Adsorption of O-phospho-L-serine and L-serine onto poorly crystalline apatite

The adsorption of phosphoserine and serine was studied to determine the eff ect of amino acid functional groups on the surface reactivity of synthetic poorly crystalline apatite similar to bone mineral. The experimental result s for phosphoserine and serine uptake agree respectively with the Langmuir and Freundlich models, Phosphoserine exhibits stronger adsorption capacity and a higher affinity constant for the surface crystals compared to serine molecules, The enhanced adsorption capacity noted for phosphoserine might b e related to the presence of phosphate groups in the molecule, which are sp ecific attachment sites. This observation suggests that the strength of pho sphate bonds to the solid surface, especially to calcium ions, is higher th an that of carboxyl and hydroxyl ones. Spectroscopic observations provide e vidence of an adsorption mechanism involving the anionic species of the ami no acids and the surface of the crystals. Thus, a change in the position of the band of carboxyl groups occurred for the adsorbed molecules compared t o the native amino acids, This revealed that the molecular residues do inte ract with apatite surface calcium. The shift noted in the frequencies of th e bands associated with carboxylate vibrations is more pronounced for phosp hoserine, confirming the stronger interaction noted for this molecule. Base d on these results, one can conclude that the sorbent and sorbate charged s pecies play an important role in the mechanism of uptake of the amino acids onto crystal surfaces, This may contribute to a better understanding of th e mechanism by which phosphoproteins could influence mineralization process es and caries. (C) 2001 Academic Press.