Some semi-empirical molecular orbital studies of the origin of conformational preferences for free S2O42- and N2O4

1984 ◽  
Vol 37 (7) ◽  
pp. 1553 ◽  
Author(s):  
RD Harcourt ◽  
BJ Smith ◽  
CJ Marsden
Keyword(s):  
Molecular Orbital ◽  
Rotation Barrier ◽  
Coulombic Repulsion ◽  
Barrier Analysis ◽  
Trans Conformer ◽  
Conformational Preferences ◽  
Semi Empirical ◽  
Ci Calculations

The results of some semi-empirical MO-CI calculations of the barriers to rotation around the S-S and N-N bonds of S2O42- and N2O4 are reported. The calculated barriers are expressed in terms of atomic, cis O-O overlap, coulombic repulsion and exchange contributions. The barrier analysis for N2O4 shows that cis O-O overlap stabilizes the planar relative to the skew conformer, whereas for free S2O42-, reduced coulombic repulsions stabilize the trans conformer relative to the eclipsed. Some CNDO/2 estimates of the rotation barrier for S2O42- are also reported.

A semi-empirical molecular orbital scheme to study electron transfer in iron–sulphur proteins

2005 ◽  
Vol 33 (1) ◽  
pp. 20-21 ◽  
Author(s):  
M. Sundararajan ◽  
J.P. McNamara ◽  
M. Mohr ◽  
I.H. Hillier ◽  
H. Wang
Keyword(s):  
Electron Transfer ◽  
Electronic Structure ◽  
Molecular Orbital ◽  
Parametric Method ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Semi Empirical

We describe the use of the semi-empirical molecular orbital method PM3 (parametric method 3) to study the electronic structure of iron–sulphur proteins. We first develop appropriate parameters to describe models of the redox site of rubredoxins, followed by some preliminary calculations of multinuclear iron systems of relevance to hydrogenases.

THE INVESTIGATION OF ELECTRONIC PROPERTIES AND MICROSCOPIC SECOND-ORDER NONLINEAR OPTICAL BEHAVIOR OF 1-SALICYLIDENE-3-THIO-SEMICARBAZONE

2007 ◽  
Vol 16 (01) ◽  
pp. 91-99 ◽  
Author(s):  
ASLI KARAKAS ◽  
HUSEYIN UNVER ◽  
AYHAN ELMALI
Keyword(s):  
Molecular Orbital ◽  
Electronic Transition ◽  
Nonlinear Optical ◽  
Dipole Moments ◽  
Empirical Method ◽  
Second Order ◽  
Nlo Properties ◽  
Calculation Results ◽  
Moller Plesset ◽  
Semi Empirical

To investigate the microscopic second-order nonlinear optical (NLO) behavior of the 1-salicylidene-3-thio-semicarbazone Schiff base compound, the electric dipole moments (μ), linear static polarizabilities (α) and first static hyperpolarizabilites (β) have been calculated using finite field second-order Møller-Plesset perturbation (FF MP2) theory. The ab-initio results on (hyper)polarizabilities show that the investigated molecule might have microscopic NLO properties with non-zero values. To understand the NLO behavior in the context of molecular orbital structure, we have also examined the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and the HOMO-LUMO gap in the same theoretical framework as the (hyper)polarizability calculations. In addition to the NLO properties, the electronic transition spectra have been computed using a semi-empirical method (ZINDO). ZINDO calculation results show that the electronic transition wavelengths have been estimated to be shorter than 400 nm.

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