Search

Neutral and zwitter-ionic conformers of glycine (Gly) and alanine (L-Ala) are quantum chemically calculated at the B3LYP+GD3/def2TZVPP level of density functional theory within the discrete-continuum model in the gas phase and with regard to the effect of the aqueous medium. Structures with the minimum dipole moments prove to be the most stable neutral conformers of Gly and Ala in the gas phase. When solvation effects are taken into account within the polarized continuum model, conformers with the maximum dipole moments become energetically favorable due to the dipole-dipole interaction with the medium. Reaction activation barriers of the intramolecular proton transfer in the formation of zwitter-ions studied are calculated depending on the number of water molecules in the first coordination sphere. The inclusion of seven water molecules saturating the hydrogen bond of – and –COO– functional groups into the discrete-continuum model of a water solvent is shown to significantly decrease the activation barrier to 0.02 kcal/mol for glycine and to 0.09 kcal/mol for alanine. [ABSTRACT FROM AUTHOR]

The density functional theory was used for simulation of the NO reduction reaction with carbon monoxide on a reduced Ti8O15 nanocluster. The reaction proceeds on oxygen vacancies formed via the removal of terminal or bridging O atoms. In the case of adsorption of two NO molecules of such sites, a stable adsorption complex with the bidentate ligand ..ONNO is produced. When a CO molecule approaches one of the O atoms of this cycle, the following exothermic reaction yielding N2 and CO2 adsorbed on the Ti8O16 cluster takes place: 2NO+ CO + Ti8O15 → N2+ Ti8O16 · CO2. The proposed model of the reaction agrees well with experimental data. [ABSTRACT FROM AUTHOR]

The geometrical and basic energy parameters of monosubstituted cumulenes and their singly and doubly charged cations were calculated by the Hartree-Fock and density functional (DFT) methods at a B3LYP level of theory using the 6-31G( d) basis set. The substituent was fluorine, cyan, amino group, phenyl, cyanophenyl, aminophenyl, or dimethylaminophenyl. In extended linear carbon systems based on cumulene, rotation of a terminal fragment depends on the character of the highest occupied molecular orbital (HOMO) from which electrons are removed. The terminal group rotates through 90 only when the contribution of electron density from the π molecular orbital (MO) of unsubstituted cumulene to the HOMO of substituted cumulene is over 70%. Otherwise, the terminal group rotates through a smaller angle; with a contribution of less than 30%, the dication is planar in any substituted cumulene. Thus quantitative criteria have been determined to evaluate the specific structural effect due to ionization of substituted cumulenes. [ABSTRACT FROM AUTHOR]

The HeI photoelectron spectra of the complexes η4-1-vinylnaphthalene–Fe(CO)3 and η4-2-vinylnaphthalene–Fe(CO)3 and the free organic ligands 1-vinylnaphthalene and 2-vinylnaphthalene are measured. The spectra are interpreted on the basis of quantum-chemical calculations by the density functional method in the SVWN/6-31G(d) local density approximation and with the B3LYP/6-31G(d) hybrid exchange-correlation functional. The Kohn–Sham orbital energies with calibration corrections are shown to reproduce well the vertical ionization potentials of both the irontricarbonyl π complexes under study and their ligands. The relative ionization cross sections σi of the valence orbitals of the complexes are calculated in terms of the Gelius model. These quantities prove to agree perfectly with the relative ionization cross sections σiexp determined experimentally from direct estimation of the band areas of the photoelectron spectra. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The HeI and NeI photoelectron spectra of irontricarboniyl complexes with cyclic diene ligands—α-methylstyrene, orthoquinodimethane, and cyclooctatetraene—were obtained. The results of quantum-chemical calculations of the molecules of these compounds in the approximation of the density functional theory (B3LYP/6-31G*) are presented. It is shown that this approximation describes well the excited ionic states of the π complexes under study. The relative ionization cross sections σ[sub π] and σ[sub 3][sub d], which characterize the probability of removal of electrons from the molecular π-ligand and 3d-metal orbitals, are estimated. The mechanism of the selective coordination of the Fe(CO)[sub 3] groups to corresponding organic ligands is discussed. The energies of the L–Fe(CO)[sub 3] chemical bond are calculated. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]