H-1 NMR characterization of a combination model of the mixed micelle taurocholate and 1,2-ethylene-di-N-n-butylcarbamate

Abstract

The structures of micelles of taurocholate (TC) have been debated for many years. According to Funasaki's model based on 2D NMR studies, anti-parallel and parallel back-to-back dimers have been proposed as two major fragments in the micellar TC. However, according to Galantini's model based on X-ray crystal structure, anti-parallel and parallel face-to-face dimers have been proposed as two major fragments in the micelle. We propose a combined model from these two models for the structures of micelles of TC and suggest that these structures are equally composed of these four dimeric fragments. Lipid molecules can only insert into back-to-back dimeric fragments but not into face-to-face dimeric fragments in the mixed micelles of TC and lipid. A short-chain analog of glycerol lipid, 1,2-ethylene-di-N-n-butylcarbamate (1), was synthesized and was mixed with the micellar TC to form the mixed micelle of TC and compound 1. From the H-1 NMR spectra, the (omega-methyl and beta-methylene protons of compound 1 split after formation of the mixed micelle with TC. Therefore, half of the compound 1 molecules insert into the anti-parallel back-to-back dimers in the mixed micelle, and the other half of the compound 1 molecules insert into the parallel back-to-back dimers in the mixed micelle.