Constant Composition Studies Verify the Utility of the Cabrera−Vermilyea (C-V) Model in Explaining Mechanisms of Calcium Oxalate Monohydrate Crystallization

Abstract

The classic theory of Cabrera and Vermilyea (C-V) postulates that inhibition of crystallization by impurities is the result of pinning of step motion. Although generally accepted, the predictions of the C-V model have not been previously linked to studies of impurity adsorption in macroscopic crystallization systems. Since calcium oxalate monohydrate (COM) is the primary constituent of most human kidney stones, effects of impurities on COM crystallization are biologically relevant. Recent in situ atomic force microscopy (AFM) studies suggest that citrate molecules adsorb to COM step edges on the (-101) face, thereby pinning step motion and decreasing the velocity of the steps. We have now investigated the crystallization kinetics of COM in the presence of citrate at 37 °C and I ) 0.15 mol L -1 using the constant composition (CC) method. The dependence of growth rate on both supersaturation and citrate concentration were measured, and the behavior of the COM-citrate system was found to be in reasonable agreement with the predictions of the C-V model, provided that, in addition to pinning of step motion on the (-101) face through the Gibbs-Thomson effect, the kinetic coefficient that relates step speed to supersaturation is assumed to decrease with increasing citrate levels on all faces. The dependence of macroscopic crystal aspect ratio on citrate level in these CC studies also fits this model. Thus, we find that the results provide a mechanistic link between the microscopic AFM measurements of step kinetics and the macroscopic CC data on crystal growth rates and crystal habit.

Improved Model for Inhibition of Pathological Mineralization Based on Citrate–Calcium Oxalate Monohydrate Interaction

“…[17] Those observations suggested that citrate inhibited COM growth by pinning step motion. Recent measurements of bulk COM growth rates [21] were consistent with that conjecture. To test this hypothesis and develop a detailed physical model of COM inhibition, we used in situ AFM to quantify the dependence of step speed on supersaturation and citrate concentration and correlate the results to a molecular-scale view of the surface.…”

Inhibition of calcium oxalate monohydrate growth by citrate and the effect of the background electrolyte

“…These observations were consistent with molecular-modeling predictions of strong binding of citrate to the steps on this face [23] and led Qiu et al [23,24] to hypothesize that citrate-inhibited COM growth by binding to the step edges to create pinning sites that impeded step motion. Measurements of bulk COM growth rates by Wang et al [25] were also consistent with this picture. More recently, Weaver et al [26] showed that the dependence of COM step kinetics on citrate concentration can be understood quantitatively through the classic model of step pinning that was first proposed by Cabrera and Vermilyea (C-V) in 1958 [27], provided that model is modified to include a more realistic view of citrate adsorption dynamics, the effect of citrate on the kink site density, and an expression for the Gibbs-Thomson (G-T) effect that is correct even at high driving force, i.e., high supersaturation levels.…”

Dynamics of crystallization and dissolution of calcium orthophosphates at the near-molecular level

“…Small amino acids can also promote rapid transformation of amorphous CaPs into apatite [18]. However, some aspartic-acid-rich proteins and peptides could significantly inhibit the formation of calcium-based minerals [19][20][21][22][23]. Certain polyelectrolytes induced HAP crystallization at low temperatures and inhibited its nucleation at high temperatures [24].…”