Contribution of dipolar bridging to phospholipid membrane interactions: a mean-field analysis

TL;DR

This paper models zwitterionic membrane interactions considering dipolar effects, revealing how dipolar bridging influences membrane adhesion and ionic selectivity, with implications for nanofiltration and nanofluidic applications.

Contribution

It introduces a mean-field model capturing dipolar bridging effects in membrane interactions, highlighting non-uniform electrostatic forces and ionic selectivity based on separation distance.

Findings

Dipolar bridging causes membrane adhesion at short distances.

Electrostatic forces vary non-uniformly with separation.

Membranes exhibit ionic selectivity depending on separation.

Abstract

We develop a model of interacting zwitterionic membranes with rotating surface dipoles immersed in a monovalent salt, and implement it in a field theoretic formalism. In the mean-field regime of monovalent salt, the electrostatic forces between the membranes are characterized by a non-uniform trend: at large membrane separations, the interfacial dipoles on the opposing sides behave as like-charge cations and give rise to repulsive membrane interactions; at short membrane separations, the anionic field induced by the dipolar phosphate groups sets the behavior in the intermembrane region. The attraction of the cationic nitrogens in the dipolar lipid headgroups leads to the adhesion of the membrane surfaces via dipolar bridging. The underlying competition between the opposing field components of the individual dipolar charges leads to the non-uniform salt ion affinity of the zwitterionic membrane with respect to the separation distance; large inter-membrane separations imply anionic excess while small, nanometer size separations, favor cationic excess. This complex ionic selectivity of zwitterionic membranes may have relevant repercussions on nanofiltration and nanofluidic transport techniques.