In this work, the Supercritical AntiSolvent (SAS) process has been used to generate micronized crystals of Sulfathiazole (STZ) from different organic solutions, namely acetone, acetonitrile, tetrahydrofuran and acetic acid. The flow rates of CO 2 (2-21 g min −1) and of the organic solution (0.19-6 mL min −1), as well as STZ concentration in the organic solution (20-70% under the saturation), have been varied to identify the conditions leading to powders exhibiting only one polymorphic form. Pressure (10 MPa) and temperature (313 K) have been kept constant. In this paper, thermodynamic and hydrodynamic aspects are discussed so as to rationalize the obtained crystal characteristics and provide a new way to control the SAS process applied to drug preformulation. The influence of the organic solvent nature on both the polymorphic form and the habit of generated crystals, has been particularly discussed.
The purpose of this work is to contribute to a better control of the crystallization process which occurs in a supercritical medium, especially during the Supercritical AntiSolvent (SAS) process. It also aims to improve the prediction of crystal habit, thanks to the use of the molecular modeling software GenMol. The first part of the work was devoted to the crystal modeling of the two main forms of sulfathiazole in vacuo, considering Hartman's attachment energy formalism. The second part considers solvent−crystal interactions throughout adsorption simulations to investigate the effect of growth environments on crystal habits. Lastly, modeling predictions were compared with grown crystals of sulfathiazole, observed after recrystallization with the SAS process from acetonitrile, acetone, tetrahydrofuran and acetic acid solutions. These comparisons demonstrated good predictions of crystal habit taking into consideration the growth environment. Neither carbon dioxide (antisolvent of the SAS process) nor acetonitrile leads to a modification of the isometric, in vacuo predicted habit of both forms. Acetone and tetrahydrofuran adsorb preferentially on some identified faces and lead to flat, leaflike, or tabular crystals. Acetic acid adsorbs on every one of the faces and hinders the phase transition to a more stable form, thus leading to crystals of the least stable, kinetically favored form I. Experimental observations were also rationalized by considering the different possible crystallization pathways, in particular Crystallization by Particle Attachment and Droplet Drying mechanisms occurring in the SAS process. This work confirms that solvent nature is one of the key elements to consider in order to better control the characteristics of particles grown using the SAS process and provides a new method to help to control it.
The goal of this study was molecular modeling of cyclodextrin (CD) and carotenoid complex formation. Distinction was made between complexes resulting from interactions between carotenoids and either molecularly dispersed CDs or solid crystalline CDs, considering that both cases can occur depending on the complex formation process pathways. First, the formation of complexes from dispersed CD molecules was investigated considering five different CDs (αCD, βCD, methyl-βCD, hydroxypropyl-βCD, and γCD) and lutein, as a model carotenoid molecule. The interactions involved and the stability of the different complexes formed were evaluated according to the CD size and steric hindrance. Second, the formation of complexes between four different crystalline CDs (βCD with three different water contents and methyl-βCD) and three carotenoid molecules (lutein, lycopene, and β-carotene) was studied. The docking/adsorption of the carotenoid molecules was modeled on the different faces of the CD crystals. The findings highlight that all the CD faces, and thus their growth rates, were equally impacted by the adsorption of the carotenoids. This is due to the fact that all the CD faces are exhibiting similar chemical compositions, the three studied carotenoid molecules are rather chemically similar, and last, the water−carotenoid interactions appear to be weak compared to the CD−carotenoid interactions.
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