Photochemical reactions between 1,4-benzoquinone and O2•-

The superoxide anion radical (O-2(center dot-)) is one of the most predominant reactive oxygen species (ROS), which is also involved in diverse chemical and biological processes. In this study, O-2(center dot-) was generated by irradiating riboflavin in an O-2-saturated solution using an ultraviolet lamp (lambda(em) = 365 nm) as the light source. The photochemical reduction of 1,4-benzoquinone (p-BQ) by O-2(center dot-) was explored by 355-nm laser flash photolysis (LFP) and 365-nm UV light steady irradiation. The results showed that the photodecomposition efficiency of p-BQ was influenced by the riboflavin concentration, p-BQ initial concentration, and pH values. The superoxide anion radical originating from riboflavin photolysis served as a reductant to react with p-BQ, forming reduced BQ radicals (BQ(center dot-)) with a second-order rate constant of 1.1 x 10(9) L mol(-1) s(-1). The main product of the photochemical reaction between p-BQ and O-2(center dot-) was hydroquinone (H(2)Q). The present work suggests that the reaction with O-2(center dot-) is a potential transformation pathway of 1, 4-benzoquinone in atmospheric aqueous environments.