The study of complexation of 5,17-bis-(n-tolyliminomethyl)- 25,27-dipropoxycalix[4]arene with benzoic acids by rp hplc and molecular modeling methods

Abstract

The Host-Guest complexation of 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene with benzoic acids has been studied by reversed-phase high-performance liquid chromatography (RP HPLC) method (the mobile phase – MeCN/H2O, 86/14 v/v, the column support – LiChrosorb RP 18, UV detector, l = 254 nm). The study of the chromatographic behaviour of 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene and benzoic acids, as well as determination of their main chromatographic characteristics – the retention times tR and capacity factors k’ have been performed. On the basis of the data obtained the lipophilicity log P, as well as the binding constants and Gibbs free energies of the complexes of 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene with benzoic acids have been calculated. The binding constants and Gibbs free energies of the complexes of 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene with benzoic acids are in the range of 335-910 М-1 or -14.38 – -16.85 kJ/mol, respectively. The influence of the benzoic acids lipophilicity log P and pKa values on the binding constants KA of the complexes has been examined. It has been found that decrease of the log P and pKa values increases the binding constants KA of the complexes. Molecular modeling of the complexes 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 the hydroxyl groups at the lower rim of the calixarene macrocycle. A linear dependence of the binding constants from the acid lipophilicity log P indicates a significant role of solvatophobic interactions during the complexation process.