甘氨脱氧胆酸钠胶束对Ca^2＋离子的“缓冲”作用及其机理

Study on the Mechanism of Ca^(2+)-Buffering by Sodium Glycodeoxycholate Micelles

采用浊度滴定、激光光散射谱、透射电子显微镜和傅里叶变换红外光谱等方法研究了甘氨脱氧胆酸钠(NaGDC)胶束对Ca2+的"缓冲"作用及其机理。结果表明,NaGDC浓度在CMC以上时,将延缓甘氨脱氧胆酸钙盐的沉淀,浓度越高"缓冲"能力越大。可能的作用机理是当NaGDC浓度小于CMC时,Ca2+直接与GDC-离子作用,形成甘氨脱氧胆酸钙沉淀;当NaGDC浓度大于CMC时,首先,Ca2+与NaGDC胶束亲水面上的羧基作用,使NaGDC小胶束通过Ca2+桥连接形成纤维状的大胶束。而后,随着Ca2+浓度的增加,纤维状胶束中与Ca2+作用的COO-逐渐增多,当胶束中Ca2+/Na+比增大到一定值时,最终形成NanCam(GDC)n+2m沉淀,从而延缓了甘氨脱氧胆酸钙盐的生成。为研究胆汁中表面活性与金属离子的复杂相互作用给出了新思路。

In the present article, NaGDC was used to study the Ca^2＋ -buffering capability of bile salt micelles. NaGDC is a natu rally 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 Ca^2＋ ions fast. The Ca^2＋-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 CIVIC, the precipitation of Ca^2＋ ions with NaGDC was buffered. The Ca^2＋ -buffering capability was enhanced when the concentration of NaGDC increased. The possible mechanism of Ca^2＋ -buffering by NaGDC micelles was discussed. When the concentration of NaGDC was below the CIVIC, the Ca^2＋ 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 Ca^2＋ ions. When the ratio of Ca^2＋ to Na^＋ was enhanced to the fixed value, NanCam（GDC）n＋2m complexes were precipitated by the further addition of Ca^2＋ ions.