Proton-Coupled Electron Transfer by Pyrogallol in N,N-Dimethylformamide through Superoxide Scavenging

This chapter explains a mechanistic insight into the scavenging of superoxide radical anion (O2.-) by benzene-1,2,3-triol (pyrogallol) in N,N-dimethylformamide on the basis of cyclic voltammetry and in situ electrolytic electron spin resonance spectrum with the help of density functional theory (DFT) calculations. The presence of pyrogallol altered the quasi-reversible dioxygen/O2.- redox pair, indicating that O2.- was scavenged by pyrogallol by proton-coupled electron transfer (PCET), which involves two proton transfers and one electron transfer. According to DFT calculations, the superior kinetics of O2.- scavenging by pyrogallol as demonstrated by the electrochemical results can be explained by the pre-reactive formation of a hydrogen-bond (HB) complex and the subsequent concerted two-proton-coupled electron transfer (2PCET) characterized by the catechol moiety in pyrogallol. Furthermore, comparative tests employing related compounds revealed that the three hydroxyl groups of pyrogallol increase the formation of HB complex even if one of them is not involved in the 2PCET mechanism, leading to the promotion of O2.- scavenging.