Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, USA.
Istituto di Biologia e Biotecnologia Agraria, C.N.R., Via Bassini 15, 20133 Milano, Italy.
J Chem Phys. 2021 Feb 28;154(8):085101. doi: 10.1063/5.0038217.
To provide more insight into the excitonic structure and exciton lifetimes of the wild type (WT) CP29 complex of photosystem II, we measured high-resolution (low temperature) absorption, emission, and hole burned spectra for the A2 and B3 mutants, which lack chlorophylls a612 and b614 (Chls), respectively. Experimental and modeling results obtained for the WT CP29 and A2/B3 mutants provide new insight on the mutation-induced changes at the molecular level and shed more light on energy transfer dynamics. Simulations of the A2 and B3 optical spectra, using the second-order non-Markovian theory, and comparison with improved fits of WT CP29 optical spectra provide more insight into their excitonic structure, mutation induced changes, and frequency-dependent distributions of exciton lifetimes (T). A new Hamiltonian obtained for WT CP29 reveals that deletion of Chls a612 or b614 induces changes in the site energies of all remaining Chls. Hamiltonians obtained for A2 and B3 mutants are discussed in the context of the energy landscape of chlorophylls, excitonic structure, and transfer kinetics. Our data suggest that the lowest exciton states in A2 and B3 mutants are contributed by a611(57%), a610(17%), a615(15%) and a615(58%), a611(20%), a612(15%) Chls, respectively, although other compositions of lowest energy states are also discussed. Finally, we argue that the calculated exciton decay times are consistent with both the hole-burning and recent transient absorption measurements. Wavelength-dependent T distributions offer more insight into the interpretation of kinetic traces commonly described by discrete exponentials in global analysis/global fitting of transient absorption experiments.
为了更深入地了解光系统 II 野生型 (WT) CP29 复合物的激子结构和激子寿命，我们测量了 A2 和 B3 突变体的高分辨率（低温）吸收、发射和空穴烧蚀光谱，这两种突变体分别缺乏叶绿素 a612 和 b614 (Chls)。对于 WT CP29 和 A2/B3 突变体的实验和建模结果提供了分子水平上突变诱导变化的新见解，并进一步揭示了能量转移动力学。使用二阶非马尔可夫理论模拟 A2 和 B3 的光学光谱，并与 WT CP29 光学光谱的改进拟合进行比较，这为它们的激子结构、突变诱导的变化以及激子寿命（T）的频率相关分布提供了更多的见解。为 WT CP29 获得的新哈密顿量表明，Chls a612 或 b614 的缺失会引起所有剩余 Chls 的位点能量发生变化。讨论了 A2 和 B3 突变体的哈密顿量，内容涉及叶绿素的能量景观、激子结构和转移动力学。我们的数据表明，A2 和 B3 突变体中的最低激子态分别由 a611(57%)、a610(17%)、a615(15%)和 a615(58%)、a611(20%)、a612(15%) Chls 贡献，尽管也讨论了其他能量最低态的组成。最后，我们认为计算出的激子衰减时间与空穴烧蚀和最近的瞬态吸收测量结果一致。波长依赖性 T 分布为解释动力学轨迹提供了更多的见解，这些动力学轨迹通常在瞬态吸收实验的全局分析/全局拟合中用离散指数来描述。
