Differential scanning calorimetry studies of hydration forces with phospholipid multilamellar systems

Abstract

True differential calorimetry using a DSC device was used to study the thermal behavior of two hydrated phospholipids: DPPC or dipalmitoyl phosphatidyl choline and PI phosphatidylinositolmonophosphate. The amount of water varied between 15% (w/w) and 60% (w/w). The relevance of ice-melting thermograms to the surface forces emerging from the lipid bilayers and affecting the structural water molecules which constitute the aqueous separation (between bilayers) is demonstrated. The melting of the frozen structural water is not cooperative. For fully hydrated multibilayers, the corresponding molar enthalpy of fusion L is less than 50% of the molar enthalpy for bulk ice melting. In the present report, the difference in the aspects of the thermograms obtained with either the fluid PI or the rigid DPPC bilayers is assigned to a significant thermal expansion of the fluid PI bilayers.