EXCITED STATES OF BIOMOLECULES

点击翻译按钮获取中文摘要

Many biologically important molecules have a carbonyl group as a key functional component. Thus the peptide backbone is a chain of amides; steroid hormones contain the acrolein subgroup, and vitamin K and coenzyme Q contain para-quinone substructures. Szent-Gyorgyi has even postulated that the action of glyoxal on the amides in peptides is an important cancer regulation mechanims. In spite of their importance the electronic structures of these compounds are poorly understood. There is serious debate over the possibility of low energy biradical structures. Spectroscopy, without theory, has been unable to unravel the spectra satisfactorily. With modern computers, ad initio quantum chemistry is able to compute the excitation energies of simple systems to within plus minus 0.3 eV. These computations use contracted Cartesian Gaussian basis sets, generalized SCF procedures for each state, and extensive CI and/or perturbation theory. Our immediate objective is to determine the nature of the excited V state of dimethyl acetamide. Concurrently we will continue to investigate the possibility of a low energy biradical charge transfer complex between ammonia or formanide and glyoxal or methyl glyoxal. We will also investigate the nature of the 3(n, pi) of pyrazine with particular emphasis on an accurate evaluation of the zero-field and hyperfine magnetic parameters.