Molecular dynamics in liquid and glassy states of non-steroidal anti-inflammatory drug: Ketoprofen

Ketoprofen is a well known nonsteroidal anti-inflammatory drug (NSAID) with analgesic and antipyretic effects. It acts by inhibiting the body's production of prostaglandin. The molecular mobility of amorphous ketoprofen has been investigated by broadband dielectric spectroscopy (BDS) covering wide temperature and frequency range. Multiple relaxation processes were observed. Besides the primary α-relaxation, one secondary relaxation, γ-have been identified. The γ-process visible in the dielectric spectra at very low temperature is non-JG relaxation, and has an activation energy E = 37.91 kJ/mol typical for local mobility. Based on Ngai's coupling model smaller n or a larger Kohlrausch exponent (1 - n) of the α-relaxation associated with larger τ_β (T_g). In the case of ketoprofen we conclude that the secondary relaxation (β) emerging from intermolecular motions, is hidden under the dominant α-peak. The temperature dependence of the relaxation time of the α-process can be described over the entire measured range by a single Vogel-Fulcher-Tammann (VFT) equation. From VFT fits, the glass transition temperature (T_g) was estimated as 267.07 K, and a fragility or steepness index m = 86.57 was calculated, showing that ketoprofen is a fragile glass former. Our differential scanning calorimetry (DSC) study shows that ketoprofen is a non-crystallizing compound. To confirm the hydrogen bond patterns of ketoprofen FTIR spectroscopy was applied in both crystalline and amorphous phases. Solubility test performed at 37 C proved that amorphous phase is more soluble than the crystalline phase.