Solvent-Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor-Made Inhibitors of α-Glycine.

Abstract

Metastable polymorphs commonly emerge when the formation of the stable analogues is inhibited by using different solvents or auxiliaries. Herein, we report that when glycine is grown in aqueous solutions in the presence of low concentrations of different co-solvents, only alcohols and acetone, unlike water and acetic acid, are selectively incorporated in minute amounts within the bulk of the α-polymorph. These findings demonstrate that although water binds more strongly to the growing face of the crystal, alcohols and acetone are exclusively incorporated, and thus serve as efficient inhibitors of this polymorph, leading to the precipitation of the β-form. These solvents then create polar domains detectable by pyroelectric measurements and impedance spectroscopy. These results suggest that in the control of crystal polymorphism with co-solvents, one should consider also the different desolvation rates in addition to the energy of binding to the growing faces of the crystal.