Aqueous two phase extraction process of tryptophan based on functionalized ionic liquids

Abstract

Investigation of aqueous two-phase extraction process of tryptophan was carried out by using functionalized ionic liquids (FILs), such as 3-methyl-1-(N,N-diethylcarbonylmethyl) imidazolium chlorite ([MDCmim]Cl), 3-methyl-1-(N,N-diethylcarbonylmethyl) imidazolium tetrafluoroborate ([MDCmim]BF₄) and 3-methyl-1-(methoxycarbonylmethyl)imidazolium tetrafluoroborate ([EAmim]BF₄). Some important factors that affect extraction process, such as effect of types of IL, pH, mass of IL, the amount of phosphate, and systems temperature were probed systematically. Some important results are obtained as follows: tryptophan can be extracted with aqueous two phase systems based on FILs successfully. The sequence of partition coefficients of tryptophan in the various ionic liquids based aqueous two phase systems follows: [MDCmim]Cl > ([MDCmim]BF₄) ≈ ([EAmim]BF₄) > ([bmim]BF₄). pH influences partition coefficients greatly. When pH = 13, the partition coefficient of tryptophan can reach up to 180 by [MDCmim]Cl/K₂HPO₄ aqueous two phase system. Finally, extraction mechanisms were investigated through ¹H NMR and experimental study. The new hydrogen bond formed between tryptophan and amide group in FILs and ion exchange are found to be the main mechanisms for the extraction process. Notably, with the above valuable information, the new ionic liquids with two amide groups 1,3-bis(N,N-diethylcarbonylmethyl) imidazolium chlorite ([BMDCim]Cl) were designed and synthesized and its partition coefficient can achieve 570, which is much higher than the existing FILs and traditional ILs.