Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Chem Phys. 2012 Aug 14;137(6):065101. doi: 10.1063/1.4738953.
Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion process in which electronic excitation establishes a trans-membrane charge gradient. This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of these pigments interact very strongly and are simultaneously influenced by the surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls influenced in their excited state dynamics by strong interaction between the pigments and by interaction with the protein environment. Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical methods, which account for both pigment-pigment interaction and pigment-environment interaction. In the present study we describe the excitation dynamics within a RC and excitation transfer between light harvesting complex 1 (LH1) and RC, employing the hierarchical equation of motion method. For this purpose a set of model parameters that reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC is suggested. We find that the environment has a significant effect on LH1-RC excitation transfer and that excitation transfers incoherently between LH1 and RC.
光合作用中有效捕获太阳光的关键是第一个能量转换过程，其中电子激发建立跨膜电荷梯度。这种转换是由光合反应中心（RC）完成的，在本文研究的紫色光合细菌球形红杆菌中，RC 被光捕获复合物 1（LH1）包围。RC 使用六个色素分子来启动转换：四个细菌叶绿素和两个细菌叶红素。这些色素的激发态相互作用非常强烈，同时受到周围热蛋白环境的影响。同样，LH1 使用 32 个细菌叶绿素，其激发态动力学受到色素之间的强烈相互作用以及与蛋白质环境的相互作用的影响。在 RC 以及 LH1 中模拟激发态动力学需要理论方法，这些方法既要考虑色素-色素相互作用，也要考虑色素-环境相互作用。在本研究中，我们采用层次运动方程方法描述了 RC 内的激发动力学以及 LH1 和 RC 之间的激发转移。为此，我们提出了一组模型参数，这些参数可再现 RC 以及 LH1 的光谱，并观察到 RC 中振荡激发动力学。我们发现，环境对 LH1-RC 激发转移有显著影响，并且激发在 LH1 和 RC 之间非相干转移。
