A potentiometric titration study on the dissociation of bile acids related to the mode of interaction between different head groups of nonionic surfactants with free bile salts upon mixed micelle formation in water |
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Authors: | T Tanaka T Nakashima S Lee S Nagadome Y Sasaki M Ueno G Sugihara |
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Institution: | (1) Department of Chemistry Faculty of Science, Fakuoka University, Nanakuma, Jonan-ku, 814-80 Fukuoka, Japan;(2) Department of Chemistry Faculty of Education, Oita University, 700 Dan-noharu, 870-11 Oita, Japan;(3) San-Ei-Gen FFI, Inc., 1-1-11 Sanwa-cho, 561 Toyonaka Osaka, Japan;(4) Science University of Tokyo, 1-3 Kagurazaka, Sinjuku-ku, 162 Tokyo, Japan |
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Abstract: | By constructing an elaborate set of potentiometric titration together with data analysis system, apparent acid dissociation indices (pK
a
app
) for two bile acids were determined in the mixed surfactant system of bile salts (Sodium Deoxycholate, NaDC, and Sodium Chenodeoxycholate, NaCDC) with nonionic surfactants (Hexaethyleneglycol monon-dodecylether, C12E6, Decanoyl-N-methylglucamide, MEGA-10) in aqueous solution at ionic strength 1.5 as a function of mole fraction in the surfactant mixture. It was found that with increasing the bile salt concentration, pK
a
app
as well as pH showed an abrupt rise at a certain concentration of the bile salt being regardable as a critical micellization concentration (CMC) and reached a constant value at the range sufficiently higher than CMC for each pure bile salt system, meaning that the dissociation degree of carboxyl group in micelle is smaller than that in bulk. In the mixed systems of free bile salts with nonionic surfactants, the dissociation state of carboxyl groups in mixed micelles depends on the species of hydrophilic group of nonionic surfactants as well as on mole fraction in the surfactant mixture. |
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Keywords: | Potentiometric titration bile acid nonionic surfactant mixed micelle formation MEGA-10 |
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