The effect of ethanol on the structure of phosphatidylserine bilayers.

Thermotrophic and structural effects of ethanol on phosphatidylserine (PS) membranes were investigated by differential scanning calorimetry (DSC) and X-ray diffraction. It was found that up to 15% (v/v) added ethanol, there is little change in the melting temperature of the phospholipid and no change in the interbilayer (d) spacing in the gel phase, indicating that there is no interdigitation of the hydrocarbon chains. Above the melting temperature of the phospholipid, a large decrease of the d spacing, due primarily to a decrease in the thickness of the bilayer, was found. Ethanol molecules located in the headgroup region apparently expand the area available to the headgroups with concomitant coiling of the acyl chains, resulting in marked thinning of the lipid layer.