Formally Ferric Heme Carbon Monoxide Adduct.

Formally ferric carbonyl adducts are reported in a series of thiolate-bound iron porphyrins. Resonance Raman data indicate the presence of both Fe-S and Fe-CO bonds, and EPR data of this S = 1/2 species indicate a ligand-based electron hole, giving this complex an Fe(II)-thiyl radical electronic ground state. The FTIR data show that the C-O vibrations are substantially higher than in the corresponding ferrous-thiolate CO adducts.

Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase.

Fungal denitrification plays a crucial role in the nitrogen cycle and contributes to the total NO emission from agricultural soils. Here, cytochrome P450 NO reductase (P450nor) reduces two NO to NO using a single heme site. Despite much research, the exact nature of the critical "Intermediate I" responsible for the key N-N coupling step in P450nor is unknown.

Ferric Heme-Nitrosyl Complexes: Kinetically Robust or Unstable Intermediates?

We have determined a convenient method for the bulk synthesis of high-purity ferric heme-nitrosyl complexes ({FeNO} in the Enemark-Feltham notation); this method is based on the chemical or electrochemical oxidation of corresponding {FeNO} precursors. We used this method to obtain the five- and six-coordinate complexes [Fe(TPP)(NO)] (TPP = tetraphenylporphyrin dianion) and [Fe(TPP)(NO)(MI)] (MI = 1-methylimidazole) and demonstrate that these complexes are stable in solution in the absence of excess NO gas. This is in stark contrast to the often-cited instability of such {FeNO} model complexes in the literature, which is likely due to the common presence of halide impurities (although other impurities could certainly also play a role).

Exploring second coordination sphere effects in nitric oxide synthase.

Second coordination sphere (SCS) effects in proteins are modulated by active site residues and include hydrogen bonding, electrostatic/dipole interactions, steric interactions, and π-stacking of aromatic residues. In Cyt P450s, extended H-bonding networks are located around the proximal cysteinate ligand of the heme, referred to as the 'Cys pocket'. These hydrogen bonding networks are generally believed to regulate the Fe-S interaction.