A combined extraction and DFT study on the complexation of K+ with valinomycin

Abstract

AbstractFrom extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium K + (aq) + 1·Cs + (nb) [FORMULA]1·K + (nb) + Cs + (aq) taking place in the two-phase water-nitrobenzene system (1 = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as [FORMULA]. Further, the stability constant of the 1·K + complex in nitrobenzene saturated with water was calculated for a temperature of 25°C as log β nb (1·K + ) = 10.6 ± 0.1. By using quantum-mechanical density functional theory (DFT) calculations, the most probable structure of the 1·K + complex species was derived. In this complex having C 3 symmetry, the valinomycin part of the species 1·K + is stabilized by strong bond interactions of K + with six ester carbonyl oxygen atoms so that the position of the central cation K + in the valinomycin cage is symmetric. Finally, the calculated stabilization energy of the considered cationic complex species 1·K + is −376.1 kJ mol −1 , confirming the very high stability of this complex.Graphical Abstract[IMAGE]