Hydration of glucose in the rubbery and glassy states studied by molecular dynamics simulation

We have studied the hydration properties of an 85% (w/w) aqueous solution of glucose using molecular dynamics. The experimental values of the relative populations of α and β anomers were introduced into the description of the system. We computed the radial distribution function, hydrogen bond residence times, hydration number and mean lifetimes, as well the mean glucose and water cluster sizes. The simulated glass transition temperature (Tg) of the solution was computed to evaluate the quality of the model; the computed value of 241 K was in fair agreement with the experimental value of 232 K. It was concluded that most of the water molecules are connected to more than one glucose molecule by hydrogen bonds. The residence time of the water molecules in hydration sites changes from one site to another, but for the anomeric and chain-oxygen atoms, the residence time is greater than for the rest. The average residence time goes from 2.00 ps for the rubbery state at 280 K to 5.75 ps for the glassy state at 200 K. The mean value of the cluster size of glucose is very close to the corresponding to full connectivity and does not vary much from the rubbery to the glassy state.