Institute of Physics, Center for Physical Sciences and Technology, Vilnius, Lithuania.
J Phys Chem B. 2012 May 3;116(17):5192-8. doi: 10.1021/jp302042w. Epub 2012 Apr 22.
The variability of the exciton spectra of bacteriochlorophyll molecules in light-harvesting (LH) complexes of photosynthetic bacteria ensures the excitation energy funneling trend toward the reaction center. The decisive shift of the energies is achieved due to exciton spectra formation caused by the resonance interaction between the pigments. The possibility to resolve the upper Davydov sub-band corresponding to the B850 ring and, thus, to estimate the exciton bandwidth by analyzing the temperature dependence of the steady-state absorption spectra of the LH2 complexes is demonstrated. For this purpose a self-modeling curve resolution approach was applied for analysis of the temperature dependence of the absorption spectra of LH2 complexes from the photosynthetic bacteria Rhodobacter (Rba.) sphaeroides and Rhodoblastus (Rbl.) acidophilus. Estimations of the intradimer resonance interaction values as follows directly from obtained estimations of the exciton bandwidths at room temperature give 385 and 397 cm(-1) for the LH2 complexes from the photosynthetic bacteria Rba. sphaeroides and Rhl. acidophilus, respectively. At 4 K the corresponding couplings are slightly higher (391 and 435 cm(-1), respectively). The retained exciton bandwidth at physiological conditions supports the decisive role of the exciton coherence determining light absorption in bacterial light-harvesting antenna complexes.
在光合细菌的光捕获（LH）复合物中，细菌叶绿素分子的激子光谱的可变性确保了激发能量向反应中心的漏斗趋势。由于色素之间的共振相互作用导致激子光谱的形成，从而实现了能量的决定性转移。通过分析 LH2 复合物的稳态吸收光谱的温度依赖性，可以证明存在上 Davydov 子带（对应于 B850 环），从而可以通过分析稳态吸收光谱的温度依赖性来估计激子带宽。为此，应用自建模曲线分辨方法分析了来自光合细菌球形红杆菌（Rba.）和嗜酸红杆菌（Rbl.）的 LH2 复合物的吸收光谱的温度依赖性。从在室温下获得的激子带宽的直接估算值，可以估算出二聚体之间的共振相互作用值，结果表明，来自光合细菌 Rba. sphaeroides 和 Rhl. acidophilus 的 LH2 复合物的相互作用值分别为 385 和 397 cm(-1)。在 4 K 时，相应的耦合值略高（分别为 391 和 435 cm(-1)）。在生理条件下保留的激子带宽支持了决定细菌光捕获天线复合物中光吸收的激子相干性的决定性作用。
