A density functional theory study of the interaction of collagen peptides with hydroxyapatite surfaces

Density functional theory calculations were applied to investigate the binding of four peptide strands, which are important in the collagen protein, to the bone and tooth mineral hydroxyapatite: amphiphilic PRO-HYP-GLY and HYP-PRO-GLY, and hydrophobic PRO-LYS-GLY and PRO-HYL-GLY. The particular peptide sequences are chosen for their different functional groups, containing (i) hydrophobic; (ii) uncharged polar; and (iii) charged polar side groups, thus allowing direct comparison of the general effect of these carboxylic acid and amine functional groups, as well as hydroxylation and charge, on their interactions with two major hydroxyapatite surfaces, (0001) and (0110). The calculated results are consistent with experiments, confirming that the terminal carboxyl groups and amine groups mainly contribute to the adsorption of the peptides to the hydroxyapatite surfaces and primarily to the (0110) surface rather than the dominant (0001) plane. Of the side groups in the tripeptide motifs representing the collagen protein, the -OH and positively charged -NH(3)(+) groups in particular bind strongly to the surfaces, and their presence should therefore promote hydroxyapatite growth.