Vibrational spectra of calcium, strontium and barium valproates. Self-assembly of valproate nanostrands in aqueous solution and in the solid state

Abstract

The valproates of calcium, strontium and barium, alternative sources of the valproate (2-propylvalerate) ion—a potent anticonvulsant agent used for treatment of epilepsy—were synthesized and characterized by vibrational (IR and Raman) spectroscopy. The spectroscopic signatures of these compounds were correlated with the crystal structures of sodium hydrogenvalproate and calcium valproate, and they were employed to make predictions on the structures of the valproates of strontium and barium. The self-assembly of the valproate ions and sodium ions in aqueous solution was also studied. In the presence of protons, in solution as well as in the solid state, the valproate ions form stable sodium–valproate molecular aggregates, which in solution reach the largest size at ion : acid ratio of 3 : 1. The formation of similar, but perhaps smaller clusters, under physiological conditions, may be important for the valproate-induced blocking of the ion transport through the voltage-gated sodium ion channels in cell membranes.