Matsuoka Keisuke, Moroi Yoshikiyo
Chemistry and Physics of Condensed Matter, Graduate School of Sciences, Kyushu University-Ropponmatsu, Chuo-ku, 810-8560, Fukuoka, Japan.
Biochim Biophys Acta. 2002 Feb 28;1580(2-3):189-99. doi: 10.1016/s1388-1981(01)00203-7.
Micellization of sodium deoxycholate (NaDC) and sodium ursodeoxycholate (NaUDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle, where sodium cholate (NaC) was used as a reference. The fluorescence probe technique of pyrene was employed to determine accurately the CMC values for the bile salts, which indicated that a certain concentration range of CMC and a stepwise aggregation for micellization were reasonable. The temperature dependences of micellization for NaDC and NaUDC were studied at 288.2, 298.2, 308.2, and 318.2 K by aqueous solubility change with solution pH. Aggregations of the bile salt anions were analyzed using the stepwise association model and found to grow in size with increasing concentration, which confirmed that the mass action model worked quite well. The average aggregation number was found to be 2.5 (NaUDC) and 10.5 (NaDC) at the concentration of 20 mM and at 308.2 K. The aggregation number determined by static light scattering also agreed well with those by the solubility method in the order of size: NaUDC<NaC<NaDC at 308.2 K. The results indicated that the location of the OH group at C-7 and its orientation were the most important factors from the viewpoint of chemical structure for the growth of micelles. The activity measurement for sodium ions was made by a sodium ion selective electrode in order to confirm the low counterion binding to micelles and the validity of the present association model of bile salts, but the model did not hold good for NaDC at higher concentrations.
以胆酸钠（NaC）作为参比，研究了脱氧胆酸钠（NaDC）和熊去氧胆酸钠（NaUDC）的胶束化过程，包括临界胶束浓度（CMC）、胶束聚集数以及反离子与胶束的结合程度。采用芘荧光探针技术精确测定了胆盐的CMC值，结果表明一定浓度范围的CMC以及胶束化的逐步聚集是合理的。通过溶液pH值变化引起的水溶性变化，研究了NaDC和NaUDC在288.2、298.2、308.2和318.2 K下胶束化的温度依赖性。使用逐步缔合模型分析了胆盐阴离子的聚集情况，发现其尺寸随浓度增加而增大，这证实了质量作用模型效果良好。在20 mM浓度和308.2 K温度下，发现平均聚集数分别为2.5（NaUDC）和10.5（NaDC）。通过静态光散射测定的聚集数与溶解度法测定的结果在大小顺序上也吻合良好：在308.2 K时，NaUDC＜NaC＜NaDC。结果表明，从化学结构角度来看，C-7位OH基团的位置及其取向是胶束生长的最重要因素。为了证实反离子与胶束的低结合以及当前胆盐缔合模型的有效性，使用钠离子选择性电极对钠离子进行了活性测量，但该模型在较高浓度下对NaDC并不适用。
