Water-Soluble Nitroxyl Porphyrin Complexes FeTPPSHNO and FeTPPSNO Obtained from Isolated FeTPPSNO

The first biomimetic water-soluble Fe-porphyrin nitroxyl complexes were obtained and characterized by UV-vis in protonated and deprotonated forms by reduction of previously isolated and characterized FeTPPSNO. The p involved in the Fe-HNO ⇄ Fe-NO + H equilibrium was estimated to be around 9.7. The FeTPPSHNO complex spontaneously reoxidizes to the nitrosyl form following a first-order kinetic decay with a measured kinetic constant of = 0.017 s. Experiments show that the HNO adduct undergoes unimolecular homolytic cleavage of the H-NO bond. DFT calculations suggest a intermediate for this reaction. The deprotonated NO complex resulted to be more stable, with a half-life of about 10 min.