Theory and Calculations of Electron Transfer in Protein Media

(1)采用分子动力学模拟和量子化学相结合的方法，以光合细菌反应中心嗜菌素阴离子对原生奎宁的电子转移为例，探讨了蛋白质环境下电子转移的机理。(2)我们发现ET速率的电子隧穿矩阵元素会随着蛋白质构象的热波动而变化几个数量级。(3)研究发现，氨基酸构象变化的原因主要是氨基酸构象的波动，而不是供体-受体距离的波动。(4)我们发现存在两种主要的隧穿路线，它们的隧穿电流相反，导致了大量的破坏性量子干涉。(5)我们提出了一种新的非康登理论，适用于ET的电子因子变化非常快的情况。因此，我们推导出了将ET速率描述为两项之和的公式：第一个是由于弹性电子隧穿机制导致的ET速率，在此机制中，电子能量在ET前后是守恒的。该机制与普通ET理论相对应。二是由于非弹性电子隧穿机制导致的ET速率，在此机制下，电子在隧穿前后能量不守恒。吸收或发射的能量是由于电子隧穿矩阵元波动的傅里叶变换频率。(6)通过数值计算，我们发现非弹性隧道机制在马库斯能隙定律的实质倒转区域有明显的作用。(7)提出了一种考虑量子干涉效应的对涨落进行适当平均以获得平均隧穿路径的新方法。

(1) We investigated the mechanism of electron transfer (ET) in protein environment, by taking an example of ET of bacteriopheophitin anion to primary quinine in the reaction center of photosynthetic bacteria by the combined study of molecular dynamics simulations and quantum chemistry. (2)We found that electronic tunneling matrix element of the ET rate is varied by a few orders of magnitude according to the thermal fluctuation of the protein conformation. (3) We found that the origin of the large variation is mostly fluctuations of amino acid conformation rather than the fluctuation of donor-acceptor distance. (4) We found that there exist two main tunneling routes with opposite tunneling currents, bringing about a large amount of destructive quantum interference. (5)We developed a new non-Condon theory which is usable when the electronic factor of the ET is varied very quickly. As a result, we derived the formula describing the ET rate as a sum of the two terms: The first is the ET rate due to the elastic electron tunneling mechanism in which the electron energy is conserve before and after ET. This mechanism corresponds to the ordinary ET theory. The second is the ET rate due to the inelastic electron tunneling mechanism in which the electron energy is not conserved before and after ET. The absorbed or emitted energy is due to the frequency of Fourier transform for the fluctuation of electron tunneling matrix element. (6) By numerical calculations, we found that the inelastic tunneling mechanism works appreciably at the substantial inverted region of the Marcus energy gap law. (7) We invented a new method for properly averaging the fluctuation to obtain the average tunneling route, involving the effect of quantum interference effect.