One of the active oxygen species, superoxide (O
2-), was generated by the electrolytic reduction of molecular oxygen in acetonitrile. O
2- was determined by the ultraviolet (UV) (λ
max/nm=255, ε=1.48×10
3 M
-1cm
-3) and the electron spin resonance (ESR) (g⫽=2.083, g
⊥=2.008) spectrum. O
2- could easily react with tocopherols (vitamin E and its derivatives) to give the corresponding chromanoxyl radicals of which structures were determined by ESR. ESR studies of the reactions of O
2- with tocopherols or their model compounds indicate that the radical concentrations from tocopherol models correlate with the physiological activities of the tocopherols. O
2- could also react with some biologically active quinones such as vitamin K
8 and vitamin E quinone to give the corresponding semiquinone radicals. The fact that vitamin E quinone, an irreversible metabolite of vitamin E, was reduced by O
2- to the semiquinone radical suggests that, like vitamin E, vitamin E quinone may also scavenge O
2- and protect living cells from the effects of O
2- in a hydrophobic environment. Further, O
2- could react with some metalloporphyrins. In this case, non-redox metalloporphyrins such as Zn (II) TPP (TPP : tetraphenylporphine), Cd (II) TPP, Mg (II) TPP generated the superoxide adduct by the reaction with O
2-. On the other hand, redoxactive metalloporphyrins such as Cr (III) TPP·Cl, Mn (III) TPP·Cl, Co (II) TTP (TTP : tetra-p-tolylporphine) and Co (III) TTP·Cl underwent the addition and/or redox reactions with O
2-. Another active oxygen species, hydroxyl radical (OH·), was first detected from some copper (II) coplexes such as Cu (en)
2 (en : ethylenediamine) with hydrogen peroxide (H
2O
2) by ESR spin trapping and thiobarbituric acid (TBA) methods. Further, by using Cu (en)
2-H
2O
2 system the most active OH·scavenger was determined. This Cu (en)
2-H
2O
2 system will be useful for determing the antioxidant ability against OH·.
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