Experimental and theoretical study on interaction of the barium cation with antamanide

By using extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Ba2+(aq) + 1.Sr2+(nb) reversible arrow 1.Ba2+(nb) + Sr2+(aq) occurring in the two-phase water-nitrobenzene system (1 = antamanide; aq = aqueous phase, nb = nitrobenzene phase) was determined as logK(ex) (Ba2+, 1.Sr2+) = 0.2 0.1. Further, the stability constant of the 1.Ba2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 degrees C: log beta(nb) (1.Ba2+) = 8.8 +/- 0.2. Finally, applying quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1.Ba2+ was derived. In the resulting complex, the "central" cation Ba2+ is bound by six bond interactions to the corresponding six carbonyl oxygen atoms of the parent ligand 1. The interaction energy of the considered 1.Ba2+ complex was found to be -964.9 kJ/mol, confirming the formation of this cationic species as well. (C) 2014 Elsevier B.V. All rights reserved.