Ninomiya Ryoko, Matsuoka Keisuke, Moroi Yoshikiyo
Chemistry and Physics of Condensed Matter, Graduate School of Sciences, Kyushu University, Ropponmatsu 4-2-1, Chuo-ku, Fukuoka 810-8560, Japan.
Biochim Biophys Acta. 2003 Nov 15;1634(3):116-25. doi: 10.1016/j.bbalip.2003.09.003.
Micellization of sodium chenodeoxycholate (NaCDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle at 288.2, 298.2, 308.2, and 318.2 K. They were compared with those of three other unconjugated bile salts; sodium cholate (NaC), sodium deoxycholate (NaDC), and sodium ursodeoxycholate (NaUDC). The I(1)/I(3) ratio of pyrene fluorescence and the solubility dependence of solution pH were employed to determine the CMC values. As the results, a certain concentration range for the CMC and a stepwise molecular aggregation for micellization were found reasonable. Using a stepwise association model of the bile salt anions, the mean aggregation number (n) of NaCDC micelles was found to increase with the total anion concentration, while the n values decreased with increasing temperature; 9.1, 8.1, 7.4, and 6.3 at 288.2, 298.2, 308.2, and 318.2 K, respectively, at 50 mmol dm(-3). The results from four unconjugated bile salts indicate that the number, location, and orientation of hydroxyl groups in the steroid nucleus are quite important for growth of the micelles. Activity of the counterion (Na(+)) was determined by a sodium ion selective electrode in order to confirm the low counterion binding to micelles. The solubilized amount of cholesterol into the aqueous bile salt solutions increased in the order of NaUDC<NaC<NaCDC<NaDC. The first stepwise association or solubilization constants (K(1)) between a cholesterol monomer and a vacant micelle were evaluated at different bile salt concentrations. The constants were also determined for polycyclic aromatic compounds (benzene, naphthalene, anthracene, and pyrene). The corresponding DeltaG(0) value was most negative for cholesterol among the solubilizates studied, which indicated that cholesterol was thermodynamically stabilized most by solubilization into the bile salt micelles.
在288.2、298.2、308.2和318.2 K温度下，研究了鹅去氧胆酸钠（NaCDC）的胶束化过程，测定了其临界胶束浓度（CMC）、胶束聚集数以及反离子与胶束的结合程度。将这些结果与其他三种未结合胆汁盐（胆酸钠（NaC）、脱氧胆酸钠（NaDC）和熊去氧胆酸钠（NaUDC））的结果进行了比较。利用芘荧光的I(1)/I(3)比值和溶液pH值的溶解度依赖性来确定CMC值。结果表明，CMC存在一定的浓度范围，胶束化过程存在逐步的分子聚集现象是合理的。采用胆汁酸阴离子的逐步缔合模型，发现NaCDC胶束的平均聚集数（n）随总阴离子浓度的增加而增加，而n值随温度升高而降低；在50 mmol dm(-3)时，288.2、298.2、308.2和318.2 K下的n值分别为9.1、8.1、7.4和6.3。四种未结合胆汁盐的结果表明，甾体核中羟基的数量、位置和取向对胶束的生长非常重要。通过钠离子选择性电极测定反离子（Na(+)）的活性，以确认反离子与胶束的低结合。胆固醇在胆盐水溶液中的溶解量按NaUDC<NaC<NaCDC<NaDC的顺序增加。在不同胆盐浓度下，评估了胆固醇单体与空胶束之间的第一步逐步缔合或溶解常数（K(1)）。还测定了多环芳烃（苯、萘、蒽和芘）的常数。在所研究的溶质中，胆固醇的相应ΔG(0)值最负，这表明胆固醇通过溶解在胆盐胶束中在热力学上最稳定。
