Inhibition of hydroxyapatite formation in aqueous solutions by amino acidswith hydrophobic side groups

Four natural amino acids with hydrophobic nonpolar side group (alanine, phe nylalanine, proline, and methionine) were examined and their activity on hy droxyapatite, HAP, crystallization was assessed. The method used was the co nstant composition technique, at low supersaturation levels. Crystallizatio n took place exclusively on well-characterized HAP seed crystals introduced in supersaturated solutions only with respect to the calcium phosphate sal t. The fit of the experimental data to the Langmuir adsorption isotherm ind icates an inhibition mechanism based upon molecular adsorption of the amino acids on the HAP crystal surface at active growth sites. The inhibitory ef fect was related to the adsorption affinity constant of each amino acid to the crystal surface, which depends on the nature of the amino acids' side g roup.