Studying the Crystallization of Various Polymorphic Forms of Nifedipine from Binary Mixtures with the Use of Different Experimental Techniques

In this paper the crystal growth of nifedipine from pure system and from binary mixtures composed of active substance (API) and two acetylated disaccharides, maltose and sucrose (NIF-acMAL, NIF-acSUC, 5:1 weight ratio), was investigated. Optical snapshots supported by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) measurements showed that mainly β and α forms of nifedipine grow up in all investigated samples. They also revealed that the morphology of growing crystals strongly depends on the presence of modified carbohydrates and temperature conditions. Interestingly, it was found that the activation barrier for the crystal growth of the β polymorph is not affected by acetylated saccharides while the one estimated for the α form changes significantly from 48.5 kJ/mol (pure API) up to 122 kJ/mol (NIF-acMAL system). Moreover, the relationship between the crystal growth rate and structural relaxation times for pure NIF and solid dispersions were analyzed. It turned out that there is a clear decoupling between the crystal growth rate and structural dynamics in both NIF-acMAL and NIF-acSUC binary mixtures. This is in line with recent reports indicating the decoupling phenomenon to be a universal feature of soft matter in the close vicinity of the glass transition temperature.