假根羽藻外周天线三聚体超快荧光动力学研究

Ultrafast Dynamics Study of Fluorescence in Trimeric Light-Harvesting Complex II of Bryopsis Corticulans

通过对稳态、瞬态吸收谱以及瞬态荧光发射谱的测量分析得出：在三聚体内存在以下六个特征叶绿素分子Chlb628、Chlb646、Chlb654、657、652、Chla666、664、Chla677、680、674、Chla683、682（下标为吸收峰，上标为发射峰）．在波长为655nm、666nm、680nm、683nm时分别采用时间相干单光子技术（TCSPC）记录其荧光动力学谱．根据荧光产生的物理学机制，对这些荧光动力学谱的分析采用的是分子同时接受能量与耗散能量的指数模型，得出在离体的外周天线三聚体内，Chlb654、657、652、Chla666、664、Chla677、680、674和Chla683、682分子在接受Chlb628分子的传能时，大部分经过了Chlb646分子，传能时间发生在97～157ps的时间间隔内，可见Chlb646分子在外周天线三聚体中是连接Chlb和Chla传能的主要分子；Chlb654，657，652…→Chla666 646…→Chla677,680,674…→Chla683,682分子依次传能的时间在10ps左右，这种传递过程可归结为是处于激发态分子首先经过内转换后再将能量以Foerster共振机制的形式传给了其它分子；大量小于1ps的传能过程是叶绿素分子之间以激子共振的方式进行直接传能；Chlb654,657,652、Chla666,664、Chla667,680,674和Chla683,682分子以时间常量分别为1．44ns，1．43ns，636ps，713ps发射荧光回到基态．

An ultrafast dynamics study of fluorescence in LHC Ⅱ on energy transfer among chlorophyll in a trimeric unit of major light-harvesting complex （LHC Ⅱ ） from bryopsis corriculan were conducted by technique of Time Correlated Single Photon Counting （ TCSPC ） . Six characteristic molecules marked as Chlb628、Chlb646、Chlb654、657、652、Chla666、664、Chla677、680、674、Chla683、682 were discriminated in the chlorophyll Q region of LHC Ⅱ by transient absorption spectrum and fluorescence emission spectrum. According to the principle of fluorescence kinetics, these kinetics data recorded by TCSPC were analyzed with a multi-exponential model. Time constants on energy transfer and decay of excitations were obtained as： Overwhelming parts of the energy transfer among chlorophylls under a long process than 97 ps：Chl b628…→ Chl b646 …→ Chl b54,657,652 （149 ps）,Chl b628…→ Chl b646…→ Chl 666,664（157 ps）,Chl b628…→ Chl b646 …→ Chl 677,680,674 （103 ps） and Chl b628…→ Chl b646…→ Chla683,682 （97 ps） which denotes that Chl b636 is the main moleculars that transfer energy from Chlbs to Chlas. Some slower process of energy transfer such as Chl b654,657,652…→ 14.5ps Chla682,683, Chla664,666 Chl a682,683, Chl a674,677,680…→ 9.3ps Chl a683,682 were also obtained. The pathway can be described as that the excited Chls goes through internal conversion before transferring energy to another Chls. Although with higher standard deviation, time constants in femtosecond level can be attributed to the process of directly energy transfer, such as C628→ C654,657,652,C628→C666,664,→C677,680,674,C628→C683,682,C654,657,652,→C666,664,C628→C654,657,652→C666,664,C628→C654,657,652→C677,680,674, Owing to the arrangement and direction of dipole moment of Chls in LHC Ⅱ, the probability of these 683 processes is different. The fluorescence lifetimes of Chl b654,657,652 , Chl a664,666, Chl a674,677,680 and Chl a682 were determined to be 1.44 ns, 1.43 ns,636 ps,713 ps respectively. The percentages of energy dissipation in the pathway of fluorescence emission are no more than 40% in the trimeric unit of LHC Ⅱ.