Hydroxyapatite crystallization on sodium cholate

Bile acids are known to promote pathological calcification in vivo through the formation of their calcium salts. The role of cholic acid's sodium salt regarding its capability of inducing hydroxyapatite was investigated. It was found that the precipitation of hydroxyapatite was favored by the presence of this organic molecule. In this work, the constant composition kinetics technique was used, which has been proved suitable for the study of the formation of a sparingly soluble salts in the presence of another compound. Kinetic analysis of the nucleation rates as a function of the solution supersaturation yielded a value of 2 for the number of ions forming the critical nucleus. It was suggested that the formation of hydroxyapatite is initiated via interaction of the calcium ions with the negative end of C = O bond. The apparent order found from kinetics data was 1.7 +/- 0.4 suggesting a surface diffusion-controlled mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.