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^1O_2 quenching abilities of several carotenoids which contain hydroxy, carbonyl and ester groups were compared quantitatively with beta-carotene, and the capacity of the quenching was interpreted in the light of electronic effects. The rate constans of ^1O_2 quenching of lutein diester and astaxanthin diester in MeOH solution were shown to be 1.9times10^{10}M^{-1}Sec^{-1}, 2.3times10^{10}M^{-1}Sec^{-1}$ respectively. Under the experimental conditions, and within the carotenoid tested results, the larger the resonance energy is, the larger becomes the rate constant and consequently the lower the transition energy is, the better becomes the quencher.
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