Václav Kašička, Jan Bílek, Dušan Koval, Petra Sázelová, Filip Teplý
Recently, new diquats (DQs), derivatives of widely used herbicide diquat, were prepared . These chiral N heteroaromatic dicationic compounds comprising 2,2’-bipyridine moiety are attractive for variable applications, e.g. as catalysts, dyes, redox indicators, DNA intercalators, and chiral selectors. For these applications, enantiopurity of (P)- and (M)-isomers of DQs has to be checked. For this purpose, a new capillary electrophoresis (CE) method was developed. CE analyses were performed on Agilent Technologies 7100 CE system (Waldbronn, Germany) in a hydroxypropylcellulose coated fused silica capillary (id/od 50/375 µm, total/effective length 385/300 mm), at –12 kV separation voltage and 25°C. The DQs (0.2 mM) were injected hydrodynamically (700 Pa × 10 s) and detected at 200 nm. (P)- and (M)-enantiomers of all 11 DQs were baseline or better resolved by CE using aqueous 22/35 mM sodium/phosphate buffer, pH 2.5, as background electrolyte (BGE) and 6 mM randomly highly sulfated α-, β- and γ-cyclodextrins (S-CDs) as chiral selectors. Interactions of dicationic DQs with highly sulfated CDs resulted in formation of strongly negatively charged fast migrating DQ-CD complexes  that were separated with high resolution within a short time of 5–8 min. In addition, strength of the complexes of DQ enantiomers with S CDs was evaluated. The apparent stability constants of the DQ-CD complexes were determined from the dependence of effective mobilities of (P)- and (M)-enantiomers of the DQs on concentration of S-CDs in the BGE by nonlinear regression analysis as described in . The DQs enantiomers formed moderate to strong complexes with all three types of S-CDs with the apparent stability constants in the range (7.80–547.4) × 10^3 L/mol.
This work was supported by the GACR (project 20-03899S) and the CAS (project RVO 61388963).
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