FLASH PHOTOLYSIS OF FLAVINS‐I. PHOTOREDUCTION IN NON‐AQUEOUS SOLVENTS*

Abstract— The photoreduction of riboflavin, FMN, and lumiflavin in a series of hydroxylic solvents has been examined using flash photolysis. A comparison of the relative quantum yields for the photoxidation of several alcohols and esters by lumiflavin demonstrated that the hydroxyl hydrogen of the alcohol is abstracted approximately twice as readily as is the alpha hydrogen. The use of glycerol as both solvent and reductant provided direct evidence that the initial reaction proceeds by a one‐electron reduction to form the flavin semi‐quinone. In the case of riboflavin (and FMN) the kinetic results are consistent with an initial intra molecular hydrogen atom transfer, analogous to photobleaching in aqueous solution, followed by a reaction of the semi‐quinone with the reductant which prevents degradation of the ribityl side‐chain. Quenching by iodide indicates that all the reactions proceed via the flavin triplet state, as is the case in aqueous systems.