Novel surface phase containing cholesteryl esters. 1. Structural characteristics determined from surface...

Area of Science:

• Biochemistry
• Surface Chemistry
• Lipid Bilayer Studies

Background:

• Cholesteryl myristoleate and dioleoylphosphatidylcholine are key lipid components.
• Understanding lipid mixtures at interfaces is crucial for biological membranes.
• Previous studies identified a monolayer phase in these mixtures.

Purpose of the Study:

• To investigate the behavior of cholesteryl myristoleate in mixtures with dioleoylphosphatidylcholine at the air-water interface.
• To identify and characterize new surface phases beyond the known monolayer.
• To determine the influence of lecithin on cholesteryl ester organization.

Main Methods:

• Surface pressure and molecular area measurements were analyzed.
• Data was collected as a function of mixture composition.
• Thermodynamic analysis of the air-water interface behavior was performed.

Main Results:

• A second surface phase, distinct from the previously described monolayer, was identified.
• This second phase exists in two miscible double-layer states.
• One state involves a mixed double-layer with a specific stoichiometry of cholesteryl ester to lecithin, showing pressure-dependent composition and area.
• The other state resembles a cholesteryl ester monolayer covered by another cholesteryl ester layer.
• Lecithin demonstrates an ordering effect on cholesteryl ester molecules up to 50 Å from the interface.

Conclusions:

• The presence of dioleoylphosphatidylcholine (lecithin) significantly influences the organization of cholesteryl myristoleate at the air-water interface.
• A novel mixed double-layer state is preferentially formed, indicating specific molecular packing arrangements.
• Lecithin induces ordering in cholesteryl ester molecules, extending beyond the immediate interface.