Unravelling speciation in amino acid-based ionic liquids: The existence of anions with zwitterionic moieties

Abstract

Biocompatible ionic liquids based on aspartic and glutamic acid anions are usually considered with monovalent (n(−1)) forms. pH measurements, however, imply a zwitterionic (z(−1)) anion in aqueous solution. Thus, we wondered whether this highly polar structure persist in other solvation environments, including the neat ionic solvent. While (i) ab initio calculations and FTIR spectrum suggest the predominance of z(−1) forms in ionic liquids, (ii) Molecular Dynamics simulations of these systems demonstrates clear differences in inter-ionic interplays and show that the outlier properties of these solvents are better explained under the z(−1) assumption, shifting the paradigm for these ionic liquids.