Characterization of a High-Spin Non-Heme {FeNO}~8 Complex: Implications for the Reactivity of Iron Nitroxyl Species in Biology

摘要

Nitric oxide (NO') has long been implicated in numerous signaling and immune defense pathways in mammalian systems. More recently, its one-electron-reduced and potentially protonated form nitroxyl (NO~/HNO) has been shown to elicit a variety of biological responses, although the endogenous production of nitroxyl has not yet been established. HNO has been suggested to bind to both ferric and ferrous hemes to yield {FeNO}-type species (in the Ene-mark-Feltham notation in the former case and {Fe-(H)NO}-type species in the latter. Non-heme iron centers are an alternative target for HNO, but non-heme iron nitroxyl adducts have not been well investigated. However, since non-heme {FeNO} complexes have more positive reduction potentials than their heme counterparts, it is feasible that {FeNO} species could be formed from non-heme {FeNO} complexes under physiological conditions. Furthermore, non-heme {Fe-(H)NO}-type species have also been proposed as key intermediates in the catalytic cycles of bacterial respiratory NO reductases (NorBC) and flavodiiron NO reductases (FNORs) Although multiple low-spin (diamagnetic) {FeNO} model complexes have been reported previously there are no corresponding examples of model complexes for biological non-heme iron centers.