Quantum-chemical study,IR spectra,and intramolecular hydrogen bonds in dimeric 5- and 6-methyluracils

Comparative analysis of the geometry, atomic charges, force constants, and IR spectra of crystals of isomeric 5- and 6-methyluracils was performed by quantum-chemical methods. Dimeric and trimeric associates of C-methyluracil molecules and their dimers with adenine were calculated in order to estimate the energies of intramolecular hydrogen bonds. Thymine in DNA is impossible to replace by 6-methyluracillargely by steric reasons.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 12, 2004, pp. 2038–2047.Original Russian Text Copyright © 2004 by Naumov, Tafipolskii, Reznik.This revised version was published online in April 2005 with a corrected cover date.     

Unexpected formation of a novel macrocyclic tetraphosphine: (RSSR)-1,9-dibenzyl-3,7,11,15-tetramesityl-1,9-diaza-3,7,11,15-tetraphosphacyclohexadecane

The title compound was synthesised in moderate yield via stereoselective self-assembly of two bisphosphine, four formaldehyde and two primary amine molecules.     

Optical and gain properties of series of crystals LiF-YF3-LuF3 doped with Ce and Yb ions

Here, we present first results of systematic studies of host cation variation impact on spectral-kinetic, photochemical and gain properties of Ce³⁺-doped LiYF₄ (YLF), LiLuF₄ (LLF) and LiY_1−xLu_xF₄ family crystals. 5d-4f luminescence decay of Ce³⁺ ions studies, together with pump-probe experiments, indicate that previously reported twice higher luminescence quantum yield in LLF compared with that of YLF crystals is provided by more efficient upper lasing level feeding due to recombination and higher color center destruction rate in LLF against YLF crystals. Namely, it is responsible for higher energetic characteristics of laser based on Ce³⁺:LLF crystals. Strong and wide pump-induced absorption band centered at 310 nm is observed in Ce³⁺:YLF. This band is shifted to blue and its intensity goes down with Lu content. We have evaluated free charges recombination rate, excited state absorption cross-section for Ce³⁺ ions and some other photodynamic processes related microparameters. Fitting results indicate that pump-induced color centers lifetime decreases with Lu-content in LiYF₄-LiLuF₄ mixture and it can be associated with more efficient color center bleaching by Ce³⁺ ions 5d-4f fluorescence.     

Investigation of the anisotropy of the properties of glass-reinforced plastic shells

The load-carrying capacity and deformation of cylindrical and conical glass-reinforced plastic (ÉDT-10 resin) shells loaded in axial compression have been investigated experimentally in relation to the orientation of the fabric reinforcement. The results of the tests are compared with the relations of the theory of elasticity of an orthotropic body.Zhukovskii Central Aerohydrodynamics Institute, Moscow Region; Scientific Research Institute of Production Technology and Organization, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 814–818, September–October, 1969.     

The effect of alkyl chain length on the thermodynamic properties of the half esters of o-phthalic acid

The temperature, heat and entropy of fusion of four half esters of o-phthalic acid have been measured. These values are compared to other aromatic acid properties on the basis of molecular weight. The calorimetric data have an accuracy of ±5% and agree well with values predicted from simple entropy, geometric and electronic considerations.     

Light confinement and supercontinuum generation switching in photonic-molecule modes of a microstructure fiber

The modes guided in a ring system of microstructure-integrated fibers are shown to have much in common with electron wave functions in a two-dimensional polyatomic cyclic molecule. This photonic-molecule analogy provides, in particular, an illustrative and physically clear model of dispersion properties and the mode structure of an electromagnetic field in microstructure fibers of the considered type. A high degree of light confinement in waveguide modes of such a photonic molecule enhances nonlinear-optical processes, permitting an octave spectral broadening to be achieved for low-energy femtosecond laser pulses.     

Large magnetoresistance in an inhomogeneous magnetic semiconductor

A new way of attaining large values of magnetoresistance in a magnetic semiconductor was investigated. The mechanism of magnetoresistance is based on the formation of a space charge, a depletion layer, and a contact potential U _c at the interface between two semiconductors with different Fermi levels E _n ^F and E _p ^f and on the dependence of U _c, the electrical resistivity, and the size of the depletion layer in the magnetic semiconductor on the magnetic field strength. The model proposed was experimentally verified using a microstructure consisting of an HgCr₂Se₄ n-layer with a thickness of up to several tens of microns deposited on the surface of a bulk p-HgCr₂Se₄ single crystal. Depending on microstructure parameters, a sharp (up to ～30 times) rise in the current flowing through the n-layer was observed in the region of Curie temperature upon switching on a magnetic field (H～15 kOe).