Abstract
Nowadays the study of physiochemical stability of amorphous pharmaceuticals is of great interest in the field of medicinal application due to its enhanced water solubility and bioavailability than its crystalline counterpart. Molecular relaxations play an important role in understanding the physical stability of amorphous drugs. Hence herein, we investigated the molecular dynamics of three pharmaceutically important drugs, namely clofoctol, droperidol and probucol by means of broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). The dielectric spectra in the supercooled state were fitted by Havriliak-Negami (HN) function, while in the glassy state with Cole-Cole equation. The structural relaxation followed non-Arrhenius temperature dependence and followed time-honored Vogel-Fulcher-Tamman (VFT) equation and the secondary relaxation followed Arrhenius equation. The Coupling model (CM) prediction was used to find the origin of the secondary relaxations. Although the three drugs were found to be fragile, clofoctol and droperidol showed recrystallization tendency. It was amazing that the three samples showed a good correlation between the stretch exponent βKWW and the dielectric strength Δε(Tg). In addition, the molecular simulation was used to verify the presence of non-JG (Johari-Goldstein) secondary relaxation due to side chain rotation.
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