Investigation of thermal properties of glassy itraconazole: identification of a monotropic mesophase

The purpose of the present work is the elucidation of two endothermic transitions at 74 and 90°C, respectively, observed during differential scanning calorimetry of glassy itraconazole. Modulated temperature DSC (MTDSC), hot-stage microscopy (HSM), HPLC and high temperature X-ray diffraction (HT-X ray) were used to examine the thermal properties of glassy itraconazole. It was found that the preparation mode of the glass does not seem to influence the appearance of both endothermic transitions since they were present during heating of glassy itraconazole which was prepared by cooling the melt or by rapid solvent evaporation of an itraconazole solution. These observations suggest that the appearance of the two endothermic transitions require the liquid state prior to glass formation. The transitions are not due to impurities in the starting material, nor are they caused by thermal decomposition. This was further confirmed by HPLC-analysis. HSM showed structure formation following cooling of the melt, at approximately 87°C; cooling the product further showed a second change in optical contrast. HT-X ray confirmed and identified the formation of a nematic mesophase. The appearance of the two endothermic signals during scanning of glassy itraconazole points to the formation of a mesophase. Due to the nature of itraconazole, it appears as a chiral nematic phase of which the mobility is frozen into a glass upon cooling below 59°C thereby impeding further crystallization.