Kinetics of parallel electron transfer from beta-carotene to phenoxyl radical and adduct formation between phenoxyl radical and beta-carotene.
Phenoxyl radicals generated by laser flash photolysis were found to react with beta-carotene with concomitant beta-carotene bleaching in two parallel reactions with similar rates: (i) formation of a beta-carotene adduct with a (pseudo) first order rate constant of 1-1.5 x 10(4) s-1 with absorption maximum around 800 nm, and (ii) formation of a beta-carotene radical cation with a (pseudo) first order rate constant of 2-3 x 10(4) s-1 with absorption maximum around 920 nm. Both beta-carotene radicals decay on a similar time scale and have virtually disappeared after 100 ms, the beta-carotene adduct by a second order process. Oxygen had no effect on beta-carotene bleaching or radical formation and decay. The reduction of phenoxyl radicals by beta-carotene may prove important for an understanding of how beta-carotene acts as an antioxidant.
Mortensen
A
A
Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
Skibsted
L H
LH
D004579:Electron Transport; D005609:Free Radicals; D007700:Kinetics; D010636:Phenols / Q000737:chemistry*; D010782:Photolysis; D019097:Spin Trapping; D019207:beta Carotene / Q000737:chemistry*
D005609:Free Radicals; D010636:Phenols; D019207:beta Carotene; C042329:phenoxy radical