Transport properties of polyphenylquinoxalines

The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H₂, He, O₂, N₂, CO, CO₂, and CH₄; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases.     

V4S9Br4: a novel high-spin vanadium cluster thiobromide with square-planar metal core

The novel vanadium thiobromide, V4S9Br4, with a square-planar metal cluster core was synthesized and characterized by single-crystal X-ray diffraction, measurements of magnetic properties and the heat capacity, and DFT calculations of the electronic structure. At the room temperature, the compound displays paramagnetic properties with an independent spin on each V atom and with a weak exchange constant (J approximately 10 cm(-1)). The paramagnetic state is transformed into a low-spin state (AF-type ordering) at low temperatures. This change is accompanied by a heat-capacity anomaly. The observed magnetic and heat-capacity anomalies can be explained by the thermal excitation of electrons on the closely spaced molecular energy levels in the presence of the Jahn-Teller effect.     

Synthesis of Esters of Dioxane Alcohols and Their Performance as Plasticizers for Polyvinyl Chloride Compounds

A procedure was developed for preparing a plasticizer for polyvinyl chloride compounds from the fraction of dioxane alcohols. The main physicochemical properties of the new plasticizer were determined. Items prepared from formulations containing the new plasticizer were fabricated and tested in laboratory.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 972–976.Original Russian Text Copyright © 2005 by Glazko, Gur’yanova, Levanova, Kozlova, Neiman.     

Sorption-photometric and test determination of lead in environmental materials

The main analytical characteristics of the reaction of hexaoxacycloazochrom with lead were determined. A method for the sorption preconcentration of lead on the Thiopan 14 sorbent was proposed. Procedures were developed for the photometric determination of lead in natural waters, air, and soil at the level of the maximum permissible concentration. A new melange gel technique for preparing silicic acid xerogels modified with hexaoxacycloazochrom was developed for the test determination of lead in environmental samples at the level of the maximum permissible concentration.     

IR spectral study of the effect of the reaction medium on the state of cobalt in a 10% Co/Al2O3 catalyst for aliphatic hydrocarbons from CO and H2

Diffuse scattering IR spectroscopy was used to study the 10% Co/Al₂O₃ catalyst for the synthesis of aliphatic hydrocarbons from CO and H₂. Ionic and metallic cobalt forms were identified in the IR spectroscopy. The adsorption of CO on these forms is accompanied by the appearance of linear and bridged complexes. After prolonged treatment of the catalyst by a CO + 2H₂ mixture, the ions and surface of metallic cobalt remain available for the adsorption of CO. Modification of the surface of metallic cobalt occurs upon the action of the reaction medium. This modification is seen in a bathochromic displacement of the IR bands for the adsorbed and linear CO forms. This displacement is accompanied by a reduction in the strength of the metal-carbon bond in the Co^o-CO complex.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2640–2643, November, 1990.     

The preparation of chloroplatinic acid labelled with platinum radioisotopes

A procedure has been worked out for the preparation of chloroplatinic acid from natural metallic platinum irradiated in a nuclear reactor and purified from¹⁹⁹Au impurities by extraction from acidic solutions with ethyl acetate. It was shown that the effective K X-ray activity of natural platinum on irradiation with moderate neutron fluxes /3×10¹³/ was comparable with that of^195mPt obtained from 100%¹⁹⁴Pt/with identical neutron fluxes/. Contaminations from¹⁹³Pt /50 years/ is insignificant and do not produce noticeable radiation loads on the organism on medical tests in vivo.     

Fractionation and Determination of Different Lead Species in Contaminated Soils

A new approach was proposed to fractionating soil lead species differing in mobility and biological availability. Ground solid samples were retained as a stationary phase in a rotating coiled column while continuously pumping aqueous solutions of salts and complexing agents necessary for the sequential leaching of different element species. It was shown that field-flow fractionation in a rotating coiled column is suitable for separating three lead species in an automatic mode within 4 h, as compared to several days for conventional methods of sequential extraction. The study of lead elution curves at different fractionation steps provides additional information about its mobilization under changing environmental conditions.     

Quantum-chemical study of C<Subscript>n</Subscript>F2<Subscript><Emphasis Type="Italic">n</Emphasis>+2</Subscript> conformers. Structure and IR spectra

Quantum-chemical calculations of the geometrical structure and vibrational spectra of C_nF_2n+2 oligomers (n = 5–8) in the chain and branched conformations are reported. The lengthening of the chain of C_nF_2n+2 does not substantially affect the geometrical parameters of the oligomers. In all cases under study, the most optimal structure of the molecule is a zigzag chain with bond lengths R(C-C) = 1.53 –1.54 and R(C-F) = 1.36 –1.34 ; the chain is rolled into a helix, which makes an angle of 17° with the plane. The IR spectra are sensitive to the structural deficiency of oligomers C_nF_2n+2 associated with the lateral trifluoromethyl groups formed in the chain; the spectra can be used for revealing defects of this type in the structure of polytetrafluoroethylene (PTFE). The possibility of defects associated with the lateral CF₃ groups in the structure of PTFE and its low-temperature modifications is explained based on the calculated total energies of C_nF2 _n+2.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. Yu. Beloliptsev, S. G. Kozlova, and V. M. BuznikTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 632–643, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Hopanoids of methylotropic acetobacteria

Squalene, 35-methoxyho-6-ene-32R,33R,34S-triol, hop-22(29)-ene, and hopan-22-ol have been isolated fromAcetobacter sp. VSB 917. The structures of the substances isolated and of the 35-methoxyhop-6-ene-32R,33R,34S-triol triacetate obtained have been established by IR, mass, and¹H and¹³C NMR spectroscopies.Vitaminy Scientific-Production Association, Moscow. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 367–372, May–August, 1992.