Manipulating of Crystal Morphology and Polymorph by Crystallization in Microemulsions

Effect of Additives on the Morphology of γ-Aminobutyric Acid Crystals

The effect of surfactant, polymer, and tailor-made additives on the crystallization of γ-aminobutyric acid (GABA) was studied in this work. Cooling crystallization of GABA in water yielded plate-like crystals. In the presence of sodium stearate, polyhedral block-like crystals of GABA were obtained. Hydroxyethyl cellulose (HEC) led to rod-like crystals, in which the morphology was associated with additive concentrations. Six kinds of amino acids were used as tailor-made additives, and they exhibit different influences on crystal shape and size. The induction time of GABA was determined in the absence and presence of additives. The results showed that sodium stearate promoted nucleation, while HEC, l-Lysine, l-histidine, and l-tyrosine inhibited nucleation. Crystal face indexing, Hirshfeld surface analysis, and molecular dynamics (MD) simulation in aqueous solution-crystal systems were carried out to investigate the affecting factors of different crystal faces. The polymer additive was selected as an example during MD simulation to calculate intermolecular interactions between the crystal face and solvent or additive. The effect of the additive on the mobility of the solute in solution was also evaluated by mean-square displacement. The additive offers an effective approach for changing crystal morphology and particle size and adapting it to different production requirements.

Spatiotemporal control of l-phenyl-alanine crystallization in microemulsion: the role of water in mediating molecular self-assembly

Water confined or constrained in a cellular environment can exhibit a diverse structural and dynamical role and hence will affect the self-assembly behavior of biomolecules. Herein, the role of water in the formation of l-phenyl-alanine crystals and amyloid fibrils was investigated. A microemulsion biomimetic system with controllable water pool size was employed to provide a microenvironment with different types of water, which was characterized by small-angle X-ray scattering, attenuated total reflectance-Fourier transform infrared spectroscopy and differential scanning calorimetry. In a bound water environment, only plate-like l-phenyl-alanine crystals and their aggregates were formed, all of which are anhydrous crystal form I. However, when free water dominated, amyloid fibrils were observed. Free water not only stabilizes new oligomers in the initial nucleation stage but also forms bridged hydrogen bonds to induce vertical stacking to form a fibrous structure. The conformational changes of l-phenyl-alanine in different environments were detected by NMR. Different types of water trigger different nucleation and growth pathways, providing a new perspective for understanding molecular self-assembly in nanoconfinement.

Simultaneous control of polymorph and morphology via gelatin induction for concomitant system: case study of sulfathiazole

Controlling the solid-state properties is particularly important in the pharmaceutical field, where polymorph and morphology have a significant impact on drug properties. Sulfathiazole (ST) is a highly and concomitantly polymorphic...