The reaction between α‐tocopheroxyl radical (VE˙) and ascorbic acid (VC) and its lipophilic derivatives ascorbyl‐6‐caprylate (VC‐8), 6‐laurate (VC‐12) and 6‐palmitate (VC‐16) was studied by stopped‐flow ESR spectroscopy in cetyltrimethylammonium bromide (CTAB) micelles. The second‐order rate constants for the reaction were found to be 9 · 0, 3 · 0, 0 · 7 and 0 · 03 × 105 1 mol−1 s−1 for VC, VC‐8, VC‐12 and VC‐16, respectively, indicating a remarkable influence of the aliphatic side‐chain on the reactivity. The lifetime of the reaction intermediate, ascorbate radical anion, was greatly enhanced by the lipophilic side‐chain, being 0 · 4, 5 and 110 s for VC‐8−., VC‐12−. and VC‐16−. respectively. Kinetic analysis shows that the inter‐ and intramicellar diffusion may be the rate‐limiting steps for the reaction carried out in micelles.
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Liu et al. (1992) studied this question.
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