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

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Sr2+(aq) + 2A-(aq) +1(nb) ↔ 1 x 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 Kex(1 x Sr2+,2A-) -0.6 ± 0.1. Further, the stability constant of the 1 x Sr2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 deg C: log βnb(1 x Sr2+) = 8.5 ± 0.1. Finally, by using quantum-mechanical DFT calculations, the most probable structure of the resulting cationic complex 1 x Sr2+ was derived. (author)