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71.
Tricarbonyl(4-alkoxyl-1-alkylcyclohexadienylium)iron complexes (I) react with metal-cation enolate nucleophiles to give in most cases a mixture of products (II) and (III), resulting from attack at the C-1 and C-5 termini of the dienylium ring. Factors that control the regioselectivity of nucleophilic addition, including the steric and electronic effects of the 4-alkoxyl and 1-alkyl substituents, the degree of association between the enolate nucleophiles and their counterions, and the polarity of the solvents, were investigated. 相似文献
72.
Guillermina Burillo Takeshi Ogawa Jimmy S. Hwang 《Journal of polymer science. Part A, Polymer chemistry》1992,30(10):2159-2164
A number of diacetylene containing acrylate and methacrylates have been synthesized and the interaction between their propagating radicals and the diacetylene groups was studied by ESR spectroscopy. In the case of polymerization at 70°C using AIBN as an initiator, the propagating radicals of methacrylates are temporarily trapped with the diacetylenes with rapid exchange of the electron, thus showing strong signals of the propagating radicals. Gamma irradiation of the frozen state produces a blue color in samples, and the ESR signals were found to be those of uninteracted acrylate and methacrylates. From a comparison of spectral widths, there seems to exist an intramolecular interaction between the radicals and the diacetylene group at the frozen state. © 1992 John Wiley & Sons, Inc. 相似文献
73.
The flow of condensible vapors through microporous Vycor glass was investigated experimentally as well as theoretically. In porous materials, adsorbable gases frequently exhibit higher permeability than predicted from the flow of nonadsorbable gases. This enhanced flow has been attributed to the surface diffusion of adsorbed molecules along the surface of the porous media or to the viscous flow of capillary condensate at high relative pressures. In the present investigation, a new flow model of condensible vapors through microporous material was developed by considering the blocking effect of the adsorbed phase on the basis of a cylindrical capillary structure. Six different flow modes were considered depending on the pressure distribution and the film thickness of the adsorbed layer. Experimental measurements were also conducted on the transport of condensible vapors (Freon-113 and water) through microporous Vycor glass at steady state in the entire range of relative pressure. The maximum peak and scattering phenomena of permeabilities were observed. The estimated values of permeability from the developed model were compared with the experimental results. Also, it was attempted to explain the maximum peak and scattering phenomena of the experimentally observed permeabilities. 相似文献
74.
The acylation of 2-methoxynaphthalene with acetic anhydride was carried out over zeolite beta catalysts having various Si/Al
ratios. It was found that the reaction performance is strongly dependent on the Si/Al ratio of the catalyst. The catalytic
reaction features were elucidated in terms of the acidic properties of the catalysts.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
75.
5-Substituted-1,3,4-oxadiazolin-2-ones 2 were synthesized by the oxidation of carbo-t-butoxyhydrazones 1 of aromatic aldehydes with lead tetraacetate or, preferably, iodosobenzene diacetate. In some instances 5-acetoxy-1,3,4-oxadiazoles 3 were obtained along with 2 . The oxidation of carboethoxyhydrazones 4 gave 2-ethoxy-1,3,4-oxadiazoles 5 . 相似文献
76.
S. C. Sheu M. L. Lee H. L. Hwang H. Y. Lin M. H. Yang 《Fresenius' Journal of Analytical Chemistry》1989,334(2):143-147
Summary CuInS2 is one of the important I–III–VI2 ternary compounds which has in recent years received increasing interest in semiconductor science. In this study an electrochemical method has been developed based on a limited amount of available sample (0.5–10mg) for the precise and accurate determination of CuInS2 composition. After decomposition of the sample in concentrated HNO3 under pressure, copper and indium were sequentially determined by constant potential coulometry, and sulfur (as sulfate) by amperometric titration. Various experimental parameters which ensure high precision and accuracy of the results were carefully evaluated and calibrated. The overall errors for the determination of copper, indium and sulfur in a 10 mg sample were found to be +0.10%, –0.12% and +0.16%, respectively, which fullfills the requirement for accurate stoichiometric assessment.
Presented at the 10th International Symposium on Microchemical Techniques, August 25–29, 1986, Antwerp, Belgium 相似文献
Reproduzierbare und genaue Bestimmung der Stöchiometrie von CuInS2-Halbleitermaterial mit Hilfe elektrochemischer Verfahren
Presented at the 10th International Symposium on Microchemical Techniques, August 25–29, 1986, Antwerp, Belgium 相似文献
77.
Depigmenting activity and low cytotoxicity of alkoxy benzoates or alkoxy cinnamte in cultured melanocytes 总被引:2,自引:0,他引:2
To obtain effective and safe topical depigmenting agents, we synthesized hydroxybenzoates, alkoxybenzoates, and 3,4,5-trimethoxycinnamate containing a thymol moiety and screened then for high-level inhibitory activity against melanin synthesis in cultured melanocytes. Eight compounds were tested for their depigmenting effect and cytotoxicity using a murine melanocyte cell line. We found that 3,4,5-trialkoxybenzoates and 3,4,5-trimethoxycinnamate, synthesized by conjugating 3,4,5-trialkoxybenzoic acids and 3,4,5-trimethoxycinnmic acid with thymol, showed a potent depigmenting effect and low cytotoxicity. Compound 4h, 5-methyl-2-(methylethyl)phenyl (2E)-3-(3,4,5-trimethoxyphenyl)prop-2-enoate, showed the most potent depigmenting effect (IC50=10 microM) with low cytotoxicity (IC50=200 microM). 相似文献
78.
Integrins are heterodimeric glycoproteins that have been found to undergo dynamic temporal and spatial changes in the endometrium during the menstrual cycle and in early pregnancy. Specificity of integrins is known to be different in human endometrial stromal cells and decidual cells. These shifts of integrins suggested to play an important role in embryo implantation and can be modulated by progesterone, cAMP derivatives, and cytokines. The mechanisms of decidualization and its precise physiological role are still not clearly understood and in vitro systems could provide an alternative that overcomes limitations of studying such complex biological phenomena in vivo at the time of implantation. This study was undertaken to establish an in vitro model system for human decidualization using 8-bromo-cAMP and to investigate the characteristics of stromal integrin expression in vitro by 8-Br-cAMP. Endometrial stromal cells were isolated and cultured, and then were induced to decidualize by 0.5 mM 8-Br-cAMP for 15 days. Immunofluorescence staining and flow cytometric analyses of the integrin subunits (alpha1, alpha4, alpha5, alpha6, beta1 and alphavbeta3) were performed at day 9. In the presence of 8-Br-cAMP, the staining intensity of alphavbeta3 was significantly higher than control and measurements for alpha1, alpha4, alpha5, alpha6, and beta1 were similar. Immunofluorescent localization of the integrins reflected the differences obtained from the flow cytometric analyses described above. In summary, the expression of alphavbeta3 integrin increased in stromal cells in vitro decidualized by 8-Br-cAMP and this up-regulation of alphavbeta3 integrin expression during decidualization might influence on human implantation. 相似文献
79.
The fluid motion of an assemblage of cohesionless granules is governed by the balance laws of mass, momentum and energy and is special because due to the variability of the mean free path of the particles the density is not preserved and the particle fluctuation energy (= granular temperature) is determined together with the mean fields. Constitutive equations are postulated for the dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate in terms of the mean free path length, the time of encounter between two collisions and geometric and dynamic quantities via dimensional arguments. The model defines the time of encounter to consist of the free flying time between collisions plus the contact duration. The inclusion of the latter brings in the elasticity of the particles and introduces a relaxation mechanism that explains the typical behaviour of shear and fluidized layers better than has been done by previous models. 相似文献
80.