Molecular dynamics study of effects of temperature and concentration on hydrogen-bond abilities of ethylene glycol and glycerol: implications for cryopreservation.

The state of intracellular water is important in all phases of cryopreservation. Intracellular water can be transported out of the cell, transferred into its solid phase, or blocked by cryoprotectants and proteins in the cytoplasm. The purpose of the present study is to determine the amount of hydrogen-bonded water in aqueous ethylene glycol and glycerol solutions. The effects of temperature and concentration on the density and the hydrogen bonding characteristics of the solution are evaluated quantitatively in this study. To achieve these aims, a series of molecular dynamics simulations of ethylene glycol/water and glycerol/water mixtures of molalities ranging from 1 to 5 m are conducted at 1 atm and at 273, 285, and 298 K, respectively. The simulation results show that temperature and concentration have variable effects on solution density. The proportion of the hydrogen-bonded water by solute molecules increases with rising molality. The ability of the solute molecules to hydrogen bond with water molecules weakens as the solution becomes more concentrated. Moreover, it turns out that the solution concentration can influence the hydrogen bonding characteristics more greatly than the temperature. The glycerol molecule should be a stronger "water blocker" than the ethylene glycol molecule corresponding to the same conditions. These findings provide insight into the cryoprotective mechanisms of ethylene glycol and glycerol in aqueous solutions, which will confer benefits on the cryopreservation.