Decay of the hydroperoxyl spin adduct of 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide: an EPR kinetic study

The decay kinetics of the hydroperoxyl spin adduct of both 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), a new β-phosphorylated cyclic nitrone and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were studied in various media by EPR spectroscopy. In organic solvents, both first- and second-order processes were shown to contribute to the decay of the two spin adducts. However, in aqueous solution the DMPO–hydroperoxyl spin adduct decay was pure first-order. The half-lives of the two spin adducts were determined in every medium tested and the DEPMPO–hydroperoxyl spin adduct was shown to be significantly more persistent (from five times in organic solvents to 30 times in a pH 5.6 buffer) than the DMPO–hydroperoxyl spin adduct.