CONVERSION OF NITROXIDE RADICALS BY PHENOLIC AND THIOL ANTIOXIDANTS

Nitrone/nitroso spin traps are often used for detection of unstable hy droxyl radical giving stable nitroxide radicals with characteristic el ectron spin resonance (ESR) signals. This technique may be useful only when the nitroxide radicals are kept stable in the reaction system. T he aim of the present study is to clarify whether the nitroxide radica ls are kept stable in the presence of the hydroxyl radical scavengers. Effect of hydroxyl radical scavengers on the ESR signals of nitroxide radicals, 2,2,6,6-tetramethyl-piperidine-N-oxyl (TEMPO) and the spin adduct (DMPO-OH) of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and hydrox yl radical, was examined. Although the ESR signals of TEMPO and the DM PO-OH spin adduct were unchanged on treatment with ethanol and dimethy l sulfoxide, their intensities were effectively decreased on treatment with 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), cysteine, glutathione, 2-mercaptoethanol and metallothionein. Hence, the results of the detection of hydroxyl radical in the presence of ph enolic and thiol antioxidants by the ESR technique using nitrone/nitro so spin trays may be unreliable.