Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, USA.
J Am Chem Soc. 2010 Mar 31;132(12):4214-29. doi: 10.1021/ja908510w.
We report low temperature (T) optical spectra of the isolated CP47 antenna complex from Photosystem II (PSII) with a low-T fluorescence emission maximum near 695 nm and not, as previously reported, at 690-693 nm. The latter emission is suggested to result from three distinct bands: a lowest-state emission band near 695 nm (labeled F1) originating from the lowest-energy excitonic state A1 of intact complexes (located near 693 nm and characterized by very weak oscillator strength) as well as emission peaks near 691 nm (FT1) and 685 nm (FT2) originating from subpopulations of partly destabilized complexes. The observation of the F1 emission is in excellent agreement with the 695 nm emission observed in intact PSII cores and thylakoid membranes. We argue that the band near 684 nm previously observed in singlet-minus-triplet spectra originates from a subpopulation of partially destabilized complexes with lowest-energy traps located near 684 nm in absorption (referred to as AT2) giving rise to FT2 emission. It is demonstrated that varying contributions from the F1, FT1, and FT2 emission bands led to different maxima of fluorescence spectra reported in the literature. The fluorescence spectra are consistent with the zero-phonon hole action spectra obtained in absorption mode, the profiles of the nonresonantly burned holes as a function of fluence, as well as the fluorescence line-narrowed spectra obtained for the Q(y) band. The lowest Q(y) state in absorption band (A1) is characterized by an electron-phonon coupling with the Huang-Rhys factor S of approximately 1 and an inhomogeneous width of approximately 180 cm(-1). The mean phonon frequency of the A1 band is 20 cm(-1). In contrast to previous observations, intact isolated CP47 reveals negligible contribution from the triplet-bottleneck hole, i.e., the AT2 trap. It has been shown that Chls in intact CP47 are connected via efficient excitation energy transfer to the A1 trap near 693 nm and that the position of the fluorescence maximum depends on the burn fluence. That is, the 695 nm fluorescence maximum shifts blue with increasing fluence, in agreement with nonresonant hole burned spectra. The above findings provide important constraints and parameters for future excitonic calculations, which in turn should offer new insight into the excitonic structure and composition of low-energy absorption traps.
我们报告了低温（T）下分离的 PSII CP47 天线复合物的光学光谱，其低温荧光发射最大值在 695nm 附近，而不是像以前报道的那样在 690-693nm 附近。后一种发射被认为是由三个不同的带组成的：一个最低能激子态 A1 的最低态发射带，位于 693nm 附近，其特征是非常弱的振子强度）以及位于部分不稳定复合物亚群的近 691nm（FT1）和 685nm（FT2）的发射峰。F1 发射的观察与完整 PSII 核心和类囊体膜中观察到的 695nm 发射非常吻合。我们认为，先前在单重态-三重态光谱中观察到的 684nm 附近的带源自最低能量陷阱位于吸收中的部分不稳定复合物的亚群，位于 684nm（称为 AT2），导致 FT2 发射。证明了 F1、FT1 和 FT2 发射带的不同贡献导致了文献中报道的荧光光谱的不同最大值。荧光光谱与吸收模式下获得的零声子空穴作用光谱、非共振烧孔的分布以及 Q（y）带的荧光线窄化光谱一致。吸收带中最低的 Q（y）态（A1）的特征是电子-声子耦合，其 Huang-Rhys 因子 S 约为 1，不均匀宽度约为 180cm（-1）。A1 带的平均声子频率为 20cm（-1）。与以前的观察结果相反，完整的分离 CP47 显示出来自三重态瓶颈孔（即 AT2 陷阱）的可忽略的贡献。已经表明，完整 CP47 中的 Chls 通过有效的激发能量转移连接到 693nm 附近的 A1 陷阱，并且荧光最大值的位置取决于燃烧的光强。也就是说，695nm 荧光最大值随光强的增加而蓝移，与非共振孔燃烧光谱一致。上述发现为未来的激子计算提供了重要的约束和参数，这反过来又应该为低能吸收陷阱的激子结构和组成提供新的见解。
