Sodium-23 solid-state nuclear magnetic resonance of commercial sodium naproxen and its solvates

We report on the investigation of sodium coordination environments with solid-state ²³Na nuclear magnetic resonance (NMR) spectroscopy of various hydrates and solvates of sodium naproxen (SN), a commercially available anti-inflammatory drug sold over the counter as Aleve®, among other names. The ²³Na quadrupolar coupling constant is found to change significantly depending on the hydration state, and subtle changes in oxygen coordination environment about the sodium cations were apparent in the NMR spectra. High-resolution double-rotation NMR experiments are also performed on powdered samples to obtain solution-like ²³Na NMR spectra. Our attempts at crystallizing various solvates of SN have led to the characterization of the first crystal structure for the heminonahydrated form. The composition of commercial SN is also investigated and it is shown that Aleve® is composed of approximately 80% monohydrate solvate. Density-functional theory calculations, using the gauge-including projector-augmented-wave formalism, allow for the assignment of ²³Na NMR peaks to specific sodium sites in the reported X-ray crystal structure.