Pure Shift Proton NMR: A Resolution of the Resolution Problem?

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Proton (hydrogen) nuclear magnetic resonance (NMR) spectroscopy is the single tool most widely used by chemists for determining the molecular structures of unknown compounds. It is a wonderfully versatile and sensitive tool, but it has a major drawback: it struggles to separate the signals from the different hydrogen atoms in a molecule, because each atom typically gives rise to multiple signals. This multiplicity of signals arises because of the magnetic interactions between hydrogen nuclei, and it typically leads to spectra being about ten times more crowded than would be the case if these interactions could be switched off. Unfortunately, while such a broadband decoupling is routine where interactions between different types of atom (e.g. hydrogen and carbon) are involved, there is no general way of achieving it for interactions between atoms of the same type. What we have recently shown, however, is that by suitable choice of experimental methods we can in many cases reverse the effects of interactions, allowing us to measure pure shift spectra in which a single signal is seen for each hydrogen atom in a molecule. The simplicity such techniques offer means that we should be able to resolve the signals of individual atoms in much larger species, or in much more complex mixtures, than is currently the case. At the moment the only way to resolve signals better is to spread them out by using a higher magnetic field, but progress in building better magnets is agonisingly slow - over the last 30 years the highest field available has increased on average by just a few per cent each year. With pure shift methods we should be able to get almost a tenfold improvement in the space of a few years. In this project, a postdoctoral research fellow and a postgraduate student will investigate turning our initial proof of principle into practical tools. If they are successful, these tools will end up being used by chemists, biochemists and other scientists all over the world.