Adsorption characteristics of oligopeptides composed of acidic and basic amino acids on titanium surface

The adsorption characteristics of octapeptides, containing different numbers of aspartic acid, lysine, and alanine residues (i.e., D4K0A4, D4K1A3, D4K3A1, D4K4A0, and D0K4A4) on the surface of titanium (Ti) particles were investigated in the pH range of 3.0–8.8 at 30°C. The adsorption isotherms for octapeptides having four plural aspartic acid residues with or without lysine residues showed two distinct adsorption modes, i.e., irreversible and reversible modes, at pHs 3.0–6.5; at pH 7.0 or higher, the adsorption mode was reversible. Increasing the number of lysine residues at a fixed number of aspartic acid residues (i.e., 4) decreased the amount of peptides adsorbed in both modes. D4K4A0 adsorbed irreversibly at pHs 3.0–6.5, due to the fact that negatively charged carboxyl groups directly interact with a positively charged Ti surface, whereas positively charged amino groups of lysine residues are directed in an opposite direction toward the solution side, as predicted by molecular mechanics/dynamics calculations.