (Au(PEI)NPs) at the water-oil interface of microemulsions, complex nanostructured films can be formed. Characterization of the reverse microemulsion phase by UV-Vis absorption revealed the formation of heteroclusters from Winsor type II phases (WPII) using Aerosol-OT (AOT) as surfactant. SAXS measurements verify the mechanism of initial nanoparticle clustering in defined dimensions. XPS suggested an influence of AOT at the MNP surface. Further cryo-SEM and TEM visualization demonstrated the elongation of the reverse microemulsions into cylindrical, wormlike structures, which subsequently build up larger nanoparticle superstructure arrangements. Such WPII phases are thus proved to be a new form of soft-template, mediating the self-assembly of different nanoparticles in hierarchical network-like filaments over a substrate during solvent evaporation.
Kwesiga, G.; Sperlich, E.; Schmidt, B. Scope and Applications of 2,3-Oxidative Aryl Rearrangements for the Synthesis of Isoflavone Natural Products. J. Org. Chem. 2021, 86, 10699-10712 DOI: 10.1021/acs.joc.1c01375AbstractIsoflavones are bioactive secondary plant metabolites isolated from numerous African medicinal plants. We have investigated the oxidative 2,3-aryl rearrangement as a hitherto underexplored route toward their synthesis.
Riemer, N.; Riemer, M.; Krüger, M.; Clarkson, G. J.; Shipman, M.; Schmidt, B. Synthesis of Arylidene-β-lactams via exo-Selective Matsuda-Heck Arylation of Methylene-β-lactams. J.Org.Chem. 2021, 86, 8786-8796 DOI: 10.1021/acs.joc.1c00638AbstractExo-methylene beta-lactams, which are sensitive to ring opening under conventional (cross)-coupling conditions, undergo a Pd-catalyzed arylation at ambient temperature in high yields and selectivity. This work resulted from an international collaboration with researchers at the University of Warwick, UK.
L. Sala, A. Zerolová, A. Rodriguez, D. Reimitz, M. Davídková, K. Ebel, I. Bald and J. Kočišek Folding DNA into origami nanostructures enhances resistance to ionizing radiation Nanoscale 2021, 13, 11197-11203 DOI: 10.1039/D1NR02013GAbstractWe report experimental results on damage induced by ionizing radiation to DNA origami triangles which are commonly used prototypes for scaffolded DNA origami nanostructures. We demonstrate extreme stability of DNA origami upon irradiation, which is caused by (i) the multi-row design holding the shape of the origami even after severe damage to the scaffold DNA and (ii) the reduction of damage to the scaffold DNA due to the protective effect of the folded structure. With respect to damage induced by ionizing radiation, the protective effect of the structure is superior to that of a naturally paired DNA double helix. Present results allow estimating the stability of scaffolded DNA origami nanostructures in applications such as nanotechnology, pharmacy or in singulo molecular studies where they are exposed to ionizing radiation from natural and artificial sources. Additionally, possibilities are opened for scaffolded DNA use in the design of radiation-resistant and radio-sensitive materials.
A. Dutta, R. Schürmann, S. Kogikoski Jr., N. S. Mueller, S. Reich, I. Bald Kinetics and Mechanism of Plasmon-Driven Dehalogenation Reaction of Brominated Purine Nucleobases on Ag and Au ACS Catal. 2021, 11, 8370-8381 DOI: 10.1021/acscatal.1c01851AbstractPlasmon-driven photocatalysis is an emerging and promising application of noble metal nanoparticles (NPs). An understanding of the fundamental aspects of plasmon interaction with molecules and factors controlling their reaction rate in a heterogeneous system is of high importance. Therefore, the dehalogenation kinetics of 8-bromoguanine (BrGua) and 8-bromoadenine (BrAde) on aggregated surfaces of silver (Ag) and gold (Au) NPs have been studied to understand the reaction kinetics and the underlying reaction mechanism prevalent in heterogeneous reaction systems induced by plasmons monitored by surface enhanced Raman scattering (SERS). We conclude that the time-average constant concentration of hot electrons and the time scale of dissociation of transient negative ions (TNI) are crucial in defining the reaction rate law based on a proposed kinetic model. An overall higher reaction rate of dehalogenation is observed on Ag compared with Au, which is explained by the favorable hot-hole scavenging by the reaction product and the byproduct. We therefore arrive at the conclusion that insufficient hole deactivation could retard the reaction rate significantly, marking itself as rate-determining step for the overall reaction. The wavelength dependency of the reaction rate normalized to absorbed optical power indicates the nonthermal nature of the plasmon-driven reaction. The study therefore lays a general approach toward understanding the kinetics and reaction mechanism of a plasmon-driven reaction in a heterogeneous system, and furthermore, it leads to a better understanding of the reactivity of brominated purine derivatives on Ag and Au, which could in the future be exploited, for example, in plasmon-assisted cancer therapy.
A. M. Voll, C. Meyners, M. C. Taubert, T. Bajaj,T. Heymann, S. Merz,A. Charalampidou,J. Kolos, P. L. Purder,T. M. Geiger, P. Wessig, N. C. Gassen, A. Bracher, F. Hausch Makrozyklische FKBP51-Liganden enthüllen einen transienten Bindungsmodus mit erhöhter Selektivität Angew. Chem. 2021, 133, 13366-13372 DOI: 10.1002/ange.202017352AbstractSubtyp-Selektivitätist oft eine Herausforderung bei der Wirkstoffentwicklung. Ein Beispiel ist das FK506-bindende Protein51 (FKBP51) als Wirkstoffziel. Die am weitesten fortgeschrittenen FKBP51-Liganden der SAFit-Klasse sind hochselektiv gegenüber FKBP52,differenzieren aber kaum gegenüberden eng verwandten Proteinen FKBP12 und FKBP12.6. Eine Makrozyklisierungsstudie ergab,dass viele dieser makrozyklischen Analoga eine unerwartete, neuartige Präferenz für FKBP51 gegenüber FKBP12 und FKBP12.6 haben. Strukturellen Studien zufolge weisen diese Makrozyklen einen neuen Bindungsmodus auf,mit einer transienten Protein-Konformation,die für die kleinen FKBPs ungünstig ist. Mithilfe eines konformationssensitiven Assays zeigen wir,dass dieser Bindungsmodus in Lösung auftritt und charakteristisch für diese neue Verbindungsklasse ist. Die Makrozyklen sind nicht immunsuppressiv, binden FKBP51 in Zellen und blockieren die zelluläre Wirkung von FKBP51 auf IKKa. Die Ergebnisse liefern ein neues chemisches Gerüst für verbesserte FKBP51-Liganden und die strukturelle Grundlage für eine erhöhte Selektivität.
A. Dev, A. Rösler, H. Schlaad Limonene as a renewable unsaturated hydrocarbon solvent for living anionic polymerization of β-myrcene Polym. Chem. 2021 2021, 12, 3084-3087 DOI: 10.1039/d1py00570gAbstractThe acyclic monoterpene β-myrcene is polymerized by anionic polymerization at room temperature using sec-butyllithium as the initiator and the cyclic monoterpene DL-limonene as an unsaturated hydrocarbon solvent. The polymerization is a living process and allows production of polymyrcenes with narrow molar mass distribution (Ð ~ 1.06) and high content of 1,4 units (~90%) as well as block copolymers.\r\n
P. Keckeis, E. Zeller, C. Jung, P. Besirske, F. Kirner, C. Ruiz-Agudo, H. Schlaad, H. Cölfen Modular toolkit of multifunctional block copoly(2-oxazoline)s for the synthesis of nanoparticles Chem. Eur. J. 2021, 27, 8283-8287 DOI: 10.1002/chem.202101327AbstractPost-polymerization modification provides an elegant way to introduce chemical functionalities onto macromolecules to produce tailor-made materials with superior properties. This concept was adapted to well-defined block copolymers of the poly(2-oxazoline) family and demonstrated the large potential of these macromolecules as universal toolkit for numerous applications. Triblock copolymers with separated water-soluble, alkyne- and alkene-containing segments were synthesized and orthogonally modified with various low-molecular weight functional molecules by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and thiol-ene (TE) click reactions, respectively. Representative toolkit polymers were used for the synthesis of gold, iron oxide and silica nanoparticles.
J. Hermanns, D. Keller A survey on the content beliefs of professors teaching organic chemistry Progress in Science Education 2021, 4, 63-70 DOI: 10.25321/prise.2021.1078AbstractContent beliefs of professors teaching organic chemistry were investigated. The survey consisted of topics recommended by the KMK (Kultusministerkonferenz –conference of the ministers for the arts and culture – also responsible for education) and important concepts. The professors rated the topics and concepts for students at school and for pre-service chemistry teachers during their study at university. Over all, the topics were rated better than the concepts. In comparison with the recommendations of the KMK the rating of the topics show a great concordance; the rating lies between 94.1 and 100.0 % agreement. The lower agreement with the concepts is surprising, because those are also part of the recommendations of the KMK. As additional relevant concepts the electrophile-nucleophile and acid-base concept were named by the professors. However, it seems that conceptual knowledge and its use in teacher training is not as common as it is desirable.
Krause, A.; Sperlich, E.; Schmidt, B. Matsuda–Heck arylation of itaconates: a versatile approach to heterocycles from a renewable resource. Org. Biomol. Chem. 2021, 19, 4292-4302 DOI: 10.1039/D1OB00392EAbstractItaconic acid is a basic chemical from a renewable resource that has mainly found applications for polymers but has hardly been used for fine chemicals production. We report applications of itaconic acid derivatives in Pd-catalyzed arylation reactions with arene diazonium salts, the so-called Matsuda-Heck reaction, and the conversion of the coupling products to previously difficult to access benzazepinones.
Sand, P.; Schmidt, B. Pd-Catalyzed Oxidative Sulfoalkenylation of Acetanilides and Traceless Removal of the Catalyst Directing Group ChemistrySelect 2021, 6, 3563-3567 DOI: 10.1002/slct.202101009AbstractThe Pd-catalyzed oxidative Heck-reaction has been applied to vinylsulfonyl compounds, using acetamides as catalyst directing groups. The traceless removal of the catalyst directing group through deacetylation-diazotation-coupling sequence was exemplified and furnishes 1,2-dialkenylated arenes.The Pd-catalyzed oxidative Heck-reaction has been applied to vinylsulfonyl compounds, using acetamides as catalyst directing groups. The traceless removal of the catalyst directing group through deacetylation-diazotation-coupling sequence was exemplified and furnishes 1,2-dialkenylated arenes.
J. Hermanns How do pre-service chemistry teachers rate the importance of content in organic chemistry during their chemistry studies at university? Chemistry Teacher International 2021, , 1-7 DOI: 10.1515/cti-2021-0004AbstractIn this article a cross-sectional study on the students' rating with regard to the contents in organic chemistry will be discussed. Pre-service teachers rated the contents with a questionnaire during their bachelor or master studies. It was shown that the pre-service chemistry teachers during their master studies rated the content as more important than the bachelor students. One possible explanation can be that the master students have teaching experience due to their internships at school whereas the bachelor students can only rely on their experience from their own school days. Overall, content belonging to the school curriculum in the federal state "Brandenburg" where the pre-service teachers' university is located was rated better than content that was not a part of this curriculum. Concepts were not rated significantly better than the content. Because of the importance of conceptual knowledge for the future profession as a teacher, the courses in organic chemistry will be redesigned with a clear focus on concepts.
K. Tapio, A. Mostafa, Y. Kanehira, A. Suma, A. Dutta, I. Bald A Versatile DNA Origami-Based Plasmonic Nanoantenna for Label-Free Single-Molecule Surface-Enhanced Raman Spectroscopy ACS Nano 2021, 15, 7065-7077 DOI: 10.1021/acsnano.1c00188AbstractDNA origami technology allows for the precise nanoscale assembly of chemical entities that give rise to sophisticated functional materials. We have created a versatile DNA origami nanofork antenna (DONA) by assembling Au or Ag nanoparticle dimers with different gap sizes down to 1.17 nm, enabling signal enhancements in surface-enhanced Raman scattering (SERS) of up to 1011. This allows for single-molecule SERS measurements, which can even be performed with larger gap sizes to accommodate differently sized molecules, at various excitation wavelengths. A general scheme is presented to place single analyte molecules into the SERS hot spots using the DNA origami structure exploiting covalent and noncovalent coupling schemes. By using Au and Ag dimers, single-molecule SERS measurements of three dyes and cytochrome c and horseradish peroxidase proteins are demonstrated even under nonresonant excitation conditions, thus providing long photostability during time-series measurement and enabling optical monitoring of single molecules.
E. Schönemann, J. Koc, J. F. Karthäuser, O. Özcan, D. Schanzenbach, L. Schardt, A. Rosenhahn, A. Laschewsky Sulfobetaine Methacrylate Polymers of Unconventional Polyzwitterion Architecture and Their Antifouling Properties Biomacromolecules 2021, 22, 1494-1508 DOI: 10.1021/acs.biomac.0c01705AbstractA family of polysulfobetaines of novel architecture was synthesized. Different from the established design, the cationic and anionic groups of their zwitterionic moieties are located at equal distances from the backbone in these polymeric inner salts. Thin hydrogel films were prepared from the polymers and photo-cured. The coatings were studied with respect to their low-fouling capability in a set of in-vitro biofouling assays, covering proteins of different net charges as well as model marine organisms. All polyzwitterions were shown to minimize biofouling effectively. Their specific fouling resistance is controlled by the detailed chemical structure of the polyzwitterions, and reaches the performance of the benchmark polyzwitterion poly(3 (N (2 methacryloyloxyethyl)-N,N-dimethyl-ammonio)propanesulfonate).
M. Bauch, W. Fudickar, T. Linker Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates Molecules 2021, 26, 804. 2021, 26, 804 DOI: 10.3390/molecules26040804AbstractStereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.\r\n
T. Haubitz, W. Fudickar, T. Linker, M. U. Kumke pH-Sensitive Fluorescence Switching of Pyridylanthracenes: The Effect of the Isomeric Pattern J. Phys. Chem. A 2020, 124, 11017-11024 DOI: 10.1021/acs.jpca.0c09911Abstract9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives’ charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.\r\n\r\n
J. Hermanns The task navigator following the STRAKNAP concept: development, application and evaluation of a new scaffold to support non-major chemistry students while solving tasks in organic chemistry. J. Chem. Educ. 2021, 98, 1077-1087 DOI: 10.1021/acs.jchemed.0c01162AbstractEducational Scaffolding was first mentioned in 1976 by Wood et al. Several examples for scaffolding in chemistry are also known from the literature. As written scaffolds, stepped supporting tools to support students while solving problems in organic chemistry were developed, applied and evaluated. Although the students rated the tool as very helpful, a think-aloud study showed that the support given by this scaffold was not sufficient. As a further development of stepped supporting tools, task navigators were therefore developed, applied and evaluated. This new scaffold gives tips on strategy, knowledge and application of knowledge after the STRAKNAP concept. The evaluation of this tool shows that the students rated the tool as being very helpful. A think-aloud study showed that the scaffold supports the students while they solve a problem. Because of the stepwise construction of the task navigators and the providing of the knowledge needed for the application, the students can solve parts of the task successfully even if they do not solve all parts correctly; the students can always start from scratch. When students use the tool regularly, their knowledge of organic chemistry increases compared to students who didn’t use the tool at all. The task navigator is not only a scaffold for the content of the task, but also for the development of methodological competences on the field of strategies and applying knowledge.
Hermanns, J., Ermler, N. Why school-related content knowledge for pre-service chemistry teachers should include basic concepts in organic chemistry Chemistry Teacher International 2021, DOI: 10.1515/cti-2020-0033AbstractIn this paper we describe and evaluate a study on the use of concepts in organic chemistry while solving tasks that are designed after the concept of school-related content knowledge. The study was designed as a mixed methods study and conducted at a German university for the content of "organic chemistry". As the results of this study show, the students rate the tasks and the use of anchoring concepts as for example "bonds" or "structure and function" as relevant for their future profession as a chemistry teacher. They therefore propose that concepts should be an integral part of their university studies as they find it lacking at the moment. Concepts can also be seen as an opportunity to build a bridge between school knowledge and university knowledge.
T. Debsharma, B. Schmidt, A. Laschewsky, H. Schlaad Ring-Opening Metathesis Polymerization of Unsaturated Carbohydrate Derivatives: Levoglucosenyl Alkyl Ethers Macromolecules 2021, 54, 2720-2728 DOI: 10.1021/acs.macromol.0c02821AbstractA series of biomass-derived levoglucosenyl alkyl ethers (alkyl = methyl, ethyl, n-propyl, isopropyl, and n-butyl) were synthesized and polymerized by ring-opening olefin metathesis polymerization using the Grubbs catalyst C793 at room temperature. Polymerizations were successfully performed in conventional solvents such as 1,4-dioxane and dichloromethane as well as in polar aprotic "green" solvents such as 2-methyltetrahydrofuran, dihydrolevoglucosenone (Cyrene), and ethyl acetate. The prepared polyacetals with degrees of polymerization of ~100 exhibit Schulz-Flory-type molar mass distributions and are thermoplastic materials with rather low glass transition temperatures in the range of 43-0 °C depending on the length of the alkyl substituent. Kinetic studies revealed that the polymerization proceeded rapidly to a steady state with a certain minimum monomer concentration threshold. When the steady state was reached, just about half of the [Ru] catalyst had been effective to initiate the polymerization, indicating that the initiation step was a slow process. The remaining catalyst was still active and did no longer react with monomers but with in-chain double bonds, cutting the formed polymer chains into shorter fragments. In the long term, all catalyst was consumed and propagating [Ru] chain ends were deactivated by the elimination of [Ru] from the chain ends to form inactive chains with terminal aldehyde groups.
Hermanns, J., Keller, D. School-related content knowledge in organic chemistry – how does the students‘ rating of their perceived relevance of tasks differ between bachelor and master studies? J. Chem. Educ. 2021, 98, 763-773 DOI: 10.1021/acs.jchemed.0c01415AbstractIn this paper the development, use and evaluation of tasks based on the construct of school-related content knowledge are described. The tasks were used in seminars on organic chemistry for bachelor and master pre-service chemistry teachers at a German university. For the evaluation a questionnaire with open and closed items was used. The tasks were rated by the pre-service chemistry teachers as relevant for their future profession as a chemistry teacher if the content of the tasks is part of the school curriculum. If the content does not belong to the school curriculum, they rated the nature of the tasks still as relevant; they seem to recognize the importance of conceptual knowledge for their future profession. However, the master’s pre-service teachers argued with this conceptual knowledge more often than the bachelor’s pre-service teachers. Although the study is cross-sectional, a certain shift from the focus on the content to conceptual knowledge from bachelor’s to master’s pre-service teachers can be observed.
V. Strauss,H. Wang, S. Delacroix, M.Ledendecker, P. Wessig Carbon nanodots revised: the thermal citric acid/urea reaction Chem. Sci. 2020, 11, 8256–8266 DOI: 10.1039/d0sc01605eAbstractLuminescent compounds obtained from the thermal reaction of citric acid and urea have been studied andutilized in different applications in the past few years. The identified reaction products range from carbonnitrides over graphitic carbon to distinct molecular fluorophores. On the other hand, the solid, non-fluorescent reaction product produced at higher temperatures has been found to be a valuable precursor for the CO2-laser-assisted carbonization reaction in carbon laser-patterning. This work addresses the question of structural identification of both, the fluorescent and non-fluorescent reaction products obtained in the thermal reaction of citric acid and urea. The reaction products produced during autoclave-microwave reactions in the melt were thoroughly investigated as a function of the reaction temperature and the reaction products were subsequently separated by a series of solvent extractionsand column chromatography. The evolution of a green molecularfluorophore, namely HPPT, was confirmed and a full characterization study on its structure and photophysical properties was conducted. The additional blue fluorescence is attributed to oligomeric ureas, which was confirmed by complementary optical and structural characterization. These two components form strong hydrogen-bond networks which eventually react to form solid, semi-crystalline particles with a size of ~7 nm and an elemental composition of 46% C, 22% N, and 29% O. The structural features and properties of all three main components were investigated in a comprehensive characterization study.
M. Hechenbichler, A. Laschewsky, M. Gradzielski Poly(N,N-bis(2-methoxyethyl)acrylamide), a Thermo-responsive Nonionic Polymer Combining the Amide and the Ethyleneglycolether Motifs Colloid Polym. Sci. 2021, 299, 205-219 DOI: 10.1007/s00396-020-04701-9AbstractPoly(N,N-bis(2-methoxyethyl)acrylamide) (PbMOEAm) featuring two classical chemical motifs from non ionic water soluble polymers, namely the amide and ethyleneglycolether moieties, was synthesized by Reversible Addition Fragmentation Transfer (RAFT) polymerization. The thermoresponsive behavior in aqueous solution, exhibiting a lower critical solution temperature (LCST), was investigated. A series of homo and block copolymers with functional end-groups were prepared accordingly, and their capability for acting as \"smart\" surfactants was explored.
M. Al-Naji, H. Schlaad, M. Antonietti New (and old) monomers from biorefineries to make polymer chemistry more sustainable Macromol. Rapid Commun. 2021, 42, 2000485 DOI: 10.1002/marc.202000485AbstractThis opinion article describes recent approaches to use the \"biorefinery\" concept to lower the carbon footprint of typical mass polymers, by replacing parts of the fossil monomers with similar or even the same monomer made from regrowing dendritic biomass. Herein, the new and green catalytic synthetic routes are for lactic acid (LA), isosorbide (IS), 2,5-furandicarboxylic acid (FDCA), and p-xylene (pXL). Furthermore, the synthesis of two unconventional lignocellulosic biomass derivable monomers, i.e., α-methylene-γ-valerolactone (MeGVL) and levoglucosenol (LG), are presented. All those have the potential to enter in a cost-effective way, also the mass market and thereby recover lost areas for polymer materials. The differences of catalytic unit operations of the biorefinery are also discussed and the challenges that must be addressed along the synthesis path of each monomers.
J. Hermanns Training OC - a new course concept for training the application of basic concepts in organic chemistry Journal of Chemical Education 2021, 98, 374-384 DOI: https://dx.doi.org/10.1021/acs.jchemed.0c00567AbstractThe course design “Training OC” for training the application of basic concepts consists of four topics: formula language, structure-property relations, reaction mechanisms and complex tasks that the students should solve with the conceptual knowledge they acquired in the first three topics. A main goal of the course was to enable the students to solve reaction mechanisms. To achieve the goals of the course, several games were specially designed and used. The course was conducted at a German university with ca. 30 students who participated voluntarily. The course was evaluated by several tools: students’ products were collected in the course, two pre-post-tests and additionally interviews on the strategy of designing reaction mechanisms were conducted. The performance of the teacher and the self-assessment of the students were also part of the evaluation. The results of the written exam were compared with the results of the major bachelor chemistry students. The course “Training OC” was rated very well by the students. They were of the opinion that they learned the application of basic concepts taught in this course. This is supported by the results of the evaluation and the written exams. The course concept of Training OC will therefore become a permanent part of the course “Organic Chemistry I” which will be redesigned for the next round in 2020/21.
P. Wessig, L. John, E. Sperlich, A. Kelling Sulfur Tuning of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) Fluorescent Dyes Eur. J. Org. Chem. 2021, , 499-511 DOI: 10.1002/ejoc.202001418AbstractThe replacement of oxygen by sulfur atoms of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes is an efficient way to adjust the photophysical properties (sulfur tuning). While previously developed S4-DBD dyes exhibit considerably red-shifted absorption and emission wavelength, the heavy atom effect of four sulfur atoms cause low fluorescence quantum yields and short fluorescence lifetimes. Herein we demonstrate that the replacement of less than four sulfur atoms (S1-DBD, 1,2-S2-DBD, and 1,4-S2-DBD dyes) permits a fine-tuning of the photophysical properties. In some cases, a similar influence on the wavelength without the detrimental effect on the quantum yields and lifetimes is observed. Furthermore, the synthetic accessibility of S1- and S2-DBD dyes is improved, compared with S4-DBD dyes. For coupling with biomolecules a series of reactive derivatives of the new dyes were developed (azides, OSu esters, alkynes, maleimides).
J. Hermanns, O. Thomanek A Delphi study on the school related content knowledge in organic chemistry RISTAL 2020, 3, 146-165 DOI: 10.23770/rt1835AbstractA Delphi study on the topic “school-related content knowledge in organic chemistry” was conducted in two rounds. National and international experts from the academic and school fields participated. The aim of the study was to investigate what kind of knowledge is practically needed for the future teachers in order to effectively teach in school. The category of the school-related knowledge was recognized as a category providing a sufficient amount of knowledge covering the basics and considering the enhanced conceptual aspects of each topic.
R. Fortes Martín, C. Prietzel, J. Koetz Template-mediated self-assembly of magnetite-gold nanoparticle superstructures at the water-oil interface of AOT reverse microemulsions J. Coll. Interface Sci. 581,2021, 44-55 2021, 581, 44-55 DOI: 10.1016/j.jcis.2020.07.079AbstractHypothesis: Bimetallic magnetite-gold nanostructures are interesting candidates to combine and enhance individual properties of each metal element in catalytic and analytical applications. Microemulsions have been employed in templated synthesis of nanoparticles, and their combination with different types of nanoparticles can further mediate interactions at the water-oil interface, providing new forms of hybrid nanostructures. Experiments: Reverse water-in-oil microemulsions of droplet sizes below 50 nm were prepared from ternary mixtures of Aerosol-OT (AOT) as surfactant, incorporating 4 nm sized superparamagnetic nanoparticles (MNPs) to the hexane-pentanol oil phase and 5 nm sized polyethyleneimine-stabilized gold nanoparticles (Au(PEI)-NPs) to the water phase. The resulting isotropic L2 phase, Winsor phases and organized nanostructures were investigated using conductometry, calorimetry, UV-Vis spectroscopy, cryo-SEM and HRTEM. Findings: Droplet-droplet interactions, morphology and surfactant film properties of AOT microemulsions could be modulated in different ways by the presence of the different nanoparticles from each liquid phase. Additionally, phase separation into Winsor phases allows the formation upon solvent evaporation of films with bimetallic heterostructures on the micrometer scale. This demonstrates a new way of nanoparticle templated assembly at liquid interfaces by assisted interactions between microemulsions and nanoparticles, as a promising strategy to obtain thin films of small, isotropic nanoparticles with hierarchical ordering.
J. Glatzel, S. Noack, D. Schanzenbach, H. Schlaad Anionic polymerization of dienes in ′green′ solvents Polym. Int. 2021, 70, 181-184 DOI: 10.1002/pi.6152AbstractIsoprene and ß-myrcene were polymerized by anionic polymerization in bulk and in the ′green′ ether solvents cyclopentyl methyl ether and 2-methyltetrahydrofuran and, for comparison, in cyclohexane and tetrahydrofuran. The polydienes produced in bulk and in cyclohexane contained high amounts of 1,4 units (>90%) whereas those produced in ether solvents were rich in 1,2 and 3,4 units (36%-86%). Comparison of the microstructures and glass transition temperatures of the polydienes obtained in the various solvents suggests that conventionally used solvents can be substituted by environmentally more friendly alternatives.
A. Hess, B. V. K. J. Schmidt, H. Schlaad Aminolysis induced functionalization of (RAFT) polymer-dithioester with thiols and disulfides Polym. Chem. 2020, 11, 7677-7684 DOI: 10.1039/d0py01365jAbstractA series of polystyrene- and poly(methyl methacrylate)-dithioesters was subjected to aminolysis under ambient atmospheric conditions, i.e., in the presence of oxygen. Polymer disulfide coupling by oxidation occurred within tens of minutes and the yield of disulfide-coupled polymer increased with decreasing polymer molar mass. Oxidation of thiolates is usually an unwanted side reaction, here it is employed to obtain exclusively polymeric mixed disulfides through in situ aminolysis/functionalization in the presence of a thiol. The in situ aminolysis/functionalization in the presence of a disulfide, Ellman\'s reagent or polymer disulfide, resulted in the exclusive formation of polymer-dithionitrobenzoic acid, which can be further reacted with a thiol to exchange the terminal functionality, or block copolymer with dynamic disulfide linker, respectively.
Schultze, C.; Foß, S.; Schmidt, B. 8-Prenylflavanones via Microwave Promoted Tandem Claisen Rearrangement/6-endo-trig Cyclization and Cross Metathesis Eur. J. Org. Chem. 2020, , 7373-7384 DOI: 10.1002/ejoc.202001378AbstractA microwave-promoted one-pot Claisen-rearrangement / 6-endo-trig cyclization yields allylflavanones, which undergo selective cross metathesis reactions with 2-methyl-2-butene to furnish prenylated flavanone natural products. One example is maximaflavanone, a secondary metabolite isolated from the Indian medicinal plant Tephrosia maxima.
Y. Bourgat, B. Tiersch, J. Koetz, H. Menzel Enzyme Degradable Polymersomes from Chitosan-g-[poly-l-lysine-block-ε-caprolactone] Copolymer Macromolecular Bioscience 2020, , 2000259 DOI: 10.1002/mabi.202000259AbstractThe scope of this study includes the synthesis of chitosan-g-[peptide-poly-ε-caprolactone] and its self-assembly into polymeric vesicles employing the solvent shift method. In this way, well-defined core–shell structures suitable for encapsulation of drugs are generated. The hydrophobic polycaprolactone side-chain and the hydrophilic chitosan backbone are linked via an enzymecleavable peptide. The synthetic route involves the functionalization of chitosan with maleimide groups and the preparation of polycaprolactone with alkyne end-groups. A peptide functionalized with a thiol group on one side and an azide group on the other side is prepared. Thiol-ene click-chemistry and azide–alkyne Huisgen cycloaddition are then used to link the chitosan and poly-ε-caprolactone chains, respectively, with this peptide. For a preliminary study, poly-l-lysin is a readily available and cleavable peptide that is introduced to investigate the feasibility of the system. The size and shape of the polymersomes are studied by dynamic light scattering and cryo-scanning electron microscopy. Furthermore, degradability is studied by incubating the polymersomes with two enzymes, trypsin and chitosanase. A dispersion of polymersomes is used to coat titanium plates and to further test the stability against enzymatic degradation.
J. Koc, E. Schönemann, R. Wanka, N. Aldred, A. S. Clare, H. Gardner, G. W. Swain, K. Hunsucker, A. Laschewsky, A. Rosenhahn Effects of crosslink density in zwitterionic hydrogel coatings on their antifouling performance and susceptibility to silt uptake. Biofouling 2020, 36, 646-659 DOI: 10.1080/08927014.2020.1796983AbstractZwitterionic hydrogels excel as antifouling coatings against the attachment of proteins and organisms in laboratory assays. This is largely attributed to their high hydrophilicity and swelling in water. However in field experiments in the ocean, the soft coatings suffer from the incorporation of particulate matter, strongly deteriorating the anti-fouling performance. In this study, we investigate comparatively the effect of increasing amounts of photo-crosslinker in hydrogels made from a sulfobetaine methacrylate in laboratory assays as well as in fields tests. Surprisingly in both cases, the fouling resistance was improved by increasing the crosslinker content, and this throughout all types of foulant (proteins, diatoms, microalgae) studied.
J. Koc, L. Schardt, K. Nolte, C. Beyer, T. Eckhard, P. Schwiderowski, J. L. Clarke, J. A. Finlay, A. S. Clare, M. Muhler, A. Laschewsky, A. Rosenhahn Effect of the dipole orientation in mixed, charge-equilibrated self-assembled monolayers on protein adsorption and marine biofouling ACS Appl. Mater. Interfaces 2020, 12, 50953-50961 DOI: 10.1021/acsami.0c11580AbstractZwitterionic interfaces exhibit excellent low-fouling properties. Still, the underlying molecular principles are not clear. In particular, the role of the zwitterion orientation at the interface has been discussed recently. To clarify the importance of this parameter, densely packed self-assembled monolayers (SAMs) on gold were prepared from stoichiometric mixtures of oppositely charged alkyl thiols bearing either a quaternary ammonium or a carboxylate group. By varying the alkyl chain length of the anionic thiols, different charged groups were preferentially exposed at the interface, although overall, the SAMs maintain full charge neutrality. In model biofouling studies, protein adsorption, diatom accumulation and the settlement of zoospores were all sensitive to the interfacial charge distribution of the SAMs. Overall biofouling was the lowest when the anionic and cationic groups were placed at the same distance from the substrate. This demonstrates the importance of the zwitterion dipole orientation in mixed charged SAMs for their inertness to fouling.
J. Hermanns Scaffolding for chemistry students - which tools are assessed as being more helpful: stepped supporting tools or task navigators? Chemistry Teacher International 2020, DOI: 10.1515/cti-2020-0019AbstractIn this paper the use of two different scaffolds in a seminar on the topic of heterocycles is discussed. The students first used both scaffolds (stepped supporting tools and a task navigator) on two tasks and could then choose for one other task the scaffold that suited them more. The scaffolds were evaluated in a mixed-methods study by the use of questionnaires and the conducting of a focus group interview. Both scaffolds were assessed as being helpful. However, students who thought they didn’t need different sorts of tips, as provided by the task navigator, chose the stepped supporting tools. All students reflected on their use of the scaffolds; their choices for one of both are therefore well-founded. As the reasons for choosing the scaffold are very individual, in future seminars both types of scaffolds will be provided.
G. Kwesiga, A. Kelling, S. Kersting, E. Sperlich, M. von Nickisch-Rosenegk, B. Schmidt Total Syntheses of Prenylated Isoflavones from Erythrina sacleuxii and Their Antibacterial Activity: 5-Deoxy-3´-prenylbiochanin A and Erysubin F J. Nat. Prod. 2020, 83, 3445-3453. 2020, 83, 3445-3453 DOI: 10.1021/acs.jnatprod.0c00932AbstractThe synthesis of prenylated isoflavones that were previously isolated from the East-African Medicinal plant Erythrina sacleuxii is described via a flavanone-isoflavone oxidative rearrangement mediated by hypervalent iodine compounds. In contrast to previous reports, synthetic erysubin F showed antibiotic activity against methicillin-resistant Staphylococcus aureus at micromolar concentrations.
K. Kaya, T. Debsharma, H. Schlaad, Y. Yagci Cellulose-based polyacetals by direct and sensitized photocationic ring-opening polymerization of levoglucosenyl methyl ether Polym. Chem. 2020, 11, 6884-6889 DOI: 10.1039/d0py01307bAbstractThis study aims to explore the photoinitiated cationic ring-opening polymerization of levoglucosenyl methyl ether (LGME), a chemical obtained from the most abundant biomass – cellulose. Direct and sensitized photopolymerizations of LGME using photoinitiators acting at the near UV or visible range in conjunction with diphenyliodonium hexafluorophosphate (DPI) yielded unsaturated polyacetals with varying molar masses and distributions.
J. Koetz The Effect of Surface Modification of Gold Nanotriangles for Surface-Enhanced Raman Scattering Performance Nanomaterials 2020, 10, 2187 DOI: 10.3390/nano10112187AbstractA surface modification of ultraflat gold nanotriangles (AuNTs) with different shaped nanoparticles is of special relevance for surface enhanced Raman scattering (SERS) and the photo-catalytic activity of plasmonic substrates. Therefore, different approaches are used to verify the flat platelet morphology of the AuNTs by oriented overgrowth with metal nanoparticles. The most important part for the morphological transformation of the AuNTs is the coating layer, containing surfactants or polymers. By using well established AuNTs stabilized by a dioctyl sodium sulfosuccinate (AOT) bilayer, different strategies of surface modification with noble metal nanoparticles are possible. On the one hand undulated superstructures were synthesized by in situ growth of hemispherical gold nanoparticles in the polyethyleneimine (PEI) coated AOT bilayer of the AuNTs. On the other hand spiked AuNTs were obtained by a direct reduction of Au3+ ions in the AOT double layer in presence of silver ions and ascorbic acid as reducing agent. Additionally, crumble topping of the smooth AuNTs can be realized after an exchange of the AOT bilayer by hyaluronic acid, followed by a silver-ion mediated reduction with ascorbic acid. Furthermore, a decoration with silver nanoparticles after coating the AOT bilayer with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC) can be realized. In that case the UV-absorption of the undulated Au@Ag nanoplatelets can be tuned in dependence on the degree of decoration with silver nanoparticles. Comparing the Raman scattering data for the plasmon driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4\'-dimercaptoazobenzene (DMAB) one can conclude that the most important effect of surface modification with a 75 times higher enhancement factor in SERS experiments becomes available by a decoration with gold spikes.
J. Hermanns, B. Schmidt, I. Glowinski, D. Keller Online teaching in the course \"organic chemistry\" for non-major chemistry students: from necessity to opportunity J. Chem. Educ. 2020, 97, 3140-3146 DOI: 10.1021/acs.jchemed.0c00658AbstractIn this paper the development of an online course on the topic „organic chemistry“ for non-major chemistry students is described and discussed. For this online course, the existing classroom course was further developed. New elements such as podcasts, task navigators and a forum for discussing the solving of tasks or problems with the content were added. This new online course was evaluated. Therefore a questionnaire was developed. This consists of questions with regard to the longtime learning behavior of the students and to the online learning. The results of this evaluation show that a preference for online learning and a preference for classroom teaching can be measured separately in two scales. Students’ values on the scale representing a preference for online learning correlate positive and significantly with confidence in the choice of the study subject, the enthusiasm about the subject and the ability to organize their learning, learning environment and time management. They correlate also with the satisfaction concerning the materials provided. Students’ values for one of those teaching methods also correlate with their rating with regard to their exam preparation. Values representing a preference for online teaching correlate positively with students’ better feeling of exam preparation. Values representing a preference for classroom teaching show negative correlations with the values representing students’ similar or even better preparation for the exams as a result of online teaching. . It is therefore not surprising that the ratings for the two scales correlate with the wish for a combination of online teaching and classroom teaching in the future. As a solution, a new course concept for the time after the corona virus crisis that suits all students is outlined in the outlook.\r\n\r\n
R. Henning, F. Liebig, C. Prietzel, B. Klemke, J. Koetz Gold Nanotriangles with Magnetite Satellites Colloids and Surfaces A 2020, 600, 124913 DOI: 10.1016/j.colsurfa.2020.124913Abstracthis work describes the synthesis of hybrid particles of gold nanotriangles (AuNTs) with magnetite nanoparticles (MNPs) by using 1-Mercaptopropyl-3-trimethoxysilan (MPTMS) and L-cysteine as linker molecules. Due to the combination of superparamagnetic properties of MNPs with optical properties of the AuNTs, hybrid nanoparticles with combined features become available. By using MPTMS with silan groups as linker molecule a magnetic "cloud" with embedded AuNTs can be separated. In presence of L-cysteine as linker molecule at pH > pHiso a more unordered aggregate structure of MNPs is obtained due to the dimerization of the L-cysteine. At pH < pHiso water soluble positively charged AuNTs with satellite MNPs can be synthesized. The time-dependent loading with MNP satellites under release of the extinction and magnetization offer a hybrid material, which is of special relevance for biomedical applications and plasmonic catalysis.
J. Hermanns Perceived relevance of tasks in organic chemistry by preservice chemistry teachers Chemistry Teacher International 2020, DOI: 10.1515/cti-2020-0002AbstractIn this article the development, use and evaluation of tasks in organic chemistry is discussed. These tasks are designed following the concept of school-related content knowledge. In this study the perceived relevance of these new tasks by preservice chemistry teachers was evaluated. Of special interest was the question how this new tasks should be designed to be perceived as relevant; are some features of the tasks more suitable than others? To answer all research questions a mixed methods study was conducted. To understand the students’ rating of the new tasks by using questionnaires, focus group interviews were conducted as well. The suitability of these new tasks for use in written exams was also evaluated. The results show that the students perceived the tasks as relevant for their future profession if the tasks included contents of the school curriculum, realistic situations and were personalized. They perceived the new tasks also as relevant for practicing skills in communication and explanations.
Marin, V.; Iturra, A.; Opazo, A.; Schmidt, B.; Heydenreich, M.; Ortiz, L.; Jiménez, V. A.; Paz, C. Oxidation of Isodrimeninol with PCC Yields Drimane Derivatives with Activity against Candida Yeast by Inhibition of Lanosterol 14-Alpha Demethylase Biomolecules 2020, 10, 1101 DOI: 10.3390/biom10081101AbstractIsodrimeninol is a natural product isolated from the bark of the tree Drimys winteri. It was used for the synthesis of four other sesquiterpenoids through oxidation with PCC. The products were tested for their antifungal activity against various Candida species that cause Candidiasis, an opportunistic yeast infection responsible for more than 50000 deaths per year worldwide. Isodrimeninol and one of its oxidation products bind to the catalytic site of lanosterol-14-alpha-demethylase as shown by in-silico analysis, which provides the mechanistic rationale for the observed antifungal activity.   The paper results from a collaborative project of Prof. Cristian Paz from the Universidad de la Frontera in Temuco, Chile, with Dr. Matthias Heydenreich and Prof. Bernd Schmidt.   Prof. Paz is a regular visiting scientist at our department.
A. Das, S. Noack, H. Schlaad, G. Reiter, R. Reiter Exploring Pathways to Equilibrate Langmuir Polymer Films Langmuir 2020, 36, 8184-8192 DOI: 10.1021/acs.langmuir.0c01268AbstractFocusing on the phase-coexistence region in Langmuir films of poly(L-lactide), we investigated changes in nonequilibrated morphologies and the corresponding features of the isotherms induced by different experimental pathways of lateral compression and expansion. In this coexistence region, the surface pressure Π was larger than the expected equilibrium value and was found to increase upon compression, i.e., exhibited a nonhorizontal plateau. As shown earlier by using microscopic techniques [Langmuir 2019, 35, 6129-6136], in this plateau region, well-ordered mesoscopic clusters coexisted with a surrounding matrix phase. We succeeded in reducing Π either by slowing down the rate of compression or through increasing the waiting time after stopping the movement of the barriers, which allowed for relaxations in the coexistence region. Intriguingly, the most significant pressure reduction was observed when recompressing a film that had already been compressed and expanded, if the recompression was started from an area value smaller than the one anticipated for the onset of the coexistence region. This observation suggests a "self-seeding" behavior, i.e., pre-existing nuclei allowed to circumvent the nucleation step. The decrease in ? was accompanied by a transformation of the initially formed metastable mesoscopic clusters into a thermodynamically favored filamentary morphology. Our results demonstrate that it is practically impossible to obtain fully equilibrated coexisting phases in a Langmuir polymer film, neither under conditions of extremely slow continuous compression nor for long waiting times at a constant area in the coexistence region which allow for reorganization.
S. Laroque, M. Reifarth, M. Sperling, S. Kersting, S. Klöpzig, P. Budach, J. Storsberg, M. Hartlieb Impact of Multivalence and Self-Assembly in the Design of Polymeric Antimicrobial Peptide Mimics ACS Appl. Mater. Interfaces 2020, 12, 30052-30065 DOI: 10.1021/acsami.0c05944AbstractAntimicrobial resistance is an increasingly serious challenge for public health and could result in dramatic negative consequences for the health care sector during the next decades. In order to solve this problem, antibacterial materials which are unsusceptible towards the development of bacterial resistance are a promising branch of research. Within this work, a new type of polymeric antimicrobial peptide mimic featuring a bottle brush architecture is developed, using a combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening metathesis polymerization (ROMP). This approach enables multivalent presentation of antimicrobial subunits resulting in improved bioactivity and an increased hemocompatibility, boosting the selectivity of these materials for bacterial cells. Direct probing of membrane integrity of treated bacteria revealed a highly potent membrane disruption caused by bottle brush copolymers. Multivalent bottle brush copolymers clearly out-performed their linear equivalents regarding bioactivity and selectivity.The effect of segmentation of cationic and hydrophobic sub-units within bottle brushes was probed using hetero graft-copolymers. These materials were found to self-assemble under physiological conditions, which reduced their antibacterial activity, highlighting the importance of precise structural control for such applications.To the best of our knowledge this is the first example to demonstrate the positive impact of multivalence, generated by a bottle brush topology in polymeric antimicrobial peptide mimics, making these polymers a highly promising material platform for the design of new bactericidal systems.
T. Haubitz, L. John, D. Freyse, P. Wessig, M. U. Kumke Investigating the Sulfur "Twist" on the Photophysics of DBD Dyes J. Phys. Chem. A 2020, 124, 4345-4353 DOI: 10.1021/acs.jpca.0c01880AbstractThe so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes are a new class of fluorescent dyes, with tunable photophysical properties like absorption, fluorescence lifetime, and Stokes shift. With the development of sulfur based DBDs, this dye class is extended even further for possible applications in spectroscopy and microscopy. In this paper we are investigating the basic photophysical properties and their implications for future applications for S4-DBD as well as O4-DBD. On the basis of time-resolved laser fluorescence spectroscopy, transient absorption spectroscopy, and UV/vis-spectroscopy, we determined the rate constants of the radiative and nonradiative deactivation processes as well as the energy of respective electronic states involved in the electronic deactivation of S4-DBD and of O4-DBD. For S4-DBD we unraveled the triplet formation with intersystem crossing quantum yields of up to 80%. By TD-DFT calculations we estimated a triplet energy of around 13500-14700 cm–1 depending on the DBD dye and solvent. Through solvent dependent measurements, we found quadrupole moments in the range of 2 B.
W. Fudickar, T. Linker Structural motives controlling the binding affinity of 9,10-bis(methylpyridinium)anthracenes towards DNA Bioorg. Med. Chem. 2020, 28, 115432 DOI: 10.1016/j.bmc.2020.115432AbstractIn the search of new DNA groove binding agents a series of substituted 9,10-methylpyridiniumanthracenes have been synthesized and their interactions with DNA have been studied by UV/vis absorption, CD and fluorescence spectroscopy. A minor groove binding mode is confirmed by DNA melting studies, strong CD effects, the dependence of the binding affinity on ionic strength, and the differentiation between AT and GC base pairs. No binding occurs to GC sequences. Binding constants to calf thymus DNA (ct-DNA) and poly(dA:dT) in the range between 1 x 104 and 3 x 105 M-1 have been determined. The binding strength decreases with the size of substituents attached at the anthracene site. Variation of the substitution pattern of the charged groups shows that methyl groups in meta position cause slightly stronger binding than methyl groups in para position. In contrast, with these groups in ortho position, no binding interaction has been observed. The strongest binding is achieved with an expansion of the peripheral heterocycle from pyridine to quinoline. Molecular modeling reveals the pivotal role of the substitution pattern: Anthracenes with para and meta pyridines align along the minor grooves. On the other hand, the ortho derivative adopts no groove-alignment.
F. Liebig, R. M. Sarhan, C. N.Z. Schmitt, A. F. Thünemann, C. Prietzel, M. Bargheer, J. Koetz Gold Nanotriangles with Crumble Topping and their Influence on Catalysis and Surface-Enhanced Raman Spectroscopy ChemPlusChem 2020, 85, 519-526 DOI: 10.1002/cplu.201900745AbstractBy adding hyaluronic acid (HA) to AOT-stabilized gold nanotriangles (AuNTs) with an average thickness of 7.5 ± 1 nm and an edge length of about 175 ± 17 nm the AOT-bilayer is replaced by a polymeric HA-layer leading to biocompatible nanoplatelets. The following reduction process of tetrachloroauric acid in the HA-shell surrounding the AuNTs leads to the formation of spherical gold nanoparticles on the platelet surface. With increasing tetrachloroauric acid concentration the decoration with gold nanoparticles can be tuned. SAXS measurements reveal an increase of the platelet thickness up to ~14.5 nm, twice to the initial one of bare AuNTs. HRTEM micrographs show welding phenomena between densely packed particles on the platelet surface, leading to a crumble formation while preserving the original crystal structure. Crumbles crystallized on top of the platelets enhance the Raman signal by a factor of ~20, and intensify the plasmon-driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4\'-dimercaptoazobenzene up to a yield of 50%. The finally received crumbled nanotriangles, with a biopolymer shell and the absorption maximum in the second window for in vivo imaging, are promising candidates for biomedical sensing.
J. Herrmanns How should stepped supporting tools be designed to support non-major chemistry students while solving tasks in organic chemistry - results of a think-aloud study, Progress in Science Education 2020, 3, 9-25 DOI: 10.25321/prise.2020.960AbstractIn this article the use of stepped supporting tools by non-major chemistry students will be discussed. The students used this scaffold while solving a task on the electrophilic addition on the double bond. To know how the students proceed a think-aloud study with ten students was conducted and will be discussed here. The results show that the students are then successful in solving the task if they have sufficient prior knowledge and methodical skills. When they lack these knowledge or methodical skills the stepped supporting tools can only partly support the students.
M. Hartlieb, E. D. H. Mansfield, S. Perrier, A guide to supramolecular polymerizations Polym. Chem. 2020, 11, 1083-1110 DOI: 10.1039/C9PY01342CAbstractSupramolecular polymers or fibers are non-covalent assemblies of unimeric building blocks connected by secondary interactions such as hydrogen bonds or π-π interactions. Such structures hold enormous potential in the development of future materials, as their non-covalent nature makes them highly modular and adaptive. Within this review we aim to provide a broad overview over the area of linear supramolecular polymers including the different mechanisms of their polymerization as well as methods essential for their characterization. The different non-covalent interactions able to form supramolecular polymers are discussed, and key examples for each species are shown. Particular emphasis is laid on the development of living supramolecular polymerization able to produce fibers with a controlled length and low length dispersity, and even enable the production of supramolecular block copolymers. Another important and very recent field is the development of out-of-equilibrium supramolecular polymers, where the polymerization process can be temporally controlled enabling access to highly adaptive materials.
K. Lood, B. Schmidt Stereoselective Synthesis of Conjugated Polyenes Based on Tethered Olefin Metathesis and Carbonyl Olefination: Application to the Total Synthesis of (+)-Bretonin B J. Org. Chem. 2020, 85, 5122-5130 DOI: 10.1021/acs.joc.0c00446AbstractWe report the total synthesis of enantiomerically pure (+)-bretonin B, a marine natural product that was first isolated from a sponge collected off the coast of Brittany. The structure comprises a synthetically challenging E,Z,E-triene pattern that was accessed using an unconventional tethered olefin metathesis reaction in combination with a Julia-Kocienski-olefination.
P. Wessig, D. Freyse, D. Schuster, A. Kelling Fluorescent Dyes with Large Stokes Shifts Based on Benzo[1,2-d:4,5-d´]bis([1,3]dithiole) ("S4-DBD Dyes") Eur. J. Org. Chem. 2020, , 1732-1744 DOI: 10.1002/ejoc.202000093AbstractWe report on a further development of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes by replacement of the four oxygen atoms of the heterocyclic core by sulphur atoms. This variation causes striking changes of the photophysical properties. Whereas absorption and emission significantly shifted to longer wavelength, the fluorescence lifetimes and quantum yields are diminished compared to DBD dyes. The latter effect is presumably caused by an enhanced intersystem crossing to the triplet state due to the sulphur atoms. Especially to be emphasized are the very large Stokes shifts of the S4-DBD dyes. By analogy with DBD dyes a broad variation of absorption and emission wavelength is possible by introducing different electron withdrawing substituents. Moreover, some derivatives for coupling with biomolecules were developed.
F. Liebig, R. M. Sarhan, M. Bargheer, C. N.Z. Schmitt, A. H. Poghosyan, A. A. Shahinyan, J. Koetz Spiked gold nanotriangles: Formation, characterization and applications in surface-enhanced Raman spectroscopy and plasmon-enhanced catalysis RSC Advances 2020, 10, 8152-8160 DOI: 10.1039/D0RA00729CAbstractWe show the formation of metallic spikes on the surface of gold nanotriangles (AuNTs) by using the same reduction process, which has been used for the synthesis of gold nanostars. We confirm that silver nitrate operates as a shape-directing agent in combination with ascorbic acid as the reducing agent and investigate the mechanism by dissecting the contribution of each component, i.e., anionic surfactant dioctyl sodium sulfosuccinate (AOT), ascorbic acid (AA), and AgNO3. Molecular dynamics (MD) simulations show that AA attaches to the AOT bilayer of nanotriangles, and covers the surface of gold clusters, which is of special relevance for the spike formation process at the AuNT surface. The surface modification goes hand in hand with a change of the optical properties. The increased thickness of the triangles and a sizeable fraction of silver atoms covering the spikes lead to a blue-shift of the intense near infrared absorption of the AuNTs. The sponge-like spiky surface increases both the surface enhanced Raman scattering (SERS) cross section of the particles and the photo-catalytic activity in comparison with the unmodified triangles, which is exemplified by the plasmon-driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4\\\'-dimercaptoazobenzene (DMAB).
Y. Mai-Linde, T. Linker Radical Clock Probes to Determine Carbohydrate Radical Stabilities Org. Lett. 2020, 22, 1525–1529 DOI: 10.1021/acs.orglett.0c00111AbstractCarbohydrate radical stabilities in the 1- and 2-position have been determined by a radical clock approach, starting from cyclopropanated sugars with xanthate as precursors. Various hexoses and pentoses afforded 1-deoxy sugars as main products, indicating that anomeric radicals are more stable than radicals in the 2-position. An additional influence of the configurations on radical stabilities has been observed. Our results should be interesting for the understanding of 1,2-radical rearrangements in carbohydrate chemistry and offer an easy access to deoxy-vinyl sugars.
R. R. Raju, F. Liebig, B. Klemke, J. Koetz Ultralight Magnetic Aerogels from Janus Emulsions RSC Advances 2020, 10, 7492-7499 DOI: 10.1039/c9ra10247gAbstractMagnetite containing aerogels were synthesized by freeze-drying olive oil/silicone oil- based Janus emulsion gels containing gelatin and sodium carboxymethylcellulose (NaCMC). The magnetite nanoparticles dispersed in olive oil are processed into the gel and remain in the macroporous aerogel after removing the oil components. The coexistence of macropores from the Janus droplets and mesopores from freeze-drying of the hydrogels in combination with the magnetic properties offers a special hierarchical pore structure, which is of relevance for smart supercapacitors, biosensors, and spilled oil sorption and separation. The morphology of the final structure was investigated in dependence on initial compositions. More hydrophobic aerogels with magnetic responsiveness were synthesized by bisacrylamide-crosslinking of the hydrogel. The crosslinked aerogels can be successfully used in magnetically responsive clean up experiments of the cationic dye methylene blue.
Y.-Q. He, W. Fudickar, J.-H. Tang, H. Wang, X. Li, J. Han, Z. Wang, M. Liu, Y.-W. Zhong, T. Linker, P. J. Stang Capture and Release of Singlet Oxygen in Coordination-Driven Self-Assembled Organoplatinum(II) Metallacycles J. Am. Chem. Soc. 2020, 142, 2601-2608 DOI: 10.1021/jacs.9b12693AbstractSinglet oxygen (1O2), as an important active reagent, has found wide applications in photodynamic therapy (PDT), synthetic chemistry, and materials science. Organic conjugated aromatics serving as hosts to capture and release singlet oxygen have been systematically investigated over the last decades. Herein, we present a [6 + 6] organoplatinum(II) metallacycle by using ~180° dipyridylanthracene donor and ~120° Pt(II) acceptor as the building blocks, which enables the capture and release of singlet oxygen with relatively high photooxygenation and thermolysis rate constants. The photooxygenation of the metallacycle to the corresponding endoperoxide was performed by sensitized irradiation, and the resulting endoperoxide is stable at room temperature and can be stored under ambient condition over months. Upon simple heating of the neat endoperoxide under inert atmosphere at 120 °C for 4 h, the resulting endoperoxide can be reconverted to the corresponding parent form and singlet oxygen. The photooxygenation and thermolysis products were characterized by NMR spectroscopy and electrospray ionization time-of-flight mass spectrometric analysis. Density functional theory calculations were conducted in order to reveal the frontier molecular orbital interactions and reactivity. This work provides a new material platform for singlet oxygen related promising applications.
A. Matic, A. Hess, D. Schanzenbach, H. Schlaad Epoxidized 1,4-Polymyrcene Polym. Chem. 2020, 11, 1364-1368 DOI: 10.1039/C9PY01783FAbstract1,4-Polymyrcene was synthesized by anionic polymerization and epoxidized using meta-chloroperbenzoic acid. Samples with different degrees of epoxidation (25%, 49%, 74%, and 98%) were prepared and examined according to their chemical and thermal properties. Epoxidation was found to increase the glass transition temperature (Tg = 14 °C for the 98% epoxidized 1,4-polymyrcene) as well as the shelf live (>10 months). The trisubstituted epoxide groups were remarkably stable against nucleophiles under basic conditions but cross-linked or hydrolyzed in the presence of an acid. Also, highly epoxidized 1,4-polymyrcene readily cross-linked upon annealing at 260 °C to produce an epoxy resin.
E. Schönemann, J. Koc, N. Aldred, A. S. Clare, A. Laschewsky, A. Rosenhahn, E. Wischerhoff Synthesis of Novel Sulfobetaine Polymers with Differing Dipole Orientations and Their Effects on the Antifouling Properties Macromol. Rapid Commun. 2020, 41, [1900447] DOI: 10.1002/marc.201900447AbstractIncited by the ongoing discussion about differences in the binding behavior of natural zwitterionic phosphatidylcholines compared to the one of non-natural isomeric choline phosphates, we investigated the effect of the molecular orientation of zwitterionic sulfobetaine groups on the anti-fouling performance of thin polymer hydrogel films. To this end, we designed an isomeric set of three photocurable poly(sulfobetaine methacrylate)s, in which the positions of the cationic and the anionic groups relative to the polymer backbone were systematically altered. The effect of the varied segmental dipole orientation onto their water solubility, wetting of their films by water, and their fouling resistance against model proteins as well as typical marine fouling organisms was studied. The results demonstrate the important role of the orientation of a given zwitterionic group on the specific behavior of the polymers including their fouling resistance.
N. Lüdecke, S. M. Weidner, H. Schlaad Poly(2-oxazoline)s Based on Phenolic Acids Macromol. Rapid. Commun. 2020, 41, 1900404 DOI: 10.1002/marc.201900404AbstractMethylated phenolic acid-based 2-oxazolines are synthesized and polymerized in a microwave reactor at 140 °C using methyl tosylate as the initiator. Polymerizations are fast and completed within ≈10 min for monomer-to-initiator ratios of ≤25 to produce polymers with number-average molar masses of up to 6500 g/mol and low dispersity (1.2-1.3). Demethylation yields a poly(2-oxazoline) with pendent catechol groups.
T. Debsharma, Y. Yagci, H. Schlaad Cellulose-Derived Functional Polyacetal by Cationic Ring-Opening Polymerization of Levoglucosenyl Methyl Ether Angew. Chem. Int. Ed. 2019, 58, 18492-18495 DOI: 10.1002/anie.201908458AbstractThe unsaturated bicyclic acetal levoglucosenyl methyl ether was readily obtained from sustainable feedstock (cellulose) and polymerized by cationic ring-opening polymerization to produce a semicrystalline thermoplastic unsaturated polyacetal with relatively high apparent molar mass (up to ca. 36 kg mol-1) and decent dispersity (ca. 1.4). The double bonds along the chain can undergo hydrogenation and thiol-ene reactions as well as crosslinking, thus making this polyacetal potentially interesting as a reactive functional material.
Otte, F., Schmidt, B. Matsuda-Heck Arylation of Glycals for the stereoselective Synthesis of Aryl C-Glycosides J. Org. Chem. 2019, 84, 14816-14829. DOI: 10.1021/acs.joc.9b02410AbstractAryl C-glycosides occur as structural patterns in many natural and non-natural bioactive compounds. We devise a novel synthetic strategy that relies on a Heck-type arylation of glycals (in turn synthesized de novo from lactic acid derivatives using olefin metathesis methods) with arene diazonium salts (commonly known as Matsuda-Heck-reaction). The gliflozin derivative shown in the graphical abstract is a representative application example.
J. Hermanns, D. Keller School related content knowledge in organic chemistry - how different school curricula should be considered for the development of tasks Progress in Science Education 2019, 2, 17 DOI: 10.25321/prise.v2i1.888AbstractThe professional knowledge of teachers, as described by Shulman (1968) consists of content knowledge, pedagogical content knowledge and pedagogical knowledge. Woehlecke and Massolt et al. (2017) describe the school-related content knowledge (SRCK) as a cross-disciplinary construct. We developed tasks in organic chemistry using their construct. In these tasks often a school context was used. The tasks were evaluated by using a questionnaire and by conducting focus group interviews. We wanted to know how the different school curricula of the federal states in Germany should be considered by the development of new tasks. The differences between the school curricula of the federal states are significant. These differences should be considered for the development and use of the tasks. The students are focused on their own school biography and the state where they went to school and where they want to be a chemistry teacher. By changing the contexts in the tasks these differences can be positively used for the development of new tasks.
R.M. Sarhan, W. Koopman, J. Pudell, F. Stete, M. Rössle, M. Herzog, C.N.Z. Schmitt, F. Liebig, J. Koetz, M. Bargheer Scaling Up Nanoplasmon Catalysis: The Role of Heat Dissipation Journal Physical Chemistry C 2019, 123, 9352-9357 DOI: 10.1021/acs.jpcc.8b12574AbstractNanoscale heating by optical excitation of plasmonic nanoparticles offers a new perspective of controlling chemical reactions, where heat is not spatially uniform as in conventional macroscopic heating but strong temperature gradients exist around microscopic hot spots. In nanoplasmonics, metal particles act as a nanosource of light, heat, and energetic electrons driven by resonant excitation of their localized surface plasmon resonance. As an example of the coupling reaction of 4-nitrothiophenol into 4,4'-dimercaptoazobenzene, we show that besides the nanoscopic heat distribution at hot spots, the microscopic distribution of heat dictated by the spot size of the light focus also plays a crucial role in the design of plasmonic nanoreactors. Small sizes of laser spots enable high intensities to drive plasmon-assisted catalysis. This facilitates the observation of such reactions by surface-enhanced Raman scattering, but it challenges attempts to scale nanoplasmonic chemistry up to large areas, where the excess heat must be dissipated by onedimensional heat transport.
T. Schwarze, J. Riemer, H. Müller, L. John, H.-J. Holdt, P. Wessig Na+ Selective Fluorescent Tools Based on Fluorescence Intensity Enhancements, Lifetime Changes, and on a Ratiometric Response Chemistry Eur. J. 2019, 25, 12412 – 12422 DOI: 10.1002/chem.201902536AbstractOver the years, we developed highly selective fluorescent probes for K+ in water, which show K+-induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1–K4). In this paper, we introduce selective fluorescent probes for Na+ in water, which also show Na+ induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent\r\nprobes 2, 4, 5, 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na+ responsive ionophore unit and the fluorophore moiety to adjust different Kd values for an intra- or extracellular Na+ analysis. Thus, we found that 2, 4 and 5 are Na+ selective fluorescent tools, which are able to measure physiologically important Na+ levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na+ levels by fluorescence lifetime changes.\r\nHerein, only 8 (Kd=106 mM) is a capable fluorescent tool to measure Na+ levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na+\r\ninduced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 (Kd=78 mM) showed a ratiometric fluorescence response towards Na+ ions and is a suitable tool to measure physiologically relevant Na+ levels by the intensity change of two emission wavelengths at 404 nm and 492 nm.
C. M. Papadakis, P. Müller-Buschbaum, A. Laschewsky Switch it Inside-out - "Schizophrenic" Behavior of All Thermo-responsive UCST-LCST Diblock Copolymers. Feature Article Langmuir 2019, 35, 9660-9676 DOI: 10.1021/acs.langmuir.9b01444AbstractWe summarize and discuss our recent advancements in the synthesis, the phase behavior and the micellar structures of "doubly smart" block copolymers, which are composed of oppositely thermoresponsive blocks. These copolymers unite blocks that exhibit lower critical solution temperature (LCST) behavior in aqueous media, with blocks that feature an upper critical solution temperature (UCST). The proper design of the polymers\' structure allows for implementing the sequence of the UCST and LCST transitions of the polymers at will. By adjusting either molecular or, alternatively, physical parameters, the relative locations of the transition temperatures of both blocks can be controlled. In this way, different switching scenarios are realized from micelles to inverse micelles, namely via the molecularly dissolved state, the aggregated state or directly. We discuss the possible use of such diblock copolymers, e.g. as "smart" emulsifiers or nanocarriers.
J. Holec, J. Rybáček, J. Vacek, M. Karras, L. Bednárová, M. Buděšínský, M. Slušná, P. Holý, B. Schmidt, I. G. Stará, I. Starý Chirality-Controlled Self-Assembly of Amphiphilic Dibenzo[6]helicenes into Langmuir-Blodgett Thin Films. Chem. Eur. J. 2019, 25, 11494-11502. Chem. Eur. J. 2019, 25, 11494-11502 DOI: 10.1002/chem.201903286AbstractLangmuir layers of racemic and enantiopure helicenes with pendant alcohol, carboxylic acid or ester groups differ significantly in stability. This is reflected in the cover picture, which shows (on the left) a frog floating on a stable "racemic raf", and on the right a frog sinking with a less stable "enantiopure raft". See also the cover profile on page 11393 at https://onlinelibrary.wiley.com/doi/10.1002/chem.201903286
F. Liebig, R. Henning, R.M. Sarhan, C. Prietzel, C.N.Z. Schmitt, M. Bargheer, J. Koetz A simple one-step procedure to gold nanostars in concentrated aqueous surfactant solutions RSC Advances 2019, 9, 23633-23641 DOI: 10.1039/c9ra02384dAbstractDue to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in presence of Ag+ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption.
M. Kirste, T. Brietzke, H.-H. Holdt, U. Schilde The crystal structure of 1,12-diazaperylene, C18H10N2 Z. Kristallogr. - NCS 2019, , aop DOI: 10.1515/ncrs-2019-0385Abstract
E. Schönemann, .A. Laschewsky, E. Wischerhoff, J. Koc, A. Rosenhahn Surface Modification by Polyzwitterions of the Sulfabetaine-Type, and Their Resistance to Biofouling Polymers 2019, 11, 1014 DOI: 10.3390/polym11061014AbstractWe synthesize a series of new zwitterionic polymers that combine ammonium and sulfate groups in their betaine moieties. The chemical structure of these so-called poly(sulfabetaine)s is varied systematically for monomers carrying methacrylate, methacrylamide, or styrene moieties as polymerizable groups. Free radical polymerization yields high molar mass homopolymers. Solubilities in most solvents are low, but brine and lower fluorinated alcohols were effective solvents in most cases. A set of sulfabetaine copolymers containing ~1 mol % (based on the repeat units) of reactive benzophenone methacrylate is prepared, spin-coated onto solid substrates, and photo-cured. The resistance of these films against the nonspecific adsorption of model proteins BSA and fibrinogen is explored. The various polyzwitterions reduce protein adsorption strongly compared to films of poly(n butyl methacrylate) that are used as negative control. The poly(sulfabetaine)s show mostly slightly higher anti-fouling activity than their poly(sulfobetaine) analogues, though detailed efficacies depend on the individual polymer–protein pairs. Best samples approach the excellent performance of a poly(oligo(ethylene oxide) methacrylate) reference.
S. Vogel, K. Ebel, R. Schürmann, C. Heck, T. Meiling, A. Milosavljevic, A. Giuliani, I. Bald Vacuum-UV and Low-Energy Electron Induced DNA Strand Breaks – Influence of the DNA Sequence and Substrate ChemPhysChem 2019, 20, 823-830 DOI: 10.1002/cphc.201801152AbstractDNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. They are irradiated directly with vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7-2.3x10-16 cm2. The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies kleiner 3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold.
R. Schürmann, K. Ebel, C. Nicolas, A. R. Milosavljevic, I. Bald; J. Phys. Chem. Lett. 2019, 10, 3153-3158 Role of Valence Band States and Plasmonic Enhancement in Electron-Transfer-Induced Transformation of Nitrothiophenol J. Phys. Chem. Lett. 2019, 10, 3153-3158 DOI: 10.1021/acs.jpclett.9b00848AbstractHot-electron-induced reactions are more and more recognized as a critical and ubiquitous reaction in heterogeneous catalysis. However, the kinetics of these reactions is still poorly understood, which is also due to the complexity of plasmonic nanostructures. We determined the reaction rates of the hot-electron-mediated reaction of 4-nitrothiophenol (NTP) on gold nanoparticles (AuNPs) using fractal kinetics as a function of the laser wavelength and compared them with the plasmonic enhancement of the system. The reaction rates can be only partially explained by the plasmonic response of the NPs. Hence, synchrotron X-ray photoelectron spectroscopy (XPS) measurements of isolated NTP-capped AuNP clusters have been performed for the first time. In this way, it was possible to determine the work function and the accessible valence band states of the NP systems. The results show that besides the plasmonic enhancement, the reaction rates are strongly influenced by the local density of the available electronic states of the system.
L. P. Kreuzer, T. Widmann, N. Hohn, K. Wang, L. Bießmann, L. Peis, J. F. Moulin, V. Hildebrand, A. Laschewsky, C. M. Papadakis, P. Müller-Buschbaum Swelling and Exchange Behavior of Poly(sulfobetaine)-based Block Copolymer Thin Films Macromolecules 2019, 52, 3486 DOI: 10.1021/acs.macromol.9b00443AbstractThe water exchange in thin diblock copolymer films is investigated by time-of-flight neutron reflectometry (TOF-NR).. The block copolymer is composed of a nonionic block, namely poly(N-isopropylacrylamide) PNIPAM, and a zwitterionic block, namely [poly(N,N-dimethyl-N-(3-(methacrylamido)propyl) ammoniopropanesulfonate)] PSPP. Swelling in H2O atmosphere is monitored in situ, followed by water exchange with D2O. It is compared to the reverse experiment , i.e., swelling in D2O atmosphere and subsequent water exchange with H2O. Static and kinetic TOF-NR measurements indicate clear differences in the interactions between the PSPP80-b-PNIPAM130 thin film and H2O or D2O. These are attributed to the different H- and D-bonds between water and the polymer. FTIR spectroscopy probes the changes in the chain conformation and hydrogen bonding during the swelling and exchange processes, revealing the key role of the anionic -SO3- group in the PSPP block and the polar amide groups of both blocks during water uptake and exchange.
R. R.Raju, F. Liebig, A. Hess, H. Schlaad, J. Koetz Temperature-triggered reversible breakdown of polymer-stabilized olive-silicone oil Janus emulsions RSC Advances 2019, 9, 19271-19277 DOI: 10.1039/c9ra03463cAbstractA one-step moderate energy vibrational emulsification method was successfully employed to produce thermo-responsive olive/silicone-based Janus emulsions stabilized by poly(N,N-diethylacrylamide) carrying 0.7 mol% oleoyl side chains. Completely engulfed emulsion droplets remained stable at room temperature and could be destabilized on demand upon heating to the transition temperature of the polymeric stabilizer. Time-dependent light micrographs demonstrate the temperature-induced breakdown of the Janus droplets, which opens new aspects of application, for instance in biocatalysis.
T. Haubitz, L. John, P. Wessig, M. U. Kumke Photophysics of Acyl- and Ester-DBD Dyes: Quadrupole-Induced Solvent Relaxation Investigated by Transient Absorption Spectroscopy J. Phys. Chem. A 2019, 123, 4717-4726 DOI: 10.1021/acs.jpca.9b02973AbstractA new generation of wavelength-tunable, fluorescent dyes, so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes, were developed a few years ago, and they showed great potential as probes, for example, for fluorescence microscopy. However, their photophysics is not fully explored and leaves open questions regarding their large fluorescence Stokes shifts and sensitivity to solvent conditions of differently substituted DBD dyes. To improve the understanding of the influence of the substitution pattern of the DBD dyes on their respective photophysics, transient absorption spectroscopy (TAS) was used, that is, a pump–probe experiment on the femtosecond timescale. TAS allows measurements of excited states, ground state recovery, solvent relaxation, and fluorescence properties on time scales of up to several nanoseconds. Two different DBD dye samples were investigated: acyl- and ester-substituted DBD dyes. Experiments were carried out in solvents with different polarities using different excitation energies and at different viscosities. Based on the experimental data and theoretical calculations, we were able to determine the conformational changes of the molecule due to electronic excitation and were able to investigate solvent relaxation processes for both types of DBD dyes. By generalizing the theory for quadrupole-induced solvent relaxation developed by Togashi et al., we derived quadrupole moments of both molecules in the ground and excited state. Our data showed differences in the binding of polar solvent molecules to the dyes depending on the substituent on the DBD dye. In the case of water as the solvent, an additional efficient quenching process in the electronically excited state was revealed, which was indicated by the observation of solvated electrons in the TAS signals.
W. Fudickar, T. Linker Theoretical insights into the effect of solvents on the [4+2] cycloaddition of singlet oxygen to substituted anthracenes: A change from a stepwise to a concerted process J. Phys. Org. Chem. 2019, , e3951 DOI: 10.1002/poc.3951AbstractThe [4+2] cycloadditions of singlet oxygen to 9,10-diphenylanthracene (1) and the meta and para isomers of 9,10-dipyridylanthracene (2m/p) and 9,10-methoxyphenylanthracene (3m/p) have been studied by density functional calculations in the gas phase at the UB3LYP/6-31G* level and for the first time in solvents at the CPCM UM062X/6-31G* level. The differences in calculated TS energies derived from this method are in line with experimentally observed reactivity orders in solution. For the gas phase reaction the first TS of the stepwise pathway (TS1) has biradical character and its energy lies below the energy of the TS of the concerted path (TSconc). In contrast, in the solvent acetonitrile TS1 resembles a zwitterion and lies significantly higher than the TSconc. Thus, a concerted mechanism applies in solvents, and the energy gap between the TS of the two processes decreases with decreasing polarity. A change from a pyridyl against a methoxyphenyl substituent in para position causes a maximal reduction of the activation barrier by ~1.7 kcal/mol resulting in a fivefold increased reactivity.
N. S. Vishnevetskaya, V. Hildebrand, N. M. Nizardo, C. H. Ko, Z. Di, A. Radulescu, L. C. Barnsley, P. Müller Buschbaum, A. Laschewsky, C. M. Papadakis All-in-One \"Schizophrenic\" Self-assembly of Orthogonally Tuned Thermo-responsive Diblock Copolymers Langmuir 2019, 35, 6441 DOI: 10.1021/acs.langmuir.9b00241AbstractSmart, fully orthogonal switching is implemented in a diblock copolymer system with variable trigger-induced aqueous self-assembly. The polymers are made of a non-ionic and a zwitterionic block, which exhibit either lower or upper critical solution temperature in aqueous solutions. Here poly(N-isopropyl methacrylamide) PNIPMAM and a poly(sulfobetaine methacrylamide) PSBP are combined. Successive thermal switching of the block copolymers results in \"schizophrenic\" micellization, in which the roles of the hydrophobic core block and the hydrophilic shell block are interchanged in dependence on temperature. In these systems, the UCST can be efficiently modulated by adding specific amounts of electrolytes. This allows for realizing the switching between the two types of micelles via two distinct scenarios: (i) via a molecularly dissolved state, if the LCST-type cloud point is lower than the UCST-type cloud point, which is the case at low salt concentrations. Or (ii) via an insoluble state, if the LCST-type cloud point is higher than the UCST-type cloud point, which is the case at high salt concentrations.
T. Krüger, A. Kelling, T. Linker, U. Schilde Crystal structures of three cyclohexane-based spirolactams: determination of configurations and conformations BMC Chemistry 2019, 13:69, 1-9 DOI: 10.1186/s13065-019-0586-7AbstractThe title compounds, 2-azaspiro[4.5]deca-1-one, C9H15NO, (1a), cis-8-methyl-2-azaspiro[4.5]deca-1-one, C10H17NO, (1b), and trans-8-methyl-2-azaspiro[4.5]deca-1-one, C10H17NO, (1c), were synthesized from benzoic acids 2 in only 3 steps in high yields. Crystallization from n-hexane afforded single crystals, suitable for X-ray diffraction. Thus, the configurations, conformations, and interesting crystal packing effects have been determined unequivocally. The bicyclic skeleton consists of a lactam ring, attached by a spiro junction to a cyclohexane ring. The lactam ring adopts an envelope conformation and the cyclohexane ring has a chair conformation. The main difference between compound 1b and compound 1c is the position of the carbonyl group on the 2-pyrrolidine ring with respect to the methyl group on the 8-position of the cyclohexane ring, which is cis (1b) or trans (1c). A remarkable feature of all three compounds is the existence of a mirror plane within the molecule. Given that all compounds crystallize in centrosymmetric space groups, the packing always contains interesting enantiomer-like pairs. Finally, the structures are stabilized by intermolecular N–H···O hydrogen bonds.
A. R. Sardarian, I. Dindarloo Inaloo, A. R. Modarresi-Alam, E. Kleinpeter, U. Schilde Metal-Free Regioselective Monocyanation of Hydroxy-, Alkoxy- and Benzyloxyarenes by Potassium Thiocyanate and Silica Sulfuric Acid as a Cyanating Agent J. Org. Chem. 2019, 84, 1748-1756 DOI: 10.1021/acs.joc.8b02191AbstractA novel and efficient metal- and solvent-free regioselective para-C-H cyanation of hydroxy-, alkoxy-, and benzyloxyarene derivs. has been introduced, using nontoxic potassium thiocyanate as a cyanating reagent in the presence of silica sulfuric acid (SSA). The desired products are obtained in good to high yields without any toxic byproducts
S. Kosmella, B. Klemke, I. Häusler, J. Koetz From gel-like Pickering emulsions to highly ordered superparamagnetic magnetite aggregates with embedded gold nanoparticles Colloids and Surfaces A 2019, 570, 331-338 DOI: 10.1016/j.colsurfa.2019.03.017AbstractPickering emulsions with two types of nanoparticles, i.e., superparamagnetic magnetite nanoparticles dispersed in n-hexane and gold nanoparticles dispersed in water, were formed by rigorous mixing in presence of surface active polymeric surfactants. Monodisperse magnetite nanoparticles with a mean particle size of 4 nm were obtained by a microwave-assisted synthesis in n-hexane in presence of oleic acid, and gold nanoparticles were produced in aqueous solution in presence of the hyperbranched poly(ethyleneimine) (PEI) or sodium citrate as reducing and stabilizing agent. After mixing the prepared nanoparticle dispersions in presence of the Pluronics an intermediate gel-like phase is formed. The Pickering emulsion droplets in the intermediate phase are stabilized by both types of nanoparticles, as to be seen by cryo-SEM micrographs. After separating, solvent evaporation and redispersion in water highly ordered Pluronic-stabilized superparamagnetic magnetite nanoparticle aggregates with embedded gold nanoparticles can be obtained.
A. Das, A. S. El-Tawargy, E. Khechine, S. Noack, H. Schlaad, G. Reiter, R. Reiter Controlling Nucleation in Quasi-Two-Dimensional Langmuir Poly(L-lactide) Films through Variation of the Rate of Compression Langmuir 2019, 35, 6129-6136 DOI: 10.1021/acs.langmuir.9b00619AbstractWe studied morphological changes in a quasi-two-dimensional Langmuir film of low molar mass poly(L-lactide) upon increasing the surface density, starting from randomly distributed molecules to a homogeneous monolayer of closely packed molecules, followed by nucleation and growth of mesoscopic, three-dimensional clusters from an overcompressed monolayer. The corresponding nucleation density of mesoscopic clusters within the monolayer can be tailored through variation of the rate of compression. For a given surface density and temperature, the nucleation probability was found to increase linearly with the rate of compression, allowing to adjust the density of mesoscopic clusters over nearly 2 orders of magnitude.
T. Debsharma, F. N. Behrendt, A. Laschewsky, H. Schlaad Ring-Opening Metathesis Polymerization of Biomass-Derived Levoglucosenol Angew. Chem. Int. Ed. 2019, 58, 6718-6721 DOI: 10.1002/anie.201814501AbstractThe readily available cellulose-derived bicyclic compound levoglucosenol was polymerized through ring-opening metathesis polymerization (ROMP) to yield polylevoglucosenol as a novel type of biomass-derived thermoplastic polyacetal, which, unlike polysaccharides, contains cyclic as well as linear segments in its main chain. High-molar-mass polyacetals with apparent weight-average molar masses of up to 100 kg/mol-1 and dispersities of approximately 2 were produced despite the non-living/controlled character of the polymerization due to irreversible deactivation or termination of the catalyst/active chain ends. The resulting highly functionalized polyacetals are glassy in bulk with a glass transition temperature of around 100°C. In analogy to polysaccharides, polylevoglucosenol degrades slowly in an acidic environment.
N. Riemer, M. Shipman, P. Wessig, B. Schmidt Iterative Arylation of Itaconimides with Diazonium Salts through Electrophilic Palladium Catalysis: Divergent ß-H-Elimination Pathways in Repetitive Matsuda-Heck Reactions J. Org. Chem. 2019, 84, 5732-5746 DOI: 10.1021/acs.joc.9b00627AbstractN-Arylitaconimides, accessible from maleic anhydride, anilines, and paraformaldehyde, react with arene diazonium salts in Pd-catalyzed Matsuda-Heck arylation to the pharmacologically relevant E-configured 3-arylmethylidene pyrrolidine-2,5-diones (also known as arylmethylidene succinimides) through exo-selective ß-H elimination. The coupling proceeds at ambient temperature with the simple and easy-to-handle precatalyst Pd-II-acetate under ligandand base-free conditions. Notable features are high isolated yields, regio- and stereoselectivities, and short reaction times. In a comparative investigation, aryl iodides, bromides, and triflates were shown to be inferior coupling reagents in this reaction. The 3- arylmethylidene pyrrolidine-2,5-diones undergo second Matsuda-Heck coupling, which proceeds via endo-selective ß-H-elimination to give diarylmethyl-substituted maleimides as coupling products. These products can also be accessed in one flask by sequential addition of different arene diazonium salts to the starting itaconimide. The potential of 3-arylmethylidene succinimides as photoswitches was tested. Upon irradiation of the E-isomer at 300 nm, partial isomerization to the Z-isomer (E/Z = 65:35 in the photostationary state) was observed. The isomerization was found to be nearly completely reversible by irradiating the mixture at 400 nm.
F. N. Behrendt, A. Hess, M. Lehmann, B. Schmidt, H. Schlaad Polymerization of cystine-derived monomers Polym.Chem. 2019, 10, 1636-1641 DOI: 10.1039/C9PY00118BAbstractCystine was used as a platform chemical to prepare cyclic and acyclic monomers for entropy-driven ring-opening polymerization (ED-ROMP) via olefin or disulfide metathesis and for step-growth polymerization. The olefin ED-ROMP of an olefin/disulfide containing 16-atom macrocycle using the 3rd generation Grubbs catalyst was examined in greater detail. Kinetic studies revealed that the catalyst turned inactive during the polymerization, which limited the achievable (apparent) polymer molar mass to ~70 kg mol-1. Such limitation could be overcome with the disulfide ED-ROMP of the same macrocycle to yield polymers with molar masses of up to 180 kg mol-1. The step-growth polymerizations of acyclic diene and dithiol monomers via olefin metathesis or oxidation were far less effective and yielded just low molar mass polymers or oligomers; photopolymerization of a thiol–ene monomer produced a polyester with a molar mass of 35 kg mol-1.
S. Noack, D. Schanzenbach, J. Koetz, H. Schlaad Polylactide-Based Amphiphilic Block Copolymers: Crystallization-Induced Self-Assembly and Stereocomplexation Macromol. Rapid Commun. 2019, 40, 1800639 DOI: 10.1002/marc.201800639AbstractThe aqueous self-assembly behavior of a series of poly(ethylene glycol)-poly(l-/d-lactide) block copolymers and corresponding stereocomplexes is examined by differential scanning calorimetry, dynamic light scattering, and transmission electron microscopy. Block copolymers assemble into spherical micelles and worm-like aggregates at room temperature, whereby the fraction of the latter seemingly increases with decreasing lactide weight fraction or hydrophobicity. The formation of the worm-like aggregates arises from the crystallization of the polylactide by which the spherical micelles become colloidally unstable and fuse epitaxically with other micelles. The self-assembly behavior of the stereocomplex aggregates is found to be different from that of the block copolymers, resulting in rather irregular-shaped clusters of spherical micelles and pearl-necklace-like structures.\\r\\n
J. Koc, E. Schönemann, A. Amuthalingam, J. Clarke, J.A. Finlay, A.S. Clare, A. Laschewsky, A. Rosenhahn Low Fouling Thin Hydrogel Coatings Made of Photo-crosslinked Polyzwitterions Langmuir 2019, 35, 1552 DOI: 10.1021/acs.langmuir.8b02799AbstractAlthough zwitterionic materials are among the most promising ones for preparing low-fouling surfaces, structural diversity has been quite limited until now. We therefore have synthesized a set of new, systematically varied zwitterionic hydrogel coatings, and compared their fouling behavior against a series of proteins, as well as against non-motile and motile marine model organisms. Overall, certain of these sulfo- and sulfabetaine coatings even match the high anti-fouling effectivity of poly(ethylene glycol)-based ones used as control, while offering enhanced chemical stability. Importantly, performances vary individually for a given fouler-hydrogel pair. Even seemingly minor chemical changes of the polymer structure influence the antifouling performance markedly. Therefore, the antifouling performance of a specific polymer cannot be generally ranked as "more performing" or "less performing", but depends on the particular ensemble, and has to be adapted accordingly.
T. Preller, G. Runge, S. Zellmer, D. Menzel, S. Azimi Saein, J. Peters, A. Raatz, B. Tiersch, J. Koetz, G. Garnweitner Particle-reinforced and functionalized hydrogels\\r\\nfor SpineMan, a soft robotics application\\r\\n J. Mater. Sci. 2019, , 4444-4456 DOI: 10.1007/s10853-018-3106-6AbstractSpineMan is designed as a prototype of a soft robotic manipulator that is constructed of alternating hard and soft segments similar to the human spine.\\r\\nImplementing such soft segments allows to surpass the rigidity of conventional\\r\\nrobots and ensures safer workspaces where humans and machines can work\\r\\nside by side with less stringent safety restrictions. Therefore, we used a hydrogel\\r\\nas viscoelastic material consisting of poly(vinyl alcohol) and borax. The\\r\\nmechanical properties of the hydrogel were tailored by embedding silica particles\\r\\nof various particles sizes as well as in different mass fractions. Increased\\r\\nmass contents as well as larger particle sizes led to strongly enhanced rigidity\\r\\nwith a more than doubled storage modulus of the composite compared to the\\r\\npure hydrogel. Furthermore, specific functionalities were induced by the\\r\\nincorporation of superparamagnetic Fe3O4 nanoparticles that can in principle be\\r\\nused for sensing robotic motion and detecting malfunctions. Therefore, we\\r\\nprecisely adjusted the saturation magnetization of the soft segments using\\r\\ndefined mass contents of the nanoparticles. To ensure long-time shape stability\\r\\nand prevention of atmospheric influences on the prepared composites, a silicone\\r\\nskin of specific shore hardness was used. The composites and the soft segments\\r\\nwere characterized by oscillation measurements, cryo-SEM, bending tests and\\r\\nSQUID measurements, which give insights into the properties in the passive and\\r\\nin the moving state of SpineMan. The utilization of tailored composites led to\\r\\nhighly flexible, reinforced and functional soft segments, which ensure stability,\\r\\neasy movability by springs of the shape memory alloy nitinol and prevention of\\r\\ntotal failure.\\r\\n
A. H. Poghosyan, M. P. Adamyan, A. A. Shahinyan, J. Koetz AOT Bilayer Adsorption on Gold Surfaces: A Molecular Dynamics Study J. Phys. Chem. B 2019, 123, 948-953 DOI: 10.1021/acs.jpcb.8b11471AbstractA molecular dynamics study was done to reveal the adsorption properties of sodium dioctyl sulfosuccinate (AOT) bilayers on gold Au(111) surfaces. Examining the rotational mobility of AOT molecules, we track that the correlation time of\\\\r\\\\nAOT molecules on the adsorbed layer is much higher. The data estimating the diffusive motion of AOT molecule show a substantially lower rate of diffusion (~10 -10 cm2/s) in the adsorbed layers in comparison to other ones. The results show that an adsorbed layer is more rigid, whereas the outer layers undergo considerable lateral and vertical fluctuations.
A. Laschewsky, A. Rosenhahn Molecular Design of Zwitterionic Polymer Interfaces: Searching for the Difference (Feature article). Langmuir 2019, 35, 1056 DOI: 10.1021/acs.langmuir.8b01789AbstractZwitterionic polymers are currently in the focus of interest for preparing non-toxic and highly biocompatible low-fouling surfaces. After a concise introduction to strategies for preparing zwitterionic surfaces, recent efforts are presented for diversifying the structure of zwitterionic monomers and polymers, which has been quite limited up to now and is considered to be a bottleneck. Key structural variables are identified, and their influences on essential properties such as overall hydrophilicity and long-term stability are considered. Finally, promising targets for new variants are discussed.
E. C. Schulz, P. Mehrabi, H. M. Müller-Werkmeister, F. Tellkamp, A. Jha, W. Stuart, E. Persch, R. De Gasparo, F. Diederich, E. F. Pai, R. J. Dwayne Miller The hit-and-return system enables efficient time-resolved serial synchrotron crystallography Nature Methods 2018, 15, 901-904 DOI: 10.1038/s41592-018-0180-2AbstractWe present a \"hit-and-return\" (HARE) method for time-resolved serial synchrotron crystallography with time resolution from milliseconds to seconds or longer. Timing delays are set mechanically, using the regular pattern in fixed-target crystallography chips and a translation stage system. Optical pump-probe experiments to capture intermediate structures of fluoroacetate dehalogenase binding to its ligand demonstrated that data can be collected at short (30 ms), medium (752 ms) and long (2,052 ms) intervals.\r\n\r\n
A. López de Guereñu, P. Bastian, P. Wessig, L. John, M. U. Kumke Energy Transfer between Tm-Doped Upconverting Nanoparticles and a Small Organic Dye with Large Stokes Shift Biosensors 2019, 9, 9 DOI: 10.3390/bios9010009AbstractLanthanide-doped upconverting nanoparticles (UCNP) are being extensively studied for bioapplications due to their unique photoluminescence properties and low toxicity. Interest in RET applications involving UCNP is also increasing, but due to factors such as large sizes, ion emission distributions within the particles, and complicated energy transfer processes within the UCNP, there are still many questions to be answered. In this study, four types of core and core-shell NaYF4-based UCNP co-doped with Yb3+ and Tm3+ as sensitizer and activator, respectively, were investigated as donors for the Methyl 5-(8-decanoylbenzo[1,2-d:4,5-d\']bis([1,3]dioxole)-4-yl)-5-oxopentanoate (DBD-6) dye. The possibility of resonance energy transfer (RET) between UCNP and the DBD-6 attached to their surface was demonstrated based on the comparison of luminescence intensities, band ratios, and decay kinetics. The architecture of UCNP influenced both the luminescence properties and the energy transfer to the dye: UCNP with an inert shell were the brightest, but their RET efficiency was the lowest (17%). Nanoparticles with Tm3+ only in the shell have revealed the highest RET efficiencies (up to 51%) despite the compromised luminescence due to surface quenching.
S. Kudaibergenov, J. Koetz, N. Nuraje Nanostructured hydrophobic polyampholytes: self-assembly,\r\nstimuli-sensitivity, and application Adv. Compos. Hybrid Mater. 2018, 1, 649-681 DOI: 10.1007/s42114-018-0059-9AbstractThis review is devoted to recent applications and fundamental aspects of hydrophobic polyampholytesùunique macromolecules containing acid, base, and hydrophobic groups that simulate the behavior of proteins, amphoteric polypeptides, or poly(nucleotides) in solutions. Attention was primarily focused on hydrophobically modified polyampholytes (HMPA), sometimes called hydrophobic polyampholytes or amphoteric ôpolysoaps.ö The dependence of structural, morphological, hydrodynamic, and conformational properties of HMPA on external stimuli such as pH medium, temperature, ionic strength, water-organic solvents is outlined. This work demonstrates the self-assembly of HMPA into micelles, reverse micelles, vesicles, lamellar aggregates, dendrimers, fractal structures, clusters, and other highly organized matters. The self-organization of HMPA at air-liquid, liquidliquid,\r\nand solid-liquid interphase is a key problemfor designing Langmuir-Blodgett (LB), layer-by-layer (LbL) films and surface modifications. The preparation and characterization of metal nanoparticles stabilized by HMPA along with applications of HMPA-protected metal nanoparticles in catalysis are summarized. Recent research and applications include HMPA as an enhanced oil recovery (EOR) agent, pour point depressant (PPD), and wax inhibitor. Biomedical and agricultural applications of HMPA, including cryopreservation of living cells by hydrophobic polyampholytes in the clinical practice of reproductive medicine, are outlined. Thus, the systematic analysis of literature data regarding the characterization and application of HMPA inspires other researchers to take new directions and viewpoints on this exclusive and exciting subject.
H. T. Hoang, M. Mertens, P. Wessig, F. Sellrie, J. A. Schenk, M. U. Kumke Antibody Binding at the Liposome-Water Interface: A FRET Investigation toward a Liposome-Based Assay ACS Omega 2018, 3, 18109-18116 DOI: 10.1021/acsomega.8b03016AbstractDifferent signal amplification strategies to improve the detection sensitivity of immunoassays have been applied which utilize enzymatic reactions, nanomaterials, or liposomes. The latter are very attractive materials for signal amplification because liposomes can be loaded with a large amount of signaling molecules, leading to a high sensitivity. In addition, liposomes can be used as a cell-like "bioscaffold" to directly test recognition schemes aiming at cell-related processes. This study demonstrates an easy and fast approach to link the novel hydrophobic optical probe based on [1,3]dioxolo[4,5-f ]-[1,3]benzodioxole (DBD dye mm239) with tunable optical properties to hydrophilic recognition elements (e.g., antibodies) using liposomes for signal amplification and as carrier of the hydrophobic dye. The fluorescence properties of mm239 (e.g., long fluorescence lifetime, large Stokes shift, high photostability, and high quantum yield), its high hydrophobicity for efficient anchoring in liposomes, and a maleimide bioreactive group were applied in a unique combination to build a concept for the coupling of antibodies or other protein markers to liposomes (coupling to membranes can be envisaged). The concept further allowed us to avoid multiple dye labeling of the antibody. Here, anti-TAMRA-antibody (DC7-Ab) was attached to the liposomes. In proof-of-concept, steady-state as well as time-resolved fluorescence measurements (e.g., fluorescence depolarization) in combination with single molecule detection (fluorescence correlation spectroscopy, FCS) were used to analyze the binding interaction between DC7-Ab and liposomes as well as the binding of the antigen rhodamine 6G (R6G) to the antibody. Here, the Fo¨rster resonance energy transfer (FRET) between mm239 and R6G was monitored. In addition to ensemble FRET data, single-molecule FRET (PIE-FRET) experiments using pulsed interleaved excitation were used to characterize in detail the binding on a single-molecule level to avoid averaging out effects.
M. Czarnecki, P. Wessig Scaling Up UV-Mediated Intramolecular Photodehydro-Diels Alder Reactions Using a Homemade High-Performance Annular Continuous-Flow Reactor Org. Process Res. Dev. 2018, 22, 1823-1827 DOI: 10.1021/acs.oprd.8b00353AbstractHere we present a self-made annular continuous-flow reactor that can be used in the UV/vis range in an internal numbering-up manner. As a model reaction, we chose a powerful batch-scale-limited benzoannelation method, namely, an intramolecular photodehydro-Diels-Alder (IMPDDA) reaction. The scale-up potential of this particular photochemical benchmark reaction toward the preparation of macrocylic (1,7)naphthalenophanes by variation of selected flow parameters is presented.
J. Hermanns, B. Schmidt Developing and Applying Stepped Supporting Tools in Organic Chemistry To Promote Students’ Self-Regulated Learning J. Chem. Ed. 2019, 96, 47-52 DOI: 10.1021/acs.jchemed.8b00565AbstractTo support the self-regulated learning of students, stepped supporting tools were developed and applied in the university seminar Organic Chemistry for nonmajor chemistry students. The stepped supporting tools were evaluated using a four-item Likert scale in order to verify the hypotheses: Stepped supporting tools show the logical way to solve an exercise, stepped supporting tools help to focus on the essence of the exercise and stepped supporting tools are especially suitable for solving complex tasks. The students assessed the stepped supporting tools as useful and verified the first two hypotheses. An additional evaluation showed that stepped supporting tools are very suitable for complex tasks. Therefore the third hypothesis is also verified. Stepped supporting tools proved to be a useful scaffold for promoting self-regulated learning.\\\\r\\\\n
J. G. Hardy, A. Bertin, J. G. Torres-Rendon, A. Leal-Egana, M. Humenik, F. Bauer, A. Walther, H. Cölfen, H. Schlaad, T. R. Scheibel Facile Photochemical Modification of Silk Protein–Based Biomaterials Macromol. Biosci. 2018, 18, 1800216 DOI: 10.1002/mabi.201800216AbstractSilk protein–based materials show promise for application as biomaterials for tissue engineering. The simple and rapid photochemical modification of silk protein–based materials composed of either Bombyx mori silkworm silk or engineered spider silk proteins (eADF4(C16)) is reported. Radicals formed on the silk-based materials initiate the polymerization of monomers (acrylic acid, methacrylic acid, or allylamine) which functionalize the surface of the silk materials with poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(allylamine) (PAAm). To demonstrate potential applications of this type of modification, the polymer-modified silks are mineralized. The PAA- and PMAA-functionalized silks are mineralized with calcium carbonate, whereas the PAAm-functionalized silks are mineralized with silica, both of which provide a coating on the materials that may be useful for bone tissue engineering, which will be the subject of future investigations.
B. Zheng, T. Bai, X. Tao, H. Schlaad, J. Ling Identifying the Hydrolysis of Carbonyl Sulfide as a Side Reaction Impeding the Polymerization of N-Substituted Glycine N-Thiocarboxyanhydride Biomacromolecules 2018, 19, 4263 DOI: 10.1021/acs.biomac.8b01119AbstractPolypeptoids are noticeable biological materials due to their versatile properties and various applications in drug delivery, surface modification, self-assembly, etc. N-Substituted glycine N-thiocarboxyanhydrides (NNTAs) are more stable monomers than the corresponding N-carboxyanhydrides (NNCAs) and enable one to prepare polypeptoids via ring-opening polymerization even in the presence of water. However, larger amounts of water (>10,000 ppm) cause inhibition of the polymerization. Herein, we discover that during polymerization hydrogen sulfide evolves from the hydrolysis of carbonyl sulfide, which is the byproduct of ring-opening reaction, and reacts with NNTA to produce cyclic oligopeptoids. The capture of N-ethylethanethioic acid as an intermediate product confirms the reaction mechanism together with density functional theory quantum computational results. By bubbling the polymerization solution with argon, the side reaction can be suppressed to allow the synthesis of polysarcosine with high molar mass (Mn = 11,200 g/mol, D = 1.25) even in the presence of ~10,000 ppm of water.
D. Büchner, L. John, M. Mertens, P. Wessig Detection of dsDNA with [1,3]Dioxolo[4,5-f]benzodioxol (DBD) Dyes Chemistry Eur. J. 2018, 24, 16183-16190 DOI: 10.1002/chem.201804057AbstractDBD fluorescent dyes have proven to be useful in\r\nnumerous applications. To widen the range of biological applications,\r\nwe propose three different types of DBD molecules\r\nthat have been modified in such a way that DNA interaction\r\nbecomes probable. After the successful synthesis of\r\nall three compounds, we tested their fluorescent properties\r\nand their DNA binding abilities. Two of the three probes exhibit\r\nan interaction with dsDNA with subsequent fluorescence\r\nenhancement. The determined binding constants of\r\nthe two new DNA dyes are comparable to other minorgroove-\r\nbinding dyes. Their large Stokes shifts and their long\r\nfluorescent lifetimes are outstanding features of these dyes.
C. Goldhahn, J. Schubert , H. Schlaad, J. K. Ferri, A. Fery, M. Chanana Synthesis of Metal@Protein@Polymer Nanoparticles with Distinct Interfacial and Phase Transfer Behavior Chem. Mater. 2018, 30, 6717 DOI: 10.1021/acs.chemmater.8b02314AbstractIn this study, we present a novel and facile method for the synthesis of multiresponsive plasmonic nanoparticles with an interesting interfacial behavior. We used thiol-initiated photopolymerization technique to graft poly(N-isopropylacrylamide) onto the surface of protein-coated gold nanoparticles. The combination of the protein bovine serum albumin with the thermoresponsive polymer leads to smart hybrid nanoparticles, which show a stimuli-responsive behavior of their aggregation and a precisely controllable phase transfer behavior. Three interconnected stimuli, namely, temperature, ionic strength, and pH, were identified as property tuning switches. The aggregation was completely reversible and was quantified by determining Smoluchowski’s instability ratios with time-resolved dynamic light scattering. The tunable hydrophobicity via the three stimuli was used to study interfacial activity and phase transfer behavior of the nanoparticles at an octanol/water interface. Depending on the type of coating (i.e., protein or protein/polymer) as well as the three external stimuli, the nanoparticles either remained in the aqueous phase (aggregated or nonaggregated), accumulated at the oil/water interface, wet the glass wall between the glass vial and the octanol phase, or even crossed the oil/water interface. Such smart and interfacially active nanoparticles with external triggers that are capable of crossing oil/water interfaces under physiological conditions open up new avenues for a variety of applications ranging from the development of drug-delivery nanosystems across biological barriers to the preparation of new catalytic materials.
W. Fudikar, T. Linker Chemisch induzierte Freisetzung von Singulettsauerstoff aus aromatischen Endoperoxiden Angew. Chem. 2018, 130, 13153–13157 DOI: 10.1002/ange.201806881AbstractDie Erzeugung von reaktivem Singulettsauerstoff unter milden Bedingungen ist von aktuellem Interesse in der Chemie, Biologie und Medizin. Durch einfache chemische Induktion können wir Sauerstoff aus Endoperoxiden (EPOs) bei niedriger Temperatur freisetzen. Tatsächlich beschleunigt die Protonierung und Methylierung von Dipyridylanthracenen solche Reaktionen stark. Zudem sind die Methylpyridin-Derivate wasserlöslich und dienen somit als Sauerstoffüberträger in wässriger Phase. Die Methylierung des ortho-Isomers der EPOs erzeugt direkt die ursprünglichen Vorläufer, ohne Erhöhung der Temperatur unter sehr milden Bedingungen. Dieser ungewöhnliche Reaktionsverlauf ist auf den geringen Abstand zwischen dem Stickstoffatom und der Peroxidgruppe zurückzuführen. Der freigesetzte Singulettsauerstoff wurde zur Oxygenierung von Akzeptoren wie Tetramethylethen im Dunkeln bei Raumtemperatur genutzt. Somit haben wir durch einfache chemische Induktion eine neue Quelle für Singulettsauerstoff gefunden.
C. D. Vacogne, C. Wei, K. Tauer, H. Schlaad Self-Assembly of α-Helical Polypeptides into Microscopic and Enantiomorphic Spirals J. Am. Chem. Soc. 2018, 140, 11387-11394 DOI: 10.1021/jacs.8b06503AbstractHelical structures are ubiquitous in biological materials and often serve a structural purpose. Bioinspired helical materials can be challenging to synthesize and rarely reach the degree of hierarchy of their natural counterparts. Here we report the first example of particles synthesized by direct emulsification of polypeptides found to display spiral morphologies in the dry state. The polypeptides were α-helical homo- and copolypeptides of γ-benzyl glutamate and allylglycine. The chirality of the spirals was controlled by the chirality of the α-helices. Notably, right-handed α-helical polypeptides (rich in l residues) produced clockwise spirals, whereas left-handed α-helical polypeptides (rich in d residues) produced the enantiomorphs, i.e., counterclockwise spirals. The disruption of the α-helical conformation by the introduction of chiral defects led to less regular spirals and in some cases their suppression. A hypothesis for the transmission of helicity and chirality from a molecular to a higher hierarchical level, involving fibril bundling of coiled α-helices, is proposed.\r\n\r\n
M. Mertens, M. Hilsch, I. Haralampiev, R. Volkmer, P. Wessig, P. Müller Synthesis and Characterization of a New Bifunctionalized, Fluorescent, and Amphiphilic Molecule for Recruiting SH-Containing Molecules to Membranes ChemBioChem 2018, 19, 1643-1647 DOI: 10.1002/cbic.201800268AbstractThis study describes the synthesis and characterization of an amphiphilic construct intended to recruit SH-containing molecules to membranes. The construct consists of 1) an aliphatic chain to enable anchoring within membranes, 2) a maleimide moiety to react with the sulfhydryl group of a soluble (bio)molecule, and 3) a fluorescence moiety to allow the construct to be followed by fluorescence spectroscopy and microscopy. It is shown that the construct can be incorporated into preformed membranes, thus allowing application of the approach with biological membranes. The close proximity between the fluorophore and the maleimide moiety within the construct causes fluorescence quenching. This allows monitoring of the reaction with SH-containing molecules by measurement of increases in fluorescence intensity and lifetime. Notably, the construct distributes into laterally ordered membrane domains of lipid vesicles, which is probably triggered by the length of its membrane anchor. The advantages of the new construct can be employed for several biological, biotechnological, and medicinal applications.
M. Karras, M. Dabrowski, R. Pohl, J. Rybacek, J. Vacek, L. Bednarova K. Grela, I. Stary, I. G. Stara, B. Schmidt Helicenes as chirality inducing groups in transition metal catalysis: the first helically chiral olefin metathesis catalyst Chemistry Eur. J. 2018, 24, 10994-10998 DOI: 10.1002/chem.201802786AbstractAn enantiopure helicene serves as a chirality inducing element in a Grubbs-type transition metal-N-heterocyclic ruthenium carbene complex. This first helically chiral olefin metathesis catalyst was studied extensively by spectroscopic methods. A DFT-optimized structure was obtained, and based on these data the percent-buried-volume values and a topographic steric map were calculated. As a proof of concept, it was shown that the new enantiopure catalyst mediates an enantioselective RCM with moderate enantioselectivity. This work is the result of an international project with participating colleagues from Potsdam, Prague and Warsaw.
T. Schwartze, J. Riemer, H.-J. Holdt A Ratiometric Fluorescent Probe for K+ in Water Based on a Phenylaza-18-Crown-6 Lariat Ether Chemistry - A European Journal 2018, 24, 10116-10121 DOI: 10.1002/chem.201802306AbstractThis work presents two molecular fluorescent probes 1 and 2 for the selective determination of physiologically relevant K+ levels in water based on a highly K+/Na+ selective building block, the o-(2-methoxyethoxy)phenylaza-18-crown-6-lariat ether unit. Fluorescent probe 1 showed high K+-induced fluorescence enhancement (FE) by a factor of 7.7 of the anthracenic emission and a dissociation constant (Kd) value of 38 mm in water.Further, for 2 + K+ , we observed adualemission behavior at 405 and 505 nm. K+ increases the fluorescence intensity of 2 at 405 nm by a factor of approximately 4.6 and K+ decreases the fluorescence intensity at 505 nm by a factor of about 4.8. Fluorescent probe 2 + K+ exhibited a Kd value of approximately 8 mm in Na+-free solutions and in combined K+/Na+ solution a similar Kd value of about 9 mm was found, reflecting the high K+/Na+ selectivity of 2 in water.Therefore, 2 is a promising fluorescent tool to measure ratiometrically and selectively physiologically relevant K+ levels.
W. Fudickar, T. Linker Release of Singlet Oxygen from Organic Peroxides under Mild Conditions ChemPhotoChem 2018, 2, 548–558 DOI: 10.1002/cptc.201700235Abstract Singlet oxygen can be released in the dark in nearly quantitative yield from endoperoxides of naphthalenes, anthraces and pyridones as an alternative to its generation by photosensitization. Recently, new donor systems have been designed, which operate at very low temperatures but which are prepared from their parent forms at acceptable rates. Enhancement of the reactivity of donors is conveniently achieved by the design of the substitution pattern or the use of plasmic heating of nanoparticle-bound donors. The most important aim of these donor molecules is to transfer singlet oxygen in a controlled and directed manner to a target. Low temperatures and the linking between donors and acceptors reduce the random walk of oxygen and may force an attack at the desired position. By using chiral donor systems, new stereo centers might be introduced into prochiral acceptors.
C. Heck, Y. Kanehira, J. Kneipp, I. Bald Placement of Single Proteins within the SERS Hot Spots of Self-\r\nAssembled Silver Nanolenses Angew. Chem. Int. Ed. 2018, 57, 7444-7447. DOI: 10.1002/anie.201801748AbstractThis study demonstrates the bottom-up synthesis of silver nanolenses. A robust coating protocol enabled the functionalization of differently sized silver nanoparticles with DNA single strands of orthogonal sequence. Coated particles 10 nm, 20 nm, and 60 nm in diameter were self-assembled by DNA origami scaffolds to form silver nanolenses. Single molecules of the protein streptavidin were selectively placed in the gap of highest electric field enhancement. Streptavidin labelled with alkyne groups served as model analyte in surface-enhanced Raman scattering (SERS) experiments. By correlated Raman mapping and atomic force microscopy, SERS signals of the alkyne labels of a single streptavidin molecule, from a single silver nanolens, were detected. The discrete, self-similar aggregates of solid silver nanoparticles are promising for plasmonic applications.
Y. Chen, Q. Song, J. Zhao, X. Gong, H. Schlaad, G. Zhang Betulin-Constituted Multiblock Amphiphiles for Broad-Spectrum Protein Resistance ACS Appl. Mater. Interfaces 2018, 10, 6593–6600 DOI: 10.1021/acsami.7b16255AbstractMultiblock-like amphiphilic polyurethanes constituted by poly(ethylene oxide) and biosourced betulin are designed for antifouling and synthesized by a convenient organocatalytic route comprising tandem chain-growth and step-growth polymerizations. The doping density of betulin (DB) in the polymer chain structure is readily varied by a mixed-initiator strategy. The spin-coated polymer films exhibit unique nanophase separation and protein resistance behaviors. Higher DB leads to enhanced surface hydrophobicity and, unexpectedly, improved protein resistance. It is found that the surface holds molecular-level heterogeneity when DB is substantially high due to restricted phase separation; therefore, broad-spectrum protein resistance is achieved despite considerable surface hydrophobicity. As DB decreases, the distance between adjacent betulin units increases so that hydrophobic nanodomains are formed, which provide enough landing areas for relatively small-sized proteins to adsorb on the surface.
H.-C. Lee, J. Hwang, U. Schilde, M. Antonietti, K. Matyjaszewski, B. V. K. J. Schmidt Toward Ultimate Control of Radical Polymerization: Functionalized Metal–Organic Frameworks as a Robust Environment for Metal-Catalyzed Polymerizations Chemistry of Materials 2018, 30, 2983-2994 DOI: 10.1021/acs.chemmater.8b00546AbstractHerein, an approach via combination of confined porous textures and reversible deactivation radical polymerization techniques is proposed to advance synthetic polymer chemistry, i.e., a connection of metal - organic frameworks (MOFs) and activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP)Zn2(benzene-1,4-dicarboxylate)2(1,4-diazabicyclo[2.2.2]-octane) [Zn2(bdc)2(dabco)] is utilized as a reaction environment for polymerization of various methacrylate monomers (methyl, ethyl, benzyl, and isobornyl methacrylate) in a confined nanochannel, resulting in polymers with control over dispersity, end functionalities, and tacticity with respect to distinct molecular size. To refine and reconsolidate the compartmentation effect on polymer regularity, initiator-functionalized Zn MOF was synthesized via cocrystallization with an initiator-functionalized ligand, 2-(2-bromo-2-methylpropanamido)-1,4-benzenedicarboxylate (Brbdc), in different ratios (10%, 20%, and 50%). Through the embedded initiator, surface-initiated ARGET ATRP was directly initiated from the walls of the nanochannels. The obtained polymers had a high molecular weight up to 392 000. Moreover, a significant improvement in end-group functionality and stereocontrol was observed, entailing polymers with obvious increments in isotacticity. The results highlight a combination of MOFs and ATRP that is a promising and universal methodology to prepare various polymers with high molecular weight exhibiting well-defined uniformity in chain length and microstructure as well as the preserved chain-end functionality.
E. Schönemann, A. Laschewsky, A. Rosenhahn Exploring the Long-Term Hydrolytic Behavior of Zwitterionic Polymethacrylates and Polymethacrylamides Polymers 2018, 10, 639 DOI: 10.3390/polym10060639AbstractLong-term hydrolytic stability is crucial for many polymers to be used in aqueous environments, e.g. for coatings with anti-fouling properties. While this is generally not verified (at best assuming tacitly that the stability of polymers is similar to the one of low molar mass analogs), we demonstrate that the stability of methacrylic polymers is much higher than the one of their monomers. In our investigations, we synthesized a set of polymers that are typically used for low-fouling coatings (such as non-ionic poly(oligo(ethylene glycol) methacrylate) and zwitterionic polysulfobetaines and -sulfabetaines. We studied their hydrolysis resistance upon extended storage in aqueous solution at ambient temperature in various pH regime by 1H NMR. Whereas the monomers suffered slow (in PBS, pH=7.4) to very fast hydrolysis (in 1 M NaOH), the polymers, including the ones containing ester groups, proved to be highly stable. No degradation of the carboxyl ester or amide moieties was observed after 1 year in PBS, 1 M HCl or in sodium carbonate buffer of pH 10. This demonstrates the basic suitability of such polymers for anti-fouling applications. Poly(sulfobetaine methacrylamide) proved even to be stable for 1 year in 1 M NaOH without any signs of degradation. The excellent stability is ascribed to a steric shielding effect. The hemisulfate group in the polysulfabetaines, however, was found to be partially labile.
R. R. Raju, F. Liebig, B. Klemke, J. Koetz pH-responsive magnetic Pickering Janus emulsions Colloid and Polymer Science 2018, 296, 1039-1046 DOI: 10.1007/s00396-018-4321-zAbstractWe report ultrasonically generated pH-responsive Pickering Janus emulsions of olive oil and silicone oil with controllable droplet size and engulfment. Chitosan was used as a pH-responsive emulsifier. The increase of pH from 2 to 6 leads to a transition from completely engulfed double emulsion droplets to dumbbell-shaped Janus droplets accompanied by a significant decrease of droplet diameter and a more homogeneous size distribution. The results can be elucidated by the conformational change of chitosan from a more extended form at pH 2 to a more flexible form at pH 4-5. Magnetic responsiveness to the emulsion was attributed by dispersing superparamagnetic nanoparticles (Fe3O4 with diameter of 13 ± 2 nm) in the olive oil phase before preparing the Janus emulsion. Incorporation of magnetic nanoparticles leads to superior emulsion stability, drastically reduced droplet diameters, and opened the way to control movement and orientation of the Janus droplets according to an external magnetic field.
C. Schultze, B. Schmidt Prenylcoumarins in One or Two Steps by a Microwave-Promoted Tandem Claisen Rearrangement/Wittig Olefination/Cyclization Sequence J. Org. Chem. 2018, 83, 5210-5224 DOI: 10.1021/acs.joc.8b00667AbstractNaturally occurring 8-prenyl coumarins are ubiquitious secondary metabolites. This paper describes a short and high-yielding route to their synthesis, based on a tandem Claisen-rearrangement/Wittig-olefination sequence and a highly selective cross metathesis.
H. R. Arias, D. Feuerbach, B. Schmidt, M. Heydenreich, C. Paz, M. O. Ortells Drimane Sesquiterpenoids Noncompetitively Inhibit Human α4β2 Nicotinic Acetylcholine Receptors with Higher Potency Compared to Human α3β4 and α7 Subtypes J. Nat. Prod. 2018, 81, 811-817 DOI: 10.1021/acs.jnatprod.7b00893AbstractDrimane sesquiterpenoids were isolated from the Canelo tree (Drimys winteri), which is native in Southern Chile and considered as a sacred plant by the local people, because of its medicinal properties. This paper describes the joint efforts of scientists from five institutions, including our institute, in five countries toward the isolation, structure elucidation and pharmacological evalutation of secondary metabolites with sesquiterpenoid structure from this plant. Some of the compounds display inhibitory activity towards human nicotinic acetylcholine receptors (AChRs) on a low micromolar level.
F. Liebig, S. Morenob, A. F. Thünemann, A. Temmed, D. Appelhans, J. Koetz Toxicological investigations of "naked" and polymer-entrapped AOT-based gold nanotriangles Colloids and Surfaces B: Biointerfaces 2018, 167, 560-567 DOI: 10.1016/j.colsurfb.2018.04.059AbstractNegatively charged ultrathin gold nanotriangles (AuNTs) were synthesized in a vesicular dioctyl sodiumsulfosuccinate (AOT)/phospholipid-based template phase. These "naked" AuNTs with localized surfaceplasmon resonances in the NIR region at about 1300 nm and special photothermal properties are of particular interest for imaging and hyperthermia of cancerous tissues. For these kinds of applications the toxicity and the cellular uptake of the AuNTs is of outstanding importance. Therefore, this study focuses on the toxicity of "naked" AOT-stabilized AuNTs compared to polymer-coated AuNTs. Polymeric coating consisted of non-modified hyperbranched poly(ethyleneimine) (PEI), maltose-modifiedpoly(ethyleneimine) (PEI-Mal) and heparin. The toxicological experiments were carried out with twodifferent cell lines (embryonic kidney carcinoma cell line HEK293T and NK-cell leukemia cell line YTS).This study revealed that the heparin-coating of AuNTs improved biocompatibility by a factor of 50 whencompared to naked AuNTs. Of note, the highest nontoxic concentration of the AuNTs coated with PEI and PEI-Mal is drastically decreased. Overall, this is mainly triggered by the different surface charges of polymeric coatings. Therefore, AuNTs coated with heparin were selected to carry out uptake studies. Their promising high biocompatibility and cellular uptake may open future studies in the field of biomedical applications.
F. Liebig, R. M. Sarhan, C. Prietzel, C. N. Z. Schmitt, M. Bargheer, J. Koetz Tuned Surface-Enhanced Raman Scattering Performance of Undulated Au@Ag Triangles ACS Appl. Nano Mater. 2018, 1, 1995-2003 DOI: 10.1021/acsanm.8b00570AbstractNegatively charged ultraflat gold nanotriangles (AuNTs) stabilized by the anionic surfactant dioctyl sodium sulfosuccinate (AOT) were reloaded with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC). Because of the spontaneous formation of a catanionic AOT micelle/BDAC bilayer onto the surface of the reloaded AuNTs, nreduction of Ag+ ions leads to the formation of spherical silver nanoparticles (AgNPs). With increasing concentration of AgNPs on the AuNTs, the localized surface plasmon resonance (LSPR) is shifted stepwise from 1300 to 800 nm. The tunable LSPR enables to shift the extinction maximum to the wavelength of the excitation laser of the Raman microscope at 785 nm. Surface-enhanced Raman scattering (SERS) experiments performed under resonance conditions show an SERS enhancement factor of the analyte molecule rhodamine RG6 of 5.1 × 105, which can be related to the silver hot spots at the periphery of the undulated gold nanoplatelets.
N. S. Vishnevetskaya, V. Hildebrand, M. A. Dyakonova, B. J. Niebuur, K. Kyriakos, K. N. Raftopoulos, Z. Di, P. Müller-Buschbaum, A. Laschewsky, C. M. Papadakis Dual, orthogonal switching of the "schizophrenic" self-assembly of diblock copolymers. Macromolecules 2018, 51, 3985 DOI: 10.1021/acs.macromol.8b00096AbstractA pair of \"schizophrenic\" micellar systems is compared that combines a zwitterionic polysulfobetaine block with a non-ionic and block of either PNIPAM or PNIPMAM. Both block copolymers are twofold thermoresponsive and exhibit LCST as well as UCST behavior in aqueous solution. The zwitterionic block is designed such that its phase transition temperature in pure water is significantly higher than the ones of PNIPAM or PNIPMAM. By temperature dependent turbidimetry, 1H NMR and SANS, we study the overall phase behavior, the structure and the interaction between the micelles. We demonstrate dual thermosensitive and salt-sensitive behavior with \"schizophrenic\" micelle formation, whereby the width of the intermediate regime when both blocks are hydrophilic, can be tuned by the addition of electrolyte.
F. Liebig, R. M. Sarhan, C. Prietzel, A. F. Thünemann, M. Bargheer, J. Koetz Undulated Gold Nanoplatelet Superstructures: In Situ Growth of Hemispherical Gold Nanoparticles onto the Surface of Gold Nanotriangles Langmuir 2018, 34, 4584-4594 DOI: 10.1021/acs.langmuir.7b02898AbstractNegatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 °C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in\r\ncombination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of ~6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor.
P. Wessig, L. John, M. Mertens Extending the Class of [1,3]-Dioxolo[4.5-f]benzodioxole (DBD) Fluorescent Dyes Eur. J. Org. Chem. 2018, , 1674-1681 DOI: 10.1002/ejoc.201800002AbstractSynthetic routes to a collection of new fluorescent dyes are described, which are based on the [1,3]-dioxolo-[4.5-f]benzodioxole (DBD) core. By introducing different electron withdrawing groups in 4- and 8-position of the DBD moiety the emission wavelength could be adjusted over a large spectral range from blue to orange light.
J. Rackwitz, I. Bald Low-Energy Electron-Induced Strand Breaks in Telomere-Derived DNA Sequences - Influence of DNA Sequence and Topology Chem. Eur. J. 2018, 24, 4680-4688 DOI: 10.1002/chem.201705889AbstractDuring cancer radiation therapy high-energy radiation is used to reduce tumour tissue. The irradiation produces a shower of secondary low-energy (<20 eV) electrons, which are able to damage DNA very efficiently by dissociative electron attachment. Recently, it was suggested that low-energy electron-induced DNA strand breaks strongly depend on the specific DNA sequence with a high sensitivity of G-rich sequences. Here, we use DNA origami platforms to expose G-rich telomere sequences to low-energy (8.8 eV) electrons to determine absolute cross sections for strand breakage and to study the influence of sequence modifications and topology of telomeric DNA on the strand breakage. We find that the telomeric DNA 5\'-(TTA GGG)2 is more sensitive to low-energy electrons than an intermixed sequence 5\'-(TGT GTG A)2 confirming the unique electronic properties resulting from G-stacking. With increasing length of the oligonucleotide (i.e., going from 5\'-(GGG ATT)2 to 5\'-(GGG ATT)4), both the variety of topology and the electron-induced strand break cross sections increase. Addition of K+ ions decreases the strand break cross section for all sequences that are able to fold G-quadruplexes or G-intermediates, whereas the strand break cross section for the intermixed sequence remains unchanged. These results indicate that telomeric DNA is rather sensitive towards low-energy electron-induced strand breakage suggesting significant telomere shortening that can also occur during cancer radiation therapy.
A.H. Poghosyana, A. A. Shahinyan, J. Koetz Self-assembled monolayer formation of distorted cylindrical AOT micelles on gold surfaces Colloids and Surfaces A 2018, 546, 20-27 DOI: 10.1016/j.colsurfa.2018.02.067AbstractSelf-assembling features of sodium dioctyl sulfosuccinate (AOT) molecules and micelle adsorption on gold Au(111) surfaces have been examined using molecular dynamics simulation. We argue that AOT micelles display a strong adsorption on gold surfaces resulting in distorted cylindrical micelles attached to the (111) facets. The well protected Au(111) facets decorated by a dense packed elongated ellipsoidal AOT layer hinder the diffusion of the reactant to the (111) facets and could result in the preferential growth of ultra-thin gold nanoplatelets.
N. M. Nizardo, D. Schanzenbach, E. Schönemann, A. Laschewsky Exploring Poly(ethylene glycol)-Polyzwitterion Diblock Copolymers as Biocompatible Smart Macrosurfactants Featuring UCST-Phase Behavior in Normal Saline Solution. Polymers 2018, 10, 325 DOI: 10.3390/polym10030325AbstractThermo-responsive polymeric surfactants in form of nonionic-zwitterionic diblock copolymers were made from biocompatible blocks via ATRP using a PEG macroinitiator and a set of sulfobetaine and sulfabetaine monomers. The polymers were designed to show upper critical solution temperature (UCST) behavior under physiologically relevant conditions, i.e., between 30 and 50°C in physiological saline solution. The possibility for UCST-transition triggered encapsulation and release of solvatochromic fluorescent dyes as model \"cargos\" was explored.
A. Matic, H. Schlaad Thiol-ene photofunctionalization of 1,4-polymyrcene Polym. Int. 2018, 67, 500–505 DOI: 10.1002/pi.5534Abstract1,4-Polymyrcene was synthesized by anionic polymerization of ß-myrcene and was subjec ted to photochemical functionalization with various thiols (i.e. methyl thioglycolate, methy l 3-mercaptopropionate, butyl 3-mercaptopropionate, ethyl 2-mercaptopropionate and 2-methyl-2-propanethiol) using benzophenone/UV light as the radical source. The yield of thiol addition to the trisubstituted double bonds of 1,4-polymyrcene decreased in the order 1° thiol (ca 95%) > 2° thiol (ca 80%) > 3° thiol (<5%), due to the reversibility of the thiol-ene reaction. Remarkably, thiol addition to the side-chain double bonds was 8 - 10 times (1° thiol) or 24 times (2° thiol) faster than to the main-chain double bonds, which can be explained by the di?erent accessibility of the double bonds and steric hindrance. Despite the use of a 10-fold excess of thiol with respect to myrcene units, the thiol-ene addition was accompanied by chain coupling reactions, which in the extreme case of 3° thiol (or in the absence of thiol) resulted in the formation of insoluble crosslinked material. As an example, a methyl-thioglycolate-functionalized 1,4-polymyrcene was saponi?ed/crosslinked to give submicron polyelectrolyte particles in dilute alkaline solution.
F. N. Behrendt, H. Schlaad Entropy-Driven Ring-Opening Disulfide Metathesis Polymerization for the Synthesis of Functional Poly(disulfide)s Macromol. Rapid Commun. 2018, 39, 1700735 DOI: 10.1002/marc.201700735AbstractMetal-free entropy-driven disulfide metathesis polymerization of unsaturated L-cystine based macrocycles produces high-molar-mass heterofunctional poly(disulfide)s, i.e., poly(ester-disulfide-alkene) and poly(amide-disulfide-alkene); Mwapp = 44–60 kDa, Ð > 1.7. The polymerization is fast and reaches equilibrium within 1–5 minutes (monomer conversion 70–90%) in polar aprotic solvents such as N,N-dimethylacetamide, dimethylsulfoxide, or γ-valerolactone. Thiol-terminated polymers are stable in bulk or when dissolved in weakly polar solvents, but rapidly depolymerize in dilute polar solution.
F. Liebig, R. Henning, R. M Sarhan, C. Prietzel, M. Bargheer, J. Koetz A new route to gold nanoflowers Nanotechnology 2018, 29, 185603 DOI: 10.1088/1361-6528/aaaffdAbstractCatanionic vesicles spontaneously formed by mixing the anionic surfactant bis(2-ethylhexyl) sulfosuccinate sodium salt with the cationic surfactant cetyltrimethylammonium bromide were used as a reducing medium to produce gold clusters, which are embedded and well-ordered into the template phase. The gold clusters can be used as seeds in the growth process that follows by adding ascorbic acid as a mild reducing component. When the ascorbic acid was added very slowly in an ice bath round-edged gold nanoflowers were produced. When the same experiments were performed at room temperature in the presence of Ag+ ions, sharp-edged nanoflowers could be synthesized. The mechanism of nanoparticle formation can be understood to be a nondiffusion- limited Ostwald ripening process of preordered gold nanoparticles embedded in catanionic vesicle fragments. Surface-enhanced Raman scattering experiments show an excellent\\\\r\\\\nenhancement factor of 1.7x105 for the nanoflowers deposited on a silicon wafer.
Schmidt, B.; Petersen, M. H.; Braun, D. Bidirectional Synthesis of 6-Acetoxy-5-hexadecanolide, the Mosquito Oviposition Pheromone of Culex quinquefasciatus, from a C2-Symmetric Building Block Using Olefin Metathesis Reactions J. Org. Chem. 2018, 83, 1627-1633 DOI: 10.1021/acs.joc.7b02944AbstractMosquitoes of the species Culex quinquefasciatus are vectors of many serious pathogens. Recent outbreaks of the Zika epidemic have raised concerns that this mosquito, which is more common than the established vector of the Zika virus, may also be capable of transferring Zika. A vector control and monitoring approach that has been discussed for many years relies on the use of pheromone traps. In the particular case of Cx. quinquefasciatus the ε-lactone (5R,6S)-6-Acetoxy-5-hexadecanolide was identified as the pheromone that regulates and initiates oviposition. In this contribution a short enantiocontrolled synthesis of this pheromone and its epimer, which relies on two successive cross metathesis reactions, a tandem assisted catalytic metathesis-hydrogenation sequence and a Mitsunobu-inversion, is presented.
A. Abouserie, K. Zehbe, P. Metzner, A. Kelling, C. Günter, U. Schilde, P. Strauch, T. Körzdörfer, A. Taubert Alkylpyridinium Tetrahalidometallate Ionic Liquids and Ionic Liquid Crystals: Insights into the Origin of Their Phase Behavior Eur. J. Inorg. Chem. 2017, , 5640-5649 DOI: 10.1002/ejic.201700826AbstractSix N-alkylpyridinium salts [CnPy]2[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py]4[MCl4] compounds are monoclinic and crystallize in the space group P21/n. The crystals of the longer chain analogues [C12Py]2[MCl4] are triclinic and crystallize in the space group P1. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4]2– ions in the Cu-based ILs have a distorted tetrahedral geometry.
T. Schwarze, M. Mertens, P. Müller, J. Riemer, P. Wessig, H.-J. Holdt Highly K+-Selective Fluorescent Probes for Lifetime Sensing of Kalium-Ionen in Living Cells Chemistry - A European Jornal 2017, 23, 17186 DOI: 10.1002/chem.201703799AbstractCoupling of K+ selective N-(o-isopropoxy)phenylaza-18-crown-6 with [1,3]dioxolo[4,5-f][1,3]benzo-dioxole ester fluorophore yields a new fluorescent probe for the sensing of Kalium-Ionen by increasing the averaged fluorescence decay time. This fluorescent tool is a good candidate for a reliable analysis of physiologically relevant K+ levels by fluorescence lifetime imaging microscopy (FLIM) in vivo.(Cover Profile)
T. Brietzke, T. Dietz, A. Kelling, U. Schilde, J. Bois, H. Kelm, M. Reh, M. Schmitz, T. Körzdörfer, S. Leimkühler, U. Wollenberger, H.-J. Krüger, H.-J. Holdt The 1,6,7,12-Tetraazaperylene Bridging Ligand as an Electron Reservoir and Its Disulfonato Derivative as Redox Mediator in an Enzyme-Electrode Process Chemistry - A European Journal 2017, 23, 15583 DOI: 10.1002/chem.201704226AbstractThe homodinuclear ruthenium(II) complex [{Ru(l-N₄Me₂)}₂(μ-tape)](PF₆)₄ {[1](PF₆)₄}(l-N₄Me₂=N,N′-dimethyl-2,11-diaza[3.3](2,6)-pyridinophane, tape=1,6,7,12-tetraazaperylene) can store one or two electrons in the energetically low-lying π* orbital of the bridging ligand tape. The corresponding singly and doubly reduced complexes [{Ru(l-N₄Me₂)}₂(μ-tape.−)](PF₆)₃ {[2](PF₆)₃} and [{Ru(l-N₄Me₂)}₂(μ-tape2−)](PF6)₂ {[3](PF₆)₂}, respectively, were electrochemically generated, successfully isolated and fully characterized by single-crystal X-ray crystallography, spectroscopic methods and magnetic susceptibility measurements. The singly reduced complex [2](PF₆)₃ contains the π-radical tape.− and the doubly reduced [3](PF₆)₂ the diamagnetic dianion tape2− as bridging ligand, respectively. Nucleophilic aromatic substitution at the bridging tape in [1]4+ by two sulfite units gave the complex [{Ru(l-N₄Me₂)}₂{μ-tape-(SO3)₂}]2+ ([4]2+). Complex dication [4]2+ was exploited as a redox mediator between an anaerobic homogenous reaction solution of an enzyme system (sulfite/sulfite oxidase) and the electrode via participation of the low-energy π*-orbital of the disulfonato-substituted bridging ligand tape–(SO₃3)₂2− (Ered1=−0.1 V versus Ag/AgCl/1 m KCl in water).
P. Wessig, T. Schulze, A. Pfennig, S. M. Weidner, S. Prentzel, H. Schlaad Thiol–ene polymerization of oligospiroketal rods Polym. Chem. 2017, 8, 6879-6885 DOI: 10.1039/c7py01569kAbstractThe nucleophilic thiol–ene (thia-Michael) reaction between molecular rods bearing terminal thiols and bis-maleimides was investigated. The molecular rods have oligospiroketal (OSK) and oligospirothioketal (OSTK) backbones. Contrary to the expectations, cyclic oligomers were always obtained instead of linear rigid-rod polymers. Replacing the OS(T)K rods with a flexible chain yielded polymeric products, suggesting that the OS(T)K structure is responsible for the formation of cyclic products. The reason for the preferred formation of cyclic products is due to the presence of folded conformations, which have already been described for articulated rods.
W. Fudickar, T. Linker Synthesis of Pyridylanthracenes and Their Reversible Reaction with Singlet Oxygen to Endoperoxides J. Org. Chem. 2017, 82, 9258–9262 DOI: 10.1021/acs.joc.7b01765AbstractThe ortho, meta, and para isomers of 9,10-dipyridylanthracene 1 have been synthesized and converted into their endoperoxides 1O2 upon oxidation with singlet oxygen. The kinetics of this reaction can be controlled by the substitution pattern and the solvent: in highly polar solvents, the meta isomer is the most reactive, whereas the ortho isomer is oxidized fastest in nonpolar solvents. Heating of the endoperoxides affords the parent anthracenes by release of singlet oxygen.
R. R.Rajua, S. Kosmella, S. E. Friberg, J. Koetz Pickering Janus emulsions and polyelectrolyte complex-stabilized Janus gels Colloids and Surfaces A 2017, 533, 241-248 DOI: 10.1016/j.colsurfa.2017.08.022AbstractJanus emulsions, containing olive oil (OO) and silicone oil (SiO), were formed in presence of polyelectrolyte complex particles, i.e., gelatin-sodium polyacrylate (NaPAA) complexes. The diameter of completely engulfed Janus droplets can be tuned between 50 and 200 μm by varying the gelatin/NaPAA complex particle size between 200 and 400 nm. The gelatin/NaPAA complex particles adsorbed at the olive oil interface decrease the interfacial tension and stabilize the resulting completely engulfed Pickering Janus emulsions. Long-term stable Janus gels can be synthesized in presence of gelatin/sodium carboxymethylcellulose (NaCMC) mixtures. In that case Coulombic forces are of relevance with regard to the stabilization of the Janus droplets embedded in a gelatin/NaCMC gel matrix. Janus gels show elastic reological behavior and thixotropic properties.
R. Schürmann, T. Tsering, K. Tanzer, S. Denifl, S. V. K. Kumar, I. Bald Resonante Bildung von Strangbrüchen in sensibilisierten Oligonucleotiden induziert durch niederenergetische Elektronen (0.5-9 eV) Angew. Chem. 2017, 129, 11094-11098 DOI: 10.1002/ange.201705504AbstractIn der Krebs-Strahlentherapie werden halogenierte Nukleinbasen als Radiosensibilisatoren eingesetzt, um die Reaktivität der DNA gegenüber niederenergetischen Elektronen (NEEs) zu erhöhen. NEEs erzeugen DNA-Strangbrüche bei spezifischen Energien (Resonanzen) durch dissoziative Elektronenanlagerung (DEA). Obwohl halogenierte Nukleinbasen intensive DEA-Resonanzen bei verschiedenen Elektronenenergien in der Gasphase aufweisen, kann der Einfluss der halogenierten Nukleinbasen auf tatsächliche DNA-Strangbrüche grundsätzlich nur schwer über den Energiebereich,in dem DEA stattfindet (<12 eV), untersucht werden. Mithilfe von DNA-Origami-Nanostrukturen haben wir die Energieabhängigkeit der Wirkungsquerschnitte für DNA-Strangbrüche von Oligonukleotiden bestimmt, die mit 8-Bromadenin (8BrA) modifiziert wurden. Diese Ergebnisse wurden mit DEA-Messungen an isoliertem 8BrA in der Gasphase verglichen. Entgegen der Erwartungen wird der Großteil der Strangbrüche durch Resonanzen um 7 eV hervorgerufen, wohingegen der Einfluss von Resonanzen bei sehr niedrigen Energien (<2 eV) auf die Strangbrüche gering ist.
A. Dani, K. Täuber, W. Zhang, H. Schlaad, J. Yuan Stable Covalently Photo-Crosslinked Poly(Ionic Liquid) Membrane with Gradient Pore Size Macromol. Rapid Commun. 2017, 38, 1700167 DOI: 10.1002/marc.201700167AbstractPorous polyelectrolyte membranes stable in a highly ionic environment are obtained by covalent crosslinking of an imidazolium-based poly(ionic liquid). The crosslinking reaction involves the UV light-induced thiolene (click) chemistry, and the phase separation, occurring during the crosslinking step, generates a fully interconnected porous structure in the membrane. The porosity is on the order of the micrometer scale and the membrane shows a gradient of pore size across the membrane cross-section. The membrane can separate polystyrene latex particles of different size and undergoes actuation in contact with acetone due to the asymmetric porous structure.
C. D.Vacogne, H. Schlaad Controlled ring-opening polymerization of α-amino acid N-carboxyanhydrides in the presence of tertiary amines Polymer 2017, 124, 203 DOI: 10.1016/j.polymer.2017.07.062AbstractThe mechanism of the primary ammonium/tertiary amine-mediated ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BlG-NCA) was investigated. Kinetic analyses revealed that the normal amine mechanism (NAM) together with a dormant-active chain end equilibrium were responsible for the controlled nature of this polymerization pathway, but that the polymerization also proceeded via the activated monomer mechanism (AMM). Mixtures of primary amines (1 equiv) and tertiary amines (0-1.5 equiv) were therefore tested to confirm the co-existence of the NAM and AMM and determine the limits for a controlled polymerization. For tertiary amine molar fractions smaller than 0.8 equiv, the reaction times were greatly reduced (compared to primary amine-initiated polymerization) without compromising the control of the reaction. Hence, the polymerization of NCA can proceed in a controlled manner even when the AMM contributes to the overall chain growth mechanism.
E. Peh, C. Liedel, A. Taubert, K. Tauer Composition inversion to form calcium carbonate mixtures CrystEngComm 2017, 19, 3573 DOI: 10.1039/C7CE00433HAbstractComposition inversion takes place in equimolar solid mixtures of sodium or ammonium carbonate and calcium chloride with respect to the combination of anions and cations leading to the corresponding chloride and calcite in complete conversion. The transformation takes place spontaneously under a variety of different situations, even in a powdery mixture resting under ambient conditions. Powder X-ray diffraction data and scanning electron microscopy micrographs are presented to describe the course of the reaction and to characterize the reaction products. The incomplete reaction in the interspace between two compressed tablets of pure starting materials leads to an electric potential due to the presence of uncompensated charges.
A. Bogomolova, C. Secker, J. Koetz, H. Schlaad Thermo-induced multistep assembly of double-hydrophilic block copolypeptoids in water Colloid and Polymer Science 2017, 295, 1305 DOI: 10.1007/s00396-017-4044-6AbstractThe aqueous solution behavior of thermoresponsive-hydrophilic block copolypeptoids, i.e., poly(N-(n-propyl)glycine)x-block-poly(N-methylglycine)y (x = 70; y = 23, 42, 76), in the temperature range of 20-45 °C is studied. Turbidimetric analyses of the 0.1 wt% aqueous solutions reveal two cloud points at Tcp∼30 and 45 °C and a clearing point in between at Tcl∼42 °C. Temperature-dependent dynamic light scattering (DLS) suggest that right above the first collapse temperature, single polymer molecules assemble into large structures which upon further heating, i.e., at the clearing point temperature, disassemble into micelle-like structures. Upon further heating, the aggregates start to grow again in size, as recognized by the second cloud point, through a crystallization process.
N. Vishnevetskaya, V. Hildebrand, B.-J. Niebuur, I. Grillo, S. K. Filippov, A. Laschewsky, P. Müller-Buschbaum, C. M. Papadakis "Schizophrenic" Micelles from Doubly Thermoresponsive Polysulfobetaine-b-poly(N-isopropylmethacrylamide) Diblock Copolymers Macromolecules 2017, 50, 3985 DOI: 10.1021/acs.macromol.7b00356AbstractBy a 2-step RAFT polymerization sequence, a twofold thermoresponsive diblock copolymer is synthesized that bears a zwitterionic poly(sulfobetaine methacrylamide) block (PSPP) and a nonionic poly(N-isopropylmethacrylamide) (PNIPMAM) block. Combining the lower and upper critical solution temperature (LCST and UCST) behaviors of the constitutive homopolymers in aqueous solution, its temperature-dependent phase behavior and multifaceted induced self-assembly in D₂O is investigated in detail, using in particular turbidimetry and small-angle neutron scattering (SANS) in salt-free solution as well as in the presence of small amounts of NaCl and NaBr.
V. Hildebrand, M. Heydenreich, A. Laschewsky, H. M. Möller, P. Müller-Buschbaum, C. M. Papadakis, D. Schanzenbach, E. Wischerhoff "Schizophrenic" Self-assembly of Dual Thermoresponsive Block Copolymers Bearing a Zwitterionic and a Non-Ionic Hydrophilic Block Polymer 2017, 122, 347 DOI: 10.1016/j.polymer.2017.06.063AbstractSeveral sets of dual thermo-responsive diblock copolymers were prepared by consecutive reversible addition-fragmentation chain transfer (RAFT) polymerizations. While all copolymers contain poly(N-isopropylmethacrylamide) as non-ionic block that shows a coil-to-globule collapse transition of the lower critical solution temperature (LCST) type, the chemical structure of the second block, which is zwitterionic and belongs to the class of poly(sulfobetaine methacrylate)s, was varied systematically. In combination with the adjustment of the block sizes, its coil-to-globule collapse transition of the upper critical solution temperature (UCST) type can be fine-tuned. Due to the dual thermo-responsive behavior, the copolymers show a rich temperature-controlled self-assembly in aqueous solution. This was explored by turbidimetry, dynamic light scattering, as well as 1H NMR and fluorescence spectroscopies,. Depending on the relative positions of the UCST-type and LCST-type transition temperatures, various modes of stimulus-induced micellization are realized, including classical induced micellization due to a change from a double hydrophilic, or respectively, from a double hydrophobic to an amphiphilic state, as well as \\\\\\\"schizophrenic\\\\\\\" behavior, where the core- and shell-forming blocks exchange their roles.
J. Hermanns, B. Schmidt Zur Verwendung von QR-Codes in Uni-Seminaren - ein Baustein in den neu konzipierten Übungen zur Vorlesung \"Organische Chemie für Studierende im Nebenfach\" CHEMKON 2017, 24, 139-141. DOI: 10.1002/ckon.201710300AbstractIn dieser hochschuldidaktischen Publikation wird die Verwendung von QR-codes als Zugang zu weiterführenden Hilfen für die Bearbeitung von begleitenden Hausaufgaben zu den Übungen des Moduls \"Organische Chemie für Studierende mit Chemie als Nebenfach\" vorgestellt. Der Einsatz der QR-codes und die Neukonzeption der Übungen wurde evaluiert.
W. Fudickar, P. Pavashe,T. Linker Thiocarbohydrates on Gold Nanoparticles: Strong Influence of Stereocenters on Binding Affinity and Interparticle Forces Chemistry Eur. J. 2017, 23, 8685-8693 DOI: 10.1002/chem.201700846AbstractCarbohydrates carrying thiol groups at the C-2 position have been attached to gold nanoparticles (AuNP) with stereocenters in close proximity to the surface for the first time. Their configurations can be clearly distinguished by the tendency of particle aggregation. AuNP surface plasmon resonance (SPR), x-ray photoelectron spectroscopy (XPS), and IR spectroscopy indicate that the thiocarbohydrates replace citrate molecules at different rates, causing aggregation and eventually precipitation. A quantitative formulation of this aggregation process shows that reactivities can vary by several magnitudes. Adsorption isotherms and kinetics also demonstrate that the number of thiocarbohydrates varies by a factor of two. Molecular mechanics force field (MMFF) calculations reveal their relative orientations. Based on these models, the different binding behavior can be ascribed to attractive van der Waals forces and hydrogen bonds. Such interactions occur either between the carbohydrate and AuNPs, by lateral intermolecular forces at the surface, or by interparticle attraction, in analogy to cell-surface carbohydrates of biological recognition systems. Aggregation of NPs therefore act as an indicator to differentiate between various carbohydrates with defined configurations.
F. Liebig, R. M. Sarhan, M. Sander, W. Koopman, R. Schuetz, M. Bargheer, J. Koetz Deposition of Gold Nanotriangles in Large Scale Close-Packed Monolayers for X-ray-Based Temperature Calibration and SERS Monitoring of Plasmon-Driven Catalytic Reactions ACS Appl. Mater. Interfaces 2017, 9, 20247-20253 DOI: 10.1021/acsami.7b07231AbstractAnisotropic plasmonic particles such as gold nanotriangles have extraordinary structural, optical, and physicochemical properties. For many applications in different fields, it is essential to prepare them in a chemically and physically stable, structurally well-defined manner, e.g., as large and uniform coverage on a substrate. We present a direct method for the large scale close-packed monolayer formation of edge-to-edge ordered, ultrathin crystalline gold nanotriangles on Si wafers or quartz glass via the transfer of these asymmetric particles to the air-liquid interface after adding ethanol - toluene mixtures without any subsequent surface functionalization. X-ray diffraction monitoring of the close-packed, large area monolayer with a mosaicity of less than 0.1° allows for calibrating the temperature of the particles during continuous laser heating. This is important for characterizing the microscopic temperature of the metal particles in the plasmon-driven dimerization process of 4- nitrothiophenol (4-NTP) into 4,4´-dimercaptoazobenzene (DMAB), monitored in real time by surface-enhanced Raman scattering (SERS). The gold nanotriangles can act as a source of hot electrons and initiate the dimerization process.
C. Heck, J.Prinz, A. Dathe, V. Merk, O. Stranik, W. Fritzsche, J. Kneipp, I. Bald Gold Nanolenses Self-Assembled by DNA Origami ACS Photonics 2017, 4, 1123-1130 DOI: 10.1021/acsphotonics.6b00946AbstractNanolenses are self-similar chains of metal nanoparticles, which can theoretically provide extremely high field enhancements. Yet, the complex structure renders their synthesis challenging and has hampered closer analyses so far. Here, DNA origami is used to self-assemble 10, 20, and 60 nm gold nanoparticles as plasmonic gold nanolenses (AuNLs) in solution and in billions of copies. Three different geometrical arrangements are assembled, and for each of the three designs, surface-enhanced Raman scattering (SERS) capabilities of single AuNLs are assessed. For the design which shows the best properties, SERS signals from the two different internal gaps are compared by selectively placing probe dyes. The highest Raman enhancement is found for the gap between the small and medium nanoparticle, which is indicative of a cascaded field enhancement.
T. Schwarze, H. Müller, D. Schmidt, J. Riemer, H.-J. Holdt Design of Na+ Selective Fluorescent Probes: A Systematic Study of the Na+ Complex Stability and the Na+/K+ Selectivity in Acetonitrile and Water Chemistry - A European Journal 2017, 23, 1 DOI: 10.1002/chem.201605986AbstractThere is a tremendous demand for highly Na+-selective fluoroionophores to monitor the top analyte Na+ in life science. Here, we report a systematic route to develop highly Na+/K+ selective fluorescent probes. Thus, we synthesized a set of fluoroionophores 1, 3, 4, 5, 8 and 9 (see Scheme 1) to investigate the Na+/K+ selectivity and Na+- complex stability in CH3CN and H2O. These Na+-probes bear different 15-crown-5 moieties to bind Na+ stronger than K+. In the set of the diethylaminocoumarin-substituted fluoroionophores 1–5, the following trend of fluorescence quenching 1>3>2>4>5 in CH3CN was observed. Therefore, the flexibility of the aza-15-crown-5 moieties in 1–4 determines the conjugation of the nitrogen lone pair with the aromatic ring. As a consequence, 1 showed in CH3CN the highest Na+-induced fluorescence enhancement (FE) by a factor of 46.5 and a weaker K+ induced FE of 3.7. The Na+-complex stability of 1–4 in CH3CN is enhanced in the following order of 2>4>3>1, assuming that the O-atom of the methoxy group in the ortho-position, as shown in 2, strengthened the Na+-complex formation. Furthermore, we found for the N-(o-methoxyphenyl)aza-15-crown-5 substituted fluoroionophores 2, 8 and 9 in H2O, an enhanced Na+-complex stability in the following order 8>2>9 and an increased Na+/K+ selectivity in the reverse order 9>2>8. Notably, the Na+-induced FE of 8 (FEF=10.9), 2 (FEF=5.0) and 9 (FEF=2.0) showed a similar trend associated with a decreased K+-induced FE [8 (FEF=2.7)>2 (FEF=1.5)>9 (FEF=1.1)]. Here, the Na+-complex stability and Na+/K+ selectivity is also influenced by the fluorophore moiety. Thus, fluorescent probe 8 (Kd=48 mm) allows high-contrast, sensitive, and selective Na+ measurements over extracellular K+ levels. A higher Na+/K+ selectivity showed fluorescent probe 9, but also a higher Kd value of 223 mm. Therefore, 9 is a suitable tool to measure Na+ concentrations up to 300 mm at a fluorescence emission of 614 nm.
J. Lutz, M. A. Bañares, M. Pita, A. Haase, A. Luch, A. Taubert α-((4-Cyanobenzoyl)oxy)-ω-methyl poly(ethylene glycol): a new stabilizer for silver nanoparticles Beilstein Journal of Nanotechnology 2017, 8, 627 DOI: 10.3762/bjnano.8.67AbstractThe article describes the synthesis and properties of α-((4-cyanobenzoyl)oxy)-ω-methyl poly(ethylene glycol), the first poly(ethylene glycol) stabilizer for metal nanoparticles that is based on a cyano rather than a thiol or thiolate anchor group. The silver particles used to evaluate the effectiveness of the new stabilizer typically have a bimodal size distribution with hydrodynamic diameters of ca. 13 and ca. 79 nm. Polymer stability was evaluated as a function of the pH value both for the free stabilizer and for the polymers bound to the surface of the silver nanoparticles using 1H NMR spectroscopy and zeta potential measurements. The polymer shows a high stability between pH 3 and 9. At pH 12 and higher the polymer coating is degraded over time suggesting that α-((4-cyanobenzoyl)oxy)-ω-methyl poly(ethylene glycol) is a good stabilizer for metal nanoparticles in aqueous media unless very high pH conditions are present in the system. The study thus demonstrates that cyano groups can be viable alternatives to the more conventional thiol/thiolate anchors.
J. Rumschöttel, S. Kosmella, C. Prietzel, D. Appelhans, J. Koetz DNA polyplexes with dendritic glycopolymer-entrapped gold nanoparticles Colloids and Surfaces B: Biointerfaces 2017, 154, 74-81 DOI: 10.1016/j.colsurfb.2017.03.001AbstractPolyplexes, composed of Salmon DNA and very small gold nanoparticles embedded into a dendritic glycopolymer architecture of sugar-modified poly(ethyleneimine) (PEI-Mal) with a molar mass of about 25,000 g/mol, were characterized by dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (μ-DSC) and transmission electron microscopy (TEM). The PEIMal-entrapped gold nanoparticles of about 2 nm in diameter influence the polyplex formation of the hyperbranched PEI containing bulky maltose, and in consequence the DNA is more compactized in the inner part of spherical polyplex particles of about 150 nm in diameter. The resulting more compact coreshell polyplex particles with embedded gold nanoparticles in the outer polymer shell will be used as components in forthcoming gene delivery experiments.
S. Reinicke, H. C. Reesb, P. Espeelc, N. Vanparijsd, C. Bisterfelde, M. Dicke, R. R. Rosencrantza, G. Brezesinski, B. G. de Geestd, F. E. Du Prezc, J. Pietruszka, A. Böker Immobilization of 2-Deoxy-D-Ribose-5-Phosphate Aldolase in Polymeric Thin Films via the Langmuir-Schaefer Technique ACS Appl. Mater. Interfaces 2017, DOI: 10.1021/acsami.6b13632AbstractA synthetic protocol for the fabrication of ultrathin polymeric films containing the enzyme 2-deoxy-D-ribose-5-phosphate aldolase from Escherichia coli (DERAEC) is presented. Ultrathin enzymatically active films are useful for applications in which only small quantities of active material are needed and at the same time quick response and contact times without diffusion limitation are wanted. We show how DERA as an exemplary enzyme can be immobilized in a thin polymer layer at the air-water interface, and transferred to a suitable support by the Langmuir-Schaefer technique under full conservation of enzymatic activity. The polymer in use is a poly(N-isopropyl acrylamide-co-N-2-thiolactone acrylamide) (P(NIPAAm-co-TlaAm)) statistical copolymer in which the thiolactone units serve a multitude of purposes including hydrophobization of the polymer, covalent binding of the enzyme and the support and finally crosslinking of the polymer matrix. The application of this type of polymer keeps the whole approach simple as additional co-components such as crosslinkers are avoided.
R. Schürmann, I. Bald Real-time monitoring of plasmon induced dissociative electron transfer to the potential DNA radiosensitizer 8-bromoadenine Nanoscale 2017, 9, 1951 DOI: 10.1039/c6nr08695kAbstractThe excitation of localized surface plasmons in noble metal nanoparticles (NPs) results in different nanoscale effects such as electric field enhancement, the generation of hot electrons and a temperature increase close to the NP surface. These effects are typically exploited in diverse fields such as surfaceenhanced Raman scattering (SERS), NP catalysis and photothermal therapy (PTT). Halogenated nucleobases are applied as radiosensitizers in conventional radiation cancer therapy due to their high reactivity towards secondary electrons. Here, we use SERS to study the transformation of 8-bromoadenine (8BrA) into adenine on the surface of Au and AgNPs upon irradiation with a low-power continuous wave laser at 532, 633 and 785 nm, respectively. The dissociation of 8BrA is ascribed to a hot-electron transfer reaction and the underlying kinetics are carefully explored. The reaction proceeds within seconds or even milliseconds. Similar dissociation reactions might also occur with other electrophilic molecules, which must be considered in the interpretation of respective SERS spectra. Furthermore, we suggest that hot-electron transfer induced dissociation of radiosensitizers such as 8BrA can be applied in the future in PTT to enhance the damage of tumor tissue upon irradiation.
T. Krüger, A. Kelling, U. Schilde, T. Linker Simple Synthesis of γ-Spirolactams by Birch Reduction of Benzoic Acids Eur. J. Org. Chem. 2017, , 1074-1077 DOI: 10.1002/ejoc.201601650AbstractA convenient synthesis of γ-spirolactams in only two steps is described. Birch reduction of benzoic acids and immediate alkylation with chloroacetonitrile afford cyclohexadienes in high yields. The products can be isolated by crystallization on a large scale in analytically pure form. Subsequent hydrogenation with platinum(iv) oxide as catalyst reduces the nitrile and the double bonds in the same step and with excellent stereoselectivity. The relative configurations have been determined unequivocally by X-ray analyses. Direct cyclization of the intermediary formed amino acids affords the desired γ-spirolactams in excellent overall yields. The procedure is characterized by few steps, cheap reagents, and can be performed on a large scale, interesting for industrial processes.
C. Paz, L. Ortiz, U. Schilde Crystal structure of erioflorin isolated from Podanthus mitiqui (L.) Acta Cryst. E 2017, 73, 334-337 DOI: 10.1107/S2056989017001700AbstractThe title compound, erioflorin, C19H24O6 [systematic name: (1aR,3S,4Z,5aR,8aR,9R,10aR)-1a,2,3,5a,7,8,8a,9,10,10a-decahydro-3-hydroxy-4,10a-dimethyl-8-methylidene-7-oxooxireno[5,6]cyclodeca[1,2-b]furan-9-yl methacrylate] is a tricyclic germacrane sesquiterpene lactone which was isolated from Podanthus mitiqui (L.). The compound crystallizes in the space group P212121, and its molecular structure is basically a methacrylic ester of a ten-membered ring sesquiterpenoid annelated with an epoxide between C1---C10 and a butyrolactone between C6---C7. The molecule is stabilized by one hydrogen bond. Further intermolecular hydrogen bonds can be observed in the packing.
B. Schmidt, S. Audörsch Stereoselective total syntheses of polyacetylene plant metabolites via ester-tethered ring closing metathesis J. Org. Chem. 2017, 82, 1743-1760 DOI: 10.1021/acs.joc.6b02987AbstractTotal syntheses of five naturally occurring polyacetylenes from three different plants are described. These natural products have an E,Z-configured conjugated diene linked to a di- or triyne chain in common. As the key method to stereoselectively establish the E,Z-diene part, an ester-tethered ring-closing metathesis/base-induced eliminative ring opening sequence was used. The results presented herein do not only showcase the utility of this tethered RCM variant, but have also prompted us to suggest that the originally assigned absolute configurations of chiral polyacetylenes from Atractylodes macrocephala should be revised or at least reconsidered.
B. Schmidt, F. Wolf, C. Ehlert Systematic Investigation into the Matsuda-Heck Reaction of α-Methylene Lactones: How Conformational Constraints Direct the β-H-Elimination Step J. Org. Chem. 2016, 81, 11235-11249 DOI: 10.1021/acs.joc.6b02207Abstractα-Methylene-γ-butyrolactone and α-methylene-δ-valerolactone undergo Pd-catalyzed Matsuda-Heck couplings with arene diazonium salts to α-benzyl butenolides or pentenolides, respectively, or to α-benzylidene lactones. The observed regioselectivity is strongly ring size dependent, with six-membered rings giving exclusively α-benzyl pentenolides, whereas the five-membered α-methylene lactone reacts to mixtures of regioisomers with a high proportion of (E)-α-benzylidene-γ-butyrolactones. DFT calculations suggest that the reasons for these differences are not thermodynamic but kinetic in nature. The relative energies of the conformers of the Pd σ-complexes resulting from insertion into the Pd-aryl bond were correlated with the dihedral angles between Pd and endo-β-H. This correlation revealed that in the case of the six-membered lactone an energetically favorable conformer adopts a nearly synperiplanar Pd/endo-β-H arrangement, whereas for the analogous Pd σ-complex of the five-membered lactone the smallest Pd/endo-β-H dihedral angle is observed for a conformer with a comparatively high potential energy. The optimized conditions for Matsuda-Heck arylations of exo-methylene lactones were eventually applied to the synthesis of the natural product anemarcoumarin A.
F. N. Behrendt, H. Schlaad Metathesis polymerization of cystine-based macrocycles Polym. Chem. 2017, 8, 366-369 DOI: 10.1039/C6PY01864EAbstractMacrocycles based on L-cystine were synthesized by ring-closing metathesis (RCM) and subsequently polymerized by entropy-driven ring-opening metathesis polymerization (ED-ROMP). Monomer conversion reached ∼80% in equilibrium and the produced poly(ester-amine-disulfide-alkene)s exhibited apparent molar masses (Mappw) of up to 80 kDa and dispersities (Ð) of ∼2. The polymers can be further functionalized with acid anhydrides and degraded by reductive cleavage of the main-chain disulfide.
V. Hildebrand, A. Laschewsky, M. Päch, P. Müller-Buschbaum, C. M. Papadakis Effect of the Zwitterion Structure on the Thermo-responsive Behaviour of Poly(Sulfobetaine Methacrylate)s Polym. Chem. 2017, 8, 310-322 DOI: 10.1039/c6py01220eAbstractA series of zwitterionic poly(sulfobetaine methacrylate)s was synthesized by RAFT (reversible addition-fragmentation chain transfer) polymerization. The chemical structure of the well-defined polyzwitterions was varied systematically, to elucidate the influences of the various substituents and substitution patterns on their thermoresponsive behavior in aqueous solutions. While all polymers exhibit upper critical solution temperatures (UCSTs), small changes of the chemical structure result in big changes of the transition temperature. Additionally, the phase behavior depends sensitively and in a complex way on the amount and type of salt(s) added, and moreover, shows marked H-D isotope effects in H2O/D2O.
Ch. Herfurth, A. Laschewsky, L. Noirez, B. von Lospichl, M. Gradszielski Thermoresponsive (Star) Block Copolymers from One Pot Sequential RAFT Polymerizations and their Self-Assembly in Aqueous Solution Polymer 2016, 107, 422-433 DOI: 10.1016/j.polymer.2016.09.089AbstractA series of thermo-responsive, "smart" associative telechelics bearing hydrophobic dodecyl end groups is made from N,N-dimethyl- and N,N-diethylacrylamide. The well-defined block and star block copolymers could be synthesized by RAFT polymerization via a convenient one-pot procedure. The star arms feature an inner hydrophilic and an outer thermoresponsive block. Light and neutron scattering studies demonstrate responsive aggregation in aqueous solution, with the control of solution viscosity and gel formation. The extent of aggregation and the systems' viscosities are controlled by the macromolecular architecture.
N. Vishnevetskaya, V. Hildebrand, B.-J. Niebuur, I. Grillo, S. Filippov, A. Laschewsky, P. Müller-Buschbaum, C. M. Papadakis Aggregation behavior of doubly thermo-responsive polysulfobetaine-b-poly(N-isopropylacrylamide) diblock copolymers Macromolecules 2016, 49, 6655 DOI: 10.1021/acs.macromol.6b01186AbstractA twofold thermo-responsive diblock copolymer containing a zwitterionic polysulfobetaine block (P-SPP) and a non-ionic block of poly(N-isopropylacrylamide) (P-NiPAm) was synthesized. While both homopolymers P-SPP and P-NIPAM are thermoresponsive in aqueous solution, exhibiting upper and lower critical solution temperatures (UCST and LCST), respectively, the diblock copolymer undergoes "schizophrenic" temperature-induced aggregation. This is investigated in detail by turbidimetry and small-angle neutron scattering (SANS), revealing marked differences of the polymer micelles formed below the UCST-type and above the LCST-type transitions.
G. Storch, F. Maier, P. Wessig, O. Trapp Rotational Barriers of substituted Biphep Ligands – A Comparative Experimental and Theoretical Study Eur. J. Org. Chem. 2016, , 5123-5126 DOI: 10.1002/ejoc.201600836AbstractThe interconversion barriers of 14 different 3,3’- and 5,5’-disubstituted tropos BIPHEP [2,2’-bis(diphenylphosphino)-1,1’-biphenyl and BIPHEP(O) [2,2’-bis(diphenylphosphoryl)-1,1’-biphenyl] ligands were investigated by enantioselective dynamic high performance liquid chromatography (DHPLC) and DFT calculations using the B3LYP/6-31G* and M06-2X/6-31G* levels of theory. The experimentally determined enantiomerization barriers varied from 86.8 to 101.4 kJ/mol-1 and were found to be in excellent agreement with the calculated data.The root-mean-square deviations are 7.3 kJ/mol-1 for the B3LYP functional and 11.3 kJ/mol-1 for the M06-2X method.
F. Liebig, A. F. Thünemann, J. Koetz Ostwald Ripening Growth Mechanism of Gold Nanotriangles in Vesicular Template Phases Langmuir 2016, 32, 10928 DOI: 10.1021/acs.langmuir.6b02662AbstractThe mechanism of nanotriangle formation in multivesicular vesicles (MMV) is investigated by using time-dependent SAXS measurements in combination with UV–vis spectroscopy, light, and transmission electron microscopy. In the first time period 6.5 nm sized spherical gold nanoparticles are formed inside of the vesicles, which build up soft nanoparticle aggregates. In situ SAXS experiments show a linear increase of the volume and molar mass of nanotriangles in the second time period. The volume growth rate of the triangles is 16.1 nm3/min, and the growth rate in the vertical direction is only 0.02 nm/min. Therefore, flat nanotriangles with a thickness of 7 nm and a diameter of 23 nm are formed. This process can be described by a diffusion-limited Ostwald ripening growth mechanism. TEM micrographs visualize soft coral-like structures with thin nanoplatelets at the periphery of the aggregates, which disaggregate in the third time period into nanotriangles and spherical particles. The 16 times faster growth of nanotriangles in the lateral than that in the vertical direction is related to the adsorption of symmetry breaking components, i.e., AOT and the polyampholyte PalPhBisCarb, on the {111} facets of the gold nanoplatelets in combination with confinement effects of the vesicular template phase.
J. Prinz, A. Matković, J. Pešić, R. Gajić, I. Bald Hybrid Structures for Surface-Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene Small 2016, 12, 5458 DOI: 0.1002/smll.201601908AbstractA combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface-enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in effi cient fl uorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami–AuNP dimer–graphene hybrid structures.
P. Pavashe, E. Elamparuthi, C. Hettrich, H. M. Möller, T. Linker Synthesis of 2-Thiocarbohydrates and Their Binding to Concanavalin A J. Org. Chem. 2016, 81, 8595 DOI: 10.1021/acs.joc.6b00987Abstract A convenient and general synthesis of 2-thiocarbohydrates via cerium ammonium nitrate oxidation of the thiocyanate ion is described. Radical addition to glycals proceeds with excellent regio- and good stereoselectivities in only one step, deprotection affords water-soluble 2-thiosaccharides. Binding studies to Con A have been performed by isothermal titration calorimetry (ITC) and saturation transfer difference (STD) NMR spectroscopy. The 2-thiomannose derivative binds even stronger to Con A than the natural substrate, offering opportunities for new lectin or enzyme inhibitors.
P. Wessig, M. Czarnecki, D. Badetko, U. Schilde, A. Kelling Photochemical Synthesis of Both Strained and Macrocyclic (1,7)Naphthalenophanes J. Org. Chem. 2016, 81, 9147 DOI: 10.1021/acs.joc.6b01707AbstractNaphthalenophanes are a special type of cyclophanes. While in the past (1,5), (1,6) and (1,8)Naphthaleno-phanes were successfully prepared by using the (Photo)-Dehydro-Diels-Alder (DDA) reaction, the access to (1,7)Naphthalenophanes by this method was hitherto unknown. After numerous unsuccessful attempts to prepare these compounds by thermal DDA, we found that the photoinitiated variant (PDDA) represents a very efficient method to [k](1,7)Naphthalenophanes 13. The scope ranged from highly strained (k = 11, 12) to macrocyclic products (k = 22, 24). The extraordinary reactivity could be explained by folded ground state geometries of diketones 12 used as reactants of the PDDA. Furthermore, we calculated the ring strain energies with the help of an isodesmic reaction and evaluated structural and spectroscopic (NMR) consequences of ring strain.
U. Eisold, N. Behrends, P. Wessig, M. U. Kumke Rigid Rod-Based FRET Probes for Membrane Sensing Applications J. Phys. Chem. 2016, 120, 9935 DOI: 10.1021/acs.jpcb.6b07285AbstractOligospirothioketal (OSTK) rods are presented as an adjustable scaffold for optical membrane probes. The OSTK rods are readily incorporated into lipid bilayers due to their hydrophobic backbones. Because of their high length-over-diameter aspect ratio, only a minimal disturbance of the lipid bilayer is caused. OSTK rods show outstanding rigidity and allow defined labeling with fluorescent dyes, yielding full control of the orientation between the dye and OSTK skeleton. This allows the construction of novel Förster resonance energy transfer probes with highly defined relative orientations of the transition dipole moments of the donor and acceptor dyes and makes the class of OSTK probes a powerful, flexible toolbox for optical biosensing applications. Data on steady-state and time-resolved fluorescence experiments investigating the incorporation of coumarin- and [1,3]dioxolo[4,5-f][1,3]benzo-dioxole-labeled OSTKs in large unilamellar vesicles are presented as a show case.
P. Wessig, N. Behrends, M. U. Kumke, U. Eisold FRET Pairs with Fixed Relative Orientation of Chromophores Eur. J. Org. Chem. 2016, 2016, 4476 DOI: 10.1002/ejoc.201600489AbstractSynthetic routes to different OSTK FRET constructs are described and the photophysics of these constructs were determined in different solvents. Based on the experimental data the FRET efficiencies was determined and compared to theoretical. The influence of the outstanding rigidity of the novel OSTK compounds on the FRET is shown and discussed.
J. Rackwitz, J. Kopyra, I. Dabkowska, K. Ebel, M. L. Rankovic, A. R. Milosavljevic, I. Bald Sensitizing DNA Towards Low-Energy Electrons with 2-Fluoroadenine Angew. Chem. Int. Ed. 2016, 55, 10248 –10252 DOI: 10.1002/anie.201603464Abstract2-Fluoroadenine (2FA) is a therapeutic agent, which is suggested for application in cancer radiotherapy. The molecular mechanism of DNA radiation damage can be ascribed to a significant extent to the action of low-energy (<20 eV) electrons (LEEs), which damage DNA by dissociative electron attachment. LEE induced reactions in 2FA are characterized both isolated in the gas phase and in the condensed phase when it is incorporated into DNA. Information about negative ion resonances and anion-mediated fragmentation reactions is combined with an absolute quantification of DNA strand breaks in 2FA-containing oligonucleotides upon irradiation with LEEs. The incorporation of 2FA into DNA results in an enhanced strand breakage. The strandbreak cross sections are clearly energy dependent, whereas the strand-break enhancements by 2FA at 5.5, 10, and 15 eV are very similar. Thus, 2FA can be considered an effective radiosensitizer operative at a wide range of electron energies.
S. M. J. Khadem, C. Hille, H.-G. Löhmannsröben, I. M. Sokolov What information is contained in the fluorescence correlation spectroscopy curves, and where Physical Review E 2016, 94, 022407 DOI: 10.1103/PhysRevE.94.022407AbstractWe discuss the application of fluorescence correlation spectroscopy (FCS) for characterization of anomalous diffusion of tracer particles in crowded environments. While the fact of anomaly may be detected by the standard fitting procedure, the value of the exponent α of anomalous diffusion may be not reproduced correctly for non-Gaussian anomalous diffusion processes. The important information is however contained in the asymptotic behavior of the fluorescence autocorrelation function at long and at short times. Thus, analysis of the short-time behavior gives reliable values of α and of lower moments of the distribution of particles' displacement, which allows us to confirm or reject its Gaussian nature. The method proposed was tested on the FCS data obtained in artificial crowded fluids and in living cells.
J. Sun, P. Černoch, A. Völkel, Y. Wei, J. Ruokolainen, H. Schlaad Aqueous Self-Assembly of a Protein-Mimetic Ampholytic Block Copolypeptide Macromolecules 2016, 49, 5494 DOI: 10.1021/acs.macromol.6b00817AbstractThis report describes the aggregation behavior of an ABC-type ampholytic block copolypeptide, poly(ethylene oxide)-block-poly(l-lysine)-block-poly(l-glutamate), in aqueous media in dependence of pH. Polypeptide secondary structures and self-assemblies are investigated by circular dichroism (CD), Fourier transform infrared (FT-IR) and NMR spectroscopy, zeta potential measurements, analytical ultracentrifugation (AUC), dynamic/static light scattering (DLS/SLS), and cryogenic transmission electron microscopy (cryo-TEM). The polymer chains tend to form vesicles when the hydrophobic polypeptide helix is located at the chain end (acidic pH) and are existing as single chains when it is located in the center and flanked by the two hydrophilic segments (basic pH). Precipitation occurs in the intermediate pH range due to polyion complexation of the charged polypeptide segments.
A. H. Poghosyan, L. H. Arsenyan, A. A. Shahinyan, J. Koetz Polyethyleneimine loaded inverse SDS micelle in pentanol/toluene media Colloids and Surfaces A: Physicochemical and Engineering Aspects 2016, 506, 402 DOI: 10.1016/j.colsurfa.2016.07.018AbstractAn atomic scale molecular dynamics simulation (100 ns) was carried out to reveal the conformational features of a cationic polyelectrolyte, i.e., hyperbranched polyethyleneimine (PEI), inside of water-in-oil microemulsion droplets stabilized by the anionic sodium dodecyl sulfate surfactant (SDS) layer. Simulations show that the polymer reorients very quickly and is localized at the headgroup region, i.e., the polymer nitrogens are close to SDS sulfur atoms. In spite of the availability of surface roughness caused by the polymer, we track a stable inverse micelle during the production run. In overall, the obtained parameters are well compared with experimental findings.
Schmidt, B.; Wolf, F.; Brunner, H. Styrylsulfonates and -Sulfonamides through Pd-Catalysed Matsuda–Heck Reactions of Vinylsulfonic Acid Derivatives and Arenediazonium Salts Eur. J. Org. Chem. 2016, 2972-2982 DOI: 10.1002/ejoc.201600469AbstractArene diazonium salts undergo Matsuda–Heck reactions with vinylsulfonates and -sulfonamides to give styrylsulfonic acid derivatives in high to excellent yields and with high to excellent selectivities. By quantifying the evolution of nitrogen over time in a gas-meter apparatus, the reactivities of ethylvinylsulfonate and the benchmark olefin methyl acrylate were compared for an electron-rich and an -deficient arene diazonium salt. Tertiary sulfonamides react in Matsuda–Heck couplings with high conversions, but require long reaction times, which prevents the determination of kinetic data through the measurement of nitrogen evolution. Secondary sulfonamides were found to be unreactive. From these results, the following order of reactivity could be deduced: H2C=CHCO2Me > H2C=CHSO2OEt > H2C=CHSO2N(Me)Bn >> H2C=CHSO2NHBn. Through the Matsuda–Heck coupling of 5-indolyldiazonium salt and a tertiary vinylsulfonamide, the synthesis of the C-5-substituted indole part of the antimigraine drug naratriptan was accomplished in high yield.
C. D. Vacogne, M. Schopferer, H. Schlaad Physical Gelation of α-Helical Copolypeptides Biomacromolecules 2016, 17, 2384 DOI: 10.1021/acs.biomac.6b00427AbstractOwing to its rod-like α-helical secondary structure, the synthetic polypeptide poly(γ-benzyl-l-glutamate) (PBlG) can form physical and thermoreversible gels in helicogenic solvents such as toluene. The versatility of PBlG can be increased by introducing functionalizable comonomers, such as allylglycine (AG). In this work we examined the secondary structure of PBlG and a series of statistical poly(γ-benzyl-l-glutamate-co-allylglycine) copolypeptides, varying in composition and chain length, by circular dichroism (CD), Fourier-transform infrared (FTIR) and Raman spectroscopy, and wide-angle X-ray scattering (WAXS). The secondary structure of PBlG and the copolypeptides presented dissimilarities that increased with increasing AG molar fraction, especially when racemic AG units were incorporated. The physical gelation behavior of these copolypeptides was analyzed by temperature-sweep 1H NMR and rheological measurements. The study revealed that both copolypeptide composition and chain length affected secondary structure, gelation temperature, and gel stiffness.
M. Klaper, W. Fudickar, T. Linker Role of Distance in Singlet Oxygen Applications: A Model System J. Am. Chem. Soc. 2016, 138, 7024–7029 DOI: 10.1021/jacs.6b01555AbstractHerein, we present a model system which allows the investigation of a directed intramolecular singlet oxygen (1O2) transfer. Furthermore, we show the influence of singlet oxygen lifetime and diffusion coefficient (D) on the preference of the intra- over the intermolecular reaction in competition experiments. Finally, we demonstrate the distance dependence in quenching experiments, which enables us to draw conclusions about the role of singlet oxygen and 1O2 carriers in PDT.
I. Kovach, J. Rumschöttel, S.E. Friberg, J. Koetz Janus emulsion mediated porous scaffold bio-fabrication Colloids and Surfaces B: Biointerfaces 2016, 145, 347 DOI: 10.1016/j.colsurfb.2016.05.018AbstractA three dimensional biopolymer network structure with incorporated nano-porous calcium phosphate (CaP) balls was fabricated by using gelatin-chitosan (GC) polymer blend and GC stabilized olive/silicone oil Janus emulsions, respectively. The emulsions were freeze-dried, and the oil droplets were washed out in order to prepare porous scaffolds with larger surface area. The morphology, pore size, chemical composition, thermal and swelling behavior was studied by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and micro-Differential Scanning Calorimetry (micro-DSC). Microscopic analysis confirmed that the pore size of the GC based sponges after freeze-drying may be drastically reduced by using Janus emulsions. Besides, the incorporation of nanoporous calcium phosphate balls is also lowering the pore size and enhancing thermal stability.
L. Olejko, P. J. Cywinski, I. Bald An ion-controlled four-color fluorescent telomeric switch on DNA origami structures Nanoscale 2016, 8, 10339-10347 DOI: 10.1039/C6NR00119J AbstractThe folding of single-stranded telomeric DNA into guanine (G) quadruplexes is a conformational change that plays a major role in sensing and drug targeting. The telomeric DNA can be placed on DNA origami nanostructures to make the folding process extremely selective for K+ ions even in the presence of high Na+ concentrations. Here, we demonstrate that the K+-selective G-quadruplex formation is reversible when using a cryptand to remove K+ from the G-quadruplex. We present a full characterization of the reversible switching between single-stranded telomeric DNA and G-quadruplex structures using Förster resonance energy transfer (FRET) between the dyes fluorescein (FAM) and cyanine3 (Cy3). When attached to the DNA origami platform, the G-quadruplex switch can be incorporated into more complex photonic networks, which is demonstrated for a three-color and a four-color FRET cascade from FAM over Cy3 and Cy5 to IRDye700 with G-quadruplex-Cy3 acting as a switchable transmitter.
S.S. Mondal, D. Marquardt, C. Janiak, H.-J. Holdt Use of a 4,5-dicyanoimidazolate anion based ionic liquid for the synthesis of iron and silver nanoparticles Dalton Trans. 2016, 45, 5476 DOI: 10.1039/C6DT00225KAbstractSixteen new ionic liquids (ILs) with tetraethylammonium, 1-butyl-3-methylimidazolium, 3-methyl-1-octylimidazolium and tetrabutylphosphonium cations paired with 2-substituted 4,5-dicyanoimidazolate anions (substituent at C2 = methyl, trifluoromethyl, pentafluoroethyl, N,N′-dimethyl amino and nitro) have been synthesized and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA). The effects of cation and anion type and structure of the resulting ILs, including several room temperature ionic liquids (RTILs), are reflected in the crystallization, melting points and thermal decomposition of the ILs. ILs exhibited large liquid and crystallization ranges and formed glasses on cooling with glass transition temperatures in the range of -22 to -71°C. We selected one of the newly designed ILs due to its bigger size, compared to the common conventional IL anion and high electron-withdrawing nitrile group leads to an overall stabilization anion that may stabilize the metal nanoparticles. Stable and better separated iron and silver nanoparticles are obtained by the decomposition of corresponding Fe₂(CO)₉ and AgPF₆, respectively, under N₂-atmosphere in newly designed nitrile functionalized 4,5-dicyanoimidazolate anion based IL. Very small and uniform size for Fe-nanoparticles of about 1.8 ± 0.6 nm were achieved without any additional stabilizers or capping molecules. Comparatively bigger size of Ag-nanoparticles was obtained through the reduction of AgPF₆ by hydrogen gas. Additionally, the AgPF₆ precursor was decomposed under microwave irradiation (MWI), fabricating nut-in-shell-like, that is, core-separated-from-shell Ag-nano-structures.
J.-P. Couturier, E. Wischerhoff, R. Bernin, C. Hettrich, J. Koetz, M. Sütterlin, B. Tiersch, A. Laschewsky Thermoresponsive Polymers and Inverse Opal Hydrogels for the Detection of Diols Langmuir 2016, 32, 4333 DOI: 10.1021/acs.langmuir.6b00803AbstractResponsive inverse opal hydrogels functionalized by boroxole moieties were synthesized and explored as sensor platforms for various low molar mass as well as polymeric diols and polyols, including saccharides, glycopolymers and catechols, by exploiting the diol induced modulation of their structural color. The underlying thermoresponsive water-soluble copolymers and hydrogels exhibit a coil-to-globule or volume phase transition, respectively, of the LCST-type. They were prepared from oligoethylene oxide methacrylate (macro)monomers and functionalized via copolymerization to bear benzoboroxole moieties. The resulting copolymers represent weak polyacids, which can bind specifically to diols within an appropriate pH window. Due to the resulting modulation of the overall hydrophilicity of the systems and the consequent shift of their phase transition temperature, the usefulness of such systems for indicating the presence of catechols, saccharides, and glycopolymers was studied, exploiting the diol/polyol induced shifts of the soluble polymers’ cloud point, or the induced changes of the hydrogels’ swelling. In particular, the increased acidity of benzoboroxoles compared to standard phenylboronic acids allowed performing the studies in PBS buffer (phosphate buffered saline) at the physiologically relevant pH of 7.4. The inverse opals constructed of these thermo- and analyte-responsive hydrogels enabled following the binding of specific diols by the induced shift of the optical stop band. Their highly porous structure enabled the facile and specific optical detection of not only low molar mass but also of high molar mass diol/polyol analytes such as glycopolymers. Accordingly, such thermoresponsive inverse opal systems functionalized with recognition units represent attractive and promising platforms for the facile sensing of even rather big analytes by simple optical means, or even by the bare eye.
A. Doriti, S. M. Brosnan, S. M. Weidner, H. Schlaad Synthesis of polysarcosine from air and moisture stable N-phenoxycarbonyl-N-methylglycine assisted by tertiary amine base Polym. Chem. 2016, 7, 3067 DOI: 10.1039/C6PY00221HAbstractPolysarcosine (Mn = 3650 - 20 000 g mol⁻¹, Ð ≈ 1.1) was synthesized from the air and moisture stable N-phenoxycarbonyl-N-methylglycine. Polymerization was achieved by in situ transformation of the urethane precursor into the corresponding N-methylglycine-N-carboxyanhydride, when in the presence of a non-nucleophilic tertiary amine base and a primary amine initiator.
E. Steeples, A. Kelling, U. Schilde, D. Esposito Amino acid-derived N-heterocyclic carbene palladium complexes for aqueous phase Suzuki–Miyaura couplings New J. Chem. 2016DOI: 10.1039/C5NJ03337CAbstractIn this work, three ligands produced from amino acids were synthesized and used to produce five bis- and PEPPSI-type palladium–NHC complexes using a novel synthesis route from sustainable starting materials. Three of these complexes were used as precatalysts in the aqueous-phase Suzuki–Miyaura coupling of various substrates displaying high activity. TEM and mercury poisoning experiments provide evidence for Pd-nanoparticle formation stabilized in water.
F. Liebig, R. M. Sarhan, C. Prietzel, A. Reinecke, J. Koetz “Green” gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering RSC Advances 2016, 6, 33561 - 33568 DOI: 10.1039/C6RA04808KAbstractThe aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering.
P. Wessig, N. Behrends, M. U. Kumke, U. Eisold, T. Meiling, C. Hille Two-Photon FRET Pairs based on Coumarin and DBD dyes RSC Advances 2016, 6, 33510 - 33513 DOI: 10.1039/c6ra03983aAbstractThe synthesis and the photophysical properties of two new FRET pairs based on coumarin as donor and DBD dye as acceptor are described. The introduction of a bromo atom dramatically increases the two-photon excitation (2PE) cross section providing a 2PE-FRET system, which is also suitable für 2PE-FLIM.
I. Kovach, J. Won, S. E. Friberg, J. Koetz Completely engulfed olive/silicone oil Janus emulsions with gelatin and chitosan Colloid and Polymer Science 2016, 294, 705 DOI: 10.1007/s00396-016-3828-4AbstractJanus emulsions, formed by mixing two oil components (i.e., olive oil (OO) and silicone oil (SiO)) with water in the presence of two surface active biopolymers, i.e., gelatin and chitosan, are investigated in more detail. The stability of Janus droplets formed strongly depends on the polymer components used. The mixture of both biopolymers represents an extraordinary effect which can be related to the complex formation of gelatin and chitosan. Taken into account that under the given pH conditions, in the acidic pH range between 4 and 6, below the isoelectric point of gelatin, both polymers are polycations, one can conclude that non-Coulombic interactions are of relevance for the enhanced surface activity of the complexes. Dynamic interfacial tension (γ) measurements by using the drop profile analysis tensiometry (PAT) indicate a strong adsorption of the polymer complexes at the olive oil/water interface in contrast to the silicone/water interface. In a first step, the polymer complexes are adsorbed at the interface, and in a second step, a more rigid skin-like polymer layer is formed. This first example of a polymer-stabilized Janus emulsion opens new perspectives for the application, e.g., in food emulsions or for making scaffold materials.
J. Prinz, C. Heck, L. Ellerik, V. Merkc, I. Bald DNA origami based Au–Ag-core–shell nanoparticle dimers with single-molecule SERS sensitivity Nanoscale 2016, 8, 5612 DOI: 10.1039/C5NR08674DAbstractDNA origami nanostructures are a versatile tool to arrange metal nanostructures and other chemical entities with nanometer precision. In this way gold nanoparticle dimers with defined distance can be constructed, which can be exploited as novel substrates for surface enhanced Raman scattering (SERS). We have optimized the size, composition and arrangement of Au/Ag nanoparticles to create intense SERS hot spots, with Raman enhancement up to 1010, which is sufficient to detect single molecules by Raman scattering. This is demonstrated using single dye molecules (TAMRA and Cy3) placed into the center of the nanoparticle dimers. In conjunction with the DNA origami nanostructures novel SERS substrates are created, which can in the future be applied to the SERS analysis of more complex biomolecular targets, whose position and conformation within the SERS hot spot can be precisely controlled
B. Schmidt, S. Audörsch Stereoselective Total Synthesis of Atractylodemayne A, a Conjugated 2(E),8(Z),10(E)-Triene-4,6-diyne Org. Lett. 2016, 18, 1162 DOI: 10.1021/acs.orglett.6b00274AbstractThe first total synthesis of the polyacetylene natural product atractylodemayne A is reported. Stereoselective construction of the conjugated (8Z, 10E)-diene moiety was achieved through a tethered ring closing metathesis approach, comprising a Ru-catalyzed RCM, followed by base-induced elimination. A Pd-catalyzed Cadiot-Chodkiewicz coupling was used for the synthesis of the diyne. Overall, atractylodemayne A was synthesized in nine steps for the longest linear sequence.
J. Rumschöttel, S. Kosmella, C. Prietzel, D. Appelhans, J. Koetz Change in size, morphology and stability of DNA polyplexes with hyperbranched poly(ethyleneimines) containing bulky maltose units Colloids and Surfaces B: Biointerfaces 2016, 138, 78 DOI: 10.1016/j.colsurfb.2015.11.061AbstractPolyplexes between Salmon DNA and non-modified hyperbranched poly(ethyleneimines) of varying molar mass, i.e., PEI(5 k) with 5000 g/mol and PEI(25 k) with 25,000 g/mol, and modified PEI(5 k) with maltose units (PEI-Mal) were investigated in dependence on the molar N/P ratio by using dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (μ-DSC), scanning-transmission electron microscopy (STEM), and cryo-scanning electron microscopy (cryo-SEM). A reloading of the polyplexes can be observed by adding the unmodified PEI samples of different molar mass. In excess of PEI a morphological transition from core-shell particles (at N/P 8) to loosely packed onion-like polyplexes (at N/P 40) is observed. The shift of the DSC melting peak from 88 °C to 76 °C indicates a destabilization of the DNA double helix due to the complexation with the unmodified PEI. Experiments with the maltose-modified PEI show a reloading already at a lower N/P ratio. Due to the presence of the sugar units in the periphery of the polycation electrostatic interactions between DNA become weaker, but cooperative H-bonding forces are reinforced. The resulting less-toxic, more compact polyplexes in excess of the PEI-Mal with two melting points and well distributed DNA segments are of special interest for extended gene delivery experiments.
N. Gangloff, J. Ulbricht, T. Lorson, H. Schlaad, R. Luxenhofer Peptoids and Polypeptoids at the Frontier of Supra- and Macromolecular Engineering Chemical Reviews 2016, 116, 1753 DOI: 10.1021/acs.chemrev.5b00201Abstract
C. Secker, A. Völkel, B. Tiersch, J.Koetz, H. Schlaad Thermo-Induced Aggregation and Crystallization of Block Copolypeptoids in Water Macromolecules 2016, 49, 979 DOI: 10.1021/acs.macromol.5b02481AbstractBlock copolypeptoids comprising a thermosensitive, crystallizable poly(N-(n-propyl)glycine) block and a water-soluble poly(N-methylglycine) block, P70My (y = 23, 42, 76, 153, and 290), were synthesized by ring-opening polymerization of the corresponding N-alkylglycine N-carboxyanhydrides (NCAs) and examined according to their thermo-induced aggregation and crystallization in water by turbidimetry, micro-differential scanning calorimetry (micro-DSC), cryogenic scanning electron microscopy (cryo-SEM), analytical ultracentrifugation (AUC), and static light scattering (SLS). At a temperature above the cloud point temperature, the initially formed micellar aggregates started to crystallize and grow into larger complex assemblies of about 100–500 nm, exhibiting flower-like (P70M23), ellipsoidal (P70M42 and P70M72), or irregular shapes (P70M153 and P70M290).
M. W. Thielke, C. Secker, H. Schlaad, P. Theato Electrospinning of Crystallizable Polypeptoid Fibers Macromolecular Rapid Communications 2016, 37, 100 DOI: 10.1002/marc.201500502AbstractA unique fabrication process of low molar mass, crystalline polypeptoid fibers is described. Thermoresponsive fiber mats are prepared by electrospinning a homogeneous blend of semicrystalline poly(N-(n-propyl) glycine) (PPGly; 4.1 kDa) with high molar mass poly(ethylene oxide) (PEO). Annealing of these fibers at ≈ 100 °C selectively removes the PEO and produces stable crystalline fiber mats of pure PPGly, which are insoluble in aqueous solution but can be redissolved in methanol or ethanol. The formation of water-stable polypeptoid fiber mats is an important step toward their utilization in biomedical applications such as tissue engineering or wound dressing.
P. Wessig, M. Gerngroß, D. Freyse, P. Bruhns, M. Przezdziak, U. Schilde, A. Kelling Molecular Rods Based on Oligo-spiro-thioketals J. Org. Chem. 2016, 81, 1125 DOI: 10.1021/acs.joc.5b02670AbstractWe report on an extension of the previously established concept of oligospiroketal (OSK) rods by replacing a part or all ketal moieties by thioketals leading to oligospirothioketal (OSTK) rods. In this way, some crucial problems arising from the reversible formation of ketals are circumvented. Furthermore, the stability of the rods toward hydrolysis is considerably improved. To successfully implement this concept, we first developed a number of new oligothiol building blocks and improved the synthetic accessibility of known oligothiols, respectively. Another advantage of thioacetals is that terephthalaldehyde (TAA) sleeves, which are too flexible in the case of acetals can be used in OSTK rods. The viability of the OSTK approach was demonstrated by the successful preparation of some OSTK rods with a length of some nanometers.
A.-C. Schöne, K. Richau, K. Kratz, B. Schulz and A. Lendlein Influence of Diurethane Linkers on the Langmuir Layer Behavior of Oligo[(rac-lactide)-co-glycolide]-based Polyesterurethanes Macromol. Rapid Commun. 2016, 36, 1910-1915 DOI: 10.1002/marc.201500316AbstractThree oligo[(rac-lactide)-co-glycolide] based polyesterurethanes (OLGA-PUs) containing different diurethane linkers are investigated by the Langmuir monolayer technique and compared to poly[(rac-lactide)-co-glycolide] (PLGA) to elucidate the influence of the diurethane junction units on hydrophilicity and packing motifs of these polymers at the air-water interface. The presence of diurethane linkers does not manifest itself in the Langmuir layer behavior both in compression and expansion experiments when monomolecular films of OLGA-PUs are spread on the water surface. However, the linker retard the evolution of morphological structures at intermediate compression level under isobaric conditions (with a surface pressure greater than 11 mM/m) compared to the PLGA, independent on the chemical structure of the diurethane moiety. The layer thicknesses of both OLGA-PU and PLGA films decrease in the high compression state with decreasing surface pressure, as deduced from ellipsometric data. All films must be described with the effective medium approximation as water swollen layers.
M. Klaper, P. Wessig and T. Linker Base catalysed decomposition of anthracene endoperoxide Chem. Commun. 2016, 52, 1210-1213 DOI: 10.1039/C5CC08606JAbstractCatalytic amounts of a weak base are sufficient to induce the decomposition of anthracene endoperoxides to anthraquinone. The mechanism has been elucidated by isolation of intermediates in combination with DFT calculations. The whole process is suitable for the convenient generation of hydrogen peroxide under very mild conditions.
A. Prestel, H. M. Möller Spatio-temporal control of cellular uptake achieved by photoswitchable cell-penetrating peptides Chem. Commun. 2016, 52, 701-704 DOI: 10.1039/C5CC06848GAbstractThe selective uptake of compounds into specific cells of interest is a major objective in cell biology and drug delivery. By incorporation of a novel, thermostable azobenzene moiety we generated peptides that can be switched optically between an inactive state and an active, cell-penetrating state with excellent spatio-temporal control.
S. S. Mondal, H.-J. Holdt Breaking Down Chemical Weapons by Metal-Organic Frameworks Angew. Chem. Int. Ed. 2016, 55, 42 - 44 DOI: 10.1002/anie.201508407AbstractFiltration schemes and self-detoxifying protective fabrics based on the ZrIV-containing metal—organic frameworks (MOFs) MOF-808 and UiO-66 doped with LiOtBu have been developed that capture and hydrolytically detoxify simulants of nerve agents and mustard gas. Both MOFs function as highly catalytic elements in these applications.
S. Vogel, J. Rackwitz, R. Schürman, J. Prinz, A. R. Milosavljević, M. Réfrégiers, A. Giuliani, and I. Bald Using DNA Origami Nanostructures To Determine Absolute Cross Sections for UV Photon-Induced DNA Strand Breakage J. Phys. Chem. Lett. 2015, 6, 4589 DOI: 10.1021/acs.jpclett.5b02238AbstractWe have characterized ultraviolet (UV) photon-induced DNA strand break processes by determination of absolute cross sections for photoabsorption and for sequence-specific DNA single strand breakage induced by photons in an energy range from 6.50 to 8.94 eV. These represent the lowest-energy photons able to induce DNA strand breaks. Oligonucleotide targets are immobilized on a UV transparent substrate in controlled quantities through attachment to DNA origami templates. Photon-induced dissociation of single DNA strands is visualized and quantified using atomic force microscopy. The obtained quantum yields for strand breakage vary between 0.06 and 0.5, indicating highly efficient DNA strand breakage by UV photons, which is clearly dependent on the photon energy. Above the ionization threshold strand breakage becomes clearly the dominant form of DNA radiation damage, which is then also dependent on the nucleotide sequence.
M. Klaper, T. Linker Intramolecular Transfer of Singlet Oxygen J. Am. Chem. Soc. 2015, 137, 13744­ DOI: 10.1021/jacs.5b07848AbstractThe intramolecular transfer of energy (FRET) and electrons (Dexter) are of great interest for the scientific community and well understood. On the other hand, the intramolecular transfer of singlet oxygen (1O2), a reactive and short-lived oxygen species, has been hitherto unknown. This process would be very interesting, since 1O2 plays an important role in the photodynamic therapy (PDT). Herein, we present the first successful intramolecular transfer of 1O2 from a donor to an acceptor. Furthermore, we found a dependence of conformation and temperature comparable with FRET. We provide several pieces of evidence for the intramolecular character of this transfer, including competition experiments. Our studies should be interesting not only from the theoretical and mechanistic point of view, but should offer the basis for the design of new 1O2 donors and applications in PDT.
S. M. Brosnan, H. Schlaad, M. Antonietti Aqueous Self-Assembly of Purely Hydrophilic Block Copolymers into Giant Vesicles Angew. Chem. Int. Ed. 2015, 54, 9715 DOI: 10.1002/anie.201502100AbstractSelf-assembly of macromolecules is fundamental to life itself, and historically, these systems have been primitively mimicked by the development of amphiphilic systems, driven by the hydrophobic effect. Herein, we demonstrate that self-assembly of purely hydrophilic systems can be readily achieved with similar ease and success. We have synthesized double hydrophilic block copolymers from polysaccharides and poly(ethylene oxide) or poly(sarcosine) to yield high molar mass diblock copolymers through oxime chemistry. These hydrophilic materials can easily assemble into nano sized (< 500 nm) and microsized (> 5 μm) polymeric vesicles depending on concentration and diblock composition. Because of the solely hydrophilic nature of these materials, we expect them to be extraordinarily water permeable systems that would be well suited for use as cellular mimics.
T. Schwarze, J. Riemer, S. Eidner, H.-J. Holdt A Highly K+-Selective Two-Photon Fluorescent Probe Chemistry, A European Journal 2015, 21, 11306 DOI: 10.1002/chem.201501473AbstractA highly K+-selective two-photon fluorescent probe for the in vitro monitoring of physiological K+ levels in the range of 1-100 mM is reported. The two-photon excited fluorescence (TPEF) probe shows a fluorescence enhancement (FE) by a factor of about three in the presence of 160 mM K+, independently of one-photon (OP, 430 nm) or two-photon (TP, 860 nm) excitation and comparable K+-induced FEs in the presence of competitive Na+ ions. The estimated dissociation constant (Kd) values in Na+-free solutions (KdOP=(28 ± 5) nM and KdTP=(46 ± 25) nM) reflecting the high K+ ⁄ Na+ selectivity of the fluorescent probe. The TP absorption cross-section (σ2PA) of the TPEF probe +160 mM K+ is 26 GM at 860 nm. Therefore, the TPEF probe is a suitable tool for the in vitro determination of K+.
C. D. Vacogne, S. M. Brosnan, A. Masic, H. Schlaad Fibrillar gels via the self-assembly of poly(L-glutamate)-based statistical copolymers Polym. Chem. 2015, 6, 5040 DOI: 10.1039/C5PY00491HAbstractPolypeptides having secondary structures often undergo self-assembly which can extend over multiple length scales. Poly(γ-benzyl-L-glutamate) (PBLG), for example, folds into α-helices and forms physical organogels, whereas poly(L-glutamic acid) (PLGA at acidic pH) or poly(L-glutamate) (PLG at neutral/basic pH) do not form hydrogels. We explored the gelation of modified PBLG and investigated the deprotection of the carboxylic acid moieties in such gels to yield unique hydrogels. This was accomplished through photo-crosslinking gelation of poly(γ-benzyl-L-glutamate-co-allylglycine) statistical copolymers in toluene, tetrahydrofuran, and 1,4-dioxane. Unlike most polymer-based chemical gels, our gels were prepared from dilute solutions (<20 g L-1, i.e., <2% w⁄v) of low molar mass polymers. Despite such low concentrations and molar masses, our dioxane gels showed high mechanical stability and little shrinkage; remarkably, they also exhibited a porous fibrillar network. Deprotection of the carboxylic acid moieties in dioxane gels yielded pH responsive and highly absorbent PLGA/PLG-based hydrogels (swelling ratio of up to 87), while preserving the network structure, which is an unprecedented feature in the context of crosslinked PLGA gels. These outstanding properties are highly attractive for biomedical materials.
D. Kedracki, S. K. Filippov, N. Gour, H. Schlaad, C. Nardin Formation of DNA-Copolymer Fibrils Through an Amyloid-Like Nucleation Polymerization Mechanism Macromolecular Rapid Communications 2015, 36, 768 DOI: 10.1002/marc.201400728AbstractConjugation of a hydrophobic poly(2-oxazoline) bearing tertiary amide groups along its backbone with a short single stranded nucleotide sequence results in an amphiphilic comb/graft copolymer, which organizes in fibrils upon direct dissolution in water. Supported by circular dichroism, atomic force microscopy, transmission electron microscopy, and scattering data, fibrils are formed through inter- and intramolecular hydrogen bonding between hydrogen accepting amide groups along the polymer backbone and hydrogen donating nucleic acid grafts leading to the formation of hollow tubes.
P. Wessig, D. Budach, A. F. Thünemann Dendrimers with Oligospiroketal (OSK) Building Blocks: Synthesis and Properties Chem. Eur. J. 2015, 21, 10466-10471 DOI: 10.1002/chem.201501386AbstractThe development of novel dendrimers containing oligospiroketal (OSK) rods as building blocks is described. The linkage between the core unit (CU), branching units (BU), and OSK rods relies on the CuAAC reaction between terminal alkynes and azides. Two different strategies of dendrimer synthesis were investigated and it was found that the convergent approach is clearly superior to the divergent one. SAXS measurements and MD simulations indicate that the obtained dendrimer features a globular structure with very low density. Obviously, the OSK rods stabilize a rather loose mass-fractal structure.
M. Klaper, T. Linker New Singlet Oxygen Donors Based on Naphthalenes: Synthesis, Physical Chemical Data, and Improved Stability Chem. Eur. J. 2015, 21, 8569–8577 DOI: 10.1002/chem.201500146AbstractLive longer! More than 25 new peroxides based on differently substituted naphthalenes have been synthesized. Their stability, both thermodynamic and kinetic, was determined through experiments in combination with density functional calculations (see figure). They are sufficiently stable at room temperature but release singlet oxygen efficiently, which might be interesting for applications in photodynamic therapy (PDT).
S. Umbreen, T. Linker Simple Synthesis of Conformationally Fixed Glycosamine Analogues by Beckmann Rearrangement at the Carbohydrate Ring Chem. Eur. J. 2015, 21, 7340­-7344 DOI: 10.1002/chem.201406546AbstractConformationally fixed carbohydrate analogues are promising small-molecule inhibitors for hydrolases like O-GlcNAcase (OGA); however, their synthesis usually requires many steps. Herein we describe cycloadditions of dichloroketene to various glycals and subsequent Beckmann rearrangements, which offer an easy and stereoselective entry to glycosamine derivatives in good yields. The reactions are applicable for hexoses, pentoses, and disaccharides, and transformations to the corresponding imidates proceed smoothly. First biological tests reveal that such imidates indeed inhibit human OGA
B. Schmidt, N. Elizarov, U. Schilde, A. Kelling Dual Role of Acetanilides: Traceless Removal of a Directing Group through Deacetylation/Diazotation and Palladium-Catalyzed C–C-Coupling Reactions J. Org. Chem. 2015, 80, 4223-4234 DOI: 10.1021/acs.joc.5b00272AbstractPalladium(II) acetate is the precatalyst for Pd2+-catalyzed oxidative C–H-activation reactions and for Pd0-catalyzed coupling and cross-coupling reactions. Both types of transformations can be used for regioselective arene functionalization, with the acetamide group playing a dual role, first as a catalyst directing group and then as a leaving group precursor.
S.S. Mondal, K. Behrens, P. R. Matthes, F. Schönfeld, J. Nitsch, A. Steffen, P.-A. Primus, M. U. Kumke, K. Müller-Buschbaum, H.-J. Holdt White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ J. Mater. Chem. C 2015, 3, 4623 DOI: 10.1039/C4TC02919DAbstractCo-doping of the MOF 3[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a–d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+.
P. Wessig, R. Merkel, P. Müller Articulated rods – a novel class of molecular rods based on oligospiroketals (OSK) Beilstein J. Org. Chem. 2015, 11, 74-84 DOI: 10.3762%2Fbjoc.11.11AbstractWe developed a new type of molecular rods consisting of two (or more) rigid units linked by a flexible joint. Consequently we called these constructs articulated rods (ARs). The syntheses of ARs were carried out by a flexible and modular approach providing access to a number of compounds with various functionalizations in terminal positions. First applications were presented with pyrene, cinnamoyl and anthracenyl labelled ARs.
L. Olejko, P. J. Cywinski, I. Bald Ion-Selective Formation of a Guanine Quadruplex on DNA Origami Structures Angew. Chem. Int. Ed. 2015, 54, 673-677 DOI: 10.1002/anie.201409278AbstractDNA origami nanostructures are a versatile tool that can be used to arrange functionalities with high local control to study molecular processes at a single-molecule level. Here, we demonstrate that DNA origami substrates can be used to suppress the formation of specific guanine (G) quadruplex structures from telomeric DNA. The folding of telomeres into G-quadruplex structures in the presence of monovalent cations (e.g. Na+ and K+) is currently used for the detection of K+ ions, however, with insufficient selectivity towards Na+. By means of FRET between two suitable dyes attached to the 3'- and 5’-ends of telomeric DNA we demonstrate that the formation of G- quadruplexes on DNA origami templates in the presence of sodium ions is suppressed due to steric hindrance. Hence, telomeric DNA attached to DNA origami structures represents a highly sensitive and selective detection tool for potassium ions even in the presence of high concentrations of sodium ions.
I. Haralampiev, M. Mertens, R. Schwarzer, A. Herrmann, R. Volkmer, P. Wessig, P. Müller Recruitment of SH-Containing Peptides to Lipid and Biological Membranes through the Use of a Palmitic Acid Functionalized with a Maleimide Group Angew. Chem. 2015, 127, 328-332 DOI: 10.1002/ange.201408089AbstractThis study presents a novel and easily applicable approach to recruit sulfhydryl-containing biomolecules to membranes by using a palmitic acid which is functionalized with a maleimide group. Notably, this strategy can also be employed with preformed (biological) membranes. The applicability of the assay is demonstrated by characterizing the binding of a Rhodamine-labeled peptide to lipid and cellular membranes using methods of fluorescence spectroscopy, lifetime measurement, and microscopy. Our approach offers new possibilities for preparing biologically active liposomes and manipulating living cells.
D. Kedracki, M. Chekini, P. Maroni, H. Schlaad, C. Nardin Synthesis and Self-Assembly of a DNA Molecular Brush Biomacromolecules 2014, 15, 3375 DOI: 10.1021/bm5008713AbstractWe report herein on the polymer-crystallization-assisted thiol-ene photosynthesis of an amphiphilic comb/graft DNA copolymer, or molecular brush, composed of a hydrophobic poly(2-oxazoline) backbone and hydrophilic short single-stranded nucleic acid grafts. Coupling efficiencies are above 60% and thus higher as compared with the straight solid-phase-supported synthesis of amphiphilic DNA block copolymers. The DNA molecular brushes self-assemble into sub-micron-sized spherical structures in water as evidenced by light scattering as well as atomic force and electron microscopy imaging. The nucleotide sequences remain functional, as assessed by UV and fluorescence spectroscopy subsequent to isoindol synthesis at the surface of the structures. The determination of a vesicular morphology is supported by encapsulation and subsequent spectroscopy monitoring of the release of a water-soluble dye and spectroscopic quantification of the hybridization efficiency (30% in average) of the functional nucleic acid strands engaged in structure formation: about one-half of the nucleotide sequences are available for hybridization, whereas the other half are hindered within the self-assembled structure. Because speciation between complementary and non complementary sequences in the medium could be ascertained by confocal laser scanning microscopy, the stable self-assembled molecular brushes demonstrate the potential for sensing applications.
R. Göbel, P. Hesemann, A. Friedrich, R. Rothe, H. Schlaad, A. Taubert Modular Thiol–Ene Chemistry Approach towards Mesoporous Silica Monoliths with Organically Modified Pore Walls Chemistry, A European Journal 2014, 20, 17579 DOI: 10.1002/chem.201403982AbstractThe surface modification of mesoporous silica monoliths through thiol–ene chemistry is reported. First, mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol–gel hydrolysis–polycondensation reaction from tetramethyl orthosilicate (TMOS) and vinyltriethoxysilane, allyltriethoxysilane, and (3-mercaptopropyl)trimethoxysilane, respectively. By variation of the molar ratio of the comonomers TMOS and functional silane, mesoporous silica objects containing different amounts of vinyl, allyl, and thiol groups were obtained. These intermediates can subsequently be derivatized through radical photoaddition reactions either with a thiol or an olefin, depending on the initial pore wall functionality, to yield silica monoliths with different pore-wall chemistries. Nitrogen sorption, small-angle X-ray scattering, solid-state NMR spectroscopy, elemental analysis, thermogravimetric analysis, and redox titration demonstrate that the synthetic pathway influences the morphology and pore characteristics of the resulting monoliths and also plays a significant role in the efficiency of functionalization. Moreover, the different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore-wall functionalization. This report demonstrates that thiol–ene photoaddition reactions are a versatile platform for the generation of a large variety of organically modified silica monoliths with different pore surfaces.
U. Tritschler, I. Zlotnikov, P. Keckeis, H. Schlaad, H. Cölfen Optical Properties of Self-Organized Gold Nanorod–Polymer Hybrid Films Langmuir 2014, 30, 13781 DOI: 10.1021/la503507uAbstractHigh fractions of gold nanorods were locally aligned by means of a polymeric liquid crystalline phase. The gold nanorods constituting >80 wt % of the thin organic–inorganic composite films form a network with side-by-side and end-to-end combinations. Organization into these network structures was induced by shearing gold nanorod–LC polymer dispersions via spin-coating. The LC polymer is a polyoxazoline functionalized with pendent cholesteryl and carboxyl side groups enabling the polymer to bind to the CTAB stabilizer layer of the gold nanorods via electrostatic interactions, thus forming the glue between organic and inorganic components, and to form a chiral nematic lyotropic phase. The self-assembled locally oriented gold nanorod structuring enables control over collective optical properties due to plasmon resonance coupling, reminiscent of enhanced optical properties of natural biomaterials.
F. N. Führer, H. Schlaad ADMET Polymerization of Amino-Acid-Based Diene Macromolecular Chemistry and Physics 2014, 215, 2268 DOI: 10.1002/macp.201400166Abstract
U. Tritschler, F. Beck, H. Schlaad, H. Cölfen Electrochromic properties of self-organized multifunctional V2O5–polymer hybrid films Journal of Materials Chemistry C 2014, 3, 950 DOI: 10.1039/C4TC02138JAbstractBio-inspired V2O5–polymer hybrid films were prepared following a one-step self-organization procedure based on liquid crystal formation of organic and inorganic components. These materials were previously reported to exhibit advantageous mechanical properties, comparable to biomaterials, such as human bone and dentin. Here, we show that these hybrid films prepared via a fast and simple synthesis procedure have an additional function as an electrochromic material, exhibiting a long-term cycle stability under alternating potentials. The structures were found to remain intact without visible changes after more than hundred switching cycles and storing the devices for several weeks. Consequently, this multifunctional V2O5–polymer hybrid system shows great promise for various technical applications.
I. Bald, A. Keller Molecular Processes Studied at a Single-Molecule Level Using DNA Origami Nanostructures and Atomic Force Microscopy Molecules 2014, 19, 13803 DOI: 10.3390/molecules190913803AbstractDNA origami nanostructures allow for the arrangement of different functionalities such as proteins, specific DNA structures, nanoparticles, and various chemical modifications with unprecedented precision. The arranged functional entities can be visualized by atomic force microscopy (AFM) which enables the study of molecular processes at a single-molecular level. Examples comprise the investigation of chemical reactions, electron-induced bond breaking, enzymatic binding and cleavage events, and conformational transitions in DNA. In this paper, we provide an overview of the advances achieved in the field of single-molecule investigations by applying atomic force microscopy to functionalized DNA origami substrates.
T. Schwarze,H. Müller, S. Ast, D. Steinbrück, S. Eidner, F. Geißler, M. U. Kumke, H.-J. Holdt Fluorescence lifetime-based sensing of sodium by an optode Chem. Commun. 2014, 50, 14167 DOI: 10.1039/C4CC06112HAbstractWe report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1–10 mM by measuring reversible fluorescence decay time changes.
E. Unuabonaha, A. O. Adedapob, C. O. Nnamdia, A. Adewuyia, M. O. Omorogiea, K. O. Adebowaleb, B. I. Olu-Owolabib, A. E. Ofomajac, A. Taubert Successful scale-up performance of a novel papaya-clay combo adsorbent: up-flow adsorption of a basic dye Desalination & Water Treatment 2014DOI: 10.1080/19443994.2014.944572AbstractA novel low-cost papaya-clay combo adsorbent, hybrid clay (HYCA), was prepared from a combination of Carica papaya seeds and Kaolinite clay. HYCA breakthrough adsorption capacity was 35.46 mg/g for the adsorption of methylene blue (MB) dye in a pilot-scale fixed-bed reactor. In ca. 20 min, regeneration of MB dye-loaded HYCA reached at least 90% each cycle for five regeneration cycles. However, above 40°C, the HYCA adsorbent lost more than 50% of its adsorption capacity after five regeneration cycles. The AdDesignSTM software was used to successfully predict the breakthrough curve and scale-up performance of MB dye adsorption onto the HYCA adsorbent. The pore and surface diffusion model (PSDM) described experimental data better than the constant pattern homogeneous surface diffusion model. From economic assessment using the PSDM, the AdDesignSTM software predicted that 1 kg of HYCA can effectively treat 1.45 m3 (0.29 m3 each cycle) of water containing 1 mg/L of MB dye (with a treatment objective of 50 μg/L MB dye) in effluent solution in 9 h 35 min with run time of ca. 15 h in a day including time for five regeneration cycles It was further predicted that the presence of other organic pollutants in low concentrations reduce the breakthrough adsorption capacity of HYCA by 10%. Finally, the cost of preparing 1 kg of HYCA adsorbent was calculated to ≈$6.31 vs. ≈$31.25/kg for medium quality commercial activated carbon.
E. Unuabonah, A. Taubert Clay-Polymer Nanocomposites: Adsorbents of the Future for Water Treatment Appl. Clay Sci. 2014, 99, 83 DOI: 10.1016/j.clay.2014.06.016AbstractToday's world is burdened with the need for potable water even with the numerous water bodies that exist. Among several other techniques, adsorption has become widely used for the removal of inorganic and organic micropollutants from aqueous solution and numerous adsorbents for water treatment have therefore been prepared over the years. A class of adsorbents currently receiving growing attention is the clay–polymer nanocomposite (CPN) adsorbents. CPNs effectively treat water by adsorption and flocculation of both inorganic and organic micropollutants from aqueous solutions. Some of these CPNs – when modified with biocides – also have the ability to efficiently remove microorganisms such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans from water. CPNs are far more easily recovered from aqueous media than neat clay. They also exhibit far better treatment times than either polymer or clay adsorbents. They have higher adsorption capacity and better life cycles compared with clay alone. CPNs therefore show an excellent potential as highly efficient water and waste treatment agents. This article reviews the various CPNs that have been prepared recently and used as adsorbents in the removal of micropollutants (inorganic, organic and biological) from aqueous solutions. A special focus is placed on CPNs that are not only interesting from an academic point of view but also effectively reduce the concentration of micropollutants in water to safe limits and also on new developments bordering on CPN use as water treatment agent that have not yet realized their full potential.
A.Salama, M. Neumann, C. Günter, A. Taubert Ionic liquid-assisted formation of cellulose/calcium phosphate hybrid materials Beilstein J. Nanotechnol. 2014, 5, 1553 DOI: 10.3762/bjnano.5.167AbstractCellulose/calcium phosphate hybrid materials were synthesized via an ionic liquid-assisted route. Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis/differential thermal analysis show that, depending on the reaction conditions, cellulose/hydroxyapatite, cellulose/chlorapatite, or cellulose/monetite composites form. Preliminary studies with MC3T3-E1 pre-osteoblasts show that the cells proliferate on the hybrid materials suggesting that the ionic liquid-based process yields materials that are potentially useful as scaffolds for regenerative therapies.
T. Körzdörfer and J.-L. Brédas Organic Electronic Materials: Recent Advances in the DFT Description of the Ground and Excited States Using Tuned Range-Separated Hybrid Functionals Acc. Chem. Res. 2014DOI: 10.1021/ar500021tAbstractDensity functional theory (DFT) and its time-dependent extension (TD-DFT) are powerful tools enabling the theoretical prediction of the ground- and excited-state properties of organic electronic materials with reasonable accuracy at affordable computational costs. Due to their excellent accuracy-to-numerical-costs ratio, semilocal and global hybrid functionals such as B3LYP have become the workhorse for geometry optimizations and the prediction of vibrational spectra in modern theoretical organic chemistry. Despite the overwhelming success of these out-of-the-box functionals for such applications, the computational treatment of electronic and structural properties that are of particular interest in organic electronic materials sometimes reveals severe and qualitative failures of such functionals. Important examples include the overestimation of conjugation, torsional barriers, and electronic coupling as well as the underestimation of bond-length alternations or excited-state energies in low-band-gap polymers. In this Account, we highlight how these failures can be traced back to the delocalization error inherent to semilocal and global hybrid functionals, which leads to the spurious delocalization of electron densities and an overestimation of conjugation. The delocalization error for systems and functionals of interest can be quantified by allowing for fractional occupation of the highest occupied molecular orbital. It can be minimized by using long-range corrected hybrid functionals and a nonempirical tuning procedure for the range-separation parameter. We then review the benefits and drawbacks of using tuned long-range corrected hybrid functionals for the description of the ground and excited states of π-conjugated systems. In particular, we show that this approach provides for robust and efficient means of characterizing the electronic couplings in organic mixed-valence systems, for the calculation of accurate torsional barriers at the polymer limit, and for the reliable prediction of the optical absorption spectrum of low-band-gap polymers. We also explain why the use of standard, out-of-the-box range-separation parameters is not recommended for the DFT and/or TD-DFT description of the ground and excited states of extended, pi-conjugated systems. Finally, we highlight a severe drawback of tuned range-separated hybrid functionals by discussing the example of the calculation of bond-length alternation in polyacetylene, which leads us to point out the challenges for future developments in this field.
Z.-L. Xie, X. Huang, M.-M. Titirici, and A. Taubert Mesoporous Oligo-layer Graphene Nanoflakes via Ionothermal Carbonization of Fructose and Their Use in Dye Removal RSC Adv. 2014, 4, 37423 DOI: 10.1039/c4ra05146gAbstractThe large-scale green synthesis of graphene-type two-dimensional materials is still challenging. Herein, we describe the ionothermal synthesis of carbon-based composites from fructose in the iron-containing ionic liquid 1-butyl-3-methylimidazolium tetrachloridoferrate(III), [Bmim][FeCl4] serving as solvent, catalyst, and template for product formation. The resulting composites consist of oligo-layer graphite nanoflakes and iron carbide particles. The mesoporosity, strong magnetic moment, and high specific surface area of the composites make them attractive for water purification with facile magnetic separation. Moreover, Fe3C-free graphite can be obtained via acid etching, providing access to fairly large amounts of graphite material. The current approach is versatile and scalable, and thus opens the door to ionothermal synthesis towards the larger-scale synthesis of materials that are, although not made via a sustainable process, useful for water treatment such as the removal of organic molecules.
P. Wessig, M. Gerngroß, S. Pape, P. Bruhns, J. Weber Novel porous materials based on oligospiroketals (OSK) RSC Adv. 2014, 4, 31123-31129 DOI: 10.1039/c4ra04437aAbstractNew porous materials based on covalently connected monomers are presented. The key step of the synthesis is an acetalisation reaction. In previous years we used acetalisation reactions extensively to build up various molecular rods. Based on this approach, investigations towards porous polymeric materials were conducted by us. Here we wish to present the results of these studies in the synthesis of 1D polyacetals and porous 3D polyacetals. By scrambling experiments with 1D acetals we could prove that exchange reactions occur between different building blocks (evidenced by MALDI-TOF mass spectrometry). Based on these results we synthesized porous 3D polyacetals under the same mild conditions.
Z.-L. Xie, X. Huang, A. Taubert DyeIonogels: Proton-Responsive Ionogels Based on a Dye-Ionic Liquid Exhibiting Reversible Color Change Adv. Func. Mat. 2014, 24, 2837 DOI: 10.1002/adfm.201303016AbstractTransparent, ion-conducting, and flexible ionogels based on the room temperature ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide [Bmim][N(Tf)2], the dye-IL (DIL) 1-butyl-3-methylimidazolium methyl orange [Bmim][MO], and poly(methylmethacrylate) (PMMA) are prepared. Upon IL incorporation the thermal stability of the PMMA matrix significantly increases from 220 to 280 °C. The ionogels have a relatively high ionic conductivity of 10−4 S cm−1 at 373 K. Most importantly, the ionogels exhibit a strong and reversible color change when exposed to aqueous or organic solutions containing protons or hydroxide ions. The resulting material is thus a prototype of soft multifunctional matter featuring ionic conductivity, easy processability, response to changes in the environment, and a strong readout signal, the color change, that could be used in optical data storage or environmental sensing.
S.S. Mondal, A. Bhunia, A, Kelling, U. Schilde, C. Janiak, H.-J. Holdt Giant Zn14 Molecular Building Block in Hydrogen-Bonded Network with Permanent Porosity for Gas Uptake J. Am. Chem. Soc. 2014, 136, 44 DOI: 10.1021/ja410595qAbstractIn situ imidazolate-4,5-diamide-2-olate linker generation leads to the formation of a [Zn14(L2)12(O)-(OH)2(H2O)4] molecular building block (MBB) with a Zn6 octahedron inscribed in a Zn8 cube. The MBBs connect by amide−amide hydrogen bonds to a 3D robust supramolecular network which can be activated for N2, CO2, CH4, and H2 gas sorption.
J. Prinz, B. Schreiber, L. Olejko, J. Oertel, J. Rackwitz, A. Keller, I. Bald DNA Origami Substrates for Highly Sensitive Surface-Enhanced Raman Scattering J. Phys. Chem. Lett. 2013, 4, 4140-4145 DOI: 10.1021/jz402076bAbstractDNA nanotechnology holds great promise for the fabrication of novel plasmonic nanostructures and the potential to carry out single-molecule measurements using optical spectroscopy. Here, we demonstrate for the first time that DNA origami nanostructures can be exploited as substrates for surface-enhanced Raman scattering (SERS). Gold nanoparticles (AuNPs) have been arranged into dimers to create intense Raman scattering hot spots in the interparticle gaps. AuNPs (15 nm) covered with TAMRA-modified DNA have been placed at a nominal distance of 25 nm to demonstrate the formation of Raman hot spots. To control the plasmonic coupling between the nanoparticles and thus the field enhancement in the hot spot, the size of AuNPs has been varied from 5 to 28 nm by electroless Au deposition. By the precise positioning of a specific number of TAMRA molecules in these hot spots, SERS with the highest sensitivity down to the few-molecule level is obtained.
S. Ast, T. Schwarze, H. Müller, A. Sukhanov, S. Michaelis, J. Wegener, O. S. Wolfbeis, T. Körzdörfer, A. Dürkop, H.-J. Holdt A Highly K+-Selective Phenylaza-[18]crown-6-Lariat-Ether-Based Fluoroionophore and Its Application in the Sensing of K+ Ions with an Optical Sensor Film and in Cells Chem. Eur. J. 2013, 19, 14911 DOI: 10.1002/chem.201302350AbstractHerein, we report the synthesis of two phenylaza-[18]crown-6 lariat ethers with a coumarin fluorophore (1 and 2) and we reveal that compound 1 is an excellent probe for K+ ions under simulated physiological conditions. The presence of a 2-methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat-free phenylaza-[18]crown-6 ether analogues. Probe 1 shows a high K+/Na+ selectivity and a 2.5-fold fluorescence enhancement was observed in the presence of 100 mm K+ ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8 % per 1 mm K+ within the range 1–10 mm K+. The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K+ ions on both the extracellular and intracellular levels.
B. Schmidt, O. Kunz Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C2-symmetric building block: a strategy for the synthesis of decanolide natural products Beilstein J. Org. Chem. 2013, 9, 2544 DOI: 10.3762/bjoc.9.289AbstractStarting from the conveniently available ex-chiral pool building block (R,R)-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i) a site-selective cross metathesis, (ii) a highly diastereoselective extended tethered RCM to furnish a (Z,E)-configured dienyl carboxylic acid and (iii) a Ru-lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.
A. Keller, J. Kopyra, K. V Gothelf, I. Bald Electron-induced damage of biotin studied in the gas phase and in the condensed phase at a single-molecule level New J. Phys. 2013, 15, 083045 DOI: 10.1088/1367-2630/15/8/083045AbstractBiotin is an essential vitamin that is, on the one hand, relevant for the metabolism, gene expression and in the cellular response to DNA damage and, on the other hand, finds numerous applications in biotechnology. The functionality of biotin is due to two particular sub-structures, the ring structure and the side chain with carboxyl group. The heterocyclic ring structure results in the capability of biotin to form strong intermolecular hydrogen and van der Waals bonds with proteins such as streptavidin, whereas the carboxyl group can be employed to covalently bind biotin to other complex molecules. Dissociative electron attachment (DEA) to biotin results in a decomposition of the ring structure and the carboxyl group, respectively, within resonant features in the energy range 0–12 eV, thereby preventing the capability of biotin for intermolecular binding and covalent coupling to other molecules. Specifically, the fragment anions (M–H)−, (M–O)−, C3N2O−, CH2O2− , OCN−, CN−, OH− and O− are observed, and exemplarily the DEA cross section of OCN− formation is determined to be 3×10−19 cm2. To study the response of biotin to electrons within a complex condensed environment, we use the DNA origami technique and determine a dissociation yield of (1.1±0.2)×10−14cm2 at 18 eV electron energy, which represents the most relevant energy for biomolecular damage induced by secondary electrons. The present results thus have important implications for the use of biotin as a label in radiation experiments.
R. Wawrzinek, J. Ziomkowska, J. Heuveling, M. Mertens, A. Herrmann, E. Schneider, P. Wessig DBD Dyes as Fluorescence Lifetime Probes to Study Conformational Changes in Proteins Chemistry Eur. J. 2013, 19, 17349-17357 DOI: 10.1002/chem.201302368AbstractPreviously described [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD)-based fluorophores have been used as highly sensitive fluorescence lifetime probes reporting on their microenvironmental polarity. Now, a new generation of DBD dyes has been developed. Still being sensitive to the polarity, contrary to former DBD dyes, they have extraordinary spectroscopic properties, even in aqueous surroundings. They are characterized by long fluorescence lifetimes (10-20 ns), large Stokes shifts (~100 nm), high photostability and high quantum yields (>0.56). Here, spectroscopic properties and the synthesis of functionalized derivates to label biological targets are described. Furthermore thio-reactive maleimido derivates of both DBD generations show strong intramolecular fluorescence quenching. This mechanism has been investigated and found to undergo a photo electron transfer (PET). Once reacted with a thiol group, this fluorescence quenching is prevented, indicating successful bonding. Sensitive to their environmental polarity, these compounds were used as powerful fluorescence lifetime probes to investigate conformational changes in the maltose ATP-binding cassette transporter via fluorescence lifetime spectroscopy. The differing tendencies of fluorescence lifetime change for both DBD dye generations promote their combination as a powerful toolkit to study microenvironments in proteins.
M. Klaper, T. Linker Evidence for an Oxygen Anthracene Sandwich Complex Angew. Chem. Int. Ed. 2013, 52, 11896 DOI: 10.1002/anie.201304768AbstractOxygen sticks in between acenes: The rate of the photooxygenation of bis(anthryl)alkanes with singlet oxygen shows a maximum for a defined chain length (n=4). In combination with calculations, a bathochromic shift of the UV/Vis absorption for only one endoperoxide and a CT absorption band, this gives considerable evidence for an oxygen anthracene sandwich complex.
A. Taubert, J. F. Mano, J. C. Rodriguez-Cabello Biomaterials in Science Wiley-VCH 2013, 0 DOI: AbstractThe book provides an overview of the highly interdisciplinary field of surface science in the context of biological and biomedical applications. The covered topics range from micro- and nanostructuring for imparting functionality in a top-down manner to the bottom-up fabrication of gradient surfaces by self-assembly, from interfaces between biomaterials and living matter to smart, stimuli-responsive surfaces, and from cell and surface mechanics to the elucidation of cell-chip interactions in biomedical devices.
B. Schmidt, M. Riemer, M. Karras 2,2'-Biphenols via protecting group free thermal or microwave accelerated Suzuki-Miyaura coupling in water J. Org. Chem. 2013, 78, 0 DOI: 10.1021/jo401398nAbstract2,2'-Biphenols are ubiquitious in nature. In this publication, a convenient protocol for their synthesis is described which uses a Suzuki-Miyaura cross coupling in water, catalyzed by Palladium on charcoal. No protecting groups are required, and less reactive aryl bromides undergo the cross coupling under microwave conditions.
B. Schmidt, O. Kunz Stereoselective synthesis of dienyl phosphonates via extended tethered ring-closing metathesis Org. Lett. 2013, 15, 0 DOI: 10.1021/ol4020078AbstractZ,E-configured dienylphosphonates were synthesized through a sequence of ring closing metathesis and base-induced ring opening with very high diastereoselectivity. The protocol is operationally simple and makes products accessible which are potentially useful for the synthesis of various phosphorus containing mimics of biomolecules or as nucleophiles for olefination reactions.
S. S. Mondal, A. Bhunia, I. A. Baburin, C. Jäger, A. Kelling, U. Schilde, G. Seifert, C. Janiak, H.-J. Holdt Gate Effects in a Hexagonal Zinc-Imidazolate-4-amide-5-imidate Framework with Flexible Methoxy Substituent and CO2 Selectivity Chem. Comm. 2013, 49, 7599 DOI: 10.1039/C3CC42156BAbstractA new imidazolate-4-amide-5-imidate based MOF, IFP-7 is generated, having flexible methoxy groups, which act as molecular gates for guest molecules. This allows highly selective CO2 sorption over N2 and CH4 gases.
G. Füchsel, J. C. Tremblay, T. Klamroth, P. Saalfrank Quantum dynamical simulations of the femtosecond laser induced ultrafast desorption of H2 and D2 from Ru(0001) Chem. Phys. Chem. 2013, 14, 1471 DOI: 10.1002/cphc.201200940 AbstractWe investigate the recombinative desorption of hydrogen and deuterium from a Ru(0001) surface initiated by femtosecond laser pulses. We adopt a quantum mechanical two-state model including three molecular degrees of freedom to describe the dynamics within the desorption induced by electronic transition (DIET) limit. The energy distributions as well as the state-resolved and ensemble properties of the desorbed molecules are analyzed in detail by using the time-energy method. Our results shed light on the experimentally observed 1) large isotopic effects regarding desorption yields and translational energies and 2) the nonequal energy partitioning into internal and translational modes. In particular, it is shown that a single temperature is sufficient to characterize the energy distributions for all degrees of freedom. Further, we confirm that quantization effects play an important role in the determination of the energy partitioning.
K. Bleek, A. Taubert New Developments in Polymer-controlled, Bio-inspired Calcium Phosphate Mineralization from Aqueous Solution Acta Biomater. 2013, 9, 6283 DOI: 10.1016/j.actbio.2012.12.027AbstractThe polymer-controlled and bioinspired precipitation of inorganic minerals from aqueous solution at near-ambient or physiological conditions avoiding high temperatures or organic solvents is a key research area in materials science. Polymer-controlled mineralization has been studied as a model for biomineralization and for the synthesis of (bioinspired and biocompatible) hybrid materials for a virtually unlimited number of applications. Calcium phosphate mineralization is of particular interest for bone and dental repair. Numerous studies have therefore addressed the mineralization of calcium phosphate using a wide variety of low- and high-molecular-weight additives. In spite of the growing interest and increasing number of experimental and theoretical data, the mechanisms of polymer-controlled calcium phosphate mineralization are not entirely clear to date, although the field has made significant progress in the last years. A set of elegant experiments and calculations has shed light on some details of mineral formation, but it is currently not possible to preprogram a mineralization reaction to yield a desired product for a specific application. The current article therefore summarizes and discusses the influence of (macro)molecular entities such as polymers, peptides, proteins and gels on biomimetic calcium phosphate mineralization from aqueous solution. It focuses on strategies to tune the kinetics, morphologies, final dimensions and crystal phases of calcium phosphate, as well as on mechanistic considerations.
P. Wessig, A. Matthes, U. Schilde, A. Kelling Asymmetric Synthesis of (1,5)Naphthalenophanes by Dehydro-Diels-Alder Reaction Eur. J. Org. Chem. 2013, 2132 DOI: 10.1002/ejoc.201201594AbstractAn asymmetric variant of the dehydro-Diels–Alder (DDA) reaction has been developed and applied in the atropselective synthesis of various (1,5)naphthalenophanes. Whereas the suitability of the photochemically induced DDA (PDDA) was limited, the thermally induced DDA provided the desired product, depending on the chiral auxiliary used and the length of the linker, with nearly perfect stereoselectivity. Furthermore, the mechanism of the DDA was investigated by means of DFT calculations, and a stepwise mechanism involving 1,4-biradicals was suggested.
K. Lemke, C. Prietzel, J. Koetz Fluorescent gold clusters synthesized in a poly(ethyleneimine) modified reverse microemulsion J. Coll. Interf. Sci. 2013, 394, 141 DOI: 10.1016/j.jcis.2012.11.057AbstractThis paper is focused on the formation of gold clusters in a tailor-made polyelectrolyte-modified reverse microemulsion using poly(ethyleneimine) (PEI) as a cationic polyelectrolyte. PEI incorporated into a ternary w/o microemulsion consisting of water/heptanol/zwitterionic surfactant 3-(N,N-dimethyl-dodecylammonio)-propanesulfonate (SB) acts as a reducing and stabilizing agent and shows an additional template effect. The nanoparticle synthesis is performed by a simple mixing of two microemulsions, one containing the PEI and the other one containing the gold chloride precursor. UV-vis measurements in the microemulsion show two pronounced absorption maxima, one at 360 nm and the other one at 520 nm, indicating two particle fractions. The absorption maximum at 360 nm in combination to the unique fluorescence properties indicate the formation of gold clusters. After a complete solvent evaporation the redispersed nanoparticles have been characterized by using UV-vis and fluorescence spectroscopy, in combination to dynamic light scattering and transmission electron microscopy (TEM). In addition to the gold nanoparticle fraction (>5 nm) the fluorescent gold cluster fraction (<2 nm) can be redispersed without particle aggregation. By means of asymmetric flow field flow fractionation (AF-FFF) two different cluster fractions with particle diameter (<2 nm) can be identified.
S. Ast, T. Fischer, Holger Müller, W. Mickler, M. Schwichtenberg, K. Rurack, H.-J. Holdt Integration of the 1,2,3-Triazole "Click" Motif as a Potent Signalling Element in Metal Ion Responsive Fluorescent Probes Chem. Eur. J. 2013, 19, 2990 DOI: 10.1002/chem.201201575AbstractIn a systematic approach we synthesized a new series of fluorescent probes incorporating donor–acceptor (D-A) substituted 1,2,3-triazoles as conjugative ?-linkers between the alkali metal ion receptor N-phenylaza-[18]crown-6 and different fluorophoric groups with different electron-acceptor properties (4-naphthalimide, meso-phenyl-BODIPY and 9-anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge-transfer (CT) type probes 1, 2 and 7, the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge-separated states. In the presence of Na+ and K+ ICT is interrupted, which resulted in a lighting-up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7, which contains a 9-anthracenyl moiety as the electron-accepting fluorophore, is the only probe which retains light-up features in water and works as a highly K+/Na+-selective probe under simulated physiological conditions. Virtually decoupled BODIPY-based 6 and photoinduced electron transfer (PET) type probes 3–5, where the 10-substituted anthracen-9-yl fluorophores are connected to the 1,2,3-triazole through a methylene spacer, show strong ion-induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3-triazole fluoroionophores.
W. Fudickar, T. Linker Why Triple Bonds Protect Acenes from Oxidation and Decomposition J. Am. Chem. Soc. 2012, 134, 15071 DOI: 10.1021/ja306056xAbstractAn experimental and computational study on the impact of functional groups on the oxidation stability of higher acenes is presented. We synthesized anthracenes, tetracenes, and pentacenes with various substituents at the periphery, identi fi ed their photooxygenation products, and measured the kinetics. Furthermore, the products obtained from thermolysis and the kinetics of the thermolysis are investigated. Density functional theory is applied in order to predict reaction energies, frontier molecular orbital inter- actions, and radical stabilization energies. The combined results allow us to describe the mechanisms of the oxidations and the subsequent thermolysis. We found that the alkynyl group not only enhances the oxidation stability of acenes but also protects the resulting endoperoxides from thermal decomposition. Additionally, such substituents increase the regioselectivity of the photooxygenation of tetracenes and pentacenes. For the fi rst time, we oxidized alkynylpentacenes by using chemically generated singlet oxygen ( 1 O 2 ) without irradiation and identi fi ed a 6,13-endoperoxide as the sole regioisomer. The bimolecular rate constant of this oxidation amounts to only 1 × 10 5 s ? 1 M ? 1 . This unexpectedly slow reaction is a result of a physical deactivation of 1 O 2 . In contrast to unsubstituted or aryl-substituted acenes, photooxygenation of alkynyl-substituted acenes proceeds most likely by a concerted mechanism, while the thermolysis is well explained by the formation of radical intermediates. Our results should be important for the future design of oxidation stable acene-based semiconductors
G. Floß, G. Granucci, P. Saalfrank Surface hopping dynamics of direct trans-cis photoswitching of an azobenzene derivative in constrained adsorbate geometries J. Chem. Phys. 2012, 137, 234701 DOI: 10.1063/1.4769087AbstractWith ongoing miniaturization of electronic devices, the need for individually addressable, switchable molecules arises. An example are azobenzenes on surfaces which have been shown to be switchable between trans and cis forms. Here, we examine the “direct” (rather than substrate-mediated) channel of the trans ? cis photoisomerization after ??* excitation of tetra-tert-butyl-azobenzene physisorbed on surfaces mimicking Au(111) and Bi(111), respectively. In spirit of the direct channel, the electronic structure of the surface is neglected, the latter merely acting as a rigid platform which weakly interacts with the molecule via Van-der-Waals forces. Starting from thermal ensembles which represent the trans-form, sudden excitations promote the molecules to ??*-excited states which are non-adiabatically coupled among themselves and to a n?*-excited and the ground state, respectively. After excitation, relaxation to the ground state by internal conversion takes place, possibly accompanied by isomerization. The process is described here by “on the fly” semiclassical surface hopping dynamics in conjunction with a semiempirical Hamiltonian (AM1) and configuration-interaction type methods. It is found that steric constraints imposed by the substrate lead to reduced but non-vanishing, trans ? cis reaction yields and longer internal conversion times than for the isolated molecule. Implications for recent experiments for azobenzenes on surfaces are discussed.
T. Schwarze, A. Kelling, H. Müller, M. Trautmann, T. Klamroth, O. Baumann, P. Strauch, H.-J. Holdt N-2-Pyridinylmethyl-N'-arylmethyl-diaminomaleonitriles: New Highly Selective Chromogenic Chemodosimeters for Copper(II) Chem. Eur. J. 2012, 18, 10506 DOI: 10.1002/chem.201201161AbstractThe copper(II)-promoted air oxidation of 1–3 to form 4–6 permits the highly selective colorimetric detection of Cu2+ ions (see figure). The formation of copper(II) complexes of 4–6 proceeds rapidly, and the chemodosimeters 1–3 are viable at physiological pH.

• Deutsches Institut für Ernährungsforschung Bergholz-Rehbrücke
• Fraunhofer Institut für Angewandte Polymerforschung
• Fraunhofer Institut für Biomedizinische Technik
• GeoForschungszentrum Potsdam
• Bundesanstalt für Materialforschung und Prüfung
• Helmholtz-Zentrum Hereon: Institut für Aktive Polymere
• Mathematisch-Naturwissenschaftliche Fakultät
• MPI für Kolloid und Grenzflächenforschung
• Wissenschaftspark Golm