ON THE MECHANISM OF THE PRIMARY CHARGE SEPARATION IN BACTERIAL PHOTOSYNTHESIS
ON THE MECHANISM OF THE PRIMARY CHARGE SEPARATION IN BACTERIAL PHOTOSYNTHESIS
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DOI：
10.1016/s0005-2728(05)80062-3
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发表时间：
1991-02-08
期刊：
影响因子：
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通讯作者：
MICHELBEYERLE, ME
中科院分区：
文献类型：
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作者：
BIXON, M;JORTNER, J;MICHELBEYERLE, ME
根据最近的实验工作飞秒电子转移动力学的反应中心（RC），我们探讨的主要过程的机制。 我们专注于细菌叶绿素单体（B）的特殊作用，位于主供体（1P *），细菌叶绿素二聚体（P），和细菌叶绿素（H），考虑一个动力学方案，结合两个平行的电子转移途径：一个通过电子相互作用与P + B-H介导的单步超交换通道，和两个步骤的顺序通道，涉及P + B-H化学中间体。 在这个动力学计划中，我们使用微观非绝热电子转移速率，这是扩展到将介质控制动力学的影响。 动力学建模的结果被呈现为供体1P * BH和（物理和/或化学）介导状态P + B-H的平衡核构型之间的自由能隙Δ-G1的函数。 平行顺序超交换机制在所有温度下对于大的负Δ-G1降低到几乎纯顺序途径的极限，并且在所有温度下对于大的正Δ-G1降低到几乎纯超交换途径的极限，并且在低温下对于中等Δ-G1降低到几乎纯超交换途径的极限。 现有的飞秒动力学数据在室温下是一致的，无论是在所有温度下的叠加顺序和超交换或超交换和顺序在室温和超交换在低温下的叠加。 10 K下可用的飞秒数据提出了这样的可能性：该机制涉及300 K下超交换和序列的叠加以及低温下超交换的主导地位。 关于磁性数据的辅助实验信息，即，自由基对P + BH-的单重态-三重态分裂，在诱变改变的RC中的电荷分离动力学，酪氨酸M208被苯丙氨酸取代，以及跨RC的A分支的电荷分离的单向性根据所提出的机制进行了分析。 平行的顺序和超交换电子转移路线的初级电荷分离的流行将引入冗余的元素，这确保了一个有效的过程，这是稳定的变化能量参数在不同的光合RC的发生。
In the light of recent experimental work on femtosecond electron transfer kinetics in the reaction center (RC) we explore the mechanism for the primary process. We focus on the special role of the bacteriochlorophyll monomer (B) located between the primary donor (1P*), a bacteriochlorophyll dimer (P), and a bacteriopheophytin (H), considering a kinetic scheme which combines two parallel pathways of electron transfer: a unistep superexchange channel mediated via electronic interactions with P+B-H, and a two-step sequential channel involving a P+B-H chemical intermediate. In this kinetic scheme we used microscopic nonadiabatic electron transfer rates, which were extended to incorporate the effects of medium-controlled dynamics. The results of the kinetic modelling are presented as a function of the free-energy gap DELTA-G1 between the equilibrium nuclear configurations of the donor 1P*BH and the (physically and/or chemically) mediating state P+B-H. The parallel sequential-superexchange mechanism reduces to the limit of nearly pure sequential pathway for large negative DELTA-G1 at all temperatures and to the limit of almost pure superexchange pathway for large positive DELTA-G1 at all temperatures and for moderate DELTA-G1 at low temperatures. The existing femtosecond kinetic data at room temperature are consistent with either the superposition of sequential and superexchange at all temperatures or to a superposition of superexchange and sequential at room temperature and superexchange at low temperatures. The available femtosecond data at 10 K raise the possibility that the mechanism involves the superposition of superexchange and sequential at 300 K and the dominance of superexchange at low temperatures. Auxiliary experimental information regarding magnetic data, i.e., the singlet-triplet splitting of the radical pair P+BH-, the kinetics of the charge separation in mutagenetically altered RCs, with tyrosine M208 being replaced by phenylalanine, and the unidirectionality of charge separation across the A branch of the RC are analysed in terms of the proposed mechanism. The prevalence of the parallel sequential and superexchange electron transfer routes for the primary charge separation would introduce an element of redundancy, which insures the occurrence of an efficient process which is stable with respect to the variation energetic parameters in different photosynthetic RCs.