03 Fakultät Chemie

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    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, Sabine
    Ionic 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.
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    Chemical design and probing of novel molecular 2-qubit systems
    (2023) Schäfter, Dennis; Slageren, Joris van (Prof. Dr.)
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    Molekulardynamische Simulation zu Fragen der smektischen Translationsordnung in thermotropen Flüssigkristallen
    (2021) Häge, Christian; Gießelmann, Frank (Prof. Dr.)
    Es wurden zwei Fragestellungen zur smektischen Translationsordnung von Flüssigkristallen bearbeitet. Der erste Teil der Arbeit befasst sich mit dem Einfluss der molekularen Ladungsanordnung von ionischen Flüssigkristallen auf deren Phasenverhalten. Der zweite Teil der Arbeit untersucht unter welchen Voraussetzungen die Gleichungen zur Bestimmung von Translationsordnungsparametern angewendet werden können und welche Rolle die molekulare Elektronendichteverteilung des Mesogens dabei spielt.
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    Macrocyclization of dienes under confinement with cationic tungsten imido/oxo alkylidene N‐heterocyclic carbene complexes
    (2023) Ziegler, Felix; Bruckner, Johanna R.; Nowakowski, Michal; Bauer, Matthias; Probst, Patrick; Atwi, Boshra; Buchmeiser, Michael R.
    Macrocyclization reactions are still challenging due to competing oligomerization, which requires the use of small substrate concentrations. Here, the cationic tungsten imido and tungsten oxo alkylidene N-heterocyclic carbene complexes [[W(N-2,6-Cl2-C6H3)(CHCMe2Ph(OC6F5)(pivalonitrile)(IMes)+ B(ArF)4-] (W1) and [W(O (CHCMe2Ph(OCMe(CF3)2)(IMes)(CH3CN)+ B(ArF)4-] (W2) (IMes=1,3-dimesitylimidazol-2-ylidene; B(ArF)4-=tetrakis(3,5-bis(trifluoromethyl)phenyl borate) have been immobilized inside the pores of ordered mesoporous silica (OMS) with pore diameters of 3.3 and 6.8 nm, respectively, using a pore-selective immobilization protocol. X-ray absorption spectroscopy of W1@OMS showed that even though the catalyst structure is contracted due to confinement by the mesopores, both the oxidation state and structure of the catalyst stayed intact upon immobilization. Catalytic testing with four differently sized α,ω-dienes revealed a dramatically increased macrocyclization (MC) and Z-selectivity of the supported catalysts compared to the homogenous progenitors, allowing high substrate concentrations of 25 mM. With the supported complexes, a maximum increase in MC-selectivity from 27 to 81 % and in Z-selectivity from 17 to 34 % was achieved. In general, smaller mesopores exhibited a stronger confinement effect. A comparison of the two supported tungsten-based catalysts showed that W1@OMS possesses a higher MC-selectivity, while W2@OMS exhibits a higher Z-selectivity which can be rationalized by the structures of the catalysts.
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    Dynamic ultrasound projector controlled by light
    (2022) Ma, Zhichao; Joh, Hyungmok; Fan, Donglei Emma; Fischer, Peer
    Dynamic acoustic wavefront control is essential for many acoustic applications, including biomedical imaging and particle manipulation. Conventional methods are either static or in the case of phased transducer arrays are limited to a few elements and hence limited control. Here, a dynamic acoustic wavefront control method based on light patterns that locally trigger the generation of microbubbles is introduced. As a small gas bubble can effectively stop ultrasound transmission in a liquid, the optical images are used to drive a short electrolysis and form microbubble patterns. The generation of microbubbles is controlled by structured light projection at a low intensity of 65 mW cm-2 and only requires about 100 ms. The bubble pattern is thus able to modify the wavefront of acoustic waves from a single transducer. The method is employed to realize an acoustic projector that can generate various acoustic images and patterns, including multiple foci and acoustic phase gradients. Hydrophone scans show that the acoustic field after the modulation by the microbubble pattern forms according to the prediction. It is believed that combining a versatile optical projector to realize an ultrasound projector is a general scheme, which can benefit a multitude of applications based on dynamic acoustic fields.
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    Magnetic tilting in nematic liquid crystals driven by self‐assembly
    (2021) Hähsler, Martin; Nádasi, Hajnalka; Feneberg, Martin; Marino, Sebastian; Giesselmann, Frank; Behrens, Silke; Eremin, Alexey
    Self‐assembly is one of the crucial mechanisms allowing the design multifunctional materials. Soft hybrid materials contain components of different natures and exhibit competitive interactions which drive self‐organization into structures of a particular function. Here a novel type of a magnetic hybrid material where the molecular tilt can be manipulated through a delicate balance between the topologically‐assisted colloidal self‐assembly of magnetic nanoparticles and the anisotropic molecular interactions in a liquid crystal matrix is demonstrated.
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    Probing molecular quantum bits
    (2021) Lenz, Samuel; Slageren, Joris van (Prof. Dr.)
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    Soft urinary bladder phantom for endoscopic training
    (2021) Choi, Eunjin; Waldbillig, Frank; Jeong, Moonkwang; Li, Dandan; Goyal, Rahul; Weber, Patricia; Miernik, Arkadiusz; Grüne, Britta; Hein, Simon; Suarez-Ibarrola, Rodrigo; Kriegmair, Maximilian Christian; Qiu, Tian
    Bladder cancer (BC) is the main disease in the urinary tract with a high recurrence rate and it is diagnosed by cystoscopy (CY). To train the CY procedures, a realistic bladder phantom with correct anatomy and physiological properties is highly required. Here, we report a soft bladder phantom (FlexBlad) that mimics many important features of a human bladder. Under filling, it shows a large volume expansion of more than 300% with a tunable compliance in the range of 12.2 ± 2.8 - 32.7 ± 5.4 mL cmH2O-1 by engineering the thickness of the bladder wall. By 3D printing and multi-step molding, detailed anatomical structures are represented on the inner bladder wall, including sub-millimeter blood vessels and reconfigurable bladder tumors. Endoscopic inspection and tumor biopsy were successfully performed. A multi-center study was carried out, where two groups of urologists with different experience levels executed consecutive CYs in the phantom and filled in questionnaires. The learning curves reveal that the FlexBlad has a positive effect in the endourological training across different skill levels. The statistical results validate the usability of the phantom as a valuable educational tool, and the dynamic feature expands its use as a versatile endoscopic training platform.
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    Asymmetric Rh diene catalysis under confinement : isoxazole ring‐contraction in mesoporous solids
    (2024) Marshall, Max; Dilruba, Zarfishan; Beurer, Ann‐Katrin; Bieck, Kira; Emmerling, Sebastian; Markus, Felix; Vogler, Charlotte; Ziegler, Felix; Fuhrer, Marina; Liu, Sherri S. Y.; Kousik, Shravan R.; Frey, Wolfgang; Traa, Yvonne; Bruckner, Johanna R.; Plietker, Bernd; Buchmeiser, Michael R.; Ludwigs, Sabine; Naumann, Stefan; Atanasova, Petia; Lotsch, Bettina V.; Zens, Anna; Laschat, Sabine
    Covalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.
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    Recent advances in biosurfactant-based association colloids : self-assembly in water
    (2023) Hellweg, Thomas; Sottmann, Thomas; Oberdisse, Julian
    Recent studies of self-assembly in binary systems of bio-surfactants, either of microbial origin or saponins extracted from plants, are reviewed. Saponins in water reported in the first section include aescin, glycyrrhizin, and quillaja saponins, while rhamnolipids are discussed in the second section on microbial surfactants. Studies of surface activities are a natural starting point of the characterization of surfactants, but here we focus mainly on physico-chemical and structural properties of self-assembled bulk structures in solution, often characterized by scattering techniques. When quantitative modelling is performed, self-assembly parameters like aggregation numbers, head group areas, and resulting shapes can be followed as a function of physical-chemical parameters like concentration, composition, temperature, or pH. Morphologies include micelles and their structural evolution with addition of other bio- or synthetic surfactants, co-surfactants, proteins or phospholipids.