Effects of amino compounds on the formation of γ‐tocopherol reducing dimers in autoxidizing linoleate

The effects of various amino compounds trimethylamine oxide (TMAO), tri‐ n ‐octylamine (TOA), phosphatidyl choline (PC), and phosphatidyl ethanolamine (PE) on the oxidative decomposition of γ‐tocopherol (γ‐Toc) and on the formation of its reducing dimers were investigated during the autoxidation of methyl linoleate (ML). In general, γ‐Toc diphenyl ether dimer (γ‐TED) was formed in preference to two atropisomers of γ‐Toc biphenyl dimers [γ‐TBD(H) and (L)] in autoxidizing ML. This relationship, however, was reversed when TMAO was added. As the presence of TOA, PC, or PE did not promote the formation of γ‐TBD, the preferential formation of γ‐TBD was believed to be based on the interaction between TMAO and oxidation products formed from γ‐Toc. Effects of TMAO and TOA on the interconversion of γ‐Toc reducing dimers were investigated. γ‐TED was found to be converted into γ‐Toc and γ‐TBD(L) in autoxidizing ML. But γ‐TBD(H) could not be detected, and the amount of γ‐TBD(L) formed was very small. γ‐TBD(H) and (L) were formed from their respective atropisomers. In this case, the formations of γ‐Toc and γ‐TED could not be detected. Therefore, it was concluded that the conversion of γ‐TED into γ‐TBD and vice versa can be neglected in any event.