Association Behavior in Steroidal Systems — NMR Spectroscopic and Vapor Pressure Osmometric Studies of Bile Acid Derivatives
Nmr and vapor pressure osmometric (VPO) studies indicate that bile acid esters self-associate and form small aggregates in organic solvents. Intermolecular hydrogen bonding between hydroxyl groups on the steroid nucleus and possibly the carboxylate on the side chain is proposed to play a vital role in the formation of aggregates. The concentration dependence of the chemical shift of the hydroxyl protons confirms the existence of H-bonds in these systems. The decrease in 13C relaxation times of methyl cholate in CDCl3 with increasing concentration is consistent with the self-association in this system. Analysis of the VPO data for methyl cholate in chloroform indicates that the model of self-association is best described by a Type III indefinite sequential type of self-association rather than a monomer-n-mer one.
KeywordsCholesterol Surfactant Chloroform CDCl3 Methylene Chloride
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