Addition of Dioxygen to an N₄S(thiolate) Iron(II) Cysteine Dioxygenase Model Gives a Structurally Characterized Sulfinato–Iron(II) Complex

The non-heme iron enzyme cysteine dioxygenase (CDO) catalyzes the S-oxygenation of cysteine by O₂ to give cysteine sulfinic acid. The synthesis of a new structural and functional model of the cysteine-bound CDO active site, [Fe^II(N3PyS)­(CH₃CN)]­BF₄ (<b>1</b>) is reported. This complex was prepared with a new facially chelating 4N/1S­(thiolate) pentadentate ligand. The reaction of <b>1</b> with O₂ resulted in oxygenation of the thiolate donor to afford the doubly oxygenated sulfinate product [Fe^II(N3PySO₂)­(NCS)] (<b>2</b>), which was crystallographically characterized. The thiolate donor provided by the new N3PyS ligand has a dramatic influence on the redox potential and O₂ reactivity of this Fe^II model complex

Light-Induced N₂O Production from a Non-heme Iron–Nitrosyl Dimer

Two non-heme iron–nitrosyl species, [Fe₂(<i>N</i>‑Et‑HPTB)­(O₂CPh)­(NO)₂]­(BF₄)₂ (<b>1a</b>) and [Fe₂(<i>N</i>‑Et‑HPTB)­(DMF)₂(NO)­(OH)]­(BF₄)₃ (<b>2a</b>), are characterized by FTIR and resonance Raman spectroscopy. Binding of NO is reversible in both complexes, which are prone to NO photolysis under visible light illumination. Photoproduction of N₂O occurs in high yield for <b>1a</b> but not <b>2a</b>. Low-temperature FTIR photolysis experiments with <b>1a</b> in acetonitrile do not reveal any intermediate species, but in THF at room temperature, a new {FeNO}⁷ species quickly forms under illumination and exhibits a ν­(NO) vibration indicative of nitroxyl-like character. This metastable species reacts further under illumination to produce N₂O. A reaction mechanism is proposed, and implications for NO reduction in flavo­diiron proteins are discussed

Synthesis and Ligand Non-Innocence of Thiolate-Ligated (N₄S) Iron(II) and Nickel(II) Bis(imino)pyridine Complexes

The known iron­(II) complex [Fe^II(LN₃S)­(OTf)] (<b>1</b>) was used as starting material to prepare the new biomimetic (N₄S­(thiolate)) iron­(II) complexes [Fe^II(LN₃S)­(py)]­(OTf) (<b>2</b>) and [Fe^II(LN₃S)­(DMAP)]­(OTf) (<b>3</b>), where LN₃S is a tetradentate bis­(imino)­pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet–visible (UV-vis) spectroscopic analysis, ¹H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel­(II) analogue, [Ni^II(LN₃S)]­(BF₄) (<b>5</b>), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed <b>1</b>–<b>3</b> and <b>5</b> undergo a single reduction process with <i>E</i>_1/2 between −0.9 V to −1.2 V versus Fc⁺/Fc. Treatment of <b>3</b> with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe­(LN₃S)­(DMAP)]⁰ (<b>4</b>), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (<i>g =</i> [2.155, 2.057, 2.038]), and Mössbauer (δ = 0.33 mm s^–1; Δ<i>E</i>_Q = 2.04 mm s^–1) spectroscopy. Computational methods (DFT) were employed to model complexes <b>3</b>–<b>5</b>. The combined experimental and computational studies show that <b>1</b>–<b>3</b> are 5-coordinate, high-spin (<i>S</i> = 2) Fe^II complexes, whereas <b>4</b> is best described as a 5-coordinate, intermediate-spin (<i>S</i> = 1) Fe^II complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (<i>S</i>_total = 1/2) ground state. Complexes <b>2</b> and <b>3</b> are shown to react with O₂ to give S-oxygenated products, as previously reported for <b>1</b>. In contrast, the monoreduced <b>4</b> appears to react with O₂ to give a mixture of sulfur oxygenates and iron oxygenates. The nickel­(II) complex <b>5</b> does not react with O₂, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O₂

Synthesis and Ligand Non-Innocence of Thiolate-Ligated (N₄S) Iron(II) and Nickel(II) Bis(imino)pyridine Complexes

The known iron­(II) complex [Fe^II(LN₃S)­(OTf)] (<b>1</b>) was used as starting material to prepare the new biomimetic (N₄S­(thiolate)) iron­(II) complexes [Fe^II(LN₃S)­(py)]­(OTf) (<b>2</b>) and [Fe^II(LN₃S)­(DMAP)]­(OTf) (<b>3</b>), where LN₃S is a tetradentate bis­(imino)­pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet–visible (UV-vis) spectroscopic analysis, ¹H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel­(II) analogue, [Ni^II(LN₃S)]­(BF₄) (<b>5</b>), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed <b>1</b>–<b>3</b> and <b>5</b> undergo a single reduction process with <i>E</i>_1/2 between −0.9 V to −1.2 V versus Fc⁺/Fc. Treatment of <b>3</b> with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe­(LN₃S)­(DMAP)]⁰ (<b>4</b>), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (<i>g =</i> [2.155, 2.057, 2.038]), and Mössbauer (δ = 0.33 mm s^–1; Δ<i>E</i>_Q = 2.04 mm s^–1) spectroscopy. Computational methods (DFT) were employed to model complexes <b>3</b>–<b>5</b>. The combined experimental and computational studies show that <b>1</b>–<b>3</b> are 5-coordinate, high-spin (<i>S</i> = 2) Fe^II complexes, whereas <b>4</b> is best described as a 5-coordinate, intermediate-spin (<i>S</i> = 1) Fe^II complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (<i>S</i>_total = 1/2) ground state. Complexes <b>2</b> and <b>3</b> are shown to react with O₂ to give S-oxygenated products, as previously reported for <b>1</b>. In contrast, the monoreduced <b>4</b> appears to react with O₂ to give a mixture of sulfur oxygenates and iron oxygenates. The nickel­(II) complex <b>5</b> does not react with O₂, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O₂

Synthesis and Ligand Non-Innocence of Thiolate-Ligated (N₄S) Iron(II) and Nickel(II) Bis(imino)pyridine Complexes

The known iron­(II) complex [Fe^II(LN₃S)­(OTf)] (<b>1</b>) was used as starting material to prepare the new biomimetic (N₄S­(thiolate)) iron­(II) complexes [Fe^II(LN₃S)­(py)]­(OTf) (<b>2</b>) and [Fe^II(LN₃S)­(DMAP)]­(OTf) (<b>3</b>), where LN₃S is a tetradentate bis­(imino)­pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet–visible (UV-vis) spectroscopic analysis, ¹H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel­(II) analogue, [Ni^II(LN₃S)]­(BF₄) (<b>5</b>), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed <b>1</b>–<b>3</b> and <b>5</b> undergo a single reduction process with <i>E</i>_1/2 between −0.9 V to −1.2 V versus Fc⁺/Fc. Treatment of <b>3</b> with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe­(LN₃S)­(DMAP)]⁰ (<b>4</b>), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (<i>g =</i> [2.155, 2.057, 2.038]), and Mössbauer (δ = 0.33 mm s^–1; Δ<i>E</i>_Q = 2.04 mm s^–1) spectroscopy. Computational methods (DFT) were employed to model complexes <b>3</b>–<b>5</b>. The combined experimental and computational studies show that <b>1</b>–<b>3</b> are 5-coordinate, high-spin (<i>S</i> = 2) Fe^II complexes, whereas <b>4</b> is best described as a 5-coordinate, intermediate-spin (<i>S</i> = 1) Fe^II complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (<i>S</i>_total = 1/2) ground state. Complexes <b>2</b> and <b>3</b> are shown to react with O₂ to give S-oxygenated products, as previously reported for <b>1</b>. In contrast, the monoreduced <b>4</b> appears to react with O₂ to give a mixture of sulfur oxygenates and iron oxygenates. The nickel­(II) complex <b>5</b> does not react with O₂, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O₂

Synthesis and Ligand Non-Innocence of Thiolate-Ligated (N₄S) Iron(II) and Nickel(II) Bis(imino)pyridine Complexes

The known iron­(II) complex [Fe^II(LN₃S)­(OTf)] (<b>1</b>) was used as starting material to prepare the new biomimetic (N₄S­(thiolate)) iron­(II) complexes [Fe^II(LN₃S)­(py)]­(OTf) (<b>2</b>) and [Fe^II(LN₃S)­(DMAP)]­(OTf) (<b>3</b>), where LN₃S is a tetradentate bis­(imino)­pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet–visible (UV-vis) spectroscopic analysis, ¹H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel­(II) analogue, [Ni^II(LN₃S)]­(BF₄) (<b>5</b>), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed <b>1</b>–<b>3</b> and <b>5</b> undergo a single reduction process with <i>E</i>_1/2 between −0.9 V to −1.2 V versus Fc⁺/Fc. Treatment of <b>3</b> with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe­(LN₃S)­(DMAP)]⁰ (<b>4</b>), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (<i>g =</i> [2.155, 2.057, 2.038]), and Mössbauer (δ = 0.33 mm s^–1; Δ<i>E</i>_Q = 2.04 mm s^–1) spectroscopy. Computational methods (DFT) were employed to model complexes <b>3</b>–<b>5</b>. The combined experimental and computational studies show that <b>1</b>–<b>3</b> are 5-coordinate, high-spin (<i>S</i> = 2) Fe^II complexes, whereas <b>4</b> is best described as a 5-coordinate, intermediate-spin (<i>S</i> = 1) Fe^II complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (<i>S</i>_total = 1/2) ground state. Complexes <b>2</b> and <b>3</b> are shown to react with O₂ to give S-oxygenated products, as previously reported for <b>1</b>. In contrast, the monoreduced <b>4</b> appears to react with O₂ to give a mixture of sulfur oxygenates and iron oxygenates. The nickel­(II) complex <b>5</b> does not react with O₂, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O₂

Synthesis and Ligand Non-Innocence of Thiolate-Ligated (N₄S) Iron(II) and Nickel(II) Bis(imino)pyridine Complexes

The known iron­(II) complex [Fe^II(LN₃S)­(OTf)] (<b>1</b>) was used as starting material to prepare the new biomimetic (N₄S­(thiolate)) iron­(II) complexes [Fe^II(LN₃S)­(py)]­(OTf) (<b>2</b>) and [Fe^II(LN₃S)­(DMAP)]­(OTf) (<b>3</b>), where LN₃S is a tetradentate bis­(imino)­pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet–visible (UV-vis) spectroscopic analysis, ¹H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel­(II) analogue, [Ni^II(LN₃S)]­(BF₄) (<b>5</b>), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed <b>1</b>–<b>3</b> and <b>5</b> undergo a single reduction process with <i>E</i>_1/2 between −0.9 V to −1.2 V versus Fc⁺/Fc. Treatment of <b>3</b> with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe­(LN₃S)­(DMAP)]⁰ (<b>4</b>), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (<i>g =</i> [2.155, 2.057, 2.038]), and Mössbauer (δ = 0.33 mm s^–1; Δ<i>E</i>_Q = 2.04 mm s^–1) spectroscopy. Computational methods (DFT) were employed to model complexes <b>3</b>–<b>5</b>. The combined experimental and computational studies show that <b>1</b>–<b>3</b> are 5-coordinate, high-spin (<i>S</i> = 2) Fe^II complexes, whereas <b>4</b> is best described as a 5-coordinate, intermediate-spin (<i>S</i> = 1) Fe^II complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (<i>S</i>_total = 1/2) ground state. Complexes <b>2</b> and <b>3</b> are shown to react with O₂ to give S-oxygenated products, as previously reported for <b>1</b>. In contrast, the monoreduced <b>4</b> appears to react with O₂ to give a mixture of sulfur oxygenates and iron oxygenates. The nickel­(II) complex <b>5</b> does not react with O₂, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O₂

Critical role <i>E2F-1</i> in <i>p53</i> knockdown-mediated upregulation of <i>p73</i> transcription.

<p>A. Additive effect of <i>E2F-1</i> overexpression on <i>p53</i> knockdown mediated increase in <i>p73</i> promoter activity. MCF-7 cells were co-transfected with p73-PF/luciferase, pSV-β-Gal, and control or p53siRNA plasmids either in presence or in absence of <i>E2F-1</i>. Luciferase and β-galactosidase activity was determined 40 hours post-transfection. B. <i>TAp73</i> mRNA levels in MCF-7 cells transfected with control vector, p53siRNA and/or <i>E2F-1</i> cDNA. MCF-7 cells were transiently transfected with either control siRNA or <i>p53</i>-specific siRNA either in the presence or in the absence of <i>E2F-1</i>. RT-PCR analysis was performed using gene-specific primers. C & D. <i>E2F-1</i> binding is required for <i>p53</i> knockdown mediated increase in <i>p73</i> promoter activity. MCF-7 cells were co-transfected with control or p53siRNA vector and reporter construct encoding wild type or mutant <i>p73</i> promoter (p73PVUII, −220 to +71), in addition to pSV-β-Gal plasmid. The mutant PVUII promoter fragment contains mutant <i>E2F-1</i> binding sites at −155 and −132 (C). Luciferase and β-gal activity was determined 40 hours post- transfection (D). E. Occupancy of the E2F responsive element in the TAp73 promoter by E2F-1 is enhanced in MCF-7/p53siRNA cells. Detected with chromatin immunoprecipitation (ChIP) assay, DNA fragment of the TAp73 promoter was amplified from the complexes immunoprecipitated with E2F-1 antibody from the paired cell lines. Input row were the DNA fragment amplified from the extracts before immunoprecipitation. In the control immunoglobulin G (IgG) reaction, PCR was done in the eluates from beads collected after preclearing of these extracts with normal rabbit serum.</p

Mapping of the DNA sequence that is responsible for <i>p53</i> inactivation mediated <i>p73</i> upregulation.

<p>A. Reporter constructs of <i>TAp73</i> promoter with a serious of deletions from the 5′ end. Putative binding sites for <i>E2F</i> and <i>p53</i> are depicted. The drawing is not proportional to the actual size. B. MCF-7 cells were co-transfected with luciferase reporter constructs with different lengths of <i>p73</i> promoter, pSV-β-Gal, and vectors of control siRNA or p53siRNA. Luciferase activity was measured 40 hours after transfection, which was followed by β-galactosidase normalization.</p

<i>p21</i> is a mediator of <i>p53</i> inactivation induced upregulation of <i>p73</i> transcription.

<p>A. Overexpression of <i>p21</i> abolishes <i>p73</i> upregulation in control and MCF-7/p53siRNA cells. MCF-7/control and MCF-7/p53siRNA cells were cotransfected with p73-PF/pSV-β-Gal and control vector or pcDNA3/p21. Cell lysate was collected for luciferase assay 40 hours post-transfection. All the experiments were performed at least three times in triplicates. B. Overexpression of wtp53 reverses p53siRNA induced <i>p73</i> transcription in the presence or absence of <i>E2F-1</i> overexpression. p73-PF/pSV-β-Gal and pcDNA3/E2F-1 or control vector were cotransfected with the plasmids encoding control siRNA, p53siRNA or wtp53 into MCF-7 cells. Luciferase activity was determined as described above. C. Overexpression of <i>p21</i> abrogates p53siRNA induced <i>p73</i> transcription in the presence or absence of <i>E2F-1</i> overexpression. p73-PF/pSV-β-Gal and pcDNA3/E2F-1 or control vector were cotransfected with the plasmids encoding control siRNA, p53siRNA or pcDNA3/p21 into MCF-7 cells. Luciferase activity was determined as described above.</p