Solubilization of cholesterol in two binary mixed micelles of bile salt and nonionic surfactant |
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Authors: | Hiroyuki Asano Hiroki Sasamoto Minoru Ueno |
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Affiliation: | (1) Department of Applied Chemistry, Faculty of Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku-ku, 162 Tokyo, Japan;(2) Institute of Colloid and Interface Chemistry, 1-3 Kagurazaka, Shinjuku-ku, 162 Tokyo, Japan |
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Abstract: | The saturated amounts of solubilized cholesterol (Cch) in mixed micelles of sodium cholate (NaC) and octaoxy-ethylene glycol monon-decyl ether (C10E8) and of sodium zyme assay at 25, 29, 33 and 37°C. The Cch values in both systems increase with the total surfactant concentration. Because the mixed micelles for both systems tend
to form C10E8-rich micelles near the critical micellar concentration (CMC) of the mixed system, the curves of cholesterol solubility approached
the Cch curve for C10E8 alone near the CMC. The tendency of Cch to decrease in both systems with increasing mole fractions of bile salts resembled that of the mean aggregation number of
micelles. Thermodynamic analyses of cholesterol solubilization showed that the free energy of solubilization, if considered
as the transfer of cholesterol from solid state to micellar environment, increased with increasing mole fraction of bile salt.
The enthalpy of cholesterol solubilization (ΔHS→M) decreased with the mole fraction of bile salts and showed break points around the mole fraction of 0.75 for the NaC−C10E8 system and at 0.60 for the NaDC−C10E8 system, respectively. These phenomena resemble earlier hydrophobicity data for mixed micelles by fluorescence measurements.
Furthermore, Cch values for the NaDC−C10E8 system were larger than those for the NaC−C10E8 system because of the structural differences at the 7α hydroxyl group between NaC and NaDC. This fact was confirmed by thermodynamic
calculations. |
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Keywords: | Cholesterol octaoxyethylene glycol monon-decyl ether sodium cholate sodium deoxycholate solubilization |
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