| Abstract: | Abstract— Both anaerobic and aerobic photolysis of riboflavin in pyridine yielded several photoproducts, analogous to the photochemical reaction in aqueous solution. Lumiflavin was also photoreduced in pyridine (an electron donor) without decomposition of the isoall-oxazine ring Differences in the reactivity of excited singlet and triplet states with respect to formation of photoproducts have been confirmed in pyridine. In the photoreduction of riboflavin by N, N'-dimethyl-N-benzylethylene diamine, an initial rate with a higher relative quantum yield than that of the reaction at a later stage was observed both in water and pyridine. Photolysis in D2O with the donor showed no significant solvent isotope effect. These results strongly suggest that the photolysis of riboflavin in water does not involve the water molecule in the primary photochemical act. A detailed mechanism of flavin photoreaction in water to account for solvent oxygen incorporation into a photoproduct (benzaldehyde) from N, N'-dimethyl-N-benzylethylene diamine has been proposed without involving photochemical splitting of water based on our results and molecular orbital computations. Preliminary results on the kinetics of free radical decay were obtained using an ESR spectrometer and the significance of the results are discussed. |
