Phospholipid surface bilayers at the air-water interface. I. Thermodynamic properties

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Phospholipids like dimyristoylphosphatidylcholine (DMPC) can form surface bilayers at the air/water interface.
• This phenomenon was previously observed for DMPC dispersions in water.

Purpose of the Study:

• To investigate surface bilayer formation in other phospholipid dispersions.
• To characterize the composition and structure of these surface bilayers.
• To compare surface bilayer properties with the bulk liquid-crystal phase.

Main Methods:

• Preparation of dispersions of dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC), and a DMPC/DOPC mixture.
• Observation of surface bilayer formation at characteristic temperatures.
• Analysis of surface bilayer composition and partial molar entropies.
• Comparison with the bulk liquid-crystal phase properties.

Main Results:

• DOPC, DPPC, and DMPC/DOPC mixtures also form surface bilayers at characteristic temperatures.
• The surface bilayer in the lipid mixture has the same composition as the bulk liquid-crystal phase.
• Surface and bulk lipid components exhibit identical partial molar entropies.

Conclusions:

• Surface bilayer formation is a general phenomenon for various phospholipid dispersions.
• The surface bilayer possesses the same structure as the bilayer in the bulk liquid-crystal phase.
• This suggests a conserved molecular organization between the air/water interface and the bulk phase.