2Organic Reaction Chemistry, Showa Pharmaceutical University,

The solubility of cholesterol in the binary solubilizates system (cholesterol and -sitosterol) of a sodium taurode-oxycholate solution decreased to almost half of that in the single cholesterol system. On the other hand, the cholesterol solubilities in other binary other systems (cholesterol and certain aromatics) of those solutions were the same as that of the single cholesterol system. The results of competitive solubilization between sterols and aromatics suggested that both were solubilized at different solubilization sites of a micelle. Their molecular dynamics and solubilization sites were measured by the 1HNMR method. The rotating-frame nuclear Overhauser effect and exchange spectroscopy (ROESY) contour plot of aromatics solubilized micellar solution exhibited direct cross-peaks between the aromatics and bile salt of 19-methyl protons. The observed ROESY spectra of the sterol-solubilized solutions were almost identical to those of the pure micellar solution. The spin-lattice relaxation time (T1) for aromatics solubilized in the micellar solutions increased for 18-, 19-, and 21-methyl protons of the bile salt in comparison with those of a pure micellar solution, which indicated that the micellar core changed to a loosely packed state owing to the penetration of aromatics. On the other hand, the T1 values for sterols solubilized in micelles were lesser than those for pure micellar solutions for almost all proton positions, which suggested that the sterols were compatible with the micelle. These results indicated that the aromatics were solu-bilized in micellar palisade layer interacting with bile salt of methyl protons, whereas, the sterols were solubilized to match the micellar structure via the steroids interaction