PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Ferrous Compounds”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMed2002

Olefin cis-dihydroxylation versus epoxidation by non-heme iron catalysts: two faces of an Fe(III)-OOH coin.

The oxygenation of carbon-carbon double bonds by iron enzymes generally results in the formation of epoxides, except in the case of the Rieske dioxygenases, where cis-diols are produced. Herein we report a systematic study of olefin oxidations with H(2)O(2) catalyzed by a group of non-heme iron complexes, i.e., [Fe(II)(BPMEN)(CH(3)CN)(2)](2+) (1, BPMEN = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) and [Fe(II)(TPA)(CH(3)CN)(2)](2+) (4, TPA = tris(2-pyridylmethyl)amine) and their 6- and 5-methyl-substituted derivatives. We demonstrate that olefin epoxidation and cis-dihydroxylation are different facets of the reactivity of a common Fe(III)-OOH intermediate, whose spin state can be modulated by the electronic and steric properties of the ligand environment. Highly stereoselective epoxidation is favored by catalysts with no more than one 6-methyl substituent, which give rise to low-spin Fe(III)-OOH species (category A). On the other hand, cis-dihydroxylation is favored by catalysts with more than one 6-methyl substituent, which afford high-spin Fe(III)-OOH species (category B). For catalysts in category A, both the epoxide and the cis-diol product incorporate (18)O from H(2)(18)O, results that implicate a cis-H(18)O-Fe(V)=O species derived from O-O bond heterolysis of a cis-H(2)(18)O-Fe(III)-OOH intermediate. In contrast, catalysts in category B incorporate both oxygen atoms from H(2)(18)O(2) into the dominant cis-diol product, via a putative Fe(III)-eta(2)-OOH species. Thus, a key feature of the catalysts in this family is the availability of two cis labile sites, required for peroxide activation. The olefin epoxidation and cis-dihydroxylation studies described here not only corroborate the mechanistic scheme derived from our earlier studies on alkane hydroxylation by this same family of catalysts (Chen, K.; Que, L, Jr. J. Am. Chem. Soc. 2001, 123, 6327) but also further enhance its credibility. Taken together, these reactions demonstrate the catalytic versatility of these complexes and provide a rationale for Nature's choice of ligand environments in biocatalysts that carry out olefin oxidations.

Alkenes↗
PubMed2002

Iron complexes capped with dendrimer-appended triazacyclononanes as the novel spatially encumbered models of non-heme iron proteins.

Poly(benzyl ether) dendrimers with a 1,4,7-triazacyclononane (TACN) focal core (Ln(3)TACN, 2a-4a) and nondendritic L1(3)TACN (1a), upon reaction with FeCl(2), followed by NaOAc and NH(4)PF(6), afforded mononuclear iron(II) complexes [Fe(II)(eta(2)-OAc)(Ln(3)TACN)](+) (1b-4b), which were oxidized under O(2) to form dinuclear (mu-O)(mu-OAc)(2)diiron(III) complexes (1c-4c) in 54-74% isolated yields. The formation of 1c-4c obeyed second-order kinetics with respect to 1b-4b, respectively, where the observed rate constants (k(2)) were clearly dependent on the generation number of the dendritic substituents. Photoirradiation of 1c-4c in the presence of NaOAc gave diiron(II) complexes (1d-4d), which were reoxidized to 1c-4c by O(2), following first-order kinetics with respect to 1d-4d, respectively. The crystal structure of nondendritic 1cshowed that the diiron(III) center is surrounded by an aromatic wall of the six 3,5-dimethoxybenzyl substituents, while spectroscopic profiles of dendritic 2c-4c suggested that the geometries of their diiron(III) centers are little different from that of 1c. The diiron(III) center of the largest 4c was highly robust toward alkaline hydrolysis and also insulated electrochemically.

Binding Sites↗
PubMed2002

Redox thermodynamics of the Fe(3+)/Fe(2+) couple in horseradish peroxidase and its cyanide complex.

The thermodynamics of Fe3+ to Fe2+ reduction for the five-coordinate high-spin native form of horseradish peroxidase and for its six-coordinate low-spin cyanide adduct have been determined from variable-temperature UV-vis spectroelectrochemical experiments. In both cases, the DeltaH degrees 'rc and DeltaS degrees 'rc values are positive. Hence, the negative reduction potentials turn out to be the result of two opposing and partially compensating contributions: a large enthalpic term, which is the determinant of the negative E degrees ' values for both species, and a smaller, yet relevant, entropic contribution. The decrease in E degrees ' of the Fe3+/Fe2+ couple on cyanide binding turns out to be a fully entropic effect, unequivocally demonstrating the importance of entropic effects in determining the E degrees ' values of redox metal centers.

Cyanides↗
PubMed2002

Mechanism of the six-electron reduction of nitrite to ammonia by cytochrome c nitrite reductase.

Cytochrome c nitrite reductase catalyzes the six-electron reduction of nitrite to ammonia without the release of potential reaction intermediates, such as NO or hydroxylamine. On the basis of the crystallographic observation of reaction intermediates and of density functional calculations, we present a working hypothesis for the reaction mechanism of this multiheme enzyme which carries a novel lysine-coordinated heme group (Fe-Lys). It is proposed that nitrite reduction starts with a heterolytic cleavage of the N-O bond which is facilitated by a pronounced back-bonding interaction of nitrite coordinated through nitrogen to the reduced (Fe(II)) but not the oxidized (Fe(III)) active site iron. This step leads to the formation of an [FeNO](6) species and a water molecule and is further facilitated by a hydrogen bonding network that induces an electronic asymmetry in the nitrite molecule that weakens one N-O bond and strengthens the other. Subsequently, two rapid one-electron reductions lead to an [FeNO](8) form and, by protonation, to an Fe(II)-HNO adduct. Hereafter, hydroxylamine will be formed by a consecutive two-electron two-proton step which is dehydrated in the final two-electron reduction step to give ammonia and an additional water molecule. A single electron reduction of the active site closes the catalytic cycle.

Ammonia↗
PubMed2003

Mechanistic implications for the formation of the diiron cluster in ribonucleotide reductase provided by quantitative EPR spectroscopy.

The small subunit of Escherichia coli ribonucleotide reductase (R2) is a homodimeric (betabeta) protein, in which each beta-peptide contains a diiron cluster composed of two inequivalent iron sites. R2 is capable of reductively activating O(2) to produce a stable tyrosine radical (Y122*), which is essential for production of deoxyribonucleotides on the larger R1 subunit. In this work, the paramagnetic Mn(II) ion is used as a spectroscopic probe to characterize the assembly of the R2 site with EPR spectroscopy. Upon titration of Mn(II) into samples of apoR2, we have been able to quantitatively follow three species (aquaMn(II), mononuclear Mn(II)R2, and dinuclear Mn(2)(II)R2) and fit each to a sequential two binding site model. As previously observed for Fe(II) binding within apoR2, one of the sites has a greater binding affinity relative to the other, K(1) = (5.5 +/- 1.1) x 10(5) M(-)(1) and K(2) = (3.9 +/- 0.6) x 10(4) M(-)(1), which are assigned to the B and A sites, respectively. In multiple titrations, only one dinuclear Mn(2)(II)R2 site was created per homodimer of R2, indicating that only one of the two beta-peptides of R2 is capable of binding Mn(II) following addition of Mn(II) to apoR2. Under anaerobic conditions, addition of only 2 equiv of Fe(II) to R2 (Fe(2)(II)R2) completely prevented the formation of any bound MnR2 species. Upon reaction of this sample with O(2) in the presence of Mn(II), both Y122* and Mn(2)(II)R2 were produced in equal amounts. Previous stopped-flow absorption spectroscopy studies have indicated that apoR2 undergoes a protein conformational change upon binding of metal (Tong et al. J. Am. Chem. Soc. 1996, 118, 2107-2108). On the basis of these observations, we propose a model for R2 metal incorporation that invokes an allosteric interaction between the two beta-peptides of R2. Upon binding the first equiv of metal to a beta-peptide (beta(I)), the aforementioned protein conformational change prevents metal binding in the adjacent beta-peptide (beta(II)) approximately 25 A away. Furthermore, we show that metal incorporation into beta(II) occurs only during the O(2) activation chemistry of the beta(I)-peptide. This is the first direct evidence of an allosteric interaction between the two beta-peptides of R2. Furthermore, this model can explain the generally observed low Fe occupancy of R2. We also demonstrate that metal uptake and this newly observed allosteric effect are buffer dependent. Higher levels of glycerol cause loss of the allosteric effect. Reductive cycling of samples in the presence of Mn(II) produced a novel mixed metal Fe(III)Mn(III)R2 species within the active site of R2. The magnitude of the exchange coupling (J) determined for both the Mn(2)(II)R2 and Fe(III)Mn(III)R2 species was determined to be -1.8 +/- 0.3 and -18 +/- 3 cm(-)(1), respectively. Quantitative spectral simulations for the Fe(III)Mn(III)R2 and mononuclear Mn(II)R2 species are provided. This work represents the first instance where both X- and Q-band simulations of perpendicular and parallel mode spectra were used to quantitatively predict the concentration of a protein bound mononuclear Mn(II) species.

Apoproteins↗
PubMed2003

Electron and hydrogen-atom self-exchange reactions of iron and cobalt coordination complexes.

Reported here are self-exchange reactions between iron 2,2'-bi(tetrahydro)pyrimidine (H(2)bip) complexes and between cobalt 2,2'-biimidazoline (H(2)bim) complexes. The (1)H NMR resonances of [Fe(II)(H(2)bip)(3)](2+) are broadened upon addition of [Fe(III)(H(2)bip)(3)](3+), indicating that electron self-exchange occurs with k(Fe,e)(-) = (1.1 +/- 0.2) x 10(5) M(-1) s(-1) at 298 K in CD(3)CN. Similar studies of [Fe(II)(H(2)bip)(3)](2+) plus [Fe(III)(Hbip)(H(2)bip)(2)](2+) indicate that hydrogen-atom self-exchange (proton-coupled electron transfer) occurs with k(Fe,H.) = (1.1 +/- 0.2) x 10(4) M(-1) s(-1) under the same conditions. Both self-exchange reactions are faster at lower temperatures, showing small negative enthalpies of activation: DeltaH++(e(-)) = -2.1 +/- 0.5 kcal mol(-1) (288-320 K) and DeltaH++(H.) = -1.5 +/- 0.5 kcal mol(-1) (260-300 K). This behavior is concluded to be due to the faster reaction of the low-spin states of the iron complexes, which are depopulated as the temperature is raised. Below about 290 K, rate constants for electron self-exchange show the more normal decrease with temperature. There is a modest kinetic isotope effect on H-atom self-exchange of 1.6 +/- 0.5 at 298 K that is close to that seen previously for the fully high-spin iron biimidazoline complexes.(12) The difference in the measured activation parameters, E(a)(D) - E(a)(H), is -1.2 +/- 0.8 kcal mol(-1), appears to be inconsistent with a semiclassical view of the isotope effect, and suggests extensive tunneling. Reactions of [Co(H(2)bim)(3)](2+)-d(24) with [Co(H(2)bim)(3)](3+) or [Co(Hbim)(H(2)bim)(2)](2+) occur with scrambling of ligands indicating inner-sphere processes. The self-exchange rate constant for outer-sphere electron transfer between [Co(H(2)bim)(3)](2+) and [Co(H(2)bim)(3)](3+) is estimated to be 10(-)(6) M(-1) s(-1) by application of the Marcus cross relation. Similar application of the cross relation to H-atom transfer reactions indicates that self-exchange between [Co(H(2)bim)(3)](2+) and [Co(Hbim)(H(2)bim)(2)](2+) is also slow, < or =10(-3) M(-1) s(-1). The slow self-exchange rates for the cobalt complexes are apparently due to their interconverting high-spin [Co(II)(H(2)bim)(3)](2+) with low-spin Co(III) derivatives.

Cobalt↗
PubMed2003

Iron chelation properties of an extracellular siderophore exochelin MN.

The coordination chemistry of an extracellular siderophore produced by Mycobacterium neoaurum, exochelin MN (ExoMN), is reported along with its pK(a) values, Fe(III) and Fe(II) chelation constants, and aqueous solution speciation as determined by spectrophotometric and potentiometric titration techniques. Exochelin MN is of particular interest as it can efficiently transport iron into pathogenic M. leprae, which is responsible for leprosy, in addition to its own parent cells. The Fe(III) coordination properties of ExoMN are important with respect to understanding the Fe(III) acquisition and uptake mechanism in pathogenic M. leprae, as the siderophores from this organism are very difficult to isolate. Exochelin MN has two hydroxamic acid groups and an unusual threo-beta-hydroxy-l-histidine available for Fe(III) chelation. The presence of threo-beta-hydroxy-l-histidine gives rise to a unique mode of Fe(III) coordination. The pK(a) values for the two hydroxamic acid moieties, the histidine imidazole ring and the alkylammonium groups on ExoMN, correspond well with the literature values for these moieties. Proton-dependent Fe(III)- and Fe(II)-ExoMN equilibrium constants were determined using a model involving sequential protonation of the Fe(III)- and Fe(II)-ExoMN complexes. These data were used to develop a model whereby deprotonation reactions on the surface of the complex in the second coordination shell result in first coordination shell isomerization. The overall formation constants were calculated: log beta(110) = 39.12 for Fe(III)-ExoMN and 16.7 for Fe(II)-ExoMN. The calculated pFe value of 31.1 is one of the highest among all siderophores and their synthetic analogues and indicates that ExoMN is thermodynamically capable of removing Fe(III) from transferrin. The E(1/2) for the Fe(III)ExoMN/Fe(II)ExoMN(-) couple was determined to be -595 mV from quasi-reversible cyclic voltammograms at pH = 10.8, and the pH-dependent E(1/2) profile was used to determine the Fe(II)-ExoMN protonation constants.

Ferric Compounds↗
PubMed2003

Monomeric MnIII/II and FeIII/II complexes with terminal hydroxo and oxo ligands: probing reactivity via O-H bond dissociation energies.

Non-heme manganese and iron complexes with terminal hydroxo or oxo ligands are proposed to mediate the transfer of hydrogen atoms in metalloproteins. To investigate this process in synthetic systems, the monomeric complexes [M(III/II)H(3)1(OH)](-/2-) and [M(III)H(3)1(O)](2-) have been prepared, where M(III/II) = Mn and Fe and [H(3)1](3-) is the tripodal ligand, tris[(N'-tert-butylureaylato)-N-ethyl)]aminato. These complexes have similar primary and secondary coordination spheres, which are enforced by [H(3)1](3-). The homolytic bond dissociation energies (BDEs(O-H)) for the M(III/II)-OH complexes were determined, using experimentally obtained values for the pK(a)(M-OH) and E(1/2) measured in DMSO. This thermodynamic analysis gave BDEs(O-H) of 77(4) kcal/mol for [Mn(II)H(3)1(O-H)](2-) and 66(4) kcal/mol for [Fe(II)H(3)1(O-H)](2-). For the M(III)-OH complexes, [Mn(III)H(3)1(OH)]- and [Fe(III)H(3)1(OH)]-, BDEs(O-H) of 110(4) and 115(4) kcal/mol were obtained. These BDEs(O-H) were verified with reactivity studies with substrates having known X-H bond energies (X = C, N, O). For instance, [Fe(II)H(3)1(OH)](2-) reacts with a TEMPO radical to afford [Fe(III)H(3)1(O)](2-) and TEMPO-H in isolated yields of 60 and 75%, respectively. Consistent with the BDE(O-H) values for [Mn(II)H(3)1(OH)](2-), TEMPO does not react with this complex, yet TEMPO-H (BDE(O-H) = 70 kcal/mol) reacts with [Mn(III)H(3)1(O)](2-), forming TEMPO and [Mn(II)H(3)1(OH)](2-). [Mn(III)H(3)1(O)](2-) and [Fe(III)H(3)1(O)](2-) react with other organic substrates containing C-H bonds less than 80 kcal/mol, including 9,10-dihydroanthracene and 1,4-cyclohexadiene to produce [M(II)H(3)1(OH)](2-) and the appropriate dehydrogenated product in yields of greater than 80%. Treating [Mn(III)H(3)1(O)](2-) and [Fe(III)H(3)1(O)](2-) with phenolic compounds does not yield the product expected from hydrogen atom transfer but rather the protonated complexes, [Mn(III)H(3)1(OH)]- and [Fe(III)H(3)1(OH)]-, which is ascribed to the highly basic nature of the terminal oxo group.

Electrochemistry↗
PubMed2004

Synthesis and characterization of carboxylate-rich complexes having the [Fe2(mu-OH)2(mu-O2CR)]3+ and [Fe2(mu-O)(mu-O2CR)]3+ cores of O2-dependent diiron enzymes.

The {Fe2(mu-OH)2(mu-O2CR)}3+ and {Fe2(mu-O)(mu-O2CR)}3+ cores of the carboxylate-bridged diiron(III) centers in the enzyme active sites were reproduced by small molecule model complexes that were prepared through direct oxygenation of the mononuclear iron(II) complexes. Upon oxygenation of [Fe(O2CArTol)2(Hdmpz)2], where -O2CArTol is 2,6-di(p-tolyl)benzoate and Hdmpz is 3,5-dimethylpyrazole, [Fe2(mu-OH)2(mu-O2CArTol)(O2CArTol)3(OH2)(Hdmpz)2] was generated and characterized to share close physical properties with sMMOHox, including delta = 0.45 (2) mm/s, DeltaEQ = 1.21 (2) mm/s, and J = -7.2 (2) cm-1. The compound [Fe2(mu-O)(mu-O2CAr4-FPh)(O2CAr4-FPh)3(Hdmpz)3], where -O2CAr4-FPh is 2,6-di(4-fluorophenyl)benzoate, with delta = 0.51 (2) mm/s, DeltaEQ = 1.26 (2) mm/s, and J = -117.4 (1) cm-1, was isolated as the oxygenation product of [Fe(O2CAr4-FPh)2(Hdmpz)2].

Binding Sites↗
PubMed2004

Comparison between the geometric and electronic structures and reactivities of [FeNO]7 and [FeO2]8 complexes: a density functional theory study.

In a previous study, we analyzed the electronic structure of S = 3/2 [FeNO](7) model complexes [Brown et al. J. Am. Chem. Soc. 1995, 117, 715-732]. The combined spectroscopic data and SCF-X alpha-SW electronic structure calculations are best described in terms of Fe(III) (S = 5/2) antiferromagnetically coupled to NO(-) (S = 1). Many nitrosyl derivatives of non-heme iron enzymes have spectroscopic properties similar to those of these model complexes. These NO derivatives can serve as stable analogues of highly labile oxygen intermediates. It is thus essential to establish a reliable density functional theory (DFT) methodology for the geometry and energetics of [FeNO](7) complexes, based on detailed experimental data. This methodology can then be extended to the study of [FeO(2)](8) complexes, followed by investigations into the reaction mechanisms of non-heme iron enzymes. Here, we have used the model complex Fe(Me(3)TACN)(NO)(N(3))(2) as an experimental marker and determined that a pure density functional BP86 with 10% hybrid character and a mixed triple-zeta/double-zeta basis set lead to agreement between experimental and computational data. This methodology is then applied to optimize the hypothetical Fe(Me(3)TACN)(O(2))(N(3))(2) complex, where the NO moiety is replaced by O(2). The main geometric differences are an elongated Fe[bond]O(2) and a steeper Fe[bond]O[bond]O angle in the [FeO(2)](8) complex. The electronic structure of [FeO(2)](8) corresponds to Fe(III) (S = 5/2) antiferromagnetically coupled to O(2)(-) (S = 1/2), and, consistent with the extended bond length, the [FeO(2)](8) unit has only one Fe(III)-O(2)(-) bonding interaction, while the [FeNO](7) unit has both sigma and pi type Fe(III)-NO(-) bonds. This is in agreement with experiment as NO forms a more stable Fe(III)-NO(-) adduct relative to O(2)(-). Although NO is, in fact, harder to reduce, the resultant NO(-) species forms a more stable bond to Fe(III) relative to O(2)(-) due to the different bonding interactions.

Ferric Compounds↗
PubMed2004

Facile ring opening of iron(III) and iron(II) complexes of meso-amino-octaethylporphyrin by dioxygen.

Pyridine solutions of ClFe(III)(meso-NH(2)-OEP) undergo oxidative ring opening when exposed to dioxygen. The high-spin iron(III) complex, ClFe(III)(meso-NH(2)-OEP), has been isolated and characterized by X-ray crystallography. In the solid state, it has a five-coordinate structure typical for high-spin (S = 5/2) iron(III) complex. In chloroform-d solution, ClFe(III)(meso-NH(2)-OEP) displays an (1)H NMR spectrum characteristic of a high-spin, five-coordinate complex and is unreactive toward dioxygen. However, in pyridine-d(5) solution a temperature-dependent equilibrium exists between the high-spin (S = 5/2), six-coordinate complex, [(py)ClFe(III)(meso-NH(2)-OEP)], and the six-coordinate, low spin (S = 1/2 with the less common (d(xz)d(yz))(4)(d(xy))(1) ground state)) complex, [(py)(2)Fe(III)(meso-NH(2)-OEP)](+). Such pyridine solutions are air-sensitive, and the remarkable degradation has been monitored by (1)H NMR spectroscopy. These studies reveal a stepwise conversion of ClFe(III)(meso-NH(2)-OEP) into an open-chain tetrapyrrole complex in which the original amino group and the attached meso carbon atom have been converted into a nitrile group. Additional oxidation at an adjacent meso carbon occurs to produce a ligand that binds iron by three pyrrole nitrogen atoms and the oxygen atom introduced at a meso carbon. This open-chain tetrapyrrole complex itself is sensitive to attack by dioxygen and is converted into a tripyrrole complex that is stable to further oxidation and has been isolated. The process of oxidation of the Fe(III) complex, ClFe(III)(meso-NH(2)-OEP), is compared with that of the iron(II) complex, (py)(2)Fe(II)(meso-NH(2)-OEP); both converge to form identical products.

Crystallography, X-Ray↗
PubMed2005

Synthesis and electrochemical characterization of a transition-metal-modified ligand-receptor pair.

The energetics of weak interactions (van der Waals forces, hydrogen bonding) are difficult to quantify in biological ligand-receptor pairs. Insight into the biochemical role these forces play is critical to an understanding of signal transduction events and the drug discovery process. Ruthenium pentaammine and iron tetracyano complexes modified with either biotin or desthiobiotin have been synthesized and characterized. These modified biological ligands bind to the protein avidin in a manner similar to that of native biotin. Experiments using redox mediators show that the avidin-bound complexes are electrochemically accessible.

Avidin↗
PubMed2004

Metal-catalyzed anaerobic disproportionation of hydroxylamine. Role of diazene and nitroxyl intermediates in the formation of N2, N2O, NO+, and NH3.

The catalytic disproportionation of NH(2)OH has been studied in anaerobic aqueous solution, pH 6-9.3, at 25.0 degrees C, with Na(3)[Fe(CN)(5)NH(3)].3H(2)O as a precursor of the catalyst, [Fe(II)(CN)(5)H(2)O](3)(-). The oxidation products are N(2), N(2)O, and NO(+) (bound in the nitroprusside ion, NP), and NH(3) is the reduction product. The yields of N(2)/N(2)O increase with pH and with the concentration of NH(2)OH. Fast regime conditions involve a chain process initiated by the NH(2) radical, generated upon coordination of NH(2)OH to [Fe(II)(CN)(5)H(2)O](3)(-). NH(3) and nitroxyl, HNO, are formed in this fast process, and HNO leads to the production of N(2), N(2)O, and NP. An intermediate absorbing at 440 nm is always observed, whose formation and decay depend on the medium conditions. It was identified by UV-vis, RR, and (15)NMR spectroscopies as the diazene-bound [Fe(II)(CN)(5)N(2)H(2)](3)(-) ion and is formed in a competitive process with the radical path, still under the fast regime. At high pH's or NH(2)OH concentrations, an inhibited regime is reached, with slow production of only N(2) and NH(3). The stable red diazene-bridged [(NC)(5)FeHN=NHFe(CN)(5)](6)(-) ion is formed at an advanced degree of NH(2)OH consumption.

Ammonia↗
PubMed2004

Bismercaptoethanediazacyclooctane as a N2S2 chelating agent and Cys-X-Cys mimic for Fe(NO) and Fe(NO)2.

The N-protonated bismercaptoethanediazacyclooctane serves as a bidentate dithiolate ligand to oxidized Fe(NO)(2) of Enemark-Feltam notation, E-F [Fe(NO)(2)],(9) mimicking Cys-X-Cys binding of Fe(NO)(2) to proteins or thio-biomolecules. The neutral compound is characterized by the well-known g = 2.03 EPR signal which is a hallmark of dinitrosyl iron complexes, DNIC's. The Fe(NO)(2) unit can be removed from the chelate by excess PhS(-), producing (PhS)(2)Fe(NO)(2)(-). Transfer of NO from Fe(H(+)bme-daco)(NO)(2) (nu(NO) = 1740, 1696 cm(-)(1)) to Fe(II) of [(bme-daco)Fe](2) yields the five-coordinate, square-pyramidal N(2)S(2)Fe(NO) (nu(NO) = 1649 cm(-)(1)), where NO is in the apical position. Its isotropic EPR signal at g = 2.05 is consistent with E-F [Fe(NO)](7) formulation. In excess NO, Roussin's red ester-type molecules are formed as dinuclear or tetranuclear species, [(micro-SRS)[Fe(2)(NO)(4)]](n)() (n =1, 2). These well-characterized molecules furnish reference points for positions and patterns in nu(NO) vibrational spectroscopy expected to be useful for in vivo studies of NO degradation of iron-sulfur clusters in ferredoxins.

Chelating Agents↗
PubMed2005

De novo design of a redox-active minimal rubredoxin mimic.

Metal-binding sites in metalloproteins frequently occur at the interfaces of elements of secondary structure, which has enabled the retrostructural analysis of natural proteins and the de novo design of helical bundles that bind metal ion cofactors. However, the design of metalloproteins containing beta-structure is less well developed, despite the frequent occurrence of beta-conformations in natural metalloproteins. Here, we describe the design and construction of a beta-protein, RM1, that forms a stable, redox-active 4-Cys thiolate Fe(II/III) site analogous to the active site of rubredoxin. The protein folds into a beta-structure in the presence and absence of metal ions and binds Fe(II/III) to form a redox-active site that is stable to repeated cycles of oxidation and reduction, even in an aerobic environment.

Binding Sites↗
PubMed2005

Proton-mediated electron configuration change in high-spin iron(II) porphyrinates.

The synthesis, molecular structure, and electronic structure characterization of two five-coordinate high-spin imidazolate-ligated iron(II) porphyrinates are reported. Their electronic structure, as deduced from Mössbauer spectra obtained in strong magnetic fields, is distinctly different from that of the analogous imidazole-ligated species. The resulting electronic structure models are consistent with all observed differing features in the two classes.

Electron Spin Resonance Spectroscopy↗