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91.
Acidity measurements in trifluoroethanol and hexafluoroisopropanol as solvents, and in their mixtures with water, are reported. The hydrogen electrode and the glass electrode were used for pH measurements. The “experimental” autoprotolysis constants were determined from measurements in strongly acidic (trifluoromethanesulfonic) media and in strongly basic (alcoholate) media: for trifluoroethanol, pK = -log K/mol2 l-2 = 15 and for hexafluoroisopropanol, pK = 14.8. Evaluation of the pH-indicator potential systems with reference to the ferrocene/ferricinium couple gives the acidity function R0(H). The values obtained are compared to the H0 values evaluated in the same conditions. 相似文献
92.
A series of 2-substituted 4H-3,1-benzoxazinones and 2,3-disubstituted 4-(3H)quinazolinones have been synthesized in mild conditions by the use of triphenyl phosphite and pyridine as cyclising medium. Benzox-azinones are produced either by ring closure of 2-(acylamino)benzoic acids or in the reaction of benzoic acid with anthranilic acids. In the presence of aniline, the reaction leads to quinazolinones. 相似文献
93.
The free energy barriers to ring inversion for 3,3-dimethylcyclohexene, 4,4-dimethylcyclohexene and 3,3,6,6-tetramethylcyclohexene were determined by low temperature PMR studies. The results were interpreted in terms of a mechanism whereby the boat conformation is of highest energy on the energy profile for conformational interconversion. The very high ΔG≠ value for 3,3,6,6-tetramethylcyclohexane (8·4 kcal/mole) is considered a reflection of the serious non bonded interaction that exists between methyl groups at the “prow” positions of the boat form. 相似文献
94.
Victoria Bejar Concepcion Calvo Juan Moliz Francisco Diaz-Martinez Emilia Quesada 《Applied biochemistry and biotechnology》1996,59(1):77-86
The exopolysaccharide produced byVolcaniella eurihalina, an halophilic eubacterium, under different environmental and nutritional conditions, is studied.V. eurihalina synthesizes an acidic heteropolysaccharide, composed by rhamnose, glucose, and mannose, as well as amino sugars, uronic acids,
and acetyl and sulphate residues. This composition varies depending on the nutrients of culture medium. Viscosity and pseudoplasticity
of the polymer solutions are also influenced by the nutritional conditions in which the microorganism was grown. 相似文献
95.
Photoinduced morphism of gemini surfactant aggregates 总被引:5,自引:0,他引:5
Faure D Gravier J Labrot T Desbat B Oda R Bassani DM 《Chemical communications (Cambridge, England)》2005,(9):1167-1169
The photochemical behaviour of an azobenzene chromophore inserted in a gemini surfactant imparts photocontrol to the resulting amphiphile assemblies, including the collapse, upon irradiation, of the multi lamellar vesicles formed in aqueous solution. 相似文献
96.
Numerical Algorithms - A two-step quadratic spline collocation method is formulated for the solution of the Dirichlet biharmonic problem on the unit square rewritten as a coupled system of two... 相似文献
97.
Recently B.Y. CHEN initiated the study of the tensor product immersion of two immersions of a given Riemannian manifold [3]. In [6] the particular case of tensor product of two Euclidean plane curves was studied. The minimal one were classified, and necessary and sufficient conditions for such a tensor product to be totally real or complex or slant were established. In the present paper we study for tensor product of Euclidean plane curves the problem of B.Y. CHEN: to what extent do the properties of the tensor product immersion f ? h of two immersions f, h determines the immersions f, h ? [3] 相似文献
98.
99.
100.
Bernard R. Brooks Duanka Janei
Martin Karplus 《Journal of computational chemistry》1995,16(12):1522-1542
Methods have been developed for the determination of vibrational frequencies and normal modes of large systems in the full conformational space (including all degrees of freedom) and in a reduced conformational space (reducing the number of degrees of freedom). The computational method, which includes Hessian generation and storage, full and iterative diagonalization techniques, and the refinement of the results, is presented. A method is given for the quasiharmonic analysis and the reduced basis quasiharmonic analysis. The underlying principle is that from the atomic fluctuations, an effective harmonic force field can be determined relative to the dynamic average structure. Normal mode analysis tools can be used to characterize quasiharmonic modes of vibration. These correspond to conventional normal modes except that anharmonic effects are included. Numerous techniques for the analyses of vibrational frequencies and normal modes are described. Criteria for the analysis of the similarity of low-frequency normal modes is presented. The approach to determining the natural frequencies and normal modes of vibration described here is general and applicable to any large system. © 1995 John Wiley & Sons, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America. 相似文献