ABSTRACT
B. Antioxidant Reactions 1 , Deactivation of Singlet Oxygen ~~Carotene has been !mown to be an efficient quencher of 102 since the study of Foote and Denny (39), Using a variety techniques (reviewed in Ref. 40), quenching rate constants have been determined for the biological carotenoids and xanthophylls, and they fall within the range of diffusion control (Table 1). Lycopene, the open-chain analog of {3-carotene (Figure 1), exhibits the highest rate constant among the biologically occurring carotenoids ( 40-42). Several synthetic pigments, which possess conjugated polyene chains analogous to the
li"<1llble 1 Rate Constants (109 ~1 sec-1) for the Reaction of Biological Camtenoids and Synthetic Analogs with Singlet Oxygen 21111d Radicals
Compound
Carotenoids" Lycopene fl-Carotene a~Carotene y-Carotene
Oxycarotenoids (Xanthophylls)" Astaxanthin Canthaxanthin Zeaxanthin Lutein Cryptoxanthin """"""'"~ polyenesc
Czs-Polyene-tetrone C28-Polyene-tetrone-diacetal Cw-Epiisocapsorubin
quenching
9-19 4-14 6-8
0.8-7
7-14 6-18 3-12 2-21
16 9 8
reduction
carotenoids but different end groups (Figure 1), were recently shown to have equivalent or even slightly higher quenching abilities (43) (Table 1).
