Molecular mobility in the supercooled and glassy states of nizatidine and perphenazine.

The dielectric properties of two pharmaceuticals nizatidine and perphenazine were investigated in the supercooled liquid and glassy states by broadband dielectric spectroscopy. Two relaxation processes were observed in both the pharmaceuticals. The relaxation process observed above the glass transition temperature is the structural alpha relaxation and below the glass transition temperature is the gamma relaxation of intramolecular origin. The Johari-Goldstein beta relaxation coming from the motion of the entire molecule is found to be hidden under the structural relaxation peak in both the pharmaceuticals.

Molecular dynamics of amorphous pharmaceutical fenofibrate studied by broadband dielectric spectroscopy.

Fenofibrate is mainly used to reduce cholesterol level in patients at risk of cardiovascular disease. Thermal transition study with the help of differential scanning calorimetry (DSC) shows that the aforesaid active pharmaceutical ingredient (API) is a good glass former. Based on our DSC study, the molecular dynamics of this API has been carried out by broadband dielectric spectroscopy (BDS) covering wide temperature and frequency ranges. Dielectric measurements of amorphous fenofibrate were performed after its vitrification by fast cooling from a few degrees above the melting point (Tm=354.11 K) to deep glassy state. The sample does not show any crystallization tendency during cooling and reaches the glassy state. The temperature dependence of the structural relaxation has been fitted by single Vogel-Fulcher-Tamman (VFT) equation. From VFT fit, glass transition temperature (Tg) was estimated as 250.56 K and fragility (m) was determined as 94.02. This drug is classified as a fragile glass former. Deviations of experimental data from Kohlrausch-Williams-Watts (KWW) fits on high-frequency flank of α-peak indicate the presence of an excess wing in fenofibrate. Based on Ngai׳s coupling model, we identified the excess wing as true Johari-Goldstein (JG) process. Below the glass transition temperature one can clearly see a secondary relaxation (γ) with an activation energy of 32.67 kJ/mol.

Molecular dynamics of amorphous pharmaceutical fenofibrate studied by broadband dielectric spectroscopy$ / 药物分析学报

Fenofibrate is mainly used to reduce cholesterol level in patients at risk of cardiovascular disease. Thermal transition study with the help of differential scanning calorimetry (DSC) shows that the aforesaid active pharmaceutical ingredient (API) is a good glass former. Based on our DSC study, the molecular dynamics of this API has been carried out by broadband dielectric spectroscopy (BDS) covering wide temperature and frequency ranges. Dielectric measurements of amorphous fenofibrate were per-formed after its vitrification by fast cooling from a few degrees above the melting point (Tm ? 354.11 K) to deep glassy state. The sample does not show any crystallization tendency during cooling and reaches the glassy state. The temperature dependence of the structural relaxation has been fitted by single Vogel–Fulcher–Tamman (VFT) equation. From VFT fit, glass transition temperature (Tg) was estimated as 250.56 K and fragility (m) was determined as 94.02. This drug is classified as a fragile glass former. Deviations of experimental data from Kohlrausch–Williams–Watts (KWW) fits on high-frequency flank of α-peak indicate the presence of an excess wing in fenofibrate. Based on Ngai's coupling model, we identified the excess wing as true Johari–Goldstein (JG) process. Below the glass transition temperature one can clearly see a secondary relaxation (γ) with an activation energy of 32.67 kJ/mol.

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 τß (Tg). In the case of ketoprofen we conclude that the secondary relaxation (ß) 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 (Tg) 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.