A Comparative Study of Enantioseparations of Nα-Fmoc Proteinogenic Amino Acids on Quinine-Based Zwitterionic and Anion Exchanger-Type Chiral Stationary Phases under Hydro-Organic Liquid and Subcritical Fluid Chromatographic Conditions

Abstract

Abstract:The focus of this contribution is a comparative investigation of enantioseparations of 19 N α -Fmoc proteinogenic amino acids on Quinine-based zwitterionic and anion-exchanger type chiral stationary phases employing hydro-organic and polar-ionic liquid and subcritical fluid chromatographic conditions. Effects of mobile phase composition (including additives, e.g., water, basis and acids) and nature of chiral selectors on the chromatographic performances were studied at different chromatographic modes. Thermodynamic parameters of the temperature dependent enantioseparation results were calculated in the temperature range 5-50 • C applying plots of lnα versus 1/T. The differences in standard enthalpy and standard entropy for a given pair of enantiomers were calculated and served as a basis for comparisons. Elution sequence in all cases was determined, where a general rule could be observed, both in liquid and subcritical fluid chromatographic mode the D-enantiomers eluted before the L ones. In both modes, the principles of ion exchange chromatography apply.

Liquid chromatographic enantioseparation of limonene‐based carbocyclic β‐amino acids on zwitterionic Cinchona alkaloid‐based chiral stationary phases

“…The slopes of the log k versus log c plots in this study (0.25–0.31) are in accordance with our results obtained on ZWIX phases working in zwitterionic mode . However, ZWIX phases working in a “uni‐ionic” mode as anion‐exchanger or cation‐exchanger exhibited steeper slopes (0.6–1.0). These values indicate a marked difference between the concerted zwitterionic and a “uni‐ionic” ion‐exchange mechanism.…”

Liquid and subcritical fluid chromatographic enantioseparation of Nα‐Fmoc proteinogenic amino acids on Quinidine‐based zwitterionic and anion‐exchanger type chiral stationary phases. A comparative study

“…According to Kopaciewicz et al, 38 the ratio of the effective charges of the solute and the counterions determines the slopes of log k 1 and log c FA curves. The observed slopes around 0.29-0.36 correspond with the values of around 0.19-0.28 and 0.18-0.26 previously found for the ZWIX(+) system for the same SAs under LC 40 and SFC conditions 27 and for ß-amino acids in PIM. 41,42 The slight differences in the slopes obtained on ZWIX(−) for each enantiomer indicate that the enantioselectivity remained almost constant by varying the counterion concentration (data not shown).…”

Enantioseparation of chiral pharmaceuticals by vancomycin‐bonded stationary phase and analysis of chiral recognition mechanism

“…14,15 The interaction between the analyte and the CSP totally depended on chromatographic modes and mobile phase additives. 16,17 It was found that enantiorecognition mechanisms on vancomycin in polar ionic mode was mainly derived from hydrogen bonding, electrostatic forces, and steric hindrance, whereas hydrophobic, electrostatic, and steric interactions were more dominant in reversedphase mode. [18][19][20] Unequivocally, the acidic and basic additives in mobile phase impacted chiral recognition mechanism by regulating ion-pairing interaction and altering proton activity of the mobile phase medium, further influencing electrostatic interactions between analyte and the CSP.…”