Tetrameric Capsule

Figure 6. Top The two enantiomeric forms of the "american football" monomer 40 and views of the tetrameric capsule formed from four identical monomers along the mutually perpendicular C2-axes. Bottom Chiral guests 41 -46 and the corresponding de values obtained from 1H-NMR integrations.

A tennis-ball-shaped molecular aggregate can be constructed by the self-assembly of curved molecule I. Tetrameric assembly of II generates a pseudo-spherical capsule. Dimeric assembly of III can be induced by the encapsulation of smaller molecules of appropriate size and shape at the center of a spherical complex. 

Fig. 14 Tetrameric capsule made of L-shaped components held together by 16 hydrogen bonds. Aryl and OH groups have been removed for clarity...

Table 1 Diastereoselective excess in the binding of chiral racemic ketone guests by chiral enantiopure tetrameric capsule...

Hof F, Nuckolls C, Rebek J Jr (2000) Diversity and selection in self-assembled tetrameric capsules. J Am Chem Soc 122 4251 -252... 

A tetrameric capsule of ideal D2 symmetry has been reported by Rebek.65 In particular, a molecule with glycoluril and sulfamide functionality self-assembled in the solid state via 24 hydrogen bonds to form a finite assembly that accommodated 2,6-adamantanedione as a guest. The volume of the cavity of the capsule was determined to be approximately 184 A3 (Fig. 35). Each carbonyl oxygen atom of the... 

Scheme 4-12 Formation of tetrameric hydrogen-bonded capsule 52.

Rebck and coworkers extended their studies on the hydrogen-bond-based self-assembly of tetrameric capsules around guest molecules using a combinatorial approach. Starting from two different monomers, a small dynamic library of guest-filled capsules was produced. The distribution of capsule compositions was analyzed by MS and found to depend on the nature of the guest, with methylquinuclidinium cation as the most... 

Figure 4.4 Supramolecular hydrogen bonded capsule developed by Rebek et ai (left) a dimeric structure and (right) various tetrameric structures.

Figure 13 Tetrameric capsule showing binding of a diketone that makes multipoint hydrogen bonding with the top and bottom of the capsule.

Figure 26 Amphiphilic hexagram-shaped molecules self-assemble via the hydrophobic effect, forming a hexameric box or a tetrameric tetrahedral-shaped capsule as a function of the templating hydrophobic guest.

FIGURE 8.4 Structural drawing (left) and model (right) of tetrameric capsule 3. Peripheral groups have been removed for viewing clarity. 

The calix[4]arene-based ligand syntones 129-133 with either aryl urea or sulfonylurea fragments on the upper rims in their cone-conformation gave small hydrogen-bonded capsules 338-342 by Scheme 3.24, while their heterodimeric capsules have been exclusively formed when both aryl- and sulfonylureas-containing syntones are present in solution [25]. All these homo- and het-erodi- and tetrameric capsules are able to reversibly encapsulate suitable guests in organic media. 

Solid-state and solution studies of a tetrameric hydrogen-bonded capsules 385 and 386... 

The tetrameric macrocycle 170, obtained from the reaction of 161 with p-phenylenediamine, has an unusual folded conformation in the solid state and contains a roughly tetrahedral arrangement of endo N-H groups providing the potential for tetrahedral capsulation of anionic guests [155]. 

---