Charged bilayer membranes in asymmetric ionic solutions: Phase diagrams and critical behavior

TL;DR

This paper investigates how electrostatic interactions influence phase separation in asymmetric charged lipid bilayers in contact with ionic solutions of differing strengths, revealing how coupling and salt asymmetry affect phase behavior.

Contribution

It provides a theoretical analysis of phase diagrams and critical points for charged bilayer membranes considering ionic strength asymmetry and electrostatic coupling.

Findings

Higher coupling constants increase phase separation temperature.

Asymmetric ionic solutions expand the phase-coexistence region.

Possible three-phase coexistence regions are predicted.

Abstract

We consider the phase separation in an asymmetrically charged lipid bilayer membrane consisting of neutral and negatively charged lipids that are in contact with in/out ionic solutions having different ionic strengths. The two asymmetric leaflets are coupled through electrostatic interactions. Based on a free energy approach, the critical point and phase diagrams are calculated for different ionic strength of the two solutions and coupling parameter. An increase of the coupling constant or asymmetry in the salt concentration between the in/out solutions yields a higher phase separation temperature because of electrostatic interactions. As a consequence, the phase-coexistence region increases for strong screening (small Debye length). Finally, possible three-phase coexistence regions in the phase diagram are predicted.