Hence, the second PT predominantly determined the direction of ET. This HOMO-LUMO relation is similar whether the second PT occurs from 4'OH forming a PiceH2 ΔG°s (kJ mol -1 , 298.15 K) along the PCET were calculated using the vibrational frequency calculation combined with the PCM method for the thermodynamically mechanistic analysis of the O2 •-scavenging by PiceH4 in DMF (Table ). Figure shows the redox equilibrium scheme and the ΔG°s of PCET involving one ET and two PTs from PiceH4 to O2 •-, calculated using the B3LYP/PCM/6-311+G(d,p) method (M06-2X and TPSSh results are shown in Figure ). The ΔG°s of the individual reactions of the components in Figure , ET1-ET3 and PT1-PT4, are the main drivers of the sequential pathway. Because ET1 (354.4) was strongly endergonic, PT1