Mechanistic study of the electron transfer of L-ascorbic acid at an oil/water interface by a digital simulation of cyclic voltammograms

摘要

水溶性抗酸化剤として知られるアスコルビン酸(AsA)は,生体膜表面においてビタミンEのような脂溶性抗酸化剤と反応することによって相乗的抗酸化作用を示すことが知られている.本研究では,生体膜の最も単純なモデルとして考えられるニトロベンゼン/水界面におけるクロラニル(Q)によるAsAの酸化反応を,四電極式サイクリックボルタンメトリー法を用いて測定し,デジタルシミュレーション法を用いて反応機構の解析を行った.水相のpHやAsA及びQの濃度を変えて測定したボルタモグラムについて,幾つかの異なった反応機構を仮定する回帰分析を行った結果,AsAの酸化反応が界面ではなく,水相中で起こるという先の反応機構が支持された.しかしながら,このAsAの2電子酸化反応は,1電子ずつ2段階で進行することが新たに示された. L-ascorbic acid (AsA), a water-soluble antioxidant, is known to exhibit a synergistic inhibition of oxidation by reacting with a lipophilic antioxidant, such as vitamin E, at biomembrane surfaces. In this study, we electrochemically investigated the oxidation of AsA by chloranil (Q) at a nitrobenzene (NB)/water (W) interface, which is considered to be the simplest model of a biomembrane, by using a four-electrode electrolytic cell. The cyclic voltammograms obtained by changing the pH of the W phase and the concentrations of AsA and Q were analyzed using a digital simulation technique. Regression analyses based on various reaction mechanisms have supported the previously proposed mechanism in which the oxidation of AsA occurs not at the NB/W interface, but homogeneously in the W phase. However, it has been clarified that the two electron oxidation of AsA occurs in two one-electron steps.