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.