The interactions of carotenoids with NO·_ 2 were investigated by pulse radiolysis. Optical traces show bleaching of the ground-state absorption of β-carotene, zeaxanthin and canthaxanthin at 450 nm, and bixin at 460—510 nm. The transient absorption spectrum shows that the positive absorption attributed to the formation of carotenoid addition radicals cannot be observed in the range of 600—700 nm. It is suggested that carotenoids undergo more readily electron transfer with NO·_ 2 to yield the carotenoid radical cations. The rate constants for the reaction of β-carotene, zeaxanthin, bixin and canthaxanthin with NO·_ 2 obtained are 1.6×10 8, 2.41×10 8, 5.41×10 7 and 1.75×10 7 mol/(L -1·s -1), respectively.
