Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992, Russia.
Biochemistry (Mosc). 2023 May;88(5):704-715. doi: 10.1134/S0006297923050139.
Process of photosynthesis in the green bacteria Chloroflexus (Cfx.) aurantiacus starts from absorption of light by chlorosomes, peripheral antennas consisting of thousands of bacteriochlorophyll c (BChl c) molecules combined into oligomeric structures. In this case, the excited states are formed in BChl c, energy of which migrates along the chlorosome towards the baseplate and further to the reaction center, where the primary charge separation occurs. Energy migration is accompanied by non-radiative electronic transitions between the numerous exciton states, that is, exciton relaxation. In this work, we studied dynamics of the exciton relaxation in Cfx. aurantiacus chlorosomes using differential femtosecond spectroscopy at cryogenic temperature (80 K). Chlorosomes were excited by 20-fs light pulses at wavelengths in the range from 660 to 750 nm, and differential (light-dark) absorption kinetics were measured at a wavelength of 755 nm. Mathematical analysis of the obtained data revealed kinetic components with characteristic times of 140, 220, and 320 fs, which are responsible for exciton relaxation. As the excitation wavelength decreased, the number and relative contribution of these components increased. Theoretical modelling of the obtained data was carried out based of the cylindrical model of BChl c. Nonradiative transitions between the groups of exciton bands were described by a system of kinetic equations. The model that takes into account energy and structural disorder of chlorosomes turned out to be the most adequate.
在绿菌（Chloroflexus）属的橙色光合菌（Cfx. aurantiacus）中，光合作用的过程始于由数千个细菌叶绿素 c（BChl c）分子结合成寡聚体结构的类囊体吸收光。在这种情况下，激发态在 BChl c 中形成，其能量沿着类囊体向基片迁移，然后进一步向反应中心迁移，在那里发生初级电荷分离。能量迁移伴随着众多激子态之间的非辐射电子跃迁，即激子弛豫。在这项工作中，我们使用低温（80 K）下的差分飞秒光谱法研究了 Cfx. aurantiacus 类囊体中激子弛豫的动力学。类囊体在 660 至 750nm 的波长范围内用 20fs 的光脉冲激发，并在 755nm 的波长下测量差分（亮暗）吸收动力学。对所得数据的数学分析揭示了特征时间为 140、220 和 320fs 的动力学分量，它们负责激子弛豫。随着激发波长的降低，这些分量的数量和相对贡献增加。基于 BChl c 的圆柱模型对所得数据进行了理论建模。激子带组之间的非辐射跃迁由一组动力学方程描述。结果表明，考虑到类囊体的能量和结构无序的模型是最合适的。
