Factors affecting the precipitation of calcium phosphate in vitro.

Abstract

The precipitation of calcium phosphatein vitro was studied in order to define the processes of homogeneous and heterogeneous nucleation and to study the effect of certain inhibitors of crystallization on these processes. It was shown that the solubility-determining surface phase of the calcium phosphate formed by homogeneous nucleation had a Ca/P molar ratio close to that of octacalcium phosphate (OCP) and that the most constant formation product in solution at the onset of spontaneous precipitation was that of OCP. Known inhibitors of crystallization had no effect on the formation product of homogeneous nucleation. Below the formation product of spontaneous precipitation nucleation was essentially heterogeneous and was markedly influenced by adding nucleating material to the system, by increasing the time of incubation, and by adding inhibitors of crystallization containing the grouping P-X-P (where X=O, C, or N). The level of supersaturation at the point of maximum inhibition was close to the formation product of spontaneous precipitation of calcium phospate. The implications of these observations are discussed in relation to the precipitation of calcium salts in urine.