The effect of aromatic amines and phenols in the thiyl-induced reactions of polyunsaturated fatty acids

• LH micelles were used for the parallel study of peroxidation/cis–trans isomerization.
• Both 2-mercaptoethanol and diphenylamine alone protect LH from oxidation.
• Aminyl radicals promote thiyl-radical-induced cis–trans isomerization of LH in air.

Thiols are well known for their role in cellular redox homeostasis, while aromatic amines and phenols are the best known classes of chain-breaking antioxidants. On the other hand, thiyl radicals are known to catalyse the double bond isomerization in PUFA. We investigated the role and interplay of 2-mercaptoethanol and diphenylamine in the parallel processes of peroxidation and cis–trans isomerization of linoleic acid (LA) during gamma radiolysis, both in solution and micelles. Both compounds, used alone were able to protect LA from oxidation; however pro-oxidant activity and enhanced isomerization was observed when they were used together, depending on the experimental settings. Instead, α-tocopherol protected LA from both oxidation and isomerization in the presence of thiols under any tested settings. The mechanistic scenario is discussed highlighting the role of diphenylaminyl radicals in promoting thiyl-radical-induced cis–trans isomerization in the presence of oxygen.