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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.
U. Wannagat F. Vielberg H. Voß K. Hensen W. Sarholz 《Monatshefte für Chemie / Chemical Monthly》1969,100(4):1127-1132
The enthalpies of formation of the addition compounds F4Si(py)2, Cl4Si(py)2, Br4Si(py)2 and I4Si(py)4 have been measured calorimetrically by two different ways (see table 1). It was not possible to confirm enthalpy data published in7, 8. The sequence SiF44~SiBr4>SiI4(?) is proposed for the acceptor power of the silicon tetrahalides towards pyridine. 相似文献
3.
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
4.
Karl Hensen Bjrn Spangenberg Michael Bolte 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(2):208-210
The crystal and molecular structures of two phenanthroline hydrochlorides have been determined at 173 K. 1,10‐Phenanthrolin‐1‐ium chloride, C12H9N2+·Cl?, crystallizes in two stacks of exactly planar molecules. Both stacks are approximately parallel to the (02) plane and the planes composing the different stacks enclose an angle of 13.29 (3)°. Tris(1,10‐phenanthrolin‐1‐ium) dichloride (hydrogen chloride) chloride chloroform solvate, 3C12H9N2+·2Cl?·HCl·Cl?·CHCl3, displays an interesting network of Cl? mediated hydrogen bonds between the two different phenanthrolinium moieties and between a phenanthrolinium and the chloroform solvate. In addition, a hydrogen bond between the HCl and the third Cl? ion is formed. The C—N—C angle at the protonated N atoms is, in all phenanthrolinium units of both structures, significantly larger than the C—N—C angle at the non‐protonated N atom. 相似文献
5.
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
6.
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
7.
Zusammenfassung Mit Hilfe eines einfachen quantenmechanischen Näherungsansatzes wird versucht, Bindungsabstände und Normalfrequenzen des Hydrogendifluoridions sowie des entsprechenden deuterierten Ions zu berechnen. Hierbei wird die Elektronenwechselwirkung der beiden Fluoridionen untereinander durch einen der Statistik entlehnten Ausdruck berücksichtigt. Die Methode liefert für die Abstände gute, für die Normalfrequenzen durchaus befriedigende Ergebnisse.
Der Deutschen Forschungsgemeinschaft danken wir für die Gewährung eines Stipendiums an Karl Hensen. 相似文献
On the basis of a quantum mechanical treatment the bond distances and the normal frequences of the hydrogen difluoride ion and its deuterated analogue are calculated. The electronic interaction of the two fluoride ions is approximated by a statistical calculation. The results are in fairly good agreement with the experimental values.
Résumé Sur la base d'un traitement quantique simple, le calcul des distances de liaison et des fréquences normales est tenté pour l'ion de bifluorure d'hydrogène et son analogue deutéré. L'intéraction électronique des deux ions fluorures est approximée au moyen d'un calcul statistique. Les résultats sont en très bon accord avec les valeurs expérimentales.
Der Deutschen Forschungsgemeinschaft danken wir für die Gewährung eines Stipendiums an Karl Hensen. 相似文献
8.
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
9.
Zhu Q Hensen EJ Mojet BL van Wolput JH van Santen RA 《Chemical communications (Cambridge, England)》2002,(11):1232-1233
Fe-oxide species in Fe/ZSM-5 (prepared by chemical vapor deposition of FeCl3)--active in N2O decomposition--react with zeolite protons during high temperature calcination to give highly active cationic Fe species, this transformation being reversible upon exposure to water vapor at lower temperature. 相似文献
10.