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In this study LiFePO 4 /C composite particles were synthesized using five different carbon sources via a one-step sol-gel method. La-doped LiFePO 4 was also synthesized using the sol-gel method. The XRD pattern of Li x La y FePO 4 ( x = 0.9~1.0, y = 0~0.1) after being calcined at 700 °C for 10 h indicates that as the doping ratio increased, the sample's cell volume first increased then decreased, reaching a maximum value of 293.36 Å 3 ( x = 0.94, y = 0.06). The XRD patterns of Li 0.92 La 0.08 FePO 4 after being calcined at different temperatures for 10 h indicate that with increasing calcination temperature, the (311) diffraction peak drifted toward a smaller diffraction angle. Similarly, the XRD patterns of Li 0.92 La 0.08 FePO 4 after being calcined at 700 °C for different durations indicate that with increasing calcination times, the (311) diffraction peak drifted toward a larger diffraction angle. The infrared spectrum pattern of Li x La y FePO 4 ( x = 0.9~1.0, y = 0~0.1) after being calcined at 700 °C for 10 h shows absorption peaks corresponding to the vibrations of the Li-O bond and PO 4 3- group. An SEM analysis of Li x La y FePO 4 ( x = 1, y = 0; x = 0.96, y = 0.04; x = 0.92, y = 0.08) after being calcined at 700 °C for 10 h indicates that the particles were irregular in shape and of uniform size. The hysteresis loops of Li 0.92 La 0.08 FePO 4 after being calcined at 600 °C, 700 °C, or 800 °C for 10 h indicate that with increasing calcination temperature, the Ms gradually increased, while the Mr and Hc decreased, with minimum values of 0.08 emu/g and 58.21 Oe, respectively. The Mössbauer spectra of Li x La y FePO 4 ( x = 1, y = 0; x = 0.96, y = 0.04; x = 0.92, y = 0.08) after being calcined at 700 °C for 10 h indicate that all samples contained Doublet(1) and Doublet(2) peaks, dominated by Fe 2+ compounds. The proportions of Fe 2+ were 85.5% ( x = 1, y = 0), 89.9% ( x = 0.96, y = 0.04), and 96.0% ( x = 0.92, y = 0.08). The maximum IS and QS of Doublet(1) for the three samples were 1.224 mm/s and 2.956 mm/s, respectively.

The syntheses, coordination chemistry, and Mössbauer spectroscopy of hepta-iron(III) complexes using derivatised salicylaldoxime ligands from two categories; namely, 'single-headed' (H 2 L ) and 'double-headed' (H 4 L ) salicylaldoximes are described. All compounds presented here share a [Fe 3 -µ 3 -O] core in which the iron(III) ions are µ 3 -hydroxo-bridged in the complex C1 and µ 3 -oxo-bridged in C2 and C3 . Each compound consists of 2 × [Fe 3 -µ 3 -O] triads that are linked via a central [Fe(µ 2 -OH) 6 ] 3- ion. In addition to the charge balance and microanalytical evidence, Mössbauer measurements support the fact that the triads in C1 are µ 3 -OH bridged and are µ 3 -O bridged in C2 and C3 .

The mobility and bioavailability of phosphate in paddy soils are closely coupled to redox-driven Fe-mineral dynamics. However, the role of phosphate during Fe-mineral dissolution and transformations in soils remains unclear. Here, we investigated the transformations of ferrihydrite and lepidocrocite and the effects of phosphate pre-adsorbed to ferrihydrite during a 16-week field incubation in a flooded sandy rice paddy soil in Thailand. For the deployment of the synthetic Fe-minerals in the soil, the minerals were contained in mesh bags either in pure form or after mixing with soil material. In the latter case, the Fe-minerals were labeled with 57 Fe to allow the tracing of minerals in the soil matrix with 57 Fe Mössbauer spectroscopy. Porewater geochemical conditions were monitored, and changes in the Fe-mineral composition were analyzed using 57 Fe Mössbauer spectroscopy and/or X-ray diffraction analysis. Reductive dissolution of ferrihydrite and lepidocrocite played a minor role in the pure mineral mesh bags, while in the 57 Fe-mineral-soil mixes more than half of the minerals was dissolved. The pure ferrihydrite was transformed largely to goethite (82-85%), while ferrihydrite mixed with soil only resulted in 32% of all remaining 57 Fe present as goethite after 16 weeks. In contrast, lepidocrocite was only transformed to 12% goethite when not mixed with soil, but 31% of all remaining 57 Fe was found in goethite when it was mixed with soil. Adsorbed phosphate strongly hindered ferrihydrite transformation to other minerals, regardless of whether it was mixed with soil. Our results clearly demonstrate the influence of the complex soil matrix on Fe-mineral transformations in soils under field conditions and how phosphate can impact Fe oxyhydroxide dynamics under Fe reducing soil conditions.

Two novel isostructural cyanide-bridged hexadecanuclear complexes with the general formula {[Fe(CN) 6 ] 6 [M{en(Bn)py}] 10 } 2+ [M=Fe (1 2+ ), Ni (2 2+ )] have been synthesized. The structural analyses disclose the presence of multivalent Fe centres with different spin states in complex 1 2+ whereas all the Fe centres share a conserved oxidation state in complex 2 2+ . The DC magnetic study revealed antiferromagnetic interactions between the adjacent metal centres and ferrimagnetic behaviour in 1 2+ . On the other hand, ferromagnetic interactions were observed in complex 2 2+ due to nearly orthogonal orientation of the interacting orbitals and poor spatial overlap as observed in BS-DFT calculations., (© 2024 Wiley-VCH GmbH.)

Coordination compounds, like iron(II) triazole complexes, exhibit spin crossover (SCO) behavior at around room temperature. Therefore, they are interesting for a variety of possible applications, and it is convenient to integrate them into polymers. Due to a reduction of the iron content and thus also 57 Fe content in the sample through integration in polymers, Mössbauer measurements are only possible with greater difficulty or very long measurement times without expensive enrichment of the samples with 57 Fe. So, other ways of improving the Mössbauer signal for these composite materials are necessary. Therefore, we pressed these composite materials to improve the Mössbauer spectra. In this study, we synthesized an iron(II) triazole spin crossover complex and an electrospun polymer complex composite nanofiber material including the same complex. For both products, Mössbauer measurements were performed at room temperature before and after using a press to show that the complex composite is not harmed through pressing. We investigate the influence of the pressing impact on the Mössbauer measurements in the context of measurement statistics and the measured signals. We show that pressing is not connected to any changes in the sample regarding the spin and oxidation state. We present that pressing improves the statistics of the Mössbauer measurements significantly. Furthermore, we use SEM measurements and PXRD to investigate whether or not the obtained fiber mats are destroyed in the pressing process.

Two trinuclear oxo-centred iron(III) coordination compounds of monensic and salinomycinic acids (HL) were synthesized and their spectral properties were studied using physicochemical/thermal methods (FT-IR, TG-DTA, TG-MS, EPR, Mössbauer spectroscopy, powder XRD) and elemental analysis. The data suggested the formation of [Fe 3 (µ 3 -O)L 3 (OH) 4 ] and the probable complex structures were modelled using the DFT method. The computed spectral parameters of the optimized constructs were compared to the experimentally measured ones. In each complex, three metal centres were joined together at the axial position by a μ 3 -O unit to form a {Fe 3 O} 7+ core. The antibiotics monoanions served as bidentate ligands through the carboxylate and hydroxyl groups located at the termini. The carboxylate moieties played a dual role bridging each two metal centres. Hydroxide anions secured the overall neutral character of the coordination species. Mössbauer spectra displayed asymmetric quadrupole doublets that were consistent with the existence of two types of high-spin iron(III) sites with different environments-two Fe[O 5 ] and one Fe[O 6 ] centres. The solid-state EPR studies confirmed the +3 oxidation state of iron with a total spin S t = 5/2 per trinuclear cluster. The studied complexes are the first iron(III) coordination compounds of monensin and salinomycin reported so far.

Iron and 2-oxoglutarate dependent (Fe/2OG) enzymes exhibit an exceedingly broad reaction repertoire. The most prevalent reactivity is hydroxylation, but many other reactivities have also been discovered in recent years, including halogenation, desaturation, epoxidation, endoperoxidation, epimerization, and cyclization. To fully explore the reaction mechanisms that support such a diverse reactivities in Fe/2OG enzyme, it is necessary to utilize a multi-faceted research methodology, consisting of molecular probe design and synthesis, in vitro enzyme assay development, enzyme kinetics, spectroscopy, protein crystallography, and theoretical calculations. By using such a multi-faceted research approach, we have explored reaction mechanisms of desaturation and epoxidation catalyzed by a bi-functional Fe/2OG enzyme, AsqJ. Herein, we describe the experimental protocols and computational workflows used in our studies., (Copyright © 2024. Published by Elsevier Inc.)

Intravenous iron-carbohydrate nanomedicines are widely used to treat iron deficiency and iron deficiency anemia across a wide breadth of patient populations. These colloidal solutions of nanoparticles are complex drugs which inherently makes physicochemical characterization more challenging than small molecule drugs. There have been advancements in physicochemical characterization techniques such as dynamic light scattering and zeta potential measurement, that have provided a better understanding of the physical structure of these drug products in vitro. However, establishment and validation of complementary and orthogonal approaches are necessary to better understand the 3-dimensional physical structure of the iron-carbohydrate complexes, particularly with regard to their physical state in the context of the nanoparticle interaction with biological components such as whole blood (i.e. the nano-bio interface)., (Copyright © 2023. Published by Elsevier B.V.)

Magnetic Functional Nanomaterials Co 1-y Zn y RE x Fe 2-x O 4 (RE (rare-earth) = La,Sm,Gd) were prepared using the sol-gel combustion method. XRD characterization confirms that the ferrite samples we synthesized are single-phase cubic structures. The variation in the average crystalline size and lattice parameter is related to RE ion doping. The Mössbauer spectra of CoRE x Fe 2-x O 4 are two sets of magnetic six-wire peaks that indicate the ferrimagnetic behavior of the sample. The calcination temperature greatly influences the absorption area of Mössbauer for CoFe 2 O 4 , indicating that the calcination temperature affects the iron ion content at the octahedral B and tetrahedral A sites. Additionally, scanning electron microscopy measurements of the substituted specimens reveal that the ferrite powders are nanoparticles. With an increase in RE ions, the coercivity increases, and the saturation magnetization changes obviously. The XRD characterization of Co 0.7 Zn 0.3 La x Fe 2-x O 4 shows that the main crystalline phase of the sample is the cubic spinel structure phase, and there are fewer secondary crystalline phases. The lattice parameter tends to decrease with the substitution of La 3+ ions. The average grain size decreased significantly with the increase in La content. From ferrimagnetic state transition to relaxation behavior, the hyperfine magnetic field decreases in La concentration by room temperature Mössbauer spectra. With the substitution of La 3+ ions, both the saturation magnetization and coercivity of the samples were reduced, and the coercivity of all samples was lower.

A y B 1- y C x Fe 2- x O 4 (C=Ho,Gd,Al) ferrite powders have been synthesized by the sol-gel combustion route. The X-ray diffraction of the CoHo x Fe 2- x O 4 ( x = 0 ~ 0.08) results indicated the compositions of single-phase cubic ferrites. The saturation magnetisation of CoHo x Fe 2- x O 4 decreased by the Ho 3+ ions, and the coercivity increased initially and then decreased with the increase of the calcination temperature. The Mössbauer spectra indicated that CoHo x Fe 2- x O 4 displays a ferrimagnetic behaviour with two normal split Zeeman sextets. The magnetic hyperfine field tends to decrease by Ho 3+ substitution owing to the decrease of the A-B super-exchange by the paramagnetic rare earth Ho 3+ ions. The value of the quadrupole shift was very small in the CoHo x Fe 2- x O 4 specimens, indicating that the symmetry of the electric field around the nucleus is good in the cobalt ferrites. The absorption area of the Mössbauer spectra changed with increasing Ho 3+ substitution, indicating that the substitution influences the fraction of iron ions at tetrahedral A and octahedral B sites. The X-ray diffraction of Mg 0.5 Zn 0.5 C x Fe 2- x O 4 (C=Gd,Al) results confirmed the compositions of single-phase cubic ferrites. The variation of the average crystalline size and lattice constant are related to the doping of gadolinium ions and aluminum ions. With increasing gadolinium ions and aluminum ions, the coercivity increased and the saturation magnetization underwent a significant change. The saturation magnetization of AlMg 0.5 Zn 0.5 FeO 4 ferrite reached a minimum value ( M S = 1.94 mu/g). The sample exhibited ferrimagnetic and paramagnetic character with the replacement with Gd 3+ ions, that sample exhibited paramagnetic character with the replacement with Al 3+ ions, and the isomer shift values indicated that iron is in the form of Fe 3+ ions.

Different doping elements have been used to enhance the dielectric properties of BaTiO 3 ceramic. In this work, the effect of substitution of Ba by Bi in A site and Ti by Fe in B site on structural, dielectric and electrical properties of Ba 1-x Bi x Ti 0.80 Fe 0·20 O 3 ceramics at (x = 0.00, 0.05, 0.10 and 0.15) was investigated by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy (SEM), Mössbauer spectroscopy as well as dielectric measurements. The Rietveld refinement results revealed that the prepared compounds crystallize in both tetragonal ( P 4 mm ) and hexagonal ( P 6 3 / mmc ) phases for x = 0.00 and 0.05 while at x = 0.10 and 0.15, the hexagonal phase disappears and only the tetragonal phase is fitted. The Raman spectra confirmed the disappearance of hexagonal phase in benefit of tetragonal phase as the Bi 3+ substitution increases. Based on Mössbauer analyses results, all the samples are in paramagnetic state at room temperature and the Fe is oxidized under Fe 3+ without the presence of Fe 2+ or Fe 4+ ions. The dielectric measurements as function of temperature are studied and tree broad and relaxor phase transitions were detected: from rhombohedral to orthorhombic phase T R-O and to tetragonal ferroelectric phase T O-T then to cubic paraelectric phase T m . These phase transitions were displaced to the lower temperature with increasing of Bi 3+ substitution. The values of ε' r increase gradually with increasing of Bi 3+ contents which confirmed the enhancement of dielectric properties of BaTi 0·80 Fe 0·20 O 3 by Bi substitution on Ba site. The diffuse phase transitions were described by fitting the modified Uchino relation. The Cole-Cole analyses showed that both the grain and grain boundaries resistivity values are higher for Bi 3+ substituted samples which are responsible to the dielectric properties improvement., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (© 2023 The Authors. Published by Elsevier Ltd.)

l-Cysteine (Cys) is an essential building block for the synthesis of new proteins and serves as a precursor for several biologically important sulfur-containing molecules, such as coenzyme A, taurine, glutathione, and inorganic sulfate. However, organisms must tightly regulate the concentration of free Cys, as elevated levels of this semi-essential amino acid can be extremely harmful. The non-heme iron enzyme cysteine dioxygenase (CDO) serves to maintain the proper levels of Cys by catalyzing its oxidation to cysteine sulfinic acid. Crystal structures of resting and substrate-bound mammalian CDO revealed two surprising structural motifs in the first and second coordination spheres of the Fe center. The first is the existence of a neutral three histidine (3-His) facial triad that coordinates the Fe ion, as opposed to an anionic 2-His-1-carboxylate facial triad that is typically observed in mononuclear non-heme Fe(II) dioxygenases. The second unusual structural feature exhibited by mammalian CDO is the presence of a covalent crosslink between the sulfur of a Cys residue and an ortho-carbon of a tyrosine residue. Spectroscopic studies of CDO have provided invaluable insights into the roles that these unusual features play with regards to substrate Cys and co-substrate O 2 binding and activation. In this chapter, we summarize results obtained from electronic absorption, electron paramagnetic resonance, magnetic circular dichroism, resonance Raman, and Mössbauer spectroscopic studies of mammalian CDO carried out in the last two decades. Pertinent results obtained from complementary computational studies are also briefly summarized., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Hyperfine parameters and the pressure dependence of the magnetic transition temperatures of FeRhGe 2 have been investigated. Sample has been prepared using high pressure-high temperature synthesis technique. FeRhGe 2 consists of two B20 structure phases with close lattice constants. The phase separation stays constant in the temperature range 4-300 K. The magnetic transition temperaturesTc1= 213 K andTc2= 135 K of FeRhGe 2 slightly increases with pressure in the range 0-4.5 GPa. We have compared this pressure dependence with some others compounds in the family Fe1-xRh x Ge. The two phases in FeRhGe 2 have slightly different values of the hyperfine magnetic fields., (© 2022 IOP Publishing Ltd.)

Novel iron(II) coordination compounds containing a ligand 2,6-bis(1 H -imidazol-2-yl)pyridine (L), having such a composition as [FeL 2 ]SO 4 ·0.5H 2 O, [FeL 2 ]Br 2 ·H 2 O, [FeL 2 ](ReO 4 ) 2 , [FeL 2 ]B 10 H 10 ∙H 2 O, [FeL 2 ]B 12 H 12 ∙1.5H 2 O had been synthesized and studied using UV-Vis (diffuse reflectance), infrared, extended X-ray absorption fine structure (EXAFS), and Mössbauer spectroscopy methods, as well as X-ray diffraction and static magnetic susceptibility methods. The analysis of the μ eff (T) dependence in the temperature range of 80-600 K have shown that all the obtained complexes exhibit a high-temperature spin crossover 1 A 1 ↔ 5 T 2 .

Pulsed laser ablation in liquids was utilized to prepare NiFe 2 O 4 (NFO) and CoFe 2 O 4 (CFO) nanoparticles from ceramic targets. The morphology, crystallinity, composition, and particle size distribution of the colloids were investigated. We were able to identify decomposition products formed during the laser ablation process in water. Attempts to fractionate the nanoparticles using the high-gradient magnetic separation method were performed. The nanoparticles with crystallite sizes in the range of 5-100 nm possess superparamagnetic behavior and approximately 20 Am 2 /kg magnetization at room temperature. Their ability to absorb light in the visible range makes them potential candidates for catalysis applications in chemical reactions and in biomedicine.

Mössbauer isomer shift and quadrupole splitting properties have been calculated using the OLYP-D3(BJ) density functional method on previously obtained (W.-G. Han Du, et al., Inorg Chem. 2020, 59, 8906-8915) geometry optimized Fe a3 3+ -H 2 O-Cu B 2+ dinuclear center (DNC) clusters of the resting oxidized (O state) "as-isolated" cytochrome c oxidase (CcO). The calculated results are highly consistent with the available experimental observations. The calculations have also shown that the structural heterogeneities of the O state DNCs implicated by the Mössbauer experiments are likely consequences of various factors, particularly the variable positions of the central H 2 O molecule between the Fe a3 3+ and Cu B 2+ sites in different DNCs, whether or not this central H 2 O molecule has H-bonding interaction with another H 2 O molecule, the different spin states having similar energies for the Fe a3 3+ sites, and whether the Fe a3 3+ and Cu B 2+ sites are ferromagnetically or antiferromagnetically spin-coupled., (© 2022 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Properties of Co-based alloys with high Glass Forming Ability (GFA) in the form of powder are still not widely known. However, powders of high GFA alloys are often used for the development of bulk metallic glasses by additive manufacturing. In this work Co 47.6 B 21.9 Fe 20.4 Si 5.1 Nb 5 % at. and Co 42 B 26.5 Fe 20 Ta 5.5 Si 5 Cu 1 % at. were developed by gas-atomization. Obtained powders in size 50-80 µm were annealed at T g and T x of each alloy. Then SEM observation, EDS analyses, differential thermal analysis, X-ray diffraction, nanoindentation, Mössbauer, and magnetic properties research was carried out for as-atomized and annealed states. The gas atomization method proved to be an efficient method for manufacturing Co-based metallic glasses. The obtained powder particles were spherical and chemically homogeneous. Annealing resulted in an increase of mechanical properties such as hardness and the elastic module of Co 47.6 B 21.9 Fe 20.4 Si 5.1 Nb 5 % at and Co 42 B 26.5 Fe 20 Ta 5.5 Si 5 Cu 1 %, which was caused by crystallization. The magnetic study shows that Co 47.6 B 21.9 Fe 20.4 Si 5.1 Nb 5 and Co 42 B 26.5 Fe 20 Ta 5.5 Si 5 Cu 1 are soft magnetic and semi-hard magnetic materials, respectively.

Constructing synthetic models of the nitrogenase P N -cluster has been a long-standing synthetic challenge. Here, we report an optimal nitrogenase P N -cluster model [{(TbtS)(OEt 2 )Fe 4 S 3 } 2 (μ-STbt) 2 (μ 6 -S)] (2) [Tbt=2,4,6-tris{bis(trimethylsilyl)methyl}phenyl] that is the closest synthetic mimic constructed to date. Of note is that two thiolate ligands and one hexacoordinated sulfide are connecting the two Fe 4 S 3 incomplete cubanes similar to the native P N -cluster, which has never been achieved. Cluster 2 has been characterized by X-ray crystallography and relevant physico-chemical methods. The variable temperature magnetic moments of 2 indicate a singlet ground state (S=0). The Mössbauer spectrum of 2 exhibits two doublets with an intensity ratio of 3:1, which suggests the presence of two types of iron sites. The synthetic pathway of the cluster 2 could indicate the native P N -cluster maturation process as it has been achieved from the Fe 4 S 4 cubane Fe 4 S 4 (STbt) 4 (1)., (© 2021 Wiley-VCH GmbH.)

Nanoparticles that combine several magnetic phases offer wide perspectives for cutting edge applications because of the high modularity of their magnetic properties. Besides the addition of the magnetic characteristics intrinsic to each phase, the interface that results from core-shell and, further, from onion structures leads to synergistic properties such as magnetic exchange coupling. Such a phenomenon is of high interest to overcome the superparamagnetic limit of iron oxide nanoparticles which hampers potential applications such as data storage or sensors. In this manuscript, we report on the design of nanoparticles with an onion-like structure which has been scarcely reported yet. These nanoparticles consist of a Fe 3-δ O 4 core covered by a first shell of CoFe 2 O 4 and a second shell of Fe 3-δ O 4 , e.g., a Fe 3-δ O 4 @CoFe 2 O 4 @Fe 3-δ O 4 onion-like structure. They were synthesized through a multistep seed-mediated growth approach which consists consists in performing three successive thermal decomposition of metal complexes in a high-boiling-point solvent (about 300 °C). Although TEM micrographs clearly show the growth of each shell from the iron oxide core, core sizes and shell thicknesses markedly differ from what is suggested by the size increasing. We investigated very precisely the structure of nanoparticles in performing high resolution (scanning) TEM imaging and geometrical phase analysis (GPA). The chemical composition and spatial distribution of atoms were studied by electron energy loss spectroscopy (EELS) mapping and spectroscopy. The chemical environment and oxidation state of cations were investigated by 57 Fe Mössbauer spectrometry, soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The combination of these techniques allowed us to estimate the increase of Fe 2+ content in the iron oxide core of the core@shell structure and the increase of the cobalt ferrite shell thickness in the core@shell@shell one, whereas the iron oxide shell appears to be much thinner than expected. Thus, the modification of the chemical composition as well as the size of the Fe 3-δ O 4 core and the thickness of the cobalt ferrite shell have a high impact on the magnetic properties. Furthermore, the growth of the iron oxide shell also markedly modifies the magnetic properties of the core-shell nanoparticles, thus demonstrating the high potential of onion-like nanoparticles to accurately tune the magnetic properties of nanoparticles according to the desired applications.

Pyrococcus furiosus is a hyperthermophilic anaerobic archaeon whose metabolism depends on whether elemental sulfur is (+S 0 ) or is not (-S 0 ) included in growth medium. Under +S 0 conditions, expression of respiratory hydrogenase declines while respiratory membrane-bound sulfane reductase and the putative iron-storage protein IssA increase. Our objective was to investigate the iron content of WT and ΔIssA cells under these growth conditions using Mössbauer spectroscopy. WT-S 0 cells contained ∼1 mM Fe, with ∼85% present as two spectroscopically distinct forms of S = 0 [Fe 4 S 4 ] 2+ clusters; the remainder was mainly high-spin Fe II . WT+S 0 cells contained 5 to 9 mM Fe, with 75 to 90% present as magnetically ordered thioferrate-like (TFL) iron nanoparticles. TFL iron was similar to chemically defined thioferrates; both consisted of Fe III ions coordinated by an S 4 environment, and both exhibited strong coupling between particles causing high applied fields to have little spectral effect. At high temperatures with magnetic hyperfine interactions abolished, TFL iron exhibited two doublets overlapping those of [Fe 4 S 4 ] 2+ clusters in -S 0 cells. This coincidence arose because of similar coordination environments of TFL iron and cluster iron. The TFL structure was more heterogeneous in the presence of IssA. Presented data suggest that IssA may coordinate insoluble iron sulfides as TFL iron, formed as a byproduct of anaerobic sulfur respiration under high iron conditions, which thereby reduces its toxicity to the cell. This was the first Mössbauer characterization of the ironome of an archaeon, and it illustrates differences relative to the iron content of better-studied bacteria such as Escherichia coli., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The aim of this work consists in the use of cashew gum (Anacardium occidentale), a naturally occurring tropical specie from the Brazilian northeastern coast, for the synthesis of CoFe 2 O 4 (CF) and NiFe 2 O 4 (NF) nanoparticles. The structural, morphological and vibrational properties of nanoparticles were characterized by analytical and spectroscopic techniques such as X-ray diffraction (XRD), FTIR, Raman spectroscopy, TEM, SAED and TG. Magnetic properties were investigated through Mössbauer spectroscopy and DC magnetometry. The XRD results showed single phase nanoparticles with space group Fd-3m and crystallite size of 7.4 and 6.0 for CF and NF, respectively. TEM images showed agglomerated particles with mode sizes of 5.0 and 6.5 nm for CF and NF. SAED confirmed the crystalline spinel structure. The TGA and FTIR showed the presence of a carbonaceous material in the samples. FTIR and Raman spectroscopy demonstrated vibrational modes characteristic of metal‑oxygen bonds in the tetrahedral and octahedral sites. Magnetization measurements showed that both samples are superparamagnetic at 300 K. The Mössbauer spectra at 90 K showed the presence of single-phase CF and NF., (Published by Elsevier B.V.)

This study focuses on the synthesis of FeRh nanoparticles via pulsed laser ablation in liquid and on controlling the oxidation of the synthesized nanoparticles. Formation of monomodal γ-FeRh nanoparticles was confirmed by transmission electron microscopy (TEM) and their composition confirmed by atom probe tomography (APT). For these particles, three major contributors to oxidation were analysed: (1) dissolved oxygen in the organic solvents, (2) the bound oxygen in the solvent and (3) oxygen in the atmosphere above the solvent. The decrease of oxidation for optimized ablation conditions was confirmed through energy-dispersive X-ray (EDX) and Mössbauer spectroscopy. Furthermore, the time dependence of oxidation was monitored for dried FeRh nanoparticles powders using ferromagnetic resonance spectroscopy (FMR). By magnetophoretic separation, B2-FeRh nanoparticles could be extracted from the solution and characteristic differences of nanostrand formation between γ-FeRh and B2-FeRh nanoparticles were observed.

Enzymes and protein's immobilization on magnetic nano supports is emerging as a promising candidate in the food, medical field, and areas of environmental studies. This work presents a study on purified Bacillus thermoamylovorans lipase (BTL) by utilizing tetraethoxysilane (TEOS)-modified magnesium nano ferrite (MgNF) of 20 nm size. Its structural and morphological studies were investigated by powder X-ray diffractometry, high-resolution transmission electron microscopy, etc. Binding of BTL with MgNF was supported by using Fourier transform infrared spectroscopy. Magnetic behavior was examined by the vibrational sample magnetometer and Mössbauer spectrometer graphs. The enzymatic activity of BTL before and after immobilization was studied at different temperatures and reaction time. As per the Lineweaver-Burk plot, immobilized lipase has more biological affinity for fatty acids in comparison to the free lipase, and K max values of immobilized and free BTL were computed as 6.6 and 7.5 mM respectively, with excellent reusability(> 50%) even till 13 consecutive assay runs. Graphical Abstract.

The presence of synthetic dyes in water causes serious environmental issues owing to the low water quality, toxicity to environment and human carcinogenic effects. Adsorption has emerged as simple and environmental benign processes for wastewater treatment. This work reports the use of porous Fe-based composites as adsorbents for Acid Red 66 dye removal in an aqueous solution. The porous FeC and Fe/FeC solids were prepared by hydrothermal methods using iron sulfates and sucrose as precursors. The physicochemical properties of the solids were evaluated through X-ray diffraction (XRD), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared s (FTIR), Raman and Mössbauer spectroscopies, nitrogen adsorption-desorption isotherms, Electron Paramagnetic Resonance (EPR) and magnetic saturation techniques. Results indicated that the Fe species holds magnetic properties and formed well dispersed Fe 3 O 4 nanoparticles on a carbon layer in FeC nanocomposite. Adding iron to the previous solid resulted in the formation of γ-Fe 2 O 3 coating on the FeC type structure as in Fe/FeC composite. The highest dye adsorption capacity was 15.5 mg·g -1 for FeC nanocomposite at 25 °C with the isotherms fitting well with the Langmuir model. The removal efficiency of 98.4% was obtained with a pristine Fe sample under similar experimental conditions.

Ferritin-like carboxylate-bridged non-heme diiron enzymes activate O 2 for a variety of difficult reactions throughout nature. These reactions often begin by abstraction of hydrogen from strong CH bonds. The enzymes activate O 2 at their diferrous cofactors to form canonical diferric peroxo intermediates, with a range of possible coordination modes. Herein, we explore the ability of high-energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD XAS) to provide insight into the nature of peroxo level intermediates in non-heme diiron proteins. Freeze quenched (FQ) peroxo intermediates from p-aminobenzoate N-oxygenase (AurF), aldehyde-deformylating oxygenase (ADO), and the β subunit of class Ia ribonucleotide reductase from Escherichia coli (Ecβ) are investigated. All three intermediates are proposed to adopt different peroxo binding modes, and each exhibit different Fe Kα HERFD XAS pre-edge features and intensities. As these FQ-trapped samples consist of multiple species, deconvolution of HERFD XAS spectra based on speciation, as determined by Mössbauer spectroscopy, is also necessitated - yielding 'pure' diferric peroxo HERFD XAS spectra from dilute protein samples. Finally, the impact of a given peroxo coordination mode on the HERFD XAS pre-edge energy and intensity is evaluated through time-dependent density functional theory (TDDFT) calculations of the XAS spectra on a series of hypothetical model complexes, which span a full range of possible peroxo coordination modes to a diferric core. The utility of HERFD XAS for future studies of enzymatic intermediates is discussed., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Fibrous chrysotile has been the most commonly applied asbestos mineral in a range of technical applications. However, it is toxic and carcinogenic upon inhalation. The chemical reactivity of chrysotile fiber surfaces contributes to its adverse health effects by catalyzing the formation of highly reactive hydroxyl radicals (HO • ) from H 2 O 2 . In this Haber-Weiss cycle, Fe on the fiber surface acts as a catalyst: Fe 3+ decomposes H 2 O 2 to reductants that reduce surface Fe 3+ to Fe 2+ , which is back-oxidized by H 2 O 2 (Fenton-oxidation) to yield HO • . Chrysotile contains three structural Fe species: ferrous and ferric octahedral Fe and ferric tetrahedral Fe (Fe 3+ tet ). Also, external Fe may adsorb or precipitate onto fiber surfaces. The goal of this study was to identify the Fe species on chrysotile surfaces that catalyze H 2 O 2 decomposition and HO • generation., Results: We demonstrate that at the physiological pH 7.4 Fe 3+ tet on chrysotile surfaces substantially contributes to H 2 O 2 decomposition and is the key structural Fe species catalyzing HO • generation. After depleting Fe from fiber surfaces, a remnant fiber-related H 2 O 2 decomposition mode was identified, which may involve magnetite impurities, remnant Fe or substituted redox-active transition metals other than Fe. Fe (hydr)oxide precipitates on chrysotile surfaces also contributed to H 2 O 2 decomposition, but were per mole Fe substantially less efficient than surface Fe 3+ tet . Fe added to chrysotile fibers increased HO • generation only when it became incorporated and tetrahedrally coordinated into vacancy sites in the Si layer., Conclusions: Our results suggest that at the physiological pH 7.4, oxidative stress caused by chrysotile fibers largely results from radicals produced in the Haber-Weiss cycle that is catalyzed by Fe 3+ tet . The catalytic role of Fe 3+ tet in radical generation may also apply to other pathogenic silicates in which Fe 3+ tet is substituted, e.g. quartz, amphiboles and zeolites. However, even if these pathogenic minerals do not contain Fe, our results suggest that the mere presence of vacancy sites may pose a risk, as incorporation of external Fe into a tetrahedral coordination environment can lead to HO • generation.

Myoglobin (Mb) binds oxygen with high affinity as a low spin singlet complex and thus functions as an oxygen storage protein. Yet, hybrid Density Functional Theory/Molecular Mechanical (DFT/MM) calculations of oxy-Mb models predict that the O 2 bond is much less resistant to breaking in the presence of hydrogen sulfide (H 2 S) compared with water. Specifically, a hydrogen atom from H 2 S can be transferred to the distal oxygen atom through homolytic cleavage of the S-H bond to form the intermediate Compound (Cpd) 0 structure and a thiyl radical. In the presence of a neutral His64 (Nε protonation, His64-ε) and H 2 S, only a metastable Cpd 0 would be formed as the active site is devoid of any additional proton donor to fully break the O 2 bond. In contrast, the calculations predict that the triplet state is significantly favored over the open shell singlet diradical state throughout the entire reaction coordinate in the presence of H 2 S and a positively charged His64. Furthermore, a positively charged His64 can readily donate a proton to Cpd 0 to fully break the O 2 bond resulting in a configuration analogous to reported reaction models of a hemoglobin mutant bound to H 2 O 2 with H 2 S present. Typically, exotic techniques are required to generate Cpd 0 but under the conditions just described the intermediate is readily detected in UV-Vis spectra at room temperature. The effect is observed as a 2 nm red shift of the Soret band from 414 nm to 416 nm (pH 5.0, His64-εδ) and from 416 nm to 418 nm (pH 6.6, His64-ε)., (Copyright © 2019 Elsevier Inc. All rights reserved.)

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 N 2 O 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 N 2 O 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 = JS 1 ·S 2 ), 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 N 2 O.

The phase Na 5 FeSi 4 O 12 [pentasodium iron(III) silicate] crystallizes readily from the Na 2 O-Fe 2 O 3 -SiO 2 glass system in a relatively large compositional range. However, its crystal structure and properties have not been studied in detail since its discovery in 1930. In this work, the Na 5 FeSi 4 O 12 phase was crystallized from a host glass with 5Na 2 O·Fe 2 O 3 ·8SiO 2 stoichiometry, and both the glass and the crystal were studied. It was found that the Na 5 FeSi 4 O 12 phase crystallizes at ∼720 °C from the glass and melts at ∼830 °C when heated at a rate of 10 °C min -1 . The crystal structure was solved using single-crystal X-ray diffraction and the refined data are reported for the first time for the Na 5 FeSi 4 O 12 phase. It exhibits trigonal symmetry, space group R-3c, with a = 21.418 and c = 12.2911 Å. The Na atoms located between adjacent structural channels exhibit positional disorder and splitting which was only refined by using low-temperature data collection (150 K). While ∼7% of the total Fe cations occur as Fe 2+ in the glass, four-coordinated Fe 3+ constitutes ∼93% of the total Fe cations. However, iron in the crystal, which exhibits a paramagnetic behavior, is solely present as six-coordinated Fe 3+ . The magnetic and vibrational properties of the glass and crystal are discussed to provide additional insight into the structure.

Cobalt-chromium ferrite, CoCr x Fe 2- x O₄ ( x = 0 ⁻ 1.2), has been synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD) indicates that samples calcined at 800 °C for 3 h were a single-cubic phase. The lattice parameter decreased with increasing Cr concentration. Scanning electron microscopy (SEM) confirmed that the sample powders were nanoparticles. It was confirmed from the room temperature Mössbauer spectra that transition from the ferrimagnetic state to the superparamagnetic state occurred with the doping of chromium. Both the saturation magnetization and the coercivity decreased with the chromium doping. With a higher annealing temperature, the saturation magnetization increased and the coercivity increased initially and then decreased for CoCr 0.2 Fe 1.8 O₄.

Zinc ion-substituted cobalt ferrite powders Co 1- x Zn x Fe₂O₄ ( x = 0⁻0.7) were prepared by the sol-gel auto-combustion process. The structural properties and magnetic of the samples were investigated with X-ray diffraction (XRD), superconducting quantum interference device, and a Mössbauer spectrometer. The results of XRD showed that the powder of a single cubic phase of ferrites calcined when kept at 800 °C for 3 h. The lattice constant increases with increase in Zn concentration, but average crystallite size does not decrease constantly by increasing the zinc content, which is related to pH value. It was confirmed that the transition from ferrimagnetic to superparamagnetic behaviour depends on increasing zinc concentration by Mössbauer spectra at room temperature. Magnetization at room temperature increases for x ≤ 0.3, but decreases for increasing Zn 2+ ions. The magnetization of Co 0.7 Zn 0.3 Fe₂O₄ reached maximum value (83.51 emu/g). The coercivity decreased with Zn 2+ ions, which were doped on account of the decrease of the anisotropy constant.

A sol-gel autocombustion method was used to synthesize Al 3+ ion-substituted cobalt ferrite CoAl x Fe 2- x O₄ ( x = 0⁻1.5). According to X-ray diffraction analysis (XRD), cobalt ferrite was in a single cubic phase after being calcined at 1000 °C for 3 h. Moreover, the lattice constant decreased with increase in aluminum substituents. When the sample was analyzed by Scanning Electron Microscopy (SEM), we found that uniformly sized, well-crystallized grains were distributed in the sample. Furthermore, we confirmed that Al 3+ ion-substituted cobalt ferrite underwent a transition from ferrimagnetic to superparamagnetic behavior; the superparamagnetic behavior was completely correlated with the increase in Al 3+ ion concentration at room temperature. All these findings were observed in Mössbauer spectra. For the cobalt ferrite CoAl x Fe 2- x O₄, the coercivity and saturation magnetization decrease with an increase in aluminum content. When the annealing temperature of CoAl 0.1 Fe 1.9 O₄ was steadily increased, the coercivity and saturation magnetization initially increased and then decreased.

The synchrotron radiation technique of nuclear resonant inelastic X-ray scattering (NRIXS), also known as nuclear resonance vibrational spectroscopy or nuclear inelastic scattering, provides a wealth of information on the vibrational properties of solids. It has found applications in studies of lattice dynamics and elasticity, superconductivity, heme biochemistry, seismology, isotope geochemistry and many other fields. It involves probing the vibrational modes of solids by using the nuclear resonance of Mössbauer isotopes such as 57 Fe, 83 Kr, 119 Sn, 151 Eu and 161 Dy. After data reduction, it provides the partial phonon density of states of the Mössbauer isotope that is investigated, as well as many other derived quantities such as the mean force constant of the chemical bonds and the Debye velocity. The data reduction is, however, not straightforward and involves removal of the elastic peak, normalization and Fourier-Log transformation. Furthermore, some of the quantities derived are highly sensitive to details in the baseline correction. A software package and several novel procedures to streamline and hopefully improve the reduction of the NRIXS data generated at sector 3ID of the Advanced Photon Source have been developed. The graphical user interface software is named SciPhon and runs as a Mathematica package. It is easily portable to other platforms and can be easily adapted for reducing data generated at other beamlines. Several tests and comparisons are presented that demonstrate the usefulness of this software, whose results have already been used in several publications. Here, the SciPhon software is used to reduce Kr, Sn, Eu and Dy NRIXS data, and potential implications for interpreting natural isotopic variations in those systems are discussed., (open access.)

The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu 2 + and Eu 3 + ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between - 12 and - 15 mm/s for Eu 2 + compared to around 0 mm/s for Eu 3 + . Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu⁻X bond length.

Ferritins are ubiquitous and conserved proteins endowed with enzymatic ferroxidase activity, that oxidize Fe(II) ions at the dimetal ferroxidase centre to form a mineralized Fe(III) oxide core deposited within the apo-protein shell. Herein, the in vitro formation of a heterodimetal cofactor constituted by Fe and Mn ions has been investigated in human H ferritin (hHFt). Namely, Mn and Fe binding at the hHFt ferroxidase centre and its effects on Fe(II) oxidation have been investigated by UV-Vis ferroxidation kinetics, fluorimetric titrations, multifrequency EPR, and preliminary Mössbauer spectroscopy. Our results show that in hHFt, both Fe(II) and Mn(II) bind the ferroxidase centre forming a Fe-Mn cofactor. Moreover, molecular oxygen seems to favour Mn(II) binding and increases the ferroxidation activity of the Mn-loaded protein. The data suggest that Mn influences the Fe binding and the efficiency of the ferroxidation reaction. The higher efficiency of the Mn-Fe heterometallic centre may have a physiological relevance in specific cell types (i.e. glia cells), where the concentration of Mn is the same order of magnitude as iron., (Copyright © 2018 Elsevier Inc. All rights reserved.)

An easy, low-cost, repeatable seed-mediated growth approach in solvothermal condition has been proposed to synthesize bimagnetic spinel ferrite core-shell heterostructures in the 10-20 nm particle size range. Cobalt ferrite and manganese ferrite nanoparticles (CoFe 2 O 4 and MnFe 2 O 4 ) have been coated with isostructural spinel ferrites like maghemite/magnetite, MnFe 2 O 4 , and CoFe 2 O 4 with similar cell parameters to create different heterostructures. The conventional study of the structure, morphology, and composition has been combined with advanced techniques in order to achieve details on the interface at the nanoscale level. Clear evidence of the heterostructure formation have been obtained (i) indirectly by comparing the 57 Fe Mössbauer spectra of the core-shell samples and an ad hoc mechanical mixture and (ii) directly by mapping the nanoparticles' chemical composition by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscopy mode (STEM). In addition, chemical-sensitive electron tomography in STEM-EDX mode has been applied in order to obtain detailed 3D images with a sub-nanometer spatial resolution.

Isotope effects of four broad and overlapping categories have been applied to the study of the mechanisms of chemical reaction and regulation of nonheme diiron cluster-containing oxygenases. The categories are: (a) mass properties that allow substrate-to-product conversions to be tracked, (b) atomic properties that allow specialized spectroscopies, (c) mass properties that impact primarily vibrational spectroscopies, and (d) bond dissociation energy shifts that permit dynamic isotope effect studies of many types. The application of these categories of isotope effects is illustrated using the soluble methane monooxygenase system and CmlI, which catalyzes the multistep arylamine to arylnitro conversion in the biosynthetic pathway for chloramphenicol., (© 2017 Elsevier Inc. All rights reserved.)

Wetlands mitigate the migration of groundwater contaminants through a series of biogeochemical gradients that enhance multiple contaminant-binding processes. The hypothesis of this study was that wetland plant roots contribute organic carbon and release O2 within the rhizosphere (plant-impact soil zone) that promote the formation of Fe(III)-(oxyhydr)oxides. In turn, these Fe(III)-(oxyhydr)oxides stabilize organic matter that together contribute to contaminant immobilization. Mineralogy and U binding environments of the rhizosphere were evaluated in samples collected from contaminated and non-contaminated areas of a wetland on the Savannah River Site in South Carolina. Based on Mössbauer spectroscopy, rhizosphere soil was greatly enriched with nanogoethite, ferrihydrite-like nanoparticulates, and hematite, with negligible Fe(II) present. X-ray computed tomography and various microscopy techniques showed that root plaques were tens-of-microns thick and consisted of highly oriented Fe-nanoparticles, suggesting that the roots were involved in creating the biogeochemical conditions conducive to the nanoparticle formation. XAS showed that a majority of the U in the bulk wetland soil was in the +6 oxidation state and was not well correlated spatially to Fe concentrations. SEM/EDS confirm that U was enriched on root plaques, where it was always found in association with P. Together these findings support our hypothesis and suggest that plants can alter mineralogical conditions that may be conducive to contaminant immobilization in wetlands., (Copyright © 2016 Elsevier B.V. All rights reserved.)

We have applied 57 Fe nuclear resonance vibrational spectroscopy (NRVS) for the first time to study the dynamics of Fe centers in Fe-S protein crystals, including oxidized wild type rubredoxin crystals from Pyrococcus furiosus , and the MoFe protein of nitrogenase from Azotobacter vinelandii . Thanks to the NRVS selection rule, selectively probed vibrational modes have been observed in both oriented rubredoxin and MoFe protein crystals. The NRVS work was complemented by extended X-ray absorption fine structure spectroscopy (EXAFS) measurements on oxidized wild type rubredoxin crystals from Pyrococcus furiosus . The EXAFS spectra revealed the Fe-S bond length difference in oxidized Pf Rd protein, which is qualitatively consistent with the X-ray crystal structure.

Aldehyde-deformylating oxygenase (ADO) catalyzes O 2 -dependent release of the terminal carbon of a biological substrate, octadecanal, to yield formate and heptadecane in a reaction that requires external reducing equivalents. We show here that ADO also catalyzes incorporation of an oxygen atom from O 2 into the alkane product to yield alcohol and aldehyde products. Oxygenation of the alkane product is much more pronounced with C 9-10 aldehyde substrates, so that use of nonanal as the substrate yields similar amounts of octane, octanal, and octanol products. When using doubly-labeled [1,2- 13 C]-octanal as the substrate, the heptane, heptanal and heptanol products each contained a single 13 C-label in the C-1 carbons atoms. The only one-carbon product identified was formate. [ 18 O]-O 2 incorporation studies demonstrated formation of [ 18 O]-alcohol product, but rapid solvent exchange prevented similar determination for the aldehyde product. Addition of [1- 13 C]-nonanol with decanal as the substrate at the outset of the reaction resulted in formation of [1- 13 C]-nonanal. No 13 C-product was formed in the absence of decanal. ADO contains an oxygen-bridged dinuclear iron cluster. The observation of alcohol and aldehyde products derived from the initially formed alkane product suggests a reactive species similar to that formed by methane monooxygenase (MMO) and other members of the bacterial multicomponent monooxygenase family. Accordingly, characterization by EPR and Mössbauer spectroscopies shows that the electronic structure of the ADO cluster is similar, but not identical, to that of MMO hydroxylase component. In particular, the two irons of ADO reside in nearly identical environments in both the oxidized and fully reduced states, whereas those of MMOH show distinct differences. These favorable characteristics of the iron sites allow a comprehensive determination of the spin Hamiltonian parameters describing the electronic state of the diferrous cluster for the first time for any biological system. The nature of the diiron cluster and the newly recognized products from ADO catalysis hold implications for the mechanism of C-C bond cleavage.

We overexpressed human mitochondrial ferritin in frataxin-deficient yeast cells (Δyfh1), but also in another mutant affected in [Fe-S] assembly (Δggc1). Ferritin was correctly processed and expressed in the mitochondria of these cells, but the fraction of total mitochondrial iron bound to ferritin was very low, and most of the iron remained in the form of insoluble particles of ferric phosphate in these mitochondria, as evidenced by gel filtration analysis of the mitochondrial matrix (fast protein liquid chromatography [FPLC]) and by Mössbauer spectroscopy. Mutant cells in which ferritin was overexpressed still accumulated iron in the mitochondria and remained deficient in [Fe-S] assembly, suggesting that human mitochondrial ferritin is not a functional homologue of yeast frataxin. However, the respiratory function was improved in these mutants, which correlates with an improvement of cytochrome and heme synthesis. Overexpression of mitochondrial ferritin in [Fe-S] mutants resulted in the appearance of a small pool of high-spin ferrous iron in the mitochondria, which was probably responsible for the improvement of heme synthesis and of the respiratory function in these mutants.

Extensive mats of Fe oxyhydroxides and associated Fe-oxidizing microbial organisms form in diverse geochemical settings - freshwater seeps to deep-sea vents - where ever opposing Fe(II)-oxygen gradients prevail. The mineralogy, reactivity, and structural transformations of Fe oxyhydroxides precipitated from submarine hydrothermal fluids within microbial mats remains elusive in active and fossil systems. In response, a study of Fe microbial mat formation at the Loihi Seamount was conducted to describe the physical and chemical characteristics of Fe-phases using extended X-ray absorption fine structure spectroscopy, powder X-ray diffraction, synchrotron radiation X-ray total scattering, low-temperature magnetic measurements, and Mössbauer spectroscopy. Particle sizes of 3.5-4.6 nm were estimated from magnetism data, and coherent scattering domain (CSD) sizes as small as 1.6 nm are indicated by pair distribution function (PDF) analysis. Disorder in the nanostructured Fe-bearing phases results in limited intermediate-range structural order: less than that of standard two-line ferrihydrite (Fh), except for the Pohaku site. The short-range ordered natural Fh (Fh(SRO)) phases were stable at 4°C in the presence of oxygen for at least 1 year and during 400°C treatment. The observed stability of the Fh(SRO) is consistent with magnetic observations that point to non-interacting nanoparticles. PDF analyses of total scattering data provide further evidence for Fh(SRO) particles with a poorly ordered silica coating. The presence of coated particles explains the small CSD for the mat minerals, as well as the stability of the minerals over time and against heating. The mineral properties observed here provide a starting point from which progressively older and more extensively altered Fe deposits may be examined, with the ultimate goal of improved interpretation of past biogeochemical conditions and diagenetic processes.

Four (57)Fe-labeled tetrachloroferrates(III) of organic cations (1-butyl-3-methylimidazolium, 1-allyl-3-methylimidazolium, 1-methyl-1-propylpyrrolidinium, tetraphenylphosphonium) were examined by temperature-dependent Mössbauer spectroscopy. The hyperfine and dynamic parameters of the iron(III) site were determined. Single crystal X-ray diffraction data of [Ph(4)P][FeCl(4)] were collected at four temperatures (295, 223, 173, and 123 K), and the dynamics of the iron atom inferred from the Mössbauer data and the single crystal U(i,j) parameters have been compared.