An Electron Spin Resonance Study of the Spin Adducts of OH and HO₂ Radicals with Nitrones in the Ultraviolet Photolysis of Aqueous Hydrogen Peroxide Solutions

Abstract

. Can. J. Chem. 52,3549 (1974) The photolysis of H,02 in aqueous solution has been used to study and characterize electron spin resonance (e.s.r.) spectra of the .OH and HO,. radical spin adducts with the spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and phenyl-t-butyl nitrone (PBN). At high concentrations of spin trap and low concentrations of H 2 0 2 an e.s.r. spectrum is obtained which we assign to the .OH radical adduct (for DMPO, nN = 15.3 G, aBH = 15.3 G, a Y i H = 0.61 G, a,!," = 0.25 G, and g = 2.0060; for PBN, a N = 15.3 G, upH = 2.75 G, and g = 2.0057). At low concentrations of spin trap and high concentrations of H,O, a second spin adduct spectrum is obtained mhich we assign to the spin adduct of the H 0 2 radical (for DMPO, a' = 14.3 G, aDH = 11.7 G , = 1.25 G , g = 2.0061; for PBN, a N = 14.8 G, a," = 2.75 G, and g = 2.0057). Introduction through the cornpilation of the e.s.r. parameters The technique of spill trapping of short-lived for a wide variety of spin adducts, One should radical intermediates (R.) by nitrones and other be able to identify an unknown radical interspin traps has become a valuable addition to mediate by a comparison of the e.s.r. Paramthe methods of studying reaction mechanisms. eters. This technique has been reviewed recently by The two nitrone spin traps which have found Janzen (1). The basic reaction can be described wide use are 5,5-dimethyl-l-pyrroline-l-oxide as (DMPO)

The production of hydroxyl radical by bleomycin and iron (II)

“…The reaction mixture contained 160 PM bleomycm, 100 mM DMPO, and 100 PM FeSO, in 50 mM potassium phosphate buffer (pH 7.8). The spectral properties are identical to those found in [20] for the hydroxyl spin adduct.…”

“…1 appeared. The spectrum is essentrally Identical to that identified [20] as the hydroxyl spin adduct of DMPO. When the same experiment 1s carned out with Fe(II1) as FeCla, no signal results.…”

The kinetics of the reaction of superoxide radical with Fe(III) complexes of EDTA, DETAPAC and HEDTA

“…were introduced into a solution of Hz02 (80 FM) and DMPO (50 mM) an ESR signal consistent with the spin trapping of the hydroxyl free radical was observed (aN = aH = 15.0 G [25,26] …”

Quantitation of the hydroxyl radical by reaction with dimethyl sulfoxide

“…Ultraviolet exposure of hydrogen peroxide was used to create hydroxyl radicals from the cleavage of H 2 O 2 molecules as previously described [11,12]. A Mineralight lamp at 254 nm wavelength (Ultra-violet Products, Inc., San Gabriel, CA) was used to irradiate 0.5 to 1.5 mM unbuffered aqueous solutions of hydrogen peroxide for periods of 0 to 15 min.…”