engleski

The solvation influence on the complexation of alkali-metal cations with calix[4]arene derivates

The p-tert-butyl calix[4]arenes with carbonyl- containing substituents at the lower rim are known to be effective receptors for alkali- metal cations. Apart from the chemical nature of the attached functionalities, and the cation size, the complexation thermodynamics is strongly influenced by the reactant and the product solvation.[1, 2] In the first part of the work the thermodynamic parameters of alkali-metal cation complexation with a simple calix[4]arene ketone derivative (L) in methanol, ethanol, N-methylformamide, N, N- dimethylformamide, dimethyl sulfoxide, and acetonitrile were determined.[1] The compound L was found to be rather efficient receptor for alkali-metal cations. The cation binding was enthalpically controlled with the peak affinity for Na+. To examine the possible inclusion of the investigated solvent molecules into the hydrophobic basket of the receptor and its sodium complex detailed spectro-photometric, calorimetric and 1H NMR titrations in chloroform were carried out. The solvent binding was much more favorable in the case of NaL+ when compared to free ligand. The sodium complex exhibited the highest affinity for the acetonitrile, which can, at least in part, explain the highest stability of the complexes in this solvent. In the second part of the work, the inclusion of acetonitrile molecule in the hydrophobic cavity of a more rigid tertiary amide calix[4]arene derivative and the corresponding sodium complex was investigated. The obtained data provided an insight into the influence of the calixarene flexibility on the thermodynamics of adduct formation.

calixarenes ; cations ; host-guests systems ; thermodynamics ; solvent effects

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