STUDIES ON SIMPLE AND MIXED BILE SALT MICELLES BY NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

High resolution nuclear magnetic resonance (NMR) spectroscopy has been used to study (a) the spectra of the common bile acids in organic solvents, (b) the structure of the bile-salt micelle and (c) the interaction of bile salt with lecithin in mixed micelles. The following is concluded: 1. 1. The common bile acids may be identified by their NMR spectra in organic solvents. 2. 2. When bile salt micelle formation takes place in 'HaO, a differential broadening occurs of the signals from the hydrophobic side of the bile salt molecule compared with those of the hydrophilic side. This observation suggests that the bile salt micelle associates hydrophobically with the hydrocarbon parts of the bile salt on the inside of the micelle and the hydroxyls and ionic parts of the molecule on the outside in contact with the aqueous environment. 3. 3. Relatively small amounts of bile salt convert the broad spectrum of lecithin in 2H2O to a high resolution NMR spectrum. As the ratio of lecithin to bile salt in the mixed micelle is increased, the signals from the hydrophobic side of the bilesalt molecule are broadened indicating decreased molecular motion of these protons. Further, the percent of lecithin alkyl chains present as a high resolution peak increases as the amount of bile salt is decreased. These facts are consistent with the hypothesis that the lecithin-bile salt micelle exists as a bilayer of lecithin surrounded on its hydrophobic surfaces by bile salt molecules. The hydrocarbon side of the bile salt molecules associate with some of the alkyl chains of the lecithin thus hiding them from the aqueous environment. The entire exterior of the micelle is hydrophilic, the ends being covered with the polar groups of the lecithin and the sides with the polar groups and hydroxyls of the bile salts. © 1969.