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1.
Katrin Leschke 《Annals of Global Analysis and Geometry》1997,15(1):51-69
On every isoparametric submanifold M a connection with parallel second fundamental form is constructed geometrically such that M is an orbit of an s-representation if and only if the connection is a canonical one. If the rank of M is greater than one this connection is in case of homogeneity the canonical connection of the reductive decomposition given
by the orbit of s-representation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Graham DL Lowe PN Grime GW Marsh M Rittinger K Smerdon SJ Gamblin SJ Eccleston JF 《Chemistry & biology》2002,9(3):375-381
The formation of complexes between small G proteins and certain of their effectors can be facilitated by aluminum fluorides. Solution studies suggest that magnesium may be able to replace aluminum in such complexes. We have determined the crystal structure of RhoA.GDP bound to RhoGAP in the presence of Mg(2+) and F(-) but without Al(3+). The metallofluoride adopts a trigonal planar arrangement instead of the square planar structure of AlF(4)(-). We have confirmed that these crystals contain magnesium and not aluminum by proton-induced X-ray emission spectroscopy. The structure adopted by GDP.MgF(-) possesses the stereochemistry and approximate charge expected for the transition state. We suggest that MgF3(-) may be the reagent of choice for studying phosphoryl transfer reactions. 相似文献
3.
The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated. 相似文献
4.
Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of ‘isotopically sensitive branching’ in FeI-mediated C? H bond activation. For the hexane-1,6-diol/Fe+-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D ,L - and meso-[3,4-D2]-isotompomers 1e and 1f demonstrates that dehydrogenation proceedes via two competing pathways (i.e. ‘anti’- vs. ‘syn’-route). The contribution of these routes to the product formation is – due to a kinetic isotope effect – controlled by the relative configuration at the labeled positions C(3)/C(4). For the D ,L -form 1e , we estimate a ratio of 49:1 in favor of the ‘anti’-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f . 相似文献
5.
Hans‐Peter Kormann Günter Schmid Katrin Pelzer K. Philippot Bruno Chaudret 《无机化学与普通化学杂志》2004,630(12):1913-1918
Nanoporous alumina membranes, loaded with palladium and ruthenium nanoparticles of various size, were used for gas phase hydrogenation of 1, 3‐butadiene and for oxidation of carbon monoxide, respectively. Those membranes contain 109 ‐ 1011 pores per cm2, all running perpendicular to the surface. Membrane discs of 20 mm in diameter and only 60 μm thick, incorporated in a reactor in which the reactants can be pumped in a closed circuit through the pores, turned out to very actively catalyze hydrogenation of butadiene (Pd) and oxidation of CO (Ru). The activity of the Pd catalysts depends characteristically on the particles size, the gas flow, and of the educts ratio. As could be expected, larger particles are less active than smaller ones, whereas increasing gas flows in case of hydrogenation accelerates the reactions. Excessive hydrogen reduces selectivity with respect to the various butenes, but favours formation of butane. 相似文献
6.
A. Katrin Krieg 《Analytical and bioanalytical chemistry》2013,405(20):6387-6388
7.
Olesya V. Zillich Ute Schweiggert‐Weisz Katrin Hasenkopf Peter Eisner Martina Kerscher 《Biomedical chromatography : BMC》2013,27(11):1444-1451
Permeation of polyphenols through the stratum corneum barrier is a precondition for the protective action of polyphenols against oxidative skin damage. Prior to in vitro skin permeation experiments, we developed a method for the quantification of polyphenols in pig skin, including organic solvent extraction and HPLC analysis. Catechine hydrate, epigallocatechin gallate, trans‐resveratrol, quercetin, rutin and protocatechuic acid were chosen for this study as representatives of phenolics with different lipophilicity and molecular weight. The antioxidative activities of polyphenols as well as their octanol–water partition coefficients at different pH values were determined. Extraction of polyphenols from pig skin was optimized by variation of solvent composition, homogenization intensity and time, as well as partial exclusion of oxygen during extraction. The highest recovery rates could be reached by extraction with the methanol–water mixture (90:10, v/v), containing 0.2 g/L l ‐ascorbic acid, after the cryo‐milling for 4 min. Recoveries of 72% for total phenolics, 96% for quercetin and protocatechuic acid, 90% for rutin and 74% for trans‐resveratrol, were achieved. These extraction parameters will be selected for the polyphenol extraction from pig skin for further in vitro drug permeation studies. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
8.
Inside Back Cover: Synthesis and Isolation of the Titanium–Scandium Endohedral Fullerenes—Sc2TiC@Ih‐C80, Sc2TiC@D5h‐C80 and Sc2TiC2@Ih‐C80: Metal Size Tuning of the TiIV/TiIII Redox Potentials (Chem. Eur. J. 37/2016) 下载免费PDF全文
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