title: Evidence against the 1:2:2:1 quartet DMPO spectrum as the radical adduct of the lipid alkoxyl radical.
abstract: It was reported that the electron paramagnetic resonance (EPR) spectrum of 5,5-dimethyl-1-pyrroline N-oxide (DMPO)/lipid alkoxyl radical exhibited a quartet with 1:2:2:1 relative intensity that is identical to that of DMPO/hydroxyl radical (K. M. Schaich and D. C. Borg, 1990, Free Radicals Res. Commun. 9, 267-278). We repeated these EPR experiments using HPLC separation of radical adducts and isotope substitution. We found that the HPLC/EPR chromatogram of the radical adduct with a 1:2:2:1 quartet obtained by the reduction of methyl linoleate hydroperoxide (MLOOH) with Fe2+ exhibited identical retention time to that of the DMPO/OH radical adduct obtained from the Fenton reaction in two different solvent systems. Upon performing the same reaction in 17O-enriched water, the 17O-hyperfine coupling constants due to DMPO/17OH were identified. Ultimately, approximately 80-90% of the total DMPO/OH is derived from water by an iron-dependent nucleophilic addition reaction. Initially, a water-independent mechanism also significantly contributes to DMPO/OH formation. Regardless of its mechanism of formation, the 1:2:2:1 quartet radical adduct of DMPO formed during the reduction of MLOOH by Fe2+ is in fact DMPO/OH.
authors.affiliation: National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: W
authors.initials: W
authors.lastname: Chamulitrat
authors.forename: H
authors.initials: H
authors.lastname: Iwahashi
authors.forename: D J
authors.initials: DJ
authors.lastname: Kelman
authors.forename: R P
authors.initials: RP
authors.lastname: Mason
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D002374:Catalase / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005296:Ferrous Compounds / Q000737:chemistry; D005609:Free Radicals; D006861:Hydrogen Peroxide; D007501:Iron; D008054:Lipid Peroxides / Q000737:chemistry; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes; D013113:Spin Labels; D014867:Water
chemical_list: D000438:Alcohols; D003497:Cyclic N-Oxides; C045076:Fenton's reagent; D005296:Ferrous Compounds; D005609:Free Radicals; D008054:Lipid Peroxides; D010103:Oxygen Isotopes; D013113:Spin Labels; C059688:alkoxyl radical; D014867:Water; C008464:methyl linoleate hydroperoxide; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D006861:Hydrogen Peroxide; D007501:Iron; D002374:Catalase