Hydroxyapatite surfaces in interaction with biomolecules from H2O to amino acids

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] is the main constituent of the mineral phase in mammalian bones and teeth enamel and it is widely applied as an orthopaedic and dental biomaterial. Despite the various applications, fundamental knowledge of the interaction mechanisms of hydroxyapatite with biomolecules is still poorly understood. In the present work, B3LYP periodic simulations of the adsorption processes of different molecules (H2O, CO, HCOOH, glycine and some other amino acids) on two of the most studied HA surfaces, namely the (001) and the (010), have been carried out by means of the quantum-mechanical CRYSTAL06 code. Gaussian basis set of double-zeta quality in combination with the accurate B3LYP functional have assured the best compromise between cost of the calculation and reliability of the obtained results. In this communication, the reference methodology and the complete characterization of the hydration process as well as the preliminary acid dissolution steps of HA surfaces are addressed. Both energetic and vibrational properties of the models examined will be discussed and compared to experimental data (microcalorimetric and IR spectroscopic measurements). As for amino acids adsorption simulations, which are fundamental for the knowledge of HA in vivo behaviour, the stability of different forms of interaction, neutral vs zwitterionic, as well as H2O role in the interaction will be presented.