Detection of free radicals in aqueous extracts of cigarette tar by electron spin resonance.

Aqueous extracts of cigarette tar (ACT) autooxidize to produce semiquinone, hydroxyl, and superoxide radicals in air-saturated buffered aqueous solutions. The semiquinone species were detected by direct electron spin resonance (ESR) measurements and identified as o- and p-benzosemiquinone radicals by comparison with the ESR signals of catechol and hydroquinone radicals under similar conditions. The rate of formation of these radicals was dependent on pH. Hydroxyl and superoxide radicals were detected as 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin adducts by ESR spin trapping. Superoxide dismutase (SOD) (20 units/ml) inhibited the formation of the superoxide spin adduct of DMPO completely. Addition of Fe2+ to this system increased the ESR signal intensity of hydroxyl radical spin adduct of DMPO three to five times. These results indicate that superoxide and hydroxyl radicals are produced during the autooxidation of hydroquinone- and catechol-related species in ACT.