Number Of Iron Atoms Research Articles

Evidence of Grain Alignment by Magnetically Enhanced Radiative Torques from Multiwavelength Dust Polarization Modeling of HL Tau

The Atacama Large Millimeter/Submillimeter Array has revolutionized the field of dust polarization in protoplanetary disks across multiple wavelengths. Previous observations and empirical modeling have suggested multiple mechanisms of dust polarization toward HL Tau, including grain alignment and dust scattering. However, a detailed modeling of dust polarization based on grain alignment physics is not yet available. Here, using an updated POLARIS code, we perform numerical modeling of dust polarization arising from both grain alignment by the magnetically enhanced radiative torque mechanism and self-scattering to reproduce the HL Tau polarization observed at three wavelengths of 0.87, 1.3, and 3.1 mm. Our modeling results show that the observed multiwavelength polarization could be reproduced only when large grains contain embedded iron inclusions and those with slow internal relaxation must have wrong internal alignment (i.e., the grain’s major axis parallel to its angular momentum). The abundance of iron embedded inside grains in the form of clusters is constrained to be ≳16%, and the number of iron atoms per cluster is N cl ∼ 9 × 102. Maximum grain sizes probed at wavelengths of λ = 0.87, 1.3, and 3.1 mm are constrained at ∼60, 80, and 90 μm, respectively.

Effect of partial substitution of iron for group IV elements on the structure and superconducting properties of the Fe(Se-=SUB=-0.2-=/SUB=-Te-=SUB=-0.8-=/SUB=-)-=SUB=-0.82-=/SUB=- compound

The structure and superconducting properties of the Fe1-x(A)x(Se0.2Te0.8)0.82 (x = 0.1, 0.2) compound, where A is Cu, Zn, Bi or Group IV elements (Pb, Sn, Ge), were studied. It was shown that the effect of substitution of some iron atoms on the structure and superconducting properties of the Fe(Se,Te) compound depends on whether a solid solution with a substituting element was formed. If complete dissolution of the replacement element occured (Cu, Zn), then a significant degradation of the superconducting properties was observed. If a separate chalcogenide phase was formed (substitution by Pb, Sn, Ge), then a slight change in the superconducting properties was observed. Such a slight change and even improvement in the superconducting properties upon precipitation of the chalcogenide phase can be associated with both the positive effect of an increase in the relative content of iron and a decrease in the number of iron atoms in the interstitial sites of the β-phase. The preservation of the superconducting properties of the Fe(Se,Te) compound with a small substitution of iron for group IV elements can be used to create wires based on Fe(Se,Te), since impurity chalcogenide particles can act as effective pinning centers. Keywords: Iron-based superconductor, FeSeTe, critical parameters, substitution, structure, electrical resistivity, magnetoresistance, pressure effect.

Влияние частичного замещения железа на элементы IV группы на структуру и сверхпроводящие свойства соединения Fe(Se-=SUB=-0.2-=/SUB=-Te-=SUB=-0.8-=/SUB=-)-=SUB=-0.82-=/SUB=-

The structure and superconducting properties of the Fe1 – x(A)x(Se0.2Te0.8)0.82 (x = 0.1, 0.2) compound, where A is Cu, Zn, Bi or Group IV elements (Pb, Sn, Ge), were studied. It was shown that the effect of substitution of some iron atoms on the structure and superconducting properties of the Fe(Se,Te) compound depends on whether a solid solution with a substituting element was formed. If complete dissolution of the replacement element occured (Cu, Zn), then a significant degradation of the superconducting properties was observed. If a separate chalcogenide phase was formed (substitution by Pb, Sn, Ge), then a slight change in the superconducting properties was observed. Such a slight change and even improvement in the superconducting properties upon precipitation of the chalcogenide phase can be associated with both the positive effect of an increase in the relative content of iron and a decrease in the number of iron atoms in the interstitial sites of the β phase. The preservation of the superconducting properties of the Fe(Se,Te) compound with a small substitution of iron for group IV elements can be used to create wires based on Fe(Se,Te), since impurity chalcogenide particles can act as effective pinning centers.

Influence of the size of iron nanoclusters on their magnetization

The size of iron nanocrystals significantly affects the value of their magnetization. However, an adequate model of the structure of nanocrystalline formations comprising different numbers of iron atoms still does not exist. In this work, spatial models of nanocrystalline iron clusters differing in configuration and the number of their constituent atoms are constructed. Tetrahedrally close-packed cluster assemblies of iron atoms are taken as the basis for the proposed structures of nanocrystals. The spectra of the density of electronic states for the proposed clusters are constructed using the theory of the electron density functional. The calculation was carried out by the method of scattered waves in accordance with the band theory of crystals. The appearance of magnetization in tetrahedral close-packed cluster formations is associated with excited electronic states of atoms located on the surface of the nanocluster. Excited atoms have an increased electron density, that is, electrons are able to transition to states with higher energy, approaching the Fermi energy. In this case, the Stoner criterion necessary for the occurrence of magnetization is fulfilled. The configurations of electrons with spin up and down differ, which is why uncompensated magnetic moments appear. It is shown that the proposed models of iron nanoclusters are in satisfactory agreement with the known experimental data.

Possible role of iron containing proteins in physiological responses of soybean to static magnetic field

Iron is a component of many proteins that have crucial roles in plant growth and development, such as ferritin and catalase. Iron also, as a ferromagnetic element, is assumed to be influenced by a static magnetic field (SMF). In the present study, we examined the relationship between ferrous content and gene expression and activity of ferritin and catalase in soybean plants under the influence of 0, 20, and 30 mT SMF for 5 day, 5 h each. Exposure to 20 mT decreased gene expression of Fe transporter, ferrous and H2O2 contents and gene expression, content and activity of ferritin and catalase. Opposite responses were observed under 30 mT treatments. The results suggest that SMF triggered a signaling pathway that is mediated by iron. The structure and activity of purified ferritin and apoferritin from horse spleen, and catalase from bovine liver proteins under SMF were evaluated as well. Secondary structure of proteins were not influenced by SMF (evidenced by far-UV circular dichroism), whereas their tertiary structure, size, and activity were altered (shown by fluorescence spectroscopy and dynamic light-scattering). From these results, it is likely that the number of iron atoms is involved in the nature of influence of SMF on protein structure.

Structural and magnetic properties of Fe-membranes embedded in hexagonal graphene nanoholes

The structure and magnetism of Fe-doped hexagonal graphene nanoholes (h-GNHs) were studied on the basis of density-functional theory. The nonzero magnetic moment of carbon in zigzag edge can be greatly reduced in Fe-doped h-GNHs due to the local CFe interaction. The reduced magnetic moment is almost zero, and its direction is opposite to that of iron atoms. Therefore, Fe-adsorption may be used to destroy the spin polarization of graphene zigzag edge. In Fe-doped h-GNHs, iron atom would prefer to adsorb on graphene armchair edge and form five-member (1Fe + 4C) ring. In stable Fe-doped h-GNHs, the bond length of CFe is about 1.9 Å. And in the most stable Fe-membrane embedded h-GNH with the largest binding energy, the average FeFe bond length is about 2.36 Å. Besides, the mean magnetic moment induced by iron atoms changes greatly from 1.45 μB per iron atom to 3.46 μB per iron atom in Fe-doped h-GNHs. The magnetism of iron seems to be sophisticated. It is related to the type of graphene edge, the size of GNH and the number of iron atoms.

Synthesis, structure, and catalytic properties of iron complexes with mono- and bisformazans in sulfide oxidation and ethylene oligomerization reactions

Metal complexes with different numbers of iron atoms in a predominantly nitrogen-containing coordination environment have been synthesized on basis of benzothiazole mono- and bisformazans. The composition and structures of the resulting iron coordination compounds have been characterized by electronic absorption spectroscopy, elemental analysis, mass spectrometry, electron spin resonance, and magnetochemistry. The catalytic behavior of these metal chelates in the liquid-phase oxidation of sulfides and the oligomerization of ethylene has been studied.

Structural, electronic and magnetic properties of Fen@C60 and Fen@C80 (n=2–7) endohedral metallofullerene nano-cages: First principles study

We studied the structural, electronic and magnetic properties of small Fen clusters (n=2–7) endohedrally doped in icosahedral C60 and C80 fullerenes using first principles calculations based on the density functional theory. It is found that the encapsulated Fen clusters inside icosahedral C80 are energetically favorable while Fen@C60 metallofullerene nano-cages are not. The binding energies of the Fen encapsulated in C60 are positive and increase with the number of iron atoms (n) while those of the Fen@C80 are negative and their absolute values increase up to n=6. The encapsulation does not significantly change the enclosed cluster structure, but the total magnetic moment of the larger clusters reduces due to a stronger Fe–C hybridization.

Differential expression from two iron-responsive promoters in Salmonella enterica serovar Typhimurium reveals the presence of iron in macrophage-phagosomes

The metal status of macrophage-phagosomes during Salmonella infection is largely unknown. In this study, we have precisely calibrated the metal-specificities of two metal-responsive promoters, P iroBCDE and P sodB , from Salmonella enterica serovar Typhimurium and used these to directly monitor iron-levels in Salmonella-containing macrophage-phagosomes. Expression from the P iroBCDE promoter is highly elevated in metal-depleted media but low in media supplemented with iron or cobalt, and to a lesser extent manganese. In contrast, P sodB shows low levels of expression in metal-depleted media but is induced in media supplemented with iron but no other metals at maximum permissive concentrations. In both cases, iron-responsive expression corresponds to changes in the number of iron atoms per bacterial cell and is unaffected by pH or the presence of reactive oxygen species (hydrogen peroxide and superoxide). Importantly, expression from P iroBCDE remained low while expression from P sodB was elevated during infection of both Nramp1 +/+ and Nramp1 −/− macrophages. Expression from a control promoter, P polA , unaffected by metal ions, remained unchanged. These findings are therefore consistent with the presence of iron within Salmonella-containing macrophage-phagosomes and support a model in which the toxic potential of iron may be exploited as a component of the respiratory burst killing mechanism.

Mixing characterization of mechanically milled Fe75Si15M10 powders using Mössbauer spectroscopy

Mixing characteristics of Si and Al or Cr in Fe has been studied in ball milled Fe75Si15M10 (with M = Al, Cr) alloys in detail. Mossbauer spectroscopic study shows that even up to 80 h of milling a large number of iron atoms remain uninteracted and give 33.0 T sextet. The portion which mixes up gives a magnetic component with 31.5 T of B hf and paramagnetic components showing up in doublets. It is proposed that Fe diffuses in the matrices of the other elements and vice versa. This is in contrast to our earlier studies on ball milled Fe–Cr alloy where Fe shows no sign of diffusion in Cr, but Cr diffuses in Fe freely.

Oxidation of Steel Surfaces in Water Solutions

Abstract Oxide film formation on the surface of carbon steels during contact with solutions of reagents such as oxygen, hydrogen peroxide (H2O2), hydrazine-hydrate (N2H4·H2O), ammonium acetate (CH3COONH4), and ethylene-diamin-tetraacetate (Na2H2Y2) was studied. By means of a number of physical and chemical methods (radioactive indicators, spectrophotometry, gel-chromatography, and Mossbauer spectroscopy, etc.), it has been proven that iron compounds in the solution contacting the steel surface play the decisive role in the formation of oxide films. Oxide films on steels with maximal protective properties are shown to form in water solutions of Fe(III) complexes or solutions containing polymer forms of its hydrolysis products with the number of iron atoms in the molecule being <13.

Dependence of the Electrochemical Response of Ferritin on the Number of Iron Atoms at the Ferritin Core

Abstract The well-defined redox reaction of ferritin was observed at an indium oxide electrode with a fully hydrophilic surface at a low concentration of ferritin solution (0–7 μmol dm−3). This was a diffusion-controlled electrode reaction process. Conversely, at a higher concentration of ferritin (7 μmol dm−3 &amp;lt;), ferritin was weakly adsorbed on the electrode surface. The electrochemical redox response of ferritin was strongly affected by the number of iron atoms at the core of the ferritin molecule.

Structure and Mechanisms of Formation of FeOOH(NO3) Oligomers in the Early Stages of Hydrolysis

The partial hydrolysis of ferric nitrate solutions (0.1 M) and the structural evolution of the smallest oligomers were studied by using X-ray absorption spectroscopy at aging times between 1 h and 20 days at room temperature. The samples evolve differently with time, depending on the hydrolysis ratio. At the same aging time t, the number of iron atoms in the atomic environment of the central atom increases with hydrolysis ratio, but the growth does not follow a defined pathway. Only N3 (the number of iron atoms around each central atom at a distance of ≈3.50 Å) has a monotonous evolution with time. It seems that the growth of nuclei is associated with the increase of the amount of double-corner sharing. Edge-sharing linkages between Fe octahedra are associated with the early steps of the nucleation, and single-corner linkages are present in all samples. In the case of the hydrolysis of ferric nitrate salts, the local structure of oligomers does not prefigure the structure of the well crystallized infinite phase as opposed to ferric chloride salts and Cr.

Magnetic properties of ultrafine ferrihydrite clusters studied by Mossbauer spectroscopy and by thermodynamical analysis

Magnetic properties of ultrafine clusters of Fe5HO8·4H2O (ferrihydrite, FH), isolated in pores of polysorb, were studied by Mossbauer spectroscopy and by thermodynamical analysis. Thermodynamical analysis allowed the conclusion that magnetic properties of ultrafine clusters cannot be interpreted in terms of a secondorder magnetic phase transition or of superparamagnetic behavior alone but require the consideration of a jumplike first order magnetic phase transition (JMT). The critical radius R cr below which the JMT is to be expected in clusters was derived from thermodynamic criteria. It was determined as R cr = 2 α β η/(1 - T cc/T 0), where α, β and η are constants derived from surface energy, magnetostriction, compressibility and T cc = 3/2 Nκ B T o 2 ηβ 2 (N is the number of iron atoms, κ B is the Boltzmann constant, T o is the Curie temperature of the clusters). For the smallest FH clusters isolated in pores of polysorb, the critical radius and the JMT temperature were estimated by Mossbauer spectroscopy to be R cr ∼ 1.5–2.0 nm and T JMT ∼ 4.2–6 K, respectively. Satisfactory agreement between the value R cr, estimated from the experimental data and the one derived by thermodynamical analysis was achieved. Interfacial (cluster-surface) and intercluster interactions were found to destroy the JMT effect and to give rise to a second-order magnetic phase transition.

Classical and Quantum Magnetic Phenomena in Natural and Artificial Ferritin Proteins

Artificial ferritin has been synthesized with control of both the magnetic state (antiferromagnetic or ferrimagnetic) and the particle size over an ofer of magnitude in the number of iron atoms. The magnetic properties of the artificial ferritin were compared with those of natural horse spleen ferritin in a range of temperatures (20 millikelvin to 300 kelvin) and fields (1 nanotesla to 27 tesla). In the classical regime, the blocking temperature was found to correlate with the average particle size. A correlation was also observed in the quantum regime between the resonance frequency of macroscopic quantum tunneling of the Néel vector and the particle size. At high magnetic fields (to 27 tesla), a spin flop transition with a strong dependence on orientation was seen in the natural ferritin, providing evidence of antiferromagnetism in this system.

Mossbauer study on the distribution of iron in high coercivity chromium dioxide particles

/sup 57/Fe Mossbauer spectroscopy is applied to determine the level of iron doping in high-coercivity CrO/sub 2/ particles. It is found that, compared with the conventional preparation process, the particles contain an increased amount of Fe/sup 3+/ ions in the CrO/sub 2/ crystal lattice, giving rise to higher magnetocrystalline anisotropy. This is reflected in coercivities up to over 900 Oe. All samples contain as a secondary iron-containing phase some (Cr/sub 1-x/Fe/sub x/)/sub 2/O/sub 3/. The valence of the iron doping is predominantly +3; very weak signals in the Mossbauer spectra suggest the existence of Fe/sup 4+/ in an amount 2-3% of the total number of iron atoms. >

Mössbauer and Magnetization Study of YBa2(Cu1-xFex)3O∼6.9

Mossbauer spectra of 57 Fe in YBa 2 (Cu 1- x Fe x ) 3 O y were studied for the samples keeping the oxygen concentration constant, y =6.87±0.05. Using the results of EXAFS measurement, we find that changes in the Mossbauer pattern with iron concentration can be explained from changes in the oxygen coordination around iron. The number of iron atoms with an octahedral coordination increases rapidly with a change in the crystal structure from orthorhombic to tetragonal. This increase has a close correlation with the decrease in a zero-field cooled magnetization in the superconducting state. These results are consistent with that the tetragonal structure observed by X-ray diffraction is induced by the increase of the number of octahedrally coordinated iron and consists of microdomains with the orthorhombic structure inside the domains.

Purification of a high specific activity methane monooxygenase hydroxylase component from a type II methanotroph

The purification of the hydroxylase component of a 3 component methane monooxygenase from the type II methanotroph Methylosinus trichosporium OB3b is reported. The enzyme (240 kDa) has an (αβγ) 2 subunit structure as observed for hydroxylases isolated from other Type I and Type II methanotrophs, but it exhibits a 5 to 10 fold higher specific activity and is isolated in 2 to 10 fold higher yield. EPR and Mössbauer spectra of the hydroxylase show that it contains a coupled iron center containing an even number of iron atoms. The spectra are similar to those of proteins known to contain oxo-bridged binuclear iron centers. The presence of such a center is unprecedented in a monooxygenase and suggests that a novel mechanism is utilized.

Heart ferritin of Gallus domesticus (L.)

1. 1. Ferritin from chicken heart has been isolated by salt fractionation followed by chromatographic purification. 2. 2. The identification of the protein was carried out by acryl-amid gel electrophoresis showing two bands with 24 and 28 subunits respectively. 3. 3. The characterization of ferritin has been made by determination of the mol. wt, amino acids analysis and the number of iron atoms which bound the ferritin. 4. 4. The chicken heart ferritin is compared with ferritin from other fowl tissues and mammal hearts.

The iron content of iron superoxide dismutase: determination by anomalous scattering.

The number of iron atoms in the dimeric iron-containing superoxide dismutase from Pseudomonas ovalis and their atomic positions have been determined directly from anomalous scattering measurements on crystals of the native enzyme. To resolve the long-standing question of the total amount of iron per molecule for this class of dismutase, the occupancy of each site was refined against the measured Bijvoet differences. The enzyme is a symmetrical dimer with one iron site in each subunit. The iron position is 9 A from the intersubunit interface. The total iron content of the dimer is 1.2 +/- 0.2 moles per mole of protein. This is divided between the subunits in the ratio 0.65:0.55; the difference between them is probably not significant. Since each subunit contains, on average, slightly more than half an iron atom we conclude that the normal state of this enzyme is two iron atoms per dimer but that some of the metal is lost during purification of the protein. Although the crystals are obviously a mixture of holo- and apo-enzymes, the 2.9 A electron density map is uniformly clean, even at the iron site. We conclude that the three-dimensional structures of the iron-bound enzyme and the apo-enzyme are identical.