Selectivity and Stability in Supramolecular Complexes

Receptors for guest molecules larger than simple ions make use of interactions at different sites and are necessarily more limited with respect to a simultaneous optimization of selectivity and sensitivity. In favorable cases, the selection site will provide additional binding forces, as illustrated by the model peptide receptor in 

In other cases, one of the interactions can be so strong that optimal contact with other binding sites cannot materialize. Examples for this have been discussed above, e.g., with the porphyrin-based host, which cannot differentiate between nucleotides and nucleosides due to fhe dominating stacking effects. Even adverse, anti-cooperative effects between selectivity and affinity sites can be tolerated, in particular if fhe aim is stereoselectivity. In the chiral crown ether (Fig. 2.16), which is the basis of Crarris chiral resolution machine [69], stereoselection is due to interactions between amino acid side groups and the crown ether 

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