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.     

Transformation of Acetalized Polyhyroxyketene Thioacetal in Acid-Alcohol Medium

2,3:4,5-Di-O-cyclohexylidene-L-arabinose diethyl dithioacetal was treated with sodium methylsulfinylmethylide to prepare a novel compound, 4,5-cyclohexylidene-2-deoxy-L-erythro-pent-1-enose diethyl dithioacetal. The product undergoes a series of transformations in anhydrous ethanol in the presence of p-toluenesulfonic acid: alcoholysis of the cyclohexylidene protection, elimination of water, migration of the double bond, formation of an acyclic allyl cation, elimination of the ethylthio group, formation of a cyclic allyl cation, migration of the mercapto group from C^{1 t}o C³,addition of alcohol, and formation of an acetalized lactone. The latter was acetalized to obtain a diastereomeric mixture of 5-O-acetyl-2-deoxy-3-S-ethyl-L-threo- and -erythro-pentono-1,4-lactones.     

Accelerated semimicro method of determining the amount of free gossypol in cotton seeds and the products of their processing

A semimicro method is proposed for determining the amount of free gossypol in liquid and solid materials using 70% aqueous acetone as the gossypol extractant.