Matrix-Assisted DOSY

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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 one major drawback: it is poor at analysing mixtures, so it is mostly used on carefully purified single compounds. Because many of Nature's most challenging problems - and many of those posed by synthetic chemists and by industry - are presented to us as mixtures, a great deal of effort goes into separating mixtures into their individual components so that they can be identified. Diffusion-ordered spectroscopy (DOSY) tries to get around this limitation by separating the NMR signals of different molecules, so that the signals from different species can be distinguished. Over the last decade our research group and others have developed the technique and applied it with great success - but almost always to simple solutions. In this project, a postdoctoral research fellow will investigate separating the spectra of mixture components more effectively by adding substances such as surfactants (the active ingredients of soaps and detergents), gels and soluble polymers to solvents to make a solution (a matrix ) that changes the way that molecules diffuse. These substances diffuse very slowly, but they also attract other molecules. The result is that the rates at which solute molecules diffuse in such a matrix are changed, by an amount that depends on how strong the attraction is. By tuning the properties of the matrix we should be able to optimise the separation of the NMR signals of different species, even resolving the spectra of isomers that cannot be separated by normal DOSY experiments. Initially DOSY was used largely by chemists, but it is now being applied in fields as varied as food science, forensic medicine, and environmental science. Using different matrices for DOSY will give such users much greater control over how signals of different species in a mixture are separated, opening up new applications.