Comparison of controlled crystallization of calcium phosphates under three kinds of monolayers

Abstract

The three different kinds of monolayers, stearic amide, stearic acid and hexadecanol, have been used in the controlled crystallization of calcium phosphates to understand “molecular recognition” effect on the inorganic-organic interface better. Although the “molecular recognition” effect between stearic amide monolayer and hydroxyapatite (HAp) is more intensive and the conglomeratic stratum of the tiny HAp crystals has been observed, the principle of controlled crystallization under stearic amide monolayers is almost the same as under stearic acid monolayer. In contrast, the hexadecanol monolayer has no such obvious effect on the crystallization of calcium phosphates as the former ones. It can been explained that whereas stearic acid and stearic amide monolayers can accumulate Ca2+ and PO3−4, OH− ions around the −COO− and −NH3+ headgroups and build the beneficial lattice configuration for the (0 0 0 1) plane of HAp, respectively, the neutral headgroups −OH of hexadecanol monolayers can not concentrate the mineral ions to accelerate the nucleation of HAp. These results clearly show that although these three kinds of monolayers have almost the same two-dimensional lattice structure, the difference of electrostatic potential of three headgroups results in the different crystallization process of calcium phosphates. From the view of “molecular recognition”, beneficial lattice matching and electrostatic interaction are two essential conditions in the biomineralization of calcium phosphate in our experiment systems. The coordination of these two factors influence the crystallization profoundly.