College of Chemistry and Molecular Engineering, State Key Laboratory of Rare Earth Material Chemistry and Application, Peking University, Beijing 100871, China
Abstract：In the present article, NaGDC was used to study the Ca2+-buffering capability of bile salt micelles. NaGDC is a naturally occurring bile salt which constitutes approximately 10 molar percent of bile salt composition in gallbladder. The authors selected glycine conjugated bile salts NaGDC because it precipitates with Ca2+ ions fast. The Ca2+-buffering property of sodium glycodeoxycholate (NaGDC) micelles was studied by utilizing turbidity titration, quasi-elastic light scattering (QELS), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). When the concentration of NaGDC was above the CMC, the precipitation of Ca2+ ions with NaGDC was buffered. The Ca2+-buffering capability was enhanced when the concentration of NaGDC increased. The possible mechanism of Ca2+-buffering by NaGDC micelles was discussed. When the concentration of NaGDC was below the CMC, the Ca2+ ions reacted with GDC-anions to form the Ca(GDC)2 precipitation. However, at the concentration above the CMC, NaGDC simple micelles were connected by Ca2+-bridge to form larger fibriform micelles via the interaction of carboxyl groups of NaGDC simple micelles with Ca2+ ions. When the ratio of Ca2+ to Na+ was enhanced to the fixed value, NanCam(GDC)n+2m complexes were precipitated by the further addition of Ca2+ ions.
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