Glutamic acid cation based ionic liquids: microwave synthesis, characterization, and theoretical study

Some new members of amino acid ionic liquids (ILs) with glutamic acid (Glu) cation were studied. GluBF4, GluCl, GluNO3, and Glu2SO4 were synthesized using the one-step microwave synthesis method, and their physicochemical properties, including the IR spectrum, melting point, conductivity, solubility, and thermostability, were investigated in detail experimentally. Systematic theoretical study on the series molecules were also performed by quantum chemistry calculation. Geometry optimization on the single molecule was carried out with the B3LYP/6-311++G** level of theory, and the vibration frequencies of each optimized molecule were analyzed at the same level. The binding energies were calculated, and the basis set superposition error (BSSE) was corrected by the counterpoise method (CP). A close relation between the experimental melting points and the intramolecular interaction was found: the smaller the absolute value of the biding energy between ions is, the lower the melting point would be. This conclusion shows the probability of designing ILs with the help of theoretical way in the future exploitation.