Scavenging Effects of Dihydric and Polydric Phenols on Superoxide Anion Radicals, Studied by Electron Spin Resonance Spectrometry.

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Abstract
We investigated the scavenging effects of dihydric, trihydric phenols and related polyphenols on superoxide anion radicals (O-2) generated form the hypoxanthine-xanthine oxidase system by ESR (electron spin resonance) spin trapping technique using 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as a trapping reagent.The O-2 scavenging activities of non-substituted dihydric phenols were in the order of pyrocatechol»hydroquinone»resorcinol.Trihydric phenols, pyrogallol and gallic acid, which have phenolic OH groups at ortho positions, had stronger activities than pyrocatechol; phloroglucinol, on the other hand, which has phenolic OH groups at meta positions, had much weaker effect. Polyhydric phenols like quercetin and hematoxylin, which have catechol groups, had significant O-2 scavenging activities. In order to clarify the physico-chemical property of these phenolic compounds which determines their O-2 scavenging acivities, we investigated the effects of six 4-substituents of pyrocatechol on O-2 scavenging effects. The effects of these substituents were well correlated with their redox potentials, indicating that O-2 scavenging activities of catechol derivatives are controlled by their electron donor activities.We also observed the scavenging effects of these phenolic compounds on O-2 from a defferent source : potassium superoxide (KO2) solubilized in dimethyl sulfoxide by 18-crown-6. ESR analysis in this system revealed that one-electron oxidized products of these compounds were concomitantly formed accompanied by the reduction of O-2. The results revealed that phenolic compounds directly react with O-2 to form stable radicals, which account for the O-2 scavenging activities of the compounds.

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