Carotenoid reaction with free radicals in acetone and toluene at different oxygen partial pressures. An ESR spin-trapping study of structure - activity relationships.
1997
Haila, K.M. | Nielsen, B.R. | Heinonen, M.I. | Skibsted, L.H.
The influence of eight commonly occurring carotenoids on (1) the production of spin adducts, (2) the hyperfine splitting constants aH and aN of the spin adduct electron spin resonance (ESR) spectra, and (3) the production of the oxidized N-tert-butyl-alpha-phenylnitrone (PBN) derivative N-benzoyl-N-tert-butylnitroxide (PBNOx) was investigated in ESR spin-trappimg experiments. In the polar solvent acetone under air, all carotenoids except beta-carotene were shown to diminish the number of spin adducts formed by about 20 %. A prooxidative effect of beta-carotene was even demonstrated at a higher concentration. In the less polar solvent toluene under air, most carotenoids lowered the amount of spin adducts, but effects were not aslarge as in acetone, and differences were found between (1) the more effective carotenoids with two cyclohexene rings conjugated to the polyene backbone (and lycopene), and (2) carotenoids with zero or one conjugated cyclohexene ring. The formation of PBNOx in toluene, which was essentially due to breakdown of peroxyl spin adducts, was significantly inhibited by astaxanhin, canthaxanthin and lycopene. Throughout, only alkoxyl radical adducts of PBN were observed. However, a significant difference was found between the aH values of zeaxanthin and the carbonyl carotenoid astaxanthin, indicating structural differences of the spin adducts.
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