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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 ␤-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 ␤-methyl D-glucopyranoside inside. The multiplicity of guest proton signals shows that the capsule provides an asymmetric magnetic environment that persists on the 1 H 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. 2). They provided the modules from which open-ended container molecules, the cavitands, were elaborated and led to the first covalent structures that completely surrounded other molecules, the carcerands (3). These shallow, bowl-shaped structures have intrinsic properties as receptors for molecular recognition as introduced by Aoyama and coworkers (4, 5). They described complexes of 1 in organic solvents with a number of guests, small diacids, alcohols, and even steroids, featuring a 1:1 stoichiometry. Intermolecular hydrogen bonding was proposed to hold the guest in the concavity of the resorcinarene host, as shown for glutaric acid in Fig. 2. The NMR spectra confirmed that the signals of the guest were upfield-shifted, as expected for their positions above the four aromatic units of the resorcinarene. However, the same spectra showed an unexpected feature: guest exchange took place slowly on the NMR time scale, with separate signals for free and bound guests. The broad range of molecules recognized and the slow on͞off dynamics appeared at odds with the simple structures proposed for the complexes, and raised some questions as to the extent of the intermolecular forces involved. We have now examined the glutaric acid, ␤-methyl D-glucopyranoside, and related complexes of 1 in solution through modern NMR techniques and report on them here. We find that the unprecedented behavior can be reconciled through encapsulation complexes involving the self-assembly of six resorcinarenes in a capsular host. The host surrounds six glutaric acid or three ␤-methyl D-glucopyranoside guests.A blueprint to the solution structure came from the crystallographic studies of Atwood and MacGillivray (6). They found that, unlike the many previous solid-state structures of resorcinarenes and guests that involve layered arrays of the molecules (7-10), resorcin[4]arene 1Ј crystallized from hot nitrobenzene as a rather large closed shell, a hexameric capsule surrounding a space of nearly 1,400 Å 3 (6). The six resorcin [4]arene molecules appear at the sides of a notional cube, and one molecule of water is at each of the eight corners (Fig. 1). An unknown number of highly disordered solvent molecules are inside the cavity. S...

The phenomenon of latent inhibition

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