@article{63962, author = {{Gutmann, Torsten and Kumari, Bharti and Zhao, Li and Breitzke, Hergen and Schöttner, Sebastian and Rüttiger, Christian and Gallei, Markus}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{7}}, pages = {{3896–3903}}, publisher = {{American Chemical Society}}, title = {{{Dynamic Nuclear Polarization Signal Amplification as a Sensitive Probe for Specific Functionalization of Complex Paper Substrates}}}, doi = {{10.1021/acs.jpcc.6b11751}}, volume = {{121}}, year = {{2017}}, } @article{63956, abstract = {{The synthesis of novel robust and stable iridium-based immobilized catalysts on silica-polymer hybrid materials (Si-PB-Ir) is described. These catalysts are characterized by a combination of 1D P-31 CP-MAS and 2D P-31-H-1 HETCOR and J-resolved multinuclear solid state NMR experiments. Different binding situations such as singly and multiply coordinated phosphines are identified. Density functional theory (DFT) calculations are performed to corroborate the interpretation of the experimental NMR data, in order to propose a structural model of the heterogenized catalysts. Finally, the catalytic activity of the Si-PB-Ir catalysts is investigated for the hydrogenation of styrene employing para-enriched hydrogen gas.}}, author = {{Gutmann, Torsten and Alkhagani, S. and Rothermel, N. and Limbach, H. H. and Breitzke, H. and Buntkowsky, G.}}, issn = {{0942-9352}}, journal = {{Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics}}, keywords = {{Chemistry, dynamic nuclear-polarization, solid-state nmr, DFT, heterogeneous catalysis, hydrido complexes, hydrogenation, immobilized catalyst, inorganic hybrid, iridium, materials, mesoporous, molecular-orbital methods, PHIP, phosphine complexes, reusable catalysts, silica, solid-state-NMR, wilkinsons catalyst}}, number = {{3}}, pages = {{653–669}}, title = {{{P-31-Solid-State NMR Characterization and Catalytic Hydrogenation Tests of Novel heterogenized Iridium-Catalysts}}}, doi = {{10.1515/zpch-2016-0837}}, volume = {{231}}, year = {{2017}}, } @inbook{63958, author = {{Gutmann, Torsten and Buntkowsky, Gerd}}, booktitle = {{Modern Magnetic Resonance. Solid-state NMR Studies of Supported Transition Metal Catalysts and Nanoparticles}}, editor = {{Webb, Graham A.}}, isbn = {{978-3-319-28275-6}}, pages = {{1–21}}, publisher = {{Springer International Publishing}}, title = {{{Solid-state NMR Studies of Supported Transition Metal Catalysts and Nanoparticles}}}, doi = {{10.1007/978-3-319-28275-6_39-1}}, year = {{2017}}, } @article{63949, abstract = {{In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control.}}, author = {{Dubois, C. and Herzog, N. and Ruettiger, C. and Geissler, A. and Grange, E. and Kunz, U. and Kleebe, H. J. and Biesalski, M. and Meckel, T. and Gutmann, Torsten and Gallei, M. and Andrieu-Brunsen, A.}}, issn = {{0743-7463}}, journal = {{Langmuir}}, number = {{1}}, pages = {{332–339}}, title = {{{Fluid Flow Programming in Paper-Derived Silica-Polymer Hybrids}}}, doi = {{10.1021/acs.langmuir.6b03839}}, volume = {{33}}, year = {{2017}}, } @article{63927, abstract = {{A detailed study of the magnetic field dependent signal enhancement in solid-state dynamic nuclear polarization (DNP) experiments is presented for a specific sample consisting of AMUPol dissolved in the nonionic surfactant C10E6. C10E6 displays a superposition of “direct” and “indirect channel” resonances in 13C MAS DNP NMR spectra. The shapes of the DNP enhancement profiles are essentially identical for the 1H MAS, 1H → 13C CP MAS, and 13C MAS indirect channel signals, which confirms that the same polarization transfer process from electron to proton is responsible for the obtained enhancements of these experiments. The shape of the DNP enhancement profiles of 1H and of 13C direct channel resonances reveals that the cross effect is the dominant polarization transfer mechanism for the studied sample. The magnitudes of the 13C MAS DNP enhancement profiles for 1H → 13C CP MAS, direct and indirect channel signals were found to be not uniform. For 1H → 13C CP MAS and the indirect channel signals, this observation is related to relaxation effects of the methyl group carbon. For the 13C MAS direct channel resonances, differences in magnitudes are discussed in terms of preferential structural orientation of the polar ethylene oxide headgroup of C10E6 toward the AMUPol radical.}}, author = {{Bothe, Sarah and Hoffmann, Markus M. and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{48}}, pages = {{27089–27097}}, publisher = {{American Chemical Society}}, title = {{{Comparative Study of the Magnetic Field Dependent Signal Enhancement in Solid-State Dynamic Nuclear Polarization Experiments}}}, doi = {{10.1021/acs.jpcc.7b07967}}, volume = {{121}}, year = {{2017}}, } @article{63920, abstract = {{Coordinatively unsaturated sites (CUS) present a key feature of alumina based catalysts as they are believed to act as Lewis-acid sites in heterogeneously catalyzed reactions. In the present study, the direct observation of active species on a fluoride-doped aluminum oxide catalyst is demonstrated. This new fluoride-doped aluminum oxide exhibits strong Lewis-acid sites and superior catalytic activity as compared to gamma-Al2O3. To emphasize the labile state of Lewis-acid sites, two distinctive states of the catalysts surface are addressed using H-1-Al-27 cross polarization (CP) MAS NMR. On the one hand, the highly dehydrated and active state after calcination at 700 degrees C and on the other hand the rehydrated and catalytically inactive surface (produced by contact to air) are probed. These experiments revealed the presence of significant amounts of coordinatively unsaturated sites in the form of 4-and 5-fold coordinated Al-sites on the highly dehydrated surface. In contrast to this, the rehydrated sample exhibited a severely restructured surface caused by the chemisorption of H2O which is ’constituted in a manner that was proposed in earlier models for gamma-Al2O3 surfaces.}}, author = {{Ahrem, L. and Scholz, G. and Gutmann, Torsten and Calvo, B. and Buntkowsky, G. and Kemnitz, E.}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, keywords = {{al-27 nmr, characterization, Chemistry, cross-polarization, dynamic nuclear-polarization, eta-alumina, gamma-alumina, hydroxy fluorides, ions, Materials Science, pentacoordinated al3+, Science & Technology - Other Topics, solid-state nmr, spectroscopic, structural insights}}, number = {{22}}, pages = {{12206–12213}}, title = {{{Direct Observation of Coordinatively Unsaturated Sites on the Surface of a Fluoride-Doped Alumina Catalyst}}}, doi = {{10.1021/acs.jpcc.7b02535}}, volume = {{121}}, year = {{2017}}, } @article{64065, abstract = {{The structure and proton tautomerism of imidazole-doped cellulose (Cell-Im), an excellent solid state proton conductor, has been studied by N-15 solid-state NMR techniques. H-1-N-15 HETCOR NMR experiments allowed us to assign the water and cellulose-OH resonances and to establish H-1-N-15 connectivities. N-15 CPMAS NMR experiments showed that imidazole is immobile and its tautomerism quenched below 263 K, whereas at higher temperatures, a broad distribution of slow and fast exchanging protons is observed, where the fraction of the latter increases with temperature. The tautomerism is found to be coupled to proton exchange with water molecules. From an analysis of the temperature-dependent fractions of both phases, a broad distribution of energies of activation of the tautomerization of Cell-Im is obtained, exhibiting a maximum at 42 kJ mol(-1) and a width of 8.2 kJ mol(-1). The tautomerization is slower than in the case of imidazole dissolved in wet organic solvents. These results indicate that imidazole is located in an aqueous fluid phase between cellulose microfibrils, where proton exchange is assisted by a fast molecular reorientation in transient hydrogen-bonded imidazole-water complexes. The implications of these findings for the mechanism of proton conductivity of Cell-Im are discussed. Finally, the potential of Dynamic Nuclear Polarization (DNP) enhanced 15N-natural abundance CP-MAS NMR of these heterocyclic systems is evaluated.}}, author = {{Zhao, L. and Smolarkiewicz, I. and Limbach, H. H. and Breitzke, H. and Pogorzelec-Glaser, K. and Pankiewicz, R. and Tritt-Goc, J. and Gutmann, Torsten and Buntkowsky, G.}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, number = {{35}}, pages = {{19574–19585}}, title = {{{Imidazole-Doped Cellulose as Membrane for Fuel Cells: Structural and Dynamic Insights from Solid-State NMR}}}, doi = {{10.1021/acs.jpcc.6b07049}}, volume = {{120}}, year = {{2016}}, } @article{64047, abstract = {{A novel strategy for the immobilization of Wilkinson’s catalyst on silica nanoparticles is presented, employing pyridyl linkers as anchoring groups. The coordination binding of the catalyst to the pyridyl linker via ligand exchange of the trans-phosphine group is verified by 1 D and 2 D solid-state NMR spectroscopy. Catalytic activities are monitored by GC employing the hydrogenation of styrene as model reaction, and the leaching properties as well as the robustness of the catalyst are investigated. The resulting immobilized catalyst shows high catalytic activity, which is within a factor of three comparable to the homogeneous catalyst, and excellent stability in leaching tests. Finally, it is efficient to produce hyperpolarization in solution by employing parahydrogen-enriched hydrogen gas for hydrogenation.}}, author = {{Srour, Mohamad and Hadjiali, Sara and Sauer, Grit and Brunnengräber, Kai and Breitzke, Hergen and Xu, Yeping and Weidler, Heiko and Limbach, Hans-Heinrich and Gutmann, Torsten and Buntkowsky, Gerd}}, journal = {{ChemCatChem}}, keywords = {{heterogeneous catalysis, hydrogenation, immobilization, phosphane ligands, rhodium}}, number = {{21}}, pages = {{3409–3416}}, title = {{{Synthesis and Solid-State NMR Characterization of a Robust, Pyridyl-Based Immobilized Wilkinson’s Type Catalyst with High Catalytic Performance}}}, doi = {{10.1002/cctc.201600882}}, volume = {{8}}, year = {{2016}}, } @article{64039, abstract = {{The preparation of hierarchical and sophisticated particle architectures for mimicking structural colors known from nature still remains a challenge. In this study, the preparation of novel opal and double-inverse opal films based on thermally treated metallopolymer core particles with a silica shell is described. Thermal treatment leads to the formation of magnetic nanorattle-type particles. The main challenge of artificial particles is to ensure sufficient dispersibility after several synthetic steps. Especially silica particles providing surface hydroxyl groups tend to sinter at high temperatures leading to agglomeration. We present the introduction of trimethyl ethoxy silane (TMES) as an excellent functionalization reagent as the key reaction step. The necessity and success of functionalization are investigated by transmission electron microscopy (TEM) and zeta potential measurements. Importantly, solid state NMR techniques are employed to gain deeper insights into the chemical structure of the surface-attached reagent. Finally, by this convenient functionalization the preparation of elastomeric opal films and double-inverse opal films is proven successful revealing excellent optical film properties. Moreover, magnetic properties of these novel films are investigated by using magnetic force microscopy (MFM). The herein established route is expected to pave the way for the preparation of a variety of advanced and stimuli-responsive optical materials.}}, author = {{Scheid, D. and Stock, D. and Winter, T. and Gutmann, Torsten and Dietz, C. and Gallei, M.}}, issn = {{2050-7526}}, journal = {{Journal of Materials Chemistry C}}, keywords = {{Materials Science, silica, Physics, nmr, colloidal photonic crystals, light, polymerization, solids, structural color, thermo}}, number = {{11}}, pages = {{2187–2196}}, title = {{{The pivotal step of nanoparticle functionalization for the preparation of functional and magnetic hybrid opal films}}}, doi = {{10.1039/c5tc04388c}}, volume = {{4}}, year = {{2016}}, } @article{64011, abstract = {{Catalytically active dirhodium sheet-like coordination polymers are synthesized from their precursors via ligand exchange. The individual lamellae of the dirhodium-bdc frameworks are stacked as parallel sheets, which are randomly oriented or slightly ordered. As inorganic building blocks Rh2(TFA)4 and Rh2(OAc)4, and as organic linker benzene 1,4-dicarboxylate (bdc) are employed. The successful synthesis of the Rh2-bdc(Tf) and Rh2-bdc(Ac) catalysts is proven by ATR-IR, XPS and 13C CP MAS NMR. Residual trifluoroacetate species are investigated by quantitative 19F MAS NMR which further reflects the configuration of trifluoroacetate in the obtained Rh2-bdc(Tf), and defects in the structure. DR-UV-vis and XPS demonstrate that the oxidation state and the Rh-Rh single bond in the dirhodium node are maintained during the ligand substitution process. The stability and reusability of the catalysts are verified by TG-DTA measurements and leaching tests. The catalysts show similar catalytic efficiency as the homogeneous catalyst in the model cyclopropanation between ethyl diazoacetate (EDA) and styrene.}}, author = {{Liu, Jiquan and Fasel, Claudia and Braga-Groszewicz, Pedro and Rothermel, Niels and Lilly Thankamony, Aany Sofia and Sauer, Grit and Xu, Yeping and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{2044-4753}}, journal = {{Catalysis Science & Technology}}, number = {{21}}, pages = {{7830–7840}}, publisher = {{The Royal Society of Chemistry}}, title = {{{Heterogeneous self-supported dirhodium(ii) catalysts with high catalytic efficiency in cyclopropanation - a structural study}}}, doi = {{10.1039/C6CY00915H}}, volume = {{6}}, year = {{2016}}, } @article{63939, abstract = {{The controlled catalytic functionalization of alkanes via the activation of C-H bonds is a significant challenge. Although C-H activation by transition metal catalysts is often suggested to operate via intermediate sigma-alkane complexes, such transient species are difficult to observe due to their instability in solution. This instability may be controlled by use of solid/gas synthetic techniques that enable the isolation of single-crystals of well-defined sigma-alkane complexes. Here we show that, using this unique platform, selective alkane C-H activation occurs, as probed by H/D exchange using D-2, and that five different isotopomers/isotopologues of the sigma-alkane complex result, as characterized by single-crystal neutron diffraction studies for three examples. Low-energy fluxional processes associated with the sigma-alkane ligand are identified using variable-temperature X-ray diffraction, solid-state NMR spectroscopy, and periodic DFT calculations. These observations connect sigma-alkane complexes with their C-H activated products, and demonstrate that alkane-ligand mobility, and selective C-H activation, are possible when these processes occur in the constrained environment of the solid-state.}}, author = {{Chadwick, F. M. and Kramer, T. and Gutmann, Torsten and Rees, N. H. and Thompson, A. L. and Edwards, A. J. and Buntkowsky, G. and Macgregor, S. A. and Weller, A. S.}}, journal = {{Journal of the American Chemical Society}}, number = {{40}}, pages = {{13369–13378}}, title = {{{Selective C-H Activation at a Molecular Rhodium Sigma-Alkane Complex by Solid/Gas Single-Crystal to Single-Crystal H/D Exchange}}}, doi = {{10.1021/jacs.6b07968}}, volume = {{138}}, year = {{2016}}, } @article{64060, author = {{Werner, Mayke and Heil, Andreas and Rothermel, Niels and Breitzke, Hergen and Groszewicz, Pedro Braga and Thankamony, Aany Sofia and Gutmann, Torsten and Buntkowsky, Gerd}}, journal = {{Solid State Nuclear Magnetic Resonance}}, pages = {{73–78}}, title = {{{Synthesis and solid state NMR characterization of novel peptide/silica hybrid materials}}}, doi = {{10.1016/j.ssnmr.2015.09.008}}, volume = {{72}}, year = {{2015}}, } @article{64028, author = {{Ratajczyk, Tomasz and Gutmann, Torsten and Bernatowicz, Piotr and Buntkowsky, Gerd and Frydel, Jaroslaw and Fedorczyk, Bartlomiej}}, journal = {{Chemistry A European Journal}}, number = {{36}}, pages = {{12616–12619}}, title = {{{NMR Signal Enhancement by Effective SABRE Labeling of Oligopeptides}}}, doi = {{10.1002/chem.201501552}}, volume = {{21}}, year = {{2015}}, } @article{64013, author = {{Liu, Jiquan and Plog, Andreas and Groszewicz, Pedro and Zhao, Li and Xu, Yeping and Breitzke, Hergen and Stark, Annegret and Hoffmann, Rudolf and Gutmann, Torsten and Zhang, Kai and Buntkowsky, Gerd}}, journal = {{Chemistry A European Journal}}, number = {{35}}, pages = {{12414–12420}}, title = {{{Design of a Heterogeneous Catalyst Based on Cellulose Nanocrystals for Cyclopropanation: Synthesis and Solid-State NMR Characterization}}}, doi = {{10.1002/chem.201501151}}, volume = {{21}}, year = {{2015}}, } @article{63972, author = {{Harrach, M. and Drossel, B. and Winschel, W. and Gutmann, Torsten and Buntkowsky, G.}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, pages = {{28961–28969}}, title = {{{Mixtures of Isobutyric Acid and Water Confined in Cylindrical (Silica)Nanopores Revisited - A Combined Solid-State NMR and Molecular Dynamics Simulation Study}}}, volume = {{119}}, year = {{2015}}, } @article{63963, abstract = {{A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh2(OAc)4) units, which are covalently linked to amine- and carboxyl-bifunctionalized mesoporous silica (SBA-15NH2COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis- and trans-1-ethoxycarbonyl-2-phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid-state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal-enhanced 13C CP MAS and 15N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes.}}, author = {{Gutmann, Torsten and Liu, Jiquan and Rothermel, Niels and Xu, Yeping and Jaumann, Eva and Werner, Mayke and Breitzke, Hergen and Sigurdsson, Snorri T. and Buntkowsky, Gerd}}, journal = {{Chemistry A European Journal}}, keywords = {{heterogeneous catalysis, immobilized catalyst, dynamic nuclear polarization, hyperpolarization, NMR spectroscopy}}, number = {{9}}, pages = {{3798–3805}}, publisher = {{WILEY-VCH Verlag}}, title = {{{Natural Abundance 15N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine-Carboxyl-Linked Immobilized Dirhodium Catalyst}}}, doi = {{10.1002/chem.201405043}}, volume = {{21}}, year = {{2015}}, } @article{63937, author = {{Cano, Israel and Huertos, Miguel A. and Chapman, Andrew M. and Buntkowsky, Gerd and Gutmann, Torsten and Groszewicz, Pedro B. and van Leeuwen, Piet W. N. M.}}, journal = {{Journal of the American Chemical Society}}, number = {{24}}, pages = {{7718–7727}}, title = {{{Air-Stable Gold Nanoparticles Ligated by Secondary Phosphine Oxides as Catalyst for the Chemoselective Hydrogenation of Substituted Aldehydes: a Remarkable Ligand Effect}}}, doi = {{10.1021/jacs.5b02802}}, volume = {{137}}, year = {{2015}}, } @article{63935, author = {{Buntkowsky, Gerd and Gutmann, Torsten}}, journal = {{Angewandte Chemie International Edition}}, number = {{33}}, pages = {{9450–9451}}, title = {{{A Mousetrap for Carbenium Ions: NMR Detectives at Work}}}, doi = {{10.1002/anie.201504899}}, volume = {{54}}, year = {{2015}}, } @article{64066, abstract = {{Multi-stimuli responsive materials based on cellulose nanocrystals (CNCs), especially using non-conventional stimuli including light, still need more explorations, to fulfill the requirements of complicated application environments. The structure determination of functional groups on the CNC surface constitutes a significant challenge, partially due to their low amounts. In this study, rhodamine spiroamide groups are immobilized onto the surface of CNCs leading to a hybrid compound being responsive to pH-values, heat and UV light. After the treatment with external stimuli, the fluorescent and correlated optical color change can be induced, which refers to a ring opening and closing process. Amine and amide groups in rhodamine spiroamide play the critical role in this switching process. Solid-state NMR spectroscopy coupled with sensitivity-enhanced dynamic nuclear polarization (DNP) was used to measure 13C and 15N in natural abundance, allowing the determination of structural changes during the switching process. It is shown that a temporary bond through an electrostatic interaction could be formed within the confined environment on the CNC surface during the heat treatment. The carboxyl groups on the CNC surface play a pivotal role in stabilizing the open status of rhodamine spiroamide groups.}}, author = {{Zhao, Li and Li, Wei and Plog, Andreas and Xu, Yeping and Buntkowsky, Gerd and Gutmann, Torsten and Zhang, Kai}}, journal = {{Physical Chemistry Chemical Physics}}, number = {{47}}, pages = {{26322–26329}}, publisher = {{The Royal Society of Chemistry}}, title = {{{Multi-responsive cellulose nanocrystal-rhodamine conjugates: an advanced structure study by solid-state dynamic nuclear polarization (DNP) NMR}}}, doi = {{10.1039/C4CP04096A}}, volume = {{16}}, year = {{2014}}, } @article{64064, author = {{Xu, Yeping and Watermann, Tobias and Limbach, Hans-Heinrich and Gutmann, Torsten and Sebastiani, Daniel and Buntkowsky, Gerd}}, journal = {{Physical Chemistry Chemical Physics}}, number = {{20}}, pages = {{9327–9336}}, title = {{{Water and small organic molecules as probes for geometric confinement in well-ordered mesoporous carbon materials}}}, doi = {{10.1039/c4cp00808a}}, volume = {{16}}, year = {{2014}}, }