We report the reactions of deprotonated tyrosine ([Tyr-H]-) and tryptophan ([Trp-H]-) with 1O2, including the measurement of the effects of collision energy (Ecol) on reaction cross sections.  Electronic structure calculations were used to examine the reaction coordinate.  For [Tyr-H]- + 1O2, the reaction corresponds to formation of a hydroperoxide, and subsequent dissociation to -OC6H4CH2CHNH, H2O2 and CO2.  Despite being exothermic, the reaction shows a threshold-like behavior at low Ecol, suggesting that the reaction proceeds with an activation energy barrier above the reactants.  Quasi-classical direct dynamics trajectory simulations were calculated for [Tyr-H]- + 1O2 at Ecol = 0.75 eV using B3LYP/4-31G*.  Most trajectories formed intermediate complexes, implying the importance of complex formation in reaction.  A similar product channel was observed for [Trp-H]- + 1O2, yielding -N-indo-CH2CHNH, H2O2 and CO2.  However, the reaction of [Trp-H]- + 1O2 shows exothermic behavior, indicating that this reaction proceeds without energy barriers above the reactants.

Reactions of deprotonated tyrosine and tryptophan with electronically excited singlet molecular oxygen (a<sup>1</sup>[Delta]<sub>g</sub>): Effects of deprotonation of amino acids on oxidation reactivity

244th National Meeting (2012)

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Reactions of deprotonated tyrosine and tryptophan with electronically excited singlet molecular oxygen (a1[Delta]g): Effects of deprotonation of amino acids on oxidation reactivity

Reactions of deprotonated tyrosine and tryptophan with electronically excited singlet molecular oxygen (a¹[Delta]_g): Effects of deprotonation of amino acids on oxidation reactivity