Ammonium ionic liquids as convenient co-solvents for the structure and stability of succinylated Con A

Highlights: ► Prepared alkyl ammonium ionic liquids (ILs). ► We have studied the biomolecular interactions succinylated Con A with ILs. ► We have used biophysical techniques including CD, fluorescence, and NMR. ► Phosphate anions of ILs are strong stabilizers for S Con A. ► Phosphate anions of ILs acted as refolding enhancers for denatured protein. - Abstract: In this article, we present the synthesis of a series ionic liquids (ILs) having different kosmotropicity including dihydrogen phosphate (H2PO4-) and hydrogen sulphate (HSO4-) as anions and chaotropic cation such as alkylammonium. Here, we have investigated the biomolecular interactions and related associated structural changes of succinylated Con A (S Con A) with alkylammonium ILs by using several biophysical techniques including circular dichroism (CD) and fluorescence. The ILs studied in the present research includes diethylammonium dihydrogen phosphate [(CH3CH2)2NH+][H2PO4-] (DEAP), diethylammonium hydrogen sulphate [(CH3CH2)2NH+][HSO4-] (DEAS), triethylammonium dihydrogen phosphate [(CH3CH2)3NH+][H2PO4-] (TEAP) and triethylammonium hydrogen sulphate [(CH3CH2)3NH+][HSO4-] (TEAS). We observed that all ILs have a dominant contribution to the stabilization of the native structure of the S Con A. Our experimental results distinctly demonstrate that the long alkyl chain IL TEAP is a strong stabilizer and therefore more biocompatible for S Con A. Furthermore, the results reveal that phosphate anions of ILs are strong stabilizers and acted as effective refolding enhancers for thermally denatured protein structure, whereas the protein was not refolded in the sulphate anions of ILs. These findings suggest a new generation of protein stabilizers that can be applied to other protein folding studies and biological systems.