EFFECTS OF CO3(2)-ION ON THE FORMATION OF OCTACALCIUM PHOSPHATE AT PH 7.4 AND 37-DEGREES-C

The effects of carbonate (CO32-) ion on the formation of octacalcium phosphate (OCP) were studied at pH 7.4 and 37-degrees-C. The reaction was carried out in solutions with various amounts of KHCO3 (0 20mM) and with an initial solution Ca/P ratio of 0.075-0.25. CO32- ion changes the OCP/apatite ratio of the product, depending upon the Ca/P ratio of the solution, that is, with the increase in CO3 concentration, the amount of OCP increases and then decreases, while the amount of apatite decreases and then increases: when the Ca/P of the solution is high, a smaller amount of CO32- ion disturbs the crystal growth of OCP. The morphology of the products is plate-like under various amounts CO3, but the thickness decreases and the crystal size becomes small with increasing CO3 concentration. These results indicate thal CO32- ion significantly affects the product and morphology of final crystals. Possible roles of CO32- ion in the biological crystallization are discussed.