NMR Self-diffusion Study of Amino Acid Ionic Liquids Based on 1-Methyl-3-Octylimidazolium in Water

Abstract

In comparison with the conventional ionic liquids, water-miscible amino acid ionic liquids (AAILs) are considered as more biodegradable and biocompatible, less toxic, and as able to enhance the biomaterials stability. An application of some long-chain ionic liquids in catalysis, extraction, etc. requests the detailed analysis of ionic and water transport properties of their diluted aqueous solutions close to the area of its critical micelle concentration (cmc). In this work, the molecular transport properties of two 1-methyl-3-octylimidazolium-based AAILs, [C8mim][Val], and [C8mim][Leu] (with anions of l-Leucine or l-Valine), in the aqueous solutions were studied by measuring the self-diffusion coefficients and the solution’ viscosities in the temperature ranges 273–343 K at the AAIL’s concentrations below and above its cmc. The data on self-diffusion coefficients of water molecules and cations/anions of AAILs are discussed in terms of activation energies and of hydration effects. Above the cmc, the [C8mim][Val] molecules demonstrate the strengthening effect on the solvent structure, while the molecules of [C8mim][Leu] have structure-destructive effect. The results obtained for the relative dynamic viscosities show a decrease of micellar size with increasing temperature. In addition, it was found that the degrees of counterion binding for both AAILs are higher than for 1-methyl-3-octylimidazolium halides.