Determination of stability constants of valinomycin complexes with ammonium and alkali metal ions by capillary affinity electrophoresis

• Published in: Electrophoresis 2008-02, Vol.29 (3), p.652-657
• Main Authors: Ehala, Sille, Kašička, Václav, Makrlík, Emanuel
• Format: Article
• Language: English
• Subjects: Alkali metal cations; Alkalies - chemistry; Anti-Bacterial Agents - chemistry; Binding constant; Capillary affinity electrophoresis; Cations, Monovalent - chemistry; Drug Stability; Electrophoresis, Capillary - methods; Ionophores - chemistry; Quaternary Ammonium Compounds - chemistry; Stability constant; Valinomycin; Valinomycin - analogs & derivatives; Valinomycin - chemistry
• ISSN: 0173-0835; 1522-2683
• DOI: 10.1002/elps.200700583

Capillary affinity electrophoresis (CAE) has been employed to investigate quantitatively the interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with univalent cations, ammonium and alkali metal ions, K⁺, Cs⁺, Na⁺, and Li⁺, in methanol. The study involved measuring the change in effective electrophoretic mobility of valinomycin while the cation concentrations in the BGE were increased. The corresponding apparent stability (binding) constants of the valinomycin-univalent cation complexes were obtained from the dependence of valinomycin effective mobility on the cation concentration in BGE using a nonlinear regression analysis. The calculated apparent stability constants of the above-mentioned complexes show the substantially higher selectivity of valinomycin for K⁺ and Cs⁺ ions over Li⁺, Na⁺, and NH₄⁺ ions. CAE proved to be a suitable method for the investigation of both weak and strong interactions of valinomycin with small ions.