Spectroscopic Studies of Amino Acid Ionic Liquid-Supported Schiff Bases

Amino acid ionic liquid-supported Schiff bases, derivatives of salicylaldehyde and various amino acids (L-threonine, L-valine, L-leucine, L-isoleucine and L-histidine) have been investigated by means of various spectroscopic techniques (NMR, UV-Vis, IR, MS) and deuterium isotope effects on C-13-NMR chemical shifts. The results have shown that in all studied amino acid ionic liquid-supported Schiff bases (except the L-histidine derivative) a proton transfer equilibrium exists and the presence of the COO- group stabilizes the proton transferred NH-form.