Q. Liu, K. K. Wu, and F. Tang contributed equally to this work.
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Full Paper
Amino Acid Ionic Liquids as Chiral Ligands in Ligand-Exchange Chiral Separations
Article first published online: 18 AUG 2009
DOI: 10.1002/chem.200900982
Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Additional Information
How to Cite
Liu, Q., Wu, K., Tang, F., Yao, L., Yang, F., Nie, Z. and Yao, S. (2009), Amino Acid Ionic Liquids as Chiral Ligands in Ligand-Exchange Chiral Separations. Chemistry - A European Journal, 15: 9889–9896. doi: 10.1002/chem.200900982
Publication History
- Issue published online: 23 SEP 2009
- Article first published online: 18 AUG 2009
- Manuscript Received: 14 APR 2009
Funded by
- National Natural Science Foundation of China. Grant Number: 20575019
- National Basic Research Program of China. Grant Number: 2006CB504701
Keywords:
- amino acids;
- chirality;
- electrophoresis;
- ionic liquids;
- ligand design
Graphical Abstract
Liquids as ligands: A new type of task-specific ionic liquid, amino acid ionic liquids (AAILs), has been used as a chiral ligand in chiral ligand exchange HPLC and capillary electrophoresis (see image). This work demonstrates that AAILs are good alternatives to conventional amino acid ligands for ligand-exchange-based chiral separation.
Abstract
Recently, amino acid ionic liquids (AAILs) have attracted much research interest. In this paper, we present the first application of AAILs in chiral separation based on the chiral ligand exchange principle. By using 1-alkyl-3-methylimidazolium L-proline (L-Pro) as a chiral ligand coordinated with copper(II), four pairs of underivatized amino acid enantiomers—dl-phenylalanine (dl-Phe), dl-histidine (dl-His), dl-tryptophane (dl-Trp), and dl-tyrosine (dl-Tyr)—were successfully separated in two major chiral separation techniques, HPLC and capillary electrophoresis (CE), with higher enantioselectivity than conventionally used amino acid ligands (resolution (Rs)=3.26–10.81 for HPLC; Rs=1.34–4.27 for CE). Interestingly, increasing the alkyl chain length of the AAIL cation remarkably enhanced the enantioselectivity. It was inferred that the alkylmethylimidazolium cations and L-Pro form ion pairs on the surface of the stationary phase or on the inner surface of the capillary. The ternary copper complexes with L-Pro are consequently attached to the support surface, thus inducing an ion-exchange type of retention for the dl-enantiomers. Therefore, the AAIL cation plays an essential role in the separation. This work demonstrates that AAILs are good alternatives to conventional amino acid ligands for ligand-exchange-based chiral separation. It also reveals the tremendous application potential of this new type of task-specific ILs.