Morphology study of progesterone polymorphs prepared by polymer-induced heteronucleation (PIHn)

Emerging role of primary heterogeneous nucleation in pharmaceutical crystallization

Crystallization is an important and difficult to control unit operation in the pharmaceutical industry. Crystallization can control molecular (i.e., polymorphism) and particulate (i.e., particle size and crystal habit) properties of active pharmaceutical ingredient (API). Moreover, these molecular and particulate properties govern the manufacturability, stability, and biopharmaceutical performance of the API and drug product. Nucleation is a key step and primary heterogeneous nucleation is a common mode of nucleation during crystallization. Hence, it is important to understand the parameters affecting primary heterogeneous nucleation, to achieve desirable properties in crystalline APIs. Primary heterogeneous crystallization has usually been linked to the surface characteristics like topography and functionality of the heteronucleant. The review outlines recent findings in the primary heterogeneous crystallization with specific emphasis on its pharmaceutical applications including regulatory considerations. Molecular-level mechanisms governing heteronucleation and subsequent outcome in terms of molecular as well as particulate-level properties of API have also been discussed. Moreover, general guidance for the selection of heteronucleant has also been included. Heterogeneous crystallization is a promising tool for efficient crystallization of API having properties for optimal pharmaceutical performance.

Influence of Chemical Functionality on the Rate of Polymer-Induced Heteronucleation

Polymer-induced heteronucleation can dramatically increase the nucleation rate of pharmaceuticals. However, directly comparing the heteronucleation rates of different polymer functionalities is often convoluted with changing physical or structural aspects of heteronuclei. Here, we report a methodology for comparing nucleation efficiencies of different functionalities on polymer heteronuclei of uniform topology with the goal of identifying those functionalities that best accelerate nucleation of a model pharmaceutical. It was found that the previously employed design for additives to speed acetaminophen crystallization underperforms a modified framework that accounts for the effect of competitive solvent binding. These findings are informed by a survey of interactions from the CSD and not only serve to aid in the controlled crystallization of pharmaceuticals, but also provide insight into the mechanism of heteronucleation.

Understanding pharmaceutical polymorphic transformations II: crystallization variables and influence on dosage forms

Excipients or formulation variables have often been exploited to improve stability, modify release, or improve physicochemical properties of dosage forms. In pharmaceutical field, it is generally expected that excipients work at macromolecular level where they might influence the crystal structure of a solid. These polymers/colloidal particles may modify the rate and direction of crystal growth. It has also been observed, that different polymorphic crystals exhibit different colors on exposure to same colorant, predominantly due to difference in surface pH of different crystal lattices. Apart from physicochemical affect, crystal habit also influences pharmacokinetic parameters of the dosage form. Crystals with smaller size or lower lattice energy have shown to exhibit higher bioavailability with faster rate of release.

The Bioenhancer Piperine is at Least Trimorphic

Polymer-induced heteronucleation (PIHn), a powerful crystalline polymorph discovery method, has revealed two novel polymorphs of the low solubility bioenhancer piperine. Both of these forms exhibit enhanced solubility when compared to the commercial polymorph, thereby potentially improving the efficacy of piperine as a bioenhancer. Structural comparison of the three forms reveals that π-π interactions are only present in the two newly discovered forms. Combined with the stability data this reveals that despite the extended conjugation present in the moleculesuch interactions are not preferred in thesolid state.

On the origin of surface imposed anisotropic growth of salicylic and acetylsalicylic acids crystals during droplet evaporation

In this paper droplet evaporative crystallization of salicylic acid (SA) and acetylsalicylic acid (ASA) crystals on different surfaces, such as glass, polyvinyl alcohol (PVA), and paraffin was studied. The obtained crystals were analyzed using powder X-ray diffraction (PXRD) technique. In order to better understand the effect of the surface on evaporative crystallization, crystals deposited on glass were scraped off. Moreover, evaporative crystallization of a large volume of solution was performed. As we found, paraffin which is non-polar surface promotes formation of crystals morphologically similar to those obtained via bulk evaporative crystallization. On the other hand, when crystallization is carried out on the polar surfaces (glass and PVA), there is a significant orientation effect. This phenomenon is manifested by the reduction of the number of peaks in PXRD spectrum recorded for deposited on the surface crystals. Noteworthy, reduction of PXRD signals is not observed for powder samples obtained after scraping crystals off the glass. In order to explain the mechanism of carboxylic crystals growth on the polar surfaces, quantum-chemical computations were performed. It has been found that crystal faces of the strongest orientation effect can be characterized by the highest surface densities of intermolecular interactions energy (IIE). In case of SA and ASA crystals formed on the polar surfaces the most dominant faces are characterized by the highest adhesive and cohesive properties. This suggests that the selection rules of the orientation effect comes directly from surface IIE densities.