A simple patchy colloid model for the phase behavior of lysozyme dispersions

TL;DR

This paper introduces a minimal patchy colloid model for spherical proteins to accurately predict the phase behavior of lysozyme dispersions, integrating experimental data and theoretical calculations.

Contribution

The model combines electrostatic repulsion and patchy attraction to describe lysozyme phase behavior, validated against experimental coexistence curves.

Findings

Predicted solubility curves align with experimental data.

Attractive potential strength is weakly affected by salt concentration.

Model accurately captures gas-liquid coexistence in lysozyme dispersions.

Abstract

We propose a minimal model for spherical proteins with aeolotopic pair interactions to describe the equilibrium phase behavior of lysozyme. The repulsive screened Coulomb interactions between the particles are taken into account assuming that the net charges are smeared out homogeneously over the spherical protein surfaces. We incorporate attractive surface patches, with the interactions between patches on different spheres modeled by an attractive Yukawa potential. The parameters entering the attractive Yukawa potential part are determined using information on the experimentally accessed gas-liquid-like critical point. The Helmholtz free energy of the fluid and solid phases is calculated using second-order thermodynamic perturbation theory. Our predictions for the solubility curve are in fair agreement with experimental data. In addition, we present new experimental data for the gas-liquid coexistence curves at various salt concentrations and compare these with our model calculations. In agreement with earlier findings, we observe that the strength and the range of the attractive potential part only weakly depend on the salt content.