The Effects of Ethanol on the Phase Behavior of Phosphatidylethanolamine Membranes
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Differential scanning calorimetry (DSC) was used to study the themotropic phase behavior of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE). As a result of strong hydrogen bonding between the head groups of the lipid, DPPE does not naturally interdigitate. Consequently, this study specifically focused on the capacity of DPPE to interdigitate with the addition of ethanol. In DSC thermograms, interdigitation manifests itself in three ways: an increase in the main transition temperature (Tm) hysteresis, the presence of a biphasic effect, and an increase in the main transition enthalpy. With the addition of ethanol, the hysteresis of DPPE, or the difference between the Tm of the heating and cooling scans, drastically increases above the threshold concentration for interdigitation. Similarly, within the heating scans, the Tm decreases below and increases above the threshold concentration indicating a biphasic effect. Furthermore, the main transition enthalpy greatly increases at the threshold concentration. These characteristics suggest that high concentrations of ethanol may induce interdigitation in DPPE membranes.