Crystal structure of polymorphous modifications of Tm2S3 and related compounds

The role of symmetry in crystal structure formation is revealed for the polymorphous modifications of Tm₂S₃ and related compounds Tm₁₅S{ib22}, Tm₅S₇, and Tm₈S₁₁ using the procedure of selecting and analyzing closepacked planes with cationic, anionic, and combined motifs. The laws of mutual agreement between the cation and anion matrices determining the size of the unit cells are examined, and relationships between the specific cation volumes and symmetry are traced. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 4, pp. 669–675, July–August, 1998.     

Rheology of PVC plastisol--VI: criteria for yielding and fracture of an immobilized layer

PVC plastisol exhibits pseudo-plastic flow in steady shear; that is, viscosity decreases with the increasing shear rate. At higher shear rates viscosity reaches a minimum and then increases, i.e., dilatant behavior. Previously, pseudo-plastic behavior was explained by a mechanism in which the suspended particles partition into an immobilized layer and a mobile phase. The development of the immobilized layer with the increase in shear rate was shown to quantitatively account for pseudo-plastic behavior. In higher shear rates dilatation of the immobilized layer was shown to be the cause of dilatacy. At even higher shear rates the immobilized layer fractures. In this paper the viscosity minimum was interpreted as the yielding of the immobilized layer. Subsequently, data in the literature were analyzed to find criteria for the yielding and fracture of the immobilized layer. Yielding was found to obey Coulomb's criterion, from which the coefficient of friction and the cohesive strength of the immobilized layer were evaluated. These properties were controlled by the nature of particle assembly in the immobilized layer and the plasticizer type had only a minor effect. The value of the coefficient of friction was on the lower side and within the range of values found in the literature for other materials. There were two modes of fracture of the immobilized layer, one with low strength, low strain to break, and the other with high strength, high strain to break. The former is analogous to the brittle fracture of solids and the latter ductile failure. The strength of brittle fracture was somewhat higher than cohesive strength, which was evaluated from yielding data. This is akin to Griffith's criterion for brittle fracture of a solid. Ductile failure occurred when the shear stress exceeded normal stress.     

Vibrational spectra and conformations of 2- and 3-methylbicyclo[4.4.0]decanes

The conformations and heats of formation of all trans(T)- and cis(C)-2- and 3-methyl-substituted T- and Cbicyclo[4.4.0]decanes (BD) were calculated by the MM2 method of molecular mechanics. It was shown that the conformationally mobile T-2-Me-CBD and T-3-Me-CBD can exist in normal conditions as an inseparable mixture of conformers with a different equatorial or axial orientation of the Me groups. The Raman scattering (RS) spectra of TBD and CBD were investigated. RS bands whose frequencies were sensitive to the type of ring linkage and orientation (but not the position) of the Me substituents were detected in the 700–300 cm^–1 region.A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 117912 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2089–2097, September, 1992.     

7-Aryl-6,7-dihydro-8h-indeno[1′,2′∶2,3]pyrano-[5,6-c]benzo[c]pyran-6,8-diones and their thio analogs

The ability of 3-[-(1,3-dioxo-2-indanyl)benzyl]-4-hydroxy-substituted 2H-benzo [b]pyran-2-ones and benzo[b]thiopyran-2-ones to undergo dehydration under the influence of dehydrating agents to give 7-aryl-6,7-dihydro-8H-indeno[1,2-2,3]pyrano[5,6-c]benzo[c]pyran-6,8-diones and their thio analogs was demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1475–1476, November, 1985.     

Quinoid pigments of echinodermata III. Minor pigments of the sea urchin Strongylocentrotus nudus

Summary 1. 3-Acetyl-2,7-dihydroxy-6-methylnaphthazarin, not previously described, has been isolated from the test and needles of the sea urchinStronglyocentrotus nudus.2. The pigments of this sea urchin have been shown to include 2,7-dihydroxynaphthazarin and spinochrome E.3. A number of minor pigments forming naphthazarin derivatives has been isolated. One of them is connected with spinochrome C by mutual transformations.The subject matter of the present paper was given in part at the All-Union Conference on Biological Resources of the Seas of the Far East (Vladivostok, 1975).Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center of the Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 202–207, March–April, 1977.     

Itinerant electron ferromagnetism in Sr2+-, Ca2+-, and Ba2+-doped rare-earth orthocobaltites (Ln3+1−xM2+xCoO3)

Electronic and magnetic properties of Ln_1?xSr_xCoO₃ (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba²⁺ in LaCoO₃ favors itinerant electron ferromagnetism relative to Sr²⁺ while Ca²⁺ is less favorable than Sr²⁺.     

Chromatographic analysis of hydrocarbons in marine sediments and seawater.

The low concentration of hydrocarbons anticipated in pollution baseline studies necessitates the development of analytical techniques sensitive at the sub-microgram per kilogram concentration level. The method of analysis developed in this laboratory involves dynamic headspace sampling for volatile hydrocarbon components of the sample, followed by coupled-column liquid chromatography for the non-volatile components. These techniques require minimal sample handling, reducing the risk of sample component loss and/or sample contamination. Volatile sample components are separated from the matrix in a closed system and concentrated on a TENAX-GC packed pre-column, free from large amounts of solvent and ready for GC/GC-MS analysis. Non-volatile compounds, such as the benzpyrenes, may be extracted from large volumes of water and concentrated on a Bondapak C18 packed pre-column for coupled-column liquid chromatographic separation and analysis. Results of the application of these techniques to the analysis of samples from sites of known low level hydrocarbon contamination are presented and discussed.     

Gamma radiolytic decomposition of solid binary mixtures of potassium nitrate with halides

Gamma-ray induced decomposition of solid binary mixtures of KNO₃ with halides viz. KCl, KBr and KI has been studied at room temperature. G(NO ₂ ^– ) values were found to vary with absorbed dose. Size and electronegativity of anions and molar composition of halides are the other factors influencing radiolysis.     

Diffusion coefficients from stopped-flow gas chromatography

Summary Mutual diffusion coefficients of two gases A and B can be determined in an empty gas chromatographic column by letting component B enter at an intermediate position of the column and continuously flow through a part only of it, as a carrier gas. The other component A is injected in a small amount instantaneously at the closed end of the column with the detector placed at the other end. By repeatedly stopping and then restoring after a short time the flow of B, narrow extra peaks are produced on the chromatographic elution curve, owing to diffusion of A into B. An equation is derived giving the area under the curve of each stop-peak as a function of time of the corresponding stop. Plotting the experimental data according to this equation permits the determination of the diffusion coefficient of A into B. Some results obtained by this method show negligible variations with changes in the experimental parameters.     

Acetylation of lagochilin

The acetylation of lagochilin and its derivatives with acetic anhydride in the presence of pyridine has been studied by PMR spectroscopy. It has been shown that the manifestation of the polyfunctionality of lagochilin in acetylation reactions with acetic anhydride is connected with a change in the nature of the process of solvation of the reaction forms with the subsequent replacement of the hydrogen atoms of the hydroxy groups by acetyl groups.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 46–49, January–February, 1980.