Characterizing the adsorption of peptides to TiO2 in aqueous solutions by liquid chromatography

The interactions between titanium oxide (TiO(2)) and flexible peptides, decorated by amine, carboxyl, and phosphoserine functional groups, were characterized using analytical liquid chromatography with various loading and eluting solutions. This approach enabled discernment of the type of intermolecular interactions generated between the peptides and the metal oxide surfaces in addition to unraveling more subtle effects, specific ions, and oxide phase may have on the adsorption. The peptide presenting Lys residues adsorbed to the oxide surface in the presence of Tris buffer and eluted under conditions that indicated its binding via electrostatic interactions at physiological pH values. Upon adsorption to the oxide in the presence of phosphate buffer, the same peptide exhibited stronger electrostatic interactions with the surface, mediated by the buffer phosphate ions. In Tris-buffered saline (TBS), pH 7.4, as the adsorption medium, the peptide with the phosphoserine residues exhibited affinity indicative of coordinative binding to the titanium oxide, whereas a similar peptide decorated by carboxylate groups failed to adsorb. On the basis of differences in the interactions of these peptides with the TiO(2), the efficient separation of the two peptides was demonstrated. A basic amphiphilic peptide, composed mostly of Lys and Leu residues, was found to strongly adsorb to TiO(2) while in helical conformation only, demonstrating the strong impact the secondary structure may have on adsorption to the surface. The methodology presented in this study allows the elucidation of in situ binding mechanism and relative strengths to titanium oxide surfaces at conditions which resemble biologically relevant environments.