Clearing the undergrowth: new NMR techniques for high dynamic range mixtures

Nuclear magnetic resonance (NMR) spectroscopy is one of the most useful methods for studying the structures and behaviours of molecules, and of critical importance both in understanding the world around us and in developing new technologies. It is a particularly powerful tool for determining the chemical structures of pure compounds. However, Nature is more complicated, and some of the most interesting scientific challenges present themselves as complex mixtures. These often have very crowded NMR spectra, due to the presence of many species with many different concentrations, and the spectra are therefore very difficult (sometimes impossible) to interpret. Chemists and life scientists fight a continual battle to extract qualitative and quantitative information from the multiple overlapping signals that are found in most NMR spectra of complex mixtures. New NMR methods are urgently needed to allow us to address a wider range of scientific problems, and to reduce the time and effort needed to extract chemical and biological information from mixtures.

This proposal describes a series of novel NMR methods that address some of the most challenging problems in the field of mixture analysis, especially those of high dynamic range mixtures. We will demonstrate how ultraclean spectra, free of extraneous signals (e.g. satellites and artefacts), can be obtained, allowing us to identify and quantify components at least down to the 0.1% level (the current regulatory limit in the pharmaceutical industry). We will also show how - by reducing the complexity of NMR spectra, using "pure shift" methods that collapse multiplet signals into singlets and/or "spectral editing" methods that pick out the signals of individual components - structure determination of the components of intact mixtures can be achieved simply and efficiently. The common thread is that all these new methods are focused on increasing the amount of qualitative, quantitative and structural information obtainable from the spectra of intact mixtures.

These new methods will have direct applications across a wide range of academic and industrial research areas, including chemistry, biochemistry, biology, pharmacy, petrochemistry, agrochemistry, healthcare, and flavours and fragrances.

Who will benefit from this research?

NMR spectroscopy is a crucial underpinning technique for many of the UK's wealth-generating industrial sectors, including the pharmaceutical, petrochemical and biotechnological industries, and a vital component of almost all research in synthetic chemistry. It is essential to the development of healthcare technologies, in particular for drug discovery and pharmaceutical process development, and throughout the chemical industry. NMR is widely used in chemical, biological and medical research, in academic, industrial and government laboratories, and is crucial to the identification of species and the determination of their structures. In real life, scientists rarely work with completely pure compounds, and most of their samples present themselves as mixtures. For many NMR users the easy and reliable analysis of complex mixtures is still one of the greatest challenges.

How will they benefit from this research?

We will develop significantly more powerful tools for NMR spectroscopy, pushing back the limits of current methods for mixture analysis. We will equip both academic researchers and core UK industries with enhanced resolution and spectral quality. The new methods will produce cleaner, simpler spectra, allowing faster, easier and more reliable extraction of structural information than with current methods. They will work on industry-standard commercial spectrometers, without the need for hardware modification. Equipping researchers with higher resolution NMR tools will enhance wealth generation in all of the sectors noted above, and impact on health through improved methods for the characterisation of potential drugs and APIs, for the development and regulatory approval of new processes for the production of APIs, and for the analysis of biofluids in toxicology and metabolomics. Current regulations require that all species present in active pharmaceutical ingredients at levels above 0.1% be identified and quantified, but present NMR methods struggle to deliver clean results below the 1% level. Here the novel methods we propose will reduce the levels of interfering signals by over an order of magnitude.

Our results will be made freely available on the web, enabling early adoption by industrial and academic users alike, and we will collaborate with instrument manufacturers to minimise barriers to the implementation of the new experiments. A secondary impact of the research will be the enhanced development of a highly-skilled postdoctoral fellow and researcher co-investigator, with transferable skills in organisation, communication, critical and creative thinking, and exploitation of information technologies that are fundamental to research in the physical sciences. From previous experience we anticipate take-up of new methods within 12-18 months of development; it is never easy to second-guess progress, particularly where NMR is concerned, but previous methodological developments in this area (e.g. multidimensional NMR methods) have had useful lifetimes measured in decades.