Calorimetric (DSC) and dielectric (TSDC) investigation on the thermal behavior and molecular mobility in the supercooled liquid and glassy states of bifonazole and lamotrigine

Abstract

The thermal behavior of the two glass-forming drugs bifonazole and lamotrigine was studied by differential scanning calorimetry (DSC); we reported a bifonazole polymorph not yet described in the literature, as well as weak evidence for lamotrigine polymorphism; still by DSC we investigated the glass-forming ability, the tendency for crystallization from the glass (glass stability) from the metastable and equilibrium melt, for the two glass-formers under analysis. Finally, this technique was used to characterize the glass transition of the two active pharmaceutical ingredients by determining the activation energy of the structural relaxation, the dynamic fragility and the heat capacity jump associated with the glass transformation. Using thermally stimulated depolarization currents (TSDC) and, on the other hand, different aspects of the molecular mobility of these glass-formers were analyzed; the glass transition relaxation and the dynamic fragility, as well as the secondary mobility of the two glass-forming systems, were characterized by this dielectric technique. The absence of other dynamic studies on these glass-formers does not allow the comparison of our results with those of other techniques, namely with dielectric spectroscopy; however, despite this, attention was drawn to the general need to understand in their mutual relationship the TSDC and DRS results on the secondary relaxations.