Spin Trapping of Superoxide

Abstract

Due to conflicting reports in the literature, the spin trapping of superoxide by the nitrone, DMPO, has been re-investigated. We found that superoxide can indeed be trapped and that the DMPO-OOH and DMPO-OH adducts are distinguishable, in agreement with the original work of Harbour et al. (10). In contrast to their work, we found that DMPO-OOH was highly unstable and that it decomposed into DMPO-OH. We observed that TMPO, a spin trap structurally similar to DMPO, but lacking a β-hydrogen, formed a stable nitroxide upon reaction with superoxide. Rate constants for the reaction of superoxide with DMPO and TMPO were measured and indicated that spin trapping was an extremely inefficient method for the detection of superoxide. The new spin trap described by Janzen et al. (18), 4-POBN, was also capable of distinguishing the difference between superoxide and hydroxyl radical. The nitroxide formed upon the reaction of superoxide with 4-POBN (4-POBN-OOH) was found to be unstable. However, unlike DMPO-OOH, 4-POBN-OOH does not decompose into the hydroxynitroxide, 4-POBN-OH.