03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Designing covalent organic framework‐based light‐driven microswimmers toward therapeutic applications(2023) Sridhar, Varun; Yildiz, Erdost; Rodríguez‐Camargo, Andrés; Lyu, Xianglong; Yao, Liang; Wrede, Paul; Aghakhani, Amirreza; Akolpoglu, Birgul M.; Podjaski, Filip; Lotsch, Bettina V.; Sitti, MetinWhile micromachines with tailored functionalities enable therapeutic applications in biological environments, their controlled motion and targeted drug delivery in biological media require sophisticated designs for practical applications. Covalent organic frameworks (COFs), a new generation of crystalline and nanoporous polymers, offer new perspectives for light‐driven microswimmers in heterogeneous biological environments including intraocular fluids, thus setting the stage for biomedical applications such as retinal drug delivery. Two different types of COFs, uniformly spherical TABP‐PDA‐COF sub‐micrometer particles and texturally nanoporous, micrometer‐sized TpAzo‐COF particles are described and compared as light‐driven microrobots. They can be used as highly efficient visible‐light‐driven drug carriers in aqueous ionic and cellular media. Their absorption ranging down to red light enables phototaxis even in deeper and viscous biological media, while the organic nature of COFs ensures their biocompatibility. Their inherently porous structures with ≈2.6 and ≈3.4 nm pores, and large surface areas allow for targeted and efficient drug loading even for insoluble drugs, which can be released on demand. Additionally, indocyanine green (ICG) dye loading in the pores enables photoacoustic imaging, optical coherence tomography, and hyperthermia in operando conditions. This real‐time visualization of the drug‐loaded COF microswimmers enables unique insights into the action of photoactive porous drug carriers for therapeutic applications.Item Open Access Counterion effects on the mesomorphic and electrochemical properties of guanidinium salts(2024) Ebert, Max; Lange, Alyna; Müller, Michael; Wuckert, Eugen; Gießelmann, Frank; Klamroth, Tillmann; Zens, Anna; Taubert, Andreas; Laschat, SabineIonic liquid crystals (ILCs) combine the ion mobility of ionic liquids with the order and self-assembly of thermotropic mesophases. To understand the role of the anion in ILCs, wedge-shaped arylguanidinium salts with tetradecyloxy side chains were chosen as benchmark systems and their liquid crystalline self-assembly in the bulk phase as well as their electrochemical behavior in solution were studied depending on the anion. Differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS, SAXS) experiments revealed that for spherical anions, the phase width of the hexagonal columnar mesophase increased with the anion size, while for non-spherical anions, the trends were less clear cut. Depending on the anion, the ILCs showed different stability towards electrochemical oxidation and reduction with the most stable being the PF6 based compound. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest a possible contribution of the guanidinium cation to the oxidation processes.Item Open Access Interphases between alkali metals (Li, Na) and battery electrolytes : ion transport and growth behavior(2022) Lim, Kyungmi; Maier, Joachim (Prof. Dr.)Item Open Access Confirmation of siderazot, Fe3N1.33, the only terrestrial nitride mineral(2021) Bette, Sebastian; Theye, Thomas; Bernhardt, Heinz-Jürgen; Clark, William P.; Niewa, RainerSiderazot, the only terrestrial nitride mineral, was reported only once in 1876 to occur as coating on volcanic rocks in a fumarolic environment from Mt. Etna and, to date, has been neither confirmed nor structurally characterized. We have studied the holotype sample from the Natural History Museum, London, UK, originally collected by O. Silvestri in 1874, and present siderazot with epsilon-Fe3N-type crystal structure and composition of Fe3N1.33(7) according to crystal structure Rietveld refinements, in good agreement with electron microprobe analyses. Crystal structure data, chemical composition, and Raman and reflectance measurements are reported. Possible formation conditions are derived from composition and phase stability data according to synthetic samples.Item Open Access Highly active cooperative Lewis acid : ammonium salt catalyst for the enantioselective hydroboration of ketones(2021) Titze, Marvin; Heitkämper, Juliane; Junge, Thorsten; Kästner, Johannes; Peters, RenéEnantiopure secondary alcohols are fundamental high‐value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5-3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.Item Open Access Stereoretentive regio‐ und enantioselektive Allylierung von Isoxazolinonen per planar chiralem Palladacyclus‐Katalysator(2022) Yu, Xin; Hu, Lingfei; Frey, Wolfgang; Lu, Gang; Peters, RenéDie katalytische allylische Substitution ist eines der wichtigsten Werkzeuge in der asymmetrischen Synthese zur enantioselektiven Bildung von C-C-Bindungen. Während in vorigen Arbeiten eine hohe Effizienz in Bezug auf Enantio- und Regiokontrolle unter Verwendung verschiedener Katalysatortypen erreicht wurde, besteht eine starke allgemeine Einschränkung in einer sehr ausgeprägten Präferenz für die Bildung von allylischen Substitutionsprodukten mit (E)-konfigurierten C=C-Doppelbindungen. Hier berichten wir, dass mit einem planar-chiralen Palladacyclus-Katalysator unter Verwendung von Isoxazolinonen und Allylimidaten als Substrate ein diastereospezifisches Reaktionsergebnis erzielt wird, wodurch die C=C-Doppelbindungsgeometrie der Allylsubstrate in den hoch enantiomerenangereicherten Produkten beibehalten wird. DFT-Rechnungen zeigen, dass die Reaktionen über einen SN2-Mechanismus und nicht über π-Allyl-Pd-Komplexe ablaufen. Entscheidend für die hohe Kontrolle ist die Stabilisierung des allylischen Fragments im SN2-Übergangszustand durch π-Wechselwirkungen mit den Phenylsubstituenten des Pentaphenylferrocen-Katalysatorkerns.Item Open Access Methacrylate‐based polymer foams with controllable pore sizes and controllable polydispersities via foamed emulsion templating(2020) Dabrowski, Miriam Lucia; Stubenrauch, CosimaThis study reports on a novel templating route, which uses foamed emulsions as templates for porous polymers. The concept is based on the generation of a monomer‐in‐water emulsion, which is subsequently foamed via microfluidics. The monomer of choice is 1,4‐butanediol dimethacrylate (1,4‐BDDMA). After polymerization of the foamed emulsion, one obtains open‐cell polymer foams with porous pore walls. Foamed emulsions and polymer foams are generated. It is shown that foamed emulsion templating in combination with microfluidics is well‐suited to synthesize 1) monodisperse poly(1,4‐BBDMA) foams with controllable pore sizes and 2) their polydisperse counterparts with controllable polydispersities. Monodisperse templates with different bubble sizes and thus polymer foams with different pore sizes ranging from about 100-400 μm in diameter are synthesized. Microfluidics is also used for the generation of polydisperse poly(1,4‐BDDMA) foams with polydispersities between 18% and 27% but the same mean pore sizes as the monodisperse ones, i.e., we have access to polymer foams that only differ in their polydispersity.Item Open Access The Bacteroidetes Aequorivita sp. and Kaistella jeonii produce promiscuous esterases with PET-hydrolyzing activity(2022) Zhang, Hongli; Perez-Garcia, Pablo; Dierkes, Robert F.; Applegate, Violetta; Schumacher, Julia; Chibani, Cynthia Maria; Sternagel, Stefanie; Preuss, Lena; Weigert, Sebastian; Schmeisser, Christel; Danso, Dominik; Pleiss, Juergen; Almeida, Alexandre; Höcker, Birte; Hallam, Steven J.; Schmitz, Ruth A.; Smits, Sander H. J.; Chow, Jennifer; Streit, Wolfgang R.Certain members of the Actinobacteria and Proteobacteria are known to degrade polyethylene terephthalate (PET). Here, we describe the first functional PET-active enzymes from the Bacteroidetes phylum. Using a PETase-specific Hidden-Markov-Model- (HMM-) based search algorithm, we identified several PETase candidates from Flavobacteriaceae and Porphyromonadaceae. Among them, two promiscuous and cold-active esterases derived from Aequorivita sp. (PET27) and Kaistella jeonii (PET30) showed depolymerizing activity on polycaprolactone (PCL), amorphous PET foil and on the polyester polyurethane Impranil® DLN. PET27 is a 37.8 kDa enzyme that released an average of 174.4 nmol terephthalic acid (TPA) after 120 h at 30°C from a 7 mg PET foil platelet in a 200 μl reaction volume, 38-times more than PET30 (37.4 kDa) released under the same conditions. The crystal structure of PET30 without its C-terminal Por-domain (PET30ΔPorC) was solved at 2.1 Å and displays high structural similarity to the IsPETase. PET30 shows a Phe-Met-Tyr substrate binding motif, which seems to be a unique feature, as IsPETase, LCC and PET2 all contain Tyr-Met-Trp binding residues, while PET27 possesses a Phe-Met-Trp motif that is identical to Cut190. Microscopic analyses showed that K. jeonii cells are indeed able to bind on and colonize PET surfaces after a few days of incubation. Homologs of PET27 and PET30 were detected in metagenomes, predominantly aquatic habitats, encompassing a wide range of different global climate zones and suggesting a hitherto unknown influence of this bacterial phylum on man-made polymer degradation.Item Open Access Mechanistic studies on the DNA methyltransferases DNMT3A and DNMT3B(2021) Dukatz, Michael; Jeltsch, Albert (Prof. Dr.)In this work, both regulatory and catalytic mechanisms of de novo methyltransferases were investigated, which include interactions with other proteins and the specific recognition of the substrate sequence. Another part of this work strived to elucidate how enzymatic generation of 3-methylcytosine by DNMT3A can occur.Item Open Access Kationische Wolfram-Alkylidin-N-Heterozyklische-Carben-Komplexe und deren Reaktionen zu Wolfram-Oxo- und Sulfido-Alkyliden-Komplexen(2022) Hauser, Philipp M.; Buchmeiser, Michael R. (Prof. Dr.)