Generation of semiquinone radical anion and reactive oxygen ( 1O 2, O 2•− and •OH) during the photosensitization of a water-soluble perylenequinone derivative

Abstract

5(or 8)-sulfonated hypocrellin B (5-SO 3H-HB) is a water-soluble perylenequinone derivative. Electron spin resonance studies in combination with chemical methods show that 5-SO 3H-HB is an active photosensitizer. Visible-light illumination of 5-SO 3H-HB solutions generates a semiquinone radical anion, singlet oxygen, a superoxide radical anion, a hydroxyl radical and hydrogen peroxide. In anaerobic solution, the semiquinone radical anion is predominately photoproduced, via self-electron transfer between the excited and ground states of 5-SO 3H-HB. In aerobic solution, singlet oxygen is generated in the photosensitization of 5-SO 3H-HB. In addition, a superoxide radical anion is also generated from 5-SO 3H-HB on illumination in aerobic solution, via the reduction of oxygen by the semiquinone radical anion. In aqueous solution, the superoxide radical anion formed can rapidly transformed to a hydroxyl radical via the Fenton reaction and via the reaction of the semiquinone radical anion with H 2O 2. Based on these results, the pathways for the photodynamic action of 5-SO 3H-HB have been proposed.