Electrochemical and Mechanistic Study of Reactivities of α-, β-, γ-, and δ-Tocopherol toward Electrogenerated Superoxide in <i>N</i>,<i>N</i>-Dimethylformamide through Proton-Coupled Electron Transfer

• Main Authors: Tatsushi Nakayama (Author), Ryo Honda (Author), Kazuo Kuwata (Author), Shigeyuki Usui (Author), Bunji Uno (Author)
• Format: Book
• Published: MDPI AG, 2021-12-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.

Summary

Scavenging 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 spectrum in <i>N</i>,<i>N</i>-dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible dioxygen/O₂^•− redox was modified by the presence of TOH, suggesting that the electrogenerated O₂^•− was scavenged by α-, β-, γ-TOH through proton-coupled electron transfer (PCET), but not by δ-TOH. The reactivities of α-, β-, γ-, and δ-TOH toward O₂^•− characterized by the methyl group on the 6-chromanol ring was experimentally confirmed, where the methyl group promotes the PCET mechanism. Furthermore, comparative analyses using some related compounds suggested that the <i>para</i>-oxygen-atom in 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 the preceding proton transfer (PT) forming a hydroperoxyl radical, followed by a PCET (intermolecular ET-PT). The O₂^•− scavenging by TOH proceeds efficiently along the PCET mechanism involving one ET and two PTs.

Item Description

10.3390/antiox11010009
2076-3921