Characterization of a G_M1-dependent surface interaction for alcohol with DPPC membranes

A unique surface interaction for perdeuterated ethanol and 1-butanol with dipalmitoylphosphatidylcholine (DPPC)/monosialoganglioside (G_M1) multilamellar vesicles can be detected from the fast exchange averaging of the nuclear quadrupole coupling constant of the alcohol in the free and bound states using deuterium NMR. At 1.0% perdeuterated ethanol or 0.5% perdeuterated 1-butanol, a small splitting of the alcohol resonance(s) was detected in the liquid-crystalline phase, but not in the gel phase of the bilayer. The observed splitting is proportional to the fraction of alcohol bound and is dependent on temperature, alcohol, and G_M1 concentrations. The splitting was only observed in the presence of negatively charged G_M1 but not neutral asialoganglioside (asialo-G_M1) in DPPC multilamellar vesicles. The observed splitting decreased with the addition of Ca²⁺ or Mg²⁺ ions. This effect was reversed upon the addition of chelating agents. It is proposed that the unique surface interaction for alcohol may result from small surface perturbations of the phosphatidylcholine head groups by the negatively charged sialic moieties of neighboring G_M1 molecules in the bilayer.