In Situ Radiolysis Time-Resolved ESR Studies of Spin Trapping by DMPO: Reevaluation of Hydroxyl Radical and Hydrated Electron Trapping Rates and Spin Adduct Yields

Abstract

The second-order rate constants for the reaction of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) with radiolytically produced hydroxyl radicals and hydrated electrons have been measured in aqueous solution by direct observation of spin adduct initial yield using time-resolved electron spin resonance. The rate constants are 2.8 × 109 mol-1 dm3 s-1 for the DMPO−hydroxyl radical addition reaction and 3.2 × 109 mol-1 dm3 s-1 for the reaction of DMPO and hydrated electron, using sodium formate and chloroacetic acid as competitive scavengers of the hydroxyl radical and hydrated electron, respectively. The hydrated electron−DMPO competition study determined the fraction of DMPO−H produced directly from radiolytically produced hydrogen atoms as 0.082 of the total DMPO−H yield, indicating that approximately half of the hydrogen atoms react with DMPO to produce non-aminoxyl products. The fraction of the total hydroxyl radical yield leading to DMPO−OH spin adduct was determined to be 0.94, using the bleach of 2,2,6,6-tet...