DNP-Enhanced Solid-state NMR: New Sample Preparation Approaches and Applications

DNP 增强固态 NMR：新的样品制备方法和应用

• 批准号: EP/T016701/1
• 负责人: Jeremy Titman
• 金额: $ 61.31万
• 依托单位: University of Nottingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FT016701%2F1
• 关键词: DNP; Enhanced; Solid; state; NMR

Solid-state nuclear magnetic resonance (NMR) is a powerful technique for studying the molecular-level structure of complex and heterogeneous materials. However, even with the high magnetic fields available today, solid-state NMR suffers from low sensitivity, because of the small nuclear spin polarizations involved, so that long acquisitions or large samples are required. This problem is overwhelming for dilute species and limits the usefulness of NMR studies of e.g. surfaces, adsorbates or rare isotopes. Fortunately, weak NMR signals can be enhanced at low temperatures (~100 K) by dynamic nuclear polarisation (DNP) where the large electron spin polarisation from an implanted radical is transferred to nearby nuclei. Progress with high-power microwave sources has made DNP possible at the high fields found in modern NMR spectrometers (up to 21 T). Large signal enhancements up to 300-fold (at 9.4 T) have been achieved for frozen biomolecules, corresponding to a reduction by a factor of 100,000 in experiment time. DNP is therefore a transformative technology which will result in a significant increase in the sensitivity of solid-state NMR. The potential step-change in capability it offers will eventually allow the power of solid-state NMR to be brought to bear on many real-life materials for the first time. The information gained will inform progress in the design of new materials by research scientists and hence support the commercial development of new technologies by the industrial sector.However, despite the substantial signal gains obtained with DNP for the favourable cases described in the literature, reliability and reproducibility remain major issues, and in our experience some 50% of DNP-enhanced solid-state NMR studies of materials attempted at the Nottingham DNP MAS NMR Facility result in unworkably low enhancements (< ~5). One critical aspect of DNP is sample preparation (incorporation of the radical), with many factors currently requiring empirical optimization to maximize signal enhancement, and yet systematic studies are rarely carried out, mainly because DNP instrument time is limited. Surfaces, porous materials and nanoscale particulates are usually polarised after wetness impregnation of the free volume by a radical solution, and many factors (radical concentration, solvent volume, sample morphology etc.) require empirical optimization to maximize sensitivity. As a result, most DNP studies of materials rely on published protocols which often do not result in the expected signal enhancements. These issues of reliability and reproducibility within the context of sample preparation are a major obstacle to DNP ever achieving its full potential for the molecular-level characterization of materials.The proposed research aims to overcome these problems, in order to realise the potential impact of DNP, by developing new approaches to sample preparation. The research will make use of the state-of-the-art DNP-enhanced solid-state NMR instrumentation at the Nottingham DNP MAS NMR Facility (see Track Record) purchased with the aid of a £2.4M EPSRC Strategic Equipment grant. The main items of funding sought in this proposal comprise the access charges required to cover the use of the instrument and the salary costs for a postdoctoral researcher to carry out the programme. Success with these new approaches to sample preparation will make novel high-impact applications of DNP to materials possible. This aspect of the proposed research will inform progress in the design of new materials by our research collaborators from within Nottingham and support the commercial development of new technologies by our partners from the industrial sector.

固态核磁共振 (NMR) 是研究复杂和异质材料的分子级结构的强大技术，然而，即使在当今可用的高磁场下，固态 NMR 也因尺寸较小而灵敏度较低。涉及核自旋极化，因此需要长时间采集或大量样品，这对于稀物质来说是巨大的，并且限制了核磁共振研究的有用性，例如表面、吸附物或稀有同位素，幸运的是，弱核磁共振信号可以在通过动态核极化 (DNP) 实现低温（~100 K），其中来自注入自由基的大电子自旋极化转移到附近的原子核，高功率微波源的进步使得 DNP 在现代核磁共振波谱仪的高发现场中成为可能。 （高达 21 T），冷冻生物分子的信号增强高达 300 倍（9.4 T），相当于实验中信号强度降低了 100,000 倍。因此，DNP 是一项革命性技术，它将显着提高固态 NMR 的灵敏度，其提供的潜在能力最终将让固态 NMR 的力量发挥作用。首次使用真实材料获得的信息将为研究科学家在新材料设计方面取得进展提供信息，从而支持工业部门新技术的商业开发。然而，尽管 DNP 获得了巨大的信号增益。文献中描述的有利案例，可靠性和重现性仍然是主要问题，根据我们的经验，在诺丁汉 DNP MAS NMR 设施尝试进行的材料 DNP 增强固态 NMR 研究中，大约 50% 的结果增强效果低得不可行（<~5）。DNP 的一个关键方面是样品制备。 （激进的结合），目前许多因素需要经验优化以最大限度地增强信号，但系统的研究很少进行，主要是因为DNP仪器时间有限。颗粒物通常在自由基溶液对自由体积进行润湿后发生极化，并且许多因素（自由基浓度、溶剂体积、样品形态等）需要经验优化才能最大限度地提高灵敏度。因此，大多数材料的 DNP 研究依赖于已发表的材料。样品制备过程中的这些可靠性和再现性问题通常不会导致预期的信号增强，这是 DNP 充分发挥材料分子水平表征潜力的主要障碍。本研究旨在克服这些问题。这些问题，为了实现 DNP 的潜在影响，通过开发新的样品制备方法，该研究将利用诺丁汉 DNP MAS NMR 设施最先进的 DNP 增强型固态 NMR 仪器（参见 Track）。在 EPSRC 240 万英镑战略设备拨款的帮助下购买的记录） 本提案寻求的主要资助项目包括使用该仪器所需的使用费以及博士后研究员进行该研究的工资成本。这些新的样品制备方法的成功将使 DNP 在材料上的新颖高影响力应用成为可能，这方面的拟议研究将为我们诺丁汉内部的研究合作者在新材料设计方面取得进展提供信息，并支持商业开发。我们的工业部门合作伙伴提供的新技术。