INHIBITION OF THE AMORPHOUS CALCIUM-PHOSPHATE PHASE-TRANSFORMATION REACTION BY POLYPHOSPHATES AND METAL-IONS

The induction time for amorphous calcium phosphate (ACP) phase transformation was monitored at pH 7.4 and T=25°C with [Ca2+]0=[PO4]0=4.0×10-3 M, as a function of added crystal growth inhibitors Mg2+, Sr2+, Zn2+, pyrophosphate (PP), and tripolyphosphate (TPP). Metal ions increase the induction time for the initiation of the phase change reaction in the order Zn2+<Sr2+<Mg2+. For polyphosphates it was observed that both PP and TPP are potent inhibitors with TPP more effective than PP as expected. The combination of Mg2+ or Sr2+ and PP or TPP leads to a synergistic delay in the onset of the phase conversion. The greatest inhibition was observed for Mg2+ and TPP. Reaction solutions containing 2.0×10-4 M Mg2+ and 4.0×10-5 M TPP resulted in a 90% increase in the induction time over what would be anticipated from an additive effect from these species. © 1990 Springer-Verlag New York Inc.