Deep-cavity cavitands

The template plays an important role in the formation of capsule F because no directional non-covalent bonds such as H-bonding and M-L interactions are involved in the self-assembly process. In addition, an external hydrophobic template is necessary because aqueous solvent does not template the formation of F. Capsule F consists of two octa-acid, deep-cavity cavitands with a pseudo-conical hydrophobic cavity (Figure 6.6a). The eight carboxylic acid groups are located at the periphery of the cavitand, thereby inducing... 

Figure 6.6 a) Deep-cavity cavitand. b) Self-assembly of capsule F. [6] Reproduced by permission of The Royal Society of Chemistry (RSC)... 

The generality of a DoM strategy is demonstrated for the functionalization of deep-cavity cavitands by treatment with varying equivalents of butyllithiums, for example, BuLi, and trapping of the resulting carbanions with different electrophiles. ... 

Fig. 2 Typical frameworks of (a) normal cavitands. (b) deep-cavity cavitands. and (c) wide-bodied cavitands.

The first deep-cavity cavitand to be synthesized was the 2.3-quinoxaline derivative 4 (Fig. 4). This second row of aromatic rings in this cavitand. and related cavitands formed by the condensation of resorcinarenes with 2,3-dichloropyrazines. is conformationally flexible. Thus, they exist in a range of conformers between the vaselike C4v form (shown) and a flat C21 form. These families of compounds were termed velcrands, because in the flat, "kite-like" form, they have a propensity to dimerize.When not binding themselves, these types of cal-itands also bind mono-" or di-substituted"benzene derivatives. 

With the idea of improved or more selective guest binding, recent efforts were made to instill in deep-cavity cavitands some of the stractural integrity seen in normal cavitands. Two general approaches have been demonstrated (Fig. 5). In the first, hydrogen-bonding groups were introduced into the rims of deep-cavity cavitands to... 

Xi, H. Gibb, C.L.D. Stevens. E.D. Gibb. B.C. Deep-cavity cavitands The synthesis and solid state structure of host molecules possessing large, bowl-shaped cavities. Chem. Commun. 8998. 1743-1744. 

Deep-cavity cavitands that dimerize into capsules via the hydrophobic effect, in the presence of a suitable guest molecule and in aqueous solution, have been developed by the Gibb group [110,111], Such complexes possess hydrophilic outer coats, hydrophobic rims that favor self-assembly, and deep hydrophobic pockets (up to 1 nm wide to 2 nm long). They have been used to drive the formation of high-definition assemblies with a number of guest molecules, including steroid and hydrocarbon molecules [112]. Reactions within the capsule (eg, selective oxidation of substrates) and potential applications in hydrocarbon gas separation [111] have been also achieved or demonstrated [113]. 

FIGURE 13.9 (a) Molecular structure of the deep-cavity cavitand OA. (b) Cartoon representa-... 

This property of pyrene emission has been recently used to monitor the micropolarity of the interior of the deep-cavity cavitand OA [116]. In borate buffer, pyrene (10 M) exhibits a dual-emission resulting from monomeric emission (Fig. 13.10b bands from 380 to 430 nm) and excimeric emission (broad, characteristic band at 480 nm). Addition of 2 mol equiv of OA to this solution leads to a dramatic displacement of the latter weak emission with an intense monomeric emission (Fig. 13.10a). 

Fig. 9.31 General structure of deep-cavity cavitands from the Gibb group...

Fig. 11.23 The halogen-bonded deep cavity cavitand [(25 4Br) (CCl3Br)4] (a) ball-and-stick representation with two encapsulated CCl3Br (one ordered and one disordered) molecules in CPK mode and (b) CPK representation. The halogen-bonded deep cavity cavitand [(25 4Br) (lC6F4l)2] (c) ball-and-stick representation with the encapsulated CHCI3 (disordered) in CPK mode and (d) CPK representation. The halogen-bonded deep-cavity cavitand [(26 4Br) (I-(CF2)4-I)2] (c) ball-and-stick representation with the two encapsulated 1,4-dioxane molecules in CPK mode and (d) CPK representation [54,57,58] (Image adapted from [54,57,58] with permission from The Royal Society of Chemistry and The American Chemical Society)...

The formation of container compounds with cavities for guest binding is an important and widely studied area of contemporary supramolecular chemistry. The above results have shown the NARXs to be suitable halogen-bond acceptors and forms deep cavity cavitands in the presence of suitable halogen-bond donors. 

The synthesis of quinoxaline bridges cavitand. The synthesis of quinoxaline bridges has been used for the preparation of deep cavity cavitands (1983S1177). Here, the addition of 1 equiv of 2,3-dichloroquinoxahne mainly leads to (+)-166 bearing one quinoxaline bridge, and to the bis-quinoxaline 167, isolated by column chromatography. 

Podkoscielny D, Philip 1, Gibb CLD, Gibb BC, Kaifer AE (2008) Encapsulation of ferrocene and jreripheral electrostatic attachment of viologens to dimeric molecular capsules formed by an octaadd, deep-cavity cavitand. Chem Eur J 14 4704-4710... 

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