Preparation of Non-heme {FeNO}⁷ Models of Cysteine Dioxygenase: Sulfur versus Nitrogen Ligation and Photorelease of Nitric Oxide

We present the synthesis and spectroscopic characterization of [Fe­(NO)­(N3PyS)]­BF₄ (<b>3</b>), the first structural and electronic model of NO-bound cysteine dioxygenase. The nearly isostructural all-N-donor analogue [Fe­(NO)­(N4Py)]­(BF₄)₂ (<b>4</b>) was also prepared, and comparisons of <b>3</b> and <b>4</b> provide insight regarding the influence of S vs N ligation in {FeNO}⁷ species. One key difference occurs upon photoirradiation, which causes the fully reversible release of NO from <b>3</b>, but not from <b>4</b>

Preparation of Non-heme {FeNO}⁷ Models of Cysteine Dioxygenase: Sulfur versus Nitrogen Ligation and Photorelease of Nitric Oxide

We present the synthesis and spectroscopic characterization of [Fe­(NO)­(N3PyS)]­BF₄ (<b>3</b>), the first structural and electronic model of NO-bound cysteine dioxygenase. The nearly isostructural all-N-donor analogue [Fe­(NO)­(N4Py)]­(BF₄)₂ (<b>4</b>) was also prepared, and comparisons of <b>3</b> and <b>4</b> provide insight regarding the influence of S vs N ligation in {FeNO}⁷ species. One key difference occurs upon photoirradiation, which causes the fully reversible release of NO from <b>3</b>, but not from <b>4</b>

Preparation of Non-heme {FeNO}⁷ Models of Cysteine Dioxygenase: Sulfur versus Nitrogen Ligation and Photorelease of Nitric Oxide

We present the synthesis and spectroscopic characterization of [Fe­(NO)­(N3PyS)]­BF₄ (<b>3</b>), the first structural and electronic model of NO-bound cysteine dioxygenase. The nearly isostructural all-N-donor analogue [Fe­(NO)­(N4Py)]­(BF₄)₂ (<b>4</b>) was also prepared, and comparisons of <b>3</b> and <b>4</b> provide insight regarding the influence of S vs N ligation in {FeNO}⁷ species. One key difference occurs upon photoirradiation, which causes the fully reversible release of NO from <b>3</b>, but not from <b>4</b>

Preparation of Non-heme {FeNO}⁷ Models of Cysteine Dioxygenase: Sulfur versus Nitrogen Ligation and Photorelease of Nitric Oxide

We present the synthesis and spectroscopic characterization of [Fe­(NO)­(N3PyS)]­BF₄ (<b>3</b>), the first structural and electronic model of NO-bound cysteine dioxygenase. The nearly isostructural all-N-donor analogue [Fe­(NO)­(N4Py)]­(BF₄)₂ (<b>4</b>) was also prepared, and comparisons of <b>3</b> and <b>4</b> provide insight regarding the influence of S vs N ligation in {FeNO}⁷ species. One key difference occurs upon photoirradiation, which causes the fully reversible release of NO from <b>3</b>, but not from <b>4</b>

Nuclear Resonance Vibrational Spectroscopic Definition of Peroxy Intermediates in Nonheme Iron Sites

Fe^III-(hydro)­peroxy intermediates have been isolated in two classes of mononuclear nonheme Fe enzymes that are important in bioremediation: the Rieske dioxygenases and the extradiol dioxygenases. The binding mode and protonation state of the peroxide moieties in these intermediates are not well-defined, due to a lack of vibrational structural data. Nuclear resonance vibrational spectroscopy (NRVS) is an important technique for obtaining vibrational information on these and other intermediates, as it is sensitive to all normal modes with Fe displacement. Here, we present the NRVS spectra of side-on Fe^III-peroxy and end-on Fe^III-hydroperoxy model complexes and assign these spectra using calibrated DFT calculations. We then use DFT calculations to define and understand the changes in the NRVS spectra that arise from protonation and from opening the Fe–O–O angle. This study identifies four spectroscopic handles that will enable definition of the binding mode and protonation state of Fe^III-peroxy intermediates in mononuclear nonheme Fe enzymes. These structural differences are important in determining the frontier molecular orbitals available for reactivity

A Mononuclear Nonheme Iron(V)-Imido Complex

Mononuclear nonheme iron­(V)-oxo complexes have been reported previously. Herein, we report the first example of a mononuclear nonheme iron­(V)-imido complex bearing a tetraamido macrocyclic ligand (TAML), [(TAML)­Fe^V(NTs)]⁻ (<b>1</b>). The spectroscopic characterization of <b>1</b> revealed an <i>S</i> = 1/2 Fe­(V) oxidation state, an FeN bond length of 1.65(4) Å, and an FeN vibration at 817 cm^–1. The reactivity of <b>1</b> was demonstrated in CH bond functionalization and nitrene transfer reactions

NRVS Studies of the Peroxide Shunt Intermediate in a Rieske Dioxygenase and Its Relation to the Native Fe^II O₂ Reaction

The Rieske dioxygenases are a major subclass of mononuclear nonheme iron enzymes that play an important role in bioremediation. Recently, a high-spin Fe^III–(hydro)­peroxy intermediate (BZDOp) has been trapped in the peroxide shunt reaction of benzoate 1,2-dioxygenase. Defining the structure of this intermediate is essential to understanding the reactivity of these enzymes. Nuclear resonance vibrational spectroscopy (NRVS) is a recently developed synchrotron technique that is ideal for obtaining vibrational, and thus structural, information on Fe sites, as it gives complete information on all vibrational normal modes containing Fe displacement. In this study, we present NRVS data on BZDOp and assign its structure using these data coupled to experimentally calibrated density functional theory calculations. From this NRVS structure, we define the mechanism for the peroxide shunt reaction. The relevance of the peroxide shunt to the native Fe^II/O₂ reaction is evaluated. For the native Fe^II/O₂ reaction, an Fe^III–superoxo intermediate is found to react directly with substrate. This process, while uphill thermodynamically, is found to be driven by the highly favorable thermodynamics of proton-coupled electron transfer with an electron provided by the Rieske [2Fe-2S] center at a later step in the reaction. These results offer important insight into the relative reactivities of Fe^III–superoxo and Fe^III–hydroperoxo species in nonheme Fe biochemistry