Effect of concentrations of lecithin, calcium and oxalate on crystal growth of calcium oxalate in vesicles

The crystal growth of calcium oxalate (CaOxa) in lecithin (PC)-water vesicles has been studied by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and dynamic laser scattering (DLS). The molar ratio of calcium to oxalate (Ca2+/Oxa2−), the original concentration of CaOxa [c(CaOxa)], the concentrations of PC and additive potassium citrate (K3cit) can influence the morphology and phase composition of CaOxa crystals. The diameter of CaOxa crystals obtained in vesicles (80-150 nm) is smaller than that in bulk solutions (about 1500 nm). When the ratio of Ca2+/Oxa2− is nearly 1.0, the percentage of COD in CaOxa crystals reaches the maximum. When c(CaOxa) increases, the percentage of COM decreases and that of COD increases. The content of COD reaches a constant percentage when c(CaOxa) > 0.10 mol/L. COT was obtained only at a very low CaOxa concentration of less than 0.01 mol/L. The concentration of PC greatly affects crystal planes of CaOxa crystals. When PC concentration is above critical vesicle concentration (CVC, 1.875 mg/mL), vesicles were formed. In vesicle system, the (0 2 0) crystal plane of CaOxa was preferentially grown. K3cit inhibits the pre-critical nuclei of COM and favors COD.