Cavitands guest binding

The main feature for cation recognition by tetra-bridged phosphorylated cavitands arises from the cooperative effect of the four phosphorus groups and the aromatic molecular cavity. In the phosphorus(IV) cavitands guest binding will be achieved through O (P=0) or S (P=S) coordination with different affinity for hard or soft metal ions. On the other hand, transition metal rim complexes described above can act as host for metal cation. 

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... 

Fig. 9.1 Phenyl-footed cavitand containing two guest-binding sites...

The Kobayashi group has also reported on two-substituted tetra-(dihydroxyboryl) cavitands and how they assemble in the presence of linkers such as l,2-h A-(3,4-dihydroxyphenyl)ethane to form dynamic boronic acid ester capsules (e.g., 35, Fig. 9.13) [90]. Guest binding has also been reported in these assemblies [91]. Additionally, these capsules have been shown to function as both photosensitizers and as a guard against photochemically-induced dimerization of anthracene guests [92]. Most recently, the scope of the h A-catechol linker that joins the cavitands together has been expanded [93]. 

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. 

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