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排序方式: 共有170条查询结果,搜索用时 31 毫秒
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Garcia Ruano JL Alcudia A del Prado M Barros D Maestro MC Fernandez I 《The Journal of organic chemistry》2000,65(10):2856-2862
The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported. 相似文献
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C. B. Zamboni L. C. Oliveira L. Dalaqua Jr J. Mesa 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):331-334
Summary Neutron activation analysis technique, using Au as flux monitor, was applied to determine element concentrations of Ca, K,
Na, Mg, Mn and Sr in certified reference material (NIST 1400 Bone Ash). The results were compared with those using comparative
INAA and they were compatible. The same results were obtained using the recommended k0 factors, in order to obtain the activation cross section as input in concentration for the same reference material. Some
applications in the health area aiming clinical evaluation in bone samples of medium and small-sized animals were performed
and the viability of using this methodology was discussed. 相似文献
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Alessandro D'Aprano Camillo La Mesa Noemi Proietti Bianca Sesta Sonia Tatone 《Journal of solution chemistry》1994,23(12):1331-1346
The interactions between octyl--D-glucoside and glycine in water have been investigated by surface tension, viscosity, and density measurements. The results show that the -amino acid causes an unexpected lowering of the critical micellar concentration of octyl--D-glucoside. Such a finding has been interpreted in temss of dipole-dipole interactions between the hydrophilic site of the surfactant and the peptidic cosluttes. From three to seven amino acid molecules have been estimated to be coordinated with each glucoside unity in the micellar state. The research has been extended to glycine oligopeptides and L-lysine. The latter compound has effects similar to those observed with glycine whereas diglycine and triglycine show weaker effects on the micellization process. 相似文献
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Muzzalupo R Trombino S Iemma F Puoci F La Mesa C Picci N 《Colloids and surfaces. B, Biointerfaces》2005,46(2):78-83
Vesicular formulations (liposomes and niosomes) play an increasingly important role since they can be used as drug delivery and targeting systems. We described the formation of two niosomal systems based on synthetic bolaform surfactants (4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecanedioc acid diamide (BD-16) and alpha,omega-(4,7,10,13-pentaoxa-16-aza-cyclooctadecane)-hexadecane (BC-16). Systems containing BD-16 or BC-16 and different amount of cholesterol (CH) were prepared by aqueous dispersion of films, followed by examination of methylene blue (MB) entrapment, particle size and morphology. Indeed, we also studied the hydration in the distilled water and physiological solution, in order to investigate the complexing ability on vesicle formation. The results obtained in this study show a high encapsulation capacity and this ability and the size depends on cholesterol content. 相似文献
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Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
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Guillermo Restrepo Eugenio J. Llanos Héber Mesa 《Journal of mathematical chemistry》2006,39(2):401-416
We carried out a mathematical study of 72 chemical elements taking advantage of the chemotopological method. We selected 128
properties to define the elements (physico-chemical, geochemical and chemical properties). Then, we looked for correlated
properties and we reduced the number of them to 90. In this way we defined each element as a 90-tuple. Afterwards, we applied
principal component analysis and cluster analysis (4 similarity functions and 5 grouping methodologies). Then, we calculated
a consensus tree for the 20 dendrograms generated by the CA. Afterwards, we extracted the similarity relationships from the
consensus tree and built up a basis for a topology on the set of chemical elements. Finally, we calculated some topological
properties (closures, derived sets, boundaries, interiors and exteriors) of several subsets of chemical elements. We found
that alkali metals, alkaline earth metals and noble gases appear not related to the rest of the elements. Also, we found that
the boundary of non-metals are the semimetals with a stair-shape on the periodic table 相似文献
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