TY - JOUR A1 - Zhao, Yuhang A1 - Opitz, Andreas A1 - Eljarrat, Alberto A1 - Kochovski, Zdravko A1 - Koch, Christoph A1 - Koch, Norbert A1 - Lu, Yan T1 - Kinetic study on the adsorption of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane on Ag nanoparticles in chloroform BT - implications for the charge transfer complex of Ag-F(4)TCNQ JF - ACS applied nano materials N2 - In this study, the kinetics of the adsorption of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been intensively investigated, as molecular doping is known to play a crucial role in organic electronic devices. Based on the results obtained from UV-visible (vis)-near-infrared (NIR) absorption spectroscopy, cryogenic transmission electron microscopy, scanning nanobeam electron diffraction, and electron energy loss spectroscopy, a two-step interaction kinetics has been proposed for the Ag NPs and F(4)TCNQ molecules, which includes the first step of electron transfer from Ag NPs to F(4)TCNQ indicated by the ionization of F(4)TCNQ and the second step of the formation of a Ag-F(4)TCNQ complex. The whole process has been followed via UV-vis-NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F(4)TCNQ molecules on the interaction between Ag NPs and F(4)TCNQ molecules in an organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs manifests that the charge transfer at the surface between Ag NPs and F(4)TCNQ molecules is prohibited by a silica layer of 18 nm. KW - Ag nanoparticles KW - F(4)TCNQ KW - phase transfer KW - kinetics KW - electron transfer KW - surface interaction Y1 - 2021 U6 - https://doi.org/10.1021/acsanm.1c02153 SN - 2574-0970 VL - 4 IS - 11 SP - 11625 EP - 11635 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Gu, Sasa A1 - Risse, Sebastian A1 - Lu, Yan A1 - Ballauff, Matthias T1 - Mechanism of the oxidation of 3,3′,5,5′-tetramethylbenzidine catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes BT - a kinetic study JF - ChemPhysChem N2 - Experimental and kinetic modelling studies are presented to investigate the mechanism of 3,3 ',5,5 '-tetramethylbenzidine (TMB) oxidation by hydrogen peroxide (H2O2) catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes (SPB-Pt). Due to the high stability of SPB-Pt colloidal, this reaction can be monitored precisely in situ by UV/VIS spectroscopy. The time-dependent concentration of the blue-colored oxidation product of TMB expressed by different kinetic models was used to simulate the experimental data by a genetic fitting algorithm. After falsifying the models with abundant experimental data, it is found that both H2O2 and TMB adsorb on the surface of Pt nanoparticles to react, indicating that the reaction follows the Langmuir-Hinshelwood mechanism. A true rate constant k, characterizing the rate-determining step of the reaction and which is independent on the amount of catalysts used, is obtained for the first time. Furthermore, it is found that the product adsorbes strongly on the surface of nanoparticles, thus inhibiting the reaction. The entire analysis provides a new perspective to study the catalytic mechanism and evaluate the catalytic activity of the peroxidase-like nanoparticles. KW - kinetics KW - nanoparticles KW - reaction mechanisms KW - spherical polyelectrolyte KW - brushes KW - UV KW - vis spectroscopy Y1 - 2019 U6 - https://doi.org/10.1002/cphc.201901087 SN - 1439-4235 SN - 1439-7641 VL - 21 IS - 5 SP - 450 EP - 458 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Bauch, Marcel A1 - Krtitschka, Angela A1 - Linker, Torsten T1 - Photooxygenation of oxygen-substituted naphthalenes JF - Journal of physical organic chemistry N2 - The reaction of oxygen-substituted naphthalenes with singlet oxygen (O-1(2)) has been investigated, and labile endoperoxides have been isolated and characterized at -78 degrees C for the first time. Low-temperature kinetics by UV spectroscopy revealed that alkoxy and silyloxy substituents remarkably increase the rate of photooxygenations compared to 1,4-dimethylnaphthalene, whereas acyloxy-substituted acenes are inert towards O-1(2). The reactivities nicely correlate with HOMO energies and free activation energies, which we determined by density functional theory calculations. The lability of the isolated endoperoxides is due to their very fast back reaction to the corresponding naphthalenes even at -20 degrees C under release of O-1(2), making them to superior sources of this reactive species under very mild conditions. Finally, a carbohydrate-substituted naphthalene has been synthesized, which reacts reversibly with O-1(2) and might be applied for enantioselective oxidations in future work. KW - kinetics KW - labile peroxides KW - low-temperature experiments KW - naphthalenes KW - singlet oxygen Y1 - 2017 U6 - https://doi.org/10.1002/poc.3734 SN - 0894-3230 SN - 1099-1395 VL - 30 SP - 6803 EP - 6813 PB - Wiley CY - Hoboken ER - TY - THES A1 - Vacogne, Charlotte D. T1 - New synthetic routes towards well-defined polypeptides, morphologies and hydrogels T1 - Neue Syntheserouten zu wohldefinierten Polypeptiden, Morphologien und Hydrogelen N2 - Proteins are natural polypeptides produced by cells; they can be found in both animals and plants, and possess a variety of functions. One of these functions is to provide structural support to the surrounding cells and tissues. For example, collagen (which is found in skin, cartilage, tendons and bones) and keratin (which is found in hair and nails) are structural proteins. When a tissue is damaged, however, the supporting matrix formed by structural proteins cannot always spontaneously regenerate. Tailor-made synthetic polypeptides can be used to help heal and restore tissue formation. Synthetic polypeptides are typically synthesized by the so-called ring opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCA). Such synthetic polypeptides are generally non-sequence-controlled and thus less complex than proteins. As such, synthetic polypeptides are rarely as efficient as proteins in their ability to self-assemble and form hierarchical or structural supramolecular assemblies in water, and thus, often require rational designing. In this doctoral work, two types of amino acids, γ-benzyl-L/D-glutamate (BLG / BDG) and allylglycine (AG), were selected to synthesize a series of (co)polypeptides of different compositions and molar masses. A new and versatile synthetic route to prepare polypeptides was developed, and its mechanism and kinetics were investigated. The polypeptide properties were thoroughly studied and new materials were developed from them. In particular, these polypeptides were able to aggregate (or self-assemble) in solution into microscopic fibres, very similar to those formed by collagen. By doing so, they formed robust physical networks and organogels which could be processed into high water-content, pH-responsive hydrogels. Particles with highly regular and chiral spiral morphologies were also obtained by emulsifying these polypeptides. Such polypeptides and the materials derived from them are, therefore, promising candidates for biomedical applications. N2 - Proteine, auch Polypeptide genannt, sind große Biomoleküle, die aus kleineren Aminosäuren bestehen. Diese sind zu langen Ketten miteinander verbunden, wie die Perlen auf einer Perlenkette. Sie werden in Zellen produziert, können in Tieren und Pflanzen gefunden werden und haben vielfältige Funktionen. Eine dieser Funktionen ist es, die umgebenen Zellen und Gewebe wie ein Gerüst zu stützen. Kollagen (welches in Haut, Knorpel, Sehnen und Knochen zu finden ist) und Keratin (welches in Haaren und Nägeln vorkommt) gehören zu diesen Strukturproteinen. Jedoch wenn ein Gewebe beschädigt ist, beispielsweise als Folge eines Unfalls, kann sich das Grundgerüst aus diesen Strukturproteinen manchmal nicht mehr selbst regenerieren. Maßgefertigte synthetische Polypeptide, können dafür verwendet werden, die Heilung und Wiederherstellung des Gewebes zu Unterstützen. Diese Polypeptide werden mit einer Reihe an chemischen Reaktionen synthetisiert, welche hauptsächlich darauf abzielen Aminosäuren miteinander zu verknüpfen. Synthetische Polypeptide sind weniger Komplex als die von Zellen hergestellten, natürlichen Polypeptide (Proteine). Während in den natürlichen Polypeptiden die Aminosäuren in einer von der DNA definierten Reihenfolge, welche als Sequenz bezeichnet wird, angeordnet sind, sind sie in synthetischen Polypeptiden zumeist zufällig verteilt. Die Konsequenz daraus ist, dass synthetische Polypeptide nicht immer so Leistungsfähig sind wie natürliche Proteine und ein durchdachtes Design benötigen. Zwei Aminosäuren wurden in dieser Dissertation sorgfältig ausgewählt und verwendet um eine Serie an Polypeptiden mit unterschiedlicher Zusammensetzung und Länge zu synthetisieren. Ein neuer und vielseitiger Syntheseweg wurde ebenfalls entwickelt und der zugrundeliegende Mechanismus untersucht. Die Polypeptide wurden gründlich analysiert und neue Materialien wurden aus ihnen entwickelt. In Lösung gebracht formten diese Fasern, ähnlich denen von Kollagen, welche sich wiederum zu robusten Netzwerken anordneten. Aus diesen Netzwerken ließen sich Hydrogele herstellen, welche in der Lage waren große Mengen an Wasser aufzunehmen. Diese Hydrogele wiederum stellen vielversprechende Kandidaten für biomedizinische Anwendungen dar. KW - polymer KW - chemistry KW - biomaterial KW - polymerization KW - kinetics KW - polypeptide KW - colloid KW - gelation KW - hydrogel KW - organogel KW - secondary structure KW - physical KW - NCA KW - N-carboxyanhydride KW - Polymer KW - Chemie KW - Biomaterial KW - Polymerisation KW - Kinetik KW - Polypeptid KW - Kolloid KW - Gelieren KW - Hydrogel KW - Organogel KW - Sekundärstruktur KW - physikalisch KW - NCA KW - N-carboxyanhydrid Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-396366 ER -