PHOTOINDUCED PHENOXY RADICAL OF 3, 4-BENZOPYRENE

Abstract

It was found that by photoirradiation a phenoxy radical was produced from 3, 4-benzopyrene in such organic solvents as benzene and carbon disulfide. From the analysis of hyperfine structure of the ESR signal, the radical was identified as 5-phenoxy-3, 4-benzopyrene radical which was previously found to be produced by stirring 3, 4-benzopyrene in aqueous albumin solution or incubating it with liver homogenate. No free radical was produced when the light of wavelength at which no absorbance of 3, 4-benzopyrene exists was irradiated, showing that the energy absorbed by benzopyrene was involved in the process of radical production. Dependency of the radical production on the solvent was remarkable; thus, order of reaction was different for benzene and carbon disulfide, and no ESR signal was observed when irradiated in dioxan, ethanol, or acetone. 3, 4:9, 10-Dibenzopyrene and 1, 2:4, 5-dibenzopyrene, which have the 3, 4-benzopyrene skeleton in the molecule, gave ESR signals characteristic of the phenoxy radical, whereas no signal was observed for anthracene, 2, 3:7, 8-dibenzophenanthrene, and 1, 2-benzanthracene. 5-Phenoxy radical was proved to be an intermediate from 3, 4-benzopyrene to the benzopyrene-quinones.
In the light of these findings, we proposed a mechanism of phenoxy radical production, taking into account of a participation of the singlet molecular oxygen. Significance of the formation of the phenoxy radical was discussed in relation to the photooxidation and carcinogenesis of 3, 4-benzopyrene.