THE GEOMETRY AND SPIN-DENSITY DISTRIBUTION OF THE TYROSYL RADICAL - AMOLECULAR-ORBITAL STUDY

The oxidation of the amino acid tyrosine to the tyrosyl radical is now known to be important in many electron transfer reactions in biology. Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Res onance (ENDOR) have previously been used to obtain proton hyperfine co uplings for the radical in vivo. This study uses AM1 molecular orbital calculations to provide a detailed insight into the geometry and elec tronic makeup of this important radical. Molecular orbital studies are first used to obtain an optimised geometry for the tyrosyl radical. T his is shown to differ significantly from the unoxidised form. The ext ent of the singly occupied molecular orbital is then examined and a th eoretical estimate of the unpaired electron spin distribution is obtai ned. This is then used to calculate the anisoptopic hyperfine coupling components for comparison with experimental determinations.