Cyclic voltammograms (CVs) and in situ electrolytic ESR spectrum for saturated O2 (4.8 × 10 -3 mol dm -3 ) in DMF (Figure ) were measured to infer the scavenging mechanism of electrogenerated O2 •-by RsvH3 and related compounds (Chart 1). CV and ESR spectrum in the presence of (d) p-coumaric acid and (e) α-tocopherol were already reported, although, are shown for comparison. O2 showed a quasi-reversible redox reaction (Equation ( )) with the generation of O2 •-in the initial cathodic scan and reoxidation to the starting materials (O2) in the returned anodic scan, demonstrating cathodic/anodic peaks (pc1/pa1, bold lines in Figure ). The quasi-reversible CVs investigated here became irreversible in the presence of the compounds (a)-(e) (excluding (f) stilbene) at various concentrations (0 to 5.0 × 10 -3 mol dm -3 ). The loss of reversibility in the CVs of O2/O2 •-was attributed to an acid-base reaction as the CVs of bubbled N2 showed no peak over the potential range; specifically, the O2 •-acts as a Brønsted base forming HO2 • along the initial PT (Equation ( )). Conversely, the CV in the presence of (f) stilbene showed no reactivity toward O2 •-. The generation and consequent heterogeneous-reduction of HO2 • (Equation ( )) gave rise to bielectronic CVs in the presence of pinosylvin and p-coumaric acid (Figure (b, d), cathodic peak: pc2 on pc1). This bielectronic feature disappeared in the presence of (a) RsvH3, (c) PtsH, and (e) α-tocopherol, caused by scavenging of HO2 • via the subsequent ET (Equation ( )). Then, the ET between the deprotonated anion (RsvH2 -) and HO2 • forms a hydroperoxyl anion (HO2 -) and a substrate radical (RsvH2 • ). Consequently, a monoelectronic and irreversible CV curve appeared.