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ABSTRACT: S-Nitrosothiols RSNO represent circulating reservoirs of nitric oxide activity in the plasma and play intricate roles in protein function control in health and disease. While nitric oxide has been shown to reductively nitrosylate copper(II) centers to form copper(I) com-plexes and ENO species (E = R 2 N, RO), well-characterized examples of the reverse reaction are rare. Employing the copper(I) β-diketiminate [Me 2 NN]Cu, we illustrate a clear example in which an RS−NO bond is cleaved to release NO gas with formation of a discrete copper(II) thiolate. The addition of Ph 3 CSNO to [Me 2 NN]Cu generates the three-coordinate copper(II) thiolate [Me 2 NN]CuSCPh 3 , which is unstable toward free NO. S-Nitrosothiols RSNO play an intricate role in the control of protein function in health and disease through the post-translational modification of cysteine SH residues. 1 Low-molecular-weight S-nitrosothiols such as S-nitrosoglutathione (GSNO) represent circulating reservoirs of nitric oxide activity typically present at submicromolar concentrations in the plasma, 2 which have protective effects against myocardial 3 and lung/airway 3 injuries among other functions. 1 RSNO compounds are prone to homolytic loss of NO due to the relative weakness of the RS−NO bond (20−32 kcal/mol) 4 and the strength of the RS−SR bond (65−66 kcal/mol). 5 Trace amounts of copper ions serve as efficient catalysts for RSNO decomposition to form NO gas and RSSR (Scheme 1). 6 CuZnSOD is the most abundant source of copper in red blood cells and is effective at releasing NO from GSNO. 7 It may be inhibited with neocuproine, a copper(+) chelator, suggesting copper(I) as an active oxidation state for NO loss. 7 Moreover, medical polymers with imbedded copper(2+) ions serve as long-lived NO-generating devices via the copper-catalyzed decomposition of endogenous S-nitrosothiols. 8 Copper enzymes also generate RS−NO bonds from NO via reductive nitrosylation (Scheme 2). 9 CuZnSOD has been shown to specifically S-nitrosylate β-Cys93 of hemoglobin. 10
Inorganic Chemistry 08/2012; · 4.60 Impact Factor
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ABSTRACT: S-Nitrosothiols RSNO represent circulating reservoirs of nitric oxide activity in the plasma and play intricate roles in protein function control in health and disease. While nitric oxide has been shown to reductively nitrosylate copper(II) centers to form copper(I) complexes and ENO species (E = R(2)N, RO), well-characterized examples of the reverse reaction are rare. Employing the copper(I) β-diketiminate [Me(2)NN]Cu, we illustrate a clear example in which an RS-NO bond is cleaved to release NO(gas) with formation of a discrete copper(II) thiolate. The addition of Ph(3)CSNO to [Me(2)NN]Cu generates the three-coordinate copper(II) thiolate [Me(2)NN]CuSCPh(3), which is unstable toward free NO.
Inorganic Chemistry 08/2012; 51(16):8658-60. · 4.60 Impact Factor
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ABSTRACT: The air stable complex [(PNP)FeCl(2)] (1) (PNP = N[2-P(CHMe(2))(2)-4-methylphenyl](2)(-)), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh(3), displays an unexpected S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID magnetization data, at zero field and between frequencies 10 and 1042 Hz, clearly reveal complex 1 to have frequency dependence on the out-of-phase signal and thus being a single molecular magnet with a thermally activated barrier of U(eff) = 32-36 cm(-1) (47-52 K). Variable-temperature Mössbauer data also corroborate a significant temperature dependence in δ and ΔE(Q) values for 1, which is in agreement with the system undergoing a change in spin state. Likewise, variable-temperature X-band EPR spectra of 1 reveals the S = 3/2 to be likely the ground state with the S = 5/2 being close in energy. Multiedge XAS absorption spectra suggest the electronic structure of 1 to be highly covalent with an effective iron oxidation state that is more reduced than the typical ferric complexes due to the significant interaction of the phosphine groups in PNP and Cl ligands with iron. A variable-temperature single crystal X-ray diffraction study of 1 collected between 30 and 300 K also reveals elongation of the Fe-P bond lengths and increment in the Cl-Fe-Cl angle as the S = 5/2 state is populated. Theoretical studies show overall similar orbital pictures except for the d(z(2)) orbital, which has the most sensitivity to change in the geometry and bonding, where the quartet ((4)B) and the sextet ((6)A) states are close in energy.
Journal of the American Chemical Society 07/2012; 134(33):13651-61. · 9.91 Impact Factor
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Brenda A Frazier,
Erika R Bartholomew,
Peter T Wolczanski,
Serena DeBeer,
Mitk'El Santiago-Berrios,
Hector D Abruña,
Emil B Lobkovsky,
Suzanne C Bart, Susanne Mossin,
Karsten Meyer,
Thomas R Cundari
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ABSTRACT: A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)(2)M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe(3))(2)(THF)(n) (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated ((o)Mesmif)(2)Fe (2-Fe) and ((o)Me(2)smif)(2)Fe (3-Fe) were similarly prepared. Metatheses of MX(2) variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru). Metathesis of VCl(3)(THF)(3) with 2 Li(smif) with a reducing equiv of Na/Hg present afforded 1-V, while 2 Na(smif) and IrCl(3)(THF)(3) in the presence of NaBPh(4) gave [(smif)(2)Ir]BPh(4) (1(+)-Ir). Electrochemical experiments led to the oxidation of 1-M (M = Cr, Mn, Co) by AgOTf to produce [(smif)(2)M]OTf (1(+)-M), and treatment of Rh(2)(O(2)CCF(3))(4) with 4 equiv Na(smif) and 2 AgOTf gave 1(+)-Rh. Characterizations by NMR, EPR, and UV-vis spectroscopies, SQUID magnetometry, X-ray crystallography, and DFT calculations are presented. Intraligand (IL) transitions derived from promotion of electrons from the unique CNC(nb) (nonbonding) orbitals of the smif backbone to ligand π*-type orbitals are intense (ε ≈ 10,000-60,000 M(-1)cm(-1)), dominate the UV-visible spectra, and give crystals a metallic-looking appearance. High energy K-edge spectroscopy was used to show that the smif in 1-Cr is redox noninnocent, and its electron configuration is best described as (smif(-))(smif(2-))Cr(III); an unusual S = 1 EPR spectrum (X-band) was obtained for 1-Cr.
Inorganic Chemistry 11/2011; 50(24):12414-36. · 4.60 Impact Factor
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Brenda A. Frazier,
Erika R. Bartholomew,
Peter T. Wolczanski,
Serena DeBeer,
Mitk’El Santiago-Berrios,
Hector D. Abruña,
Emil B. Lobkovsky,
Suzanne C. Bart, Susanne Mossin,
Karsten Meyer,
Thomas R. Cundari
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ABSTRACT: A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)2M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe3)2(THF)n (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated (oMesmif)2Fe (2-Fe) and (oMe2smif)2Fe (3-Fe) were similarly prepared. Metatheses of MX2 variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru). Metathesis of VCl3(THF)3 with 2 Li(smif) with a reducing equiv of Na/Hg present afforded 1-V, while 2 Na(smif) and IrCl3(THF)3 in the presence of NaBPh4 gave [(smif)2Ir]BPh4 (1+-Ir). Electrochemical experiments led to the oxidation of 1-M (M = Cr, Mn, Co) by AgOTf to produce [(smif)2M]OTf (1+-M), and treatment of Rh2(O2CCF3)4 with 4 equiv Na(smif) and 2 AgOTf gave 1+-Rh. Characterizations by NMR, EPR, and UV–vis spectroscopies, SQUID magnetometry, X-ray crystallography, and DFT calculations are presented. Intraligand (IL) transitions derived from promotion of electrons from the unique CNCnb (nonbonding) orbitals of the smif backbone to ligand π*-type orbitals are intense (ε ≈ 10 000–60 000 M–1cm–1), dominate the UV–visible spectra, and give crystals a metallic-looking appearance. High energy K-edge spectroscopy was used to show that the smif in 1-Cr is redox noninnocent, and its electron configuration is best described as (smif(−))(smif(2−))Cr(III); an unusual S = 1 EPR spectrum (X-band) was obtained for 1-Cr.
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Angewandte Chemie International Edition 11/2010; 49(47):8850-5. · 13.45 Impact Factor
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Angewandte Chemie International Edition 12/2009; 49(5):904-7. · 13.45 Impact Factor
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ABSTRACT: We describe the metal-dependent self-assembly of symmetrical protein homooligomers from protein building blocks that feature appropriately engineered metal-chelating motifs on their surfaces. Crystallographic studies indicate that the same four-helix-bundle protein construct, MBPC-1, can self-assemble into C(2) and C(3) symmetrical assemblies dictated by Cu(II) and Ni(II) coordination, respectively. The symmetry inherent in metal coordination can thus be directly applied to biological self-assembly.
Inorganic Chemistry 05/2009; 48(7):2726-8. · 4.60 Impact Factor
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ABSTRACT: One-electron reduction of the square-planar nickel precursor (PNP)NiCl ( 1) (PNP (-) = N[2-P(CHMe 2) 2-4-methylphenyl] 2) with KC 8 effects ligand reorganization of the pincer ligand to assemble a Ni(I) dimer, [Ni(mu 2-PNP)] 2 ( 2), containing a Ni 2N 2 core structure, as inferred by its solid-state X-ray structure. Solution magnetization measurements are consistent with a paramagnetic Ni(I) system likely undergoing a monomer <--> dimer equilibrium. The room-temperature and 4 K solid-state X-band electron paramagnetic resonance (EPR) spectra display anisotropic signals. Low-temperature solid-state X-band EPR data at 4 K reveal rhombic values g z = 1.980(4), g x = 2. 380(4), and g y = 2.225(4), as well as a forbidden signal at g = 4.24 for the Delta M S = 2 half field transition, in accord with 2 having two weakly interacting metal centers. Utilizing an S = 1 model, full spin Hamiltonian simulation of the low-temperature EPR spectrum on the solid sample was achieved by applying a nonzero zero-field-splitting parameter ( D = 0.001 cm (-1)), which is consistent with an S = 0 ground state with a very closely lying S = 1 state. Solid-state magnetization data also corroborate well with our solid-state EPR data and reveal weak antiferromagnetic behavior ( J = -1.52(5) cm (-1)) over a 2-300 K temperature range at a field of 1 Tesla. Evidence for 2 being a masked "(PNP)Ni" scaffold originates from its reaction with N 2CPh 2, which traps the Ni(I) monomer in the form of a T-shaped species, Ni(PNPNNCPh 2), a system that has been structurally characterized. The radical nature of complex 2, or its monomer component, is well manifested through the plethora of cooperative H-X-type bond cleavage reactions, providing the nickel(II) hydride (PNP)NiH and the corresponding rare functionalities -OH, -OCH 3, -PHPh, and -B(catechol) integrated into the (PNP)Ni moiety in equal molar amounts. In addition to splitting H 2, compound 2 can also engage in homolytic X-X bond cleavage reactions of PhXXPh to form (PNP)Ni(XPh) (X = S or Se).
Inorganic Chemistry 10/2008; 47(22):10479-90. · 4.60 Impact Factor
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ABSTRACT: Pincer-type ligands are believed to be very robust scaffolds that can support multifarious functionalities as well as highly reactive metal motifs applied in organometallic chemistry, especially in the realm of catalysis. In this paper, we describe the redox and, therefore, noninnocent behavior of a PNP (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) pincer ancillary bound to nickel. A combination of structural, spectroscopic, and theoretical techniques suggests that this type of framework can house an electron hole when coordinated to Ni(II).
Journal of the American Chemical Society 04/2008; 130(11):3676-82. · 9.91 Impact Factor
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ABSTRACT: The crystal studied is a 0.545 (1):0.455 twin, space group C\bar 1, Z = 16, and is a commensurate occupational and displacive modulation of a Z = 4 idealized parent structure with the space group A2/a and a(p) = a/2, b(p) = b/2, c(p) = c. A hierarchical approach to solution and refinement led sequentially to structures in the space groups A2/a, P2(1)/n, P\bar 1 and finally C\bar 1. The major and minor components of the reflection intensities could be identified using irreducible representations of A2/a and P2(1)/n, which in turn suggested suitable constraints and restraints for optimizing the refinement pathway. Comparative refinement was used to show the correctness of the final structure solution and how appropriately chosen constrained refinement allowed an escape from a false minima.
Acta Crystallographica Section B Structural Science 09/2005; 61(Pt 4):407-17. · 2.29 Impact Factor
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ABSTRACT: The synthesis, structure and magnetic properties of the one-dimensional chain compounds [Mn(cyclam)(SO4)]ClO4.H2O (1) and [Mn(cyclam)(HCOO)](CF3SO3)(ClO4) (2) are reported. Cyclam is the cyclic tetradentate ligand 1,4,7,11-tetraazacyclotetradecane. Both chain compounds exhibit antiferromagnetic interactions within the chains. A magnetic ordering phase transition at 5.5 K in (1) is investigated by magnetisation measurements along the three principal crystallographic axes of a single crystal and the results show unambiguously that the ferromagnetic ordering is only taking place along one crystallographic axis. The spin structure of the magnetic ordered phase and the magnitude of the ferromagnetic moment are correlated with the crystal structure and symmetry of the compound.
Dalton Transactions 03/2004; · 3.84 Impact Factor
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ABSTRACT: The positive axial zero-field splitting parameter D relevant for the S = 2 ground state of [Mn(cyclam)I2]I (cyclam = 1,4,8,11-tetraazacyclotetradecane) is interpreted using the valence bond configuration interaction model which explicitly considers the covalency of the manganese-iodide bond.
Journal of the American Chemical Society 08/2002; 124(30):8764-5. · 9.91 Impact Factor
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ABSTRACT: The crystal structure of the low-spin (S = 1) MnIII complex [Mn(CN)(2)(C(10)H(24)N(4))]ClO(4), or trans-[Mn(CN)(2)(cyclam)](ClO(4)) (cyclam is the tetradentate amine ligand 1,4,8,11-tetraazacyclotetradecane), is reported. The structural parameters in the Mn(cyclam) moiety are found to be insensitive to both the spin and the oxidation state of the Mn ion. The difference between high- and low-spin Mn(III) complexes is that a pronounced tetragonal elongation of the coordination octahedron occurs in high-spin complexes and a slight tetragonal compression is seen in low-spin complexes, as in the title complex.
Acta Crystallographica Section C Crystal Structure Communications 05/2002; 58(Pt 4):M204-6. · 0.52 Impact Factor
