Production of reactive oxygen species on photolysis of dilute aqueous quinone solutions

We have examined the generation of the reactive oxygen species (ROS) superoxide and hydrogen peroxide (H₂O₂) by irradiation of dilute aqueous solutions of disodium anthraquinone-2-6-disulfonate (AQDS) with simulated sunlight. Irradiating a solution of AQDS in 2 mMNaHCO₃ and 0.01 M NaCl produced superoxide and H₂O₂ at nanomolar concentrations. Experiments in which initial concentrations of dioxygen, H₂O₂, the superoxide radical trap nitroblue tetrazolium and the electron donor dimethyl sulfoxide were varied suggested that the interaction of solvent water with photo-excited quinone moieties produces dioxygen-reducing radicals, and that these are the primary source of ROS in the system. A kinetic model for ROS production is proposed based on our experimental data.