Attractive Interaction between Fully Charged Lipid Bilayers in a Strongly Confined Geometry

Area of Science:

• Biophysics
• Physical Chemistry
• Materials Science

Background:

• Lipid bilayers are fundamental components of cell membranes.
• Electrostatic interactions govern bilayer behavior, typically repulsion between like charges.
• Classical Poisson-Boltzmann theory is the standard model for describing these interactions.

Purpose of the Study:

• To investigate the interaction between highly charged lipid bilayers with monovalent counterions.
• To explore electrostatic interactions beyond the classical Poisson-Boltzmann theory.
• To understand the role of counterion correlations and water properties in confined geometries.

Main Methods:

• Neutron reflectivity experiments.
• X-ray reflectivity experiments.
• Analysis within the Strong Coupling limit.

Main Results:

• A thinner water layer between like-charged bilayers compared to zwitterionic lipids.
• Evidence of counterintuitive electrostatic attraction between like-charged bilayers.
• Agreement with a decrease in water dielectric constant due to surface charge-induced water molecule orientation.

Conclusions:

• Counterion correlations are crucial for understanding interactions in highly charged lipid systems.
• Classical electrostatics models are insufficient in highly confined geometries.
• Surface charge density significantly impacts local water properties and bilayer interactions.