Chemical bond and electronic structure anisotropies in the graphitic and rhombohedral modifications of boron nitride

The pseudopotential method is used to calculate the band spectra, valence charge densities, and electroneutrality levels in the graphitic (h-BN) and rhombohedral (r-BN) modifications of boron nitride. It is shown that these compounds are indirect-band insulators with the minimum energies of the indirect (4.65 and 4.8 eV) and direct (5.27 and 5.5 eV) forbidden zones in h- and r-BN, respectively. The band energies of h-BN correlate well with the experimental data. Both crystals are characterized by ionic-covalent chemical bonds. In the plane of hexagonal layers, the bonds are more covalent in h-BN. In h- and r-BN, the electroneutrality levels correspond to the energy of about 1.9 eV over the top of the valence band, which is responsible for the hole conductivity of the substances. In superlattices based on these compounds, the rhombohedral phase is a quantum well for holes and a barrier for electrons. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 1, pp. 32–42, January–February, 1997.     

Chemical Composition of <Emphasis Type="Italic">Silene viridiflora</Emphasis>

Neutral substances, carbohydrates, and microelements from the aerial part of Silene viridiflora in addition to the protein content and its amino-acid composition were determined. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 365–366, July–August, 2005.     

Secondary structure of crystals

Published experimental data on the dependence of the properties of crystal substances on crystal size are discussed. The dependence is of the same form for different properties and different crystal substances. When the crystal diminishes in size, its properties remain constant until the size decreases to 10⁻⁵–10⁻⁶ cm; smaller crystals considerably change their properties. It is shown that the currently available experimental data are sufficient to substantiate the notion of an “elementary unit of a solid crystal” (“crystal quantum”). The elementary unit of a crystal is regarded as a basis for the secondary structure (macrostructure) of a solid and an elementary carrier of its “crystal” properties. Due to this notion, we can interpret the vast experimental material on the real structures and properties of solids from a single viewpoint. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 4, pp. 724–730, July–August, 1995. Translated by L. Smolina     

Allium carbohydrates. XV. Polysaccharides from Allium motor

The content of carbohydrates in Allium motor was studied as a function of vegetation period. The qualitative and quantitative compositions and physical chemical properties of sugars soluble in alcohol, water-soluble polysaccharides, pectinic substances, and hemicellulose were characterized. Galacturonan was produced by partial hydrolysis of the pectinic substances. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 409–411, September–October, 2006.     

Lipids of <Emphasis Type="Italic">Helianthus tuberosus</Emphasis> tubers

Free and bound lipids from Helianthus tuberosus tubers were investigated. Neutral, glyco-and phospholipid classes and their fatty-acid compositions were determined. The composition of unsaponified substances was established. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 3–4, January–February, 2008.     

Polysaccharides ofUngernia. XV. A study of the pectin substances of the leaves ofUngernia tadschicorum

Pectin substances have been isolated from the leaves ofUngernia tadschicorum and characterized. A galacturonan has been obtained by partial hydrolysis. On the basis of the results of IR spectroscopy and periodiate — nitric acid oxidation, its structure has been established as an α-1→4-bound polymer-homolog. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, FAX (3712) 62 73 48. Translated from Khimiya Prirodnykh Soedinenii, No. 3, 320–322, May–June, 1994.     

Polysaccharide accumulation dynamics in Iris pseudacorus

It was established by studying carbohydrates of Iris pseudacorus during vegetative periods that the content of water-soluble polysaccharides in the rhizomes and roots is greatest during seed ripening; of pectinic substances, during budding. Glycomannan was isolated from seeds. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 216–217, May–June, 2006.     

NMR studies of the electronic structure of coumarins

¹H and¹³C NMR spectra of a series of coumarin dyes used as active laser media are studied. Electron densities and ring currents are calculated. Formulas for calculating¹³C NMR chemical shifts from quantum mechanical data for aminocoumarins are suggested. NMR data and electronic structure calculations are used to explain the generation properties of coumarins. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 3, pp. 495–502, May–June, 1997.     

Inhibition activity of ethyleneglycol and its oligomers on tin electrode

Voltammetry and electrochemical impedance spectroscopy were applied to investigate the inhibition activity of ethyleneglycol and its oligomers on tin electrode in strong acidic sulfate solutions. Tetraethyleneglycol was found to be the most active substance among compounds HO–(CH₂–CH₂–O) _m –H (m≤4) that retards diffusion-controlled Sn(II) reduction due to its inhibitive adsorption. This rather slow process is controlled both by diffusion and electrosorption steps. A comparison of exchange current densities obtained in the presence of different polyethers shows that the length of the hydrocarbon chain is the main factor responsible for inhibition activity of such substances on tin electrode.     

Computational methods in the theory of chemical bonding in solids

Popular techniques for analyzing the spatial and energy characteristics of chemical bonding in solids based on Hückel theory, Hartree-Fock method, and electron density functional theory are reviewed. Methods for calculating the total energies and dependent characteristics (cohesion energies, formation energies, partial pressures, etc.), the moments of the densities of states, bond occupations, and the pair potentials of electron density and localization function are considered. Examples of using these calculations for high-melting and laminated compounds are given. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 3, pp. 554–583, May–June, 1997.     

An approximate method of self-consistent electronic structure calculations of a crystal surface. The Ir(111) surface

The Slater approximation for atomic electron energies is employed to calculate the electronic structure of the Ir(111) surface. The results are used to estimate the shift of the 4f_7/2 level on the surface relative to its position in the volume. The electron state densities in the neighborhood of the center of the surface Brillouin zone (SBZ) are compared with photoelectronic spectra for emission normal to the Ir(111) surface. On this basis, the accuracy of this approximation is estimated. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 17–24, January–February, 1994. Translated by O. Kharlamova     

Electronic structure and spectral characteristics of Bi-Sr-Ca-Cu-O films

The electronic structure of high-temperature superconducting films of Bi-Sr-Ca-Cu-O is determined using the linearized augmented plane wave method. Total and local partial densities of states are calculated for each film using the results of band structure calculations. Theoretical OK_α and CuL_α X-ray emission spectra are found. The dependence of the electronic structure and spectra on the number of CuO₂ layers in the unit cell is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1067–1075, November–December, 1998.     

Effect of repulsive interaction on the structural and dynamic features of liquid water. The role of molecular polarizability

The effect of variation of the potential function on the structural and dynamic properties of model water when the surface of pair interactions is invariant is studied by the molecular dynamics method. Variations for the rigid and polarizable models are compared. Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 296–303, March–April, 1999.     

Computational modeling of amorphous silica. 4. Modeling the initial structures. Aerogel

A qualitative classification algorithm for constructing large clusters of aerogel model structures is used. According to this algorithm, aerogel is classified with polysilicas characterized by a packing of long chains of silicon-oxygen tetrahedra. A model of the aerogel structure is suggested, according to which aerogel is described as a set of cross-linked chains forming double or more complex ribbons. This model is in agreement with the conclusions drawn from analysis of the vibration spectra of its components. Institute of Surface Chemistry, Ukrainian Academy of Sciences. Russian University of Peoples' Friendship. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 35–38, May–June, 1994. Translated by O. Kharlamova     

Study of the electronic structure of organogermanes with extended coordination sphere of germanium

The spatial and electronic structures of some organogermanes with extended coordination spheres of the metal were calculated using AMPAC and HYPER CHEM 4.0 program packages. Interatomic distances, bond angles, torsion angles, atomic charges, electron densities, bond orders, parameters of localized and canonical molecular orbitals,etc. were determined. The nature of the additional intramolecular O→Ge interaction in the molecules of these compounds was considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 383–387, March, 1998.     

Structure of a steroid saponin from <Emphasis Type="Italic">Digitalis ciliata</Emphasis>

A new steroid glycoside was isolated from leaves of Digitalis ciliata (Scrophulariaceae) by fractionation of the total extracted substances. Its structure was determined as (25R)-5α-spirostan-3β-ol 3-O-β-D-glucopyranosyl-(1→3)[β-D-fucopyranosyl-(1→2)]-β-D-glucopyranosyl-(1→4)-β-D-galactopyranoside based on chemical transformations, physical constants, and spectral data. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 135–137, March–April, 2007.     

Supramolecular association of gossypol in the crystalline state

The natural physiologically active compound gossvpol easily forms clathrate compounds with almost all low-molecular organic substances. The clathrates and the polymorphs of gossypol with known structures are classified into 24 groups of isostructural crystals. They differ from each other in the type of molecular association of gossypol. All possible types of gossypol association with predominant intermolecular H-bonds are analyzed in detail. Zero-, one- and two- dimensional associates are formed; each type of associate, except the zero-dimensional one, is built from more than one system of interm olecular H-bonds. An attempt is made to find out the reasons for the diversity of the types of gossypol supramolecular association based on the specific features of the molecular structure of gossypol. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 849–871, September–October, 1999.     

Lamiaceae carbohydrates. 1. Pectinic substances and hemicelluloses from <Emphasis Type="Italic">Mentha x piperita</Emphasis>

Pectinic substances from the aerial part of Mentha x piperita were isolated and characterized and found to be a mixture of β-(1→4)-glucogalactan (MPG) and two α-(1→4)-rhamnopolygalacturonans (MPP′-1 and MPP′-2). It was shown that the pectin and its components exhibited membrane-stabilizing, antiatherogenic, and antioxidant activity. Hemicelluloses from M. piperita were a lignocarbohydrate complex. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 411–416, September–October, 2007.     

Clathrate formation in the tetraisoamylammonium propionate-water system

In this paper we examine clathrate formation in the tetraisoamylammonium propionate-water binary system. We have found formation of four polyhydrates, two of which are metastable over the whole temperature range studied. All polyhydrate crystals were isolated and their compositions and densities determined; for (i-C₅H₁₁)₄NC₂H₅COO·36.5H₂O, unit cell parameters were additionally found. The results are compared with data for tetra-n-butylammonium carboxylate polyhydrates, and the structure of the title compounds is suggested. It is confirmed that the isoamyl radical stabilizes the tetradecahedral void of the clathrate hydrate framework better than the n-butyl radical. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 67–71, May–June, 1994. Translated by L. Smolina     

Chemical composition of <Emphasis Type="Italic">Pinus silvestris</Emphasis> essential oil from contaminated areas

The chemical composition of Pinus silvestris essential oil from contaminated areas was studied. An apparent effect of radionuclides and toxic elements on the biosynthesis of terpenoids in common pine essential oil was found. Increasing contamination apparently increased the content of sesquiterpenes and O-containing substances and decreased the content of monoterpenes in the essential oil. The contents of α-pinene, camphene, and limonene increased and those of 3-carene, terpinolene, and β-pinene decreased in the monoterpene fraction. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 47–49, January–February, 2007.