Applications of solid-state NMR to pharmaceutical polymorphism and related matters

Magic-angle spinning NMR is now making a significant contribution to our understanding of the structure of polymorphs and solvates of pharmaceutical significance. This personal review article discusses a range of applications, with particular emphasis on information about crystallography, for which NMR can address problems that cannot be readily solved by diffraction techniques (such as dynamic disorder and non-stoichiometric hydration). Unlike diffractograms, NMR spectra yield immediate chemical information. Moreover, heterogeneous samples can be investigated and amorphous content provides no significant barrier to studies. Furthermore, NMR can be an effective technique for quantitation (down to the level of ca. 1%). Additional strength is being derived from computation of chemical shifts in solids, using a code that takes account of the spatial repetition inherent in crystalline materials.