Inhibition of Ice Nucleus Growth in Water by Alanine Dipeptide

Abstract

A molecular dynamics simulation has been carried out for the mixture of an ice nucleus, supercooled water and a molecule of alanine dipeptide (AD). The dipeptide molecule has been allocated near the nucleus surface which corresponds to the prism plane of ice crystal. The molecule is found to approach the ice surface so that the two hydrophilic sites on one side of the molecule (Oc2 and Hn1) are closest to the surface. The hydrogen bond between Hn1 site and the oxygen atom on the prism plane of the ice nucleus is expected. The perturbations of two hydrophilic sites (Oc1 and Hn2), which are surrounded by hydrophobic sites and are pointing away from the surface, attenuate the approach of water molecules to these sites. Thus, these water molecules diffuse. The hydrogen bond between the oxygen atoms on the prism plane and the hydrogen atoms of water molecules is attenuated by the diffusion.

Keywords:

• Ice Ih structure
• Alanine dipeptide molecule
• Hydrogen bond
• Water-molecule clustering