A Molecular Dynamics Approach for Predicting the Glass Transition Temperature and Plasticization Effect in Amorphous Pharmaceuticals

The objectives of this study were as follows: (i) To develop an in silico technique, based on molecular dynamics (MD) simulations, to predict glass transition temperatures (T-g) of amorphous pharmaceuticals. (ii) To computationally study the effect of plasticizer on T-g. (iii) To investigate the intermolecular interactions using radial distribution function (RDF). Amorphous sucrose and water were selected as the model compound and plasticizer, respectively. MD simulations were performed using COMPASS force field and isothermal-isobaric ensembles. The specific volumes of amorphous cells were computed in the temperature range of 440-265 K. The characteristic kink observed in volume-temperature curves, in conjunction with regression analysis, defined the T-g. The MD computed T-g values were 367 K, 352 K and 343 K for amorphous sucrose containing 0%, 3% and 5% w/w water, respectively. The MD technique thus effectively simulated the plasticization effect of water; and the corresponding T-g values were in reasonable agreement with theoretical models and literature reports. The RDF measurements revealed strong hydrogen bond interactions between sucrose hydroxyl oxygens and water oxygen. Steric effects led to weak interactions between sucrose acetal oxygens and water oxygen. MD is thus a powerful predictive tool for probing temperature and water effects on the stability of amorphous systems during drug development.