title: EPR spectra of DMPO spin adducts of superoxide and hydroxyl radicals in pyridine.
abstract: Electron spin resonance spectroscopy and the spin trapping technique were used to study the formation of the superoxide radical in pyridine. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was employed as a trapping agent. Superoxide radical was generated using chemical (potassium superoxide) and photochemical methods with anthralin, benzanthrone, rose bengal, 1,8-dihydroxyanthraquinone and zinc tetraphenylporphyrine as photoactive pigments. Hyperfine coupling (hf) constants for DMPO/O2.- were determined to be aN = 12.36 G, a beta H = 9.85, G, a gamma H = 1.34 G. The aN and a beta H hf constants are in good agreement with values calculated from a previously determined relationship between hf constants and solvent acceptor number (Reszka et al., (1992) Free Radical Res. Commun., in press). When concentrated hydrogen peroxide was added to DMPO in pyridine a similar EPR spectrum was observed. It is suggested that in this case the DMPO/.O2H adduct is formed by nucleophilic addition of H2O2 to DMPO to give a hydroxylamine, followed by oxidation to the respective nitroxide. The EPR spectrum observed when tetrapropylammonium hydroxide and H2O2 were added to DMPO in pyridine had hf couplings aN = 13.53 G, a beta H = 11.38 G, a gamma H = 0.79 G and it was assigned to a DMPO/.OH adduct. This assignment was based on similarity of this spectrum to the one produced by UV photolysis of hydrogen peroxide and DMPO in aqueous solution and subsequent transfer to pyridine.
authors.affiliation: Laboratory of Molecular Biophysics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: K
authors.initials: K
authors.lastname: Reszka
authors.forename: P
authors.initials: P
authors.lastname: Bilski
authors.forename: C F
authors.initials: CF
authors.lastname: Chignell
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006878:Hydroxides / Q000032:analysis*; D017665:Hydroxyl Radical; D015394:Molecular Structure; D011725:Pyridines; D000644:Quaternary Ammonium Compounds; D012997:Solvents; D013113:Spin Labels; D013481:Superoxides / Q000032:analysis*
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; D006878:Hydroxides; D011725:Pyridines; D000644:Quaternary Ammonium Compounds; D012997:Solvents; D013113:Spin Labels; D013481:Superoxides; C052377:tetrapropylammonium; D017665:Hydroxyl Radical; C017245:5,5-dimethyl-1-pyrroline-1-oxide; C023666:pyridine