Adsorption of o-Phospho-L-Serine and L-Serine onto Poorly Crystalline Apatite

摘要

The adsorption of phosphoserine and serine was studied to deter- mine the effect of amino acid functional groups on the surface reac- tivity of synthetic poorly crystalline apatite similar to bone mineral. The experimental results for phosphoserine and serine uptake agree respectively with the Langmuir and Freundlich models. Phospho- serine 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 be re- lated to the presence of phosphate groups in the molecule, which are specific attachment sites. This observation suggests that the strength of phosphate bonds to the solid surface, especially to calcium ions, is higher than that of carboxyl and hydroxyl ones. Spectroscopic observations provide evidence of an adsorption mechanism involv- ing the anionic species of the amino 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 to the native amino acids. This revealed that the molecular residues do inter- act with apatite surface calcium. The shift noted in the frequen- cies of the bands associated with carboxylate vibrations is more pronounced for phosphoserine, confirming the stronger interaction noted for this molecule. Based on these results, one can conclude that the sorbent and sorbate charged species play an important role in the mechanism of uptake of the amino acids onto crystal surfaces. This may contribute to a better understanding of the mechanism by which phosphoproteins could influence mineralization processes and caries.