In The Iron Research Articles

High‐pressure studies of the micro‐Raman spectra of iron cyanide complexes: Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O)

AbstractThe pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm−1 show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the FeCNFe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm−1. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm−1 GPa−1, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 John Wiley & Sons, Ltd.

(η5-Cyclopentadienyl)[(1,2,3,4,4a,12a-η)-naphtho[2,3-b][1,4]benzodioxine]iron(II) hexafluoridophosphate

At 296 (2) K, both complexed rings in the iron(II) complex cation of the title salt, [Fe(C5H5)(C16H10O2)]PF6, are almost parallel [dihedral angle between planes = 2.4 (3)°]. The quaternary C atoms of the complexed arene ring are located at the longest distance from the Fe atom, with Fe—C distances of 2.112 (4) and 2.105 (3) Å, which are slightly longer than the average Fe—C distance for this ring (2.083 Å). The Fe ion is located 1.660 (1) and 1.543 (1) Å, respectively, from the cyclo­penta­dienyl and the complexed arene ring.

Nearest-neighbor nitrogen and oxygen distances in the iron(II)–DNA complex studied by extended X-ray absorption fine structure

In mammalian cells, DNA-bound Fe(II) reacts with H 2O 2 producing the highly reactive hydroxyl radical ( OH) in situ. Since OH attacks nearby DNA residue generating oxidative DNA damage, many questions have arisen regarding iron–DNA complex formations and their implication in pre-malignant mutations and aging. In this work, a solid sample of Fe(II)–DNA complex containing one Fe(II) per 10 nucleotides was analyzed from extended X-ray absorption fine structure (EXAFS) spectra collected in a synchrotron radiation light source. Best fitting parameters of the EXAFS signal for the first two shells provide evidence of five oxygen atoms at 1.99 ± 0.02 Å and one nitrogen atom at 2.20 ± 0.02 Å in the inner coordination sphere of the Fe(II)–DNA complex. Considering that both purine base moieties bearing nitrogen atoms are prone to chelate iron, these results are consistent with the previously observed lower levels of DNA damage in cytosine nucleotides relative to adenine and guanine sites in cells under more physiological conditions of Fe(II) Fenton reaction.

Mix and match: templating chiral Schiff base ligands to suit the needs of the metal ion

One-pot reactions of 2,2'-bipyridine-6-carbaldehyde, (1S,2S)-(-)-1,2-diphenyl-1,2-diaminoethane and FeCl(2).4H(2)O or Zn(OAc)(2).2H(2)O (2 : 1 : 1) at room temperature in MeOH lead to [Fe{(S,S)-5}(2)][PF(6)]Cl or [Zn{(S,S)-5}(2)][PF(6)](2) in which (S,S)-5 contains an imidazolidine ring, produced by intramolecular cyclization. This has been confirmed with the single-crystal structure of 2{P-[Fe{(S,S)-5}(2)][PF(6)]Cl}.H(2)O. The diastereoselectivity observed in the solid state has been confirmed by NMR spectroscopy for solutions of [Fe{(S,S)-5}(2)][PF(6)]Cl and [Zn{(S,S)-5}(2)][PF(6)](2). At room temperature, a minor product competes with the formation of [Fe{(S,S)-5}(2)][PF(6)]Cl, and the preference for these complexes is switched by carrying out the reaction in MeOH at reflux. In this case the major product is M-[Fe(2){(S,S)-4}(2)][PF(6)](4) in which (S,S)-4 is the hexadentate Schiff base ligand formed by condensation of two equivalents of 2,2'-bipyridine-6-carbaldehyde with (1S,2S)-(-)-1,2-diphenyl-1,2-diaminoethane; the single-crystal structure of 4{M-[Fe(2){(S,S)-4}(2)][PF(6)](4)}.8Me(2)CO.5MeCN.3H(2)O confirms the assembly of a double helicate. When pyridine-6-carbaldehyde replaces 2,2'-bipyridine-6-carbaldehyde in the iron(II)-templated reaction with (1S,2S)-(-)-1,2-diphenyl-1,2-diaminoethane, the product is [Fe{(S,S)-7}(2)][PF(6)](2) (3 : 2 mixture of diastereoisomers in solution) in which (S,S)-7 is an asymmetrical Schiff base, formed by reaction of only one of the amine groups in (1S,2S)-(-)-1,2-diphenyl-1,2-diaminoethane. The solid state structure of P-[Fe{(S,S)-7}(2)][PF(6)](2).MeCN is presented.

(η5-Cyclopentadienyl)(η6-1,2-dipyrrolidin-1-ylbenzene)iron(II) hexafluoridophosphate

Both complexed rings in the iron(II) complex cation of the title salt, [Fe(C5H5)(C14H20N2)]PF6, are almost parallel [dihedral angle between planes = 5.34 (13)°]. Among the C atoms of the complexed arene ring, the quaternary C atoms are located at the longest, albeit unequal, distances from the Fe atom [2.252 (2) and 2.168 (2) Å].

(η5-Cyclopentadienyl)[η6-diethyl ethyl(phenyl)malonate]iron(II) hexafluoridophosphate

At 223 (2) K, the complexed rings in the iron(II) complex cation of the title salt, [Fe(C5H5)(C15H20O4)]PF6, are almost parallel [dihedral angle between planes = 4.10 (14)°]. Among the C atoms of the complexed arene ring, the quaternary C atom is located at the longest distance from the Fe atom. The F atoms of the PF6 − anion were found to be equally disordered over two sites.

Characteristic Redox Potential-Time Curve in the Iron(II)/Nitric Acid Autocatalytic Reaction and Its Application to a Time Measurement-determination of Folic Acid

A characteristic redox potential-time curve of the iron(II)/nitric acid autocatalytic reaction was applied to a time measurement-determination for sub-microM levels of folic acid. The determination range was 7.5 x 10(-7) - 1.5 x 10(-5) M, the detection limit (3 sigma) was 5.9 x 10(-7) M, and the relative standard deviation was 3.6% (n = 5).

Antioxidant properties of commercial soft and hard winter wheats (Triticum aestivum L.) and their milling fractions

AbstractThe total phenolic content (TPC), total antioxidant activity (TAA), 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) scavenging capacity, inhibition of coupled oxidation in a β‐carotene–linoleate model system, iron(II) chelation activity and inhibition of copper‐induced oxidation of human low‐density lipoprotein (hLDL) cholesterol of 80% ethanolic extracts of soft and hard winter wheat samples and their milling fractions, namely flour, germ, bran and shorts, were investigated. Soft wheat extracts examined demonstrated higher TPC and TAA compared to those of hard wheat extracts. The germ fraction possessed the highest TPC, followed by bran, shorts, whole grain and flour for both wheat types examined. The TAA of both wheat types showed similar results except that shorts performed better than bran in this assay. Free radical scavenging properties of whole grain and milling fractions of both soft and hard wheat samples were examined against DPPH radical. The germ and flour fractions demonstrated the highest and lowest DPPH radical scavenging activity, respectively, among wheat fractions. Wheat extracts were also efficient in preventing bleaching of β‐carotene, which is also known to be free radical mediated. In the iron(II) chelation assay the flour extracts demonstrated excellent activity, while the germ extracts showed a weak activity. The trends were similar in both soft and hard wheat for the iron(II) chelation assay. Wheat extracts also inhibited copper‐induced oxidation of hLDL. In LDL oxidation assay, wheat extracts performed better than the reference antioxidant, ferulic acid. Thus wheat phenolics may serve as effective antioxidative components as measured by in vitro techniques. Copyright © 2005 Society of Chemical Industry

Spectrophotometric study of iron oxidation in the iron(II)/thiocyanate/acetone system and some analytical applications

The possibility of using thiocyanate to determine iron(II) and/or iron(III) in water-acetone mixturehas been re-examined as part of a systematic and comparative study involving metallic complexes ofpseudohalide ligands. Some parameters that affect the complete oxidation of the ferrous cations, theirsubsequent complexation and the system stability have been studied to optimize the experimental conditions.Our results show the viability and potentiality of this simply methodology as an alternative analytical procedureto determine iron cations with high sensitivity, precision and accuracy. Studies on the calibration, stability,precision, and effect of various different ions have been carried out by using absorbance values measured at480 nm. The analytical curve for the total iron determination obeys Beer’s law (r = 0.9993), showing a highersensitivity (molar absorptivity of 2.10x10 4 L cm -1 mol -1 ) when compared with other traditional systems (ligands)or even with the “similar” azide ion [1.53x10 4 L cm -1 mol -1 , for iron–III/azide complexes, in 70% (v/v)tetrahydrofuran/water, at 396 nm]. Under such optimized experimental conditions, it is possible to determineiron in the concentration range from 0.5 to 2 ppm (15-65% T for older equipments, quartz cells of 1.00 cm).

Spectrophotometric study of iron oxidation in the iron(II)/thiocyanate/acetone system and some analytical applications

The possibility of using thiocyanate to determine iron(II) and/or iron(III) in water-acetone mixture has been re-examined as part of a systematic and comparative study involving metallic complexes of pseudohalide ligands. Some parameters that affect the complete oxidation of the ferrous cations, their subsequent complexation and the system stability have been studied to optimize the experimental conditions. Our results show the viability and potentiality of this simply methodology as an alternative analytical procedure to determine iron cations with high sensitivity, precision and accuracy. Studies on the calibration, stability, precision, and effect of various different ions have been carried out by using absorbance values measured at 480 nm. The analytical curve for the total iron determination obeys Beer's law (r = 0.9993), showing a higher sensitivity (molar absorptivity of 2.10x10(4) L cm-1 mol-1) when compared with other traditional systems (ligands) or even with the "similar" azide ion [1.53x10(4) L cm-1 mol-1, for iron-III/azide complexes, in 70% (v/v) tetrahydrofuran/water, at 396 nm]. Under such optimized experimental conditions, it is possible to determine iron in the concentration range from 0.5 to 2 ppm (15-65% T for older equipments, quartz cells of 1.00 cm). Analytical applications have been tested for some different materials (iron ores), also including pharmaceutical products for anemia, and results were compared with atomic absorption determinations. Very good agreement was obtained with these two different techniques, showing the potential of the present experimental conditions for the total iron spectrophotometric determinations (errors < 5%). The possibility of iron speciation was made evident by using another specific and auxiliary method for iron(II) or (III).

Spin crossover behaviour in the iron(II)-2,2-dipyridilamine system: Synthesis, X-ray structure and magnetic studies

The monomeric compounds [Fe(dpa) 2(X) 2] · solv [X = NCS −(solv = 0.5H 2O) ( 1), N ( CN ) 2 - ( 2) and dpa = 2,2-dipyridilamine] have been synthesised and characterised. They crystallise in the P2 1/ n and in the Cc monoclinic systems, respectively. Four of six nitrogen atoms coordinated to the Fe(II) ions belong to two dpa ligands which lie in cis conformation. The remaining positions are occupied by two nitrogen atoms of the pseudo-halide ligands. The magnetic susceptibility measurements at ambient pressure have revealed that compound 1 exhibits an incomplete spin crossover behaviour ( T 1/2 ≈ 88 K), whereas compound 2 remains in the high-spin configuration. Pressure studies performed on compound 1 have shown virtually complete spin crossover behaviour as pressure attains 6.5 kbar.

Assessment of Density Functionals for the High‐Spin/Low‐Spin Energy Difference in the Low‐Spin Iron(II) Tris(2,2′‐bipyridine) Complex

In the iron(II) low-spin complex [Fe(bpy)3]2+, the zero-point energy difference between the 5T2g(t4(2g)e2g) high-spin and the 1A(1g)(t(6)2g) low-spin states, Delta(E)0HL, is estimated to lie in the range of 2500-5000 cm(-1). This estimate is based on the low-temperature dynamics of the high-spin-->low-spin relaxation following the light-induced population of the high-spin state and on the assumption that the bond-length difference between the two states Delta(r)HL is equal to the average value of approximately 0.2 A, as found experimentally for the spin-crossover system. Calculations based on density functional theory (DFT) validate the structural assumption insofar as the low-spin-state optimised geometries are found to be in very good agreement with the experimental X-ray structure of the complex and the predicted high-spin geometries are all very close to one another for a whole series of common GGA (PB86, PW91, PBE, RPBE) and hybrid (B3LYP, B3LYP*, PBE1PBE) functionals. This confirmation of the structural assumption underlying the estimation of Delta(E)0HL from experimental relaxation rate constants permits us to use this value to assess the ability of the density functionals for the calculation of the energy difference between the HS and LS states. Since the different functionals give values from -1000 to 12000 cm(-1), the comparison of the calculated values with the experimental estimate thus provides a stringent criterion for the performance of a given functional. Based on this comparison the RPBE and B3LYP* functionals give the best agreement with experiment.

Spin Crossover in Pyrazolylborate and Pyrazolylmethane Complexes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Triazole-Based Magnetic Langmuir−Blodgett Films: Paramagnetic to Spin-Crossover Behavior

The behavior at the air−liquid interface of a series of metal(II) metallo-organic polymers of 4-octadecyl-1,2,4-triazole has been studied. Interactions between those amphiphilic compounds and metal ions in the subphase result in the formation of stable monolayers and well-defined Langmuir−Blodgett (LB) films incorporating oligomeric metal(II)/triazole units. Infrared, X-ray Photoelectron Microscopy, and magnetic measurements show that the obtained LB films are mostly resulting from recoordination of metal ions from the subphase with triazole ligands at the air−water interface. The relative stability of the polymers and the efficiency of association with 4-octadecyl-1,2,4-triazole have been found to follow the Ni > Fe ∼ Cu > Co and Cu > Ni > Fe > Co sequences, respectively. In the iron(II) cases, partial spin-crossovers are observed, demonstrating for the first time the feasibility of triazole-based LB films possessing interesting magnetooptical properties.

Oxalate and 2,2′-bipyrimidine as bis-chelating ligands in the honeycomb layered compound {[Fe2(bpym)(ox)2]·5H2O}n

The novel two-dimensional iron(II) compound of formula {[Fe2(bpym)(ox)2]·5H2O}n (1) [bpym = 2,2′-bipyrimidine and ox = oxalate dianion] is obtained by reaction of oxalic acid, iron(II) chloride and 2,2′-bipyrimidine in aqueous solution. The structure of 1 is made up of oxalato-bridged iron(II) chains cross-linked by bischelating bpym affording a honeycomb lattice. Variable-temperature magnetic susceptibility data of 1 show the occurrence of relatively large antiferromagnetic interactions between the high spin iron(II) ions separated by more than 5.5 Å through bridging bpym [Jbpym = −4.0(2) cm−1] and ox [Jox = ca. −7.8(2) cm−1] ligands. These values compare well with those obtained in the iron(II) chain [Fe(dpa)(ox)]n (2) [Jox = −8.0(2) cm−1] (dpa = 2,2′-dipyridylamine) and dinuclear {[Fe(H2O)4]2(bpym)}(SO4)2·2H2O (3) (Jbpym = −3.4 cm−1) compounds where bischelating ox (1 and 2) and bpym (1 and 3) groups and the bidentate dpa (2) ligand are present.

Stable, Cationic Alkyl−Olefin Complexes of Ruthenium(II) and Rhodium(III): Effects of Ligand Geometry upon Olefin Insertion/Alkyl Migration

The syntheses of ruthenium(II) and rhodium(III) model complexes of the putative active species in the iron(II)/MMAO polymerization system are reported. The cationic ruthenium methyl ethylene comple...

Characterization of a new dihemic c(4)-type cytochrome isolated from Thiobacillus ferrooxidans.

A new soluble c-type cytochrome has been purified to homogeneity from the acidophilic proteobacterium Thiobacillus ferrooxidans BRGM. It is characterized by an alpha-peak wavelength of 552 nm, a molecular mass of 26 567 Da (as determined by mass spectroscopy) and a pI value of 8. Optical redox titrations at pH 4.0 revealed the presence of two distinguishable redox species with an E(m) of 510 mV and an E(m) of 430 +/- 20 mV. EPR spectra recorded for this heme protein demonstrated the presence of stoichiometric amounts of two low-spin hemes with a g(z)() of 3.08 (510 mV species) and a g(z)() of 3.22 (430 mV species). Modifications of the physicochemical properties of the cytochrome were observed on complex formation with the blue copper protein rusticyanin, another soluble electron carrier in the genus Thiobacillus. N-Terminal sequencing yielded the polypeptide sequence up to the 50th residue. The determined sequence was found to be present (at 100% amino acid identity) in the (unfinished) genome of T. ferrooxidans ATCC 23270, and the corresponding full-length protein turned out to be surprisingly similar (34.5% amino acid identity) to another c(4)-type diheme protein from T. ferrooxidans BRGM [Cavazza, C., et al. (1996) Eur. J. Biochem. 242, 308-314], the gene of which is also present (at 97% amino acid identity) in the T. ferrooxidans ATCC 23270 genome. The physicochemical properties and sequence characteristics of both c(4) cytochromes present in the same bacteria are compared, and the functional role of this new diheme protein in the iron(II)-oxidizing electron transport chain in the genus Thiobacillus is discussed.

Spectrophotometric study of iron oxidation in the iron(II)/azide/tetrahydrofuran system and some analytical applications

A simple, sensitive and alternative method for the spectrophotometric determination of iron(II or III) has been established. The procedure is based on the formation of iron-III/azide complexes, in 70% (v/v) tetrahydrofuran (THF)/water medium. Under these present experimental conditions, ferrous iron is rapidly oxidized and complexed. The high sensitivity obtained in this method is due to the use of an interesting absorption band caused by THF solvation. In the recommended conditions, absorbances for the ferric complexes are measured at 396 nm, where the molar absorptivity is 1.53×10 4 l mol −1 cm −1. The organic solvent utilized increases the sensitivity and the stability of the measurements. The reproducibility is shown by an average deviation about 0.15%. This system obeys the Beer’s law and is suitable for iron determination in the concentration range from 0.6 to 2.8 ppm (15–65% T, quartz cells of 1.00 cm). The optimal conditions for a faster iron-II oxidation were determined by studying the different factors involved. The influence of various diverse ions was also evaluated. Analytical applications have been tested for several different materials (iron-rocks), including pharmaceutical products for anemia, in which the results were compared with atomic absorption measurements. Very good concordances were obtained between these two different techniques, showing the potential of present spectrophotometric method in iron analysis.

Oxidative DNA damage mediated by copper(II), iron(II) and nickel(II) Fenton reactions: evidence for site-specific mechanisms in the formation of double-strand breaks, 8-hydroxydeoxyguanosine and putative intrastrand cross-links

The role of metal ion–DNA interactions in the Fenton reaction-mediated formation of putative intrastrand cross-links, 8-hydroxydeoxyguanosine (8-OHdG) and single- and double-strand breaks was investigated. Salmon sperm DNA and pBluescript K+ plasmid were incubated with hydrogen peroxide and either copper(II), iron(II), or nickel(II), which differ in both their affinity for DNA and in the spectrum of oxidative DNA damage they induce in Fenton reactions. EDTA was included in these incubations according to two different strategies; the first (strategy 1) in which DNA and metal ions were mixed prior to the addition of EDTA, the second (strategy 2) in which EDTA and metal ions were mixed prior to the addition of DNA. The formation of the putative intrastrand cross-links, monitored by 32 P -postlabelling, was not affected by the addition of between 10 μM and 5 mM EDTA to the copper(II) Fenton reaction according to strategy 1. In contrast, the level of cross-links declined significantly upon inclusion of 20 μM EDTA and above when added according to strategy 2. Similarly, formation of these lesions declined in the iron(II) Fenton reaction more dramatically upon addition of 5 mM EDTA when added according to strategy 2 compared to strategy 1, while the yield of cross-links formed in the nickel(II) Fenton reaction declined equally with both strategies with up to 25 mM EDTA. The formation of single- and double-strand breaks was investigated in plasmid DNA by agarose gel electrophoresis and subsequent densitometry. The formation of linear DNA in the iron(II) Fenton reaction decreased dramatically upon inclusion of EDTA according to strategy 2, while no such decline was observed using strategy 1. In contrast, the formation of linear DNA in the copper(II) Fenton reaction decreased upon inclusion of EDTA according to both strategies. A decrease in the formation of open-circular DNA was also observed upon inclusion of EDTA according to both strategies; however this decrease occurred at a lower EDTA concentration in strategy 2 (100 μM) compared to strategy 1 (200 μM), and the level of open-circular DNA reached a lower level (8.5% compared to 24.2%). The nickel(II) Fenton reaction generated only open-circular DNA, and this was completely inhibited upon addition of 25 μM EDTA according to both strategies. There was less formation of 8-OHdG in the copper(II) and iron(II) Fenton reactions when EDTA was added according to strategy 2 than according to strategy 1. These results suggest that a site-specific mechanism is involved in the formation of double-strand breaks and, to a lesser extent, 8-OHdG and the putative intrastrand cross-links, while the formation of single-strand breaks is more likely to involve generation of hydroxyl radicals in solution.

Mixed Inorganic–Organic Anion Frameworks: Synthesis and Crystal Structure of Fe4(PO4)2(C2O4)(H2O)2

A novel inorganic–organic framework material has been prepared hydrothermally in the iron(II)–phosphate–oxalate system. Fe4(PO4)2(C2O4)(H2O)2crystallizes in space groupP21/n,a=7.974(3) Å,b=4.817(3) Å,c=14.169(3) Å,β=94.70(3)°,V=542.4(4) Å3,Z=2, finalR,Rw=0.023, 0.025 for 817 observed data (I−3σ(I)). The structure consists of sheets of interconnected FeO6, FeO5, and PO4polyhedra in theabplane, which are bridged via C2O2−4groups along thec-axis to form an infinite three-dimensional network enclosing small cavities into which terminal FeOH2groups protrude.