Segregation and phase transition in mixed lipid films

Area of Science:

• Materials Science
• Biophysics
• Chemical Physics

Background:

• Phospholipid bilayers are fundamental to biological membranes.
• Gemini surfactants are a class of molecules with unique self-assembly properties.
• Understanding lipid-surfactant interactions is crucial for drug delivery and biomimetic systems.

Purpose of the Study:

• To investigate the structural changes in dimyristoyl phosphatidylcholine (DMPC) mixed films with gemini surfactants.
• To elucidate the phase transitions induced by varying surfactant-to-lipid ratios and hydration levels.
• To characterize the emerging cubic phase and the hydration-induced pathway of phase transitions.

Main Methods:

• Energy Dispersion X-ray Diffraction (EDXD) was used to study film structures.
• Coarse-grain molecular dynamics simulations were performed.
• Experiments were conducted at varying surfactant-to-lipid molar ratios (R(S/L)) and hydration levels.

Main Results:

• Increasing R(S/L) led to the formation of a cubic phase (space group Pmn) from the lamellar lipid phase.
• At R(S/L) = 1, a complete phase transition to the cubic phase occurred.
• Hydration of the mixed film at R(S/L) = 2.3 induced a cubic to lamellar phase transition.

Conclusions:

• Gemini surfactants effectively solubilize DMPC bilayers, promoting cubic phase formation.
• The study reveals a hydration-induced pathway for the cubic to lamellar phase transition.
• The findings provide insights into the complex self-assembly behavior of lipid-surfactant systems.