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  • Title: EPR spectra of DMPO spin adducts of superoxide and hydroxyl radicals in pyridine.
    Author: Reszka K, Bilski P, Chignell CF.
    Journal: Free Radic Res Commun; 1992; 17(6):377-85. PubMed ID: 1337536.
    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.
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