Photochemical formation of free radicals

The generation of free radicals under various conditions was investigated in the presence of potential photosensitizers and chloroplasts by means of electron spin resonance spectroscopy. The production of radical species by photoexcitation of haematoporphyrin, pheophorbide a and protoporphyrin in aqueous solutions containing ethanol was detected by the spin trapping technique. An increase in the formation of different radical species, depending on the light intensity and the amount of chloroplasts, was monitored. The addition of NADPH and NADP⁺, respectively, stimulated or decreased the radical formation.