Experimental and DFT study on the complexation of Ba2+ with beauvericin

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ba2+(aq) + 1·Sr2+(nb) ⟺1·Ba2+(nb) + Sr2+(aq) taking place in the two-phase water–nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (Ba2+, 1·Sr2+) = 1.2 ± 0.1. Further, the stability constant of the beauvericin–barium complex (abbrev. 1·Ba2+) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1·Ba2+) = 9.5 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1·Ba2+ complex species was predicted.