Abstract
Irradiation (lambda less than or equal to 500 nm) of aqueous solutions (pH less than or equal to 7.0) of 5-methylphenazinium (MP/sup 9/ salts yields two products, the 5-methyl-10-hydrophenazinium cation radical (MPH.) and the pyocyanine (PYH/sup +/) (1-hydroxy-5-methylphenazinium) cation in a stoichiometric ratio of 2:1. Thus, the overall photochemical reaction is 3MP/sup +/ + H/sub 2/O ..-->.. 2MPH/sup +/+ PYH/sup +/. The MPH/sup +/ cation radical exhibits a complex EPR spectrum which has been completely analyzed. A novel method for quantum-yield measurements by EPR spectroscopy is described and applied to this system. The quantum yield formation of MPH was found to be 0.29 +- 0.03 at pH 7.0 and 1.1 +- 0.1 at pH 3.0. Studies with the spin trap 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) demonstrated the formation of a spin adduct arising from the addition of the OH radical to DMPO. However, it is not likely that free OH radicals are involved in the mechanism of this photochemical reaction.
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