Obtention and Characterization of Iron-Nitroxyl Porphyrin Complexes in aqueous media: FeIITPPSHNO, FeIITPPSNO− and FeIITPPSNO?

AGOSTINA M. MAZZEO; JUAN PELLEGRINO; FABIO DOCTOROVICH

CABA

Simposio; Exploring the Frontiers of Chemistry: Challenges for the 21st Century; 2019

Interest in HNO (azanone according to IUPAC; usually nitroxyl) has increased in the last decade due to itsremarkable chemical properties and increasing biological relevance.1 In addition, FeII-nitroxyl complexes areimportant intermediates in NO and nitrite-reducing enzymes in bacteria and fungi, which catalyze importantprocesses related to the biogeochemical cycle of nitrogen. It has been considered that the protonated adductis stabilized by amino acids,2 and bulky substituents.3 The stability reported for [Fe(CN)5(HNO)]3? 4 led usto consider that factors like H-bonds with water, could stabilize the Fe-HNO moiety. In this work, the hemewater soluble nitroxyl complexes [FeII(TPPS)HNO]4? and [FeII(TPPS)NO]5? were obtained andcharacterized by UV-Vis spectroscopy. The pKa was estimated from both spectroscopic and electrochemicalmeasurements. The protonated complex spontaneously reoxidizes to the nitrosyl species within minutes,much slower than in organic media.5 Kinetic measurements in different conditions, along with otherexperimental results and DFT calculations support an unimolecular reoxidation mechanism involving anhomolytic rupture of the H-NO bond, via a phlorin intermediate also proposed and detected in similar systems.