Characterization of Polymorphic Crystals: Glycine as a Case Study

This chapter explores the methodologies and techniques employed to study and identify various polymorphic forms of crystals, focusing on the amino acid glycine. The chapter details the morphological, structural, and thermal characterization of these polymorphs to segregate and confirm their stability. Single crystals of the α, β, and γ polymorphs of glycine were prepared from aqueous solutions, either with or without selective additives or by incorporating an anti-solvent. These crystalline polymorphs were segregated from their nucleation stage using in-situ microscopic analysis. Initial morphological analysis identified the nucleated polymorphs, which were then confirmed through powder Xray diffraction. Absolute structural refinement was achieved using single crystal X-ray diffraction analysis. The thermal stability of the polymorphic crystals was assessed using differential scanning calorimetry, revealing that the α-polymorph is metastable, the β-polymorph is unstable, and the γ-polymorph is the most stable under ambient conditions.