Host-guest inclusion systems of tetra(alkyl)resorcin[]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.