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Towards molecular movies: exploring reaction dynamics using electron diffraction

迈向分子电影：利用电子衍射探索反应动力学

基本信息

批准号：
EP/I004122/1
负责人：
Derek Wann
金额：
$ 112.77万
依托单位：
University of Edinburgh
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FI004122%2F1
关键词：
Towards molecular movies exploring reaction

项目摘要

So much of our knowledge and understanding of the world around us comes from a consideration of the structures of molecules. But how do scientists know what is happening at a molecular or atomic level? Diffraction techniques can give us directly information such as the geometry that a molecule adopts, whether that geometry changes depending on the physical state of the substance, and what products are yielded when two or more molecules react. In the 20th century no fewer than 22 Nobel Prizes were awarded for work based around structural studies using X-ray and electron diffraction, leading to such important discoveries as the double-helix structure of DNA and the role of haemoglobin in the life cycle. In the 21st century the new goal is to understand the dynamics of chemical reactions. This requires us not just to observe structures before and after reactions have occurred, but also to gain a deeper knowledge of how and why reactions proceed in particular ways and, ultimately, to use this information to control reactions.The use of pump-probe experiments to study ultrafast events in chemistry, biology and materials science has already begun to revolutionise our understanding of chemical reactions. Such experiments use an intense laser beam to provide energy to molecules (the pumping), changing their fundamental structures, which are then observed (probed). Until now the emphasis has been on using lasers for both the pump and probe phases or, more recently, using X-ray diffraction to probe the structures. Diffraction methods yield transient structures of molecules directly, which is greatly preferable to inferring structural information from spectroscopy.My research takes this one step further and uses electron diffraction as a probe to study the structures of chemical species undergoing changes that occur on a variety of timescales. Electrons are particularly well suited to studying structures in the gas phase, where the lack of influence from neighbouring molecules (an issue with solid-state techniques) allows model systems to be studied. Electrons are efficient probes of molecular structure, with a high scattering cross section and a low proportion of inelastic scattering (which contains little or no structural information). Because electrons are charged they repel one another. This has consequences when very short pulses of electrons are required, and the theoretical limit of temporal resolution in a laboratory is 0.5 picoseconds. Experiments have been performed elsewhere and reported as femtosecond electron diffraction - this is misleading as the technology dictates that the picosecond limit remains. However, it is possible to break through this barrier using electrons with very high energies. Such electrons are routinely used in accelerator physics, where they are sped up until X-rays are emitted. I will ultimately harness these electrons to give pulses with a length of around 100 femtoseconds; when used in a diffraction experiment these electrons will allow the formation and breaking of chemical bonds to be observed.One area where I will use ultrafast electron-diffraction methods is in the study of hydrogen bonds, which are of utmost importance in chemistry and biology and are common in many molecular species such as water, DNA and proteins. Despite many years of work into the mechanisms of the formation and breaking of hydrogen bonds there are still many unanswered questions. A process related to hydrogen bonding, called fast proton transport, is believed to occur in many biological systems where energy is converted from one form to another. It has been proposed that, in systems with more than one hydrogen bond, fast proton transport follows set patterns. I will also work closely with synthetic chemists to ensure that I am studying the systems that really matter to chemists today, setting my work apart from others who are currently practicising ultrafast electron diffraction.

我们对周围世界的许多知识和理解都来自于对分子结构的考虑。但是科学家如何知道在分子或原子水平上发生了什么？衍射技术可以直接给我们提供信息，例如分子采用的几何形状，几何形状是否根据物质的物理状态而变化，以及当两个或多个分子反应时产生什么产物。在20世纪，不少于22项诺贝尔奖被授予了基于X射线和电子衍射结构研究的工作，导致了DNA的双螺旋结构和血红蛋白在生命周期中的作用等重要发现。世纪的新目标是了解化学反应的动力学。这就要求我们不仅要观察反应发生前后的结构，还要更深入地了解反应是如何以及为什么以特定的方式进行的，并最终利用这些信息来控制反应。在化学、生物学和材料科学中，利用泵浦探测实验来研究超快事件已经开始彻底改变我们对化学反应的理解。这些实验使用强激光束为分子提供能量（泵浦），改变它们的基本结构，然后观察（探测）。到目前为止，重点一直是使用激光器的泵浦和探测阶段，或最近，使用X射线衍射探测的结构。衍射方法直接产生分子的瞬态结构，这比从光谱学中推断结构信息要好得多。我的研究更进一步，使用电子衍射作为探针来研究在各种时间尺度上发生变化的化学物质的结构。电子特别适合于研究气相中的结构，其中缺乏邻近分子的影响（固态技术的一个问题）允许研究模型系统。电子是分子结构的有效探针，具有高散射截面和低比例的非弹性散射（包含很少或没有结构信息）。因为电子是带电的，所以它们互相排斥。当需要非常短的电子脉冲时，这会产生后果，实验室中时间分辨率的理论极限为0.5皮秒。实验已经在其他地方进行，并报告为飞秒电子衍射-这是误导，因为技术规定皮秒极限仍然存在。然而，有可能使用具有非常高能量的电子来突破这一屏障。这种电子通常用于加速器物理学，在那里它们被加速直到发射X射线。我最终将利用这些电子产生长度约为100飞秒的脉冲;当用于衍射实验时，这些电子将允许观察到化学键的形成和断裂。我将使用超快电子衍射方法的一个领域是氢键的研究，氢键在化学和生物学中至关重要，并且在许多分子物种如水中很常见，DNA和蛋白质。尽管人们对氢键的形成和断裂机制进行了多年的研究，但仍有许多问题没有得到解答。一个与氢键有关的过程，称为快速质子传输，被认为发生在许多生物系统中，其中能量从一种形式转化为另一种形式。有人提出，在具有一个以上氢键的系统中，快速质子传输遵循设定的模式。我还将与合成化学家密切合作，以确保我正在研究对今天的化学家来说真正重要的系统，将我的工作与目前正在实践超快电子衍射的其他人区分开来。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Conformational landscape of small organosilicon compounds from the combined use of gas electron diffraction, IR and Raman spectroscopies and quantum chemical calculations: diethyldichlorosilane

DOI：
10.1002/jrs.2549
发表时间：
2010-10
期刊：
Journal of Raman Spectroscopy
影响因子：
2.5
作者：
M. Montejo;D. Wann;P. G. R. Ortega;H. Robertson;F. Márquez;D. Rankin;J. J. L. González-J.
通讯作者：
M. Montejo;D. Wann;P. G. R. Ortega;H. Robertson;F. Márquez;D. Rankin;J. J. L. González-J.

Experimental and theoretical structure and vibrational analysis of ethyl trifluoroacetate, CF 3 CO 2 CH 2 CH 3

三氟乙酸乙酯CF 3 CO 2 CH 2 CH 3 的实验和理论结构及振动分析