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Effect of Unsaturation on Ethanol-Induced Interdigitation in Model Lipid
Bilayers 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. Support provided by: National Science Foundation - Research Experience for Undergraduates Grant |
