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

例如，分子和离子的结构排列和运动决定了材料的整体性质或生物分子的功能。因此，为探测原子水平的结构和动力学而提供最先进的分析基础设施对于推动科学进步至关重要。固体核磁共振作为这样一种探头的威力正被越来越多的应用所证明，例如用于储氢和放射性废物封装的材料、药物配方以及与阿尔茨海默氏症等疾病相关的淀粉样斑块。固态核磁共振对特定原子核周围的局部化学结构(通常最多几个键长)最敏感，因此非常适合于表征许多缺乏周期性的重要系统，使其与成熟的衍射技术相辅相成。要扩大核磁共振的适用性，必须解决两个关键限制因素：敏感性，即，光谱峰值相对于噪声电平的相对强度，以及分辨率，即确定是否可以单独观察到两个接近的信号的各个峰值的线宽。通过在较高磁场下进行核磁共振实验，大大提高了灵敏度和分辨率，从而使在较低磁场下不可行的应用成为可能。因此，这项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850 MHz。不同核同位素的共振频率被很好地分开，从而使核磁共振谱特定于所选的特定同位素。在20特斯拉的核磁共振实验将尽可能多地利用元素周期表。一个特别的焦点将是那些由于其低自然丰度或低共振频率而难以处理的核--有许多重要的所谓低伽马核，例如25 mg、33S、39K、43Ca、47/49Ti，其共振频率为1H的10%。强磁场对于研究具有四极电矩，即电荷的非球形分布的超过三分之二的核磁共振活性同位素(即，具有非零自旋的)尤为重要。对于自旋为1/2的核，例如13C，常规应用的技术是围绕与磁场方向成54.7度的所谓幻角倾斜的轴物理旋转样品，产生较窄的共振峰。然而，对于许多半整数自旋的四极核，在幻角自旋实验中仍然存在剩余的展宽。这种剩余的四极展宽(在通常的核磁共振标度为ppm)与磁场的平方成反比；除了提高分辨率，信号强度的集中到更窄的线形中因此意味着对磁场强度的敏感性更高。氧是大多数有机和无机化合物的关键成分；然而，由于唯一具有核磁共振活性的同位素是四极核17O，其自然丰度仅为0.037%，因此很难用核磁共振进行研究。到目前为止，几乎所有的核磁共振研究都需要制备17O标记的样品(从富含17O的水开始)；非常令人兴奋的是，在20特斯拉的工作提供了在自然丰度下记录高分辨率17O谱的可能性。对一项强大技术的测试是它对广泛问题的适用性。高场固态核磁共振设备将使实验成为可能，通过对地质过程的新理解，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，到生命科学，例如淀粉样蛋白斑块、金属结合蛋白、骨结构、膜蛋白和酶。

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.