The charge-transfer properties of the S2 state of fucoxanthin in solution and in fucoxanthin chlorophyll-a/c2 protein (FCP) based on stark spectroscopy and molecular-orbital theory.
The charge-transfer properties of the S2 state of fucoxanthin in solution and in fucoxanthin chlorophyll-a/c2 protein (FCP) based on stark spectroscopy and molecular-orbital theory.
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基于斯塔克光谱和分子轨道理论，研究了溶液中岩藻黄质和叶绿素-a/c2 蛋白 (FCP) 中岩藻黄质 S2 态的电荷转移特性。
DOI：
10.1021/jp802689p
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发表时间：
2008-09-18
期刊：
影响因子：
--
通讯作者：
van Grondelle R
中科院分区：
文献类型：
--
作者：
Premvardhan L;Sandberg DJ;Fey H;Birge RR;Büchel C;van Grondelle R
膜固有的光捕获复合物从硅藻小环藻，岩藻黄素叶绿素-a/c2蛋白（FCP），其特征在于斯塔克光谱，以获得一个定量测量的激发态偶极特性的组成色素。的类胡萝卜素岩藻黄质（FX），在FCP的主要光收割机，的电光特性，确定从斯塔克光谱测量的MeTHF玻璃（77 K）和比较的结果从电子结构计算。在Fx的光子吸收中，静态偶极矩的17 D变化（|Δμ⃗| exp），以及一个更大的|Δμ⃗| exp，测量S 0 → S2跃迁。偶极性质的显着变化表明，Fx经历光诱导电荷转移（CT），并强调了S2状态对Fx的极性依赖的激发态动力学的影响，到目前为止，这已被归因于S 0和S1/ICT状态，并讨论。MNDO-PSDCI和SACCI-CISD计算表明，类态本质上具有比类态小得多的偶极矩，这表明溶剂场促进了这两个态的混合，并解释了这里测量的S 0 → S2跃迁的大偶极矩。这些CT性质的类状态的Fx，这是进一步增强的蛋白质，支持其光合能力的光捕获和能量转移（ET）。在FCP中，Fx的CT特性根据能量位置而变化：在450和500 nm之间，似乎存在两组表现出|Δμ⃗| exp值的顺序为5和15 D，而最红的Fx，这是非常有效的ET叶绿素-a（Chl-a），表现出惊人的大|Δμ⃗| exp值约为40 D。如此巨大的|ΔΔμ⃗| exp的结果表明，增强库仑偶联可促进ET从S2态的Fx转化为Chl-a。这三组Fx，包括第四个红色Fx，通过使用Fx在MeTHF中的斯塔克光谱对FCP的斯塔克光谱建模来识别。与蛋白质中的Fx相比，FCP中Chl的静电性质相对小得多。对于Chl-a的Qy带，a| Δμ⃗| Ecp为0.92 D，极化率变化为20 Ω 3，表明Chl-a在性质上是单体的，并且彼此解耦。
The membrane-intrinsic light harvesting complex from the diatom Cyclotella meneghiniana, fucoxanthin chlorophyll-a/c2 protein (FCP), is characterized by Stark spectroscopy to obtain a quantitative measure of the excited-state dipolar properties of the constituent pigments. The electro-optical properties of the carotenoid fucoxanthin (Fx), the primary light harvester in FCP, were determined from the Stark spectrum measured in a MeTHF glass (77 K) and compared to the results from electronic-structure calculations. On photon absorption by Fx, a 17 D change in the static dipole moment (|Δμ⃗|exp), and a somewhat larger |Δμ⃗|exp at the red edge, are measured for the S0 → S2 transition. The significant change in dipolar properties demonstrates that Fx undergoes photoinduced charge transfer (CT), and underscores the influence of the S2 state on the polarity-dependent excited-state dynamics of Fx that has so far been attributed to, and discussed in terms of, the S0 and the S1/ICT states. MNDO-PSDCI and SACCI-CISD calculations indicate that the -like state intrinsically possesses a dipole moment much smaller than the -like state, suggesting that solvent fields promote the mixing of these two states and accounts for the large dipole moments measured here for the S0 → S2 transition. These CT properties of the -like state of Fx, which are further enhanced in the protein, underpin its photosynthetic capabilities for light harvesting and energy transfer (ET). In FCP, the CT properties of the Fx’s vary according to the energetic position: between 450 and 500 nm there appear to be two sets of Fx’s that exhibit |Δμ⃗|exp values on the order of 5 and 15 D, whereas the red-most Fx’s, that are very efficient in ET to chlorophyll-a (Chl-a), exhibit strikingly large |Δμ⃗|exp values on the order of 40 D. Such magnitudes of |ΔΔμ⃗|exp suggest a mechanism to enhance Coulombic coupling to promote ET from the S2 state of Fx to Chl-a. These three sets of Fx’s, including a fourth red Fx, are identified by modeling the Stark spectrum of FCP using the Stark spectrum of Fx in MeTHF. In contrast to the Fx’s in the protein, the electrostatic properties of the Chl’s in FCP are comparatively much smaller. For the Qy band of Chl-a, a |Δμ⃗|exp of 0.92 D and a change in polarizability of 20 Å3, indicate that the Chl-a’s are monomeric in nature and decoupled from each other.
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3.3
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