New paradigms for NMR of organic solids

核磁共振 (NMR) 波谱是跨科学领域的重要分析工具。 NMR 最常应用于溶解在溶液中的物质，因为这大大简化了对所获得的结果（光谱）的解释；分子运动平衡了相互作用，例如磁核之间的偶极（通过空间磁力）相互作用。然而，在许多应用中，特别是在材料化学和生物学中，不可能或不适合将 NMR 应用于溶液中的样品，而有必要使用固体样品。这给使用氢 (1H) NMR 的研究带来了特别的困难，氢 (1H) NMR 是最广泛使用的 NMR 形式（包括在医学成像应用中）。典型的有机（含碳）分子含有高密度的氢核。尽管在 NMR 信号强度方面具有优势，但氢核之间的多重磁（偶极）相互作用会导致 NMR 信号快速衰减，并将 NMR 谱线拓宽为无信息的广泛特征。传统上可以通过多种方式解决这个问题。首先通过旋转样品（魔角旋转），但需要不可行的高旋转速率才能完全消除偶极相互作用。其次，使用射频辐射来平均偶极相互作用，但这在技术上可能很复杂，而且结果很容易受到实验缺陷的影响。由于谱线展宽涉及多个核自旋的相互作用，因此很难进行计算建模和数学研究。因此，改进固体 1H NMR 谱的进展相当不稳定。该项目将解决固态 NMR 发展的这一瓶颈。首先，通过组建一个由具有互补专业知识（实验、计算和理论）和设备（包括在全球一些最高磁场下运行的核磁共振波谱仪）的国际研究小组组成的联盟，我们将能够从不同的方向同时、系统地解决这个问题。其次，光谱仪硬件、模拟和核磁共振理论的最新进展意味着各个工具已经到位，可以取得协调一致的进展。最后，我们将关注一个参数，即磁化强度的衰减率，这是关键的限制因素。之前的工作已经解决了最终的核磁共振谱，但由于这些谱受到许多其他因素的影响，这往往会混淆根本问题。模拟与当前实验之间的巨大差异表明潜在的重大改进是可能的。寻找以常规方式产生高质量含氢有机固体核磁共振谱的途径将对固态核磁共振的实践产生重大影响。一些目前因耗时较长而不切实际的实验将变得实用，并且缩小核磁共振谱线将允许测量新的、更精细的光谱细节，例如连接晶体结构不同成分的氢键之间的弱相互作用。因此，这一提议得到了广泛科学家的支持，从固态 NMR 用户到药品制造商，再到 NMR 设备供应商。

Nuclear Magnetic Resonance (NMR) spectroscopy is a vital analytical tool across science. NMR is most usually applied to substances dissolved in solution since this considerably simplifies the interpretation of the results (spectra) that are obtained; molecular motion averages out interactions, such as the dipolar (through space magnetic) interaction between the magnetic nuclei. However, in many applications, particularly in materials chemistry and biology, it is impossible or inappropriate to apply NMR to samples in solutions and it is necessary to work with solid samples. This creates particular difficulties for studies using hydrogen (1H) NMR which is otherwise the most widely used form of NMR (including in medical imaging applications). Typical organic (carbon-containing) molecules contain high densities of hydrogen nuclei. Although an advantage in terms of the strength of the NMR signal, the multiple magnetic (dipolar) interactions between the hydrogen nuclei cause the NMR signal to decay quickly and broaden the NMR lines into uninformative broad features. This problem has traditionally been tackled in a couple of ways. Firstly by spinning the sample (magic-angle spinning), but unfeasibly high spinning rates would be required to completely remove the dipolar interactions. Secondly using radio-frequency irradiation to average out the dipolar interactions, but this can be technically complex and the results are very susceptible to experimental deficiencies. Since the line-broadening involves the interactions of multiple nuclear spins it has been difficult to model computationally and to investigate mathematically. As a result, progress in improving 1H NMR spectra in solids has been rather fitful.This project will tackle this bottle-neck for the development of solid-state NMR. Firstly by putting together a consortium of international research groups with complementary expertise (experimental, computational and theoretical) and equipment (including NMR spectrometers operating at some of the highest magnetic fields available worldwide) we will be able to tackle the problem simultaneously and systematically from different directions. Secondly, recent advances in spectrometer hardware, simulation and NMR theory mean that the individual tools are in place to make concerted progress. Finally we will be focussing on one parameter, the decay rate of the magnetisation, which is the key limiting factor. Previous work has addressed final NMR spectra, but since these are affected by a number of additional factors, this has tended to confuse the underlying issues. The large discrepancies between simulations and current experiments suggest that potentially major improvements are possible.Finding routes to producing high-quality NMR spectra of hydrogen-containing organic solids in a routine fashion will have a major impact on the practice of solid-state NMR. Some experiments which are currently impractical due to the length of time they would take will become practical and narrowing the NMR lines will allow new, finer spectral detail to be measured, such as weak interactions across hydrogen bonds connecting different components of crystal structures. As a result this proposal is being supported by a wide range of scientists, varying from users of solid-state NMR to manufacturers of pharmaceutics to suppliers of NMR equipment.