Amphiphilic binding site of ethanol in reversed lipid micelles

Proton and phosphorous NMR spectroscopy were used to study a model membrane system consisting of reversed lipid micelles to test the hypothesis that alcohol and anesthetics compete with water for the same hydrogen bonding sites on lipid surfaces. When low concentrations of water and ethanol were added in equal parts in the absence of lipid and nonpolar solvent, the NMR spectrum consisted of a combination of all water and ethanol peaks, except for the ethanol OH peak. Compared with pure water, the bulk water peak became broader and shifted downfield to 5.1. In reversed micelles made of water, DPPC, and nonpolar solvent, the addition of ethanol caused a conspicuous upfield shift of the bulk water peak and also broadened and decreased its height. This effect was magnified as ethanol concentration increased, indicating that alcohol alters the organization of water and moves water protons into a new domain where nearby atoms are more able to shield water protons. Water shifted the P-31 resonant frequency of DPPC downfield, and the effect magnitude varied with water concentration. Ethanol did not cause such a shift, suggesting that only water was interacting in the phosphorous region. Two-dimensional nuclear Overhauser effect (NOESY) spectroscopy indicated that the ethanol methylene is adjacent to the methylene next to the carbonyl of the DPPC fatty acid moiety, at least in some configurations. Interaction at this point is also indicated by the transformation from an apparent pentet to a doublet of triplets at certain ethanol/water ratios.