Molecular recognition, cryptand-based

Supramolecules containing metal-polypyridine units, especially the Ru(dpp)-based dendrimers, could be used as electron reservoirs or components of molecular-electronic devices. Supramolecules in which an electroactive M(N,N) group is attached to a receptor capable of molecular recognition (crown ethers, calixarenes, cryptands etc.) can work as electrochemical sensors. Electrochemical recognition of cations as well as anions has been reported [33-35, 257, 263]. 

The complexes of the polycarboxylate crown ethers of Figure 1 are substantially more stable than those of their parent, 18-crown-6. The stability constants of Table I, in fact, fall into the range usually associated with cryptands 2.2.1 and 2.2.2 [19] and EDTA [20]. However, relative to these ligands, the polycarboxylate crown ethers appear as relatively indiscriminant cation complexing agents. Very little molecular recognition based on ion size difference is occurring. Nonetheless, there are a number of features of the complexation of cations by polycarboxylate crown ethers which have lead to some simple but unique applications. 

Crown ether-based cryptands are important building blocks for molecular machines. Gibson et al. reported a molecular switch (Figure 6) based on a cryptand/paraquat (A, A -dimethyl-4,4 -bipyridinium) recognition motif. ... 

Figure 6 A molecular switch based on a cryptand/paraquat recognition motif. ...

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