Characterization of the Crystallization Pathway of Calcium Phosphate in Liposomes

Electron microscopy is currently the most powerful method to discern the mechanisms of solid-state transformation and dissolution-reprecipitation for the studies of biomineralization. In this work, we show that solid-state NMR spectroscopy can serve as a useful complementary technique to characterize the crystallization pathway of a mineral phase. On the basis of the so-called NMR spin-diffusion method, direct evidence is given to support that the formation of the apatite phase within liposomes occurs via the solid-state transformation of the disordered phase. In this thermodynamically downhill process, the final step is the depletion of the structural water in the disordered phase, whose structural order of the phosphorus species is comparable to that of apatite.