Chemistry of carotenoid oxidation and free radical reactions

When oxygenic photosynthesis evolved, one of the key functions of carotenoi ds was to protect aerobic photosynthetic organisms against destruction by p hotodynamic sensitization. Aerobic photosynthesis would not exist without t he coevolution of carotenoids alongside the chlorophylls. As carotenoids ar e abundant in nature, in many fruits and vegetables, they are able to react with excited states of appropriate energy and quench them, and they can re act with free radicals according to their reactivity, redox potentials, and X-H bond energies. This report concerns the bimolecular reactions of carot enoids with oxygen species, such as O-3(2), O-1(2) HO., HOO., O-2(.-), etc.