Lateral diffusion in substrate-supported lipid monolayers as a function of ambient relative humidity

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Supported phospholipid monolayers are model systems for cell membranes.
• Water activity is a critical environmental factor affecting membrane properties.
• Understanding lipid diffusion is key to elucidating membrane dynamics and biological functions.

Purpose of the Study:

• To investigate the effect of water activity on the lateral self-diffusion of supported phospholipid monolayers.
• To develop a diffusion model correlating activation energy with lipid hydration state.
• To explore the relationship between water activity and diffusion across various substrates and conditions.

Main Methods:

• Experimental analysis of lateral self-diffusion coefficients (D) in phospholipid monolayers.
• Utilizing polysaccharide (chitosan, agarose) and glass substrates.
• Derivation of a diffusion model based on activated diffusion and humidity-dependent disjoining pressure.
• Analysis of ln(D) versus ln(p(0)/p) plots to validate the diffusion model.

Main Results:

• A linear relationship was observed between ln(D) and ln(p(0)/p) across different lipids, pressures, temperatures, and substrates.
• The derived diffusion model accurately describes the observed diffusion behavior.
• No evidence of humidity-induced first-order phase transitions in the studied monolayers was found.
• Activation energy (E(a)) was found to be dependent on the hydration state of the lipid headgroup.

Conclusions:

• Water activity significantly impacts the lateral self-diffusion of supported phospholipid monolayers.
• The developed model provides a quantitative framework for understanding hydration-dependent lipid diffusion.
• Findings are relevant to biological processes involving dehydration/hydration cycles, such as vesicle fusion and recognition.