Solvent free model for self-assembling fluid bilayer membranes: Stabilization of the fluid phase based on broad attractive tail potentials

TL;DR

This paper introduces a solvent-free coarse-grained model for lipid bilayer membranes, demonstrating how tail-tail attraction range influences phase stability and material properties, with insights into phase transitions and pore formation.

Contribution

The study develops a new adaptable simulation method for lipid membranes without explicit solvent, emphasizing the role of tail attraction range in membrane stability and phase behavior.

Findings

A threshold attractive width stabilizes the fluid phase.

Material properties vary monotonically with attractive width.

Discontinuous gel-fluid transition with hysteresis observed.

Abstract

We present a simple and highly adaptable method for simulating coarse-grained lipid membranes without explicit solvent. Lipids are represented by one head-bead and two tail-beads, with the interaction between tails being of key importance in stabilizing the fluid phase. Two such tail-tail potentials were tested, with the important feature in both cases being a variable range of attraction. We examined phase diagrams of this range versus temperature for both functional forms of the tail-tail attraction and found that a certain threshold attractive width was required to stabilize the fluid phase. Within the fluid phase region we find that material properties such as area per lipid, orientational order, diffusion constant, inter-leaflet flip-flop rate and bilayer stiffness all depend strongly and monotonically on the attractive width. For three particular values of the potential width we investigate the transition between gel and fluid phases via heating or cooling and find that this transition is discontinuous with considerable hysteresis. We also investigated the stretching of a bilayer to eventually form a pore and found excellent agreement with a recently published analytic theory.