NMR AND DFT STUDY OF Co-C BOND ACTIVATION MECHANISM IN VITAMIN B_(12) COMPOUNDS

This report focuses on a theoretical study of the cobalt-cabon bond activation mechanism in Vitamin B12, its co enzyme complexes, and model compounds such as cobalamins (Cbl), cobaloximes and cobalt porphyrins. In particular, emphasis is placed on the nucleotide loop and its role in the base on and base off mechanism.     

DICSI station at KCSR and NT: Determination of optimal requirements to the formation of an SR beam using cylindrical x-ray optical zoom lenses

To modernize the DICSI station, new hardware and software have been created according to the conditions of the operating storage ring “Sibir’-2” beam channel. The recording system has been successfully tested on the operating channel of the storage ring VEPP-3 (Budker Institute of Nuclear Physics Siberian Branch, Russian Academy of Sciences, Novosibirsk) using the time-resolved “diffraction cinema” technique in studying real biological objects in the static and dynamic modes of data accumulation. At the DICSI station, structural changes in medical and biological objects are permanently investigated. The specific structure dimensions of these objects are in the nanometric range.     

Conduction and Transport Numbers in Metacomposites MeWO<Subscript>4</Subscript> ⋅ WO<Subscript>3</Subscript> (Me = Ca,Sr, Ba)

The conduction and transport numbers of charge carriers for composites in the systems MeWO₄-WO₃ (Me = Ca, Sr, Ba) are studied as a function of the temperature and the activity of oxygen in a gas phase. The transport numbers are determined by an emf method and are estimated from dependences of conductance on the activity of oxygen in a gas phase. The deficiencies of the given procedure as applied to investigation of properties of composite phases are analyzed. The materials under study are classified with a class of metacomposites. The concentration intervals of the ionic, mixed, and electronic conductions are determined. The conduction of composites of compositions (100 − x)MeWO₄ ⋅ xWO₃ is predominantly ionic at x ≤ 10 (Me = Ca), x ≤ 60 (Me = Sr), and x ≤ 45 (Me = Ba). The obtained data are explained in the framework of a model that represents a composite as a distributed matrix system where a film of surface phase MeW-s with a high mobility of oxygen ions plays the role of a connected matrix. It is presumed that the surface phase MeW-s possesses double-sided surface activity (α _MeW-s ≤ ) and a higher mobility with respect to MeWO₄ and WO₃. The discovered anomalies of dependences (T) and partial dependences , σ_el(T) are explained by a change in the stoichiometry, morphology, and the degree of connectedness of surface phase MeW-s caused by with a change in the temperature and composition of composites.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 680–693.Original Russian Text Copyright © 2005 by Neiman, Pestereva, Sharafutdinov, Kostikov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Using synchrotron radiation to study the structure of calcium-phosphate films on the surfaces of medical implants

In situ X-ray diffractometry with synchrotron radiation (SR) is used to study structural transformations in thin films of calcium-phosphate on the surfaces of medical implants made from alumina ceramics and oxidized titanium. The temperature limits of crystallization and structural composition of films on various substrates are found.     

A form of the elastic potential for a high-elastic material

A form of the elastic potential is proposed. A number of experiments and a procedure for determining the material constants and functions are considered. With the use of known experimental data, an elastic potential expression is obtained for vulcanized rubber as an example.     

Local atomic structure of zinc selenide films: EXAFS data

This paper presents the results of our study of the structural state and local atomic structure of zinc selenide films obtained by thermal evaporation in supervacuum at condensation temperatures of ?150°C, 0, and 150°C. Structure-sensitive methods such as X-ray diffraction, atomic force microscopy, and EXAFS spectroscopy were used. The parameters of the local atomic environment (interatomic distances, coordination numbers) of zinc and selenium atoms were obtained by Fourier transformation.     

Local audibility of a hyperbolic metric

A Riemannian metric g on a compact boundaryless manifold is said to be locally audible if the following statement is true for every metric g′ sufficiently close to g: if g and g′ are isospectral then they are isometric. The local audibility is proved of a metric of constant negative sectional curvature.     

Some applications of the Cauchy integral in problems of the deformation of thin plates

Three complex potentials are used to obtain exact solutions of problems of the deformation of infinite thin plates of constant thickness with a circular or elliptical hole under uniaxial tension or under the action of internal pressure in three-dimensional setting. Solutions are sought using the Cauchy integral, which enables the solutions to be presented in finite form. The solutions obtained are compared with known solutions.     

Thietanyl protection in the synthesis of 1-alkyl-8-bromo-3-methyl-3,7-dihydro-1<Emphasis Type="Italic">H</Emphasis>-purine-2,6-diones

The protection of the 7-NH group in 8-bromo-3-methyl-3,7-dihydro-1H-pyrine-2,6-dione during the synthesis of 7-ubsubstituted 1-alkyl-8-bromo-3-methyl-3,7-dihydro-1H-pyrine-2,6-diones with a thienyl group was applied that was introduced by the reaction with 2-chloromethylthiirane. The thietanyl protection was removed by treating with sodium alcoholate after the oxidation with hydrogen peroxide to thietane 1,1-dioxide group.