RELATIVE ONE-ELECTRON REDUCTION POTENTIALS OF CAROTENOID RADICAL CATIONS AND THE INTERACTIONS OF CAROTENOIDS WITH THE VITAMIN-E RADICAL-CATION

Pulse radiolysis studies have been used to determine the electron-tran sfer rate constants between various pairs of carotenoids, one of which is present as the radical cation. These dietary carotenoids include t hose of importance to vision, namely zeaxanthin and lutein. These resu lts have suggested the order of relative ease of electron transfer bet ween six carotenoids. Additional experiments, involving electron trans fer between astaxanthin (ASTA), beta-apo-8'-carotenal (APO), and vitam in E (TOH), lead to the following order in terms of relative ease of e lectron transfer for the seven carotenoid radical cations studied: ast axanthin > beta-apo-8'-carotenal > canthaxanthin > lutein > zeaxanthin > beta-carotene > lycopene, such that lycopene is the strongest reduc ing agent (the most easily oxidized) and astaxanthin is the weakest, a nd the radical cations of the visual carotenoids, lutein (LUT) and zea xanthin (ZEA), are reduced by lycopene (LYC) but not by beta-carotene (beta-CAR). Work on 7,7'-dihydro-beta-carotene (77DH) and vitamin E al lows us to better understand the interaction of the vitamin E radicals with carotenoids.