1.Optimization of 12 chiral analytes with 8 polymeric surfactants.
Billiot E1, Billiot F, Warner IM. J Chromatogr Sci. 2008 Oct;46(9):757-63.
This manuscript discusses the results of studies that were performed to determine optimum capillary electrophoresis (CE) conditions for the enantiomeric resolution of twelve chiral analytes with eight amino acid based polymeric surfactants. The parameters that were optimized include pH, buffer type, and concentration of surfactant. The results indicated that the optimum conditions for enantiomeric separations with the amino acid based polymeric surfactants examined in this study using CE were analyte dependent, not surfactant dependent. In other words, the optimum conditions for a particular analyte were the same for all the amino acid based polymeric surfactants examined in this study. The results of these studies indicate that when using a large group of related amino acid based polymeric surfactants only a few surfactants need to be optimized for each analyte under study. These studies were limited to anionic surfactants that contain the amino acids glycine, L-alanine, L-valine, and L-leucine only.
2.NMR characterization of 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate binding to chiral molecular micelles.
Kingsbury SA1, Ducommun CJ, Zahakaylo BM, Dickinson EH, Morris KF. Magn Reson Chem. 2010 Mar;48(3):184-91. doi: 10.1002/mrc.2561.
NMR spectroscopy was used to characterize the binding of the chiral compound 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNP) to five molecular micelles with chiral dipeptide headgroups. Molecular micelles have covalent linkages between the surfactant monomers and are used as chiral mobile phase modifiers in electrokinetic chromatography. Nuclear overhauser enhancement spectroscopy (NOESY) analyses of (S)-BNP:molecular micelle mixtures showed that in each solution the (S)-BNP interacted predominately with the N-terminal amino acid of the molecular micelle's dipeptide headgroup. NOESY spectra were also used to generate group binding maps for (S)-BNP:molecular micelle mixtures. In these maps, percentages are assigned to the (S)-BNP protons to represent the relative strengths of their interactions with a specified molecular micelle proton. All maps showed that (S)-BNP inserted into a previously reported chiral groove formed between the molecular micelle's dipeptide headgroup and hydrocarbon chain.
3.Multivariate approach for the enantioselective analysis in micellar electrokinetic chromatography-mass spectrometry. I. Simultaneous optimization of binaphthyl derivatives in negative ion mode.
He J1, Shamsi SA. J Chromatogr A. 2009 Jan 30;1216(5):845-56. doi: 10.1016/j.chroma.2008.11.093. Epub 2008 Dec 6.
A mixture of two molecular micelles polysodium N-undecenoxy carbonyl-L-leucinate, (poly-L-SUCL) and polysodium N-undecanoyl leucylvalinate, (poly-L-SULV) was utilized in micellar electrokinetic chromatography-electrospray ionization-mass spectrometry (MEKC-ESI-MS) to simultaneously separate and detect enantiomers of binaphthyl derivatives. Separation parameters such as background buffer composition, voltage, temperature, and nebulizer pressure were optimized using a multivariate central composite design (CCD). Baseline enantioseparation for both analytes was achieved. The CCD was also used in the optimization of sheath liquid and spray chamber parameters to achieve optimum ESI-MS response. The results demonstrate that CCD is a powerful tool for the optimization of MEKC-MS parameters and the response surface model analysis can provide in-depth statistical understandings of the significant factors required to achieve maximum enantioresolution and ESI-MS sensitivity.
4.Use of chiral amino acid ester-based ionic liquids as chiral selectors in CE.
Stavrou IJ1, Kapnissi-Christodoulou CP. Electrophoresis. 2013 Feb;34(4):524-30. doi: 10.1002/elps.201200469.
In this study, the applicability of a chiral ionic liquid (CIL) as the sole chiral selector in CE was investigated for the first time. In particular, five amino acid ester-based CILs were synthesized and used as additives in the BGE in order to evaluate their chiral recognition ability. The performance of these CILs as the sole chiral selectors was evaluated by using 1,1'-binaphthyl-2,2-diylhydrogenphosphate (BNP) as the analyte and by comparing the resolution values. Different parameters were examined, such as the alkyl group bulkiness and the configuration of the cation, the anion type of the CIL and its concentration, and the pH of the BGE, in order to optimize the separation of the enantiomers and to demonstrate the effect that each parameter has on the chiral-recognition ability of the CIL. Baseline separation of BNP within 13 min was achieved by using a BGE of 100 mM Tris/10 mM sodium tetraboratedecahydrate (pH 8) and a chiral selector of 60 mM l-alanine tert butyl ester lactate.