Effect of Unsaturation on Ethanol-Induced Interdigitation in Model Lipid Bilayers Bennett Addison and Eric Smith

Abstract

Differential scanning calorimetry (DSC) was used to observe the effect of unsaturation on phase transition temperatures of model lipid bilayers. In the presence of ethanol, pure 1,2-Diarachidoyl-sn-Glycero-3-Phosphocholine (DAPC), a synthetic lipid with two saturated 20 carbon-length acyl chains is known to interdigitate when the bilayer transitions between planar gel phase Lb? and liquid crystalline phase La. This interdigitation is signified by a biphasic effect while plotting phase transition temperature versus ethanol concentration. DAPC samples were hydrated with various concentrations of ethanol, and the biphasic plot was observed. Unsaturated lipids were then introduced to observe their effects on the phase transition temperatures and interdigitation. 1,2-Dieicosenoyl-sn-Glycero-3-Phosphocholine (DEiPC), a synthetic lipid with both acyl chains of 20 carbons and a cis double bond on both 11th carbons, was mixed with DAPC. Different mixtures of saturated and unsaturated lipids were prepared. The effect of ethanol was observed for each mixture using DSC. By increasing the percentage of unsaturation and therefore decreasing bilayer stability, the phase transition temperature was expected to decrease and the threshold concentration (concentration needed to induce interdigitation) to increase. Both effects were observed, but only to a small degree. Multiple hypotheses are currently being tested to explain this observation.