Concerted two-proton-coupled electron transfer from piceatannol to electrogenerated superoxide in N,N-dimethylformamide

The reactivity of 4-[(E)-2-(3,5-dihydroxyphenyl)ethenyl]benzene-1,2-diol (piceatannol) toward electrochemically generated superoxide radical anion (O2•−) was investigated using electrochemistry and in situ controlled-potential electrolytic electron spin resonance (ESR) measurements in N,N-dimethylformamide with density functional theory (DFT) calculations. The quasireversible cyclic voltammogram of dioxygen/O2•−, modified in the presence of piceatannol, indicated that the electrogenerated O2•− was scavenged by piceatannol via proton-coupled electron transfer. Differences in the reactivities of piceatannol and 5-[(E)-2-(4-hydroxyphenyl)ethen-1-yl]benzene-1,3-diol (trans-resveratrol) toward O2•−, originating from the presence of the benzene-1,2-diol (catechol) moiety, were observed in the voltammograms and ESR measurements. The electrochemical and computational results show that the reaction mechanism is a concerted two-proton-coupled electron transfer (2PCET) via the catechol moiety of piceatannol. The stilbene moiety of piceatannol kinetically promotes 2PCET via its catechol moiety. These findings indicate that piceatannol is a better O2•− scavenger than catechol and trans-resveratrol.