Cobalt(III)- and rhodium(III)-porphyrin complexes for the effective degradation of fentanyl: Biological inactivation and mechanistic insights

Cobalt(III) and rhodium(III) complexes containing the water-soluble porphyrin ligand meso-tri(4-sulfonatophenyl)mono(4-carboxyphenyl)porphine (C1S3TPP), [Rh(C1S3TPP)]Nax•nH2O (1) and [Co(C1S3TPP)]Nax•nH2O (2) were prepared from the direct reaction of free porphyrin and metal chloride salts in refluxing MeOH/DMF or EtOH/H2O. Compounds 1 and 2 were characterized using UV–vis and 1H NMR spectroscopies, and high-resolution mass spectrometry. Cell culture based assays of opioid receptor activation showed that while the rhodium complex reduced fentanyl opioid activity 113-fold to an IC50 value of 1.7 μM, the cobalt complex reduced fentanyl activity by 160-fold to an IC50 value of 2.4 μM. An oxidative mechanism for fentanyl breakdown is proposed.