Adsorption of aminoacids onto bone-like carbonated calcium phosphates.

The adsorption of alanine and phenylalanine onto apatites, containing simultaneously HPO42- and CO32- ions in various amount, was studied. These apatites are similar to the mineral part of calcified tissues at different stages of its maturation. The adsorption isotherms are Langmuirian in all cases whatever the amounts of HPO42 or CO32-. However, these amounts play a role in the adsorption properties of these apatites. The largest amounts of aminoacids were adsorbed by the compounds with the highest HPO42- content. The influence of the presence of PO43- ions in the incubation media was studied. These ions hinder the adsorption process by competing with the aminoacid carboxylate groups for the calcium ions at the surface of the solid. The nature of the aminoacid lateral chain, especially its size, plays a role in the adsorption. The amount of aminoacid bound at saturation decreases as the size of the side chain increases.