03 Fakultät Chemie
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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 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 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 Mixed valency vs radical bridge formulation in symmetrically and asymmetrically ligated diruthenium complexes(2022) Mondal, Sudipta; Schwederski, Brigitte; Záliš, Stanislav; Kaim, WolfgangThe asymmetrical dinuclear [{(trpy*)Ru}2(μ‐adc‐Salph)Cl](PF6) 1(PF6), trpy*=4,4’,4”‐tri‐tert‐butyl‐2,6,2’,6”‐terpyridine, adc‐Salph=1‐benzoyl‐2‐salicyloylhydrazido(3‐), and the related symmetrical dinuclear [{Cl(trpy*)Ru}2(μ,η2 : η2‐adc‐Ph)](PF6) 2(PF6), adc‐Ph=1,2‐bis(benzoyl)hydrazido(2‐), were synthesized and structurally characterized. Both paramagnetic compounds were compared with the previously reported symmetrical [{(trpy*)Ru}2(μ,η3 : η3‐adc‐Sal)](PF6) 3(PF6) containing the bis‐tridentate bridge 1,2‐bis(salicyloyl)hydrazido(4‐). Molecular structures and magnetic resonance features (1H NMR, EPR) indicate spin density distribution over the metal(s) and the bridging ligand. Reversible one‐electron reduction and oxidation were possible in all instances yielding comproportionation constants Kc of about 109 for the paramagnetic intermediates 1+-3+. Structural results, spin density distribution and UV‐Vis‐NIR spectroelectrochemistry were analyzed for 1+ with the help of TD‐DFT calculations for a model compound (tert‐Bu→Me). Intense absorptions around λmax=1450-1650 nm for the cations were assigned to mixed metal/ligand transitions with significant inter‐valence charge transfer (IVCT) character. For both the symmetrical and asymmetrical arrangements the cationic intermediates can be described as considerably mixed metal/ligand systems.Item Open Access Adjustable polystyrene nanoparticle templates for the production of mesoporous foams and ZnO inverse opals(2020) Abitaev, Karina; Qawasmi, Yaseen; Atanasova, Petia; Dargel, Carina; Bill, Joachim; Hellweg, Thomas; Sottmann, ThomasThe manifold applications of porous materials, such as in storage, separation, and catalysis, have led to an enormous interest in their cost-efficient preparation. A promising strategy to obtain porous materials with adjustable pore size and morphology is to use templates exhibiting the appropriate nanostructure. In this study, close-packed polystyrene (PS) nanoparticles, synthesized by emulsion polymerization, were used to produce porous PS and ZnO inverse opals. The size and distribution of the polystyrene nanoparticles, characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), and scanning electron microscopy (SEM), were controlled via the concentration of sodium dodecyl sulfate (SDS). Systematic measurements of the water/styrene-interfacial tension show that the critical micelle concentration (CMC) of the ternary water–styrene–SDS system, which determines whether monodisperse or polydisperse PS particles are obtained, is considerably lower than that of the binary water–SDS system. The assemblies of close-packed PS nanoparticles obtained via drying were then studied by small-angle X-ray scattering (SAXS) and SEM. Both techniques prove that PS nanoparticles synthesized above the CMC result in a significantly unordered but denser packing of the particles. The polystyrene particles were subsequently used to produce porous polystyrene and ZnO inverse opals. While the former consists of micrometer-sized spherical pores surrounded by extended open-cellular regions of mesopores (Rpore ≈ 25 nm), the latter are made of ZnO-nanoparticles forming a structure of well-aligned interconnected pores.Item Open Access The reduced nitridogermanates(III) Ca6[Ge2N6] and Sr6[Ge2N6] with Ge-Ge bonds(2021) Link, Lukas; Pathak, Manisha; Jach, Franziska; Koželj, Primoz; Ormeci, Alim; Höhn, Peter; Niewa, RainerThe first nitridogermanates(III) Ca6[Ge2N6] and Sr6[Ge2N6] were synthesized from sodium flux and structurally characterized by powder and single crystal X‐ray diffraction, respectively. They crystallize isostructurally to each other and homeotypic to Ca6[Cr2N6]H in space group R3‾. They feature unprecedented, mutually isolated, ethane‐like [GeIII2N6]12- anions in a staggered conformation. The compounds are semiconductors according to resistivity measurements and electronic structure calculations, yielding band gaps of 1.1 eV for Ca6[Ge2N6] and 0.2 eV for Sr6[Ge2N6].Item Open Access Mesoionic imines (MIIs) : strong donors and versatile ligands for transition metals and main group substrates(2022) Rudolf, Richard; Neuman, Nicolás I.; Walter, Robert R. M.; Ringenberg, Mark. R.; Sarkar, BiprajitWe report the synthesis and the reactivity of 1,2,3‐triazolin‐5‐imine type mesoionic imines (MIIs). The MIIs are accessible by a base‐mediated cycloaddition between a substituted acetonitrile and an aromatic azide, methylation by established routes and subsequent deprotonation. C=O‐stretching frequencies in MII-CO2 and -Rh(CO)2Cl complexes were used to determine the overall donor strength. The MIIs are stronger donors than the N‐heterocyclic imines (NHIs). MIIs are excellent ligands for main group elements and transition metals in which they display substituent‐induced fluorine‐specific interactions and undergo C-H activation. DFT calculations gave insights into the frontier orbitals of the MIIs. The calculations predict a relatively small HOMO-LUMO gap compared to other related ligands. MIIs are potentially able to act as both π‐donor and π‐acceptor ligands. This report highlights the potential of MIIs to display exciting properties with a huge potential for future development.