Relationship between thermodynamics and mechanism during photoinduced charge separation in reaction centers from Rhodobacter sphaeroides.
Relationship between thermodynamics and mechanism during photoinduced charge separation in reaction centers from Rhodobacter sphaeroides.
复制标题
球形红细菌反应中心光致电荷分离过程中热力学与机理的关系。
DOI：
10.1021/bi00192a015
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发表时间：
1994
期刊：
影响因子：
2.9
通讯作者：
Allen,JP
中科院分区：
文献类型：
--
作者：
Woodbury,NW;Peloquin,JM;Alden,RG;Lin,X;Lin,S;Taguchi,AK;Williams,JC;Allen,JP
摘要：在低温下对球形红杆菌R-26菌株和双突变体[Lh(L131)+Lh-(M160)]的反应中心进行了详细的快速瞬变吸收测量，其中P/P+氧化电位比野生型反应中心高出约140 mV(1100 cm-1)。在这两个样品中，初始给电子体的激发单重态的衰变不能很好地用单指数衰减项来描述。对于来自双突变体的反应中心尤其如此，其中至少需要三个指数动力学分量来描述衰变，时间常数从几皮秒到数百皮秒不等。然而，对随时间变化的吸收光谱的奇异值分解分析表明，R-26和双突变体的反应中心只存在两个光谱不同的状态。因此，P~*在低温下的复杂衰变似乎既不是由于P+BA~作为电子转移的独特中间态的形成，也不是由于P+BB“作为电子转移的平衡副产物形成的。相反，衰变动力学通过假设电荷分离态的动态溶剂化来建模，如所附论文[Peloquin，J.M.，Williams，J.C.，Lin，X.，Alden，RG，Taguchi，AKW，Allen，JP，&Woodbury，N.W.(1994)BioChemical 33,8089-8100]中对长寿命荧光衰变所做的那样。文中还给出了在较长时间尺度上假定电子转移速率的静态分布和电荷分离态的动态溶剂化的结果。无论用哪种模型来描述激发态衰变的早期动力学，在100ps或更长的时间尺度上，依赖时间的激发态布居可以用电荷分离态的P*的热再布居来描述，即使在20K，这导致在从皮秒到纳秒的所有时间尺度上，估计初始电子转移的依赖于时间和温度的驱动力小于200 cm-1。假设与电荷分离相关的非零内部重组能，那么小的驱动力似乎与电子转移的温度依赖性不一致，并且具有比野生型高140 mV(1100 cm-1)的P/P+氧化电位的突变体即使在低温下也仍然能够进行电子转移。这些观测结果更符合强耦合极限附近的绝热电子转移反应。
Revised Manuscript Received April 19, 1994· abstract: Detailed fast transient absorption measurements have been performed at low temperature on reaction centers from Rhodobacter sphaeroides strain R-26 and on a double mutant,[LH (L131)+ LH-(M160)], in which the P/P+ oxidation potential is roughly 140 mV (1100 cm-1) above that of wild-type reaction centers. In both samples, the decay of the excited singlet state of the initial electron donor is not well described by a single-exponential decay term. This is particularly true for reaction centers from the double mutant where at least three exponential kinetic components are required to describe the decay, with time constants rangingfrom a few picoseconds to hundreds of picoseconds. However, singular value decomposition analysis of the time-dependent absorption change spectra indicates the presence of only two spectrally distinct states in reaction centers from both R-26 and the double mutant. Thus, the complex decay of P* at low temperature does not appear to be dueto formation of eitherthe state P+ BA~ asa distinct intermediate in electron transfer or P+ Bb" as an equilibrated side product of electron transfer. Instead, the decay kinetics are modeled by assuming dynamic solvation of the charge-separated state, as was done for the long-lived fluorescence decay in the accompanying paper [Peloquin, J. M., Williams, J. C., Lin, X., Alden, RG, Taguchi, AKW, Allen, JP, & Woodbury, N. W.(1994) Biochemistry 33, 8089-8100]. The results of assuming a static distribution of electron-transfer rates at early times followed by dynamic solvation of the charge-separated states on longer time scales are also presented. Regardless of which model is used to describe the early time kinetics of excited-state decay, the time-dependent excited-state population on the 100-ps or longer time scale is best described in terms of thermalrepopulation of P* from the charge-separated state, even at 20 K. This results in a time-and temperature-dependent driving force estimated for initial electron transfer of less than 200 cm-1 on all time scales from picoseconds to nanoseconds. Assuming a nonzero internal reorganization energy associated with charge separation, the smalldriving force does notappear to be consistent with the lack of temperature dependence of electron transfer and the fact that a mutant with a P/P+ oxidation potential 140 mV (1100cm-1) higher than wild type is still able to undergo electron transfer, even at low temperature. These observations are more in line with an essentially adiabatic electron-transfer reaction near the strong coupling limit.