Molecular thermodynamics for amino‐acid adsorption at inorganic surfaces

Abstract The interaction of polypeptides and proteins with an inorganic surface is intrinsically dependent on the interfacial behavior of amino acids and sensitive to solution conditions such as pH, ion type, and salt concentration. A faithful description of amino‐acid adsorption remains a theoretical challenge from a molecular perspective due to the strong coupling of local thermodynamic nonideality and inhomogeneous ionization of both the adsorbate and substrate. Building upon a recently developed coarse‐grained model for natural amino acids in bulk electrolyte solutions, here we report a molecular theory to predict amino‐acid adsorption on ionizable inorganic surfaces over a broad range of solution conditions. In addition to describing the coupled ionization of amino acids and the underlying surface, the thermodynamic model is able to account for both physical binding and surface associations such as hydrogen bonding or bidentate coordination. It is applicable to all types of natural amino acids regardless of the solution pH, salt type and concentration. The theoretical predictions have been validated by extensive comparison with experimental data for the adsorption of acidic, basic, and neutral amino acids at rutile (α‐TiO2) surfaces.