Mossbauer Hyperfine Parameters Research Articles

Comparison of the 57Fe hyperfine interactions in silicate phases in Sariçiçek howardite and some ordinary chondrites

Silicate crystals have different thermal history in non-differentiated and differentiated meteorites. This leads to some differences in the Fe2+ and Mg2+ distribution between the M1 and M2 sites in olivine, orthopyroxene and clinopyroxene crystals in stony meteorites resulting in small variations in the Fe local microenvironment. For this reason, a comparison of Mossbauer hyperfine parameters for the 57Fe in the M1 and M2 sites in orthopyroxene and Ca-rich clinopyroxene for non-differentiated NWA 6286 LL6, NWA 7857 LL6 and Tsarev L5 ordinary chondrites and differentiated Saricicek howardite was carried out. The results obtained demonstrated small variations in quadrupole splitting and isomer shift for the studied non-differentiated and differentiated stony meteorites.

Mössbauer Study and Curie Temperature Configuration on Sintering Nano-Ni-Zn Ferrite Powder

Variations of Curie temperature and strength of magnetic phases with sintering temperature and Ni concentration is investigated in the present work. The AC susceptibility studies show a decrease in Curie temperature (TC) with an increase in Ni concentration in the samples. Comparison of Curie temperatures with the reported results reveals that samples in the present work show higher TC enabling high thermal stability. The Mossbauer spectra of nano- and sintered Ni-Zn ferrite samples were recorded at room temperature to monitor the local environment around Fe cations through Mossbauer hyperfine parameters as a function of composition and sintering temperatures. The increase in sharpness of the Mossbauer sextet with an increase in Ni concentration and sintering temperature corroborate improvement in homogeneity and ferrimagnetic ordering. The results of hyperfine parameters offer the possibility of having close view on configuring Curie temperature through monitoring hyperfine field by altering sintering temperature and/or Ni concentration. As the temperature dependence of magnetic and magnetoelastic properties is strongly influenced by the Curie temperature, the successful possible configuration of Curie temperature in the present work can be further investigated for desired sensor applications.

Spectroscopy and DFT Calculations of Flavo-Diiron Nitric Oxide Reductase Identify Bridging Structures of NO-Coordinated Diiron Intermediates.

Flavo-diiron proteins (FDPs) are widespread in anaerobic bacteria, archaea, and protozoa, where they serve as the terminal components of dioxygen and nitric oxide reductive scavenging pathways. FDPs contain an N,O-ligated diiron site adjacent to a flavin mononucleotide (FMN) cofactor. The diiron site is structurally similar to those in hemerythrin, ribonucleotide reductase, and methane monooxygenase. However, only FDPs turn over NO to N2O at significant rates and yields. Previous studies revealed sequential binding of two NO molecules to the diferrous site, forming mono- and dinitrosyl intermediates leading to N2O formation. In the present work, these mono- and dinitrosyl intermediates have been characterized by EPR and Mössbauer spectroscopies and DFT calculations. Our results show that the iron proximal to the cofactor binds the first NO to form the diiron mononitrosyl complex, implying the iron distal to the FMN binds the second NO to form the diiron dinitrosyl intermediate. The exchange-coupling constants, J (H = JS1·S2), were found to differ substantially, +17 cm-1 for the diiron mononitrosyl and +60 cm-1 for the diiron dinitrosyl. Notwithstanding this large difference, our findings indicate retention of at least one hydroxo bridge throughout the NOR catalytic cycle. The Mossbauer hyperfine parameters and DFT calculations confirmed a semibridging NO- ligand in the mononitrosyl intermediate that lowers the exchange parameter. The DFT calculations on the dinitrosyl intermediate suggest a contribution to J from direct exchange between the S = 1 spins on the NO- ligands, which could initiate N-N bond formation. Our results provide insight into why FDPs are the only known nonheme diiron enzymes that competently turn over NO to N2O.

Study of maghemite nanoparticles as prepared and coated with DMSA using Mössbauer spectroscopy with a high velocity resolution

Study of maghemite nanoparticles, native and coated with DMSA as mag- netic fluid for biomedical applications, was carried out using Mossbauer spectroscopy with a high velocity resolution at 295 and 90 K. The obtained results demonstrated differences in Mossbauer hyperfine parameters for uncoated and DMSA-coated nanoparticles which were related to the interactions of DMSA molecules with Fe 3+ ions on maghemite nanoparticle's surface.

Probing nonequivalent sites in iron phosphide Fe2P and its mechanism of phase transition

Comparative studies of two polymorphs ( \hbox{$P\overline{6}2m$} P 6 2 m and Pnma structures) of Fe2P up to 16.8 GPa and 1800 ± 200 K were performed using Mossbauer spectroscopy combined with diamond anvil cell and laser heating facilities. Mossbauer spectra were collected before and after its phase transition from \hbox{$P\overline{6}2m$} P 6 2 m to Pnma structures. Mossbauer hyperfine parameters in two non-equivalent sites Fe I and Fe II in Fe2P were evaluated and compared. An evident drop of quadrupole splitting for the 57Fe in Fe II site was observed in its high temperature polymorph, indicating that a more sensitive pyramidal Fe II site to pressure change could serve as a trigger to this phase transition.

Variations in quadrupole splitting of the 57 Fe in the M1 and M2 sites of meteoritic olivines with different origin

A comparative study of meteoritic olivine in bulk samples of Farmington L5 and Tsarev L5 ordinary chondrites and extracted from Omolon and Seymchan the main-group pallasites was performed using Mossbauer spectroscopy with a high velocity resolution. Mossbauer spectra for each specimen were measured at 295 and 90 K. Mossbauer spectral components related to the 57Fe in crystallographically non-equivalent sites M1 and M2 in olivines were determined and their Mossbauer hyperfine parameters were evaluated. It was found small variations of quadrupole splitting for the 57Fe in both the M1 and M2 sites of olivines in bulk ordinary chondrites and olivines extracted from pallasites.

Magnetite nanoparticles as-prepared and dispersed in Copaiba oil: study using magnetic measurements and Mössbauer spectroscopy

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mossbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization and Mossbauer hyperfine parameters which were related to the interactions of Copaiba oil polar molecules with iron cations on magnetite nanoparticle’s surface.

Mössbauer hyperfine parameters of iron species in the course of Geobacter-mediated magnetite mineralization

Amorphous ferric iron species (ferrihydrite or akaganeite of <5 nm in size) is the only known solid ferric iron oxide that can be reductively transformed by dissimilatory iron-reducing bacteria to magnetite completely. The lepidocrocite crystallite can be transformed into magnetite in the presence of abiotic Fe(II) at elevated pH or biogenic Fe(II) with particular growth conditions. The reduction of lepidocrocite by dissimilatory iron-reducing bacteria has been widely investigated showing varying results. Vali et al. (Proc Natl Acad Sci USA 101:16121–16126, 2004) captured a unique biologically mediated mineralization pathway where the amorphous hydrous ferric oxide transformed to lepidocrocite was followed by the complete reduction of lepidocrocite to single-domain magnetite. Here, we report the 57Fe Mossbauer hyperfine parameters of the time-course samples reported in Vali et al. (Proc Natl Acad Sci USA 101:16121–16126, 2004). Both the quadrupole splittings and linewidths of Fe(III) ions decrease consistently with the change of aqueous Fe(II) and transformations of mineral phases, showing the Fe(II)-mediated gradual regulation of the distorted coordination polyhedrons of Fe3+ during the biomineralization process. The aqueous Fe(II) catalyzes the transformations of Fe(III) minerals but does not enter the mineral structures until the mineralization of magnetite. The simulated abiotic reaction between Fe(II) and lepidocrocite in pH-buffered, anaerobic media shows the simultaneous formation of green rust and its gradual transformation to magnetite plus a small fraction of goethite. We suggested that the dynamics of Fe(II) supply is a critical factor for the mineral transformation in the dissimilatory iron-reducing cultures.

Pressure-induced structural phase transition of the iron end-member of ringwoodite ( -Fe2SiO4) investigated by X-ray diffraction and Mossbauer spectroscopy

We have carried out X-ray diffraction and Mossbauer spectroscopy measurements on the spinel phase γ-Fe 2 SiO 4 (ringwoodite) at ambient temperature and pressures up to 66 GPa using diamond anvil cells. At pressures above 30 GPa, a previously unknown structural phase transition to a rhombohedrally distorted spinel phase has been observed (space group R 3 mR ). Mossbauer spectroscopy measurements reveal two different Fe 2+ sites at high pressure with an abundance ratio of 3:1, in agreement with the two crystallographic sites occupied by the iron in this distorted spinel structure. The unit-cell volume of the low-pressure spinel phase as a function of pressure results in a bulk modulus of K 0 = 197(3) GPa using the second-order Birch-Murnaghan equation of state, and K 0 = 201(8) GPa and K′ = 3.7(7) when using a third-order equation of state. The pressure evolution of the unit-cell volume and the Mossbauer hyperfine parameters are in good agreement with previous studies, which were limited to a lower pressure range.

57Fe hyperfine interactions in M1 and M2 sites of olivine from Omolon meteorite: study using Mössbauer spectroscopy

Study of olivine (Fe, Mg)2SiO4 from Omolon meteorite was performed using Mossbauer spectroscopy with a high velocity resolution at 295 and 90 K. Components related to 57Fe in crystallographically non-equivalent M1 and M2 sites in olivine were determined and its Mossbauer hyperfine parameters were evaluated at both temperatures. A Fe2 + –Mg2 + distribution coefficient and a temperature of cation equilibrium distribution for olivine from Omolon were evaluated on the basis of Mossbauer parameters.

Recrystallization in fully metamict gadolinite from Ytterby (Sweden), annealed in air and studied by 57Fe Mossbauer spectroscopy

57 Fe Mossbauer annealing studies of fully metamict gadolinite from Ytterby (Sweden) have been carried out in air from 373 to 1473 K. The Mossbauer spectrum of the untreated sample, dated at 1795 Ma and absorbed α-dose 1.07 × 10 16 α-decay/mg, is characterized by two broad peaks solely from Fe 2+ components in octahedral coordinations. The corresponding quadrupole splitting distribution (QSD) shows two distinct maxima at 1.59 and 2.16 mm/s, which reflect the post-metamictization distributions of Fe 2+ positions up to heating at 773 K. Changes in the Mossbauer hyperfine parameters are observed only after heating to 873 K, at which point the first Fe 3+ component from the oxidation of Fe 2+ appears. The relative contribution of Fe 3+ /∑Fe reaches a maximum of 0.54 at 1073 K and then decreases with increasing temperature. A new Fe 3+ doublet is observed in the samples heated from 1173 to 1473 K. This doublet is characterized by extremely high quadrupole splitting ranging from 2.51 to 2.66 mm/s, implying extreme distortion of the coordination octahedra in partially and fully crystalline gadolinite. The transition from metamict to crystalline structure begins at 1133 K where the Mossbauer spectrum is represented by one Fe 2+ doublet and one Fe 3+ doublet. Both doublets suggest a uniform transitional octahedral site over the whole structure. With increasing annealing temperature, the line widths of the Fe 2+ doublet decrease, and, at high temperatures, an asymmetry of the absorption peaks is observed. The sample becomes completely recrystallized after annealing at 1373 K, and at this point the Mossbauer spectra are nearly exact superpositions of the pure Fe 2+ and Fe 3+ (present in minor proportion) in synthetic gadolinites.

Mossbauer spectroscopy with high velocity resolution in the study of iron-bearing minerals in meteorites

Application of Mossbauer spectroscopy with a higher velocity resolution than commonly applied appeared to be useful for obtaining hyperfine parameters of 57 Fe nuclei with a lower experimental error and for a better fit of complicated spectra. The study of iron-bearing phases in ordinary and carbonaceous chondrites as well as iron meteorite and extracted iron-nickel phosphides by Mossbauer spectroscopy with an improved velocity resolution (measurement in 4096 channels, presentation in 1024 channels) demonstrated new results which had not been obtained from Mossbauer spectra measured in 512 channels or less. In particular, it was possible to reveal spectral components related to M1 and M2 sites in olivine and pyroxene in Mossbauer spectra of bulk samples of ordinary chondrites and then to evaluate the temperatures of equilibrium cation distribution. Moreover, differences in small variations of Mossbauer hyperfine parameters were obtained for 57 Fe in M1 and M2 sites for both olivine and pyroxene.

Study of CuFe2O4–SnO2 nanocomposites by Mössbauer spectroscopy with high velocity resolution

High velocity resolution Mossbauer spectroscopy was used to study of (CuFe2O4)1 − x (SnO2) x nanocomposites (x = 0, 1, 5, 10, 20 wt.%). Mossbauer spectra were measured at room temperature with registration in 4,096 channels and further presentation in 1,024 channels. Mossbauer spectra of CuFe2O4 and (CuFe2O4)0.99 + (SnO2)0.01 were better fitted using three sextets while spectra of (CuFe2O4)0.95 + (SnO2)0.05 and (CuFe2O4)0.80 + (SnO2)0.20 were better fitted using four sextets and one doublet. In contrast, spectrum of (CuFe2O4)0.80 + (SnO2)0.20 was better fitted using five sextets and one doublet. Mossbauer hyperfine parameters were related to octahedral and tetrahedral sites in copper ferrites. The presence of two different tetrahedral sites in studied ferrites and two different octahedral sites in (CuFe2O4)0.80 + (SnO2)0.20 was supposed.

57Fe Mössbauer spectroscopic study of nanostructured zinc ferrite

Nanosize zinc ferrite particles, prepared by nitrate method, were investigated by XRD, TEM, 57Fe Mossbauer spectroscopy and VSM. The average particle size in this system varies from 10 to 62 nm as the sintering temperature increases from 300°C to 1,000°C. The lattice parameters in this system are almost constant at a value of ∼8.41 A. The Mossbauer spectra of all the sintered samples show a single doublet. The Mossbauer hyperfine parameters show little change with the change of sintering temperature. The doublets are ascribed to the presence of superparamagnetism in this system, which is also corroborated by the VSM measurements.

Determination of quadrupole splitting for 57Fe in M1 and M2 sites of both olivine and pyroxene in ordinary chondrites using Mössbauer spectroscopy with high velocity resolution

Study of 11 ordinary chondrites using Mossbauer spectroscopy with high velocity resolution revealed two crystallographically non-equivalent octahedral sites M1 and M2 in subspectra of olivine and pyroxene which were observed previously in pure natural or synthetic silicates only. Mossbauer hyperfine parameters related to M1 and M2 sites in olivine and pyroxene determined from Mossbauer spectra of ordinary chondrites were analyzed and compared with parameters of pure natural and synthetic silicates.

Study of hyperfine interactions in carbonaceous chondrite Isheyevo (CH/CB) using Mössbauer spectroscopy with high velocity resolution

The unique meteorite bencubbinite Isheyevo CH/CB which was recently found in Bashkortostan, Russia was studied using Mossbauer spectroscopy with high velocity resolution. Mossbauer hyperfine parameters of metal in Isheyevo CH/CB external and internal regions demonstrated the presence of three phases such as martensite α2)-Fe(Ni,Co), kamacite α-Fe(Ni,Co) and disordered taenite γ-Fe(Ni,Co)

The metallurgic furnaces at the Curamba Inca site (Peru): a study by Mössbauer spectroscopy and X-ray diffractometry

The Inca site at Curamba is located in the Province of Apurimac in the southern highlands of Peru where, according to some historians, several thousand furnaces used for ore smelting were found. For this work, four samples of burned soil were gathered from these furnaces and classified as Curamba1, Curamba2, Curamba3, and Curamba4, and studied using transmission Mossbauer spectroscopy (TMS) and X-ray diffractometry (XRD). The mineralogical composition of the samples was determined by XRD and the structural sites in the minerals occupied by iron cations were characterized by TMS. Moreover, an attempt was made to determine the maximum temperature reached in these furnaces using the refiring technique of the samples in an oxidizing environment and monitoring the structural modifications at the iron sites by changes in the Mossbauer hyperfine parameters. The TMS results of Curamba2 show that the maximum temperature reached in this furnace was about 900°C, in agreement with the mineralogical composition found by XRD. In the case of Curamba1 and Curamba4 the maximum temperature estimated was about 400°C.

Analysis of iron storage proteins in chicken liver and spleen tissues in comparison with human liver ferritin by Mössbauer spectroscopy

Characterization of iron storage proteins in liver and spleen from normal chicken and chicken with lymphoid leukemia in comparison with human liver ferritin were considered by Mossbauer spectroscopy (preliminary results). Small differences in Mossbauer hyperfine parameters for both normal and lymphoid leukemia chicken liver and spleen were observed. The value of quadrupole splitting for human liver ferritin was higher than those for chicken tissues. A decrease of iron content in lymphoid leukemia chicken tissues was also found, however, the reason of this fact (pathology or feeding) was not clear yet.

The Relationship of Mössbauer Hyperfine Parameters and Structural Variations of Iron Containing Proteins and Model Compounds in Biomedical Research

The relationship of Mossbauer hyperfine parameters and structural variations of iron containing proteins and model compounds was considered as applied to biomedical research. It was shown that Mossbauer hyperfine parameters give new information about structural changes of proteins during molecular diseases or effect of environment factors as well as about structural peculiarities of pharmaceutical compounds.

Study of chicken liver and spleen by Mössbauer spectroscopy

A preliminary study of purified normal human liver ferritin, normal chicken liver and spleen tissues in lyophilized form showed differences in room temperature Mossbauer hyperfine parameters. An additional study of liver and spleen tissues with lower iron content from chicken with lymphoid leukemia indicated small differences between the quadrupole splittings in these samples compared with those in normal tissues.