Quantitative Aspects of ESR and Spin Trapping of Hydroxyl Radicals and Hydrogen Atoms in Gamma-Irradiated Aqueous Solutions

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Abstract
The efficiency of 5,5-dimethylpyrroline-1-N-oxide (DMPO) and .alpha.-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) to spin trap hydroxyl radicals and hydrogen atoms, respectively, was studied in .gamma.-irradiated solutions where the radical yields are accurately known. The efects of dose, spin trap concentration, and pH and of the stability of the spin adducts on the spin-trapping efficiency was investigated. In degassed or N2-saturated solutions the spin-trapping efficiencies were 35% for DMPO and hydroxyl radicals and 14% for POBN and hydrogen atoms. The low spin-trapping efficiencies were not due to the instability of the DMPO-OH and POBN-H spin adducts or to the effects of H2O2 or O2. The low spin-trapping efficiency of DMPO may be explained by the reaction of hydroxyl radicals to abstract hydrogen from the DMPO molecule to produce carbon radicals as well as addition to the N.dbd.C double bond to form nitroxide radicals. For POBN the low spin-trapping efficiency for hydrogen atoms is explained in terms of addition reactions of hydrogen atoms to the aromatic ring and the pyridinium and nitrone oxygens.