The Spin Trapping of Superoxide and Hydroxyl Free Radicals with DMPO (5,5-Dimethylpyrroline-N-oxide): More About Iron

The reaction of superoxide with the spin trap DMPO (5,5-dimethylpyrroline-N-oxide) is widely used to study superoxide production as well as issues associated with the superoxide-related formation of hydroxyl radical. However, the interpretation of observed intensities of DMPO/.OOH and DMPO/.OH signals in electron paramagnetic resonance spin trapping experiments is not without its difficulties. In this paper, I report experiments that demonstrate: 1. That the flux of superoxide formation in a DMPO spin trapping experiment can alter the apparent importance of weak DMPO/.OH signals; 2. That iron can influence the DMPO/.OOH spin trapping results; 3. That there is very little spontaneous breakdown of DMPO/.OOH to form DMPO/.OH.