engleski

Alkali-metal cation coordination to calix[4]arenes containing triazole functionalities

The medium effects on the complexation of alkali-metal cations with calix[4]arene derivatives containing triazole subunits (compunds L and l) was systematically explored by means of microcalorimetric and UV-Vis spectrophotometric titrations in dimethylformamide, methanol water and acetonitrile. First two solvents were chosen for the purpose of comparison of receptors binding abilities as both ligands exhibit sufficient solubility required for complexation investigations in these media. The cation hosting in MeCN was studied to compare the ligand L with other tertiary amide calixarene derivatives. On the basis of ligand dissolution enthalpies, and the literature data, the enthalpies of reactants and the product transfer among solvents were obtained. The studied compounds binded alkali-metal cation rather efficiently and similarly in methanol and in dimethylformamide, whereas the acetonitrile was the most favourable reaction medium for alkalimetal cation reactions with receptor L. Compound l proved to be a remarkable host for Na+ in water. The cation binding was enthalpically controlled. The complexation of Li+ with ligand L in acetonitrile was the only entropically favourable reaction. The peak-affinity of both compounds for Na+ was noticed for all studied reactions. The 1H NMR investigations revealed relatively low affinity of the calixarene sodium complex for the inclusion of solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. In many examined cases, the considerable solvent effect on the complexation equilibria was proven to be an interesting interplay between the transfer enthalpies and entropies of the reactants and the products.

calix[4]arenes ; cation receptors ; complexation thermodynamics ; solvent effect

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