Effect of glycerol and dimethyl sulfoxide on the phase behavior of lysozyme: Theory and experiments

TL;DR

This study combines experiments and thermodynamic theory to analyze how glycerol and DMSO influence the phase behavior of lysozyme solutions, revealing that these additives increase repulsion and shift phase boundaries.

Contribution

It provides a comprehensive experimental and theoretical analysis of how glycerol and DMSO modify lysozyme phase behavior using TPT and DLVO models.

Findings

Glycerol and DMSO lower the fluid-solid transition temperature.

The additives increase the gap between fluid-solid and gas-liquid coexistence curves.

Glycerol and DMSO make the lysozyme interactions more repulsive.

Abstract

Salt, glycerol and dimethyl sulfoxide (DMSO) are used to modify the properties of protein solutions. We experimentally determined the effect of these additives on the phase behavior of lysozyme solutions. Upon the addition of glycerol and DMSO, the fluid-solid transition and the gas-liquid coexistence curve (binodal) shift to lower temperatures and the gap between them increases. The experimentally observed trends are consistent with our theoretical predictions based on the thermodynamic perturbation theory (TPT) and the Derjaguin-Landau-Verwey-Overbeek (DLVO) model for the lysozyme-lysozyme pair interactions. The values of the parameters describing the interactions, namely the refractive indices, dielectric constants, Hamaker constant and cut-off length, are extracted from literature or are experimentally determined by independent experiments, including static light scattering to determine the second virial coefficient. We observe that both, glycerol and DMSO, render the potential more repulsive, while sodium chloride reduces the repulsion.