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81.
The preparation of polyhydroxylated 6-oxa-nor-tropane glycomimetics structurally related to the glycosidase inhibitor family of the calystegines is reported. The synthetic strategy involves the furanose→piperidine rearrangement of 5-deoxy-5-ureido-l-idose precursors, followed by intramolecular glycosylation involving the primary hydroxyl group. Inversion of the configuration at C-3 in the resulting 6-oxa-(+)-calystegine B2 analogue allows accessing the elusive 3-epi-6-oxa-(+)-calystegine B2 skeleton. Acid-catalyzed opening of the nor-tropane bicycle was observed, however, which could be avoided by careful neutralization of the reaction mixture. The inhibition results suggest that (+)-calystegine B2 derivatives and the corresponding C-3 epimers can be seen as glucomimetics and galactomimetics, respectively, pointing to a 1-azasugar mode of action for this family of alkaloids. 相似文献
82.
83.
XPS spectra of YIG, YIG:Bi, YIG:Ca and YIG:Co(Ge, Ca) epitaxial garnet films were measured at room temperature. The positions of the main iron, yttrium, oxygen, bismuth, cobalt and lead spectral lines were determined and their changes with the surface treatments were investigated. It was found that divalent and trivalent states of iron and cobalt ions can be resolved, the chemical shifts being in oposite directions.The authors would like to thank Dr. J. imová for careful EPMA analysis of the samples. 相似文献
84.
Summary It is shown that certain singular integral operators with variable kernels leave invariant theL
v,
-spaces studied by Campanato, Stampacchia, Peetre and others. Our results extend Peetre's work on convolution operators. 相似文献
85.
Dupieux P Alard JP Augerat J Babinet R Bastid N Brochard F Charmensat P De Marco N Fanet H Fodor Z Fraysse L Girard J Gorodetzky P Gosset J Laspalles C Lemaire MC L'Hôte D Lucas B Marroncle J Montarou G Parizet MJ Poitou J Qassoud D Racca C Schimmerling W 《Physics letters. [Part B]》1988,200(1-2):17-21
Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed. 相似文献
86.
I. B. Plećaš A. D. Perić S. D. Glodić A. M. Kostadinović 《Journal of Radioanalytical and Nuclear Chemistry》1992,166(5):373-381
Results are presented of a series of experimental tests performed to determine the influence of matrix characteristics on the leaching mechanism of copper aluminium oxychloride immobilized into cement matrices. The objective of this research was to investigate the leaching mechanism of copper as a constituent of copper aluminium oxychloride (CAOX). 相似文献
87.
88.
89.
M. Piñeiro-Iglesias M. Miñones-Vázquez E. Vázquez-Blanco S. Muniategui-Lorenzo P. López-Mahía D. Prada-Rodríguez 《Chromatographia》2002,56(7-8):483-488
Summary The aim of this work is to establish the best conditions for concentration and purification steps in the trace analysis of
aliphatic and polycyclic aromatic hydrocarbons (PAH) from atmospheric particulate matter by gas chromatography-flame ionisation
detection (GC-FID) and high performance liquid chromatography with ultraviolet and fluorescence detection (HPLC-UV-FL). The
best results for the more volatile compound were obtained with a combination of rotary evaporation and a stream of nitrogen
(near to 100% for aliphatic hydrocarbons and from 70 to 105% for PAH). Two types of solid phase extraction (SPE)cartridges
(Supelclean
tm
LC-Silica SPE tubes and Sep-Pak? Plus silica cartridges) and glass column were examined for the purification and fractionation step. Blank chromatograms of
both types of cartridges analysed by GC-FID made this study difficult, because a PSS (programmed split-splitless) injector
was employed thereby increasing the sensitivity. This problem was not observed in the HPLC-UV-FL blank chromatograms of these
cartridges. Glass columns filled with silica and alumina were chosen because no interference was found in the GC-FID blank
chromatograms and the best recoveries in the fractionation of both aliphatic hydrocarbons and PAH were achieved. This is especially
important when aliphatic hydrocarbons concentrations are lower than 1 μg mL−1. Finally, the selected conditions were applied to the analysis of hydrocarbons in real atmospheric particulate samples. 相似文献
90.
基于PuH_2分子基态(X~7A_1)的分析势能函数,用准经典的Monte-Carlo轨线法 对Pu(~7Fg)+H_2(X~1∑_g~+,0,0)的分子反应动力学过程进行了计算。结果表明 :Pu(~7F_g)与H_2(X~1∑_g~+,0,0)碰撞是弹性碰撞。 相似文献