The separation of the enantiomers of diquats by capillary electrophoresis using randomly sulfated cyclodextrins as chiral selectors

Abstract

Diquats, derivatives of the widely used herbicide diquat, represent a new class of functional organic molecules. A combination of their special electrochemical properties and axial chirality could potentially result in their important applications in supramolecular chemistry, chiral catalysis, and chiral analysis. However, prior to their practical applications, the diquats have to be prepared in enantiomerically pure forms and the enantiomeric purity of their P‐ and M‐isomers has to be checked. Hence, a chiral capillary electrophoresis (CE) method has been developed and applied for separation of P‐ and M‐enantiomers of 11 new diquats. Fast and better than baseline CE separations of enantiomers of all 11 diquats within a short time 5–7 min were achieved using acidic buffer, 22 mM NaOH, 35 mM H3PO4, pH 2.5, as a background electrolyte, and 6 mM randomly sulfated α‐, β‐, and γ‐cyclodextrins as chiral selectors. The most successful selector was sulfated γ‐cyclodextrin, which baseline separated the enantiomers of all 11 diquats, followed by sulfated β‐cyclodextrin and sulfated α‐cyclodextrin, which baseline separated enantiomers of 10 and nine diquats, respectively. Using this method, a high enantiopurity degree of the isolated P‐ and M‐enantiomers of three diquats with a defined absolute configuration was confirmed and their migration order was identified.

Determination of the binding constants and ionic mobilities of diquat complexes with randomly sulfated cyclodextrins by affinity capillary electrophoresis

“…In accordance with this migration order, the binding constant of the first migrating enantiomer was higher than that of the second migrating enantiomer. The relative differences in the binding constants of the enantiomers of the particular DQs expressed as ( K b1 ‐ K b2 )/ K b1 ratios are rather high (20%–80%) and correlate well with the high selectivity factors and resolutions achieved in the recent CE separations of DQ enantiomers [54].…”

“…The experimental conditions were based on the previous successful separation of DQ enantiomers using randomly highly S-CDs as chiral selectors and sodium phosphate buffer (22 mM NaOH, 35 mM H 3 PO 4 , pH 2.5) as the BGE [54]. However, these conditions had to be adapted for the conditions necessary for the correct determination of the binding constants of DQ-S-CD complexes.…”

“…However, for these practical applications, the DQs have to be prepared in an enantiomerically pure form and their enantiomeric purity has to be controlled. For this purpose, a chiral CE method has been developed for separation of DQ enantiomers and for enantiopurity control of isolated pure P ‐ and M ‐isomers of selected DQs using randomly highly S‐CDs as chiral selectors in the BGE composed of 22 mM NaOH, 35 mM H 3 PO 4 , pH 2.5 [54]. High‐efficient separations with high resolutions up to 11.4 were achieved within a short time of 5–7 min.…”

Enantioseparation of agrochemicals by gas chromatography. Exploring columns based on cyclodextrin derivatives dissolved into polysiloxanes

“…Enantiomeric analysis can be performed by different analytical techniques [5][6][7][8][9][10][11]. A comprehensive compilation and classification of chiral agrochemicals according to their primarily used, [12], gathered information on enantioseparation methods for those agrochemicals by liquid chromatography (LC), gas chromatography (GC), and capillary electrophoresis (CE).…”