The kinetics of formation and dissolution of uric acid crystals

The kinetics of crystallization and dissolution of uric acid have been studied at temperatures from 15 to 45 C, using a highly reproducbile seeding technique. The rates of reaction have been followed by a precision conductometric method. The mineralization rate follows an equation second-order in relative supersaturation and the experimental evidence points to a surface controlled crystal growth. In contrast, the rapid dissolution of seed crystals into undersaturated uric acid solutions seems to be controlled by diffusion of electrolyte through the hydrodynamic boundary layer at the crystal surface. The activation energy for dissolution, 13.1 +/- 2.6 kJ/mole, is close to that expected for bulk diffusion. Values are reported for the solubility product and dissociation constant for uric acid from 15 to 45 C.