Femtosecond visible transient absorption spectroscopy of chlorophyll- f -containing photosystem II
Femtosecond visible transient absorption spectroscopy of chlorophyll- f -containing photosystem II
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含叶绿素f光系统II的飞秒可见瞬态吸收光谱
DOI：
10.1073/pnas.2006016117
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Zamzam N
中科院分区：
文献类型：
--
作者：
Zamzam N
最近发现的含叶绿素f的远红光系统II（FR-PSII）支持远红光光合作用。光谱移动的远红色素的参与和动力学是直接可观察的，并与大量叶绿素a分离。我们提出了一个超快瞬态吸收FR-PSII的研究，调查能量转移和电荷分离过程。结果表明，叶绿素-f/d在亚皮秒级有快速的能量传递。这些数据表明，在皮秒到纳秒的时间尺度上，一个720 nm的负特征的衰减，与电荷分离，二次电子转移，和受激发射衰减相一致。由于形成阳离子自由基PD 1+·，导致chl-a吸收损失，导致675 nm漂白，仅在纳秒光谱中完全发展，表明异常延迟形成。在纳秒时间尺度上在725 nm处的一个主要光谱特征归因于反应中心颜料之间的FR-叶绿素的电致变色蓝移。这些时间分辨观测为Nürnberget等人的模型提供了直接的实验支持。[D. J. Nürnberget al.，Science 360，1210-1213（2018）]，其中初级电子供体是FR-叶绿素，次级供体是叶绿素-a（中心叶绿素对的PD 1）。使用长波长叶绿素-f/d的选择性激发也发生有效的电荷分离，并且激发态在P720* 上的定位指向与常规PSII相比更小的（熵）能量损失，其中激发态在所有的二氢卟酚颜料上共享。这对理解FR-PSII中激发能量转移和电荷分离反应的整体能量学具有重要影响。
The recently discovered, chlorophyll-f-containing, far-red photosystem II (FR-PSII) supports far-red light photosynthesis. Participation and kinetics of spectrally shifted far-red pigments are directly observable and separated from that of bulk chlorophyll-a. We present an ultrafast transient absorption study of FR-PSII, investigating energy transfer and charge separation processes. Results show a rapid subpicosecond energy transfer from chlorophyll-ato the long-wavelength chlorophylls-f/d. The data demonstrate the decay of an ∼720-nm negative feature on the picosecond-to-nanosecond timescales, coinciding with charge separation, secondary electron transfer, and stimulated emission decay. An ∼675-nm bleach attributed to the loss of chl-aabsorption due to the formation of a cation radical, PD1+•, is only fully developed in the nanosecond spectra, indicating an unusually delayed formation. A major spectral feature on the nanosecond timescale at 725 nm is attributed to an electrochromic blue shift of a FR-chlorophyll among the reaction center pigments. These time-resolved observations provide direct experimental support for the model of Nürnberget al.[D. J. Nürnberget al.,Science360, 1210–1213 (2018)], in which the primary electron donor is a FR-chlorophyll and the secondary donor is chlorophyll-a(PD1of the central chlorophyll pair). Efficient charge separation also occurs using selective excitation of long-wavelength chlorophylls-f/d, and the localization of the excited state on P720* points to a smaller (entropic) energy loss compared to conventional PSII, where the excited state is shared over all of the chlorin pigments. This has important repercussions on understanding the overall energetics of excitation energy transfer and charge separation reactions in FR-PSII.