Ionic liquids as selectors for controlling the crystallization nucleation of hen egg white lysozyme

Ionic liquids (ILs) have biomaterial applications and are used for protein crystallization. The effect of two imidazolium-based ILs, 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1,3-dimethylimidazolium iodide ([dmim]I), on the nucleation kinetics of lysozyme was investigated by determining the nucleation induction time, and nucleation parameters were evaluated. The values of interfacial tension calculated for solutions with added 30 g/L ILs [C4mim]Cl and [dmim]I, and without added ILs were 99.03, 109.7, and 107.3 mJ/m2, respectively. Compared with solutions without IL addition, the critical free energy change, size, and molecular number of critical nuclei decreased and the nucleation rate increased after the addition of [C4mim]Cl. In contrast, the critical free energy change, size, and molecular number of critical nuclei increased and the nucleation rate decreased after the addition of [dmim]I. These new findings provide insights into controlling lysozyme crystallization separation, and present ILs as potentially useful additives for controlling the crystallization of macromolecules.