Identifying the pathways of energy transfer between carotenoids and chlorophylls in LHCII and CP29. A multicolor, femtosecond pump-probe study
Identifying the pathways of energy transfer between carotenoids and chlorophylls in LHCII and CP29. A multicolor, femtosecond pump-probe study
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DOI：
10.1021/jp001752i
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发表时间：
2000-10-05
影响因子：
3.3
通讯作者：
van Amerongen, H
中科院分区：
文献类型：
--
作者：
Gradinaru, CC;van Stokkum, IHM;van Amerongen, H
利用选择性Car激发（489 nm和506 nm）和460 ~ 720 nm宽光谱范围内的诱导变化，研究了类胡萝卜素（Cars）向叶绿素（Chls）传递能量的飞秒瞬态吸收光谱和动力学信息。通过检查整个光谱带的演变，而不是查看几个单一的痕迹，我们能够识别参与能量流的物种（颜料和/或电子状态），以及单个过程的寿命和量子产率。因此，发现初始激发的Car - S-2状态衰减非常快，在CP29中的寿命为70-90 fs，在LHCII中的寿命为100 +/- 20 fs，通过两个相互竞争的通道：能量转移到Chls（60-65%）和内部转换到较低的光学禁止的S-1状态（35-40%）。在CP29中，能量受体仅为Chls a，而在LHCII中，仅对叶黄素和紫黄质有效。在后一种情况下，新黄质将能量主要转移到Chls b。在这两种配合物中，约15-20%的初始Car激发通过S-1能级转移到Chls a，时间常数约为1 ps，从而使总Car- chi转移效率达到约80%。考虑到该过程的产率以及传递时间与固有S-1寿命（类似于20 ps）之间的巨大差异，叶黄素似乎是唯一在该途径上活跃的物种。根据测量的传输速率，我们估计280-330 cm（-1）的耦合通过S-2路径驱动传输，而S-1传输的耦合值估计约为100 cm（-1）。Car - S-2态通过库仑机制与Chi的Q(x)和Q(y)态耦合；根据现有的结构信息，我们估计偶极子-偶极子的贡献为450-500 cm（-1）。S-1态通过交换和/或库仑机制耦合到Chi a Q(y)跃迁。
Spectral and kinetic information on energy transfer from carotenoids (Cars) to chlorophylls (Chls) within light-harvesting complex II (LHCII) and CP29 was obtained from femtosecond transient absorption study by using selective Car excitation (489 and 506 nm) and detecting the induced changes over a wide spectral interval (460-720 nm). By examining the evolution of entire spectral bands rather than looking at a few single traces, we were able to identify the species (pigments and/or electronic states) which participate in the energy flow, as well as the lifetimes and quantum yields of individual processes. Hence, it was found that the initially excited Car S-2 state decays very fast, with lifetimes of 70-90 fs in CP29 and 100 +/- 20 fs in LHCII, via two competing channels: energy transfer to Chls (60-65%) and internal conversion to the lower, optically forbidden S-1 state (35-40%). In CP29, the energy accepters are exclusively Chls a, while in LHCII, this is only valid for lutein and violaxanthin. In the latter case, neoxanthin transfers energy mostly to Chls b. In both complexes, ca. 15-20% of the initial Car excitations are transferred to Chls a via the S-1 level, with a time constant of around 1 ps, thus bringing the total Car-Chi transfer efficiency to ca. 80%. Given the yield of this process and the large difference between the transfer time and the intrinsic S-1 lifetime (similar to 20 ps), it seems that lutein is the only species active on this pathway. From the measured transfer rates, we estimated that a coupling of 280-330 cm(-1) drives the transfer via the S-2 route, while a coupling value of around 100 cm(-1) was estimated for the S-1 transfer. The Car S-2 state is coupled to both Q(x) and Q(y) states of the Chi through a Coulombic mechanism; from the available structural information, we estimated the dipole-dipole contribution to be 450-500 cm(-1). The S-1 state is coupled to the Chi a Q(y) transition via an exchange and/or a Coulombic mechanism.