E.s.r. study of spin-trapped radicals formed during the photolysis of aqueous solutions of acid amides and H2O2.

Free radicals formed by the reactions of OH radicals with amides and their N-methylated derivatives in aqueous solutions have been studied. The OH radicals were produced by U.V.-photolysis of H2O2, and the short-lived amide radicals were converted to more stable nitroxide radicals by addition to a spin-trap, tert-nitrosobutane. The spin-trapped radicals were identified by e.s.r. spectroscopy. For acetamide, chloroacetamide, malonamide, succinamide and propionamide, the observed radicals were formed by H-abstraction from the carbon atoms attached to the carbonyl group. The H atom attached to the carbonyl group was abstracted in formamide. For N-methyl acetamide, N,N-dimethyl acetamide and the corresponding formamide derivatives, H-abstraction occurred only from the N-methyl group. The non-equivalency of the amide protons was observed in the spin-trapped radicals for acetamide, formamide, malonamide, succinamide and propionamide. The identification of the site of OH attack on N-methyl amides is helpful for the study of radical formation in peptides and proteins.