Thermochimica Acta, Vol.308, No.1-2, 77-83, 1998
Calorimetric investigation of the behavior of interlamellar water in phospholipid-water systems
The interaction of water and three phospholipids with different polar-head groups, phosphatidylethanolamine (PE), phosphatidylcholine (PC) and phosphatidylgylcerol (PG) were investigated by differential scanning calorimetry (DSC). Ice-melting DSC curves showed that two types of water molecules, nonfreezable and freezable, interacting with lipid-head groups in intra-, and inter-bilayers are present in the gel phase of three lipid-water systems of varying water content up to 40 g%. The ice-melting curves were deconvoluted according to a computer program and the number of bulk water molecules and subsequently the number of nonfreezable and freezable interlamellar water molecules was estimated from enthalpy changes of deconvoluted components. The number of nonfreezable interlamellar water molecules increased in the order of PE (2.3 H2O/ lipid, PG (4.0 H2O/lipid) and PC (5.5 H2O/lipid), that is, in the order of an increase in the effective area occupied by the three-head groups. However, a distinct difference was observed for the freezable interlamellar water : the number of this water molecules of PG system continuously increases up to 40 g%, in contrast with their limiting number of 3.7 and 4.5 H2O/lipid for PE and PC systems, respectively. This difference accounted well for a difference in the multiplicity of bilayer lamellar, that is, a single lamellar for PG system and a multilamellar for PE and PC systems shown by electron microscopy.