Abstract: Crystallization kinetics of hydroxyapatite, HAP, in the presence of Leucine, a natural amino acid with hydrophobic side groups, were investigated at conditions of sustained supersaturation, 37 degrees C, pH 7.40, ionic strength 0.15 M. In the presence of Leucine, the crystal growth rates of HAP decreased markedly. Tauhis action is due to adsorption and subsequent blocking of the active growth sites onto the surface of the HAP crystals. The kinetic results revealed that a Langmuir-type adsorption isotherm is followed and an affinity constants of k(aff )=20.26 x 10(2) L/mol for HAP crystal surface were calculated. The apparent order of the crystal growth reaction was found to be equal to two, suggesting a surface diffusion controlled mechanism.
Abstract: The effect of acetaminophen, a well known analgesic and fever-reducing medicine, on the calcium carbonate crystal growth was investigated under plethostatic conditions. The calcification rates measured was reduced by 9.1-63.2% in the presence of acetaminophen. Kinetic analysis according to a Langmuir-type adsorption isotherm lead to the calculation of an affinity constant K (aff) = 8.33 x 10(2 )dm(3 )mol(-1). The apparent order found from kinetic data was two suggesting a surface diffusion controlled spiral growth mechanism.
Abstract: The kinetics of calcite (CaCO(3)) crystallization on calcite seed crystals in the presence of taurine was investigated by the constant composition method. The presence of taurine (4 x 10(- 5)- 4 x 10(-4)M) in the supersaturated solutions lead to calcite crystals with a characteristic discontinuous planes of growth and poor habit, as compared to the hombohedral morphology of the seed crystals. The acceleration effect of taurine on the crystal growth rate was 17-96%. The apparent order of the crystal growth was found to be 2.0+/- 0.2 typical for a surface diffusion-controlled spiral growth processes.
Abstract: The effect of sodium alginate on the crystal growth of hydroxyapatite (HAP) was investigated at sustained supersaturation by the constant composition technique. Sodium alginate was found to inhibit HAP crystal growth at low concentrations and reduced the crystal growth rates by 42-86% for inhibitor concentrations of 2.1x10(-7)-12.6x10(-7) mol/l. The inhibition effect on the crystal growth rate may be explained possibly through adsorption onto the active growth sites. A detailed kinetics analysis suggested a Langmuir-type adsorption of the alginate on HAP surface and a value of 1.63x10(7) l/mol was obtained for the affinity constant of sodium alginate for the surface of HAP. The apparent order for the crystallization reaction was determined to be approximately 2, thus suggesting a surface diffusion controlled spiral growth mechanism.
