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41.
R. P. Rastogi Kehar Singh Ram Shabd B. M. Upadhyay 《Journal of colloid and interface science》1981,80(2):402-411
Electrical properties of cholesterol interfaces have been investigated. For this purpose electroosmotic and hydrodynamic permeation of water, sodium chloride, barium chloride, aluminum chloride, and urea solutions across a cholesterol plug have been investigated. Dependence of electroosmotic permeability on concentration of electrolytes has also been studied. Electrophoretic mobility of cholesterol particles of known size distribution and dispersed in solutions of varying concentrations of electrolytes and urea has also been studied. The data have been used to estimate ζ potentials in order to have a plausible picture of the electrical double layer at the cholesterol/ solution interfaces. 相似文献
42.
ágnes Zsigmond Ramóna Madácsi Ferenc Notheisz Erzsébet Mernyák and Ferenc Joó 《Reaction Kinetics and Catalysis Letters》2006,87(2):297-304
Summary [RuCl2(PPh3)3], [{RuCl2(TPPMS)2}2] and their heterogenized analogs were applied in the selective hydrogenation of 17-keto- and α,β-unsaturated ketosteroids.
In basic conditions these complexes selectively hydrogenated the C=O bonds, similarly to the results obtained in the case
of α,β-unsaturated aldehydes. A new method was developed for the synthesis of an expensive steroid alcohol, which can be prepared
traditionally in a more complicated way. 相似文献
43.
A procedure to determine 3-alkyl-2-methoxypyrazines in wines is described. It is based on the headspace solid-phase microextraction (HS-SPME) technique after a clean-up of the sample by distillation (previously acidified to pH 0.5) to remove ethanol and other volatile compounds that can interfere in the SPME. Determination is performed by means of capillary gas chromatography using a nitrogen-phosphorus detector. The method allows quantification of 3-isobutyl-2-methoxypyrazine, 3-sec-butyl-2-methoxypyrazine and 3-isopropyl-2-methoxypyrazine at their natural concentration levels and below their sensory thresholds in Cabernet Sauvignon and Merlot wines. The method was successfully applied to experimental red wines and the evolution of their pyrazine contents during the winemaking process was monitored. Pyrazine content increased during the first maceration day but did not change significantly during alcoholic and malolactic fermentation. Final contents in wines were 12-27 ng/l of 3-isobutyl-2-methoxypyrazine and 5-10 ng/l of 3-sec-butyl-2-methoxypyrazine. 相似文献
44.
Ram S. Bhatt Nitya G. Kundu T. Ling Chwang Charles Heidelberger 《Journal of heterocyclic chemistry》1981,18(4):771-774
Condensation of 2,4-dimethoxy-5-iodo-6-carbomethoxypyrimidine ( 10 ) with copper (I) 3-tetrahydropyranyloxyprop-1-ynide ( 4 ) afforded 2,4-dimethoxy-5-(3′-tetrahydropyranyloxyprop-1′-yn)-6-carbomethoxypyrimidine ( 11 ), which was hydrolyzed to produce 2,4-dimethoxy-5-(3′-hydroxyprop-1′-yn)-6-carbomethoxypyrimidine ( 12 ). Oxidation of 12 with dimethyl sulfoxide-oxalyl chloride reagent gave the acetylenic aldehyde ( 13 ), which on treatment with sodium methoxide in dry tetrahydrofuran yielded 2,4-dimethoxy-5-ethynyl-6-carbomethoxypyrimidine ( 14 ). The trimethylsilyl derivative ( 15 ) was deprotected by sequential treatment with iodotrimethylsilane and aqueous sodium hydroxide, leading to the formation of 5-ethynylorotic acid ( 1 ). 相似文献
45.
46.
The aim of this study was to investigate the influence of cosolvent polarity on the rheological flow properties of aqueous and hydroalcoholic gels obtained from the Carbopol Ultrez 10 base and used for topical applications. Specifically, we have examined the effect of pH (range 4.0--7.0) on the consistency and flow properties of dispersed systems in water and mixtures--15 : 85% v/v of methanol : water, ethanol : water, n-propanol : water and n-butanol : water--at a constant polymer concentration of 0.3% w/w. The gels, which had decreasing polarity values in the jellifying medium, showed qualitatively similar flow behavior, characteristic of pseudoplastic systems, and all of the flow curves were adjusted to the Ostwald model. Sigmoidal dose response functions were calculated to describe the flow and consistency indexes as a function of pH. As a result, the influence of alcohol polarity on the polymer network has been assessed meaningfully using the empirical parameters obtained: maximum consistency index value (k(max)), pH value required for 50% development of polymer network (pH(50)), and asymptotic flow index value (n(min)) for the fully structured gels. 相似文献
47.
Siya Ram William Evans Dean S. Wise Leroy B. Townsend John W. Mccall 《Journal of heterocyclic chemistry》1989,26(4):1053-1059
A series of methyl 2-substituted purine 8-carbamates was prepared and evaluated for antifilarial activity. These purines were synthesized as aza congeners of benzimidazole carbamates which have shown significant anthelmintic activity to determine the effect that this modification might have on anthelmintic activity. The compounds were tested against the filarial infection, B. pahangi, in jirds. None of the compounds prepared in this study demonstrated antifilarial activity. 相似文献
48.
Batlle R Carlsson H Holmgren E Colmsjö A Crescenzi C 《Journal of chromatography. A》2002,942(1-2):73-82
An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640). 相似文献
49.
Summary The species, UO2H3L–, UO2H2L2–, UO2HL3–, UO2L4–, UO2(OH)L5– and UO2(OH)2L6– are found in the equilibria between uranyl ions and 3,3-bis[N,N-di(carboxymethyl)-aminomethyl]-o-cresolsulphonphthalein (H6L; xylenol orange; dcac) in aqueous solution. The equilibria have been studied by the potentiometric method at 25° and at an ionic strength of 0.1M (KNO3). New algebraic equations have been employed to evaluate the equilibrium constants. 相似文献
50.
J. J. Ramírez-García M. Jiménez-Reyes M. Solache-Ríos E. Fernández-Ramírez H. López-González A. Rojas-Hernández 《Journal of Radioanalytical and Nuclear Chemistry》2003,255(2):299-303
The solubility of europium at 0.02M, 0.1M and 0.7M NaClO4 ionic strength solutions was determined by a radiometric method and pEus-pCH diagrams were obtained. Hydrolysis constants were also determined at the same ionic strengths by pH titration and the values found were log *1 = -7.68±0.11, -8.07±0.10 and -8.20±0.11. The log K
sp values were -23.5±0.2, -22.7±0.2 and -21.9±0.2 for 0.02M, 0.1M and 0.7M NaClO4 ionic strengths, respectively, at 303 K under CO2-free conditions and the extrapolated value at zero ionic strength was log K
sp
0 = -24.15. The working pCH ranges for the calculation of the hydrolysis constants were selected from the pEus-pCH diagrams in the region where precipitation of europium oxide or hydroxide was less than 20%. Europium removal from aqueous solutions with zeolites was explored. 相似文献