Calorimetric detection of a sub-main transition in long-chain phosphatidylcholine lipid bilayers

The existence of a sub-main transition in multilamellar bilayers composed of long-chain saturated diacyl phosphatidylcholine (DC17PC, DC18PC, DC19PC, and DC20PC) is reported for the first time using high-sensitivity differential scanning calorimetry. The highly cooperative sub-main transition which takes place over a narrow temperature range positioned between the well-known pre-transition and main-transition is characterized by a heat capacity curve with a half-height width of Delta T-1/2 similar or equal to 0.15 C degrees and an enthalpy change, Delta H, which is a few percent of the transition enthalpy for the main-transition of the lipid bilayer.