Václav Kašička, Jan Bílek, Dušan Koval, Petra Sázelová, Filip Teplý
Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 2, 166 10 Prague 6, Czechia
This email address is being protected from spambots. You need JavaScript enabled to view it.
Recently, new diquats (DQs), derivatives of widely used herbicide diquat, were prepared [1]. 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 [2] 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 [3]. 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.
Acknowledgements
This work was supported by the GACR (project 20-03899S) and the CAS (project RVO 61388963).
References
[1] H.R. Talele, D. Koval, L. Severa, P.E. Reyes-Gutiérrez, I. Císařová, D. Šaman, L. Bednárová, V. Kašička, F. Teplý, Chem.-Eur. J. 24 (2018) 7601-7604.
[2] D. Koval, L. Severa, L. Adriaenssens, J. Vávra, F. Teplý, V. Kašička, Electrophoresis 32 (2011) 2683.
[3] S. Štěpánová, V. Kašička, J. Sep. Sci. 38 (2015) 2708.
