First-principles study of the adsorption of lysine on hydroxyapatite (1 0 0) surface

The adsorption of lysine (Lys) on hydroxyapatite (HA) (1 0 0) surface was studied using density functional theory calculations within the generalized gradient approximation framework. The optimal adsorption pattern was identified from a number of interactive Lys–HA structures. The carbonyl-O, amine-H and Cɛ–H atoms are active sites in Lys that interact directly with the Ca ion and phosphate-O atoms on the HA (1 0 0) surface, respectively. Multiple interactions were noted between Lys and HA surface. The adsorption is mainly stabilized by the Casingle bondO ionic bonding, followed by hydrogen bond and/or van der Waals interaction between phosphate-O and Lys–HA. Both the Lys and HA surface structures are subjected to some changes upon adsorption. The zwitterionic form of Lys was found more stable on the HA (1 0 0) surface than its neutral form. Our calculations reveal the structural characteristics and their variations for the Lys–HA systems, which are essential for understanding the interaction mechanism of biomolecules with inorganic biomaterials.