Experimental and theoretical study on complexation of the lithium cation with [Gly⁶]-antamanide

ABSTRACT

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Li⁺(aq) + 1⋅Na⁺(nb) $\genfrac{}{}{0pt}{}{\to }{\leftarrow \phantom{{}_{to.5ex}}}$ 1⋅Li⁺ (nb) + Na⁺(aq) occurring in the two-phase water–nitrobenzene system (1 = [Gly⁶]-antamanide; aq = aqueous phase, nb = nitrobenzene phase) was determined as log K _ex(Li⁺,1·Na⁺) = 0.6 ± 0.1. Further, the stability constant of the 1⋅Li⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: logβ_nb(1⋅Li⁺) = 5.8 ± 0.2. Finally, by using quantum chemical calculations, the most probable structure of the cationic complex species 1⋅Li⁺ was derived. In the resulting complex, the ‘central’ cation Li⁺ is bound by four bonding interactions to the corresponding four carbonyl oxygen atoms of the parent ligand 1. Besides, the whole 1⋅Li⁺ complex structure is stabilised by two intramolecular hydrogen bonds. The interaction energy of the considered 1⋅Li⁺ complex was found to be –553.5 kJ/mol, confirming also the formation of this cationic species.

GRAPHICAL ABSTRACT

KEYWORDS:

• Lithium cation
• [Gly⁶]-antamanide
• complexation
• DFT calculations
• structures

Disclosure statement

No potential conflict of interest was reported by the authors.

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], and by the Czech Ministry of Education, Youth, and Sports [Grant Number MSMT 20/2015].