Capillary electrophoretic and computational study of the complexation of valinomycin with rubidium cation

• Published in: Electrophoresis 2009-03, Vol.30 (5), p.883-889
• Main Authors: Ehala, Sille, Dybal, Jiří, Makrlík, Emanuel, Kašička, Václav
• Format: Article
• Language: English
• Subjects: Binding constant; Capillary affinity electrophoresis; Cations - chemistry; Computer Simulation; Density functional theory; Drug Stability; Electrophoresis, Capillary; Ionophore; Kinetics; Models, Chemical; Models, Molecular; Rubidium - chemistry; Stability constant; Temperature; Valinomycin - chemistry
• ISSN: 0173-0835; 1522-2683
• DOI: 10.1002/elps.200800610

This study is focused on the characterization of interactions of valinomycin (Val), a macrocyclic dodecadepsipeptide antibiotic ionophore, with rubidium cation, Rb⁺. Capillary affinity electrophoresis was employed for the experimental evaluation of the strength of the Val-Rb⁺ complex. The study involved the measurement of the change of effective electrophoretic mobility of Val at increasing concentration of Rb⁺ cation in the BGE. From the dependence of Val effective electrophoretic mobility on the Rb⁺ cation concentration in the BGE (methanolic solution of 100 mM Tris, 50 mM acetic acid, 0-1 mM RbCl), the apparent binding (stability) constant (Kb) of the Val-Rb⁺ complex in methanol was evaluated as log Kb=4.63±0.27. According to the quantum mechanical density functional theory calculations employed to predict the most probable structure of Val-Rb⁺ complex, Val is stabilized by strong non-covalent bond interactions of Rb⁺ with six ester carbonyl oxygen atoms so that the position of the "central" Rb⁺ cation in the Val cage is symmetric.