Ab initio Calculation of the Electronic Structure and Equilibrium Geometry of Cortisol and Its Derivatives

The molecular geometries of a series of steroid hormones including cortisol, 9-fluorocortisol, 6-fluorocortisol, and 9-chlorocortisol were optimized by 3-21G and 6-31G* ab initio calculations. The results of calculations on both levels are well consistent with each other and with the experiment. The conformational changes and electron density redistribution occurring in going from cortisol to its 6- and 9-halo derivatives were discussed. A conclusion was made that the O and F atoms can participate in hydrogen bonding with the corresponding structural groups of glucocorticoid receptors.     

Fluctuation-Optical Method for Determining Gelation Point of Biopolymer Systems

Method for determining temperature of the transition of biopolymer systems to gellike state was developed using the earlier discovered effect of decaying amplitude of spontaneous fluctuations of system optical density, which significantly exceed the level of intrinsic noise of measuring devices of Specord M40 and Specord M400 spectrophotometers. These fluctuations are caused by the thermal convection resulting in the emergence of randomly distributed regions with different optical properties in the analyzed systems. The inhomogeneity can by amplified by the fraction of supermolecular particles (SMP). The effect of convection markedly decreases as a result of the loss of fluidity during the system gelation, thus underlying the instrumental registration of the sol–gel transition whose efficiency was confirmed in this work using aqueous preparations of plant polysaccharides (pectin, agar, furcellaran, and -carrageenan). It was shown that, in the cases of initially optically homogeneous systems, the role of the SMPs can be played (if necessary) by the relatively small amounts of the particles of chemically inert compounds (for example, cellulose) at slight mixing of a system using magnetic stirrer. This method was applied for constructing the fragment of the phase diagram of the furcellaran–water system during its cooling. The interpretation of its semi-logarithmic transformation in terms of the Eldridge–Ferry theory resulted in the estimation of the amount of heat evolved during the formation of gel network junctions (presumably, due to the pair associations of double helixes), which appeared to be equal to –63 kJ mol^–1.     

Synthesis of New 4,4a-Dihydroxanthones via [4+2]-Cycloaddition Reaction

Russian Journal of General Chemistry - The effect of electronic properties of substituents in the reactants on the [4+2]-cycloaddition of 3-vinyl-chromen-4-ones (dienes) and N-vinylpyrrolidines...     

Underground Physics and the Nonlinear Delayed Barometric Effect of the Gamma-Ray Background

Journal of Experimental and Theoretical Physics - The electronic, magnetic, and optical properties of MnGa2O4 in the structure of the normal and inverse spinels are subjected to an ab initio...     

Quantum-Chemical Study of the Equilibrium Geometry and Electronic Structure of the Defensin Molecule

The molecular geometry of rabbit NP-1 defensin is fully optimized by means of molecular mechanics and MNDO methods. Atomic charges are calculated, and an estimate for the dipole moment of the molecule is obtained ( 4.0 D). The possible mechanism of defensin-receptor interactions is discussed.     

Nonempirical quantum-chemical calculation of the electric field gradient at the <Superscript>51</Superscript>V nucleus sites in alkali metavanadates

The electric-field gradient tensor at the vanadium nucleus site was calculated ab initio within a cluster model for chained vanadates XVO₃ (X=Li, Na, K). A comparison with experiment showed that it suffices to consider only small (VO₄)^3? and (V₃O₁₀)^5? clusters in crystals of this type. The calculation scheme stability with respect to increasing cluster size was analyzed.     

On one class of solutions of a countable quasilinear system of differential equations with slowly varying parameters

For a countable quasilinear differential system whose coefficients are represented as Fourier series with slowly varying coefficients and frequency, we present conditions under which solutions of this system have analogous structure. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 8, pp. 1121–1128, August, 1998.     

The network approach to calculation of characteristic time constants of the flat two-layer superconducting cable

The matrix method was used to investigate the process of current decay in the samples of flat two-layer superconducting cables. The discrete spectrum of eigen-frequencies has been obtained. Each of these frequencies determines the rate of decay of the correspondent eigen-current. Despite of the increasing of the number of eigen-frequencies with the enlargement of the sample dimensions the spectrum remains finite, as the maximum and minimum frequencies tend to finite limits. An analysis made for the lowest eigen-frequencies showed the corresponding eigen-currents to be slowly decaying long current loops. Within the range of high frequencies the sinusoidal distribution of eigen-currents in the rows of the cable was observed.