Scientists in the UK and France have combined NMR and computational methods to determine the structures of powdered organic compounds. The protocol could be used by the pharmaceutical industry to identify if drugs contain different crystal structures (polymorphs) that could make them less effective.

Solid state NMR and density functional theory can characterise powdered drugs

Lyndon Emsley, at the University of Lyon, Villeurbanne, France, and colleagues tested their protocol, which is based on solid state NMR combined with density functional theory, on thymol, an antiseptic molecule found in thyme oil. They showed that the crystal structure they generated was the same as the single crystal X-ray structure determined previously.

Emsley says he was inspired by protein NMR, where proteins are isotopically labelled to make them easier to characterise. 'We thought: can we adapt that to small molecules that can't be easily labelled?' he says. 'Ours is the only group working toward total structure determination of small organic molecules.'

Marc Baldus, a specialist in solid state protein NMR at Utrecht University, The Netherlands, hails the work as 'a landmark in establishing solid state NMR as a high resolution structural method in pharmaceutical chemistry and beyond'.

Emsley says the method performs as well as current powder X-ray diffraction methods but he believes that the integrated use of both techniques will result in a far more effective protocol.

'Our objective is to extend the technique to all drug-sized molecules and to apply it to discriminate between polymorphs,' says Emsley. He says he is confident that the method can be used to look at disordered, non-crystalline materials, such as those used in electronics and nanotechnology.

Philip Robinson

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