Abstract
One of the active oxygen species, superoxide (O2-), was generated by the electrolytic reduction of molecular oxygen in acetonitrile. O2- was determined by the ultraviolet (UV) (λmax/nm=255, ε=1.48×103 M-1cm-3) and the electron spin resonance (ESR) (g⫽=2.083, g⊥=2.008) spectrum. O2- 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 O2- with tocopherols or their model compounds indicate that the radical concentrations from tocopherol models correlate with the physiological activities of the tocopherols. O2- could also react with some biologically active quinones such as vitamin K8 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 O2- to the semiquinone radical suggests that, like vitamin E, vitamin E quinone may also scavenge O2- and protect living cells from the effects of O2- in a hydrophobic environment. Further, O2- 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 O2-. 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 O2-. 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 (H2O2) by ESR spin trapping and thiobarbituric acid (TBA) methods. Further, by using Cu (en)2-H2O2 system the most active OH·scavenger was determined. This Cu (en)2-H2O2 system will be useful for determing the antioxidant ability against OH·.
