Theoretical study of the conformations of triosmium clusters with a chiral carane ligand

A theoretical study has been performed to investigate the conformations of triosmium clusters with a chiral carane ligand . The potential curves of internal rotation have been determined for organic ligands rotating around the S-C bond in the cluster complexes. The structures of possible conformers are analyzed along with reasons for their stability. The rotation barrier relative to the S-C bond is 439.8 kJ/mole, which hinders free rotation of ligands.Original Russian Text Copyright © 2004 by V. A. Potemkin V. A. Maksakov, and V. P. KirinTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 430–434, May–June, 2004.     

A Method for Multiconformational Modeling of the Three‐Dimensional Shape of a Molecule

A method for multiconformational modeling of the threedimensional shape of a molecule is proposed that includes search for conformers, their optimum superposition, and analysis of spatial features of the resulting structure. The method allows one to determine features of various molecular conformations of compounds under study, to assess the contributions of conformers to particular properties of the substance, to evaluate the space occupied by the molecule, and to compare the average size of the multiconformational model of the molecule with the sizes of the most stable conformations. The potentials of the model are illustrated by density calculations for 137 organic liquids.     

Theoretical Study of the Formation of Benzofurotriazines by Reaction of 3-Substituted 1,2,4-Triazines and Fused Azolo[1,2,4]triazines with Resorcinol

3-Methylthio- and 3-amino-1,2,4-triazines react with resorcinol to give benzofurotetrahydrotriazine derivatives, while reactions of [1,2,4]triazolo[4,3-b]- and tetrazolo[1,5-b][1,2,4]triazines with resorcinol stop at the stage of resorcinol addition. According to the results of quantum-chemical calculations, the possibility for further cyclization of the resorcinol addition products is determined by the following factors: tautomeric and conformational states of the compounds, which ensure spatial proximity of the hydroxy group to the cyclization center (C⁶); charges on the C⁶ atom of the triazine ring and oxygen atom of the resorcinol fragment in the conformation most favorable for cyclization; and energies of the highest occupied and lowest unoccupied molecular orbitals of the resorcinol addition products.     

Changes in the vibrational characteristics of substituted 1,2,4,5-tetrazines after complexation with 1,2,3-benzotriazole: A theoretical study

The complexation of 3,6-substituted 1,2,4,5-tetrazines with benzotriazole was studied theoretically based on the vibrational spectra. For model complexes, the energy was minimized by the geometrical parameters, and the spectral characteristics were calculated by the PM3 method. The shift of the bond vibration frequencies of the atoms involved in complexation after the formation of different various intermolecular contacts was determined. This made it possible to determine the type of intermolecular interaction and suggest the structures of the complexes.     

Atoms-in-molecules study of intra- and intermolecular bonding in the pentaerythritol tetranitrate crystal

Chemical bonding in the pentaerythritol tetranitrate crystal based on the experimental electron density obtained from X-ray diffraction data at 100 K and theoretical calculations at the experimental molecular geometry have been analyzed in terms of the Quantum Theory of Atoms in Molecules. Features of the intra- and intermolecular bond critical points and the oxygen atom lone-pair locations are discussed. Numerous intermolecular bonding interactions, including O...H and O...O, have been found and characterized. Atomic charges and atomic energies were integrated and compared with those for similar compounds. The N-O topological bond orders have been calculated for the first time, and the PETN atomic valences have been estimated.     

Experimental Investigation and Modeling of the Cathodoluminescence of 1,2,4-Triazine Derivatives

We carried out experimental and theoretical investigations of the luminescence characteristics of 1,2,4-triazine derivatives and revealed the factors of a molecular structure that determine the cathodoluminescence wavelength. We obtained a satisfactory agreement between the experimental and calculated spectral characteristics. A number of reasons for the bathochromic and hypsochromic shifts of bands and also a change in the intensity of the pulsed cathodoluminescence were determined. Luminophor fragments of compounds have been revealed. We suggested variants of structural changes to increase the intensity and shift of the luminescence bands. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 586–590, September–October, 2005.     

Thermodynamic restrictions on the mechanism of 1/f noise

Presented at the 5th All-Union Conference on Fluctuation Phenomena in Physical Systems on September 29, 1988.     

Microphase separation in multiblock copolymers

The phase diagram of a multiblock copolymer containing domains of coexistence of phases having different superlattice symmetries with a density of monomers of a given type that varies periodically in space. The parameters of such superlattices are calculated in the mean-field approximation, and it is shown that their wave vector varies continuously with the temperature. Zh. éksp. Teor. Fiz. 112, 332–341 (July 1997)     

Microphase separation of double-grafted copolymers (centipedes) with gradient, random, and regular sequence of the branch points

We propose a theory of microphase separation of the double-grafted copolymer melts with different types of branch point distribution. It is shown that copolymers with gradient sequence of the branch points form a microstructure easier (at smaller values of the Flory-Huggins parameters) than equivalent copolymers with random or regular sequences. Two characteristic types of the microphase separation, "diblock-" and "comblike" are predicted. Due to the existence of the two characteristic length scales (the length of the backbone and the length of the side chains), the two-scale switching is possible.     

Performance of the low pressure MWPCs for f ission fragments under a high background

Two couples of low pressure multi-wire proportional chambers (MWPC) were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory (Jlab). In the experiment, a continuous wave (CW) electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy (1.853 GeV) and high intensity (500 nA) primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4.