The carotenoid Bixin found to exhibit the highest measured carotenoid oxidation potential to date consistent with its practical protective use in cosmetics, drugs and food

摘要

The electrochemical oxidation potentials of cis bixin correspond to the production of the carotenoid radical cation, Car(center dot) (+) and dication Car (+ +). The oxidation is a two-electron process with oxidation potentials at similar to 0.94 and similar to 1.14 V vs SCE (reference to ferrocene at 0.528 V) in THF. These potentials are higher than that of symmetrical canthaxanthin at 0.775 V and 0.972 V and for beta-carotene at 0.634 V and 0.605 V respectively. The second oxidation potential for canthaxanthin is higher by 0.20 V than the first. Similar difference is observed for bixin. In contrast, the second oxidation potential for beta-carotene is lower by 30 mV than that of the first. Reduction potentials were found to occur at similar to - 0.69 and similar to -1.22 V vs SCE. The lifetime of the radical cation of cis bixin, Car(center dot) (+), is short and decays rapidly at ambient temperature. The suggested scavenging ability of cis bixin towards reactive oxidative oxygen species is estimated to be 44. On the other hand, that of beta-carotene, symmetrical canthaxanthin and the dicyano substituted carotenoid which exhibit oxidation potentials of 0.634 V, 0.775 V and 0.833 V vs SCE were measured to be 0.64, 1.96 and 23.60 respectively. The non-reversible electrochemical measurements suggest the tendency for bixin to react with trace amounts of reactive oxygen species ((OH)-O-center dot, O-2(-center dot), (OOH)-O-center dot).