Facet selectivity of binding on quartz surfaces : free energy calculations of amino-acid analogue adsorption

Facet selectivity of binding of small molecules onto three facets of quartz is explored using molecular dynamics (MD) simulations. The free energy of adsorption of amino-acid analogues on the (100), (001) and (011) hydroxylated α-quartz surfaces under aqueous conditions are calculated using the potential of mean constraint force method. The most favorable free energies of adsorption were observed for the aromatic and negatively charged analogues, while the positively charged analogue showed negligible binding. The polar and hydrophobic analogues, methanol and methane, had intermediate adsorption strengths. Shielding of hydrophobic regions of polar and charged adsorbates, conferred by the surface, is suggested to contribute significantly to their surface binding, with the adsorption of methanol and butyl ammonium being more favorable than that of water and ammonium, respectively. Ethanoate is the only analogue to support substantial adsorbate-silanol hydrogen bonding. All the adsorbates, other than water, showed statistically significant facet selectivity in the Gibbs free energy of binding. These findings, if used alongside peptide conformation data, may provide a basis from which we can start to design quartz-binding peptides with controllable binding properties on different quartz facets