@article {2615, title = {Orientational order of near D-3h solutes in nematic liquid crystals. II. Description via Gay-Berne model with embedded quadrupoles}, journal = {Journal of Chemical Physics}, volume = {130}, number = {15}, year = {2009}, note = {ISI Document Delivery No.: 437KLTimes Cited: 3Cited Reference Count: 19Sokolovskii, R. O. Burnell, E. Elliott}, month = {Apr}, pages = {6}, type = {Article}, abstract = {We perform Monte Carlo simulations of a mixture of soft ellipsoids with embedded quadrupoles as a model of various chloro- and methyl-substituted benzenes dissolved in nematic liquid crystals. We find that oblate Gay-Berne ellipsoids with multiple embedded quadrupoles qualitatively reproduce the trend in the order parameter asymmetry experimentally observed in NMR spectra. The trend is opposite to what is expected on the basis of the interaction of the solute{\textquoteright}s quadrupole with the solvent{\textquoteright}s average electric field gradient "felt" by dissolved dihydrogen molecules. We identify the specific minimum of the solute-solvent interaction energy landscape that may produce the unexpected sign of the order parameter asymmetry that is seen in the experiment and the simulation.}, keywords = {COMPOUNDS, deuterium, dissolving, ELECTRIC-DIPOLE INTERACTIONS, LIQUID MIXTURES, liquid theory, METHODS, Monte Carlo, MONTE-CARLO SIMULATIONS, nematic liquid crystals, nuclear magnetic resonance, ORGANIC, POTENTIALS, SHAPE, SOLVENTS}, isbn = {0021-9606}, url = {://000265486300033}, author = {Sokolovskii, R. O. and Burnell, E. E.} } @article {1592, title = {Conformational stability, molecular structure, and intramolecular hydrogen bonding of thenoyltrifluoroacetone}, journal = {J. Theor. Comput. Chem.}, volume = {5}, number = {3}, year = {2006}, note = {ISI Document Delivery No.: 098FUTimes Cited: 3Cited Reference Count: 52Tayyari, Sayyed Faramarz Nekoei, Abdo-Reza Vakili, Mohammad Hassanpour, Masoud Wang, Yan Alexander}, month = {Sep}, pages = {647-664}, type = {Article}, abstract = {

Complete conformational analysis of all possible keto and enol forms of thenoyltrifluoroacetone (TTFA) was carried out using density functional theory with the B3LYP functional and the 6-31G**, 6-311G**, and 6-311++G** basis sets. In addition, the geometries and energies of the four most stable chelated conformers and their corresponding open structures were obtained at the MP2/6-31G** level of theory. The energy differences between the four stable chelated enol conformers, in the gas phase, calculated at the B3LYP levels are negligible. However, calculations at the MP2 level indicate that the B2 conformer (the hydroxyl group in the -CF3 side) is significantly more stable than others, in agreement with the X-ray diffraction results. The calculated intramolecular hydrogen bond (IHB) energy E-HB and the strength of the bond have been compared, and an imperfection in the prevalent method of evaluating E-HB has been perceived. The IHB of TTFA was compared with those in several beta-dicarbonyls.

}, keywords = {ACETYLACETONE, beta-diketone, BETA-DIKETONES, conformational analysis, CRYSTAL-STRUCTURE, EQUILIBRIUM CONSTANTS, INFRARED-SPECTRA, intramolecular hydrogen bond, KETO-ENOL-TAUTOMERISM, nuclear magnetic resonance, PROTON CHEMICAL, SHIFTS, SYNERGISTIC EXTRACTION, thenoyltrifluoroacetone, VIBRATIONAL ASSIGNMENT}, isbn = {0219-6336}, url = {://000241507200011}, author = {S. F. Tayyari* and A.-R. Nekoei and Vakili, M. and Hassanpour, M. and Wang, Y. A.} } @article {4345, title = {Vesicular membrane permeability of monomethylarsonic and dimethylarsinic acids}, journal = {Biophysical Chemistry}, volume = {70}, number = {1}, year = {1998}, note = {ISI Document Delivery No.: YU539Times Cited: 6Cited Reference Count: 45}, month = {Jan}, pages = {75-85}, type = {Article}, abstract = {The transmembrane permeability coefficients of the environmentally sensitive arsenicals, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) have been measured for egg phosphatidylcholine large unilamellar vesicles. The determination of the vesicle concentration-independent first-order rate constants for membrane transport and the permeability coefficients were made using an NMR technique employing shift agents. The permeability coefficient of DMA was found to be two orders of magnitude greater than that of MMA. This is attributed to the presence of MMAs extra hydroxyl group. Both species are shown to permeate membranes in the neutral form. Both the temperature dependence and the dependence on cholesterol content were investigated for DMA. The activation energy and the Arrhenius preexponential factor were found to be dependent on the cholesterol content. A marked increase in both parameters was observed up to 20 mol.\% cholesterol, with a further, small increase up to 60\%, The significance of these results to our understanding of membrane transport is discussed. The importance of using permeability coefficients rather than n-octanol/water partition coefficients in determining bioavailability and bioaccumulation of environmentally sensitive compounds is also discussed. (C) 1998 Elsevier Science B.V.}, keywords = {BILE-ACIDS, CHOLESTEROL, DIFFUSION, DIMETHYLARSINIC ACID, HUMAN-ERYTHROCYTES, LIPID BILAYER-MEMBRANES, monomethylarsonic acid, NONELECTROLYTE, nuclear magnetic resonance, PARTITION-COEFFICIENTS, permeability, phosphatidylcholine membranes, RAPID EXTRUSION PROCEDURE, TRANSPORT, UNILAMELLAR VESICLES}, isbn = {0301-4622}, url = {://000071728000008}, author = {Males, R. G. and Nelson, J. C. and Phillips, P. S. and Cullen, W. R. and Herring, F. G.} }