HNO (nitroxyl, azanone), joined the ‘biologically relevant reactive nitrogen species’ family in the 2000s.

In the past decade, gasotransmitters NO^• and H₂S have been thoroughly studied in biological contexts, as their biosynthesis and physiological effects became known. Moreover, an additional intricate crosstalk reaction scheme between these compounds and related species is thought to exist as part of the cascade signaling processes in physiological conditions. In this context, heme enzymes, as modeled by iron porphyrins, play a central role in catalyzing the key interconversions involved. In this work, iron porphyrin interactions with sulfide and nitric-oxide-related species are described. The stability and reactivity of mixed ternary systems are also described, and future perspectives are discussed.

Iron water-soluble porphyrins have been long used as biomimetic compounds for modelling the active sites found in heme-enzymes. In this regard, the anionic porphyrin [Fe^III(TPPS)]^3─ and its coordination complexes have been repeatedly chosen as suitable water-soluble platforms for bioinorganic chemistry studies. In this work we report for the first time the crystal structure of the water-soluble nitrosyl complex [Fe^II(TPPS) (NO^•)]^4─ along with that of oxodimeric ferric species [μ-O-([Fe^III(TPPS)])₂]^8─.