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二维电子光谱探测植物光系统 I 中的激发传递和俘获动力学。

Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy.

机构信息

Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore.

Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, 6726, Hungary.

出版信息

Photosynth Res. 2018 Mar;135(1-3):239-250. doi: 10.1007/s11120-017-0427-2. Epub 2017 Aug 14.

Abstract

Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon's energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet-singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3-4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67-75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits-a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3-4 ps component is ascribed to equilibration with a "red" core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.

摘要

光系统 I 是一种强大且高效的生物太阳能引擎。其将几乎每个被吸收光子的能量都用于光化学反应的能力,激发了人们对激发能转移和电荷分离动力学和机制的极大兴趣。在这项工作中,我们采用室温相干二维电子光谱和时间分辨荧光光谱来跟踪完整光系统 I 复合物以及从豌豆中分离出的核心复合物中的激子平衡和激发捕获。我们进行了二维电子光谱测量,使用低激发脉冲能量来记录不受单重态-单重态湮灭影响的激发态动力学。全局寿命分析确定了能量转移和捕获寿命与时间相关的单光子计数数据非常吻合。核心天线中的激子能量平衡发生在 0.5 ps 的时间尺度内。我们还观察到核心复合物中的光谱平衡组分,其在 700nm 处吸收的状态与大量 Chl 状态之间存在 3-4 ps 的寿命。核心复合物中的捕获发生在 20 ps 的寿命内,在超复合物中分裂为 16 ps 和 67-75 ps 的两个寿命。实验数据可以用两个替代模型进行建模,得到同样好的拟合——一个是从转移到捕获的受限模型,另一个是捕获受限模型。然而,如果将 3-4 ps 组分归因于与吸收在 700nm 的“红色”核心天线池的平衡,则只能采用前一个模型。相反,如果将这些低能量状态识别为 P 反应中心,则排除了从转移到捕获的模型,转而支持捕获受限模型。

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