title: The role of the DMPO-hydrated electron spin adduct in DMPO-*OH spin trapping.
abstract: Time-resolved in situ radiolysis ESR (electron spin resonance, equivalently EPR, electron paramagnetic resonance) studies have shown that the scavenging of radiolytically produced hydroxyl radical in nitrous oxide-saturated aqueous solutions containing 2 mM DMPO is essentially quantitative (94% of the theoretical yield) at 100 micros after the electron pulse [1]. This result appeared to conflict with earlier results using continuous cobalt-60 gamma radiolysis and hydrogen peroxide photolysis, where factors of 35 and 33% were obtained, respectively [2,3]. To investigate this discrepancy, nitrogen-saturated aqueous solutions containing 15 mM DMPO were cobalt-60 gamma irradiated (dose rate = 223 Gy/min) for periods of 0.25-6 min, and ESR absorption spectra were observed approximately 30 s after irradiation. A rapid, pseudo-first-order termination reaction of the protonated DMPO-hydrated electron adduct (DMPO-H) with DMPO-OH was observed for the first time. The rate constant for the reaction of DMPO-H with DMPO-OH is 2.44 x 10(2) (+/- 2.2 x 10(1)) M(-1) s(-1). In low-dose radiolysis experiments, this reaction lowers the observed yield of DMPO-OH to 44% of the radiation-chemical OH radical yield (G = 2.8), in good agreement with the earlier results [2,3]. In the absence of the DMPO-H radical, the DMPO-OH exhibits second-order radical termination kinetics, 2k(T) = 22 (+/- 2) M(-1) s(-1) at initial DMPO-OH concentrations > or = 13 microM, with first-order termination kinetics observed at lower concentrations, in agreement with earlier literature reports [4].
authors.affiliation: Notre Dame Radiation Laboratory, University of Notre Dame, Notre Dame, IN, USA. keith.p.madden.1@nd.edu
authors.forename: K P
authors.initials: KP
authors.lastname: Madden
authors.forename: H
authors.initials: H
authors.lastname: Taniguchi
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D005720:Gamma Rays; D017665:Hydroxyl Radical; D007700:Kinetics; D009994:Osmolar Concentration; D011675:Pulse Radiolysis; D013113:Spin Labels; D014867:Water
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; D013113:Spin Labels; D014867:Water; D017665:Hydroxyl Radical; C069977:2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxy; C017245:5,5-dimethyl-1-pyrroline-1-oxide