Molecular dynamics simulation studies of cryoprotective agent solutions: the relation between melting temperature and the ratio of hydrogen bonding acceptor to donor number

Molecular dynamics simulations have been carried out for glycerol-water-sodium chloride ternary solution due to its important role in cryopreservation engineering. The radial distribution functions for atom pairs potentially related to C-H O and O-H O hydrogen bonds were calculated. The radial distribution functions for the H (connected to C)-O atom pair do not exhibit peaks between 2 and 3 , whereas the radial distribution functions for the C-O atom pair exhibit distinct peaks between 3 and 4 . The reason for this is because most C-H O geometries are bent and deviate from linearity. The ratios of acceptor to donor numbers for water and glycerol molecules decrease as the solute concentration increases. A characteristic concentration has been found that divides solutions with different mechanisms. Below the characteristic concentration, the melting temperature is linearly related to the ratio of acceptor to donor number for water molecules, whereas above the characteristic concentration, the melting temperature is linearly related to the ratio of acceptor to donor number for glycerol molecules. Further studies indicate that the relations are independent of hydrogen bonding criteria and temperature.