Gas- and Solution-Phase Properties of Aromatic Amino Acid Radicals

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Ralph Wheeler, University of Oklahoma, is funded by the Theoretical and Computational Chemistry Program to study the gas phase and solution phase properties of aromatic amino acid radicals. Wheeler will use ab initio quantum calculations and molecular dynamics to further understand the energetics, pathways, and rates of radical migration in proteins and peptides. Comparisons will be made between gas phase and solvated tyrosine and tryptophan radicals and cations. Density functional theory will be used to calculate the gas phase vibrational frequencies and spin densities of these species for comparison with organic phenoxyl, phenoxyl cation, indoyl and indoyl cation radical side chains. One of the objectives here is to identify vibrational and ESR spectroscopic features which can be used to distinguish different orientations of the aromatic amino acid radicals. Molecular dynamics will then be used to compute free energies of hydration using free energy perturbation theory together with charges and force constants obtained from the gas phase density functional calculations. The formation and migration of highly reactive radicals is implicated in carcinogenesis and aging. The recent discovery and characterization of aromatic amino acid radicals in proteins implies that amino acid radicals are much more prevalent and important than previously suspected. The long term goals of Wheeler's computational research include understanding the molecular components and their interactions responsible for the energetics, pathways, and rates of radical migration in proteins and peptides.