The interaction of proteins with silica surfaces. Part II: Free energies of capped amino acids

Binding free energies of the fifteen proteinogenic amino acids were investigated for neutral silica surfaces of varying silanol density by means of biased molecular dynamics. A new force field parameterized to reproduce the results of highly accurate ab initio calculations has been employed in atomistic simulations to provide a balanced description of the adsorbate silica interactions. The calculated free energies increase in the order quartzOH < quartz < IPC-1P. The surface heterogeneity and the local curvature enhance the binding free energy due to the cooperative effects between the silica surface and the hydrophobic and hydrophilic parts of amino acids. The propensity towards amino acids with aromatic side chains has been observed for homogenous flat surfaces, with the effect being much stronger for the quartz without surface silanol groups than for fully hydroxylated silica surfaces.