Physicochemical Study of Calcium-binding Properties of Chemical Substances as Inhibitors against Calcium Phosphate Insolubilization

Abstract

Calcium-binding properties of some chemical substances known as inhibitors against calcium phosphate insolubilization were investigated using a calcium-ion-selective electrode. First, the calcium binding properties of citrate, a well-known inhibitor, were evaluated by both the formation constant K_f and two parameters N and K in the Langmuir equation. It was confirmed that the parameters N and K were superior to the formation constant K_f to describe the calcium-binding property. Second, the calcium-binding properties of several inhibitors such as poly-L-aspartate, poly-L-glutamate, and alginates were analyzed by the Langmuir equation. They were well-described by the Langmuir equation. The tested inhibitors were classified into two groups : inhibitors of which parameters were independent of their concentrations (Group 1) and those whose parameters were dependent on their concentrations (Group 2). The values of the affinity parameter K for the Group 1 inhibitors were larger than those for the Group 2 inhibitors.