Resorcinarenes are hexameric capsules in solution

The host-guest complexes of resorcin[4]arenes with small molecules in organic solutions are examined using modern NMR spectroscopic methods. The complexation of glutaric acid and beta-methyl D-glucopyranoside in chloroform were investigated through 2D COSY, 2D NOESY, 1D NOE, and diffusion-ordered NMR spectroscopy (DOSY) techniques. These methods indicate that the complex is a self-assembled capsule composed of six resorcinarenes that surround six guest molecules of glutaric acid or three molecules of beta-methyl D-glucopyranoside inside. The multiplicity of guest proton signals shows that the capsule provides an asymmetric magnetic environment that persists on the H-1 NMR time scale. The encapsulation of these guests and common solvents suggests that the phenomenon of reversible encapsulation in chemistry may be a century old.