Cavitands encapsulated guests

Electrochemistry of Cavitand-Encapsulated Guests in Aqueous Solution... 

Figure 7.6 (a) octadentate bipyridine cavitand 25 (b) the corresponding Ag+ cage 26 (c) encapsulated guests 27a-b and 28 (d) optimized structure of the co-encapsulation complex of 26 with 28 and acetic acid. Reproduced with permission from Ref. [32]. 

Kobayashi K, Ishii K, Sakamoto S, Shirasaka T, Yamaguchi K (2003) Guest-induced assembly of tetracarboxyl-cavitand and tetra(3-pyridyl)-cavitand into a heterodimeric capsule via hydrogen bonds and CH-halogen and/or CH-n interaction control of the orientation of the encapsulated guest. J Am Chem Soc 125 10615... 

Alternatives to the square prisms are known from Cram s container molecules called carcerands [183,184]. Molecules, such as 132 [185,186], are made by quadruply linking two cavitand units, thus creating a void inside capable of incorporating a small organic molecule which is then called a carceplex. The encapsulated guests vary from simple solvent molecules to highly reactive... 

Figure 23 Hydrophobically driven dimerization of water-soluble octa-acid cavitand encapsulating apolar templating guests.

The work on the combination of calix[4]arenes and resorcinol-based cavitands was initiated primarily for the synthesis of dissymmetrical carcerands with ellipsoidal shape that are able to encapsulate guest molecules with a dipole moment in two different orientations giving rise to a new type of diastereomerism. Therefore the coupling of upper rim functionalized calix[4]arenes to resorcinol-based cavitands was investigated. We developed a stepwise route for the synthesis of calix[4]arene-based carcerand 21 because the direct coupling analogously to the synthesis of previously reported symmetrical carcerands [28] was not successful. 

Effects of remote chiral centers of the resorci-narene and cavitand ligand syntones on encapsulated guests have been observed in [127] for their hybrid supramolecular capsules 448-454 giving 1 1 cage complexes with encapsulated neutral guest 202 by Scheme 3.120. These distal effects are additive or subtractive, depending on the relative configurations of the chiral elements. 

Fig 1. Stereographic projection of the crystal structure of the 2 1 inclusion compound between CS2 and cavitand 1. One CS2 ( guest ) molecule is encapsulated within the host cavity, the second CS2 ( solvent ) being located between the complexed entities (taken from Ref.27>)... 

Figure 1 shows the crystal structure of the 5,10 12,17 19,24 26,3-tetrakis (dimethyl-siladioxa)-l, 8,15,22-tetramethyl[l4]metacyclophane cavitand (7) which has an enforced cavity appropriately sized to include only slim linear guests 12b). This cavitand forms crystals of a 1 1 molecular inclusion complex with CS2, the guest species being almost entirely encapsulated within the host cavity 27). The crystal structure of the complexed... 

The complexation of neutral guests by tetra-bridged phosphorylated cavitands has been quite seldom investigated, although some specific host-guest interactions should favor the encapsulation of neutral species (H-bonding, van der Waals forces, hydrophobic effects or specific r-interaction). With the tetra-nuclear complexes of 2 described in the previous section, evidence for the encapsulation of alkyl-amine was reported. Only amine guest can in-... 

It is noteworthy that the encapsulation of the N -CHs group allowed the dissolution of the guest in organic solvent. This remarkable property can find some application in the field of host-guest recognition processes, where extraction and transport from or through different liquid phases are of interest. Further developments can now be considered in the field of material chemistry. It is conceivable to design a cavitand dimer by lower-rim to low-... 

When organic or inorganic guests are encapsulated by such cavitands, how do the physical properties of the complex differ from those of the host and guest taken separately ... 

Haino T, Kobayashi M, Fukazawa Y (2006) Guest encapsulation and self-assembly of a cavitand-based coordination capsule. Chem Eur J 12 3310... 

A cavitand-porphyrin combination (22) has been synthesized O5ACIE3810, 06BCSJ1431, 06OL4275> and reported to have sufficient flexibility to facilitate moderate guest exchange rates for kinetic measurements the encapsulation of methane has been shown to have a half-life of 0.5 s <07JOC9448>. 

As well as the examples given in the previous section, in which complementarity of functional groups is used to form supramolecules, there are others in which selfcomplementarity generates interesting homodimeric complexes. A case in point is aminomethylbenzo[18]crown-6 which forms dimers when the amine sidearm is protonated [1]. The ammonium-[18]crown-6 motif is well known and, in this molecule, both host and guest are joined. More complex examples, such as those in Figure 5.8, include the self-complementary tennis balls [2] and other cavitands [3-5] designed by Rebek who has shown how the relative positions and orientations of solvent encapsulated within dimeric assemblies can be determined, in the absence of X-ray data, by NMR. A concise treatment of the many approaches to supramolecular self-assembly are outlined in a 1995 review [6]. 

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