Biomedical subjects

Ion Dranca

Publications and source records attributed to Ion Dranca.

3 recordsLinked to original sources

PubMed2006

Comparative relaxation dynamics of glucose and maltitol.

PURPOSE: To demonstrate the utility of differential scanning calorimetry (DSC) for determining activation energy landscape in amorphous pharmaceutical systems throughout the sub-Tg and Tg regions. MATERIALS AND METHODS: DSC was employed to determine the effective activation energies (E) of the relaxation in sub-Tg and Tg regions as well as the sizes of cooperatively rearranging regions in glassy maltitol and glucose. RESULTS: It has been found that in the sub-Tg region E decreases with decreasing T reaching the values approximately 60 (glucose) and approximately 70 (maltitol) kJ mol(-1) that are comparable to the literature values of the activation energies for the beta-relaxation. In the Tg region E decreases (from approximately 250 to approximately 150 kJ mol(-1) in maltitol and from approximately 220 to approximately 170 kJ mol(-1) in glucose) with increasing T as typically found for the alpha-relaxation. From the heat capacity measurements the sizes of cooperatively rearranging regions have been determined as 3.1 (maltitol) and 3.3 (glucose) nm. CONCLUSIONS: DSC can be used for evaluating the energy landscapes. The E values for maltitol are somewhat greater than for glucose due to the added impeding effect of the bulky substitute group in maltitol. The comparable sizes of the cooperatively rearranging regions suggest a similarity of the heterogeneous glassy structures of the two compounds.

Calorimetry, Differential Scanning↗

PubMed2006

Probing beta relaxation in pharmaceutically relevant glasses by using DSC.

PURPOSE: This study was conducted to demonstrate the use of differential scanning calorimetry (DSC) in detecting and measuring beta-relaxation processes in amorphous pharmaceutical systems. METHODS: DSC was employed to study amorphous samples of poly(vinylpyrrolidone) (PVP), indomethacin (IM), and ursodeoxycholic acid (UDA) that were annealed at temperatures (T(a)) around 0.8 of their glass transition temperatures (T(g)). Dynamic mechanical analysis (DMA) was used to measure beta-relaxation in PVP. RESULTS: Reheating the annealed samples gives rise to annealing peaks that occur below T(g). The peaks cannot be generated when annealing below the low temperature limit of beta-relaxation. These limits are around 50 degrees C for PVP, -20 degrees C for IM, and 30 degrees C for UDA. The effective activation energy (E) of the sub-T(g) relaxation has been estimated for each T(a) and found to increase with T(a), reflecting increasing contribution of the alpha-process. Estimates of E for beta-relaxation have been obtained from the lowest T(a) data, and are as follows: 68 (PVP), 56 (IM), 67 (UDA) kJ mol(-1). CONCLUSIONS: DSC can be used for detecting beta-relaxation processes and estimating its low temperature limit, i.e., the temperature below which amorphous drugs would remain stable. It can also provide comparative estimates of low temperature stability of amorphous drugs in terms of the activation energies of the beta-relaxation.

Algorithms↗

PubMed2005

Physical stability and relaxation of amorphous indomethacin.

The alpha- and beta-relaxation processes in amorphous indomethacin have been studied by using differential scanning calorimetry. The beta-process has been detected as a small endothermic peak that emerges before the glass transition step when reheating samples previously annealed in the temperature region -20 to +5 degrees C. The activation energy of the beta-process is approximately 57 kJ mol(-1), and shows an increase with increasing temperature as it approaches the glass transition region. In the glass transition region, the effective activation energy of relaxation decreases with increasing temperature from 320 to 160 kJ mol(-1). Heat capacity measurements have allowed for the evaluation of the cooperatively rearranging region in terms of the linear size (3.4 nm) and the number of molecules (90). The beta-relaxation fades below -30 degrees C, which provides a practical estimate for the lower temperature limit of physical instability in indomethacin. It is demonstrated experimentally that nucleation of indomethacin takes place in the temperature region of the beta-relaxation.

Anti-Inflammatory Agents, Non-Steroidal↗