Inhibition of the amorphous calcium phosphate phase transformation reaction by polyphosphates and metal ions

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Abstract
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+2+2+. 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.