Photo-induced electron transfer in small peptides: glycylalanine

Abstract

Participation of the peptide bond in photoinduced electron transfer accounts for product distributions in the photolysis of XG dipeptides and predicts the possibility that the side-chain will be involved in similar reactions of GX dipeptides. Product analysis following exposure of aqueous glycyl-DL-alanine to UV radiation shows this prediction is fulfilled. Thus, unlike XG peptides, glycylalanine degrades to acetamide substantially without co-production of CO2 and to products where bonding in the side-chain is involved in relaxation of the intermediate diradical. At a lower pH, decarboxylation radicals from glycylalanine have the opportunity to disproportionate as well as dimerize, and this accounts satisfactorily for the difference in product distribution when compared with that from XG photolysis under the same conditions.