Biomimetic Iron Nitroxyl Porphyrin Complexes Fe II TPPSHNO , Fe II TPPSNO and Fe II TPPSNO

MAZZEO, AGOSTINA; DOCTOROVICH, FABIO; PELLEGRINO, JUAN; GAVIGLIO, CARINA

Otro; LatinXChem; 2020

Interest in HNO has lately increased due to its biological relevance,1 and FeII-nitroxyl complexes are important intermediates in NO and nitrite-reducing enzymes.2Reports on these complexes have contributed to the spectroscopic characterization of this elusive species but more investigation is needed to elucidate mechanisticissues. We have reported a very stable {FeNO}8 complex using the perhalogenated porphyrin TFPPBr8, but attempts to protonate it were unsuccessful.3 It has beenconsidered that the protonated adduct could be stabilized by amino acids, as in protein heme complexes4, and bulky substituents.5 The stability reported for[Fe(CN)5(HNO)]3? in aqueous media6 leads us to consider that hydrogen bonds could stabilize the Fe-HNO moiety.In this work we isolated for the first time the nitrosyl adduct of the water-soluble porphyrin TPPS (Figure 1). Its reduction products, FeIITPPSHNO and FeIITPPSNO−, werechemically obtained and characterized by UV-Vis and cyclic voltammetry. The pKa for FeIITPPSHNO was estimated and its spontaneous reoxidation to the {FeNO}7adduct FeIITPPSNO? was kinetically studied via experimental measurements and DFT calculations.