Spectroscopic studies of cutaneous photosensitizing agents. V. Spin trapping and direct electron spin resonance investigations of the photoreduction of gentian (crystal) violet

The photolysis of gentian violet (crystal violet) has been studied in aqueous solution by electron spin resonance spectroscopy. The photoreduction of gentian violet to the semireduced carbon-centered radical was detected directly by electron spin resonance under anaerobic conditions. The quantum yield of radical formation could be greatly increased by physiological reducing agents such as NADH and cysteine. The radical is insoluble in aqueous buffer, and the effects of detergents and liposomes on its solubility were studied. Although no gentian violet radical could be detected under aerobic conditions, the superoxide dismutase-sensitive 5,5-dimethyl- 1-pyrroline-l-oxide (DMPO) superoxide spin adduct was observed. Apparently the gentian violet radical is formed under aerobic conditions, but it is oxidized by oxygen, which would regenerate the dye and form superoxide.