Interaction of the univalent silver cation with [Gly(6)]-antamanide: Experimental and theoretical study

On the basis of extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Ag+(aq) + 1 center dot Na+(nb) reversible arrow 1 center dot Ag+ (nb) + Na+(aq) occurring in the two phase water nitrobenzene system (1 = [Gly(6)]-antamanide; aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex (Ag+,1 center dot Na+) = 1.5 +/- 0.1. Further, the stability constant of the 1 center dot Ag+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 degrees C: log beta(nb) (1 center dot Ag+) = 4.5 +/- 0.2. Finally, by using quantum chemical OFF calculations, the most probable structure of the cationic complex species 1 center dot Ag+ was derived. In the resulting complex, the "central" cation Ag+ is coordinated by four noncovalent interactions to the corresponding four carbonyl oxygen atoms of the parent ligand 1. Besides, the whole l center dot Ag+ complex structure is stabilized by two intramolecular hydrogen bonds. The interaction energy of the considered 1 center dot Ag+ complex was found to be -465.5 kJ/mol, confirming also the formation of this cationic species. (C) 2017 Elsevier B.V. All rights reserved.