Photochemistry of biological molecules. IV. Gaseous products from the photolysis of alanine peptides in the solid state.
— Earlier studies based on ESR measurements of the photodamage induced by 254 nm irradiation of solid state alanine peptides have been supplemented by a new mechanistic probe involving mass spectrometric and gas-solid-chromatographic analyses of the gaseous products viz., carbon monoxide, carbon dioxide, hydrogen, methane and ethane. Decarboxylation, a major reaction, is temperature sensitive and independent of carbon monoxide formation. Carbon monoxide does not arise from the carboxyl group but rather by peptide bond rupture, which may lead to the generation of at least some of the hydrogen gas detected. The use of N-deuterated-DL-alanyl-DL-alanine shows that the methyl radicals generated can abstract hydrogen atoms from the solid state peptide, and the formation of H2 and HD implicate an imine intermediate in the photodegradation.