Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Electrochemical and Mechanistic Study of Structure–Activity Relationship of α-, β-, γ-, and δ-Tocopherol on Superoxide Elimination in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

Version 1 : Received: 2 December 2021 / Approved: 3 December 2021 / Online: 3 December 2021 (15:01:26 CET)

A peer-reviewed article of this Preprint also exists.

Nakayama, T.; Honda, R.; Kuwata, K.; Usui, S.; Uno, B. Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer. Antioxidants 2022, 11, 9. Nakayama, T.; Honda, R.; Kuwata, K.; Usui, S.; Uno, B. Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in N,N-Dimethylformamide through Proton-Coupled Electron Transfer. Antioxidants 2022, 11, 9.

Journal reference: Antioxidants 2021, 11, 9
DOI: 10.3390/antiox11010009

Abstract

Abstract: Elimination of superoxide radical anion (O2•−) by tocopherols (TOH), and related compounds was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectral measurements in N,N-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible O2/O2•− redox was modified by the presence of TOHs, suggesting that the electrogenerated O2•− was eliminated by α-, β-, γ-TOH through proton-coupled electron transfer (PCET), but not by δ-TOH. The structure–activity correlation of α-, β-, γ-, and δ-TOH characterized by methyl group on the 6-chromanol ring was experimentally confirmed, where the methyl group promotes the PCET mechanism. Furthermore, comparative analyses using some related chemical analogues suggested that methoxyl group of the 6-chromanol ring is required for a successful electron transfer (ET) to O2•− through the PCET. The electrochemical and DFT results in dehydrated DMF suggested that the PCET mechanism involves preceding proton transfer (PT) forming hydroperoxyl radical followed by a concerted PCET (ET–PT). The O2•− elimination by TOH proceeds efficiently along the net PCET mechanism involving one ET and two PTs.

Keywords

proton-coupled electron transfer; superoxide radical anion; antioxidants; cyclic voltammetry; electron spin resonance spectrum; tocopherol

Subject

CHEMISTRY, Food Chemistry

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