Binding Enhancements of Nicotinic Acid to Water-Soluble Zinc Porphyrins Based on Triple Attractions of Coordination, Coulomb, and CH-[pi] Interactions

The binding of amines to artificial zinc-porphyrin receptors 1--4 was examined in basic aqueous solutions. For nicotinic acid and 3,5-dicarboxypyridine, substantial binding enhancements were observed compared to other amines with no π system or carboxyl group. This observation suggested that interligand attractions of Coulomb and CH-π interactions in addition to N-atom coordination can act effectively as recognition factors. The differences in the Coulomb interaction between carboxylate and sulfonate anions were also discussed.