The structures of menoquinone MQ1(Q~A), ubiquinone UQ1(Q~B) and their radical anions are optimized by both the semiempirical AM1 and density functional theory [B3LYP/6-31G(d)] methods. The Nelsen's model is used to calculate the internal reorganization energy λi of the electron transfer (ET) reaction MQ^-~1-UQ1→ MQ1UQ^-~1. A linear reaction coordinate R is used to construct the double well potential model for the ET reaction, and the results show that the crossing of the two diabatic potential energy curve sappears at R≈0.30. The closed shell HF SCF calculations have been carried out for the electron transfer systems corresponding to different values of R, then the Koopmans' theorem is applied to estimate the energy level splitting △, and the relatonship between △ and R has been obtained. The results show that the minimal value of △ appears at R=0.342, which is corresponding to the transition state of the reaction, and Vrp has been determined according to △min. Then Marcus's two-sphere model is used to calculate the solvent reorganization energy λ0. In addition, the activation free energy △G for the ET reaction has been evaluated. The calculated rate constant ket of the ET reaction according to Marcus's theory is 5.93×10^4s^-^1, and the half-life time of the ET reaction derived from ket is well consistent with the experimental results.

Key words: ELECTRON TRANSFER REACTION, QUINONE