Effect of n-alkanes on lipid bilayers depending on headgroups

• Change in the main transition temperature of phospholipid against the length of added n-alkane depends on the head group of the lipids.
• Change in the lipid packing in the membrane shows the same head group dependence as the transition temperature upon the addition of n-alkane.
• Theoretical analysis indicates that enthalpy change by n-alkane in the gel phase causes the change in the transition temperature.
• The enhanced packing by n-alkane leads to an easy emergence of the subgel phase.

Phase behavior and structural properties were examined for phospholipid bilayers having different headgroups (DMPC, DMPS and DMPE) with added n-alkanes to study effect of flexible additives. Change in the temperatures of main transition of the lipid/alkane mixtures against the length of added alkanes depends largely on the headgroup. Theoretical analysis of the change of the temperature of transition indicates that the headgroup dependence is dominantly originated in the strong dependence of total enthalpy on the headgroups. The results of X-ray diffraction show that the enthalpic stabilization due to enhanced packing of acyl chains of the lipid by alkanes in the gel phase causes the headgroup-dependent change in the phase transition behavior. The enhanced packing in the gel phase also leads to easy emergence of the subgel phase with very short relaxation time at room temperature in the DMPE-based bilayers.

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