Abstract
The thiols cysteine (1), homocysteine (2), acetylcysteine (3), glutathione (4), and dithioerythritol (5) underwent autoxidation with controlled rates of chain initiation (Ri) when driven by azobis (2-amidino propane hydrochloride (ABAP). Cysteine exhibits the largest rate constant. Thils2 and4 inhibited the facile self-initiated autoxidation of ascorbate and regenerated ascorbate from its oxidation product, dehydroascorbic acid. Thiols1 and2 inhibited ABAP- initiated peroxidation of dilinoleoyl phosphatidylcholine (DLPC) membranes with a kinh similar to that of 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox). Thiols1–4 all acted cooperatively with Trolox to inhibit ABAP-initiated peroxidation of DLPC membranes. Stoichiometric factors, n=0.31−0.63, are attributed to oxidative wasting reactions. Each thiol,2, 4, and5 when combined with ascorbate further extended the inhibition period mediated by Trolox during peroxidation of linoleate initiated by lipid-soluble di-tert-butylhyponitrite (DBHN) in sodium dodecly sulfate (SDS) micelles. The spin trap phenyl-tert-butylnitrone (PBN) exhibited only retardant (not antioxidant) activity during peroxidation of linoleate initiated by DBHN or ABAP in SDS micelles.
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