29189-59-1Relevant academic research and scientific papers
Models of the low-spin iron(III) hydroperoxide intermediate of heme oxygenase: Magnetic resonance evidence for thermodynamic stabilization of the dxy electronic state at ambient temperatures
Rivera, Mario,Caignan, Gregori A.,Astashkin, Andrei V.,Raitsimring, Arnold M.,Shokhireva, Tatjana Kh.,Walker, F. Ann
, p. 6077 - 6089 (2002)
The 13C pulsed ENDOR and NMR study of [meso-13C-TPPFe(OCH3)(OOtBu)]- performed in this work shows that although the unpaired electron in low-spin ferrihemes containing a ROO- ligand resides
The Thiolate Trans Effect in Heme {FeNO}6 Complexes and Beyond: Insight into the Nature of the Push Effect
Hunt, Andrew P.,Lehnert, Nicolai
, (2019/04/03)
Cyt P450 nitric oxide (NO) reductase (P450nor) is an important enzyme in fungal denitrification, responsible for the large-scale production of the greenhouse gas N2O. In the first step of catalysis, the ferric heme-thiolate active site of P450nor binds NO to produce a ferric heme-nitrosyl or {FeNO}6 intermediate (in the Enemark-Feltham notation). In this paper, we present the low-temperature preparation of six new heme-thiolate {FeNO}6 model complexes, [Fe(TPP)(SPh?)(NO)], using a unique series of electron-poor thiophenolates (SPh?-), and their detailed spectroscopic characterization. Our data show experimentally, for the first time, that a direct correlation exists between the thiolate donor strength and the Fe-NO and N-O bond strengths, evident from the corresponding stretching frequencies. This is due to a σ-trans effect of the thiolate ligand, which manifests itself in the population of an Fe-N-O σ-antibonding (σ?) orbital. Via control of the thiolate donor strength (using hydrogen bonds), nature is therefore able to exactly control the degree of activation of the FeNO unit in P450nor. Vice versa, NO can be used as a sensitive probe to quantify the donor strength of a thiolate ligand in a model system or protein, by simply measuring the Fe-NO and N-O frequencies of the ferric NO adduct and then projecting those data onto the correlation plot established here. Finally, we are able to show that the σ-trans effect of the thiolate is the electronic origin of the "push" effect, which is proposed to mediate O-O bond cleavage and Compound I formation in Cyt P450 monooxygenase catalysis.
Electronic structure of metalloporphyrins. 2. Experimental electron density distribution of (meso-tetraphenylporphinato)iron(III) methoxide
Lecomte, Claude,Chadwick, Dana L.,Coppens, Philip,Stevens, Edwin D.
, p. 2982 - 2992 (2008/10/08)
The crystal structure and experimental electron density distribution of (meso-tetraphenylporphinato)iron(III) methoxide, C45H31N4OFe, has been determined from high-resolution single-crystal X-ray diffraction measurements at 100 K. Integrated X-ray intensities were collected with use of Nb-filtered Mo Kα radiation to a resolution of (sin θ)/λ = 1.15 A?-1. Averaging 18 142 symmetry-equivalent reflections from two crystals yielded a set of 8033 independent reflections, which were refined by conventional least-squares to R = 4.4%, Rw = 5.4%. The iron atom is five-coordinate with the oxygen atom of the methoxide ion coordinated in the axial position at a distance of 1.816 (2) A?. The iron is displaced 0.48 A? from the plane of the four nitrogens and 0.56 A? from the mean porphyrin plane. The O-C bond of the methoxide is eclipsed with respect to one of the Fe-N bonds. The experimental electron distribution was determined by least-squares refinement including multipole deformation functions (R = 2.3%, Rw = 2.8%). Populations of the deformation functions in the carbon atoms of the porphyrin ligand agree well with those found previously in (meso-tetraphenylporphyrinato)cobalt(II), which suggests transferability of ligand density between complexes. An approximately spherical electron distribution is found at the iron site, and experimental d-orbital occupancies calculated for the iron atom from the deformation populations are consistent with a high-spin Fe(III) state. However, small but significant deviations from spherical symmetry are observed which, together with observed net atomic charges, have been used to calculate a Mo?ssbauer quadrupole splitting constant of +0.6 (3) mm/s.
