Nuclear magnetic resonance to study the interactions acting in the enantiomeric separation of homocysteine by capillary electrophoresis with a dual system of γ‐cyclodextrin and the chiral ionic liquid EtCholNTf₂

Abstract

The enantiomeric separation of 9‐fluorenylmethoxycarbonyl chloride (FMOC)‐homocysteine (Hcy) by CE was investigated using γ‐CD and the chiral ionic liquid (R)‐(1‐hydroxybutan‐2‐yl)(trimethyl)azanium‐bis(trifluoromethanesulfon)imidate (also called (R)‐N,N,N‐trimethyl‐2‐aminobutanol‐bis(trifluoromethane‐sulfon)imidate) (EtCholNTf2) as chiral selectors. Using 2 mM γ‐CD and 5 mM EtCholNTf2 in 50 mM borate buffer (pH 9), FMOC‐Hcy enantiomers were separated with a resolution value of 3.8. A reversal in the enantiomer migration order in comparison with the single use of γ‐CD in the separation buffer was obtained. Then, NMR experiments were carried out to elucidate the interactions taking place in the enantiomeric separation of FMOC‐Hcy. NMR analyses highlighted the formation of an inclusion complex since the hydrophobic group of FMOC‐Hcy was inserted into the γ‐CD cavity. Moreover, interactions between EtCholNTf2 and γ‐CD were also observed, suggesting that the chiral ionic liquid would also enter the cavity of the γ‐CD.

Recent developments in capillary and microchip electroseparations of peptides (2019–mid 2021)

“…Electric conductivity, electrochemical, NMR, and some other detection modes are less suitable and, thus, much less employed for detection of peptides separated by CE and CEC methods than the above UV-absorption, fluorescence, and MS detection schemes. For that reason, only some recent reviews and articles are cited here, which are dealing with general developments and applications of these detectors in separation methods such as contactless capacitively coupled conductivity detection (C 4 D) [187,188], electrochemical detection [189], chemiluminiscence [190], electrochemiluminiscence [191], infrared and nuclear magnetic resonance spectroscopy [192][193][194]. In these reviews and articles, few applications of these detectors for CE and CEC separations of peptides as model analytes are presented.…”

Challenging Bioanalyses with Capillary Electrophoresis

“…87 In another application, βcyclodextrins were combined with magnetic nanoparticles to enhance the detection of an antibiotic in blood and urine. 77 Oftentimes, ionic liquids are used in combination with α-cyclodextrins, 88 β-cyclodextrins, 66,89 and γ-cyclodextrins, [90][91][92] to enhance selectivity. Ionic liquids are important to several techniques in the field of analytical chemistry.…”

Advances of capillary electrophoresis enantioseparations in pharmaceutical analysis (2017–2020)

“…This will affect complexation equilibria between CDs and chiral analytes. This has been shown for FMOC‐homocysteine and the dual selector system composed of γ‐CD and the CIL ( R )‐ N , N , N ‐trimethyl‐2‐aminobutanol‐bis(trifluoromethane‐sulfon)imidate) (EtCholNTf2) [68]. Baseline separation of the enantiomers was achieved in the presence of 2 mM γ‐CD and 1 mM EtCholNTf2, while application of γ‐CD alone resulted in only a partial separation.…”