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

2015-11-27T11:25:59Z (GMT) by Emanuel Makrlík Petr Vaňura
<div><p>From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium occurring in the two-phase water–nitrobenzene system (<b>1</b> = nonactin, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log <i>K</i><sub>ex</sub> (Ag<sup>+</sup>, <b>1 ⋅</b> Na<sup>+</sup>) = 0.6 ± 0.1. Furthermore, the stability constant of the <b>1 ⋅</b> Ag<sup>+</sup> complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β<sub>nb</sub>(<b>1 ⋅</b> Ag<sup>+</sup>) = 6.6 ± 0.2. Finally, employing quantum mechanical calculations, the most probable structure of the cationic complex species <b>1 ⋅</b> Ag<sup>+</sup> was derived. In the resulting complex, having a tennis-ball-seam conformation with the <i>C</i><sub>2</sub> symmetry, the ‘central’ cation Ag<sup>+</sup> is bound by eight relatively strong bonding interactions to eight oxygen atoms of the parent nonactin ligand. The interaction energy of the considered <b>1 ⋅</b> Ag<sup>+</sup> complex was found to be –468.5 kJ/mol, confirming also the formation of this cationic species.</p></div>