The crystallization of vaterite on fibrin

Fibrin, a protein endoproduct of blood coagulation was found to be a substr ate favoring the deposition of vaterite crystals from stable supersaturated solutions at pH 8.5 and at 25 degrees C. The apparent order for the vateri te crystallization reaction was found to be 1.0 +/- 0.1, suggesting a surfa ce diffusion-controlled mechanism. The crystallization was studied by the c onstant solution composition technique thus making it possible for relative ly large amounts of the overgrowth phase to be formed and identified exclus ively as vaterite. Fibrin stabilizes this calcium carbonate polymorph, prev enting the transformation to the thermodynamically more stable calcite. Ana lysis of the initial rates of the reaction as a function of the solution su persaturation, according to the classical nucleation theory, yielded a valu e of 21 +/- 1 mJ m(-2) for the surface energy of the growing phase and a th ree-ion cluster forming the critical nucleus. (C) 2000 Elsevier Science B.V . All rights reserved.