Using ionic liquid [EMIM][CH3COO] as an enzyme-‘friendly’ co-solvent for resolution of amino acids

Abstract: An ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate [EMIM][CH3COO], was used in 0–4.0M (∼60% IL, v/v), as a nonvolatile organic medium for the enzymatic resolution of amino acids. When dl-phenylalanine methyl ester was studied as a model substrate, high enantiomeric excesses (ee) of l-amino acid were obtained in all ionic concentrations; however, lower yields were observed at high IL concentrations. This IL is more enzyme-‘friendly’ than the hydrophilic organic solvent acetonitrile and those ILs containing chaotropic anions (such as [EMIM][OTs]). Among three proteases and two lipases investigated, lyophilized Bacillus licheniformis protease exhibited the best enantioselectivity and activity. Highly enantioselective resolutions were also produced for several other amino acids in 2.0M IL. Interestingly, high ee were also found in deuterium oxide (D2O) rather than in ordinary water, and a further enhancement was achieved with the co-existence of [EMIM][CH3COO]. The heavy water effect was explained in terms of protein stabilization by D2O. The secondary structural changes of enzyme in various media were interpreted by the second derivatives of FT-IR spectra. [Copyright &y& Elsevier]