ULTRAVIOLET PHOTOLYSIS OF RIBOFLAVIN IN PYRIDINE: A PRELIMINARY STUDY

Abstract— Ultraviolet photolysis of riboflavin in pyridine leads to the formation of a red photoproduct. This photoreaction is apparently attributed to the photochemical interaction of pyridine with riboflavin. It is found that the rate of the photoreaction follows 1/2 order kinetics with respect to pyridine. ESR spectrum of the irradiated reaction mixture appears to be identical with that of riboflavin semiquinone obtained from visible light irradiation. Whether or not such a flavin radical is the responsible intermediate in the photoreaction is not established. Possible modes of the reaction are discussed. Absorption, excitation, and emission spectra of the red photoproduct strongly suggest that the structure of the photoproduct is considerably different from that of riboflavin or pyridine, indicating an extensive photolytic process involving covalent bond alterations.