Multicomponent, Hydrogen-Bonded Cylindrical Capsules

Self-assembled, hydrogen-bonded capsules emerge from synthetic resorcinarene-derived cavitands and soluble glycolurils when appropriate guest molecules are present. The assembly consists of 2 cavitands, 4 glycolurils and guest(s), and the arrangement of glycolurils leads to a chiral structure. The capsule features a space of ∼620 Å3 and accommodates narrow guests such as n-alkanes from C14 to C19, or other molecules (e.g., capsaicin) and combinations of molecules of up to ∼22 Å in length (e.g., two p-methylstyrene molecules). Positions of encapsulated nuclei can be predicted from NMR chemical shifts, with intense shielding of δΔ = −5 ppm near the resorcinarene ends and mild deshielding of +0.5 to 1 ppm near the glycolurils at the capsule’s center. Computational methods using nucleus independent chemical shifts (NICS) were used to map the induced magnetic shielding/deshielding for the inner space of the cavity. The asymmetric arrangement of the spacers creates a chiral steric and magnetic environment in the capsule and the geminal hydrogen atoms of encapsulated alkanes show diastereotopic proton signals. The two enantiomers interconvert (racemize) through an achiral intermediate involving a slight rotation of the spacers and lengthening of the cavity. Accordingly, longer, compressed alkanes accelerate the racemization by applying pressure from the inside on the capsule’s ends. Guests that place hydrogen bond donors and acceptors near the glycolurils in the middle (e.g., p-isopropylbenzyl alcohol) also accelerate the racemization by facilitating the rotation of the glycolurils. Slow tumbling of guest on the NMR time scale inside the capsule leads to social isomerism of para-disubstituted benzenes such as p-methylstyrene. Flexible guests such as hexane tumble inside the cavity with an activation barrier of ΔG⧧ =16.2 kcal/mol. The middle of the extended capsule is narrow, but still accommodates phenyl groups such as those presented by p-quaterphenyl and alkylated biphenylcarbonitriles. The aromatic units in these guests report their positions by imparting magnetic anisotropy to the capsule components. Gases such as propane, butane, isobutane, propylene, 2-methylpropene, and 1,3-butadiene even xenon are coencapsulated with other guests and their motions inside are examined

Reaction of Isonitriles with Carboxylic Acids in a Cavitand: Observation of Elusive Isoimide Intermediates

Reaction of Isonitriles with Carboxylic Acids in a Cavitand: Observation of Elusive Isoimide Intermediate

A Functionalized, Deep Cavitand Catalyzes the Aminolysis of a Choline Derivative

The aminolysis of choline p-nitrophenyl carbonate is catalyzed with turnover by a deep cavitand bearing an introverted pyridone function. The synergy of action between the recognition of the guest in the binding pocket and the catalytic activity brought to bear by the pyridone is responsible for the high substrate specificity observed

Activation of a Water-Soluble Resorcinarene Cavitand at the Water–Phosphocholine Micelle Interface

The host–guest properties of a water-soluble resorcinarene cavitand bearing four guanidines at the feet were investigated in water and dodecylphosphocholine (DPC) micelles by NMR spectroscopy. While the binding of different guests in water was generally modest, the formation of the caviplexes was significantly enhanced in the presence of micelles and reached affinities typically observed for organic solvents. The increase in binding free energies of up to 3.2 kcal mol–1 was determined to be enthalpic in origin and was attributed to the disruption of velcrand dimers and subsequent conformational reorganization of the receptor induced by the micelles that acted as hosts for the cavitand. In agreement with the NMR data, molecular dynamics simulations reproduced the spontaneous incorporation of the cavitand into the micelle and provided a detailed picture of the positioning of the receptor at the DPC–water interface

Selective Stabilization of Self-Assembled Hydrogen-Bonded Molecular Capsules Through π–π Interactions

Subtle noncovalent forces such as π–π interactions play an import role in the folding of biological macromolecules such as DNA and proteins. We describe here a system where such interactions on the outside of a molecular capsule trigger a selective change of its structure as a self-assembled receptor

Guest-Induced, Selective Formation of Isomeric Capsules with Imperfect Walls

The majority of building blocks in self-assembled capsules feature high symmetry. Reducing this symmetry inevitably leads to expanded possibilities for isomerism. Here, we report a deep cavitand host with one short and three long walls. Its dimerization to hydrogen-bonded capsules in the presence of suitable guest molecules can lead to two constitutional isomers. A given guest induces the predominant formation of only one isomer. The unexpected selectivity is interpreted in terms of the different hydrogen-bonding patterns of the capsules and their effects on the size, shape, and dynamics of the capsules’ spaces

Formation of Discrete, Functional Assemblies and Informational Polymers through the Hydrogen-Bonding Preferences of Calixarene Aryl and Sulfonyl Tetraureas

Derivatives of the calix[4]arenes in the cone conformation featuring either aryl urea or sulfonyl urea functions on their larger (upper) rims dimerize through hydrogen bonding to give molecular capsules. The capsules act as hosts that reversibly bind smaller molecule guests in organic media. Heterodimers form when both aryl and sulfonyl ureas are present, and the heterodimers form exclusively with respect to the homodimers. The heterodimerization encodes information at the molecular level and allows the predictable formation of discrete aggregates of nanometer dimensions. Evidence for the reversible assembly of these structures is provided by 1H NMR, guest encapsulation studies, and gel permeation chromatography. Covalent attachment of these calixarene aryl and sulfonyl ureas at their smaller (lower) rims leads to polymeric assemblies in which the informational content is preserved

Steric and Magnetic Asymmetry Distinguished by Encapsulation

Guests in an achiral cavity experience asymmetric magnetic environments induced by chiral centers outside the cavity

Recognition and Catalysis in Allylic Alkylations

A cavitand outfitted with a chelated palladium atom catalyzes allylic alkylation reactions. Molecular recognition by the cavitand distinguishes between closely related structures and results in subtle substrate specificities

Expanded Capsules with Reversibly Added Spacers

Glycolurils insert as spacer elements in a capsule to create a new space with enhanced dimensions