The work aims at investigating the correlation of water sorption potential with different measures of molecular mobility in an annealed amorphous model compound (trehalose). Amorphous trehalose, prepared by freeze-drying, was annealed at 100°C (17°C < T (g)) for up to 120 h. Global molecular mobility was studied using a broadband dielectric spectrometer in the frequency range of 10(6)-10(-2) Hz. Enthalpic recovery was measured by differential scanning calorimetry and water sorption profiles were obtained using an automated vapor sorption balance. As a function of annealing time, there was an increase, both in average α-relaxation time and enthalpic recovery and a decrease in the amount of sorbed water. A strong linear correlation was observed between the water sorption potential and the dielectric relaxation time, indicating a common underlying mechanism of the effect of annealing time on these properties. Enthalpic recovery, which is widely used as a measure of structural relaxation, did not correlate well with the extent of water sorption. The α-relaxation time can be used as a predictor of the water sorption potential of amorphous trehalose. It will be of interest and value to develop such predictive models for other amorphous compounds of pharmaceutical interest.
Sunny P Bhardwaj, Raj Suryanarayanan. Molecular mobility as a predictor of the water sorption by annealed amorphous trehalose. Pharmaceutical research. 2013 Mar;30(3):714-20
PMID: 23104580
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