Experimental and theoretical study on the complexation of Ca2+ with beauvericin

From extraction experiments and gamma-activity measurements, the exchange extraction constant corresponding to the equilibrium Ca2+(aq) + 1 center dot Sr2+(nb) a double dagger" 1 center dot Ca2+(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)(Ca2+, 1 center dot Sr2+) = 1.1 +/- A 0.1. Further, the stability constant of the 1 center dot Ca2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 A degrees C: log beta (nb)(1 center dot Ca2+) = 10.1 +/- A 0.2. Finally, by using quantum mechanical density functional level of theory calculations, the most probable structures of the non-hydrated 1 center dot Ca2+ and hydrated 1 center dot Ca2+center dot H2O complex species were predicted.