Institute of Theoretical and Computational Chemistry, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea.
J Am Chem Soc. 2012 Jul 18;134(28):11640-51. doi: 10.1021/ja303025q. Epub 2012 Jul 5.
Although photosynthetic pigment-protein complexes are in noisy environments, recent experimental and theoretical results indicate that their excitation energy transfer (EET) can exhibit coherent characteristics for over hundreds of femtoseconds. Despite the almost universal observations of the coherence to some degree, questions still remain regarding the detailed role of the protein and the extent of high-temperature coherence. Here we adopt a theoretical method that incorporates an all-atom description of the photosynthetic complex within a semiclassical framework in order to study EET in the Fenna-Matthews-Olson complex. We observe that the vibrational modes of the chromophore tend to diminish the coherence at the ensemble level, yet much longer-lived coherences may be observed at the single-complex level. We also observe that coherent oscillations in the site populations also commence within tens of femtoseconds even when the system is initially prepared in a non-oscillatory stationary state. We show that the protein acts to maintain the electronic couplings among the system of embedded chromophores. We also investigate the extent to which the protein's electrostatic modulation that disperses the chromophore electronic energies may affect the coherence lifetime. Further, we observe that even though mutation-induced disruptions in the protein structure may change the coupling pattern, a relatively strong level of coupling and associated coherence in the dynamics still remain. Finally, we demonstrate that thermal fluctuations in the chromophore couplings induce some redundancy in the coherent energy-transfer pathway. Our results indicate that a description of both chromophore coupling strengths and their fluctuations is crucial to better understand coherent EET processes in photosynthetic systems.
尽管光合色素-蛋白复合物处于嘈杂的环境中，但最近的实验和理论结果表明，它们的激发能量转移（EET）可以表现出数百飞秒以上的相干特性。尽管在某种程度上几乎普遍观察到了相干性，但关于蛋白质的详细作用和高温相干性的程度仍存在疑问。在这里，我们采用了一种理论方法，该方法将光合作用复合物的全原子描述纳入半经典框架中，以研究 Fenna-Matthews-Olson 复合物中的 EET。我们观察到，色团的振动模式往往会降低整体水平的相干性，但在单个复合物水平上可能会观察到更长寿命的相干性。我们还观察到，即使系统最初处于非振荡的静止状态，在几十飞秒内，各站点的种群也会开始出现相干振荡。我们表明，蛋白质的作用是维持嵌入色团的系统之间的电子耦合。我们还研究了蛋白质的静电调制分散色团电子能量的程度如何影响相干寿命。此外，我们观察到，即使突变引起的蛋白质结构破坏可能改变耦合模式，但在动力学中仍然存在相对较强的耦合和相关的相干性。最后，我们证明了色团耦合的热波动在相干能量转移途径中引起了一些冗余。我们的结果表明，对色团耦合强度及其波动的描述对于更好地理解光合作用系统中的相干 EET 过程至关重要。
