Interaction of the univalent thallium cation with antamanide: Experimental and theoretical study

On the basis of extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Tl+(aq) + 1.Na+(nb) double left right arrow 1.Tl+ (nb) + Ne(aq) occurring in the two-phase water-nitrobenzene system (1 = antamanide; aq = aqueous phase, nb = nitrobenzene phase) was determined as log K-ex, (Tl+, 1.Na+) = 0.7 +/- 0.1. Further, the stability constant of the 1,Tl+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 degrees C: log beta(nb) (1.Tl+)= 4.5 +/- 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1.Tl+. was derived. In the resulting complex, the "central" cation Tl+ is bound by four bond interactions to the corresponding four carbonyl oxygen atoms of the parent ligand I. Besides, the whole 1.Tl+ complex structure is stabilized by two intramolecular hydrogen bonds. The interaction energy of the considered 1.Tl+ complex was found to be -359.0 kJ/mol, confirming also the formation of this cationic species. (C) 2014 Elsevier B.V. All rights reserved.