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 interactions of the tetracationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (H(2)TMPyP) and its metallo derivatives (MTMPyP) (where M=copper(II), zinc(II), and gold(III) with the octa-anionic form (at neutral pH) of 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)calix[4]arene (C(4)TsTc) lead to a series of complex species whose stoichiometry and porphyrin sequence can be easily tuned. Crystallographic, spectroscopic, and diffusion NMR studies converge towards a common picture in which a central 1:4 porphyrin/calixarene unit serves as a template for the formation of more complex species. These species arise by successive, stepwise addition of single porphyrin molecules above and below the plane of the 1:4 central core to ultimately give a 7:4 complex. Noticeably, the stoichiometry of the various complex species corresponds to the actual concentration ratio of porphyrins and calixarenes in solution allowing the stoichiometry of these species to be easily tuned. This behavior and the remarkable stability of these species allow homo-porphyrin and hetero-(metallo)porphyrin species to be formed with control of not only the stoichiometry but also the sequence of the porphyrin array. The flexibility and ease of this approach permit, in principle, the design and synthesis of porphyrin arrays for predetermined purposes. For example, we have shown that it is very easy to design and obtain mixed porphyrin species in which a foreseen photoinduced electron-transfer is indeed observed.

In recent years it has been observed that resorcin[4]arenes and pyrogallol[4]arenes form hydrogen-bonded hexameric capsules in nonpolar solvents. In the present study we have used NMR spectroscopy, with an emphasis on diffusion NMR, to investigate the self-assembly and the aggregation mode of solutions of octahydroxypyridine[4]arene (1 b) in chloroform. In spectroscopic studies, the hexameric capsule of C-undecylresorcin[4]arene (2 b) was used as a reference compound and in some cases also as an internal reference. The current diffusion NMR spectroscopy study shows, in contrast to a previous report, that compound 1 b self-assembles spontaneously into hexameric and dimeric aggregates in solutions in chloroform. The (1)H NMR and diffusion NMR spectroscopic studies on a solution of 1 b in CHCl(3) show the presence of new upfield-shifted peaks, which diffuse with the same diffusion coefficient as the hexameric peaks in the spectrum. Therefore, these new upfield-shifted peaks were attributed to encapsulated CHCl(3) molecules. Interestingly, diffusion NMR measurements showed that the addition of trifluoroacetic acid (6.7 equiv), which had no effect on the hexameric capsules of 2 b, led to the disassembly of the hexamer and the dimer of 1 b into its monomers. Therefore, we conclude that compound 1 b self-assembles spontaneously into hexameric capsules in nonpolar organic solvents, as do resorcin[4]arenes 2 b and 2 c and pyrogallol[4]arenes 3 a and 3 b.

Cation-templated self-assembly of the lipophilic isoguanosine (isoG 1) with different monovalent cations (M(+)=Li(+), Na(+), K(+), NH(4) (+), and Cs(+)) was studied in solvents of different polarity by using diffusion NMR spectroscopy. Previous studies that did not use diffusion NMR techniques concluded that isoG 1 forms both pentamers (isoG 1)(5)M(+) and decamers (isoG 1)(10)M(+) in the presence of alkali-metal cations. The present diffusion NMR studies demonstrate, however, that isoG 1 does not form (isoG 1)(5)M(+) pentamers. In fact, the diffusion NMR data indicates that both doubly charged decamers of formula (isoG 1)(10)2 M(+) and singly charged decamers, (isoG 1)(10)M(+), are formed with lithium, sodium, potassium, and ammonium tetraphenylborate salts (LiB(Ph)(4), KB(Ph)(4), NaB(Ph)(4) and NH(4)B(Ph)(4)), depending on the isoG 1:salt stoichiometry of the solution. In the presence of CsB(Ph)(4), isoG 1 affords only the singly charged decamers (isoG 1)(10)Cs(+). By monitoring the diffusion coefficient of the B(Ph)(4) (-) ion in the different mixtures of solvents, we also concluded that the anion is more strongly associated to the doubly charged decamers (isoG 1)(10)2 M(+) than to the singly charged decamers (isoG 1)(10)M(+). The (isoG 1)(10)2 M(+) species can, however, exist in solution without the mediation of the anion. This last conclusion was supported by the finding that the doubly charged decamers (isoG 1)(10)2 M(+) also prevail in 1:1 CD(3)CN:CDCl(3), a solvent mixture in which the B(Ph)(4) (-) ion does not interact significantly with the self-assembled complex. These diffusion measurements, which have provided new and improved structural information about these decameric isoG 1 assemblies, demonstrate the utility of combining diffusion NMR techniques with conventional NMR methods in seeking to characterize labile, multicomponent, supramolecular systems in solution, especially those with high symmetry.

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