Reaction products of [60]fullerene during the autoxidation of methyl linoleate in bulk phase.

The antioxidative action of fullerenes has received much attention, but their reaction mechanism toward lipid-derived peroxyl radicals has not been well elucidated. In this study, the reaction products of [60]fullerene (C(60)) during the autoxidation of methyl linoleate (MeL) were isolated and their structures were characterized. MeL containing 0.1mol% C(60) was autoxidized at 60°C in bulk phase and two reaction products of C(60), 1 and 2, were obtained. The structure of 1 was the addition products of C(60) with 9-peroxyl-10-alkyl radicals of methyl (11E)-13-hydroperoxy-11-octadecaenoate (1a and 1b) and with 12-alkyl-13-peroxyl radicals of methyl (10E)-9-hydroperoxy-10-octadecaenoate (1c and 1d). 2 was a mixture of the addition products of C(60) with 9,11-dialkyl radicals of methyl 9,12-octadecadienoate (2a) and with 11,13-dialkyl radicals of methyl 9,12-octadecadienoate (2b). When MeL containing 0.1mol% C(60) was autoxidized at 60°C under air-sufficient and air-insufficient conditions, C(60) could suppress the formation of MeL hydroperoxides in both conditions. The reaction product of C(60) first formed was 2 even under air-sufficient conditions, and then 1 was accumulated. The results indicate that the primary antioxidative action of C(60) would be trapping of chain-initiating carbon-centered radicals of unsaturated lipid to form 2.