Iron Electronic Structure Research Articles

Enhanced degradation of micropollutants over iron-based electro-Fenton catalyst: Cobalt as an electron modulator in mesochannels and mechanism insight

Heterogeneous electro-Fenton (hetero-EF) process is an emerging alternative for effective oxidation of recalcitrant micropollutants, but it is hampered by limited hydroxyl radical (•OH) generation and low stability on the iron-based cathodes. Herein, we demonstrate an enhanced hetero-EF performance via modulation of iron electronic structure in an ordered mesoporous carbon (OMC). By tuning the cobalt incorporation, the highly-dispersed iron-cobalt (FeCo) nanoalloys in mesochannels (Fe0.5Co0.5@OMC) show a 3-fold increase in •OH yield compared with Fe@OMC, achieving degradation efficiency with 92% of sulfamethazine (SMT) and 99% of rhodamine B (RhB), and the corresponding total organic carbon (TOC) removal with 66% of SMT and 85% of RhB within 2 h in neutral pH, respectively. Experimental results and density functional theory (DFT) calculations demonstrate that iron incorporated with cobalt reduces energy barrier for facile generation of H2O2 and •OH from O2 through direct electron transfer, along with decreased overpotential. Meanwhile, cobalt doping promotes H2O2 decomposition by accelerated Fe(II)/Fe(III) cycle and Co(II)/Co(III) redox. Furthermore, spatially confined and half-embedded structure endows the nanocatalyst (8 nm) excellent durability within a wide pH value range and good stability in cycle tests. A plausible reaction mechanism and degradation pathway for SMT are proposed. Moreover, the superiority of Fe0.5Co0.5@OMC cathode is maintained in simulated wastewater, suggesting an enormous potential in practical wastewater treatment.

Comparative analysis of the heme iron electronic structure and stereochemistry in tetrameric rabbit hemoglobin and monomeric soybean leghemoglobin a using Mössbauer spectroscopy with a high velocity resolution

A comparative study of tetrameric rabbit hemoglobin and monomeric soybean leghemoglobin a in the oxy- and deoxy-forms was carried out using 57Fe Mössbauer spectroscopy with a high velocity resolution in order to analyze the heme iron electronic structure and stereochemistry in relation to the Mössbauer hyperfine parameters. The Mössbauer spectra of tetrameric rabbit hemoglobin in both forms were fitted using two quadrupole doublets related to the 57Fe in ɑ– and β–subunits. In contrast, the Mössbauer spectra of monomeric soybean leghemoglobin a were fitted using: (i) two quadrupole doublets for the oxy-form related to two conformational states of the distal His E7 imidazole ring and different hydrogen bonding of oxygen molecule in the oxy-form and (ii) using three quadrupole doublets for deoxy-form related to three conformational states of the proximal His F8 imidazole ring. Small variations of Mössbauer hyperfine parameters related to small differences in the heme iron electronic structure and stereochemistry in tetrameric rabbit hemoglobin and monomeric soybean leghemoglobin a are discussed.

Aryl-substituted BIAN complexes of iron dibromide: Synthesis, X-ray and electronic structure, and catalytic hydrosilylation activity

Anhydrous iron dibromide complexes bearing bidentate α-diimine ligands ArNC(Me)(Me)CNAr and ArBIAN (BIAN=bis(imino)acenaphthene; Ar=dpp and Mes; dpp=2,6-diisopropylphenyl; Mes=2,4,6-trimethylphenyl) have been prepared and characterized by 1H NMR spectroscopy. The aryl-substituted BIAN complexes were structurally characterized by single-crystal X-ray diffraction, and their metrical parameters are consistent with a redox-innocent chelating ligand. A high-spin iron(II) electronic structure description for the ArBIAN iron complexes is supported by Mössbauer spectroscopy, solution state magnetic measurements, and quantum-chemical calculations. Upon reduction, the iron complexes promote catalytic hydrosilylation of 1-hexene with phenylsilane at 22°C. Under optimized conditions, 1 mol% of the dppBIANFeBr2 precatalyst was activated in situ to produce 1-hexylphenylsilane in high yield from a 1:1 ratio of 1-hexene:PhSiH3 in solvent-free conditions at 22°C in 24h.

A new chiral phase of BiFeO3 evidenced from resonant x-ray Bragg diffraction

Results that support a new chiral phase in the only multiferroic material known above room temperature have been obtained by a resonant x-ray Bragg diffraction experiment, with the incoming x-ray beam tuned near the Fe K-edge (7.1135 keV), performed in its ferroelectric phase. The R3c forbidden reflection (0,0,9)H was studied as a function of the rotation of the crystal about the Bragg wavector in both phases, paramagnetic (700 K) and antiferromagnetic (300 K). The data gathered is consistent with a chiral structure formed by a circular cycloid propagating along (1,1,0)H. Templeton and Templeton (T&T) scattering at 700 K is attributed in part to charge-like quadrupoles absent in a standard model of a cycloid in which a material vector generates all electronic states of the resonant ion. Extensive sets of azimuthal-angle data are used to infer values of three atomic multipoles in a satisfactory minimal model of the iron electronic structure, with a quadrupole (E1-E1 event) and a hexadecapole (E2-E2 event) contributing T&T scattering, plus a magnetic dipole (E1-E1).

Heme iron state in various oxyhemoglobins probed using Mössbauer spectroscopy with a high velocity resolution

A comparative study of oxyhemoglobins from pig, rabbit, normal human and patients with blood system malignant diseases was performed using Mössbauer spectroscopy with a high velocity resolution at 90 K. Mössbauer spectra were fitted with the help of two models: using one quadrupole doublet (model of equivalent iron electronic structure in α- and β-subunits of hemoglobins) and superposition of two quadrupole doublets (model of non-equivalent iron electronic structure in α- and β-subunits of hemoglobins). The results obtained using both models demonstrated small variations of hyperfine parameters that were related to the heme iron state variation in different hemoglobins. These results were compared with structural and functional differences of the hemoglobins investigated.

Study of human, rabbit and pig oxyhemoglobins using high velocity resolution Mössbauer spectroscopy in relation to their structural and functional variations

Normal human adult, rabbit and pig oxyhemoglobins in frozen red blood cell solutions were studied using Mössbauer spectroscopy with a high velocity resolution. Spectra were analyzed using two models with and without accounting for the heme iron electronic structure non-equivalence in α- and β-subunits of tetrameric hemoglobins. The observed differences of Mössbauer hyperfine parameters were related to structural variations in human, rabbit and pig oxyhemoglobins as well as to the differences in ligand binding affinities of these proteins.

Mössbauer spectroscopy with a high velocity resolution in the study of iron-containing proteins and model compounds

Mössbauer spectroscopy with a high velocity resolution was used for comparative studies of human adult, rabbit and pig oxyhemoglobins, human liver ferritin and its pharmaceutically important models Imferon and Maltofer ® as well as liver and spleen tissues from normal and lymphoid leukemia chicken. These studies revealed small variations of Mössbauer hyperfine parameters which were related to small variations of iron electronic structure and stereochemistry in these samples.

Mössbauer spectroscopy with high velocity resolution: an increase of analytical possibilities in biomedical research

Mossbauer spectroscopy is a useful technique for biomedical applications. To increase analytical possibilities and quality of its biomedical applications a new Mossbauer spectrometric system was developed. This system based on a highly stable, sensitive and precision spectrometer SM-2201 with high velocity resolution and a temperature variable liquid nitrogen cryostat with a moving absorber. The first results of Mossbauer spectroscopy with high velocity resolution demonstrated a decrease in the experimental error in the determination of 57Fe hyperfine parameters and, therefore, an increase of accuracy in analysis of small variations of the iron electronic structure, as well as more reliable fitting of complicated spectra.

The DFT–DVM theoretical study of the differences of quadrupole splitting and the iron electronic structure for the rough heme models for α- and β-subunits in deoxyhemoglobin and for deoxymyoglobin

Quantum chemical calculations of the iron electron structure and 57Pe quadrupole splitting were made by density functional theory and Xα discrete variation method for the rough heme models for α- and β-subunits in deoxyhemoglobin and for deoxymyoglobin accounting stereochemical differences of the active sites in native proteins. The calculations revealed differences of quadrupole splitting temperature dependences for three models indicating sensitivity of quadrupole splitting and Fe(II) electronic structure to small variations of iron stereochemistry.

Combining organic photochromism with inorganic paramagnetism—optical tuning of the iron(ii) electronic structure

The crystalline photochromism of a diarylethene pyridyl ligand is applied to the modulation of the electronic environment of a high-spin Fe(II) metal ion.

Differences of the quadrupole splitting and iron electronic structure for the heme models for α and β subunits in deoxyhemoglobin and for deoxymyoglobin: Quantum-chemical calculations by the DFT-DVM method

The quantum-chemical calculation of the iron electronic structure and 57Fe quadrupole splitting have been performed by the DFT-DVM method for rough heme models for α and β subunits in deoxyhemoglobin and for deoxymyoglobine, which take into account stereochemical differences of the active cites in native proteins. The calculations revealed differences in the temperature dependences of quadrupole splitting for the three models, indicating sensitivity of the quadrupole splitting and Fe(II) electronic structure to small stereochemical variations in the nearest iron environment. The theoretical results confirmed the possibility of approximating experimental Mossbauer spectra of tetrameric hemoglobins with allowance for the nonequivalence of the Fe(II) electronic structure in nonidentical subunits.

The Features of Mössbauer Spectra of Hemoglobins: Approximation by Superposition of Quadrupole Doublets or by Quadrupole Splitting Distribution?

Mossbauer spectra of hemoglobins have some features in the range of liquid nitrogen temperature: a non-Lorentzian asymmetric line shape for oxyhemoglobins and symmetric Lorentzian line shape for deoxyhemoglobins. A comparison of the approximation of the hemoglobin Mossbauer spectra by a superposition of two quadrupole doublets and by a distribution of the quadrupole splitting demonstrates that a superposition of two quadrupole doublets is more reliable and may reflect the non-equivalent iron electronic structure and the stereochemistry in the α- and β-subunits of hemoglobin tetramers.

Mössbauer spectroscopy in biomedical research

This work discusses the main directions and results of the application of Mössbauer spectroscopy of iron containing species in biomedical research. These studies demonstrate the wide possibilities of Mössbauer spectroscopy to obtain physical parameters and information about the iron electronic structure in normal and pathological biomolecules, model compounds and pharmaceutical samples as well as about qualitative and quantitative changes of iron containing biomolecules during pathological processes or the effect of environmental factors. The results obtained may be useful for further understanding of the molecular nature of diseases and pathological processes.

Study of the relationship of small variations of the molecular structure and the iron state in iron containing proteins by Mössbauer spectroscopy: biomedical approach

This review considers the results of experimental Mössbauer studies and theoretical calculations of the effect of small variations of protein molecular structure on the iron electronic structure and stereochemistry in order to understand the proteins structural heterogeneity and functional variety. Structural changes in iron containing proteins during various diseases are also considered. These results show the relationship of the small structural variations and Mössbauer parameters of iron containing proteins and demonstrate the possibilities of Mössbauer spectroscopy to obtain new information at the molecular level in biomedical research.

Mössbauer spectral study of the magnetic properties ofCe2Fe17Hx(x=0,1, 2, 3, 4, and 5)

The M\ossbauer spectra of ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}{\mathrm{H}}_{x},$ where $x=0,$ 1, 2, 3, 4, and 5, have been measured and analyzed between 4.2 and 295 K. Because ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}$ exhibits a helical magnetic order between 225 and 90 K and a fan magnetic order below 90 K, its M\ossbauer spectra were fit with a distribution of hyperfine fields and \ensuremath{\theta} angles for four of the eight magnetically inequivalent sites. Because the hydrides exhibit a magnetization within the basal plane of the hexagonal cell, their M\ossbauer spectra were fit with seven sextets. The four isomer shifts correlate with the Wigner-Seitz cell volume, the hyperfine fields correlate with the number of iron near neighbors and give estimates of the individual iron magnetic moments ranging from $0.91{\ensuremath{\mu}}_{B}$ to $2.13{\ensuremath{\mu}}_{B},$ and the quadrupole splittings are in agreement with a point charge calculation. The temperature dependence of the hyperfine fields in ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}$ is insensitive to the transition from the fan to the helical magnetic structure, a transition which does not modify to any extent the iron electronic structure. As a result of the sudden ferromagnetic ordering which results from the presence of as little as one hydrogen per formula unit, the increase of 70 kOe in the weighted average hyperfine field upon hydrogenation is the largest between $x=0$ and 1. The temperature dependence of the weighted average hyperfine field in the hydrides shows Brillouin behavior, a behavior which is slightly different for ${\mathrm{Ce}}_{2}{\mathrm{Fe}}_{17}.$ The temperature dependence of the isomer shift yields a Debye temperature of 345 K. The variation of the hyperfine parameters upon hydrogenation confirms that first the $9e$ octahedral site is filled by hydrogen, and second the $18g$ tetrahedral hydrogen site is filled.

Characterization of the heme iron in pyridoxylated hemoglobin cross-linked by glutaraldehyde using Mössbauer spectroscopy

The heme iron in human adult hemoglobin modified by both pyridoxal-5′-phosphate and glutaraldehyde was characterized by Mössbauer spectroscopy and compared with non-modified hemoglobin. Mössbauer spectra of the samples were measured at 87 and 295 K (1yophilized form) and at 87 K (frozen solution). The values of quadrupole splitting for the oxy-form of modified hemoglobin were found to be lower than those of the oxy-form of hemoglobin without modifications in lyophilized form and frozen solution, respectively. On the other hand, the values of quadrupole splitting for the deoxy-form of modified and non-modified hemoglobins in frozen solution were the same. The Mössbauer spectra of the oxy-form of modified hemoglobin were also analyzed in terms of the heme iron non-equivalence in α- and β-subunits of tetramer. The differences of the tendencies of temperature dependencies of quadrupole splitting for the oxy-form of modified and non-modified hemoglobins in lyophilized form were shown. These results indicated that the heme iron electronic structure and stereochemistry were changed in the oxy-form of pyridoxylated hemoglobin cross-linked by glutaraldehyde.

Variations of the heme iron electronic structure and stereochemistry in relation to the features of Mössbauer spectra of hemoglobins

Variations of the heme iron electronic structure and stereochemistry in relation to the features of Mössbauer spectra of hemoglobins

Mössbauer Effect in Biomedical Research: Variations of Quadrupole Splitting in Relation to the Qualitative Changes of Biomolecules

Abstract This review deals with studies of the variations of quadrupole splitting, electronic structure and stereochemistry of iron associated with qualitative changes of biomolecules. The possibility to determine various iron containing species resulting from the destruction of biomolecules using Mössbauer parameters is shown. A small change of iron stereochemistry leads to a small change of the iron electronic structure which could be detected by small changes of quadrupole splitting. It is expected that quadrupole splitting of iron gives new information for biomedical research on a molecular level.

The heme iron coordination complex in His64(E7)Tyr recombinant sperm whale myoglobin.

By using site-directed mutagenesis of recombinant sperm whale (SW) myoglobin, the native distal histidine residue, at position 64 (the helical position E7), has been replaced with a tyrosine. The mutation of His64Tyr SW myoglobin has an analogous heme iron electronic structure as that of native hemoglobins M Boston and M Saskatoon. Optical spectroscopy showed that the distal tyrosine bound to the heme iron had a pK value of 5.6. In the pH range of 4.7-11.0, electron spin resonance spectroscopy suggested the presence of two heme iron ligation schemes: the heme iron bound to a distal water molecule or to a distal tyrosine residue. The heme iron coordination in the wild-type myoglobin and in the His64Tyr SW Mb mutant was studied by X-ray absorption near-edge structure (XANES) spectroscopy. Indeed, the heme iron K-edge reflects the electronic organization of the metal inside the six-coordinated complex. Comparative analysis of X-ray absorption heme iron K-edge shapes showed that the heme iron of His64Tyr SW myoglobin is bound to the oxygen atom from the phenol group of the distal tyrosine residue (Fe-OH phi). When the pH value decreased from pH 7 to 5.6, the Fe-OH phi bond strength decreased, resulting in an increase of the heme iron high-spin population of His64Tyr SW myoglobin. At low pH values, the Fe-OH phi bond can be disrupted with the possibility of heme iron binding of another ligand having a higher affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

An analysis of iron-dextran complexes by Mössbauer spectroscopy and positron annihilation technique

Abstract The combination of two modern spectroscopic techniques was used for comparative microstructural analysis of several iron-dextran complexes which were used or elaborated as drugs for treatment of iron-deficiency anemias. Slight variations of the iron electronic and magnetic structure in different iron-dextran complexes were detected by Mossbauer spectroscopy. The differences of iron core structure and size were shown in studied complexes also. Variations of dextran structure were detected by the positron annihilation technique for investigated irondextran complexes. These results were considered with histological and histochemical data for iron-dextran complexes to compare the differences of their microstructural variations and biochemical pathways.