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951.
E. D. Matveeva T. A. Podrugina M. V. Prisyazhnoi I. N. Rusetskaya N. S. Zefirov 《Russian Chemical Bulletin》2007,56(4):798-805
Interaction of aliphatic and aromatic aldehydes and ketones with optically active L-α-amino acids or their esters in the three-component catalytic one-pot synthesis of α-aminophosphonates was studied. The
corresponding α-amino phosphonates are formed in high yields as mixtures of diastereomers.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 768–774, April, 2007. 相似文献
952.
A novel method for the determination of trace amounts of Al(III) based on resonance Rayleigh scattering (RRS) has been developed. In the presence of some surfactants, Al(III) can react with morin and form an Al(III)-morin-surfactant complex, which results in the enhancement of RRS intensity and the appearance of the corresponding RRS spectral characteristics. Their maximum scatter peaks are at 476 nm for the cetyltrimethylammonium bromide (CTAB) system, 489 nm for the cetylpyridinium chloride (CPC) system, 474 nm for the Triton X-100 system, and 473 nm for the Tween-20 system. The enhanced RRS intensity is directly proportional to the concentration of Al(III). The detection limits are in the range of (0.50-1.2)×10−7 mol l−1 depending on the surfactant. The characteristics of RRS spectra of the complexes, the optimum conditions of these reactions and the influencing factors have been investigated. The method has high selectivity, and was successfully applied to the determination of Al(III) in natural and biological samples. Furthermore, according to different complexation capacity of Al(III)-morin-CTAB system under two pH conditions, speciation analysis of Al(III) in natural waters was explored. The labile monomeric Al fraction (mainly inorganic Al, Ali) is determined at acidic pH and the total monomeric Al fraction (Ala) is determined at alkaline pH. The results are in agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction-ion exchange method. 相似文献
953.
A. K. Umbetova M. I. Choudhary N. A. Sultanova G. Sh. Burasheva Zh. A. Abilov 《Chemistry of Natural Compounds》2006,42(3):332-335
The taraxeran-14-ene-type triterpenoids methyl 3-β-al-D-fridoolean-14-en-28-oate (1), 3-α-[3″,4′-dihydroxytrans-cinnamoyl]-oxy-D-fridoolean-14-en-28-oic acid (2), and β-sitosterol (3) were isolated from the aerial part of plants from the genus Tamarix (T. laxa, T. elongata) (Tamaricaceae). The structures of the triterpenoids were proved using spectral data (IR, UV, PMR, 13C NMR, 2D NMR 1H-1H COSY, HMQC, HMBC, mass). Compound 1 is new and not previously described in the literature.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 271–273, May–June, 2006. 相似文献
954.
用ICP-AES法测定了东太平洋深海锰结核样品中二十多种主,次及微量元素,结果表明,表面瘤状和表面光滑两种类型锰结核的化学元素含量有较明显的区别,如表面光滑的锰结核TiO2含较高,而表面瘤状的锰结核Mn/Fe之值较高等。 相似文献
955.
Marco Vincenti Claudio Minero Stefania Lago Costanza Rovida 《Journal of separation science》1995,18(6):359-362
A rapid and effective procedure, developed for the determination of polar compounds in water, has been applied to hydroxycarbamates. In few minutes, it is possible to perform a catalyzed derivatization of such compounds directly in the aqueous medium, using n-hexyl chloroformate. Extraction with n-hexane and injection into a benchtop GC-MS system are the only two further steps to complete the analysis. Chemical ionization proved to be more effective than electron impact to produce valuable mass spectra in terms of selectivity and sensitivity. Linear quantitative responses were demonstrated over a two-order-of-magnitude range. The minimum detectable concentration was 3 ppb for acetohydroxamic acid and 10 ppb for hydroxyurethane, obtained from Po river water samples spiked with the two hydroxycarbamate standards. 相似文献
956.
微量热法研究γ-Mo2N催化剂表面氢的微分吸附热 总被引:1,自引:0,他引:1
Differential heats of H 2 adsorption on γ-Mo2N catalysts were studied by using microcalorimetry. Samples with high and medium surface areas (90 and 17 m2•g -1 ) present a homogeneous energetic distribution of surface sites, which corresponds with the preferential orientation of their (200) planes. Molybdenum nitride with low surface area (8 m2•g -1 ) displays a heterogeneous energetic distribution of H 2 adsorption sites. The higher initial differential heat of hydrogen adsorption observed for the low surface Mo nitride was attributed to species adsorbed on surface sites associated with the (111) plane. 相似文献
957.
Comprehensive studies have been carried out on the extraction behaviour of thorium matrix vis-a-vis 17 trace metallic elements using a novel extractant viz. Cyanex-923. The near total extraction of thorium and quantitative separation of these metals has been established using inductively coupled argon plasma–atomic emission spectrometry (ICP–AES). The recovery of few representative elements has been confirmed by radio-active tracer studies. The studies carried out here have enabled determination of μg/l amounts of all analyte elements with a precision of better than 1% RSD with prior chemical separation from as low as 1 g thorium sample in just five chemical extractions. 相似文献
958.
959.
The enthalpies of dissolution, transfer, and axial coordination for the Cd(II), Co(II), Mn(III), Fe(III), and Cr(III) complexes of tetraphenylporphine, H2(TPP), in nonpolar (C6H6, CCl4) and electron-donating solvents (DMF, DMSO, Py,c-C5H10NH) have been determined calorimetrically at 298.15 K. On the basis of thermogravimetrical data for the corresponding crystallosolvates the composition, thermal stability, and energy of intermolecular interaction of the metal-porphine complexes with pyridine have been calculated. Complexing in noncoordinating solvents brings about no radical change in the physicochemical characteristics of axial coordination which depend critically on the electron structure of the complex-forming metal.Translated fromfzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–850, May, 1993. 相似文献
960.