Electroreduction of benzo-1,2,3-dithiazolium salts and their selenium analogs in nonaqueous solution

The electroreduction of benzo-1,2,3-dithiazolium cations and their selenium analogs in aprotic solvents takes place in two steps. The first step is a reversible, one-electron transfer leading to the formation of stable radicals detected by EPR. As a result of further electroreduction, the radicals obtained combine with six electrons to form the corresponding o-aminothio(seleno)phenols. Analysis of the reduction potentials of the compounds studied shows that the substitution of a selenium atom for a sulfur in these cations, especially in the 2 position of the heterocycle, facilitates their electrochemical reduction. The electrochemical activity and the kinetics of nulceophilic substitution in the cations studied are compared.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 219–222, February, 1985.     

Isolation of a urease from watermelon seeds and the study of its properties

The enzyme urease has been isolated from the seeds of the watermelon of the Ogonek variety and has been characterized. The molecular weight of a rechromatographed sample of the enzyme has been determined as 480,000. The pH dependence of the activity of the urease and the kinetic parameters of the enzyme have been studied.All-Union Scientific-Research Institute of the Chemistry and Technology of Drugs, Khar'kov. Vitaminy Scientific-Production Amalgamation, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 624–628, September–October, 1983.     

Oxidation with permanganate in presence of fluoride potentiometric determination of manganese(II)

The effects of acidity, fluoride concentration, temperature and concentration of manganese in the reaction between KMnO(4) and Mn(II) were studied potentiometrically. The rate of reaction is increased by increasing the fluoride concentration and/or decreasing the acidity of the solution. The formal redox potentials of the MnO(-)(4)/Mn(III) and the Mn(III)/Mn(II) systems were determined at different pH values. The E degrees values obtained by extrapolation to pH = 0 were 1.58 and 1.52 V respectively. The amount of Mn(II) determined was varied from 5 to 56 mg. The net reaction can be represented as MnO(-)(4) + 10HF(-)(2) + 4Mn(2+) right harpoon over left harpoon 5MnF(-)(4) + 2H(+) + 4H(2)O.     

Synthesis and spectral study of chelate alkenylarenedicarbonyl complexes of Cr,Mo and W

Irradiation of alkenylarene tricarbonyl-chromium, -molybdenum, and -tungsten compounds in which the double bond is separated from the arene moiety by a two- or three-atom bridge results in intramolecular cyclization to give stable chelate alkenylarenedicarbonylmetal complexes. Chelate complexes containing four-atom bridges have low stabilities, and those with monoatomic bridges were not formed at all. Irradiation of styrenetricarbonyl-chromium and -molybdenum leads to dinuclear tricarbonylmetal—dicarbonylmetal complexes. The chelate complexes obtained have been studied by IR, proton NMR, and ¹³C NMR spectroscopy. The electron density distributions and the stereochemistry of the complexes are discussed. With nonsymmetric arenes, diastereoisomers are formed; the predominant isomers have been isolated in the pure form. According to the proton NMR data the double bond in alkenylarenechromium chelates is parallel of nearly parallel to the arene ring plane.     

Polarographic reduction of adenine and its 9-(α,ω-dihydroxy-2-alkyl) derivatives

The polarographic reduction of adenine and its 9-(,)-dihydroxy-2-alkyl) derivatives on a short-period mercury electrode in strongly acidic media is determined by the rate of diffusion of the corresponding cations and, at pH values that exceed the pK_a values, by the kinetics of surface protonation of the uncharged molecules; this was proved by the dependence of the limiting current on the height of the mercury column, the temperature, and the depolarizer concentration. The polarographic reduction of adenine, adenosine, 9-(,-di-hydroxy-2-alkyl)adenines, and the corresponding phosphates in acidic media proceeds with the loss of sic electrons per molecule. The similar trends of the change in the half-wave potentials and the numerical pK_a values is associated with the fact that the site of protonation is simultaneously the site of nucleophilic attack by the electron during electrical reduction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1675–1678, December, 1977.     

Epoxy Composites Modified with Finely Dispersed Fillers

The thermal stability and mechanical strength of composites based on ED-20 epoxy oligomer cured with isomethyltetrahydrophthalic and methylendic anhydrides was studied as influenced by the nature and properties of finely dispersed inorganic fillers, such as carbon black, aluminum oxide, and silica nanoparticles.     

State of Chromium in Solid Solutions of Multicomponent Bismuth Niobates with Pyrochlore Structure

Magnetic susceptibility of solid solutions of multicomponent bismuth niobates with pyrochlore structure containing chromium atoms was studied. The parameters determining the state of chromium atoms and the exchange coupling between the paramagnetic atoms were calculated. The best agreement between the experimental and theoretically calculated magnetic moments of the chromium atoms is observed on the condition that all the chromium atoms in the Bi₂MgNb₂O₉ structure are in the form of ferromagnetic exchange-coupled dimers with an exchange parameter J 18 cm^{- 1}.     

Effect of the morphology of polyethylene glycol esters on the distribution of C1–C4 carboxylic acids in the gas phase-sorbent system

The effect of the morphology of polymer films on the distribution of volatile C₁–C₄ carboxylic acids in the sorbent-gas system is discussed. The efficiency of sorption of vapors of formic, acetic, propionic, and butyric acids on films of polyethylene glycol esters of various structures formed on the electrodes of a piezoquartz resonator by means of static evaporation of a drop and immersion of the resonator into a sorbent solution is evaluated.     

Product structure in the reaction of dimethyl acetylenedicarboxylate with 2-furyl-1,2,3,4-tetrahydroquinolines

Dimethyl acetylenedicarboxylate reacts with 4-substituted and 3,4-fused 2-furyl-1,2,3,4-tetrahydroquinoline derivatives at the furan fragment according to the [4 + 2]-cycloaddition pattern. The reaction is not stereoselective, and it yields two diastereoisomeric 7-oxabicyclo[2.2.1]hepta-2,5-dienes whose structure was determined by X-ray analysis and NMR spectroscopy.     

Low temperature specific heat calculations for amorphous polystyrene

Numerous attempts have previously been made to explain low temperature specific heat anomalies in glasses. The potential value of low frequency Raman data in interpreting such results is demonstrated here: the density of states for the 60 cm^?1 side-group mode in amorphous polystyrene is calculated from Raman measurements. Using the harmonic approximation, the contribution to the specific heat from this side-group motion is calculated and added to the Debye term. The form of C/T³ between 1.5 and 4 K is shown to be reproduced, although the magnitude of C/T³ is only about 70% of experimental values. This discrepancy and the anomalous behaviour below 1.5 K is believed to the due to lower-lying vibrational states of the system, perhaps not accessible through Raman scattering experiments.