Encapsulation through concern of inter and intramolecular hydrogen bonding of 2-hydroxybenzoic acid with C-alkyl calix[4]resorcinarenes

Abstract

The host-guest complexation of 2-hydroxybenzoic acid (compound 4) with four C-alkyl calix[4]resorcinarenes (compounds 3a-3d) were investigated in aqueous, solid state and gas phase. The solid inclusion complexes were prepared by solvent evaporation method. The solubility of compound 4, compounds 3a-3d and inclusion complexes were analyzed in different polar, non-polar and dipolar solvents. The binding stoichiometric ratio of inclusion complexes was analyzed by phase solubility and jobs plot method. UV–Visible and fluorescence spectral studies were provided the information about binding constant, stoichiometric ratio and Gibb's free energy values. The solid inclusion complexes were characterized by FTIR, 1HNMR , 13CNMR and powder X-ray diffraction studies to determine the interactions between the compound 4 and compounds 3a-3d. The surface morphology of all were characterized by scanning electron microscopic imagining analysis. The biological activity of all were done by phosphomolybdate antioxidant assay and kirby-bauer antibacterial studies. The proposed structure of inclusion complexes were optimized for the two orientations using DFT B3LYP 3–21 G method in the gas phase. The more stable orientations of inclusion complexes were predicted from energy and band gap energy values