Axial Coordination of Pyridine- and Imidazole-Based Drug Molecules to Co(III)-Tetra(4-Carboxyphenyl)porphyrin

The substitutions of water molecules in the bisaqua axial complex of carboxy-substituted Co(III)-tetraphenylporphyrin by drug molecules based on amines and nitrogen-containing heterocycles are studied. The strongest bonded Co(III)-porphyrin complexes are formed with imidazole and pyridine derivatives. Depending on the nature and positions of functional groups in the heterocyclic moiety, imidazole- and pyridine- containing compounds can form either mono- or bis-axial complexes with Co(III) porphyrinate, these complexes having various stabilities. Aniline and quinuclidine drugs were found to react with Co(III) porphyrinate in aqueous media to produce only unstable monoaxial complexes.