General hydroxyl (OH) proton donors such as phenols and alcohols exhibit superior complexation or PT kinetics to and from O2 •-(HO2 • ), regardless of their acidity. As the complexation reactions are assumed to be fast and reversible processes, the formation constants are by Equations ( ) and (8). The formation of complex denoted Equation (8) corresponds to step (i) in the three elementary steps of 2PCET (Equation ( )). Therefore, the apparent redox potential of O2/O2 •-in the presence of H2Q was calculated by introducing the formation constants of the HB complex into the Nernst equation based on the thermodynamic equilibrium shown in Figure .