PHOTOSENSITIZATION WITH ANTICANCER AGENTS .20. EPR STUDIES ON THE PHOTODYNAMIC-ACTION OF PHLEICHROME - FORMATION OF SEMIQUINONE RADICAL ANDACTIVATED OXYGEN SPECIES ON ILLUMINATION WITH VISIBLE-LIGHT

When phleichrome was illuminated with visible light, the semiquinone r adical, singlet oxygen, and superoxide anion radical were detected. Th e formation of the semiquinone radical and activated oxygen species an d the transformations and competitions between them depend on quinone and oxygen concentration, duration and intensity of illumination, and the nature of the substrate. In anaerobic solution, the semiquinone ra dical was predominantly photoproduced via the self-electron transfer b etween the excited and ground species. In contrast, in aerobic solutio n, singlet oxygen is the principal product in the photosensitization o f phleichrome. In addition to singlet oxygen, superoxide anion radical is also generated by the quinones upon illumination in aerobic soluti on, but to a lesser extent. The generation of the superoxide anion is significantly enhanced by the presence of electron donors.