Experimental and theoretical study on interaction of the silver cation with nonactin

Abstract

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium occurring in the two-phase water–nitrobenzene system (1 = nonactin, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K_ex (Ag⁺, 1 ⋅ Na⁺) = 0.6 ± 0.1. Furthermore, the stability constant of the 1 ⋅ Ag⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β_nb(1 ⋅ Ag⁺) = 6.6 ± 0.2. Finally, employing quantum mechanical calculations, the most probable structure of the cationic complex species 1 ⋅ Ag⁺ was derived. In the resulting complex, having a tennis-ball-seam conformation with the C₂ symmetry, the ‘central’ cation Ag⁺ is bound by eight relatively strong bonding interactions to eight oxygen atoms of the parent nonactin ligand. The interaction energy of the considered 1 ⋅ Ag⁺ complex was found to be –468.5 kJ/mol, confirming also the formation of this cationic species.

Keywords:

• silver cation
• nonactin
• complexation
• extraction and stability constants
• quantum mechanical calculations
• structures

Acknowledgements

The authors of this study thank Dr Petr Toman from Prague for some theoretical calculations.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00268976.2015.1054326.

Additional information

Funding

This work was supported by the Grant Agency of Faculty of Environmental Sciences, Czech University of Life Sciences, Prague [grant number 42900/1312/3114], ‘Environmental Aspects of Sustainable Development of Society’, and by the Czech Ministry of Education, Youth, and Sports [grant number MSM 6046137307].