Determination of ethanol partition coefficients to the interior and the surface of dipalmityl-phosphatidylcholine liposomes using deuterium nuclear magnetic resonance spectroscopy

The binding of ethanol-d 6 to dipalmityl-phosphatidylcholine liposomes (DPPC) can be separated into two processes, namely, ethanol in the bilayer and on the surface of the bilayer. For the deuterons of the methylene group, the T 2 of both bound states is shorter than the respective preexchange lifetime (τ B) and therefore the amount of ethanol bound to both sites can be determined from the decrease in the methylene intensity resonance in the presence of DPPC. For the methyl resonance, however, only the T 2 of deuterons on ethanol bound to the surface is less than its τ B and the amount of surface bound ethanol-d 6 can be determined. Subtraction yields the amount of ethanol bound within the bilayer. The partion coefficient for internally bound ethanol remains constant from 0 to 3.5 m ethanol. Surface binding is, however, highly cooperative.