Studies on the stability of oxygen radical spin adducts of a new spin trap: 5-methyl-5-phenylpyrroline-1-oxide (MPPO)

A new spin trap, 5-methyl-5-phenylpyrroline-l-oxide (MPPO), has been evaluated with respect to the intrinsic stabilities of the hydroxyl and superoxide (or hydroperoxyl) radical spin adducts. Hydroxyl or superoxide radicals were generated using various sources in the presence of MPPO, and the hydroxyl or superoxide radical spin adduct of MPPO was detected by EPR spectroscopy. The time course of spontaneous decay of the EPR signal from hydroxyl or superoxide spin adducts followed first-order kinetics and the half-life was dependent on the pH of the medium. At pH 7.4 the half-life times are 76.4 and 5.7 min for the hydroxyl and hydroperoxyl/superoxide spin adducts, respectively. Structural factors which could influence the decay rates are also discussed.