| Abstract
| - Previously, structural models, observed in fibers and crystals, were proposed for sodium deoxycholate(NaDC), glycodeoxycholate (NaGDC), taurodeoxycholate (NaTDC), and taurocholate (NaTC) micellaraggregates, and were verified in aqueous solutions by means of several techniques. Here we report theX-ray analysis of sodium glycocholate (NaGC) fibers, which indicates that NaGC micellar aggregates couldbe formed by dimers and octamers as in the case of NaTC. Moreover, we present electrolytic conductanceand dielectric measurements on NaGDC, NaTC, and NaGC aqueous micellar solutions to verify our micellaraggregate models. Specific conductance values of 0.1 mol dm-3 NaDC, NaTDC, NaGDC, NaTC, and NaGCsolutions containing NaCl at concentration ranging from 0 to 0.8 mol dm-3 practically do not depend onthe particular bile salt. Comparison with NaCl values shows that bile salt contribution to conductancedecreases by increasing NaCl concentration, is nearly zero around the concentration range 0.5−0.6 moldm-3, and becomes negative at higher concentration. This behavior can be explained if Na+ ions stronglyinteract with bile salt anions and reinforce their interaction when micellar size increases. Even the inclusionof Na+ and Cl- ions, coming from NaCl, into micellar aggregates cannot be excluded, especially at highionic strength. NaDC, NaTDC, NaGDC, NaTC, and NaGC present high values of the average electricdipole moment per monomer μ that can be justified by a remarkable hydration of their micellar aggregates.Reasonably, micellar aggregate composition and population change very slightly or do not change at allwithin the temperature range 15−45 °C, because μ is nearly constant in this interval. Results also suggestthat Na+ ions are anchored to anions in dilute solution, thus forming ion pairs in the case of NaTC andNaGC, at least. Dihydroxy and trihydroxy bile salts are characterized by very similar cation−anioninteraction strengths, even though their structures are different. The trend of μ, which moderately decreasesby increasing bile salt concentration, agrees with our structural models and can be due to coexistence oftwo structures, at least.
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