Considering above, there are several possible mechanisms of ROS scavenging by RsvH3 as well as those by other phenolic antioxidants, such as SET, HAT involving proton-coupled electron transfer (PCET), sequential proton-loss electron transfer, and superoxidefacilitated oxidation (SFO). SFO is an indirect oxidation mechanism involving the initial PT from the substrate to O2 •-giving HO2 • and the rapid dismutation to give hydroperoxide (H2O2) and dioxygen (O2) follows. Then, the substrate anion is oxidized by the O2 formed in the dismutation process. Conversely, in the other mechanisms, O2 •-(HO2 • ) directly oxidizes the substrate. Previous studies reported that O2 •-is scavenged by 1,2-and 1,4-benzendiols (catechol and hydroquinone ), 1,2-and 1,4-dihydroxynaphthalenes, 27 monophenols including aminophenols, and polyphenols, through the ET involved in the PCET. In these studies, a successful O2 •-scavenging is based on the PCET mechanism characterized by quinonehydroquinone π-conjugation. O2 •-is not a moderately good electrophile that can accept electrons from phenolic substrates, however, HO2 • formed after protonation of O2 •-as a Brønsted base is a strong oxidant with a short lifetime. Thus, the deprotonation (PT) and subsequent ET between RsvH3/deprotonated anion (RsvH2 -) and O2 •-/HO2 • , is closely related, which is inferred to embody the actual ROS-scavenging mechanism.