Polar head group interactions in mixed Langmuir monolayers

Area of Science:

• Materials Science
• Physical Chemistry
• Biophysics

Background:

• Mixed monolayers are crucial for understanding molecular interactions at interfaces.
• Cholesterol (Ch) and cholesteryl acetate (ChA) differ in their polar head groups (alcohol vs. ester).
• Octyl cyano biphenyl (8CB) is a liquid crystal with a polar cyano terminal group.

Purpose of the Study:

• To investigate the miscibility of cholesterol-8CB and cholesteryl acetate-8CB mixed monolayers.
• To understand the role of polar head group interactions in monolayer miscibility.
• To analyze the phase behavior and collapse properties of these mixed systems.

Main Methods:

• Surface manometry to measure surface pressure and detect collapse.
• Epifluorescence microscopy to visualize monolayer structure and phase separation.
• Systematic variation of molar fractions (MF) of components.

Main Results:

• Both Ch-8CB and ChA-8CB mixed monolayers exhibited two distinct collapse pressures.
• Ch-8CB showed phase separation between 0.15-0.9 MF of Ch.
• ChA-8CB demonstrated miscibility across most compositions below the lower collapse pressure.
• 8CB was squeezed out into multilayers above the lower collapse pressure in both systems.

Conclusions:

• The ester group in cholesteryl acetate (ChA) facilitates better miscibility with the cyano group of 8CB compared to the alcohol group in cholesterol (Ch).
• Polar head group interactions significantly influence the miscibility and phase behavior of mixed monolayers.
• The findings provide insights into the molecular basis of lipid-protein interactions and membrane organization.