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The University of Southampton
MagRes@SotonResearch

Cryogenic NMR

Many interesting physical phenomena occur at very low temperatures, such as quantum rotation and superconductivity. NMR at cryogenic temperatures allows us to study them.

Water molecule trapped in a fullerene cage

The NMR signal originates from the interaction between a time-dependent magnetic field and nuclei with non-vanishing nuclear spin. NMR can be used to study molecular structure and dynamics with atomic resolution. Molecular motions are temperature dependent. By lowering the temperature, some motions are slowed down or even frozen, but many interesting motions involving light-weight molecules or molecular fragments, like CH3 groups, water molecules and hydrogen, persist even at very low temperature. These motions are very unhindered and fast, and they are often poorly described by classical physics. This makes it difficult to understand them in details at room temperature.

Solid state NMR spectra for static samples are often very broad and uninformative. Sample rotation (magic-angle spinning, MAS) provides resolution of unequivalent chemical sites, narrower and more intense signals. The MAS technique has been one of the major advances of the last 50 years and has contributed to the widespread of solid state NMR. Low temperature MAS NMR (cryoMAS) will broaden the range of potential NMR applications even further, due to a signal gain and to the capability to use much smaller samples. To date, most NMR studies at very low temperature have been performed on static samples due to technical limitations. The target of many of these studies are physical phenomena that typically occur only at low temperature. Important information are difficult to extract from static experiments on complicated molecular systems, due to both the lack of resolution and the averaging of some properties, with a loss of insight into the local molecular environments and the dynamics.

To date, there are only few examples in the world of instrumentation for MAS NMR at very low temperature (cryoMAS). In UK, a cryoMAS system is being developed uniquely at the University of Southampton. CryoMAS will open roads towards studies of many fundamental physical phenomena with details not available with other techniques. Our research interests focus on the physics of non classical, low temperature motions and their impact on NMR, using cryoMAS.

Our efforts in this area are focused on:

 

  1. developing new hardware to perform static and magic-angle-spinning experiments at cryogenic temperatures
  2. exploiting the technique to study spin isomerism, spin isomer conversion and quantised molecular motion in molecular endofullerenes
  3. exploiting the technique to study novel superconducting materials below their Curie temperature
  4. exploiting the technique as a way to enhance sensitivity in NMR studies of biosolids and proteins
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