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At least 829 records · Page 46Linked to original sources
PubMed2000

Theoretical Study of the Electronic Structure of the KRb Molecule.

Upon request of experimentalists now engaged in high-resolution spectroscopic investigations of the molecule KRb, we have determined the potential energy of electronic states (2S+1)Lambda((+)) correlating up to the limit K(5p) + Rb(5s) and of electronic states Omega((+/-)) correlating up to the limit K(4s) + Rb(4d(2)D(3/2)) in a large range of internuclear distance R. For the five states so far observed, the agreement between calculated and experimental molecular constants is good with DeltaR(e) < 0.08 Å, Deltaomega(e) < 6 cm(-1), and DeltaT(e) < 140 cm(-1). Extensive numerical data for energies versus R have been listed in a data base available at http://www.idealibrary.com. Copyright 2000 Academic Press.

Journal Article↗
PubMed2005

Electronic structure of the calcium monohydroxide radical.

Effective valence shell Hamiltonian H(v) calculations are used to map out three-dimensional potential energy surfaces for the 12 lowest electronic states of the CaOH radical. Excitation energies and spectroscopic constants are compared with experiment and prior computations where available, but many previously unavailable data are provided, including excited state dipole moments and oscillator strengths. Particular attention is paid to clarify the nature of nonlinear and quasilinear excited states, Renner-Teller couplings, and state mixings. The F (2)Pi and G (2)Pi (6 (2)A(') and 8 (2)A(')) states are both found to possess nonlinear local minima, due to an avoided crossing. Attention is also focused on the characteristics of basis sets necessary in high-accuracy calculations for the CaOH radical.

Journal Article↗
PubMed2002

Electronic structure description of the mu(4)-sulfide bridged tetranuclear Cu(Z) center in N(2)O reductase.

Spectroscopy coupled with density functional calculations has been used to define the spin state, oxidation states, spin distribution, and ground state wave function of the mu4-sulfide bridged tetranuclear CuZ cluster of nitrous oxide reductase. Initial insight into the electronic contribution to N2O reduction is developed, which involves a sigma superexchange pathway through the bridging sulfide.

Circular Dichroism↗
PubMed2004

Geometrical control of the active site electronic structure of pyranopterin enzymes by metal-dithiolate folding: aldehyde oxidase.

Density functional calculations on geometry-optimized oxidized (Mo(VI)) and reduced (Mo(IV)) analogues of the isolated active site of aldehyde oxidase (MOP), a member of the xanthine oxidase family of pyranopterindithiolate enzymes, show that fold angle changes of the dithiolate ligand modulate the relative metal and dithiolate contributions to the frontier redox orbitals. Proton abstraction from the equatorial aqua ligand of the oxidized Mo(VI) site also flattens the metal dithiolate fold angle. It is proposed that static and/or dynamic changes in the structure of the protein surrounding the active site can induce changes in the dithiolate fold angle and thereby provide a mechanism for electronic buffering of the redox orbital, for fine-tuning the nucleophilicity of the equatorial aqua/hydroxide ligand, and for modulating the electron-transfer regeneration of the active sites of molybdenum and tungsten enzymes via a "dithiolate folding effect".

Aldehyde Oxidase↗
PubMed2006

On the electronic structure of the hydrogenase H-cluster.

X-ray absorption spectroscopic measurements and density functional calculations suggest that the hydrogenase H-cluster is best described as an electronically inseparable 6Fe-cluster due to extensive delocalization of frontier molecular orbitals of the iron centres, sulfide and the non-innocent dithiolate ligands.

Electrons↗
PubMed2006

Theoretical study on the excited-state intramolecular proton transfer in the aromatic schiff base salicylidene methylamine: an electronic structure and quantum dynamical approach.

The proton-transfer dynamics in the aromatic Schiff base salicylidene methylamine has been theoretically analyzed in the ground and first singlet (pi,pi) excited electronic states by density functional theory calculations and quantum wave-packet dynamics. The potential energies obtained through electronic calculations that use the time-dependent density functional theory formalism, which predict a barrierless excited-state intramolecular proton transfer, are fitted to a reduced three-dimensional potential energy surface. The time evolution in this surface is solved by means of the multiconfiguration time-dependent Hartree algorithm applied to solve the time-dependent Schrödinger equation. It is shown that the excited-state proton transfer occurs within 11 fs for hydrogen and 25 fs for deuterium, so that a large kinetic isotope effect is predicted. These results are compared to those of the only previous theoretical work published on this system [Zgierski, M. Z.; Grabowska, A. J. Chem. Phys. 2000, 113, 7845], reporting a configuration interaction singles barrier of 1.6 kcal mol(-1) and time reactions of 30 and 115 fs for the hydrogen and deuterium transfers, respectively, evaluated with the semiclassical instanton approach.

Journal Article↗
PubMed2005

Effect of the axial cysteine ligand on the electronic structure and reactivity of high-valent iron(IV) oxo-porphyrins (Compound I): a theoretical study.

The effect of axial ligands on the reactivity of high-valent iron(IV) oxo-porphyrins (Compound I) was investigated using the B3LYP hybrid density functional method. We studied alkane hydroxylation using four models: Compound I with thiolate, imidazole, phenolate, and chloride anions as axial ligands. The first three ligands were employed as models for cysteinate, histidine, and tyrosinate, respectively. Our calculations show that anionic ligands and neutral ligands favor different electronic states for stationary points in the reaction coordinate, and the calculated energy barrier and energy of several reaction intermediates show similar values. A remarkable effect of axial ligands was found in the final product release step. Our calculations show that the thiolate ligand weakens a bond between heme and an alcohol. In contrast, the imidazole ligand significantly increases the interaction between heme and an alcohol, which causes the catalytic cycle to be less efficient.

Computer Simulation↗
PubMed2005

Electronic structure of thiazine-indigo pigment on the basis of the crystal structure.

Thiazine-indigos are novel hydrogen-bonded pigments developed recently by Clariant that exhibit a variety of shades from yellow to red. Among these, a commercially available chlorinated derivative (THI) gives a color of vivid red, although it is only pale yellow in solution. For this reason, electronic characterization of THI has been carried out on the basis of the crystal structure. There are chains of intermolecular hydrogen bonds between the N-H group of one molecule and the O atom of the neighboring one along the b-axis, forming a two-dimensional hydrogen bond network. The direction of the transition dipole points along the long molecular axis, and the transition dipoles are arranged in "head-to-tail" fashion along the (b,-c) diagonal direction. The large bathochromic shift upon crystallization can be mostly attributed to excitonic interactions between transition dipoles arranged diagonally along the stacking axis as well as those in head-to-tail fashion on the molecular plane.

Journal Article↗