Aubry Serge, Kopidakis Georgios
Laboratoire Léon Brillouin, CEA Saclay, 91191-Gif-sur-Yvette, France.
J Biol Phys. 2005 Dec;31(3-4):375-402. doi: 10.1007/s10867-005-1283-4.
A non-adiabatic theory of Electron Transfer (ET), which improves the standard theory near the inversion point and becomes equivalent to it far from the inversion point, is presented. The complex amplitudes of the electronic wavefunctions at different sites are used as Kramers variables for describing the quantum tunneling of the electron in the deformable potential generated by its environment (nonadiabaticity) which is modeled as a harmonic classical thermal bath. After exact elimination of the bath, the effective electron dynamics is described by a discrete nonlinear Schrödinger equation with norm preserving dissipative terms and a Langevin random force, with a frequency cut-off, due to the thermalized phonons.This theory reveals the existence of a specially interesting marginal case when the linear and nonlinear coefficients of a two electronic states system are appropriately tuned for forming a Coherent Electron-Phonon Oscillator (CEPO). An electron injected on one of the electronic states of a CEPO generates large amplitude charge oscillations (even at zero temperature) associated with coherent phonon oscillations and electronic level oscillations. This fluctuating electronic level may resonate with a third site which captures the electron so that Ultrafast Electron Transfer (UFET) becomes possible. Numerical results are shown where two weakly interacting sites, a donor and a catalyst, form a CEPO that triggers an UFET to an acceptor. Without a catalytic site, a very large energy barrier prevents any direct ET. This UFET is shown to have many qualitative features similar to those observed in the primary charge separation in photosynthetic reaction centers. We suggest that more generally, CEPO could be a paradigm for understanding many selective chemical reactions involving electron transfer in biosystems.
提出了一种电子转移（ET）的非绝热理论，该理论在反转点附近改进了标准理论，在远离反转点时与标准理论等效。不同位点处电子波函数的复振幅被用作克莱默斯变量，用于描述电子在由其环境产生的可变形势（非绝热性）中的量子隧穿，该环境被建模为经典的简谐热库。在精确消除热库后，有效的电子动力学由一个具有范数守恒耗散项和朗之万随机力的离散非线性薛定谔方程描述，由于声子热化存在频率截止。该理论揭示了一种特别有趣的边缘情况的存在，即当双电子态系统的线性和非线性系数被适当调整以形成相干电子 - 声子振荡器（CEPO）时。注入到CEPO的一个电子态上的电子会产生与相干声子振荡和电子能级振荡相关的大幅度电荷振荡（即使在零温度下）。这种波动的电子能级可能与捕获电子的第三个位点发生共振，从而使超快电子转移（UFET）成为可能。给出了数值结果，其中两个弱相互作用的位点，一个供体和一个催化剂，形成了一个CEPO，它触发了向受体的UFET。没有催化位点时，一个非常大的能垒会阻止任何直接的电子转移。结果表明，这种UFET具有许多与光合反应中心初级电荷分离中观察到的定性特征相似的特征。我们更普遍地认为，CEPO可能是理解生物系统中许多涉及电子转移的选择性化学反应的一个范例。
