An ordered metastable phase in hydrated phosphatidylethanolamine: the Y-transition

Area of Science:

• Lipid polymorphism and phase behavior
• Materials science of phospholipids
• Supramolecular chemistry

Background:

• Dihexadecylphosphatidylethanolamine (DHPE) is a phospholipid with complex phase behavior.
• Understanding lipid phase transitions is crucial for biological membranes and material applications.
• Low-temperature phases in lipids can exhibit unique structural arrangements.

Purpose of the Study:

• To investigate the low-temperature phase behavior of fully hydrated dihexadecylphosphatidylethanolamine (DHPE).
• To characterize a newly observed metastable ordered phase in DHPE.
• To elucidate the formation pathway and properties of this novel lipid phase.

Main Methods:

• Time-resolved X-ray diffraction to analyze structural changes.
• Differential scanning calorimetry to detect thermal transitions.
• Scanning densitometry to measure volume changes during phase transitions.

Main Results:

• Rapid formation of a metastable LR1 phase in DHPE at approximately 12°C upon cooling.
• The LR1 phase exhibits an orthorhombic hydrocarbon chain arrangement, distinct from the Lβ phase.
• The LR1 phase is readily reversible with minimal hysteresis and is a precursor to the Lc phase.

Conclusions:

• The LR1 phase represents a novel low-temperature ordered state in DHPE lipids.
• The formation of the equilibrium Lc phase primarily occurs from the LR1 phase.
• DHPE's low-temperature polymorphism shares similarities with long-chain normal alkanes.