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991.
Joachim Thrane Sebastian Kuld Niels D. Nielsen Prof. Anker D. Jensen Dr. Jens Sehested Prof. Jakob M. Christensen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18346-18350
Catalytic methanol synthesis is one of the major processes in the chemical industry and may grow in importance, as methanol produced from CO2 and sustainably derived H2 are envisioned to play an important role as energy carriers in a future low-CO2-emission society. However, despite the widespread use, the reaction mechanism and the nature of the active sites are not fully understood. Here we report that methanol synthesis at commercially applied conditions using the industrial Cu/ZnO/Al2O3 catalyst is dominated by a methanol-assisted autocatalytic reaction mechanism. We propose that the presence of methanol enables the hydrogenation of surface formate via methyl formate. Autocatalytic acceleration of the reaction is also observed for Cu supported on SiO2 although with low absolute activity, but not for Cu/Al2O3 catalysts. The results illustrate an important example of autocatalysis in heterogeneous catalysis and pave the way for further understanding, improvements, and process optimization of industrial methanol synthesis. 相似文献
992.
Hans Joachim Breunig Michael Denker Klaus H. Ebert 《Journal of organometallic chemistry》1994,470(1-2):87-92
MeSbCl2 (1) and SbCl3 give the adduct MeSbCl2·0.6SbCl3 (1a). MeSbBr2 (2) reacts with NaI to form MeSbI2 (3) and with Cr(CO)5 THF to give Me(Br)2SbCr(CO)5 (4). The crystal structures of 1a, 2 and 4 are reported. Derivatives of methyl antimony are obtained by reaction of 2 or 4 with Mg in tetrahydrofuran. 相似文献
993.
Stefan Sahli Bernhard Stump Tobias Welti W.Bernd Schweizer Franois Diederich Denise Blum‐Kaelin JohannesD. Aebi Hans‐Joachim Bhm 《Helvetica chimica acta》2005,88(4):707-730
Neprilysin (NEP; neutral endopeptidase EC 3.4.24.11) is a ZnII‐dependent, membrane‐bound endopeptidase. NEP is widely distributed in the organs, particularly in the kidneys and lungs, and it is involved in the metabolism of a number of smaller regulatory peptides. Inhibition of NEP has been proposed as a potential target for analgesic and antihypertensive therapies. In this study, new nonpeptidic inhibitors of neprilysin ((±)‐ 1 , (±)‐ 43 , (±)‐ 45 , and (±)‐ 46 ; Table) were designed, based on the X‐ray crystal structure of NEP complexed to phosphoramidon (Fig. 1). They feature an imidazole ring as the central scaffold, acting as a peptide bond isoster to undergo H‐bonding with the side chains of Asn542 and Arg717 (Fig. 2). The scaffold is decorated with a thiol group to ligate to the ZnII ion and two aromatic residues to bind into the hydrophobic S1′ and S2′ pockets. The synthesis of the new inhibitors was approached by two routes (Schemes 1–4 and 5–8), with the second one involving a double directed ortho‐metallation of the imidazole platform and a Stille cross‐coupling, providing the desired target molecules as hydrochloride salts. In a fluorescence assay, inhibitors (±)‐ 1 , (±)‐ 43 , (±)‐ 45 , and (±)‐ 46 all exhibit IC50 values in the single‐digit micromolar activity range (2–4 μM , Table), which validates the binding mode postulated by modeling. Useful guidelines for a next lead optimization cycle were obtained in several control runs. 相似文献
994.
Nölte J 《Analytical and bioanalytical chemistry》1996,355(7-8):889-891
An Excimer laser operating at the wavelength of 308 nm has been used to ablate soil for bulk analysis. The ablated material has been transferred to an array ICP emission spectrometer. In order to avoid a degraded reproducibility due to imhomogeneity, repetitive firings along a sampling line have been done at a firing frequency of 3 Hz. Effects of line length, read delay and internal standardization have been studied. 相似文献
995.
Variation of molecular architectures of blend compatibilizers and reactive processing reaction conditions gave excellent control on morphology development and toughness/stiffness balance of polypropene/polyamide 6 blends. Basic structure/property relationships of blends containing discrete PA6 phases, PA6 nanoparticle cores encapsulated in a rubber shell, dispersed PA6 particles with rubber subinclusions, and percolation structures of agglomerated core/shell particles were investigated. Deformation behavior of percolation structures were analyzed by means of high-voltage transmission electron microscopy. 相似文献
996.
The novel complexes M[O(R)PhCH{CH=N(tBu)}N(tBu)](2) [M = Zr, R = Me (4a), R = Ph (4b) and M = Hf, R = Me (5a), R = Ph (5b)] have been prepared in almost quantitative yield by reaction of (tBu-DAD)(2)Zr (1) and (tBu-DAD)(2)Hf (2) [tBu-DAD = (tBu)N=CHCH=N(tBu)] with 2 equiv of the ketones MeCOPh (3a) or PhCOPh (3b). The reaction proceeds via a 1,3-dipolar cycloaddition of the C=O bond across the M-N-C unit of the DAD complexes. The molecular structures of the complexes 4a and 5b have been determined by a single-crystal X-ray diffraction study (4a, triclinic, space group P&onemacr;; a = 10.395(2) ?, b = 10.865(2) ?, c = 16.842(3) ?, alpha = 93.80(3) degrees, beta = 99.84(3) degrees, gamma = 106.12(3) degrees, V = 1787.4(6) ?(3), Z = 2, R1 = 0.035 (wR2 = 0.101) for 6963 reflections with I > 2sigma(I); 5b, monoclinic, space group P2(1)/c, a = 19.961(4) ?, b = 10.482(2) ?, c = 20.150(4) ?, beta = 91.30(1) degrees, V = 4215(1) ?(3), Z = 4, R1 = 0.036 (wR2 = 0.097) for 4650 reflections with I > 2sigma(I)). The metal atoms in 4a and 5b adopt a pseudooctahedral coordination sphere consisting of four nitrogen and two oxygen atoms. The distortion is a consequence of the [2.2.1] bicyclic structure of the newly formed tridentate ligands which are not able to span three regular octahedral positions. 相似文献
997.
We studied the homogeneous nucleation kinetics of an aqueous suspension of charged colloidal spheres under de-ionized conditions. Samples of equilibrium crystalline structure were shear molten and the metastable melt left to solidify after cessation of shear. At low particle number densities n, corresponding to low metastability of the melt, nucleation was monitored directly via video microscopy. We determined the nucleation rates gamma(t) by counting the number of newly appearing crystals in the observation volume per unit time. Using a suitable discrete adaptation of Avrami's [J. Chem. Phys. 7, 1003 (1939); ibid.8, 212 (1940); ibid.9, 177 (1941)] model for solidification via homogeneous nucleation and subsequent growth, we calculate the remaining free volume VF(t) to obtain the rate densities J(t) = gamma(t)/VF(t). We observe J(t) to rise steeply, display a plateau at a maximum rate density Jmax, and to decrease again. With increased n the plateau duration shrinks while Jmax increases. At low to moderate number densities fully solidified samples were analyzed by microscopy to obtain the grain-size distribution and the average crystallite size angle brackets(L). Under the assumption of stationarity, we obtained the nucleation rate density J(Avr), which increased strongly with increasing n. Interestingly, J(Avr) agrees quantitatively to Jmax and to J(Avr) as obtained previously from scattering data taken on the same sample at large n. Thus, by combination of different methods, reliable nucleation rate densities are now available over roughly one order of magnitude in n and eight orders of magnitude in J. 相似文献
998.
999.
1000.
Tanaka M Hermann J Haase I Fischer M Boxer SG 《Langmuir : the ACS journal of surfaces and colloids》2007,23(10):5638-5644
We establish a lipid monolayer supported by a polymer interface that offers advantages over conventional solid-supported membranes for determining the frictional drag at the membrane-protein interface as well as for electric field manipulation of membrane-anchored proteins. Polymer-supported monolayers with functional lipid anchors allow for the specific docking of His-tagged green fluorescent protein variants (His-EGFP and His-DsRed tetramer) onto the membrane surface at a defined surface density. In the first part, we measure the lateral diffusion coefficients of lipids and proteins and calculate the frictional drag at the protein-membrane interface. The second part deals with the electric field-induced accumulation of recombinant proteins on a patterned surface. The mean drift velocity of proteins, which can be obtained analytically from the shape of the steady-state concentration gradient, can be controlled by tuning the interplay of electrophoresis and electroosmosis. The results demonstrate the potential of such molecular constructs for the local functionalization of solid substrates with membrane-associated proteins. 相似文献