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. The technique of Nuclear Magnetic Resonance (NMR) spectroscopy is very sensitive to the local chemical structure around a particular nucleus, making it a powerful probe of such atomic-level structure and dynamics.
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; this proposal is to provide UK researchers with new NMR capability at a world-leading magnetic field strength of 28.2 T, corresponding to a frequency for the 1H nucleus of 1.2 GHz. This builds on the very successful and well-established UK High-Field Solid-State NMR NRF with sustainable ongoing and future operation based on the key factors that have enabled the success of the existing Facility: dedicated Facility Manager support and genuine nationwide buy-in achieved through oversight by a national executive and an independent time allocation procedure.
NMR experiments at 28.2 T will make use of as much of the Periodic Table as possible. Nuclei are classified according to their so-called spin quantum number, I. Solution-state NMR on samples is most frequently applied to nuclei with I = 1/2 including such crucial isotopes as 1H, 13C and 15N with correlations between these nuclei traditionally detected on 1H for optimum sensitivity. More recently experiments detected on nuclei other than 1H, especially 13C and 15N, have gained in popularity because of the high resolution achievable for important systems such as intrinsically disordered proteins and large biomolecules including complexes. High field solution NMR is particularly beneficial for biomolecular applications, e.g. characterisation of structures, dynamics and interactions of systems implicated in diseases, but also small molecules, especially for resolving complex mixtures. To maximise the available sensitivity so called cryoprobes, where appropriate parts are kept very cold, are used.
In solid-state NMR, the experiment is usually performed by physically rotating the sample around an axis inclined at the so-called magic angle of 54.7 degrees to the magnetic field. For the two most important I = 1/2 nuclei, 1H and 13C, 1.2 GHz will much benefit so-called inverse (i.e., 1H) detection experiments, e.g., for pharmaceuticals and protein complexes, as well as 13C-13C correlation experiments, e.g., for investigating structure and dynamics in plant cell walls. High magnetic field is particularly important for the study of the over two thirds of NMR-active isotopes that possess an electric quadrupole moment, i.e., a non-spherical distribution of electric charge (I of 1 and above). The residual broadening (in the usual NMR scale of ppm) that remains in the magic-angle spinning experiment is inversely proportional to the magnetic field squared; as well as improving resolution, the concentration of the signal intensity into a narrower lineshape means a still greater sensitivity dependence on the magnetic field strength. Application examples include 14N and 35Cl for pharmaceuticals, and 25Mg, 71Ga and 91Zr in materials science.
A test of a powerful technique is its applicability to a wide range of problems. The new 1.2 GHz ultra-high magnetic field NMR facility will make possible experiments that provide unique information for applications across science, ranging from materials for catalysis and light harvesting, batteries, drug delivery, to the life sciences, e.g., plant cell walls, protein complexes, membrane proteins and bone structure.
|