An improved version of NDDO method and its use in the study of bulk and surface properties of titania

A modified scheme for evaluation of two-electron (one-and two-center) integrals within the framework of NDDO method is proposed. A set of parameters for H, C, N, O, F, Cl, Br, and Ti atoms has been obtained. Some models for titania surface active sites have been studied.     

Kinetics of the transfer of the dimethyl-carbamoyl group from N- and O-acylonium salts to azines and their N-oxides

The rate constants and activation energies were determined for a series of reactions involving the transfer of a dimethylcarbamoyl group from the N,N-dimethylcarbamoylonium salts of a series of nitrogen heterocycles and their N-oxides to nucleophiles (azines and their N-oxides) in acetonitrile. The measured values were compared with the structural, reaction, and equilibrium characteristics. L. M. Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, Donetsk. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 143–148, May–June, 1997.     

Model analysis of zeolite-like phosphates and their adsorption complexes with water molecules

Molecular models of borophosphates, aluminophosphates, and silicon-containing derivatives of these phosphates have been subjected to quantum-chemical analysis in the MNDO approximation. Bonding energies of these compounds with water molecules have been calculated. Incorporation of silicon atoms into the phosphate matrix increases its hydrophilicity and acidity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 4, pp. 223–226, July–August, 1994.     

Simultaneous Preconcentration and Separation of Chromium(III) and Chromium(VI) at the Low-Temperature Directed Crystallization of Natural Water

It was shown that low-temperature directed crystallization of natural water can be used for separating chromium(III) and chromium(VI). At a moderate crystallization rate (6–10 mm/h), the final part of the ingot (concentrate) is a suspension containing chromium(III) and chromium(VI) in the solid and liquid phases, respectively. It is proposed to separately determine these chromium species by atomic absorption spectrometry after separating the phases by centrifugation and dissolving the precipitate in acids.     

Acetyl transfer from N-acetyloxypyridinium cations to 4-(4′-N,N-dimethylaminostyryl)-pyridine N-oxide and 4-dimethylaminopyridine

Kinetic data are given for the transfer of the acetyl group from the N-acetyloxypyridinium cations of tetraphenylborate salts to 4-(4′-N,N-dimethylaminostyryl)pyridine N-oxide and 4-dimethylaminopyridine in acetonitrile solution. Structural factors were found to affect the rate constants and activation parameters. Correlation equations are given relating the acetyl transfer rate constants with pK_BH+ values of the leaving group and frequencies of the carbonyl vibrations of the salts. Translated from Teoreticheskaya i éksperimental’naya Khimiya, No. 2, pp. 75–77, March–April, 1997.     

Direct one-index transformations in multiconfiguration response calculations

The evaluation of gradient vectors of a general operator with one-index, double-one-index, or higher-order one-index transformed integrals is a key operation in multiconfiguration response theory calculations. We describe an integral-driven direct algorithm that carries out this operation efficiently without pretransforming the integrals. The use of this algorithm leads to a considerable reduction in disk space and timing. © 1994 by John Wiley & Sons, Inc.     

Quantum-chemical cluster models for hypervalency coordination environments in aluminum oxides

The MINDO/3 semiempirical approximation in SCF MO LCAO has been used to examine whether a cluster scheme can be used to calculate the electronic structures for aluminum oxides. Conditions are defined under which the hypervalent environment of the aluminum atom is stable under geometry optimization. A univalent pseudoatom model is compared with an uncharged ionic one to estimate the geometrical optimization. A univalent pseudoatom model is compared with an uncharged ionic one to estimate the geometrical and energy characteristics for clusters representing three-coordinated, four-coordinated, and six-coordinated Al.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 581–586, September–October, 1989.     

Modification of salsoline, salsolidine, and anabasine with dibenzo-24-crown-8-dicarboxylic acid dichloride

New derivatives of dibenzo-24-crown-8-dicarboxylic acid diamide with salsoline, salsolidine, and anabasine moieties were prepared by condensation of the alkaloids with 4′,4″(5″)-dibenzo-24-crown-8-dicarboxylic acid dichloride. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 471–473, September–October, 2006.     

Intercalation synthesis of cobalt silicide under a graphene layer

The silicon intercalation under single-layer graphene formed on the surface of an epitaxial Co(0001) film was investigated. The experiments were performed under conditions of ultra-high vacuum. The thickness of silicon films was varied within the range of up to 1 nm, and the temperature of their annealing was 500°C. The characterization of the samples was carried out in situ by the methods of low-energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and magnetic linear dichroism in photoemission of Co 3p electrons. New data were obtained on the evolution of the atomic and electronic structure, as well as on the magnetic properties of the system with an increase in the amount of intercalated silicon. It was shown that the intercalation under a graphene layer is accompanied by the synthesis of surface silicide Co₂Si and a solid solution of silicon in cobalt.