CALCIUM-OXALATE MONOHYDRATE CRYSTALLIZATION - CITRATE INHIBITION OF NUCLEATION AND GROWTH STEPS

The inhibitory action of citrate on calcium oxalate monohydrate (COM) crystallization has been examined in terms of nucleation and crystal growth kinetic properties. Lag-time data for the appearance of crystals and [C-14] oxalate incorporation under crystal growth conditions allowed us to investigate the influence of citrate at physiological levels (3.5mM). Moreover, through the use of the EQUIL software, we formulated our solutions based on calculations of solute composition such that free calcium concentrations were the same in the absence and presence of this tricarboxylic acid. The presence of citrate had little effect on the apparent interfacial free energy as determined by nucleation kinetic studies, but total particle production was greater in the absence of citrate; this was evident from electron microscopy and was also indicated by corresponding values of pre-exponential terms of the Gibbs-Thomson equation. Crystal growth rates were lowered in the presence of citrate to 30% of the uninhibited value, and distinctive morphological habit modifications were also observed by scanning electron microscopy. Together, these findings suggest that citrate may influence COM crystallization at several stages, and we present a model for face-specific growth inhibition by citrate acting on the (010) COM crystal face.