Selectivity and Regulation of Binding

In Section 4.8 we discussed new options for the selective binding of cations and anions that arose because of the discovery of crown ethers. Now we shall continue the discussion of this topic with more emphasis given to its relevance to enzyme mimicking. 

In fact, systems like 224 and 225 represent simple models of artificial receptors with a variable pattern of substrate recognition. It is also noteworthy that the observed properties of these ligands did not come as a surprise but, rather, as the anticipated result of a thoughtful choice in structural parameters for the designed structures. 

In order to accommodate substrates larger than simple aromatic compounds, analog 227 was synthesized this contains naphthalene rings instead of the 

Similar results were observed for bis-crown ether 229 containing an azo linkage between the binding sites.In this case the photochemical conversion 229a 229b produces strikingly different effects on the relative ability to 

Additional and very promising opportunities to exert control over the selectivity of binding can be achieved by the design of hybrid molecules containing two different types of coordination sites. Compound 232 contains two types of bonding sites a polyether chain capable of serving as a ligand for 

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