The UV photolysis of N-acetyl amino acids studies by ESR as models for biological polypeptides

The free-radical intermediates and volatile products of the UV photolysis of five N-acetyl amino acids were studied by ESR and mass spectroscopy. At low temperatures (77 or 100 K) radicals were produced by cleavage of the CH₃CO bond in the N-acetyl group and by subsequent abstraction reactions. Photolysis of frozen aqueous solutions, in which the radicals were isolated in the matrix, showed that methyl and acyl radicals were the initial radical intermediates. Carbon dioxide was the major volatile photolysis product. A non-radical decarboxylation reaction is proposed. Comparison of the photolysis products with those reported for poly(amino acid)s showed that the N-acetyl amino acids are not appropriate models for the UV photolysis of poly(amino acid)s.