The mechanistic analysis of O2 •-scavenging by RsvH3 in DMF was supplemented by a DFTbased frontier molecular-orbital analysis. Figure shows the HOMO-LUMO changes during the PCET between RsvH3 and O2 •-. After the initial PT, the reactant species, RsvH3, RsvH2 -, O2 •-, and HO2 • coexist in the solution. The singly occupied molecular orbital (SOMO) energy (Hartree/a.u.) of HO2 • (-0.31659) was much lower than the HOMO energies of RsvH3 (-0.21086) and its anions ( a RsvH2 -:-0.16717, b RsvH2 -:-0.17433), indicating that the electron acceptor was HO2 • rather than O2 •-. Meanwhile, the CV in DMF revealed that HO2 • formed after the initial PT was scavenged by RsvH3 (Figure ). Therefore, the electron donor was RsvH2 - (the downhill energy relationship during the ET is indicated by the bold red lines in Figure ).