NMR over nine orders of magnitude in the magnetic field

Nuclear magnetic resonance (NMR) is one of the most versatile forms of spectroscopy in the physical sciences, with applications spanning the full range from fundamental physics, quantum theory, chemistry, materials science and biochemistry to structural biology and clinical applications (especially in the form of magnetic resonance imaging, MRI). In most cases, NMR spectroscopy employs the strongest possible magnetic field, since this usually generates the strongest signals with high resolution of the different chemical sites of the atomic nuclei. Nevertheless, there are circumstances in which it is desirable to perform NMR over a range of magnetic fields, including the ultralow field regime, in which magnetic shielding is used to achieve very small magnetic fields over three orders of magnitude smaller than the earth's magnetic field. NMR in this ultralow field regime is very special in several ways. Firstly, the information content of the NMR spectrum is determined not by chemical shifts but by spin-spin couplings. Secondly, the line width in this regime is not governed by the magnetic field inhomogeneity, as in ordinary NMR, but by dissipation effects (relaxation). Extremely narrow linewidths (millihertz) are often achieved. Thirdly, the different species of nuclear spins are tightly coupled in the ultralow magnetic field regime, giving rise to the special phenomena such as heteronuclear long-lived states, which do not exist in larger magnetic fields. Fourthly, optical magnetometry techniques may be used to detect the magnetism of the nuclear spins, as opposed to electromagnetic induction, which is used in conventional NMR. The zero-to-ultralow field (ZULF) regime therefore offers a special form of NMR which has a quite different nature to ordinary NMR spectroscopy, and whose features and possibilities are only just starting to be explored. There is currently no equipment in the UK which allows observation of NMR signals in the ultralow magnetic field regime.

The proposed research involves the construction of a device which shuttles a sample in a rapid and highly controlled way between the high-field region of an ordinary NMR magnet and a magnetically shielded chamber, equipped with optical magnetometers for the detection of the NMR signal in the ZULF regime. This equipment will allow us to explore the spin dynamics in the ZULF regime with great precision and also exploit the ZULF regime as part of a high-field NMR procedure. This allows numerous multidimensional NMR experiments in which the advantages of both regimes may be combined. In addition the equipment allows the possibility to explore NMR relaxation over a very wide range of magnetic fields, allowing the probing of molecular motion over an extremely wide range of timescales. In addition the equipment will permit the development of advanced methodology for manipulating nuclear spin systems in the ZULF regime, such as the development of "ZULF decoupling" sequences which cause the system to behave as if spin-spin couplings between nuclei of different isotopic types are suppressed. This will make the ZULF NMR signals narrower, more informative, and easier to interpret.

The proposed equipment will be world-unique and will be made available to the UK scientific community as a research facility. A workshop and training course will be provided during the final stages of the research project in order to facilitate the transfer of knowledge on this special form of NMR to UK scientists.