“Water-free” computer model for fluid bilayer membranes

Abstract

We use a simple and efficient computer model to investigate the physical properties of bilayer membranes. The amphiphilic molecules are modeled as short rigid trimers with finite range pair interactions between them. The pair potentials have been designed to mimic the hydrophobic interactions, and to allow the simulation of the membranes without the embedding solvent as if the membrane is in vacuum. We find that upon decreasing the area density of the molecules the membrane undergoes a solid-fluid phase transition, where in the fluid phase the molecules can diffuse within the membrane plane. The surface tension and the bending modulus of the fluid membranes are extracted from the analysis of the spectrum of thermal undulations. At low area densities we observe the formation of pores in the membrane through which molecules can diffuse from one layer to the other. The appearance of the pores is explained using a simple model relating it to the area dependence of the free energy.

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

“…The model of Farago 19 and Tolpekina et al 26 gives perfect agreement with the measured data 48 ͑see lines in Fig. 12͒.…”

“…Finally, in Sec. V we study the stretching and rupture of a bilayer sheet and find near-perfect agreement with a simple theoretical model developed by Farago 19 and also Tolpekina et al 26 as well as with the experimental data.…”

“…Beyond some critical strain one would now expect a pore to open, but since this now relieves much of the stress, pore growth stops and one obtains a stable pore of well-defined size. Assuming a harmonic extensibility of the bilayer itself, as well as a constant line tension at a pore rim, Farago 19 and Tolpekina et al 26 gave a simple theoretical model which relates the resulting pore size as well as the stress-strain relation to key bilayer properties such as the extensibility and the line tension. We summarize the key results in Appendix B.…”

“…Indeed, the collective experience from the past has shown that simple choices ͑e.g., Lennard-Jones, LJ͒ do not lead to a fluid bilayer phase but only to "solid" bilayers at low temperature and low-density ͑"gas"͒ phases at high temperature. Concluding that simple pair potentials are insufficient, researchers have then turned to the use of density-dependent ͑multibody͒ interactions, 7,13,14,16,17 angular-dependent potentials, 18 or highly tuned sets of Lennard-Jones-type potentials 19 to stabilize the fluid bilayer phase without solvent ͑see Brannigan et al for a recent review 20 ͒. Unfortu-nately, each of these approaches suffers from one or more significant drawbacks.…”

Multiscale modeling of emergent materials: biological and soft matter

“…Farago has shown that it is possible to completely revert to pair potentials of Lennard-Jones (n,2n)-type, provided they are very carefully parametrized. 205 He uses again a rigid HTT-trimer and tunes the interactions between individual beads (HH, HT 1 , HT 2 , T 1 T 1 , T 1 T 2 , T 2 T 2 ) in strength, range, and functional form (for details see ref. 205).…”