Abstract
A combination of solid-state NMR techniques, including13C/1H correlation,2H magic-angle spinning NMR and first principles calculation are employed to characterise the role of water in different hydration states of sildenafil citrate.
Highlights
Understanding the solid-state characteristics of drug substances is vital within the pharmaceutical industry
The 13C spectrum is fully assigned for the first time and direct correlations made with respect to the crystal structure. 2H magic-angle spinning NMR is demonstrated to be a powerful tool for the study of dynamic and exchange processes in complex hydrate systems, allowing the behaviour at multiple solvate sites to be characterised without the need for expensive and selective labelling
The structure derived from the single-crystal XRD study was in agreement with the previously published result[21] (FEDTEO in the Cambridge Structural Database), except that the previously reported structure is presented as a simple monohydrate, without discussion of non-stoichiometry
Summary
Understanding the solid-state characteristics of drug substances is vital within the pharmaceutical industry. 13C NMR has been widely used to follow the hydration behaviour of non-stoichiometric pharmaceutical solvates.[22] Fig. 1 shows the results of acquiring the 13C CPMAS spectra of sildenafil citrate as a function of temperature, starting with a hydrated sample at 10 °C.
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