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Volkmer D Bredenkötter B Tellenbröker J Kögerler P Kurth DG Lehmann P Schnablegger H Schwahn D Piepenbrink M Krebs B 《Journal of the American Chemical Society》2002,124(35):10489-10496
Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins. 相似文献
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Yoanes Maria Vianney Pit Preckwinkel Swantje Mohr Prof. Dr. Klaus Weisz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(70):16910-16922
A parallel quadruplex derived from the Myc promoter sequence was extended by a stem-loop duplex at either its 5′- or 3′-terminus to mimic a quadruplex–duplex (Q–D) junction as a potential genomic target. High-resolution structures of the hybrids demonstrate continuous stacking of the duplex on the quadruplex core without significant perturbations. An indoloquinoline ligand carrying an aminoalkyl side chain was shown to bind the Q–D hybrids with a very high affinity in the order Ka≈107 m −1 irrespective of the duplex location at the quadruplex 3′- or 5′-end. NMR chemical shift perturbations identified the tetrad face of the Q–D junction as specific binding site for the ligand. However, calorimetric analyses revealed significant differences in the thermodynamic profiles upon binding to hybrids with either a duplex extension at the quadruplex 3′- or 5′-terminus. A large enthalpic gain and considerable hydrophobic effects are accompanied by the binding of one ligand to the 3′-Q–D junction, whereas non-hydrophobic entropic contributions favor binding with formation of a 2:1 ligand-quadruplex complex in case of the 5′-Q–D hybrid. 相似文献
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Zlámalová M. Pitňa Lásková B. Vinarčíková M. Zukalová M. Kavan L. 《Journal of Solid State Electrochemistry》2022,26(3):639-647
Journal of Solid State Electrochemistry - The addition of nanocrystalline titanium dioxide (P90) to a cathode of Li/S cell enhances its voltammetric charge capacity by 19%, from which only a small... 相似文献
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Tobias Weissenberger Rainer Leonhardt Dr. Benjamin Apeleo Zubiri Dr. Martina Pitínová-Štekrová Dr. Thomas L. Sheppard Bastian Reiprich Dr. Jürgen Bauer Dr. Ralf Dotzel Maik Kahnt Dr. Andreas Schropp Prof. Christian G. Schroer Prof. Jan-Dierk Grunwaldt Dr. John L. Casci Prof. Jiří Čejka Prof. Erdmann Spiecker Prof. Wilhelm Schwieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14430-14440
The successful synthesis of hierarchically structured titanium silicalite-1 (TS-1) with large intracrystalline macropores by steam-assisted crystallisation of mesoporous silica particles is reported. The macropore topology was imaged in 3D by using electron tomography and synchrotron radiation-based ptychographic X-ray computed tomography, revealing interconnected macropores within the crystals accounting for about 30 % of the particle volume. The study of the macropore formation mechanism revealed that the mesoporous silica particles act as a sacrificial macropore template during the synthesis. Silicon-to-titanium ratio of the macroporous TS-1 samples was successfully tuned from 100 to 44. The hierarchically structured TS-1 exhibited high activity in the liquid phase epoxidation of 2-octene with hydrogen peroxide. The hierarchically structured TS-1 surpassed a conventional nano-sized TS-1 sample in terms of alkene conversion and showed comparable selectivity to the epoxide. The flexible synthesis route described here can be used to prepare hierarchical zeolites with improved mass transport properties for other selective oxidation reactions. 相似文献
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The boundary condition for the flow velocity of a Newtonian fluid near a solid wall has been probed experimentally with a novel setup using total internal reflection-fluorescence recovery after photobleaching leading to a resolution from the wall of the order of 80 nm. For hexadecane flowing on a hydrocarbon/lyophobic smooth surface, we give what we think to be the first direct experimental evidence of noticeable slip at the wall. We show that the surface roughness and the strength of the fluid-surface interactions both act on wall slip, in antagonist ways. 相似文献
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Dr. Hilke Petersen Steffen Reichle Sebastian Leiting Dr. Pit Losch Wolfgang Kersten Tobias Rathmann Dr. Jochi Tseng Dr. Martin Etter Dr. Wolfgang Schmidt Dr. Claudia Weidenthaler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(49):12558-12565
Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmental-friendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S8 results in the sublimation of S8, observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T>1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media. 相似文献
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Characterization of the Blue–Light‐Activated Adenylyl Cyclase mPAC by Flash Photolysis and FTIR Spectroscopy 下载免费PDF全文
Silke Kerruth Pit Langner Sarah Raffelberg Wolfgang Gärtner Joachim Heberle 《Photochemistry and photobiology》2017,93(3):857-864
The recently discovered photo‐activated adenylyl cyclase (mPAC from Microcoleus chthonoplastes) is the first PAC that owes a light‐, oxygen‐ and voltage‐sensitive (LOV) domain for blue‐light sensing. The photoreaction of the mPAC receptor was studied by time‐resolved UV/vis and light‐induced Fourier transform infrared (FTIR) absorption difference spectroscopy. The photocycle comprises of the typical triplet state LOV715 and the thio‐adduct state LOV390. While the adduct state decays with a time constant of 8 s, the lifetime of the triplet state is with 656 ns significantly shorter than in all other reported LOV domains. The light‐induced FTIR difference spectrum shows the typical bands of the LOV390 and LOV450 intermediates. The negative S‐H stretching vibration at 2573 cm?1 is asymmetric suggesting two rotamer configurations of the protonated side chain of C194. A positive band at 3632 cm?1 is observed, which is assigned to an internal water molecule. In contrast to other LOV domains, mPAC exhibits a second positive feature at 3674 cm?1 which is due to the O‐H stretch of a second intrinsic water molecule and the side chain of Y476. We conclude that the latter might be involved in the dimerization of the cyclase domain which is crucial for ATP binding. 相似文献