Scavenging of electrogenerated superoxide radical anion (O₂^•−) by pyrogallol (PyH₃) was investigated on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectrum in N,N-dimethylformamide with the aid of density functional theory (DFT) calculations. Quasi-reversible dioxygen/O₂^•− redox couple was modified by the presence of PyH₃, suggesting that O₂^•− was scavenged by PyH₃ through proton-coupled electron transfer (PCET) involving two proton transfer and one electron transfer. DFT calculation suggested that the pre-reactive formation of a hydrogen-bond (HB) complex and the subsequent concerted two-proton-coupled electron transfer characterized by catechol moiety in PyH₃ is plausible mechanism that embodies the superior kinetics of the O₂^•− scavenging by PyH₃ as shown in the electrochemical results. Furthermore, it was clarified that the three hydroxyl groups of PyH₃ promote the formation of HB complex, in comparative analyses using related compounds, resulting in the promotion of the O₂^•− scavenging.

Keywords: proton-coupled electron transfer; superoxide radical anion; antioxidants; cyclic voltammetry; electron spin resonance spectrum; pyrogallol

Electrochemical and Mechanistic Study of Superoxide Scavenging by Pyrogallol in N,N-Dimethylformamide through Proton-Coupled Electron Transfer

Tatsushi Nakayama, Ryo Honda, Kazuo Kuwata, Shigeyuki Usui and Bunji Uno
Electrochem 2022, 3(1), 115-128
DOI: doi.org/10.3390/electrochem3010008