Hen egg lysozyme polymorphs mediated by two ionic liquids during batch cooling crystallization

-Lysozyme batch cooling crystallization in the presence of two ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), and 1,3-dimethylimidazolium iodide ([C1mim]I). Microscopic observation demonstrated that the crystal morphology with [C1mim]I is needle-like, while that with [C4mim]Cl and no ILs is plate-like. FTIR spectroscopy revealed that new peaks in the range of 1300-400 cm-1 occur with the case of adding [C1mim]I, meaning that the microstructure of lysozyme crystals changed. Raman spectroscopy and X-ray powder diffraction (XRD) pattern further confirmed that crystal forms of lysozyme with adding [C4mim]Cl and no ILs is completely different from that of adding [C1mim]I. Thermogravimetry (TG) and Differential Scanning Calorimeter (DSC) results indicated that addition of [C1mim]I delay the thermal deformation and degradation temperature of lysozyme crystals, suggesting that lysozyme crystals with [C1mim]I possesses higher thermal stability. The change in lysozyme crystal forms can be attributed to changes in interaction among lysozyme molecules and conformation in solution, leading to different assembly mode of molecules and formation of polymorphs. These findings could offer instructions for regulating lysozyme crystal forms and gaining initial insight into screening of potential ILs for developing polymorphs of the protein and other macromolecule crystals.