S. Koutsopoulos et E. Dalas, Inhibition of hydroxyapatite formation in aqueous solutions by amino acidswith hydrophobic side groups, LANGMUIR, 16(16), 2000, pp. 6739-6744
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.