title: Nonradical mechanism of (bi)sulfite reaction with DEPMPO: cautionary note for SO3*- radical spin trapping.
abstract: Knowledge of the formation of radicals from sulfites, in vivo, is of interest in understanding the allergic and inflammatory responses to environmental sulfur dioxide exposure. Sulfite anion trioxide (SO(3)(-*)) radical formation was measured in mice, preloaded with the spin trap, 5-(diethoxy-phosphoryl)-5-methyl-pyrrolidine-N-oxide, (DEPMPO). Based on spin trapping NMR, a surprising quantity of reduced SO(3)(-*)-adduct was observed that did not depend on co-administration of oxidizing agents, suggesting a possible nonradical reaction between (bi)sulfite and DEPMPO. The products of the reversible nucleophylic addition of (bi)sulfite to the nitrone functional group were identified using (31)P-NMR, (1)H-NMR, and (13)C-NMR spectroscopy as cis- and trans- stereoisomers of hydroxylamine and confirmed by quantum chemical calculations. Oxidation of the hydroxylamines results in the formation of two corresponding cis- and trans-isomeric nitroxides, only one of which has been earlier described as the paramagnetic adduct of genuinely trapped SO(3)(-*) radical. The results demonstrate that SO(3)(-*) detection using nitrone spin traps such as DEPMPO and DMPO may involve nonradical addition reactions except in cases when the required controls unambiguously prove a radical mechanism.
authors.affiliation: International Tomography Center, Novosibirsk, Russia.
authors.forename: Dmitrii I
authors.initials: DI
authors.lastname: Potapenko
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Clanton
authors.forename: Elena G
authors.initials: EG
authors.lastname: Bagryanskaya
authors.forename: Nina P
authors.initials: NP
authors.lastname: Gritsan
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Reznikov
authors.forename: Valery V
authors.initials: VV
authors.lastname: Khramtsov
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015203:Reproducibility of Results; D019097:Spin Trapping / Q000379:methods*
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; C098505:5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide