Macrocycle hexameric

Fig. 34 Solid-state structure of the mixed-macrocycle hexameric capsule. Diethyl ether guests are shown in dark gray.

Scheme 6.24 Alkyne metathesis for the preparation of hexameric phenylacetylene macrocycles in high yields.

Cucurbituril is a hexameric macrocyclic compound with the formula (C6H6N402)6 shaped like a pumpkin which belongs to the botanical family Cucurbitaceae. This macrocyclic cavitand has idealized symmetry Z>6h with a hydrophobic internal cavity of about 0.55 nm. The two portals, which are each laced by six hydrophilic carbonyl groups, have a diameter of 0.4 nm [Fig. 20.4.8(a)],... 

Recent studies have shown that the bowl-shaped C-alkyl substituted pyrogal-lol[4]arene macrocycles readily self-assemble to form a gobular hexameric cage, which is structurally robust and remains stable even in aqueous media (Fig. 20.4.38). Slow evaporation of a solution of C-heptylpyrogallol[4]arene in ethyl acetate gives crystalline [(C-heptylpyrogallol[4]arene)6(EtOAc)6... 

Similar molecules (17) were described by Mascal as G-C DNA base hybrids [21]. In this case, the hexameric macrocycle was beautifully evidenced in the solid state by an X-ray structure (Figure 3.6). 

A different neutral hexameric coordination cage structure was assembled from six either C-propyl- or C-pentyl-pyrogallol[4]arene units and 12 Ga(III) ions [51]. In both cases the centroids of the macrocyclic ligand components reside on the vertices of a squeezed octahedron enclosing a space of approximately 1150 A3. Only a total of 20... 

Cucurbituril (cucrbit[6]uril or CB[6]), a hexameric macrocycle 141 (R = H, = 6) with a 1,3,5,6-tetraazocane core unit, is self-assembled from an acid-catalyzed condensation reaction of glycouril and formaldehyde (see Section 14.09.9.1.1 and 1996CHEC-II(9)705). Although its synthesis first appeared in 1905, its chemical nature and structure remained unknown until 1981, when full characterization was reported by Mock and co-workers <1981JA7367>. 

Scheme 8 Tetrameric and hexameric organotin self-assembled macrocyclic supermolecules...

The viability of yet another approach to hexathia[36]hexaphyrin-(2.2.2.2.2.2) macrocycles has also been demonstrated. In this instance, the diformyl-tra 5-bithiophenylethene 7.84 is used as the starting material with a standard McMurry-type coupling providing the hexathia[36]hexaphyrin-(2.2.2.2.2.2) 7.82b in 1.3% yield (Scheme 7.7.4). This reaction was found to produce only one hexameric product. On the basis of spectroscopic studies, this single product was found to be identical to the cis,trans,cis,trans,cis,trans isomer 7.82b prepared and isolated as discussed above. 

Dicarboxylates or carboxylates containing an additional anionic function (e.g. RS , RO, etc.) capable of coordination to tin atoms (functionalized monocarboxylates) are ideal candidates for the constmction of discrete di- and oligonuclear organotin macrocycles, as is shown by a series of organotin carboxylate macrocycles having dimeric, trimeric, tetrameric, and hexameric compositions (Figure 2.5.11). 

Cucurbituril (cucurbit[6]uril, or CB[6]) is a hexameric macrocyclic compoxmd self-assembled from an acid-catalyzed condensation reaction of glycoluril and formaldehyde (Scheme 1). Although its synthesis was first reported by Behrend and coworkers in 1905j its chemical nature and stmcture were unknown until they were revealed by Mock and coworkers in 198iP CB[6] has a cavity of 5.5 A diameter, accessible from the exterior by two carbonyl-laced portals of 4 A diameter. Although the size of the cavity is similar to that of a-cyclodextrin ( < highly symmetrical structure... 

It should be noted that trinuclear metallamacrocycles with half-sandwich complexes cannot only be obtained with the ligands mentioned above but also with amino acids [21-25] and 3,4-dihydroxy-2-methylpyridine [26]. Furthermore, larger macrocycles have been synthesized with the ligands adenine [10,11], 6-purinethione [27], 2-amino-6-purinethione [27], 4-imidazole-carboxylic acid [28] (tetrameric structures) and 6-purinethione riboside (hexameric structure) [29]. So far, no special host-guest interactions have been reported for these complexes and therefore they will not be described in more detail. 

Figure 25 Self-assembly of 83 to form pentameric 84 and hexameric 85 macrocycles (a) FeCl2-4H20, MeOH, 25 °C, 24 h (left). TEM images of hierarchical self-assembled macrocycles 84 and 85 into fibers (center). Scale bars (a 500 nm b 100 nm c 500 nm d 100 nm). Space-filling models of 84 and 85 (e and f, respectively). Adapted with permission from Ref. 10CEJ1768. Copyright 2010 WiLEY-VCH Veriag GmbH Co. KOaA, Weinheim.

Stacking of ring-shaped compounds can be another good alternative to create hollow tubular structures [26,27]. However, despite recent advances in synthetic tubular nanostructure using the self-assembly, the tubules have a limitation on the dynamic response characteristics. As a part of an effort to generate the stimuli-responsive tubular nanostructures, the self-assembled tubular nanostructure that can undergo a reversible expansion-contraction motion and chirality inversion was reported. Bent-shaped aromatic amphiphiles (enantiomers 1, 2) self-assembled into hexam-eric macrocyclic nanostructures in an aqueous solution (Fig. 2.1) [28]. When the concentration of the solution was increased, the chiral tubules were formed by spontaneous ID stacking of hexameric macrocycles with a mutual rotation in the one direction (Fig. 2.1c). 

More importantly, upon addition of a silver salt, these helical tubules were segmented into slices of tubules while maintaining helical order in these discrete nanostructures. The preservation of the shape-persistent hexameric macrocycles in this transition is responsible for the retention of supramolecular chirality. Transition from chiral tubules into discrete nanostructures with maintaining the supramolecular chirality is reported for thermotropic liquid crystals of dendritic molecules [82-84], There is, however, no study about such a transition for weU-defined nanoscale synthetic... 

FIGURE 2.18 (a) Structure of bent-shaped rigid molecule 17 and helical stacking of hexameric macrocycles, (b) Dissociation into toroidal stacks. Reprinted with permission from Reference 81. Copyright 2008 John Wiley Sons, Inc. 

Figure 8 A giant hexameric porphyrin-containing macrocycle and the template that is used for its formation.

On mixing equal amounts of pyrogaUo[4]arene and resorcin[4]arene no evidence of hetero-hexameric capsules was found as a consequence of the extremely high selfrecognition process that caused the formation of only capsules based on the same macrocycle. Guest affinity is also... 

Cucurbituril (cucurbit[6]uril, or CB[6]) is a hexameric macrocyclic compound prepared from an acid-catalyzed... 

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