Molecular dynamics studies of the interactions of water and amino acid analogues with quartz surfaces

The interactions of silica surfaces with water and biomolecules are of considerable significance in bio- and nanotechnology and in geochemistry. An important goal in the fields of biomineralization and biomimetics is to fine-tune these interactions for the control, e.g., of assembly of materials at the nanoscale. Here we report molecular dynamics simulations of fully hydroxylated alpha-quartz (1010), (0001), and (0111) surfaces in explicit water. We also present free energy estimates of adsorbing water and analogues of amino acid side chains onto the quartz (1010) surface. We find that at least two layers of structured water form on the surface, which is driven by the formation of a strong hydrogen bond network at the interface. Interestingly, we find that the free energy change to move methane (analogue of the side chain of alanine) from bulk water to the (1010) interface is favorable. We ascribe this to the presence of microscopic voids on the surface, which can accommodate small hydrophobic moieties and shield them from the solvent. These observations draw some useful insights into the possible mechanisms by which biomolecules, in particular peptides and proteins, bind to quartz and other silica surfaces.