Theoretical Research on Primary Chemical Reactions in Photosynthesis.

1.应用多电子体系分子轨道理论对基本分子间电子转移(ET)过程中可能的机理进行了描述和分类。Et矩阵元包含四个项，分别代表弹性电子隧穿过程(&lt；T_1&gt；)、通过占据分子轨道的双交换过程(&lt；T_2&gt；)、非弹性电子隧穿过程(&lt；T_3&gt；)和核非绝热过程(&lt；T_4&gt；)。一个重要的发现是，电子与分子振动促进模之间的库仑相互作用产生的&lt；T_3&gt；，由于其准一维性质，当振动电荷与Et路径相近时，可以大大增强到远远超过&lt；T_1&gt；。利用多体问题中的格林函数技术，导出了考虑分子振动的非谐性(3、4)的弗兰克-康登因子的理论公式。非谐性的影响被估计为…更倾向于将速率常数最多改变一个数量级。它可能负责负激活过程，如细菌中的(BCHL)&lt；2^+&gt；i&lt；q(_A^-)&gt；-！&gt；&lt；(Bchl)_2&gt；i&lt；Q_A&gt；反应。在能隙超过重组能的反转区，电子转移速率高于经典的Marcus理论，这归因于分子振动高频模式的“声子边带”，如C-C和C-H键应变。在细胞色素氧化反应中观察到的&lt；H_2&gt；O/&lt；D_2&gt；O同位素效应似乎表明&lt；T_3&gt；项，即促进模声子诱导的电子隧穿机制，在生物体系中占优势。对于光合细菌中的电荷分离过程，我们估算了预测的每个包含氢键的最短路径的~lt；T_3和Gt；，得到了计算的速率常数和量子产率，与实验结果吻合较好。为了建立光合作用裂水反应的分子机理，基于我们的催化双核锰配合物微表面模型，我们用从头算分子轨道方法优化了&lt；S_0&gt；和&lt；S_1&gt；态的几何构型，所得的Mn-Mn原子间距与EXAFS分析得到的结果很好地吻合，并且发现&lt；S_1&gt；态比&lt；S_0&gt；态更稳定，与实验事实相符。

1. A molecular orbital theory for many electron system was applied to formulate and classify possible mechanisms in elementary intermolecular electron-transfer(ET) process. The ET matrix element was found to contain four terms which represent an elastic electron-tunneling process( <T_1> ), a doubleexchange process via occupied molecular orbitals( <T_2> ), an inelastic electron-tunneling process( <T_3> ) and a nuclear nonadiabaticity process( <T_4> ). A significant finding is that the <T_3> , which arises from the Coulombic interaction between electron and promoting modes of molecular vibration, can be greatly enhanced far beyond <T_1> when the vibrating charges exist as close as the ET pathway because of its quasi-one dimensionarity.2. A theoretical formula for the Franck-Condon factor in the ET rate taking account of the anharmonicity (3rd and 4th) of molecular vibration was derived with use of the Green's function technique in many-body problems. The effect of anharmonicity was estim … More ated to change the rate constant at most by one order of magnitude. It is likely to be responsible for negative activation processes such as the (Bchl) <2^+> I <Q(_A^-)> <-!>> <(BChl)_2> I <Q_A> reaction in bacteria.3. The enhancement of the ET rate over the classical Marcus theory in the inverted region where the energy gap exceeds the reorganization energy was ascribed to the "phonon side-bands" of high frequency modes of molecular vibrations such as the C-C and C-H bond Stretchings.4. The observed <H_2> O/ <D_2> O isotope effect in cytochrome oxidation reactions seems to indicate the predominance of the <T_3> term, i.e. the promoting mode phonon-induced electron-tunneling mechanism, in biological systems.5. As regards the charge separation process in photosynthetic bacteria, we estimated the <T_3> for each predicted shortest ET pathway which includes hydrogen-bonds and obtained the calculated rate constants and quantum yield in good agreement with experimental results.6. In order to establish the molecular mechanism of photosynthetic water-splitting reaction based on our "microsurface model of catalytic binuclear manganese complex, we optimized the geometries of the <S_0> and <S_1> states with use of ab initio molecualr orbital method. The resultant Mn-Mn atomic distances agree well with those obtained from the EXAFS analysis. Further, the <S_1> state was found to be more stable than the <S_0> state in agreement with the experimental fact. Less