Extraction and theoretical study on the complexation of the strontium cation with beauvericin

From extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Sr2+(aq) + 2A(-)(aq) +1(nb) a double dagger" 1 center dot Sr2+(nb) + 2A(-)(nb) taking place in the two-phase water-nitrobenzene system (A(-) = picrate, 1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K (ex)(1 center dot Sr2+,2A(-)) = -0.6 +/- A 0.1. Further, the stability constant of the 1 center dot Sr2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 A degrees C: log beta (nb)(1 center dot Sr2+) = 8.5 +/- A 0.1. Finally, by using quantum-mechanical DFT calculations, the most probable structure of the resulting cationic complex 1 center dot Sr2+ was derived.