Formation of tryptophan radicals in irradiated aqueous solutions of hexachloroplatinate(IV): A flash photolysis study

The oxidation of tryptophan photosensitized by PtCl62-,has been investigate d in aqueous solutions at different pH using nanosecond laser flash photoly sis, Cationic and neutral radicals of tryptophan were detected at pH 2.8 an d 8.5, respectively, The generation of the radical was attributed to oxidat ion by Cl-2(-) that was formed from the homolytic bond cleavage in the exci ted state of PtCl62- The bimolecular rate constant derived from the kinetic s analysis, 2.8 +/- 0.2 x 10(9) M-1 s(-1), is in good agreement with the va lue obtained in earlier pulse radiolysis studies, Both the cationic and neu tral radicals decayed by second-order kinetics, consistent with the dimeriz ation process.