SOME EFFECTS OF METAL-IONS ON THE PHOTOGENERATION OF HYDROXYL RADICALS

The effect of common transition metal ions on the photochemical degrad ation of a model compound, dequalinium chloride in aqueous solution, i rradiated with simulated sunlight at 38 +/- 1 degrees C has been inves tigated. The reactions follow first order kinetics; the addition of a standard volume of hydrogen peroxide markedly enhances the reaction ra te constants of these reactions, suggesting that the reactions are hyd roxyl radical-mediated in a similar manner to that of the Fenton proce ss. In order to evaluate the contribution of the hydroperoxy radical t o photochemical degradation of pharmaceutical formulations as aqueous solutions, the effect of light-generated hydroperoxy radicals was inve stigated with the same group of metals. The reactions in this case fol lowed second order kinetics and were very much slower than those media ted by hydroxyl radicals; only zinc ions showed a notable increase in the reaction rate constant as compared to that of the control system.