RADICAL INTERMEDIATES IN THE FLUORESCEIN‐AND EOSIN‐PHOTOSENSITIZED AUTOXIDATION OF l‐TYROSINE*

Abstract The Primary reactions of the cosin‐and fluorescein‐photosensitized autoxidation of L‐tyrosine were studied in aqueous media (pH = 8.6) by the flash‐photolysis technique. The dye molecules were quantitatively converted to their triplet states in a single flash. The triplet dye molecules were found to react with tyrosine or oxygen. Ground state or radical dye molecules were formed in these reactions. Some 40 per cent of the triplet‐tyrosine reactions yielded radicals, in triplet dye‐oxygen reactions the corresponding yield was less than 10 per cent. The ground state dye was regenerated from the semireduced dye in reactions with oxygen and from the semioxidized dye in reactions with tyrosine. In the absence of oxygen the radicals formed in the photoinduced electron‐transfer between the triplet dye and tyrosine recombined to a large extent.