Mechanism of lower oxidizability of eicosapentaenoate than linoleate in aqueous micelles.
The aerobic oxidation kinetics of methyl eicosapentaenoate (20:5n-3) and methyl linoleate (18:2n-6) were compared in homogeneous chlorobenzene solution and in Triton X-100 aqueous micelles at 37 degrees C. The rate of disappearance of 20:5n-3 was two times faster than that of 18:2n-6 in chlorobenzene, while the former was five times slower than the latter in aqueous micelles. It was also observed that delta O2 = delta 18:2n-6 and delta O2 = 2 delta 20:5n-3 in aqueous micelles. In the oxidation of a 1:1 mixture of 20:5n-3 and 18:2n-6 in micelles, the rate of disappearance of 20:5n-3 was 3.6 times faster than that of 18:2n-6, and the rate of total substrate disappearance was reduced by a factor of 5 as compared with 18:2n-6 oxidation. These data suggest that the peroxyl radical derived from 20:5n-3 is more polar than that from 18:2n-6, and the former is likely to diffuse from the core to the micelle surface. This lowers the oxidizability for 20:5n-3 in aqueous micelles by enhancing the termination reaction rate for peroxyl radicals and by reducing the rate of propagation since there may be more 20:5n-3 peroxyl radicals at the surface than in the micelle core.
Department of Energy Resources, National Institute for Resources and Environment, Ibaraki, Japan.
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Yazu
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Yamamoto
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K
Ukegawa
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Niki
D000578:Amidines / Q000494:pharmacology; D001391:Azo Compounds / Q000494:pharmacology; D002722:Chlorobenzenes / Q000378:metabolism / Q000494:pharmacology; D015118:Eicosapentaenoic Acid / Q000378:metabolism*; D004952:Esters / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D007700:Kinetics; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000378:metabolism*; D008823:Micelles; D008956:Models, Chemical; D009570:Nitriles / Q000494:pharmacology; D017830:Octoxynol / Q000378:metabolism / Q000494:pharmacology; D010084:Oxidation-Reduction; D010545:Peroxides / Q000378:metabolism
D000578:Amidines; D001391:Azo Compounds; D002722:Chlorobenzenes; D004952:Esters; D005231:Fatty Acids, Unsaturated; D008041:Linoleic Acids; D008823:Micelles; D009570:Nitriles; D010545:Peroxides; C055792:2,2'-azobis(2,4-dimethylvaleronitrile); C049375:perhydroxyl radical; C046728:2,2'-azobis(2-amidinopropane); D017830:Octoxynol; D019787:Linoleic Acid; D015118:Eicosapentaenoic Acid; C031294:chlorobenzene