Morphological phase diagram of a spherical crystal growing under nonequilibrium conditions at the growth rate as a quadratic function of supersaturation

The complete morphological diagram of a spherical nucleus growing from a solution under nonequilibrium conditions at a local growth rate as a quadratic function of supersaturation is calculated for the first time on the basis of a linear analysis for morphological stability and the principle of maximum entropy production. The results of calculations are compared with those obtained previously for a spherical particle in the case of a linear dependence of the growth rate on the supersaturation.     

Spectroscopic investigation of structure transformation in wavellite

The Electron Spin Resonance of VO²⁺, and the Infrared and Nuclear Magnetic Resonance of protons were studied in wavellite. Interpretation of¹H NMR by shape function calculation allows us to determine the distribution of protons between molecular water, OH-groups, the three-spin magnetic configuration H₃O⁺ and to ascertain the characteristic distances between protons. The spin-Hamiltonian parameters, Fermi contact interaction parameters and dipolar hyperfine coupling parameterPK were calculated. Three types of VO₂₊ complexes were detected in wavellite. It is found that VO²⁺(1)- and VO²⁺(2)-centres disappear and a new VO²⁺(3)-centre appears during annealing. VO²⁺(1) is more stable than VO²⁺(2). The parameters of the VO²⁺(3) complex change in the process of annealing. The transformation of VO²⁺(1) is connected with the destruction of acidic H₃O⁺-groups, and the transformation of VO²⁺(2) correlates with the loss of weakly-bonded water molecules in the wavellite structure. ThePK parameter and Δg?Δg _⊥ ratio can be used as markers of disorder in the wavellite structure.     

The first AMPA receptor negative modulators based on the tetrahydroquinazoline scaffold

A convenient approach to novel symmetric bispyrimidine diamines comprises S_NAr reactions of 4-fluoropyrimidine N-oxide with alkane-α,ω-diamines with subsequent reduction of N-oxide function. The obtained substances were tested in patch-clamp experiments for the influence on the kainateinduced currents in Purkinje neurons and showed negative modulating effect.

     

Influence of structural promoters on reduction dilatograms of iron catalyst

In each reduction step, changes in the catalyst pellet volume during reduction of precipitated iron catalysts are determined by the concentration of structural promoters and the reaction temperature.

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Gossypol-like compounds of the cotton plant. Methods of determining gossypol

This review is devoted to the study of gossypol and gossypol-like pigments. It is reported that some of them are phytoalexins with respect to certain fungal pathogens of the cotton plant and possess a high toxicity. Methods of determining free and total gossypol in cottonseed processing products are discussed particularly.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 121–139, March–April, 1981.     

1H and13C NMR spectra of transformation products of gossypol in solutions

The complete cycle of the transformation of gossypol in solutions takes place in the measuring ampul of a NMR spectrometer. It has been established for the first time that, in methanol, gossypol is converted into stereoisomeric dilactol 15,15-dimethyl ethers which change into dianhydrogossypol in chloroform and back into gossypol in aqueous acetone. The¹H and¹³C NMR spectra of the main and intermediate products of the conversion of gossypol in the solvents mentioned have been studied in detail for the first time and a complete assignment of their resonance characteristics has been made. It has been shown that dianhydrogossypol is formed through intermediate stereoisomeric 15,15-dimethyl ethers of the dilactol form of gossypol.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 166–177, March–April, 1990.     

Effect of Light on the Electrokinetic Behavior of TiO(2) Particles in Contact with Cr(VI) Aqueous Solutions

The electrokinetic behavior of titanium dioxide particles (Degussa P25, mainly composed of anatase) put in contact with chromium(VI) aqueous solutions is highly sensitive to light exposure under normal laboratory conditions. In the dark, adsorption of Cr(VI) gives rise to substantial decrements in the mobilities, especially in the acidic branch, and, at higher concentrations, to shifts in the isoelectric point (pH(piep)) to lower values, as expected for anionic chemisorption. A two-mode adsorption model accounts qualitatively for the results. Under light, pH(piep) shifts in the opposite direction as the Cr(VI) concentration increases. A maximum value is attained at [Cr(VI)] approximately 10(-3) mol dm(-3), pH(piep) 8.2, which coincides with values reported for hydrous chromium(III) oxides. At higher concentrations, Cr(VI) adsorption defines a shift of pH(piep) to lower values. It is concluded that light absorption by titanium dioxide promotes the reduction of Cr(VI) and the surface precipitation of the hydrous Cr(III) oxide. The values of pH(piep) for partially covered surfaces are well described by a simple model of surface ionization derived earlier. FTIR/ATR analysis of the surfaces supports this interpretation, and further suggests that one of the modes of Cr(VI) adsorption implies surface dimerization to yield adsorbed dichromate. Copyright 2000 Academic Press.