Lateral diffusion in phospholipid bilayer membranes and multilamellar liquid crystals

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Lipid membranes exhibit complex phase behaviors influencing molecular dynamics.
• Understanding lateral diffusion is crucial for membrane function and stability.
• Fluorescent lipid analogues serve as valuable probes for membrane studies.

Purpose of the Study:

• To measure lateral-diffusion coefficients (D) of a fluorescent lipid analogue (diI).
• To investigate the impact of lipid phase transitions on diffusion in various membrane systems.
• To compare diffusion in black lipid membranes (BLMs), solvent-free vesicles, and liquid crystals.

Main Methods:

• Fluorescence recovery after photobleaching (FRAP) or similar techniques to measure diffusion coefficients.
• Preparation of black lipid membranes (BLMs) using Mueller-Rudin and Montal-Mueller methods.
• Formation and characterization of solvent-free bilayer and multilayer vesicles.
• Studies on multilamellar liquid crystals of various phospholipids (DMPC, DPPC, egg lecithin).

Main Results:

• Lateral diffusion coefficients (D) varied by orders of magnitude with lipid phase transitions.
• In BLMs, D was approximately 10(-7)cm²/s with weak temperature dependence.
• In solvent-free bilayers and liquid crystals, D was ~10(-8)cm²/s above Tt and decreased to ~10(-10)cm²/s below Tt.
• Phase transitions from smectic A to higher ordered states were observed in isolated bilayers.
• Retained solvent in BLMs enhanced lateral diffusion.

Conclusions:

• Lipid phase transitions significantly alter lateral diffusion in membrane systems.
• Isolated bilayers exhibit distinct phase transitions affecting molecular mobility.
• Solvent presence in BLMs can influence and potentially enhance lateral diffusion.
• The study provides insights into lipid dynamics across different membrane architectures.