Equilibrium or quenched: fundamental differences between lipid monolayers, supported bilayers, and membranes

Area of Science:

• Materials Science
• Biophysics
• Surface Chemistry

Background:

• Lipid packing and structure are crucial for membrane function.
• Understanding supported lipid bilayers is key for biosensor and drug delivery applications.
• Differences in lipid organization between monolayers, bilayers, and multilayers are not fully understood.

Purpose of the Study:

• To investigate and compare the structural organization of lipids in monolayers, supported bilayers, and multilayer films.
• To elucidate the influence of deposition pressure on lipid structure and packing.
• To explore molecular-level interactions, such as acyl chain coupling and alignment, in supported lipid systems.

Main Methods:

• High-resolution grazing incidence X-ray diffraction was employed to analyze lipid structures.
• Lipid monolayers, supported bilayers (formed by vesicle fusion), and multilayer films were studied.
• Varying deposition pressures were used to control the area per molecule.

Main Results:

• Monolayer structure is largely preserved upon deposition, with area per molecule dependent on deposition pressure.
• Supported bilayers resemble those deposited at higher pressures (38 mN/m), while multilayers resemble lower pressure deposits (<30 mN/m).
• Lipid acyl chains exhibit coupling between leaflets, leading to condensation and increased tilt; preferential acyl chain alignment is observed in supported bilayers, unlike free-standing monolayers.

Conclusions:

• Supported lipid bilayer structure can be controlled and maintained by solid supports.
• Increasing surface pressure during deposition promotes preferential acyl chain alignment within and between membrane leaflets.
• These findings provide fundamental insights into the structural differences and molecular ordering of lipids in various supported film configurations.