What is NMR Hyperpolarisation?

Nuclear Magnetic Resonance is an incredibly powerful analytical tool, but unlike many other forms of spectroscopy it is inherently insensitive. For example even in very powerful NMR spectrometers, the number of 1H nuclei that contribute to a signal is less than 1 in 104 or 105 – the rest of the nuclei cancel each other out to give no signal.

However, in a hyperpolarised sample all nuclei are detected at once, and the NMR signals can be thousands of times stronger than normal, and take only a few seconds to achieve the same signal which would otherwise take hours or even days of experiment time.

A sample can be hyperpolarised in a number of ways, but a simple method uses para-hydrogen – the singlet nuclear spin state of H2, and the lowest in energy.

Normal hydrogen gas is 25% p-H2 at room temperature (and 75% ortho-hydrogen). However the p-H2 fraction can increase when it is cooled along with a catalyst. At 77K (liquid nitrogen temperature) hydrogen gas is 50% p-H2, and at ~20K it is essentially 100% p-H2.

p-H2 by itself is invisible in an NMR experiment. But when it reacts with a molecule, the spin order is transferred, the molecule can become hyperpolarised, and a signal detected. In order to achieve this, a catalyst must both bind to p-H2, and have the correct properties to allow this transfer of spin order.

Precisely how this can occur depends on the catalyst, the target, and how we want hyperpolarisation to be transferred and measured.

Currently the focus of our research group is the development of a new range of catalysts with unique chemical reactivity which can improve binding to p-H2 and their ability to transfer hyperpolarised magnetisation to various molecules of interest in NMR spectroscopy.