Amino Acid-Based Fluorescent Chiral Ionic Liquid for Enantiomeric Recognition

Abstract

We report on the synthesis and characterization of a new fluorescent chiral ionic liquid (FCIL), l-phenylalanine ethyl ester bis(trifluoromethane) sulfonimide (l-PheC(2)NTf(2)), capable of serving simultaneously as solvent, chiral selector, and fluorescent reporter in chiral analytical measurements. Enantiomers of different analytes, including fluorescent and nonfluorescent compounds, with a variety of structures were shown to induce wavelength- and analyte-dependent changes in the fluorescence intensity of this FCIL. This system may provide both chemo- and enantioselectivity toward multiple analytes simultaneously. The newly synthesized FCIL, derived from commercially available l-phenylalanine ethyl ester chloride and lithium bis(trifluoromethane) sulfonamide, was obtained as liquid at room temperature and is stable to thermal decomposition up to 270 degrees C. Absorption and fluorescence properties of neat l-PheC(2)NTf(2) were complex. While the absorption properties were similar to phenylalanine with a weakly absorbing tail extending beyond 400 nm, multiple excitation and emission bands were observed in its Excitation-Emission Matrix (EEM). A prominent excimer emission displayed the greatest intensity of all emission bands, and a long-wavelength emission shifted toward the red with increasing excitation wavelength. These different spectral regions were shown to respond differently toward several analytes, including sugars such as glucose and mannose, making this an ideal system to exploit the multidimensional properties of fluorescence. The unique properties of l-PheC(2)NTf(2) combined with EEMs resulted in reliable identification of different enantiomers and measurement of enantiomeric composition. Importantly, the choice of excitation and emission wavelength regions was an important variable shown to improve prediction of enantiomeric composition.

Use of chiral amino acid ester‐based ionic liquids as chiral selectors in CE

“…Recently, Bwambok et al used a simple metathesis reaction to synthesize some novel chiral ILs derived from amino acid esters . It was observed that l ‐alanine tert butyl ester bis(trifluromethane)sulfonamide ( l ‐AlaC 4 NTf 2 ), a room temperature IL, could serve as a chiral selector and a solvent . To the best of our knowledge, no studies have so far been performed on the enantioselective ability of the amino acid ester‐based ILs by use of any chromatographic or electrophoretic technique.…”

Ephedrinium‐based protic chiral ionic liquids for enantiomeric recognition

“…Alanine-based and more recently a phenylalanine-based CIL were also synthesized in our laboratory and investigated for enantiomeric recognition. 25,50,51 The PCILs reported in this study are intrinsically fluorescent and could therefore also be used for probing nonfluorescent enantiomers by monitoring their intrinsic fluorescence intensities.…”

Advances in analytical chemistry using the unique properties of ionic liquids

“…In a recent report, Bwambok et al [76] originally synthesized a multifunctional IL, L-phenylalanine ethyl ester bis(trifluoromethane) sulfonimide (L-PheC 2 -NTf 2 ), to serve as solvent, chiral selector, and fluorescent report at the same time in chiral analytical measurements of different analytes including fluorescent and non-fluorescent compounds. Fig.…”