Crystalline and amorphous phases of a new drug

The thermodynamic properties of a new antidepressant drug are studied from room temperature to 200 °C. In this range, the sample neither decompose, nor has a significant reactivity with water. When slowly heating a “fresh” sample, we may observe the following phenomena (in the order): melting of a form (F1, ~170 °C), crystallization of a structurally different form (F2), and melting of F2 (~180 °C). In no circumstances, the direct transition from F1 to F2 can be observed. On the other hand, F2 reverts to F1 upon cooling below ~130 °C. A glassy phase is formed upon cooling from above 180 °C, as confirmed by X-ray analysis and the appearance of a glass transition when reheating. The “reversible” (e.g., melting) and “irreversible” (e.g., glass formation) contributions to the measured enthalpies are estimated with temperature-modulated DSC measurements, resulting into a consistent description of thermodynamics of the forms, their melting and their kinetics of transformation.