Polli Dario, Cerullo Giulio, Lanzani Guglielmo, De Silvestri Sandro, Hashimoto Hideki, Cogdell Richard J
ULTRAS-INFM, Dipartimento di Fisica, Politecnico di Milano, Milan, Italy.
Biophys J. 2006 Apr 1;90(7):2486-97. doi: 10.1529/biophysj.105.069286. Epub 2006 Jan 20.
In this report, we present a study of carotenoid-bacteriochlorophyll energy transfer processes in two peripheral light-harvesting complexes (known as LH2) from purple bacteria. We use transient absorption spectroscopy with approximately 10 fs temporal resolution, which is necessary to observe the very fast energy relaxation processes. By comparing excited-state dynamics of the carotenoids in organic solvents and inside the LH2 complexes, it has been possible to directly evaluate their energy transfer efficiency to the bacteriochlorophylls. In the case of okenone in the LH2 complex from Chromatium purpuratum, we obtained an energy transfer efficiency of etaET2=63+/-2.5% from the optically active excited state (S2) and etaET1=61+/-2% from the optically dark state (S1); for rhodopin glucoside contained in the LH2 complex from Rhodopseudomonas acidophila these values become etaET2=49.5+/-3.5% and etaET1=5.1+/-1%. The measurements also enabled us to observe vibrational energy relaxation in the carotenoids' S1 state and real-time collective vibrational coherence initiated by the ultrashort pump pulses. Our results are important for understanding the dynamics of early events of photosynthesis and relating it to the structural arrangement of the chromophores.
在本报告中，我们展示了对来自紫色细菌的两种外周光捕获复合物（称为LH2）中类胡萝卜素 - 细菌叶绿素能量转移过程的研究。我们使用具有约10飞秒时间分辨率的瞬态吸收光谱，这对于观察非常快速的能量弛豫过程是必要的。通过比较类胡萝卜素在有机溶剂中和LH2复合物内部的激发态动力学，得以直接评估它们向细菌叶绿素的能量转移效率。对于来自深红红螺菌的LH2复合物中的奥克酮，我们从光学活性激发态（S2）获得的能量转移效率为ηET2 = 63±2.5%，从光学暗态（S1）获得的能量转移效率为ηET1 = 61±2%；对于嗜酸红假单胞菌的LH2复合物中含有的玫红视紫红质葡糖苷，这些值分别变为ηET2 = 49.5±3.5%和ηET1 = 5.1±1%。这些测量还使我们能够观察到类胡萝卜素S1态的振动能量弛豫以及由超短泵浦脉冲引发的实时集体振动相干性。我们的结果对于理解光合作用早期事件的动力学并将其与发色团的结构排列相关联具有重要意义。
