Computer Simulation of the Cryoprotectant Disaccharide α,α-Trehalose in Aqueous Solution

Abstract

Protecting biological molecules during freezing and lyophilization is of commercial importance to the pharmaceutical, medical, and food industries. Much work has been done on the use of a wide variety of cryoprotectant compounds for these types of processes. Chief among these compounds are the saccharides. They have been found to protect proteins during freezing and drying stresses as well as prevent membrane damage during cooling of cells. Trehalose, a naturally occurring disaccharide of glucose, has been found to be a particularly effective cryoprotectant. Although there are several prevailing structural and thermodynamic arguments as to why molecules such as trehalose act as cryoprotectants, little fundamental work has been done to corroborate or refute these hypotheses. To address this issue, our work has focused on the structural and dynamic simulation of this promising cryoprotective system. In this work, we have implemented fully flexible, all-atom models for water and trehalose and used both Monte Carlo and molecular dynamics algorithms to calculate various macroscopic properties of trehalose solutions over a wide range of concentration. We have also studied the glass transition behavior at various concentrations and compared it to experimental data. We have observed the existence of intramolecular hydrogen bonding, which has been invoked to explain compressibility and molar volume data for concentrated solutions of trehalose. We have studied the diffusivity of water molecules in concentrated trehalose solutions and found a gradual transition from continuous motion through the matrix in more diluted systems to cavity-hopping motion in concentrated and near-glassy cases. Our diffusivity results have been analyzed in terms of the Williams−Landel−Ferry equation; good agreement is found with published glass transition data.