The Influence of Ionic Liquids on Solubility and Metastable Zone Width of Hen Egg Lysozyme

The solubility and metastable zone width (MZW) are crucial to design and control of crystallization process. In this work, lysozyme solubility in different pH (4.0–6.0) aqueous solution at temperature ranging from 268.15 to 308.15 K were determined. The solubility and supersolubility of lysozyme with two ionic liquids (ILs) (1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) and 1,3-dimethylimidazolium iodine ([dmim]I)) were measured in aqueous solution at temperature ranging from 283.15 to 298.15 K at pH 5.0, and the MZW was calculated. The results demonstrate that lysozyme solubility increases with raising pH within 4.0 to 6.0. In the presence of ILs, the solubility increases with increasing [C₄mim]Cl concentrations, but decreases with increasing [dmim]I concentrations. The ILs addition concentrations were confirmed to exert obvious effect on MZW of lysozyme crystallization. Compared with no ILs added, the addition of ILs [C₄mim]Cl and [dmim]I expands significantly the MZW, and the MZW increases with increasing ILs concentrations. At constant ILs concentrations, the MZW increases with decreasing saturation temperature. These findings could provide significant insights into the development of crystallization strategy and the control of crystallization process for lysozyme.