| Description |
The processes at the surface of ice modulate crystal growth, atmospheric and biologically relevant adsorption of solutes, and chemical reactions. These processes are not well characterized, in part, due to lack of spatial and temporal resolution of the existing experimental techniques. In this dissertation, we use molecular modeling to study the role of structure and thermodynamics of ice/liquid and ice/vapor interfaces in determining the morphology of water-salt ultrafine aerosols, polymorph of ice that grows from liquid or water vapor uptake, and the behavior of ions, organics, and biological molecules at the interfaces of ice. We find that the crystallized water-salt aerosols adopt a spherical cap morphology in which the ice nanophase is exposed to vapor. Our analysis indicates that change of liquid/vapor surface tension with solute concentration is the key thermodynamic predictor that determines the morphology of crystallized binary aqueous aerosols. We find that the ice growth from liquid water and from vapor results in the stacking disordered and hexagonal ice, respectively. This can be attributed to distinct thermodynamics and kinetics of processes modulating ice growth at the ice/liquid and ice/vapor interface. Investigation of the ice/vapor interface reveals solvation properties that are distinctly different from that of bulk liquid. We find that strongly hydrophilic solutes that increase the liquidity of the ice surface experiences a water-driven long-ranged attraction at the surface of ice, resulting in solvent-separated ion clusters. iv This dissertation elucidates the molecular mechanism of ice recognition and binding by antifreeze and ice-nucleating proteins. We find two distinct ice-binding sites for the ice-nucleating protein of Pseudomonas syringae. We find that the hyperactive insect antifreeze proteins bind to ice through an ice-plane-specific anchored clathrate motif. The water at the ice-binding site of the antifreeze protein is not preordered in solution, in contradiction to the widely prevailing "preordering-binding" hypothesis. Instead, ice recognition and binding occur by slow diffusive dynamics of the protein at the surface of ice to find the appropriate orientations, followed by a fast reorganization of water at the binding site that latches the protein to ice. |
