细菌光合反应中心QA和QB间电子转移反应的量子化学研究

AM1 and ab initio Studies on the Electron Transfer Reaction from QA to QB in the Bacterial Photosynthetic Reaction Center of Rhodo - pseudomonas viridis

用量子化学半经验的AM1和密度泛函DFT(B3LYP/6-31G(d))方法分别优化了质体醌MQ1(QA)、泛醌UQ1(QB)及其阴离子自由基的结构.用Nelsen方法计算了电子转移反应MQ-1UQ1→MQ1UQ-1的内重组能λi.用线性反应坐标方法构造了该电子转移反应的双势阱,两透热势能面在反应坐标R≈0.30处相交.对该电子转移体系进行闭壳层的单点计算,并用Koopmans定理计算了体系的分裂能△,得到△随线性反应坐标R的变化关系.结果表明,在R=0.342处△有一极小值,从而得到该电子转移反应的电子转移矩阵元Vrp,并由此确定了反应的过渡态.在此基础上,用两球模型计算了反应的溶剂重组能λo.本文还计算了该电子转移反应的活化自由能△G*.最后,根据Marcus电子转移理论计算了该反应的速率常数ket为5.93×104s-1,由此得到该反应的半衰期与文献报道的结果一致.

The structures of menoquinone MQ(1) (Q(A)), ubiquinone UQ(1) (Q(B)) and their radical anions are optimized by both the semiempirical AM1 and density functional theory [ B3LYP/6 - 31G (d) ] methods. ne Nelsen's model is used to calculate the internal reorganization energy Ai of the electron transfer ( ET) reaction MQ(1)(-) UQ(1)--> MQ(1)UQ(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 curves appears at R approximate to0.30. The closed shell BF 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 Delta, and the relationship between Delta and R has been obtained. The results show that the minimal value of Delta appears at R = 0.342, which is corresponding to the transition state of the reaction, and V-rp, has been determined according to Delta (min). Then Marcus's two - sphere model is used to calculate the solvent reorganization energy lambda (0). In addition, the activation free energy DeltaG* for the ET reaction has been evaluated. The calculated rate constant k(et) of the ET reaction according to Marcus's theory is 5.93 x 10(4) s(-1), and the half - life time of the ET reaction derived from k(et) is well consistent with the experimental results.