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Abstract
In order to obtain information concerning the mechanism(s) of metallo-phthalocyanine (MePcS4) photosensitized damage of DNA constituents, the EPR-spin trapping method in conjunction with liquid chromatography was used to study thymidine (dThd) free radicals formed during photosensitization or exposure to γ-radiation in solution. Under specified conditions two dThd free radical species, 5-hydroxy-5,6-dihydrothymidine-6-yl and 6-hydroxy-5,6-dihydrothymidine-5-yl, were formed both during exposure to ionizing radiation and photosensitization. These results imply that identical reactive intermediates (•OH radicals) are involved in the radiolytic and photosensitized oxidation of dThd. A light-dependent, Fenton-type mechanism is proposed to explain the generation of hydroxyl radicals during MePcS4 photosensitization.