Meeting the Sensitivity Grand Challenges in Pulsed Electron Magnetic Resonance

本仪器开发项目旨在大幅提高电子顺磁共振（EPR）光谱仪的灵敏度、时间分辨率和能力，并在生物、化学、物理和材料科学领域展示其重大影响。支配物质基本结构和组织的基本量子力学规则之一是电子喜欢成对。然而，在许多材料中，这种配对过程留下了未配对的电子。这样的系统被称为顺磁性的，例子包括自由基、许多类型的金属原子和晶体中的缺陷。任何给定的未配对电子的反应性强烈地依赖于它的局部原子环境。一些自由基的反应性很强，它们能够从附近的任何分子中撕裂电子，并引发一系列破坏性的反应。事实上，尽管身体进化出了许多防御机制，但人们认为，正是这些自由基在体内累积的损害导致了我们的衰老过程。血液中自由基的测量可以作为健康指标。其他顺磁体可能相对稳定且非常有益。瞬态顺磁物质参与了大量生物过程中受到密切调控的反应。英国的大部分化学工业都依赖于使用自由基和过渡金属来引发和促进催化反应。晶体、薄膜或界面处的顺磁性缺陷可以决定或强烈影响材料的电子、磁性、光学、化学和机械性能，在英国的材料科学和电子工业中非常重要。通过使电子自旋与局部原子核相互作用，可以显著提高核磁共振或核磁共振实验的灵敏度。即使在没有自然发生的未配对电子的系统中，分子生物学家也已经开发出在生物分子内的特定位点常规添加自由基（电子）自旋标签的方法，这可以用作“分子间谍”，以了解反应，相互作用，大规模结构和快速动力学，其精度是其他技术无法实现的。这些结构和过程的特征可以巩固对疾病背后机制的理解和新药的开发。研究和理解这些系统最重要的工具是脉冲电子顺磁共振。该技术包括将顺磁样品置于大磁场中，并用精心控制的快速高功率微波脉冲序列照射样品，并监测样品的响应。直到最近，人们才普遍认为，脉冲EPR仪器的灵敏度几乎没有显著提高的余地。然而，十年前，我们证明了普通测量的浓度灵敏度显著提高了15到30倍。今天，商业工具几乎赶上了，但仍未赶上。这个项目现在寻求进一步提高灵敏度，再提高30倍。这一增长将通过利用快速电子技术的最新进展和使用我们已经在许多原理验证实验中展示的技术修改现有的最先进的系统来实现。这将是一个重大的进步，特别是对于分子生物学来说，因为它将首次允许使用电子磁共振在自然（细胞内）蛋白质浓度下研究自旋标记的蛋白质系统。还有许多重要的电子、材料和催化系统，都涉及薄膜或界面上的顺磁中心，其中灵敏度是至关重要的。为了最大限度地发挥仪器开发的影响，该项目与大量的应用和方法开发计划联系在一起，拥有广泛的当地合作者和共同研究者。

Summary This instrument development project seeks to substantially and dramatically increase the sensitivity and time resolution and capability of electron paramagnetic resonance (EPR) spectrometers and to demonstrate a major impact across biology, chemistry, physics and materials science. One of the fundamental quantum mechanical rules governing the basic structure and organisation of matter, is that electrons like to pair up. However, in many materials there are unpaired electrons left over from this pairing process. Such systems are known as paramagnetic and examples include radicals, many types of metal atoms, and defects in crystals. The reactivity of any given unpaired electron strongly depends on its local atomic environment. Some radicals are so reactive that they are able to tear electrons from any nearby molecules and initiate a destructive cascade of reactions. Indeed, it is the accumulated damage from such free radicals within the body that is believed to underlie our aging process, despite the body evolving many defense mechanisms. Measurements of free radicals in the blood can be health indicators. Other paramagnets can be relatively stable and highly beneficial. Transient paramagnetic species are involved in closely regulated reactions in huge numbers of biological processes. Much of the UK's chemical industry depends on the use of radicals and transition metals to initiate and promote catalytic reactions. Paramagnetic defects in crystals, thin films or at interfaces can determine or strongly affect a material's electronic, magnetic, optical, chemical and mechanical properties and are hugely important in the UK's material science and electronics industries. The sensitivity of NMR or MRI experiments can be dramatically increased by making electron spins interact with local nuclei.Even in systems where there are no naturally occurring unpaired electrons, molecular biologists have developed ways to routinely add free radical (electron) spin labels at specific sites within biomolecules, which can be used as "molecular spies" to understand reactions, interactions, large-scale structure and fast dynamics with a precision not possible with other techniques. Characterisation of such structures and processes can underpin the understanding of the mechanisms behind disease and the development of new drugs. The most important tool in studying and understanding these systems is pulsed electron paramagnetic resonance. This technique involves placing a paramagnetic sample in a large magnetic field and illuminating it with a carefully controlled sequence of rapid high power microwave pulses and monitoring the response of the sample. Until relatively recently, it was widely believed there was little scope to significantly improve the sensitivity of pulsed EPR instruments. Yet ten years ago we demonstrated a significant increase by a factor of between 15 and 30 in concentration sensitivity for common measurements. Today, commercial instruments have nearly but still not caught up. This project now seeks to further increase sensitivity, by another factor of 30. This increase will be achieved by taking advantage of recent advances in fast electronics and by modifying an existing state-of-the-art system using techniques that we have already demonstrated in many proof-of-principle experiments. This would be a major advance, particularly for molecular biology, as for the first time it would allow spin-labeled protein systems to be investigated at natural (in-cell) protein concentrations using electron magnetic resonance. There are also many important electronic, materials and catalytic systems, which involve paramagnetic centres in thin films or at interfaces where sensitivity is paramount.To maximise the impact of the instrument development, the project is linked to a large number of applications and methodology development programmes, with a wide range of local collaborators and co-investigators.