Visualizing ultrafast chemical dynamics with X-rays
Visualizing ultrafast chemical dynamics with X-rays
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用 X 射线可视化超快化学动力学
DOI：
10.1073/pnas.2017806117
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Sension, Roseanne J.
中科院分区：
文献类型：
--
作者：
Sension, Roseanne J.
我们生活在一个沐浴在阳光下的世界。光驱动光合作用，并对氧气环境负责，氧气环境使地球上发现的生命多样化。光化学提供了一种方法，通过电荷的运动、分子形状的改变或键的断裂来利用光能发挥生产功能。光化学也能裂解DNA并产生破坏性的自由基。光化学过程--无论是被利用的还是破坏性的--都是不可避免的。光谱的紫外-可见光和红外区的超快瞬变光谱使人们能够详细探测和描述在广泛的时间尺度上发生的许多光化学过程。然而，这些探针只能间接地洞察光化学转化的电子和结构动力学。X射线自由电子激光(XFELs)和桌面高次谐源的发展现在提供了直接询问在最快的化学时间尺度上发生的电子和结构变化所需的工具。这些测量提供了对光化学的洞察，但也更广泛地了解了化学中电子和核自由度的耦合。在从阿秒到秒的时间尺度上，以电子和原子分辨率可视化化学反应是可能的。在PNAS中，Bacella等人(1)结合了飞秒X射线吸收(XAS)和X射线发射(XES)光谱来解决血红素蛋白质光物理中的一个悬而未决的问题：光激发的铁血红素的衰变是否涉及一系列以铁为中心的自旋态，或者它的特征更简单地表现为亚皮秒内到基态的转换(2-5)？这个问题是由巴卡勒等人提出的。在室温的蛋白质样品上，以中等浓度、超快的时间分辨率，并利用X射线对电子和结构动力学的敏感性。Fe K边XES探测被激发金属中心的2p→1s(Kα)和3p→1s(Kβ)跃迁，对氧化和自旋态很敏感。与许多人的预期相反，时间分辨的XES数据表明，在铁的细胞色素c(Cytc)中，自旋级联在基态恢复之前产生低能量的高自旋金属中心铁态(MC)。这个态的时间尺度为650ps，寿命为∼10ps，与Fe(III)四苯基卟啉氯化物(3)的紫外可见瞬时吸收研究中观察到的结果相似。铁K边X射线吸收近边结构(XANES)的变化允许识别与自旋级联耦合的穹顶运动，从而深入了解一类重要的血红素蛋白的结构与功能关系。穹顶现在与广泛的血红素蛋白质有关，通常涉及能量低到足以热接触的状态，因此有可能在各种不同的条件下影响功能。这是最近发表的一系列研究中的最新研究，证明了超快X射线光谱分析在化学上的潜力。Wernet(6)给出了一个很好的概述，目前到2018年年中，但这是一个快速发展的领域，不断有新的发展。K-EDGE XES提供了一个敏感的探针，可以探测过渡金属的元素特定的电子构型和自旋态，就像巴卡勒等人所利用的那样。在他们对细胞色素c(1)的研究中。昆努斯和他的同事(7，8)已经证明，通过电子和核动力学的耦合，它也可以对给定电子态的结构变化敏感。在时间分辨K-α和K-β-XES-…中观察到明显的相干振荡
We live in a world bathed in light. Light drives photosynthesis and is responsible for the oxygen environment that enables the diversity of life found on our planet. Photochemistry provides the means to harness light energy for productive function through the movement of charge, a change in molecular shape, or the cleavage of a bond. Photochemistry also cleaves DNA and produces damaging free radicals. Photochemical processes—both harnessed and destructive—are unavoidable. Ultrafast transient spectroscopies in the UV-visible and infrared regions of the spectrum have allowed the detailed probing and characterization of many photochemical processes occurring on a wide range of timescales. These probes, however, provide only indirect insight into the electronic and structural dynamics of photochemical transformations. The development of X-ray free electron lasers (XFELs) and tabletop high harmonic sources have now provided the tools required to interrogate directly the electronic and structural changes that take place on the very fastest timescales of chemistry. These measurements provide insight into photochemistry, but also more generally into the coupling of electronic and nuclear degrees of freedom in chemistry. It is becoming possible to visualize chemical reactions with both electronic and atomic resolution on timescales from attoseconds to seconds. In PNAS, Bacellar et al.(1) combine femtosecond X-ray absorption (XAS) and X-ray emission (XES) spectroscopies to address an outstanding question in heme protein photophysics: Does the decay of photoexcited ferric heme involve a cascade of ironcentered spin states or is it characterized more simply by subpicosecond internal conversion to the ground state (2–5)? This question is addressed by Bacellar et al. on a room temperature protein sample, at modest concentration, with ultrafast time resolution, and exploiting the sensitivity of X-rays to both electronic and structural dynamics. Fe K-edge XES probes the 2p→ 1s (Kα) and 3p→ 1s (Kβ) transitions of the excited metal center and is sensitive to oxidation and spin state. The time-resolved XES data, contrary to the expectations of many, suggest that in ferric cytochrome c (cyt c), a spin cascade produces a low-energy high-spin metal-centered iron state (MC) prior to ground state recovery. This state is populated on a timescale of 650 fs and has a lifetime of∼ 10 ps, similar to that observed in UV-visible transient absorption studies of Fe (III) tetraphenylporphyrin chloride (3). Changes in the Fe K-edge X-ray absorption near edge structure (XANES) permit the identification of a doming motion coupled to the spin cascade, providing insight into the structure–function relationship in an important class of heme proteins. Doming has now been implicated in a wide range of heme proteins, often involving states at energies low enough to be thermally accessible and thus with the potential to influence function under a variety of different conditions.This is the latest in a series of recently published studies demonstrating the potential of ultrafast X-ray spectroscopies in chemistry. A nice overview, current through mid-2018, is given by Wernet (6), but this is a rapidly evolving field with continuing new developments. K-edge XES provides a sensitive probe of the element-specific electronic configuration and spin state of transition metals as exploited by Bacellar et al. in their study of cyt c (1). Kunnus and coworkers (7, 8) have demonstrated that it can also be sensitive to structural changes in a given electronic state through the coupling of electronic and nuclear dynamics. Pronounced coherent oscillations were observed in the time-resolved Kα and Kβ XES …
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正铁肌红蛋白超快血红素弛豫中自旋态的级联。
DOI：
10.1063/1.4861467
发表时间：
2014
期刊：
The Journal of chemical physics
影响因子：
--
作者：
C. Consani;G. Auböck;O. Bräm;F. van Mourik;M. Chergui
通讯作者：
M. Chergui
影响因子：
16.6
作者：
Katayama, Tetsuo;Northey, Thomas;Penfold, Thomas J.
通讯作者：
Penfold, Thomas J.
核对核 X 射线发射光谱对结构动力学敏感性的起源
DOI：
10.1063/4.0000022
发表时间：
2020
期刊：
Structural Dynamics
影响因子：
--
作者：
M. Vacher;K. Kunnus;Mickaël G. Delcey;K. Gaffney;M. Lundberg
通讯作者：
M. Lundberg
飞秒 X 射线光谱的化学相互作用和动力学以及 X 射线自由电子激光器的作用
DOI：
10.1098/rsta.2017.0464
发表时间：
2019
期刊：
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
影响因子：
--
作者：
P. Wernet
通讯作者：
P. Wernet
三价铁血红素中的自旋级联和隆起：飞秒 X 射线吸收和 X 射线发射研究
DOI：
10.1073/pnas.2009490117
发表时间：
2020
影响因子：
11.1
作者：
C. Bacellar;D. Kinschel;G. Mancini;R. Ingle;J. Rouxel;O. Cannelli;C. Cirelli;G. Knopp;J. Szlachetko;F. Lima;S. Menzi;G. Pamfilidis;K. Kubicek;D. Khakhulin;W. Gawelda;A. Rodriguez;M. Biednov;C. Bressler;C. Arrell;Philip J. M. Johnson;C. Milne;M. Chergui
通讯作者：
M. Chergui