Understanding the
link between solution chemistry and nucleation
is essential to control crystallization processes, in particular regarding
pharmaceutical compounds. In the present work, the link between the
solution hydration state and crystallization of the γ-amino
acid pregabalin is presented. Pregabalin is a blockbuster pharmaceutical
drug having broad therapeutic effects. Using induction time experiments
in combination with the classical nucleation theory, we show that
the ease of nucleation increases with solubility and water fraction
of the solvent. Water was found to enhance both the kinetic and thermodynamic
processes of forming a nuclei. As a result, larger clusters which
represent the hydrate form were measured using dynamic light scattering
in pure water. Once in the solid state, the hydrate form of pregabalin
was found to be physically unstable, as it rapidly converted back
into its anhydrate form, as rationalized using in-line Raman spectroscopy.
Thus, the hydration and nucleation of pregabalin in solution is highly
favored, as opposed to the solid-state situation, where the anhydrate
is the stable form. Despite these differences, a solution–crystallization
link could still be established in our work. Knowledge of the solution
chemistry and structural landscape of pharmaceutical compounds is
essential for the development of manufacturing routes and patent protections,
and we foresee that the presented approach can be used to further
reveal relationships among self-association in solution, crystallization,
and hydration of a wide range of organic compounds.