Posted: March 6, 2007

Removing interactions simplifies spectra

(Nanowerk News) Researchers at the University of Manchester, UK, have improved a technique that simplifies the NMR spectra of mixtures, enabling the spectrum of each individual component to be seen ("Pure shift proton DOSY: diffusion-ordered 1H spectra without multiplet structure").
Nuclear magnetic resonance (NMR) spectroscopy is a long-established and powerful technique for determining the structures of molecules, but up until recently, it only worked well for pure compounds. The advent of techniques such as diffusion-ordered spectroscopy (DOSY) has meant that mixtures can now be usefully analysed, avoiding the need for purification. The problem with DOSY is that it only works reliably if the peaks in the NMR spectrum of the mixture are well separated. Mathias Nilsson and Gareth Morris have now improved the DOSY technique by reducing the peak overlap.
Morris said 'NMR struggles with mixtures because it is difficult to determine unambiguously which signals come from which species'. To get around this, the DOSY technique separates the NMR peaks of different species according to their diffusion coefficient, which can be measured by analysing the peak shape. This has previously been difficult because interactions between the protons in a molecule split signals up, increasing the likelihood of overlap. What Nilsson and Morris have done is to adapt an established method that removes proton-proton interactions, simplifying the spectra. This increases the effective resolving power of DOSY 'by more than an order of magnitude', said Morris.
James Keeler, of the University of Cambridge, UK, and author of the book Understanding NMR Spectroscopy, said that Morris' group 'has already made a number of important contributions to improving the DOSY method, and this contribution looks set to be a really significant advance in the technique.'
Morris concluded that their method, combined with other techniques, would offer 'exquisite resolution for the most complicated mixtures', and 'has a potential role to play in a very wide range of science, from metabolomics to process development'.
Source: Chemistry World (David Barden)
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