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

• Published in: Antioxidants Vol. 11; no. 1; p. 9
• Main Authors: Nakayama, Tatsushi, Honda, Ryo, Kuwata, Kazuo, Usui, Shigeyuki, Uno, Bunji
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 22.12.2021; MDPI
• Subjects: Acids; antioxidants; Chemical industry; Comparative analysis; cyclic voltammetry; Dimethylformamide; Electrodes; Electrolytes; Electron spin resonance; electron spin resonance spectrum; Electron transfer; Hydrocarbons; Oxidation; proton-coupled electron transfer; Spectrum analysis; Superoxide; superoxide radical anion; tocopherol; Tocopherols; Vitamin E; Voltammetry; Japan; superoxide radical anion; tocopherol; cyclic voltammetry; proton-coupled electron transfer; antioxidants; electron spin resonance spectrum
• ISSN: 2076-3921; 2076-3921
• DOI: 10.3390/antiox11010009

Scavenging of superoxide radical anion (O ) by tocopherols (TOH) and related compounds was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectrum in , -dimethylformamide (DMF) with the aid of density functional theory (DFT) calculations. Quasi-reversible dioxygen/O redox was modified by the presence of TOH, suggesting that the electrogenerated O 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 O 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 -oxygen-atom in the 6-chromanol ring is required for a successful electron transfer (ET) to O 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 O scavenging by TOH proceeds efficiently along the PCET mechanism involving one ET and two PTs.