Simple Model of Membrane Proteins Including Solvent

TL;DR

This paper presents a numerical simulation of a two-dimensional membrane protein model that incorporates solvent effects, revealing complex phase behaviors including closed loop phase diagrams and coexistence curves with multiple critical points.

Contribution

It introduces a phenomenological solute-solvent interaction model to modify phase behavior in a 2D membrane protein system, extending prior models to include solvent effects.

Findings

Fluid-fluid coexistence curves can have both upper and lower critical points.

The model produces closed loop phase diagrams similar to 3D systems.

Solvent interactions significantly alter phase behavior.

Abstract

We report a numerical simulation for the phase diagram of a simple two dimensional model, similar to one proposed by Noro and Frenkel [J. Chem. Phys. \textbf{114}, 2477 (2001)] for membrane proteins, but one that includes the role of the solvent. We first use Gibbs ensemble Monte Caro simulations to determine the phase behavior of particles interacting via a square-well potential in two dimensions for various values of the interaction range. A phenomenological model for the solute-solvent interactions is then studied to understand how the fluid-fluid coexistence curve is modified by solute-solvent interactions. It is shown that such a model can yield systems with liquid-liquid phase separation curves that have both upper and lower critical points, as well as closed loop phase diagrams, as is the case with the corresponding three dimensional model.