Solid-State NMR at 850 MHz: A World-leading UK Facility to deliver Advances in Materials Science, Chemistry, Biology, Earth Science and Physics

正是分子和离子的结构排列和运动决定了，例如，材料的整体性质或生物分子的功能。因此，提供最先进的分析基础设施来探测原子级结构和动力学对于实现跨科学的进步至关重要。固态核磁共振（NMR）作为这种探针的能力越来越多地被应用于，例如，用于氢储存和放射性废物封装的材料、药物制剂以及与阿尔茨海默氏症等疾病相关的淀粉样斑块。固态NMR对特定核周围的局部化学结构（通常高达几个键长）最敏感，因此非常适合表征许多缺乏周期顺序的重要系统，使其成为成熟的衍射技术的补充。为了扩展NMR的适用性，必须解决两个关键限制因素：灵敏度，即，与噪声水平相比的谱峰的相对强度，以及分辨率，即，单个峰的线宽确定是否可以分别观察到两个靠近的信号。通过在高磁场下进行NMR实验，灵敏度和分辨率都得到了很大的提高，从而使在低磁场下不可行的应用成为可能。因此，该提议是在英国建立一个固态核磁共振设施，其磁场强度为世界领先的20特斯拉，相当于1H氢核的频率为850 MHz。不同核同位素的共振频率被很好地分离，使得NMR谱对于特定选择的同位素是特定的。20特斯拉的核磁共振实验将尽可能多地利用元素周期表。一个特别的重点将是核，这是困难的，由于其低天然丰度或低共振频率-有许多重要的所谓的低伽马核，例如，25 Mg，33 S，39 K，43 Ca，47/49 Ti，共振频率<1H的10%。高磁场对于研究超过三分之二的NMR活性同位素（即，具有非零自旋），其具有四极磁矩，即，电荷的非球形分布。对于自旋为1/2的原子核，例如，如图13 C所示，围绕与磁场方向成54.7度的所谓魔角倾斜的轴物理旋转样品的常规应用技术产生窄的共振峰。然而，对于许多具有半整数自旋的四极核，在魔角自旋实验中仍然存在残余加宽。这种残余的四极展宽（在通常的NMR标度ppm中）与磁场的平方成反比;以及提高分辨率，信号强度集中到更窄的线形中，因此意味着对磁场强度的更大灵敏度依赖性。氧是大多数有机和无机化合物的关键成分;然而，很难通过NMR进行研究，因为唯一的NMR活性同位素是四极核17 O，其天然丰度仅为0.037%。迄今为止，几乎所有的NMR研究都需要制备17 O标记的样品（从富含17 O的水开始）;非常令人兴奋的是，在20特斯拉下工作提供了在自然丰度下记录高分辨率17 O光谱的可能性。高场固态NMR设施将使实验成为可能，为跨科学的应用提供独特的信息，从催化材料，放射性废物封装，牙科植入物，电池，药物输送，通过获得对地质过程的新理解，到生命科学，例如，淀粉样斑块、金属结合蛋白、骨结构、膜蛋白、酶。

It is the structural arrangement and motion of molecules and ions that determine, e.g., the bulk properties of a material or the function of biomolecules. Therefore, the availability of state-of-the-art analytical infrastructure for probing atomic-level structure and dynamics is essential to enable advances across science. The power of solid-state Nuclear Magnetic Resonance (NMR) as such a probe is being increasingly demonstrated by applications to, e.g., materials for hydrogen storage and radioactive waste encapsulation, pharmaceutical formulations, and the amyloid plaques associated with diseases such as Alzheimer's. Solid-state NMR is most sensitive to the local chemical structure (usually up to a few bond lengths) around a particular nucleus and is thus well suited to characterising the many important systems that lack periodic order, making it complementary to well-established diffraction techniques.To extend the applicability of NMR, two key limiting factors must be addressed: sensitivity, i.e., the relative intensity of spectral peaks as compared to the noise level, and resolution, i.e., the linewidths of individual peaks that determine whether two close-together signals can be separately observed. Both sensitivity and resolution are much improved by performing NMR experiments at higher magnetic field, thus making possible applications that are not feasible at lower field. Hence, this proposal is to establish a UK facility for solid-state NMR at a world-leading magnetic field strength of 20 Tesla, corresponding to a frequency for the 1H hydrogen nucleus of 850 MHz. The resonant frequency of different nuclear isotopes are well separated such that an NMR spectrum is specific to a particular chosen isotope. NMR experiments at 20 Tesla will make use of as much of the Periodic Table as possible. A particular focus will be on nuclei which are difficult due to their low natural abundance or low resonance frequency - there are many important so-called low-gamma nuclei, e.g., 25Mg, 33S, 39K, 43Ca, 47/49Ti, with resonance frequencies < 10% of 1H. High magnetic field is especially important for the study of the over two thirds of NMR-active isotopes (i.e., with non-zero spin) that possess a quadrupolar electric moment, i.e., a non-spherical distribution of electric charge. For nuclei with spin 1/2, e.g., 13C, the routinely applied technique of physically rotating the sample around an axis inclined at the so-called magic angle of 54.7 degrees to the magnetic field direction yields narrow resonance peaks. However, for the many quadrupolar nuclei with half-integer spin, a residual broadening remains in the magic-angle spinning experiment. This residual quadrupolar broadening (in the usual NMR scale of ppm) is inversely proportional to the magnetic field squared; as well as improving resolution, the concentration of the signal intensity into a narrower lineshape hence means a still greater sensitivity dependence on the magnetic field strength. Oxygen is a key constituent of most organic and inorganic compounds; however, it is difficult to study by NMR since the only NMR-active isotope is the quadrupolar nucleus 17O, whose natural abundance is only 0.037 %. Nearly all NMR studies to date have required the preparation of 17O-labelled samples (starting with 17O-enriched water); very excitingly, working at 20 Tesla offers the possibility of recording high-resolution 17O spectra at natural abundance.A test of a powerful technique is its applicability to a wide range of problems. The high-field solid-state NMR facility will make possible experiments that provide unique information for applications across science, ranging from materials for catalysis, radioactive waste encapsulation, dental implants, batteries, drug delivery, through gaining new understanding of geological processes, to the life sciences, e.g., amyloid plaques, metal-binding proteins, bone structure, membrane proteins, enzymes.