Structural dynamics and photoinduced electron transfer

我们的生命与光密切相关：视觉为我们提供周围世界的信息，而光合作用为我们提供食物，以及数百万年来以化石燃料形式储存的能量。光合作用利用太阳光驱动的蛋白质中的电子流，许多研究人员正试图复制它，并在人工系统中从丰富的清洁来源中生产燃料。电子转移也是许多酶反应和呼吸作用的基础。电子通过芳香族氨基酸（色氨酸、酪氨酸）链的顺序转移最近被认为在酶中起保护作用，酶使用分子氧氧化我们体内的有机化合物。化学反应，包括电子转移，经常用静态分子或蛋白质结构来解释。然而，生命和化学是高度动态的;分子及其环境永远在运动。事实上，理查德·费曼（Richard Feynman）曾写道：“一切有生命的东西都可以用原子的抖动和摆动来理解。”在我们的工作中，我们将集中在这方面，并试图了解结构波动和电子转移之间的关系。我们将研究带有光活性基团的蛋白质，这些光活性基团能够在可见光或紫外光照射下诱导电子转移穿过蛋白质。我们将测量这种光活性组件和周围的水分子如何随时间波动，并将这些结构动态与光触发电子转移的速率，产率和方向性联系起来。在几种蛋白质系统中，我们还将研究具有几个芳香族氨基酸基团的蛋白质（天青蛋白），这些氨基酸基团本身可以进行电子转移，而它们的相互距离和方向随时间波动。这些研究将告诉我们如何设计光催化系统，用于人工光合作用，以产生燃料或特殊化学品，就像绿色植物一样。特别是，将芳香族氨基酸链引入蛋白质中，可以大大加速电子在所需方向上的转移，时间分辨振动光谱方法非常适合于这种动力学研究。报告分子振动运动的红外或拉曼光谱是在用短激光脉冲照射后作为时间的函数测量的，所述短激光脉冲触发结构弛豫和电子转移。光谱特征的位移和强度变化，以及新特征的出现，将同时揭示结构变化和电子转移过程的性质和速率。复杂的数据分析和理论计算将能够解释实验结果，并建立一个统一的相互关联的电子转移和结构动力学的机制图片。英国在牛津郡的卢瑟福阿普尔顿实验室运营着时间分辨振动光谱领域的世界领先设施，为在最高实验水平上开展拟议的研究提供了独特的机会。

Our life closely depends on light: vision provides us with information on the world around us while photosynthesis supplies us with food, as well as energy that was deposited over millions of years in fossil fuels. Photosynthesis employs a flow of electrons through proteins driven by sunlight and many researchers are trying to replicate it and produce fuels from abundant clean sources in artificial systems. Electron transfer also underlies many enzymatic reactions as well as respiration. Sequential transfer of electrons through chains of aromatic amino acids (tryptophan, tyrosine) was recently suggested to play a protective role in enzymes that use molecular oxygen to oxidize organic compounds in our bodies.Chemical reactions, including electron transfer, are too often explained in terms of static molecular or protein structures. However, life and chemistry are highly dynamic; molecules as well as their environment are perpetually in motion. Indeed, Richard Feynman famously wrote "everything that is living can be understood in terms of the jiggling and wiggling of atoms". In our work, we will focus on this aspect and try to understand the relation between structural fluctuations and electron transfer. We will study proteins bearing photoactive groups that are capable of inducing transfer of electrons across the protein upon irradiation with visible or ultraviolet light. We will measure how such photoactive assemblies and surrounding water molecules fluctuate in time and relate these structural dynamics with the rates, yields, and directionality of phototriggered electron transfer. Among several protein systems, we will also study proteins (azurins) with several aromatic amino acid groups that can themselves undergo electron transfer, while their mutual distance and orientation fluctuate in time. These investigations will tell us how to design photocatalytic systems for artificial photosynthesis to generate fuels or specialty chemicals, as green plants do. In particular, engineering aromatic amino acid chains into proteins is a promising way to strongly accelerate electron transfer in the desired direction.Time resolved vibrational spectroscopy methods are perfectly suited for such dynamics studies. Infrared or Raman spectra, which report on molecular vibrational motions, are measured as a function of time after irradiation with short laser pulses of light that trigger both structural relaxation and electron transfer. Shifts and intensity changes of spectral features, together with the emergence of new ones, will simultaneously reveal the nature and rates of structural changes and electron transfer processes. Sophisticated data analysis and theoretical calculations will enable interpretation of experimental results and building up a unifying mechanistic picture of interrelated electron transfer and structural dynamics. UK operates a world leading facility in the field of time resolved vibrational spectroscopy at the Rutherford Appleton Laboratory in Oxfordshire, providing a unique opportunity to carry out the proposed research at the highest experimental level.