Nucleation at surfaces: the importance of interfacial energy.

The nucleation and growth of stone-forming minerals on the surfaces of other crystalline phases, cellular material, and immobilized macromolecules must be important in the formation of stones in the urinary tract. The nucleation and growth of calcium oxalate monohydrate (COM) crystals were studied using the constant composition kinetics technique, in solution supersaturated with respect to COM (sigmaCOM = 1.44). The solid phases during the reaction were examined by x-ray diffraction, scanning electron microscopy, and diffuse reflectance Fourier transform infrared spectroscopy. Human serum albumin was found to nucleate COM crystals when immobilized on hydroxyapatite (HAP) surfaces. The induction period for nucleation of COM on HAP surfaces preadsorbed with albumin significantly decreased to about 65 min from about 230 min for pure HAP particles. The initial growth rate of COM on pure HAP particles, Rm approximately/= 0.56 X 10(-7) mol/min per m2, was slower than that for HAP surfaces preadsorbed with albumin, 2.14 x 10(-7) mol/min per m2. The surface properties were characterized using contact angle measurements by sessile drop and thin layer wicking. The thermodynamic results suggested that surfaces with high Lewis base parameter values (gamma-) and low interfacial tension with water (gammaSL) are more effective in the nucleation and growth of crystal phases.