A chiral water-soluble zinc porphyrin was optically resolved on a chiral HPLC column, and the binding of chiral amino acids and peptides to each of the enantiomers was examined spectrophotometrically in basic aqueous solution. The binding data apparently indicated that the zinc porphyrin has chiral selectivity for amino acids and dipeptides. This was reasonably explained in terms of the triple cooperation of coordination, Coulomb, and steric interactions of the chiral amino carboxylates with the porphyrin. A compensatory relationship among the thermodynamic parameters for chiral recognition was also shown.

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Water-soluble zinc porphyrins bearing an ammonium group and a phenyl or tertiary butyl group above each porphyrin plane were designed and synthesized. Binding data for amino carboxylates in aqueous solution suggested that these porphyrins recognize the carboxylates on the basis of coordinative, Coulomb, and hydrophobic interactions and that a chiral recognition phenomenon for glycyl-tryptophan anion is derived from the cooperation of these interactions.

The binding of several amine ligands to water-soluble zinc porphyrins 3, 4, and 5 bearing a hydrophobic binding pocket was examined spectrophotometrically in water and in chloroform. In chloroform, substantially decreased binding constants (K) of these porphyrins compared to available data for synthetic zinc porphyrins were observed and this was ascribed to the tightly bound water molecule that must be released upon amine binding. In aqueous solution, the large K values of 3 among these complexes showed that a preorganized structure of the binding pocket is necessary for binding enhancements of the amine ligands. The positive entropy changes in aqueous solution were found to contribute largely to the amine binding to 3 and 4. These results suggested that hydrophobic interactions would dominantly affect the binding behaviour of these zinc porphyrins and apparently eclipse the direct non-polar attractions between the bound amines and the superstructures of the porphyrins.

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