Host-guest inclusion systems of tetra(alkyl)resorcin [4]arenes with choline in DMSO: Dynamic NMR studies and X-ray structural characterization of the 1:1 inclusion complex

Abstract

The host-guest complex of C-tetra(methyl)calix[4]resorcinarene (1), C-tetra(pentyl)calix[4]resorcinarene (2), and C-tetra(nonyl)calix[4]resorcinarene (3) with choline in DMSO was examined via dynamic NMR. Under these conditions, only C-tetra(methyl)calix[4]resorcinarene formed a complex with choline. In order to establish the role of DMSO during the solubilization/complexation process, titration was carried out with resorcinarenes and DMSO in CDCl3. Our careful NMR analysis was based on the assignment of 1H NMR signals of the resorcinarenes in CDCl3 after the addition of variable amounts of DMSO, which showed an interesting host-guest interaction with C-tetra(pentyl)calix[4]resorcinarene. With both solvents, it is possible to define stable cone conformational arrangements based on the signals shown in the spectra of all the experiments. The results show the formation of a 1:1 inclusion complex between DMSO and C-tetra(pentyl)calix[4]resorcinarene. Suitable crystals of C-tetra(pentyl)resorcinarene in DMSO were characterized through an X-ray crystal structure determination and showed the inclusion of a molecule of DMSO in the cavity of the resorcinarene. The asymmetric unit contains one molecule of water and five molecules of DMSO, and analysis indicated that resorcinarene prefers a cone configuration (rccc conformation) in the solid state. In the crystal array, classical hydrogen bond O–H⋯O interactions and intermolecular contacts were observed.