COMPARISON OF CONTROLLED CRYSTALLIZATION OF CALCIUM PHOSPHATES UNDER 3 KINDS OF MONOLAYERS

The three different kinds of monolayers, stearic amide, stearic acid a nd hexadecanol, have been used in the controlled crystallization of ca lcium phosphates to understand ''molecular recognition'' effect on the inorganic-organic interface better. Although the ''molecular recognit ion'' effect between stearic amide monolayer and hydroxyapatite (HAp) is more intensive and the conglomeratic stratum of the tiny HAp crysta ls has been observed, the principle of controlled crystallization unde r stearic amide monolayers is almost the same as under stearic acid mo nolayer. In contrast, the hexadecanol monolayer has no such obvious ef fect on the crystallization of calcium phosphates as the former ones. It can been explained that whereas stearic acid and stearic amide mono layers can accumulate Ca2+ and PO43-, OH- ions around the -COO- and -N H3+ headgroups and build the beneficial lattice configuration for the (0 0 0 1) plane of HAp, respectively, the neutral headgroups -OH of he xadecanol monolayers can not concentrate the mineral ions to accelerat e the nucleation of HAp. These results clearly show that although thes e three kinds of monolayers have almost the same two-dimensional latti ce structure, the difference of electrostatic potential of three headg roups results in the different crystallization process of calcium phos phates. From the view of ''molecular recognition'', beneficial lattice matching and electrostatic interaction are two essential conditions i n the biomineralization of calcium phosphate in our experiment systems . The coordination of these two factors influence the crystallization profoundly.