紫色光合细菌太阳光捕获与传递过程的环境适应性

Clarifying the strutural basis and physical mechanism behind the high-efficient solar energy harvesting, transfer and photoelectronic conversion processes of photosynthetic organisms is vital for mankinds' understanding and mimicing nature to prepare performance-enhanced solar energy materials. The most powful tool in detecting ultrafast energy transfer and charge separation processes in photosynthetic system directly is ultrafast time-resolved spectroscopic technique. This research will employe several kinds of time-resolved and stready-state spectroscopic measurements ro the pigment-protein complexes of different purple bacteria: thermophilic, cryophilic and halophilic bacteria living in hot spring, Arctic tundra, to investigate how they could survive the extreme environments and at the same time optimize their structural stability and the rates of solar energy harvesting and transfer. By comparing the energy transfer rates, exciton delocalization and coherent coupling with vibrational modes between the different purple bacteria, as well as the the configuration and orientation of pigment molecules, the interaction between pigment molecules and environtal amino acids, one could explore the evolutionary strategy of the structure and dynimcs. The research will help revealing the photo-physical and photo-chemical mechanism behind the primary processes of photosynthesis, and will provide a new way to study the developing pathway of photosynthetic organisms.

阐明光合作用高效太阳光的捕获、传递与光电转化的结构基础和物理机制对于人类理解及模仿自然界以制备高效能源材料至关重要。直接探测光合作用体系中超快能量传递和电荷分离过程最有效的手段是超快时间分辨光谱技术。本项目计划应用多种超快与稳态光谱测量方法于生长于温泉、北极苔原、苏打湖中的几种嗜热、嗜寒、嗜盐紫色光合细菌的色素-蛋白复合物，来研究在不同的极端生态环境下，生物如何通过自身的结构改变来同时优化其结构稳定性与光能捕获和传递的速率。通过比较不同菌种间传能速率、激子离域、相干振动耦合等超快动力学过程，色素分子的构型取向及色素分子与周边氨基酸骨架的相互作用，来探索光合生物的结构与动力学过程的演化方式。该项目将有助于深入揭示原初光合反应的光物理光化学机制，也将为光合生物体的进化途径提供一个新思路。

本项目应用多种超快与稳态光谱测量方法于几种嗜热、嗜寒、嗜盐的紫色光合细菌的核心天线-反应中心色素-蛋白复合物（LH1-RC），研究了在不同的生长环境下，光合生物如何通过自身的结构改变来同时优化其热稳定性与光能捕获、传递与转化的效率。研究结果揭示了一个规律：为适应生长环境，LH1中色素Bchl的组合会发生变化，生长温度高时Bchl组合成的LH1环更紧密，温度低时更松散。这些组合的变化影响了Bchl间的耦合作用强度，导致激子能级的变化，表现为吸收峰的位移。然而，LH1激子态间快速的能量弛豫（<100飞秒）与LH1向RC的能量传递的时间常数（50-60皮秒）受到的影响比较小。我们认为，前者是电子态间相干机制主导的，因此能量传递速率不受激子态能级的影响；而后者是有相干振动模式参与，所以尽管能极差变化较大，能量传递速率变化较小。这些研究结果阐明了紫细菌是如何在保留高效率光能利用率的同时适应极端环境的，依据研究结果提出的物理机制将有助于更深入理解自然界的原初光合反应过程，也可以从一个侧面反映了光合细菌的进化途径。同时，也将对设计高效人工太阳能电池提供新思路，即通过三维构型的改变来调节激子能级及光电性质。