Phase Behavior and Induced Interdigitation in Bilayers Studied with Dissipative Particle Dynamics

Abstract

Bilayers formed by coarse-grained models of amphiphilic surfactants are studied using dissipative particle dynamics combined with a Monte Carlo scheme to achieve the natural state of a tensionless bilayer. We address the issue of the influence of the molecular structure and the level of coarse graining on the bilayer properties by studying two models of different complexity: a single tail and a double tail surfactant. We compute the area per surfactant, the bilayer thickness, and the orientational order parameters and show how their dependence on the surfactant structure and temperature. We reproduce the gel to liquid crystalline phase transition, and we study the conditions that induce a gel interdigitated phase in the bilayer. We show how the interdigitated state in a bilayer containing double-tail surfactants can be reproduced by adding an extra bead in the surfactant headgroup, which mimics an ester-linkage to the phosphate group. In a bilayer formed by single tail surfactants, we induce interdigitation by changing the strength of the repulsive interaction between the headgroups, which corresponds with adding salt to the system. We are then able to derive a phase diagram as function of temperature and repulsion parameter for surfactants of different chain lengths.

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

“…Nevertheless, it is worthwhile to address one particular issue in this regard which pertains to our choice of a single chain rather than a doublechain lipid. A number of previous simulation studies 44,45 have examined phase diagrams for coarse-grained singleand double-chain lipids in the liquid-gel region as a function of temperature and head group size. For single chains the interdigitated gel phase L ␤I and nontilted gel phase L ␤ were observed, but only with two-tailed lipids could one observe the tilted gel phase L ␤ Ј .…”

Lipid mediated packing of transmembrane helices – a dissipative particle dynamics study

“…It was previously shown to reproduce the phase diagram of a bilayerforming lipid. 36 It includes a head group consisting of three (h) beads and two tails each containing ve (t) beads. We therefore label the model h 3 (t 5 ) 2 (see Fig.…”

Adaptive resolution molecular-dynamics simulation: Changing the degrees of freedom on the fly

“…One first way to tackle this, was to reduce the number of de-grees of freedom by a systematic coarse-graining, which retains only those degrees of freedom that are relevant for the particular property of interest. Examples of molecular systems where the coarsegraining approach has been used with much success are fluids [9], lipid bilayers [10,11,12,13,14], and polymer systems [15,16,17,18].…”