A combined experimental and DFT study on the complexation of Mg2+ with beauvericin

From extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Mg2+(aq) + 1 center dot Sr2+(nb) a double dagger dagger 1 center dot Mg2+(nb) + Sr2+(aq) taking place in the two-phase water-nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K (ex) (Mg2+, 1 center dot Sr2+) = 0.0 +/- A 0.1. Further, the stability constant of the 1 center dot Mg2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 A degrees C as log beta(nb) (1 center dot Mg2+) = 9.1 +/- A 0.2. By using quantum mechanical DFT calculations, the most probable structures of the non-hydrated 1 center dot Mg2+ and hydrated 1 center dot Mg2+center dot 3H(2)O complex species were predicted.