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The Host-Guest complexation of 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene with a number of aromatic carboxylic acids has been studied by reversed-phase high-performance liquid chromatography. The mobile phase was acetonitrile-water (80/20, v/v) with addition of 0.1% formic acid. The column was LiChrosorb RP 18, the UV detector operated at λ = 254 nm and at 26°C. The main chromatographic characteristics (retention time tR and capacity factor k’) of the aromatic carboxylic acids have been determined. The lipophilicity values of log P of carboxylic acids, as well as the binding constants KA (387-941 М-1) and Gibbs free energies ∆G (-14.74 – -16.94 kJ/mol) of the calixarene complexes with aromatic carboxylic acids have been calculated. The molecular modelling (Hyper Chem, version 8.0) of the calixarene complexes has revealed the presence of hydrogen bonds between carboxylic groups of the acids and nitrogen atoms of imino groups at the upper rim or oxygen atoms of hydroxyl groups at the lower rim of the calixarene macrocycle. The influence of log P lipophilicity of acids on KA values of the calixarene complexes has been assessed. The linear dependence of the binding constants on the acid lipophilicity indicates a significant role of solvophobic interactions on the complexation process. The relationship between supramolecular (KA) and physicochemical (molecular weight, log P, pKa) characteristics of acids has been found. The binding constants KA of the complexes increase with increase of their molecular weight and log P values.

The reserved-phase HPLC study of the complexation of 5,17-bis-(N-tolylimino-methyl)-25,27-dipropoxycalix[4]arene with aromatic carboxylic acids