Molecular Orbital Calculations for Biological Systems

Molecular Orbital Calculations for Biological Systems is a hands-on guide to computational quantum chemistry and its applications in organic chemistry, biochemistry, and molecular biology. With improvements in software, molecular modeling techniques are now becoming widely available; they are increasingly used to complement experimental results, saving significant amounts of lab time. Common applications include pharmaceutical research and development; for example, ab initio and semi-empirical methods are playing important roles in peptide investigations and in drug design. The opening chapters provide an introduction for the non-quantum chemist to the basic quantum chemistry methods, ab initio, semi-empirical, and density functionals, as well as to one of the main families of computer programs, the Gaussian series. The second part then describes current research which applies quantum chemistry methods to such biological systems as amino acids, peptides, and anti-cancer drugs. Throughout the authors seek to encourage biochemists to discover aspects of their own research which might benefit from computational work. They also show that the methods are accessible to researchers from a wide range of mathematical backgrounds. Combining concise introductions with practical advice, this volume will be an invaluable tool for research on biological systems.

1975 ◽  
Vol 16 (11) ◽  
pp. 933-936 ◽  
Author(s):  
Gary L. Grunewald ◽  
Ibrahim M. Uwaydah ◽  
Ralph E. Christoffersen ◽  
Dale Spangler

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.


1981 ◽  
Vol 36 (11) ◽  
pp. 1246-1252 ◽  
Author(s):  
Michael H. Palmer ◽  
Isobel Simpson ◽  
J. Ross Wheeler

The photoelectron spectra of the tautomeric 1,2,3,- and 1,2,4-triazole and 1,2,3,4-tetrazole systems have been compared with the corresponding N-methyl derivatives. The dominant tautomers in the gas phase have been identified as 2 H-1,2,3-triazole, 1 H-1,2,4-triazole and 2H-tetrazole.Full optimisation of the equilibrium geometry by ab initio molecular orbital methods leads to the same conclusions, for relative stability of the tautomers in each of the triazoles, but the calculations wrongly predict the tetrazole tautomerism.


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