Identification of Radicals and Determination of Their Yields in the Radiolytic Oxidation of Glycine. Time-resolved ESR Methodology

Abstract

Both aminomethyl (•CH2NH2) and H2N−•CH−CO2- radicals were identified by time-resolved ESR spectroscopy in the oxidation of glycine anions by •OH. Previous ESR measurements had detected only the H2N−•CH−CO2- radical in these systems. The rise times of the ESR lines for these two different radicals are consistent with both of the radicals being formed in the initial reaction of •OH with the glycine anions. The yields of these two C-centered radicals relative to the total yield of •OH are approximately 29% for aminomethyl radicals and 53% for H2N−•CH−CO2- radicals. The yield of aminomethyl radicals from methlyamine was 53%. No ESR lines attributable to aminyl radicals could be directly detected in solutions of glycine (HN•−CH2−CO2-) at high pH or low pH, or in solutions of methylamine (HN•−CH3). However, clear evidence for the presence of the aminyl radicals was obtained in spin-trapping experiments using the aci-anion form of nitromethane with both methylamine and glycine. The rapid appearance of aminomethyl radicals in a complementary experiment with hydrated electrons reacting with N-chloroglycine could be simply explained on the basis of the formation of N-centered radicals in this situation. The ESR method for determining the yields was tested in the •OH oxidation of methylamine and succinic acid. The implications of the findings of this work are discussed in the context of the recently proposed scheme for the oxidation of glycine anions by •OH.