Predict the glass transition temperature and plasticization of β-cyclodextrin/water binary system by molecular dynamics simulation

The glass transition temperature, diffusion behavior and plasticization of beta-cyclodextrin (beta-CD), and three amorphous beta-CD/water mixtures (3%, 5% and 10% [w/w] water, respectively) were investigated by molecular dynamics simulation, which were performed using Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field and isothermal-isobaric ensembles. The specific volumes of four amorphous cells were obtained as a function of temperature. The glass transition temperatures (T-g) were estimated to be 334.25 K, 325.12 K, 317.32 K, and 305.41 K for amorphous beta-CD containing 0%, 3%, 5% and 10% w/w water, respectively, which compares well with the values observed in published literature. The radial distribution function was computed to elucidate the intermolecular interactions between amorphous beta-CD and water, which acts as a plasticizer. These results indicate that the hydrogen bond interactions of oxygen in hydroxyl ions was higher than oxygen in acetal groups in beta-CD amorphous mixtures with that in water, due to less accessibility of ring oxygens to the surrounding water molecules. The mobility of water molecules was investigated over various temperature ranges, including the rubbery and glassy phases of the beta-CD/water mixtures, by calculating the diffusion coefficients and the fractional free volume. In beta-CD amorphous models, the higher mobility of water molecules was observed at temperatures above T-g, and almost no change was observed at temperatures below T-g. (C) 2014 Elsevier Ltd. All rights reserved.