@article{36077, author = {{Hoppe, Thomas and Müller, Jens and Wittek, Katharina and Weinrich, Arndt}}, journal = {{iStR}}, title = {{{Eine ökonomische Einordnung des öffentlichen Country-by-Country Reporting in der EU}}}, year = {{2021}}, } @inbook{37533, author = {{Dopheide, Fredericke and Freitag, Christine and Koch, Lea and Struchholz, Caroline}}, booktitle = {{Impulse zu Methoden in der deutschsprachigen Civic Engagement-Forschung}}, editor = {{Gerholz, Karl-Heinz}}, pages = {{15--32}}, title = {{{Gesellschaftliche Wirkprozesse des Civic Engagement qualitativ erforschen}}}, year = {{2021}}, } @article{64052, abstract = {{Abstract Estuaries are key ecosystems with unique biodiversity and are of high economic importance. Along the estuaries, variations in environmental parameters, such as salinity and light penetration, can modify the characteristics of dissolved organic matter (DOM). Nevertheless, there is still limited information about the atomic-level transformations of DOM in this ecosystem. Solid-state NMR spectroscopy provides unique insights into the nature of functional groups in DOM. A major limitation of this technique is its lack of sensivity, which results in experimental time of tens of hours for the acquisition of 13C NMR spectra and generally precludes the observation of 15N nuclei for DOM. We show here how the sensitivity of solid-state NMR experiments on DOM of Seine estuary can be enhanced using dynamic nuclear polarization (DNP) under magic-angle spinning. This technique allows the acquisition of 13C NMR spectra of these samples in few minutes, instead of hours for conventional solid-state NMR. Both conventional and DNP-enhanced 13C NMR spectra indicate that the 13C local environments in DOM are not strongly modified along the Seine estuary. Furthermore, the sensitivity gain provided by the DNP allows the detection of 15N NMR signal of DOM, in spite of the low nitrogen content. These spectra reveal that the majority of nitrogen is in the amide form in these DOM samples and show an increased disorder around these amide groups near the mouth of the Seine.}}, author = {{Venel, Florian and Nagashima, Hiroki and Rankin, Andrew G. M. and Anquetil, Christelle and Klimavicius, Vytautas and Gutmann, Torsten and Buntkowsky, Gerd and Derenne, Sylvie and Lafon, Olivier and Huguet, Arnaud and Pourpoint, Frédérique}}, issn = {{1439-4235; 1439-7641}}, journal = {{Chemphyschem}}, keywords = {{dynamic nuclear polarization, 13C, 15N, dissolved organic matter, Seine estuary}}, number = {{18}}, pages = {{1907–1913}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Characterization of Functional Groups in Estuarine Dissolved Organic Matter by DNP-enhanced 15N and 13C Solid-State NMR}}}, doi = {{10.1002/cphc.202100334}}, volume = {{22}}, year = {{2021}}, } @article{64051, abstract = {{The efficiency of dynamic nuclear polarization (DNP) enhanced 19F MAS NMR spectroscopy without 19F-containing solvents and matrices, which transport polarization via 19F–19F spin diffusion, is demonstrated. By preventing solvent and matrix signals respectively masking the corresponding resonances, this enables the detection of fluorinated target molecules in nanomolar amounts. As model compound, 1,3,5-tris(2-fluoro-2-methylpropionylamino)benzene (F-BTA) is investigated in a frozen 1,1,2,2-tetrachloroethane (TCE) solution and incorporated into a matrix of isotactic polypropylene (i-PP). While the polarizing agent is homogeneously dissolved within the frozen solution, for the i-PP/F-BTA blend, it is distributed via the incipient wetness impregnation (IWI) technique. For the frozen solutions with an F-BTA concentration of 187.5 mM an εon/off of 260 was obtained. For F-BTA concentrations of 10 and 2.5 mM the sensitivity trend suggests even higher DNP gains. The substantial enhancements could be achieved by direct polarization transfer over distances up to at least 20 Å, derived from a simple geometric model assuming a homogeneous solution, engaging a large part of the sample volume. Cross-polarization (CP) to 13C nuclei allowed selection of the NMR spectroscopic resonances of the minority species in the i-PP/F-BTA blend suppressing the otherwise dominating resonances of the IWI solvent and the polymer matrix. The possibility of exciting 19F via DNP directly and of transferring the polarization to other heteronuclei within close proximity enables spatial spectral editing to clear up spectra otherwise crowded by matrix and solvent signals. We thus expect direct polarization transfer techniques for DNP enhanced NMR spectroscopy to become more important in the future.}}, author = {{van der Zwan, Kasper P. and Riedel, Wiebke and Aussenac, Fabien and Reiter, Christian and Kreger, Klaus and Schmidt, Hans-Werner and Risse, Thomas and Gutmann, Torsten and Senker, Jürgen}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{13}}, pages = {{7287–7296}}, publisher = {{American Chemical Society}}, title = {{{19F MAS DNP for Probing Molecules in Nanomolar Concentrations: Direct Polarization as Key for Solid-State NMR Spectra without Solvent and Matrix Signals}}}, doi = {{10.1021/acs.jpcc.1c01167}}, volume = {{125}}, year = {{2021}}, } @article{64046, abstract = {{The synthesis of a novel immobilized Wilkinson’s catalyst [SiO2∼PvPy-Wilk] is presented. The support material of this catalyst consists of silica particles that are modified with polymer brushes carrying pyridyl moieties that enable the coordination of Wilkinson’s catalyst. The synthesis of this catalyst is monitored by 1D and 2D multinuclear solid-state NMR techniques to confirm the success of the immobilization. The [SiO2∼PvPy-Wilk] catalyst is then tested in the hydrogenation of styrene, and its reusability is inspected showing that significant structural changes after several reaction cycles yield an activation of the catalyst. Finally, the catalyst is tested in PHIP experiments giving rise to about 200-fold enhancement of the signals of the hydrogenation product ethylbenzene.}}, author = {{Srour, Mohamad and Hadjiali, Sara and Brunnengräber, Kai and Weidler, Heiko and Xu, Yeping and Breitzke, Hergen and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{13}}, pages = {{7178–7187}}, publisher = {{American Chemical Society}}, title = {{{A Novel Wilkinson’s Type Silica Supported Polymer Catalyst: Insights from Solid-State NMR and Hyperpolarization Techniques}}}, doi = {{10.1021/acs.jpcc.1c00112}}, volume = {{125}}, year = {{2021}}, } @article{64032, abstract = {{Ruthenium nanoparticles (Ru NPs) stabilized by bis-diphenylphosphinobutane (dppb) and surface-saturated with hydrogen have been exposed to gaseous 15NH3 and studied using solid-state 15N CP MAS NMR. Three signals have been observed at 24.5, −12 and −42 ppm (reference external liquid ammonia) which are assigned to chemisorbed ammonia species RuNHx. Sample exposure to vacuum or aging leads to conversion of the 24.5 ppm species into the other ones, a process which is reversed by re-exposure to hydrogen gas. Exposure to a mixture of 15NH3 and 13CO leads to the formation of surface bound urea as demonstrated by 15N and 13C CP MAS NMR. To understand the surface reactions of ammonia and the 15N NMR results, quantum chemical calculations of the structures, energies and 15N chemical shifts of ammonia species on Ru6 and Ru55 model clusters have been performed. The calculations indicate that under the experimental conditions applied, the fractions of RuNH3 and RuNH2 species are similar, independent of the H2 pressure. No RuN and RuNH species are formed which are calculated to resonate at a lower field than the signals observed experimentally. However, the 15N chemical shifts of RuNH2 depend on the number of neighboring surface hydrogens and hence on the H2 pressure. Thus, the signal at 24.5 ppm is assigned to RuNH2 in a neighborhood rich in surface hydrogens. RuNH2 depleted in neighboring surface hydrogens and RuNH3 resonated both in a similar chemical shift range to which the signals at −12 and −42 belong. A change of the hydrogen pressure then leads to interconversion of hydrogen-rich and hydrogen-poor neighborhoods of RuNH2 but does not alter the fractions of RuNH3 and RuNH2 according to the calculated stability diagram. Nevertheless, dissociation of RuNH3 into RuNH2 and surface hydrogen is expected to take place during the initial ammonia adsorption process and at low H2 pressures and high temperatures. Finally, some preliminary quantum chemical calculations suggest stepwise binding of two NH2 groups to adsorbed CO leading to surface bound urea where the oxygen is coordinated to Ru.}}, author = {{Rothermel, Niels and Limbach, Hans-Heinrich and Del Rosal, Iker and Poteau, Romuald and Mencia, Gabriel and Chaudret, Bruno and Buntkowsky, Gerd and Gutmann, Torsten}}, issn = {{2044-4753}}, journal = {{Catalysis Science & Technology}}, number = {{13}}, pages = {{4509–4520}}, publisher = {{The Royal Society of Chemistry}}, title = {{{Surface reactions of ammonia on ruthenium nanoparticles revealed by 15N and 13C solid-state NMR}}}, doi = {{10.1039/D0CY02476G}}, volume = {{11}}, year = {{2021}}, } @article{64025, abstract = {{Dirhodium(II) complexes such as [Rh2(TFA)4] bound to a functionalized mesoporous SBA-15 carrier material have proven to be valuable candidates for heterogeneous catalysis in the field of pharmaceutical synthesis. However, the mechanistic steps of immobilization by linker molecules containing carboxyl or amine functionalities remain the subject of discussion. Here we present a theoretical study of possible mechanistic binding pathways for the [Rh2(TFA)4] complex through model representations of synthetically investigated linkers, namely n-butylamine and n-butyric acid. Experimentally proposed intermediates of the immobilization process are investigated and analyzed by density functional theory calculations to gain insights into structural properties and the influence of solvation. An evaluation of the thermodynamic data for all identified intermediates allowed distinguishing between two possible reaction pathways that are characterized by a first axial complexation of either n-butyric acid or n-butylamine. In agreement with results from NMR spectroscopy, singly or doubly n-butylamine-fixated complexes were found to present possible immobilization products. Initial binding through a carboxy-functionalized linker is proposed as the most favorable reaction pathway for the formation of the mixed linker pattern [Rh2(TFA)3]·(n-butylamine)·(n-butyrate). The linkers n-butyric acid and n-butyrate, respectively, are found to exhibit an unaltered binding affinity to the dirhodium complex despite their protonation states, indicating invariance to the acidic environment unlike an immobilization by n-butylamine. These results present a theoretical framework for the rationalization of observed product distributions while also providing inspiration and guidance for the preparation of functionalized heterogeneous SBA-15/dirhodium catalyst systems.}}, author = {{Pietruschka, Dennis S. and Kumari, Bharti and Buntkowsky, Gerd and Gutmann, Torsten and Mollenhauer, Doreen}}, journal = {{Inorganic Chemistry}}, number = {{9}}, pages = {{6239–6248}}, publisher = {{American Chemical Society}}, title = {{{Mechanism of Heterogenization of Dirhodium Catalysts: Insights from DFT Calculations}}}, doi = {{10.1021/acs.inorgchem.0c03712}}, volume = {{60}}, year = {{2021}}, } @article{64027, abstract = {{The biorelevant PyFALGEA oligopeptide ligand, which is selective towards the epidermal growth factor receptor (EGFR), has been successfully employed as a substrate in magnetic resonance signal amplification by reversible exchange (SABRE) experiments. It is demonstrated that PyFALGEA and the iridium catalyst IMes form a PyFALGEA:IMes molecular complex. The interaction between PyFALGEA:IMes and H-2 results in a ternary SABRE complex. Selective 1D EXSY experiments reveal that this complex is labile, which is an essential condition for successful hyperpolarization by SABRE. Polarization transfer from parahydrogen to PyFALGEA is observed leading to significant enhancement of the H-1 NMR signals of PyFALGEA. Different iridium catalysts and peptides are inspected to discuss the influence of their molecular structures on the efficiency of hyperpolarization. It is observed that PyFALGEA oligopeptide hyperpolarization is more efficient when an iridium catalyst with a sterically less demanding NHC ligand system such as IMesBn is employed. Experiments with shorter analogues of PyFALGEA, that is, PyLGEA and PyEA, show that the bulky phenylalanine from the PyFALGEA oligopeptide causes steric hindrance in the SABRE complex, which hampers hyperpolarization with IMes. Finally, a single-scan H-1 NMR SABRE experiment of PyFALGEA with IMesBn revealed a unique pattern of NMR lines in the hydride region, which can be treated as a fingerprint of this important oligopeptide.}}, author = {{Ratajczyk, T. and Buntkowsky, G. and Gutmann, Torsten and Fedorczyk, B. and Mames, A. and Pietrzak, M. and Puzio, Z. and Szkudlarek, P. G.}}, journal = {{ChemBioChem}}, number = {{5}}, pages = {{855–860}}, title = {{{Magnetic Resonance Signal Amplification by Reversible Exchange of Selective PyFALGEA Oligopeptide Ligands Towards Epidermal Growth Factor Receptors}}}, doi = {{10.1002/cbic.202000711}}, volume = {{22}}, year = {{2021}}, } @article{64022, abstract = {{High-field dynamic nuclear polarization is a powerful tool for the structural characterization of species on the surface of porous materials or nanoparticles. For these studies the main source of polarization are radical-containing solutions which are added by post-synthesis impregnation of the sample. Although this strategy is very efficient for a wide variety of materials, the presence of the solvent may influence the chemistry of functional species of interest. Here we address the development of a comprehensive strategy for solvent-free DNP enhanced NMR characterization of functional (target) species on the surface of mesoporous silica (SBA-15). The strategy includes the partial functionalization of the silica surface with Carboxy-Proxyl nitroxide radicals and target Fmoc-Glycine functional groups. As a proof of principle, we have observed for the first time DNP signal enhancements, using the solvent-free approach, for 13C1H CPMAS signals corresponding to organic functionalities on the silica surface. DNP enhancements of up to 3.4 were observed for 13C1H CPMAS, corresponding to an experimental time save of about 12 times. This observation opens the possibility for the DNP-NMR study of surface functional groups without the need of a solvent, allowing, for example, the characterization of catalytic reactions occurring on the surface of mesoporous systems of interest. For 29Si with direct polarization NMR, up to 8-fold DNP enhancements were obtained. This 29Si signal enhancement is considerably higher than the obtained with similar approaches reported in literature. Finally, from DNP enhancement profiles we conclude that cross-effect is probably the dominant polarization transfer mechanism.}}, author = {{Oliveira, Marcos and Herr, Kevin and Brodrecht, Martin and Haro-Mares, Nadia B. and Wissel, Till and Klimavicius, Vytautas and Breitzke, Hergen and Gutmann, Torsten and Buntkowsky, Gerd}}, journal = {{Physical Chemistry Chemical Physics}}, number = {{22}}, pages = {{12559–12568}}, publisher = {{The Royal Society of Chemistry}}, title = {{{Solvent-free dynamic nuclear polarization enhancements in organically modified mesoporous silica}}}, doi = {{10.1039/D1CP00985K}}, volume = {{23}}, year = {{2021}}, } @article{64016, abstract = {{Bacterial cellulose (BC) combined with organo-bridged porous silica nanoparticles offers potential opportunities to develop smart hybrid materials such as advanced drug delivery nanosystems. This work reports the preparation of bacterial cellulose membrane (BCM) and their modification by in situ methodology with the organo-bridged precursor 1,4-bis(triethoxysilyl)benzene (BTEB). BTEB was successfully incorporated into the BCM, and spherical hybrid silica nanoparticles with heterogeneous particle size (30–100 nm) and probably porous structure were formed and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared–attenuated total reflectance (FTIR-ATR), thermogravimetric analysis (TGA), and solid state nuclear magnetic resonance (NMR). We further combined solid-state NMR with dynamic nuclear polarization (DNP) to achieve sensitivity enhancement and to selectively enhance the NMR signal of the hydrophobic BTEB moieties on the BCM surface. This allowed us to get more detailed structural information about the BTEB–BCM multicomponent material.}}, author = {{Monteiro, Andreia S. and Oliveira, Marcos and Santagneli, Silvia and Carcel, Carole and Gutmann, Torsten and Buntkowsky, Gerd and Man, Michel Wong Chi and Barud, Hernane S. and Ribeiro, Sidney J. L.}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{8}}, pages = {{4498–4508}}, publisher = {{American Chemical Society}}, title = {{{Modification of Bacterial Cellulose Membrane with 1,4-Bis(triethoxysilyl)benzene: A Thorough Physical–Chemical Characterization Study}}}, doi = {{10.1021/acs.jpcc.0c09837}}, volume = {{125}}, year = {{2021}}, } @article{64015, abstract = {{Periodate oxidation reaction occurring directly on chitin has been neglected in polysaccharide chemistry so far. Herein, we present the first direct alkaline periodate oxidation of chitin, which demonstrates at the same time a novel approach for the preparation of chitin nanocrystals (ChNCs). This oxidation is based on an unprecedented selective reaction of non-ordered domains of chitin by the dimeric orthoperiodate ions (H2I2O104−) as the major species in alkaline surroundings. Nearly 50 wt% of non-ordered regions are dissolved after sequential accelerated partial deacetylation, periodate oxidation and β-alkoxy fragmentation, which allows the isolation of up to 50 wt% of uniform anisotropic zwitterionic ChNCs.}}, author = {{Liu, Peiwen and Liu, Huan and Schäfer, Timmy and Gutmann, Torsten and Gibhardt, Holger and Qi, Houjuan and Tian, Lin and Zhang, Xizhou Cecily and Buntkowsky, Gerd and Zhang, Kai}}, journal = {{Green Chemistry}}, number = {{2}}, pages = {{745–751}}, publisher = {{The Royal Society of Chemistry}}, title = {{{Unexpected selective alkaline periodate oxidation of chitin for the isolation of chitin nanocrystals}}}, doi = {{10.1039/D0GC04054A}}, volume = {{23}}, year = {{2021}}, } @article{64006, abstract = {{Three chiral dirhodium coordination polymers Rh2–Ln (n = 1–3) have been synthesized via ligand exchange between dirhodium trifluoroacetate Rh2(TFA)4 and differently sized chiral dicarboxylic acids derived from l-tert-leucine. SEM images indicate that the Rh2–Ln (n = 1–3) polymers have a lamellar structure. XPS data demonstrate that the oxidation state of rhodium in the dirhodium nodes is maintained during the synthesis of the polymers. The coordination polymers have been further characterized by FTIR, 1H → 13C CP MAS NMR and 19F MAS NMR spectroscopy to prove the formation of polymers via ligand exchange. Although the quantitative 19F MAS NMR spectra reveal incomplete ligand substitution in the coordination polymers, these catalysts show excellent activity and selectivity in the asymmetric cyclopropanation reaction between styrene and diazooxindole. In particular, the enantioselectivity has been significantly improved compared with previously designed dirhodium coordination polymers, which were synthesized from aromatic dicarboxylic acids derived from l-phenylalanine. Meanwhile, the dirhodium polymers can be easily recycled five times without significant reduction in their catalytic efficiency.}}, author = {{Li, Zhenzhong and Rösler, Lorenz and Wissel, Till and Breitzke, Hergen and Hofmann, Kathrin and Limbach, Hans-Heinrich and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{2044-4753}}, journal = {{Catalysis Science & Technology}}, number = {{10}}, pages = {{3481–3492}}, publisher = {{The Royal Society of Chemistry}}, title = {{{Design and characterization of novel dirhodium coordination polymers – the impact of ligand size on selectivity in asymmetric cyclopropanation}}}, doi = {{10.1039/D1CY00109D}}, volume = {{11}}, year = {{2021}}, } @article{64005, abstract = {{A novel immobilized chiral dirhodium catalyst, Rh2(S-PTTL)3(S-PTTL-linker)∼SBA-15 (8), has been prepared via click reaction of azide-groups on functionalized SBA-15 with the dirhodium complex Rh2(S-PTTL)3(S-PTTL-alkyne) (6) containing an alkyne moiety. During the synthesis of this complex, one chiral ligand of the parent Rh2(S-PTTL)4 catalyst is exchanged with an analogous chiral ligand system containing an alkyne moiety, which to a great extent maintains the intrinsic catalytic performance of the catalyst. The heterogeneous dirhodium catalyst is characterized by FT-IR and 13C solid-state NMR to validate the successful immobilization. The catalytic performance of the heterogeneous catalyst 8 is investigated in the asymmetric cyclopropanation of 3-diazooxindole with different aryl alkenes that form spiro-cyclopropyloxindoles which serve as precursors for pharmaceuticals. The resulting heterogeneous catalyst shows high catalytic activity and significant enantioselectivity. Importantly, it can be readily recovered and reused at least four times without significant loss of its catalytic performance.}}, author = {{Li, Zhenzhong and Rösler, Lorenz and Wissel, Till and Breitzke, Hergen and Gutmann, Torsten and Buntkowsky, Gerd}}, journal = {{Journal of CO2 Utilization}}, keywords = {{immobilized catalyst, asymmetric cyclopropanation, Chiral dirhodium}}, pages = {{101682}}, title = {{{Immobilization of a chiral dirhodium catalyst on SBA-15 via click-chemistry: Application in the asymmetric cyclopropanation of 3-diazooxindole with aryl alkenes}}}, doi = {{10.1016/j.jcou.2021.101682}}, volume = {{52}}, year = {{2021}}, } @article{63993, abstract = {{A synthetic strategy to β-silylphospholes with three methoxy, ethoxy, chloro, hydrido, or phenyl substituents at silicon has been developed, starting from trimethoxy, triethoxy, or triphenyl silyl substituted phenyl phosphanides and 1,4-diphenyl-1,3-butadiyne. These trifunctional silylphospholes were attached to the surface of uniform spheric silica particles (15 μm) and, for comparison, to a polyhedral silsesquioxane (POSS)–trisilanol as a molecular model to explore their luminescent properties in comparison with the free phospholes. Density functional theory calculations were performed to investigate any electronic perturbation of the phosphole system by the trifunctional silyl anchoring unit. For the immobilized phospholes, cross-polarization magic-angle-spinning NMR measurements (13C, 29Si, and 31P) were carried out to explore the bonding situation to the silica surface. Thermogravimetric analysis and X-ray photoelectron spectroscopy measurements were performed to approximate the amount of phospholes covering the silica surface. Identity and purity of all novel phospholes have been established with standard techniques (multinuclear NMR, mass spectrometry, and elemental analysis) and X-ray diffraction for the POSS derivative.}}, author = {{Klintuch, Dieter and Höfler, Mark V. and Wissel, Till and Bruhn, Clemens and Gutmann, Torsten and Pietschnig, Rudolf}}, journal = {{Inorganic Chemistry}}, number = {{18}}, pages = {{14263–14274}}, publisher = {{American Chemical Society}}, title = {{{Trifunctional Silyl Groups as Anchoring Units in the Preparation of Luminescent Phosphole–Silica Hybrids}}}, doi = {{10.1021/acs.inorgchem.1c01775}}, volume = {{60}}, year = {{2021}}, } @article{63992, abstract = {{Solid-state NMR combined with dynamic nuclear polarization (DNP NMR) is used to study hydration processes in tricalcium silicate (Ca3SiO5, abbreviated as C3S) samples. The studied C3S samples have experienced early stage hydration (1–30 h) and slow aging (9 years) processes. The appearance of Q3 and Q4 lines in the 29Si MAS and 1H → 29Si CP MAS NMR spectra obtained for partly hydrated C3S samples indicated the formation of amorphous silica which corresponds to their carbonation, which was corroborated by complementary FTIR data. Significant DNP signal enhancements obtained for the studied samples allowed to further investigate the C3S carbonation process in detail employing the 1H → 29Si CP MAS FSLG HETCOR technique. Finally, DNP enhanced 1H → 13C CP MAS and 1H → 13C CP MAS FSLG HETCOR techniques enabled to directly observe the formation of carbonate moieties in partly hydrated C3S samples.}}, author = {{Klimavicius, Vytautas and Hilbig, Harald and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{13}}, pages = {{7321–7328}}, publisher = {{American Chemical Society}}, title = {{{Direct Observation of Carbonate Formation in Partly Hydrated Tricalcium Silicate by Dynamic Nuclear Polarization Enhanced NMR Spectroscopy}}}, doi = {{10.1021/acs.jpcc.0c10382}}, volume = {{125}}, year = {{2021}}, } @article{63982, abstract = {{Polyethylene glycol (PEG) is gaining interest as an alternative green solvent in chemical synthesis and processing. This report presents density and viscosity data from 293.15 K to 358.15 K as well as self-diffusion coefficient data from 298.15 K to 358.15 K for oligomers of PEG from di- to nonaethylene glycol. The results were obtained by extrapolation from measurement series where water, the most common impurity in PEGs, was intentionally added in several increments. The obtained results are carefully compared to literature data, which are widely available only for density and viscosity, and only for the lower oligomers. Densities are found to be linearly dependent on temperatures for all studied oligomers. The temperature dependence of viscosity and self-diffusion coefficients show only slight deviations from the Arrhenius equation over the investigated temperature range. The activation energies obtained from the viscosity data agree well with the activation energies from the self-diffusion coefficient data and appear to be linearly dependent with respect to the number of ethylene oxide repeat units in the PEG oligomer. This linearity combined with the observation that the pre-exponential factor appears to be the same for all studied oligomers may serve as a tool to estimate viscosities and self-diffusion coefficients for higher oligomers within the investigated temperature range. The densities of the oligomers all fall within a rather narrow range without a clear trend in homologous series.}}, author = {{Hoffmann, Markus M. and Horowitz, Rachel H. and Gutmann, Torsten and Buntkowsky, Gerd}}, journal = {{Journal of Chemical and Engineering Data}}, number = {{6}}, pages = {{2480–2500}}, publisher = {{American Chemical Society}}, title = {{{Densities, Viscosities, and Self-Diffusion Coefficients of Ethylene Glycol Oligomers}}}, doi = {{10.1021/acs.jced.1c00101}}, volume = {{66}}, year = {{2021}}, } @article{63986, abstract = {{13C and 15N solid-state nuclear magnetic resonance (NMR) combined with dynamic nuclear polarization (DNP) is used to investigate the structure of dye-doped biopolymer-based materials that can be used in amplified spontaneous emission (ASE) experiments. By comparing calligraphic paper prepared from cellulose and scaffolds prepared from chitosan as substrates, differences in the interactions of the carrier material with the dye molecule Calcofluor White are obtained. These are most probably induced by structural changes of the carrier material due to its interaction with water forming hydrogen bonds. Such structural differences may explain the obtained variation of the emission wavelength of Calcofluor White doped on these substrates in ASE experiments.}}, author = {{Höfler, Mark V. and Hoinka, Nicolai and Schäfer, Timmy and Horn, Marilia and Aussenac, Fabien and Fuhrmann-Lieker, Thomas and Gutmann, Torsten}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{39}}, pages = {{21550–21558}}, publisher = {{American Chemical Society}}, title = {{{Light Amplification Materials Based on Biopolymers Doped with Dye Molecules—Structural Insights from 15N and 13C Solid-State Dynamic Nuclear Polarization}}}, doi = {{10.1021/acs.jpcc.1c06737}}, volume = {{125}}, year = {{2021}}, } @article{63973, abstract = {{A novel specific spin-labeling strategy for bioactive molecules is presented for eptifibatide (integrilin) an antiplatelet aggregation inhibitor, which derives from the venom of certain rattlesnakes. By specifically labeling the disulfide bridge this molecule becomes accessible for analytical techniques such as Electron Paramagnetic Resonance (EPR) and solid state Dynamic Nuclear Polarization (DNP). The necessary spin-label was synthesized and inserted into the disulfide bridge of eptifibatide via reductive followed by insertion by a double Michael addition under physiological conditions. This procedure is universally applicable for disulfide containing biomolecules and is expected to preserve their tertiary structure with minimal change due to the small size of the label and restoring of the previous disulfide connection. HPLC and MS analysis show the successful introduction of the spin label and EPR spectroscopy confirms its activity. DNP-enhanced solid state NMR experiments show signal enhancement factors of up to 19 in 13C CP MAS experiments which corresponds to time saving factors of up to 361. This clearly shows the high potential of our new spin labeling strategy for the introduction of site selective radical spin labels into biomolecules and biosolids without compromising its conformational integrity for structural investigations employing solid-state DNP or advanced EPR techniques.}}, author = {{Herr, Kevin and Fleckenstein, Max and Brodrecht, Martin and Höfler, Mark V. and Heise, Henrike and Aussenac, Fabien and Gutmann, Torsten and Reggelin, Michael and Buntkowsky, Gerd}}, journal = {{Scientific Reports}}, number = {{1}}, pages = {{13714}}, title = {{{A novel strategy for site selective spin-labeling to investigate bioactive entities by DNP and EPR spectroscopy}}}, doi = {{10.1038/s41598-021-92975-6}}, volume = {{11}}, year = {{2021}}, } @article{63947, abstract = {{The interactions of molecules such as surfactants with solid interfaces are not sufficiently understood since their study is challenging with standard spectroscopic methods. In this work, octanol-d17 as a model system confined in the mesopores of SBA-15 is studied by variable temperature deuterium solid-state NMR, and the findings are compared to those of bulk octanol-d17. The magic angle spinning (MAS) as well as the static, nonspinning case, are investigated, showing that the described observations are independent of the applied NMR method. The 2H NMR spectra of both the bulk and the confined octanol-d17 show a large and a small quadrupolar Pake pattern below the melting point, suggesting a rigid conformation of the observed molecules with a 3-fold jump motion of the terminal CD3-group. Apart from the melting of the solid, no other phase transition is observed for either sample. The confined octanol-d17 forms a pore solid, exhibiting a melting point 38 K lower than bulk octanol-d17. The interactions of the molecule with the mesoporous SBA-15 bring about a distribution of activation energies for the melting process, resulting in a gradual melting process.}}, author = {{Döller, Sonja C. and Brodrecht, Martin and Haro Mares, Nadia B. and Breitzke, Hergen and Gutmann, Torsten and Hoffmann, Markus and Buntkowsky, Gerd}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{45}}, pages = {{25155–25164}}, publisher = {{American Chemical Society}}, title = {{{Deuterium NMR Studies of the Solid–Liquid Phase Transition of Octanol-d17 Confined in SBA-15}}}, doi = {{10.1021/acs.jpcc.1c05873}}, volume = {{125}}, year = {{2021}}, } @article{64275, abstract = {{Abstract We explain by elementary means why the existence of a discrete series representation of a real reductive group G implies the existence of a compact Cartan subgroup of G. The presented approach has the potential to generalize to real spherical spaces.}}, author = {{Krötz, Bernhard and Kuit, Job J. and Opdam, Eric M. and Schlichtkrull, Henrik}}, issn = {{0075-4102}}, journal = {{Journal für die reine und angewandte Mathematik (Crelles Journal)}}, number = {{782}}, pages = {{109--119}}, publisher = {{Walter de Gruyter GmbH}}, title = {{{Ellipticity and discrete series}}}, doi = {{10.1515/crelle-2021-0063}}, volume = {{2022}}, year = {{2021}}, }