The daily intake of flavonoids, widespread in the plant

kingdom, is believed to play a preventive role in the development of certain diseases associated with free radical-induced damage in the body. The high sensitivity of flavonoids to react with free radicals makes them pharmacological effective. Flavonoids and their ability to inactivate superoxide anion radicals (O2· ) have been studied for about a decade. Flavonoids are most likely to react with O2· 2 via one electron transfer, in which the former are converted to aroxyl radicals in the B-ring and the latter to hydroxyl peroxide. It is assumed that the O2· 2 scavenging activity of flavonoids is associated with their ability to form stable aroxyl radicals. The combination of the 39,49-dihydroxyl substitution (catechol moiety) in the B-ring with a double bond at C2–3 and C4carbonyl moiety is considered to be an essential structural requirement for flavonoidal aroxyl radical stabilization. Thus, the most common flavonoid, quercetin, is generally regarded as having the most favorable structure for effective O2· 2 scavenging potency. However, there is little systematic work reported on the structure–activity relationships governing the O2· 2 scavenging activity of flavonoids. There are also inconsistencies regarding the relative O2· 2 scavenging activity of flavonoids in previous reports. We have demonstrated that pyrogallol moiety is an important component of flavonoids, making them efficient O2· 2 radical scavengers. The high O2· 2 scavenging activity of flavonoids is likely to reflect their high susceptibility to oxidation. Thus, the electrochemical oxidizability of flavonoids has been used as a model for O2· 2 scavenging ability. There are several reports suggesting that flavonoids with low redox potential, (i.e. high electrochemical oxidizability), are good O2· 2 scavengers. We measured the oxidation of flavonoids by their ability to reduce Cu ion, in addition to their electrochemical redox potential. The ability of flavonoids and aromatics which are flavonoidal components to scavenge O2· 2