Scanning calorimetric evidence for a third phase transition in phosphatidylcholine bilayers

Area of Science:

• Lipid Bilayer Research
• Materials Science
• Physical Chemistry

Background:

• Dipalmitoyl phosphatidylcholine (DPPC) is a key phospholipid in biological membranes.
• DPPC exhibits well-characterized phase transitions, including the pretransition and the main gel to liquid crystal transition.
• Understanding DPPC phase behavior is crucial for biomembrane and drug delivery research.

Purpose of the Study:

• To investigate an uncharacterized phase transition in DPPC multilamellar suspensions.
• To characterize the thermodynamic properties and kinetics of this novel transition.

Main Methods:

• Differential Scanning Calorimetry (DSC) was employed to detect and analyze phase transitions.
• Multilamellar DPPC suspensions were prepared and subjected to specific temperature treatments (storage at 0°C for extended periods).

Main Results:

• A third phase transition was observed around 18°C in DPPC suspensions stored at 0°C.
• This transition is less cooperative than the known DPPC transitions.
• The enthalpy of the 18°C transition is significant, approximately three times the pretransition and half the main transition.
• The reversal of this 18°C transition upon cooling is exceptionally slow.

Conclusions:

• A previously unreported, slow-reversing phase transition exists in DPPC multilamellar systems under specific storage conditions.
• This discovery adds complexity to the phase behavior of DPPC, impacting its use in various applications.
• Further research is needed to elucidate the structural basis and implications of this slow transition.