Electron paramagnetic resonance spectrometer for rapid scan, freeze quench and kinetic measurements

在我们跨学科的机械合成研究中，为控制生命系统中的氧化还原（电子转移）过程、仿生催化和化学能转换铺平了道路，几乎所有被研究的化合物及其催化或化学计量反应都是顺磁性的，或者分别涉及顺磁性物质的形成/衰变。因此，电子顺磁共振（EPR）作为一种直接和非侵入性技术的应用是表征感兴趣的化合物（具有氧化还原活性金属中心和/或配体的配合物和自由基物种，如超氧化物，一氧化氮，羟基自由基等）并阐明其转化机制的重要工具。特别是，当UV/Vis和NMR方法显示出其局限性时，它对于动力学研究，捕获/表征活性中间体和快速（催化）过程的实时监测至关重要，这通常是我们研究的涉及多组分顺磁性反应混合物（例如，当反应物，中间体和产物都是顺磁性的）和两个或多个平行运行的（催化）反应的过程中出现的情况。因此，我们的研究需要一种相当非常规的EPR设备，能够进行快速扫描（RS），冷冻淬火（FQ）和停流（SF）测量（RS/FQ/SF-EPR）。这种多功能，高性能的EPR仪器具有独特的快速混合和快速扫描测量能力，在LMU不存在，据我们所知，甚至在德国也不存在。为了实现我们的动力学/机械方法的目标，所需的EPR设备，除了标准的EPR测量（连续波，x波段模式）外，应能够满足以下要求：(i)在q波段微波下操作，（ii）利用液氦和液氮两种冷却系统，（iii）易于处理冻灭实验，以捕获和表征短寿命自由基中间体，（iv）与自制的介电环谐振器兼容，这是构建EPR停流设备所必需的。(v)使用rs谐振器在快速扫描模式下操作，对极短寿命自由基/顺磁性物质进行时间分辨测量；（vi）使用混合（流动）谐振器操作，研究生物介质中产生的短寿命自由基。这些仪器将允许EPR技术在不同领域的广泛应用（在我们的合作或服务测量中），并且对于我们正在进行和计划中的项目的进一步科学成就是不可或缺的，有助于开发高效的催化剂，氧化还原调节剂，治疗或诊断工具。它还将允许我们通过构建一个相当独特的快速扫描EPR止流装置来推动可能的EPR方法的界限，该装置具有改进的分辨率，目前将在生物无机化学和化学能转换领域中使用。

In our interdisciplinary mechanistic-synthetic research that paves the path for the control of redox (electron transfer) processes in living systems, biomimetic catalysis and chemical energy conversion, almost all investigated compounds and their catalytic or stoichiometric reactions are paramagnetic or implicate the formation/decay of paramagnetic species, respectively. Thus, the application of electron paramagnetic resonance (EPR) as a direct and non-invasive technique is an essential tool to characterise compounds of interest (complexes with redox-active metal centres and/or ligands and free radical species such as superoxide, nitric oxide, hydroxyl radical etc.) and clarify the mechanism of their transformation. In particular, it will be crucial for kinetic studies, trapping/characterizing of reactive intermediates and real-time monitoring of fast (catalytic) processes when UV/Vis and NMR methods exhibit their limitations, which is often the case in processes investigated by us that involve multicomponent paramagnetic reaction mixtures (e.g. when reactants, intermediates and products are all paramagnetic) and two or more parallel-running (catalytic) reactions. Thus, the nature or our research requires a rather unconventional EPR device capable of rapid scan (RS), freeze quench (FQ) and stopped-flow (SF) measurements (RS/FQ/SF-EPR). Such a multifunctional, high-performance EPR instrument with unique rapid-mixing and rapid-scan measurement capability does not exist at LMU and to best of our knowledge not even in Germany. For the objectives of our kinetic/mechanistic approaches, the required EPR device, apart from standard EPR measurements (CW, X-band mode), should be able to meet the following requirements: (i) to operate at Q-band microwaves, (ii) to utilise two cooling systems using liquid helium and liquid nitrogen, (iii) to easily handle freeze-quench experiments to catch and characterize short-lived radical intermediates, (iv) to be compatible with the home-built, dielectric ring resonator that is essential to construct the EPR stopped-flow equipment, (v) to operate in rapid-scan mode using the RS-resonator to carry out time-resolved measurements of very short-lived radical/paramagnetic species and (vi) to operate with a mixing (flow) resonator to study short-lived radicals generated in biological medium. Such instrumentation will allow broad application (within our collaborations or service measurements) of the EPR technique for interested groups in different fields and will be indispensable for further scientific achievements of our ongoing and planned projects, contributing to the development of efficient catalysts, redox-modulators, therapeutics or diagnostic tools. It will also allow us to push the boundaries of possible EPR methodology by constructing a rather unique rapid-scan EPR stopped-flow device of improved resolution that would currently be operative in the field of bioinorganic chemistry and chemical energy conversion.