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Iron-sulfur (FeS) proteins are ancient and fundamental to life, being involved in electron transfer and CO 2 fixation. FeS clusters have structures similar to the unit-cell of FeS minerals such as greigite, found in hydrothermal systems linked with the origin of life. However, the prebiotic pathway from mineral surfaces to biological clusters is unknown. Here we show that FeS clusters form spontaneously through interactions of inorganic Fe 2+ /Fe 3+ and S 2− with micromolar concentrations of the amino acid cysteine in water at alkaline pH. Bicarbonate ions stabilize the clusters and even promote cluster formation alone at concentrations >10 mM, probably through salting-out effects. We demonstrate robust, concentration-dependent formation of [4Fe4S], [2Fe2S] and mononuclear iron clusters using UV-Vis spectroscopy, 57 Fe-Mössbauer spectroscopy and 1 H-NMR. Cyclic voltammetry shows that the clusters are redox-active. Our findings reveal that the structures responsible for biological electron transfer and CO 2 reduction could have formed spontaneously from monomers at the origin of life. Iron-sulfur (FeS) proteins are involved in electron transfer and CO 2 fixation. Here, the authors show that FeS clusters can form spontaneously in the presence of the amino acid cysteine, in conditions similar those expected in Hadean alkaline hydrothermal vents, suggesting a plausible mechanism of their emergence at the origin of life.

Banded iron formations (BIFs), significant iron ore deposits formed approximately 2.3 billion years ago under low-oxygen conditions, have recently gained attention as potential geological sources for evaluating hydrogen (H₂) production. BIFs are characterized by high concentrations of iron oxide (20 to 40 wt.%) and low Fe 3 ⁺/Fe tot ratios, representing a major source of ferrous iron on Earth. This study investigates the mineralogical and geochemical characteristics of iron ore samples from the Wugang and Hengyang BIFs in China using X-ray diffraction (XRD) and Mössbauer spectroscopy to examine H 2 generation potential. XRD analysis and microscopic observations showed that the magnetite and hematite are the primary ore minerals in BIFs in China Craton. Mössbauer spectroscopic results provided the quantified information on the fractions of each iron species in varying minerals. Particularly, the Fe 3+ tetrahedral sites and octahedral sites occupied by both Fe 2+ and Fe 3+ in magnetite and Fe 3+ octahedral sites in hematite were determined. We estimated H₂ production potential by calculating the relative fraction of Fe 2+ in magnetite relative to total number of iron atoms in the bulk samples from the Mössbauer results. The pyroxene-bearing BIF in Wugang (P-BIF) contains magnetite predominantly (~30.4 wt%), and the fraction of Fe 2+ in magnetite is ~26%. Based on the quantified values, the maximum potential for H 2 generation from P-BIF in Wugang could be ~630 mmol H₂/kg rock. Due to the variation of mineralogical composition depending on the types and locations of occurrence of BIF, the H 2 generation potential also varies. For example, contrast to P-BIF in Wugang, the hematite-rich BIF from Hengyang, containing ~6.0 wt% of magnetite, showed significantly lower Fe 2+ fraction in magnetite (~5%), resulting in low H 2 potential (~120 mmol H₂/kg rock). This study presents that a prevalence of magnetite in BIFs has considerable potential for H₂ production due to low Fe 3+ /Fe tot , suggesting that the magnetite-rich iron ore can be effectively utilized as the source of stimulated hydrogen production. The current results also highlight that the Mössbauer spectroscopy is essential to provide the database of relative fractions for each iron species in BIFs, which allows us to estimate the quantity of H 2 released from BIFs.

While X-ray diffraction (XRD) is a commonly used method for quantification analysis using Rietveld refinement and quantitative Mössbauer spectroscopy is sporadically used primarily for iron speciation, laboratory X-ray Absorption Fine Structure Spectroscopy (lab-XAFS) is rarely applied for the quantitative determination of sample compositions. With the recent developments of laboratory-based XAFS spectrometers, this method becomes more interesting for many applications as well as for quantification. The goal of this study is to compare quantitative lab-XAFS via Linear Combination Fitting (LCF) of reference spectra with XRD and Mössbauer spectroscopy. Iron species analysis with the focus on the determination of the mass ratio alpha-iron(III) oxide (α-Fe 2 O 3 )/iron(II, III) oxide (Fe 3 O 4 ) was used as an example. The examinations were performed on synthetic α-Fe 2 O 3 /Fe 3 O 4 model mixtures and, predominantly, on a natural iron ore sample mainly consisting of the minerals hematite and magnetite, thus, these two iron oxides. For the iron K-edge lab-XAFS measurements an X-ray tube-based spectrometer using the von Hamos geometry with Highly Annealed Pyrolytic Graphite (HAPG) mosaic crystal optic was used. The capabilities and challenges of each method are discussed. The quantitative model mixtures examinations by lab-XAFS show results and accuracies similar to those obtained by XRD and Mössbauer spectroscopy. However, while the quantitative results for the iron ore investigations by lab-XAFS are in good agreement (deviation of 2 percent points) with the XRD results, the composition determined by Mössbauer spectroscopy differs clearly from the lab-XAFS and XRD results. Furthermore, the Mössbauer spectroscopic examinations hint the presence of an additional iron oxide species affecting the quantification. Besides the still common challenges in identification, differentiation and quantification of different iron oxides, the results show that quantitative lab-XAFS can particularly compete with quantitative XRD when determining the species composition of one element. This makes lab-XAFS particularly well-suited for routine analytics.

Iron artifacts undergo complex corrosion processes, depending on the burial environment. Understanding the formation mechanism of corrosion products is crucial for preservation of artifacts and helps design strategies for future iron artifacts protection. Mössbauer spectroscopy was primarily utilized in this work to analyze the corrosion products formed on iron artifacts. The corrosion products were identified as consisting of goethite, lepidocrocite, magnetite, and maghemite. Low-temperature Mössbauer spectroscopy was performed for the accurate identification and quantitative analysis of superparamagnetic iron corrosion products. The results indicated that the surface corrosion products mainly consist of goethite and superparamagnetic goethite, with small amounts of lepidocrocite, magnetite, and/or maghemite. A cross-sectional analysis of the corrosion layers on an artifact was performed to better understand the corrosion products and their formation mechanisms. The products formed in different sections (metal, intermediate, and surface) of the corrosion layers on the iron artifact were identified, and a corrosion mechanism was proposed. The intermediate layer adjacent to the metal contains magnetite, maghemite, and lepidocrocite. The results presented in this study provide a deeper understanding of the iron corrosion process, laying a solid foundation for the development of an effective strategy for preserving iron artifacts.

Synthetic iron-sulfur cubanes are models for biological cofactors, which are essential to delineate oxidation states in the more complex enzymatic systems. However, a complete series of [Fe₄S₄]ⁿ complexes spanning all redox states accessible by 1-electron transformations of the individual iron atoms (n = 0–4+) has never been prepared, deterring the methodical comparison of structure and spectroscopic signature. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-visible electronic absorption, variable-temperature X-ray diffraction analysis, and cyclic voltammetry reveals key trends for the geometry of the Fe₄S₄ core as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S = 4 electronic ground state of the most reduced member of the series, [Fe₄S₄]⁰, and provide electrochemical evidence that it is accessible within 0.82 V from the [Fe₄S₄]2+ state, highlighting its relevance as a mimic of the nitrogenase iron protein cluster.

In this work, CoCrFeNiNb x (x = 0.25, 0.45 and 0.65) high entropy alloys were prepared by two different methods to determine the effect of cooling rate and the niobium content on the structure and properties of ingots and plates. The structure was investigated extensively using X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. The results confirmed the dual-phase structure, consisting of the FCC solid solution and the Laves phase. The increase in niobium content changed the microstructure from hypoeutectic (x = 0.25 and 0.45) to hypereutectic (x = 0.65). The high cooling rate during solidification from the liquid state enabled the formation of ultrafine eutectic structures with an average lamellae thickness of only 130 ± 9 nm in the CoCrFeNiNb 0.65 plate. The corrosion behaviour of the alloys was studied in solutions of 3.5% NaCl and 3.5% NaCl + H 3 BO 3 . The beneficial effect of increasing the niobium content in as-cast CoCrFeNiNb x alloys on the corrosion resistance was confirmed in both environments. Furthermore, the alloys solidified with a higher cooling rate exhibited a lower corrosion susceptibility in the 3.5% NaCl solution. The results of the EIS study indicated that a higher content of niobium contributed to the formation of a more stable and compact passivation layer. The hardness of the CoCrFeNiNb x alloys increased with a higher niobium content, achieving the highest value of 669 HV 1 for the CoCrFeNiNb 0.65 plate. The increase in the cooling rate positively affected the tribological properties of the CoCrFeNiNb x alloys, contributing to the decrease in the friction coefficient for the CoCrFeNiNb 0.25 and CoCrFeNiNb 0.45 plates.

Prussian blue analogues (PBAs), A x M [ M ′ ( CN ) 6 ] 1 - y · z H 2 O , are a highly functional class of materials with use in a broad range of applications, such as energy storage, due to their porous structure and tunable composition. The porosity is particularly important for the properties and is deeply coupled to the cation, water, and [ M ′ ( CN ) 6 ] n - vacancy content. Determining internal porosity is especially challenging because the three compositional parameters are dependent on each other. In this work, we apply a new method, positron annihilation lifetime spectroscopy (PALS), which can be employed for the characterization of defects and structural changes in crystalline materials. Four samples were prepared to evaluate the method’s ability to detect changes in internal porosity as a function of the cation, water, and [ M ′ ( CN ) 6 ] n - vacancy content. Three of the samples have identical [ M ′ ( CN ) 6 ] n - vacancy content and gradually decreasing sodium and water content, while one sample has no sodium and 25% [ M ′ ( CN ) 6 ] n - vacancies. The samples were thoroughly characterized using inductively coupled plasma-optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Mössbauer spectroscopy as well as applying the PALS method. Mössbauer spectroscopy, XRD, and TGA analysis revealed the sample compositions Na 1.8 ( 2 ) Fe 0.64 ( 6 ) 2 + Fe 0.36 ( 10 ) 2.6 + [ Fe 2 + ( CN ) 6 ] · 2.09 ( 2 ) H 2 O , Na 1.1 ( 2 ) Fe 0.24 ( 6 ) 2 + Fe 0.76 ( 6 ) 2.8 + [ Fe 2.3 + ( CN ) 6 ] · 1.57 ( 1 ) H 2 O , Fe [ Fe ( CN ) 6 ] · 0.807(9) H 2 O , and Fe [ Fe ( CN ) 6 ] 0.75 · 1.5 H 2 O , confirming the absence of vacancies in the three main samples. It was shown that the final composition of PBAs could only be unambiguously confirmed through the combination of ICP, XRD, TGA, and Mössbauer spectroscopy. Two positron lifetimes of 205 and 405 ps were observed with the 205 ps lifetime being independent of the sodium, water, and/or [ Fe ( CN ) 6 ] n - vacancy content, while the lifetime around 405 ps changes with varying sodium and water content. However, the origin and nature of the 405 ps lifetime yet remains unclear. The method shows promise for characterizing changes in the internal porosity in PBAs as a function of the composition and further development work needs to be carried out to ensure the applicability to PBAs generally. Graphical abstract

LaFeO3 perovskite ceramics have been prepared via reaction flash technique using Fe2O3 and La2O3 as precursors. The obtained pellets have been investigated using several techniques. The formation of LaFeO3 has been clearly confirmed by X-ray diffraction. The scanning electron microscopy micrographs have shown the microporous character of the obtained pellets due to the low temperature and dwell time used in the synthesis process (10 min at 1173 K). The orthorhombic-rhombohedral phase transition has been observed at approximately 1273 K in differential thermal analysis measurements, which also allows us to determine the Néel temperature at 742 K. The fitted Mössbauer spectra exposed the presence of a single sextet ascribed to the Fe+3 ions in the tetrahedral site. Finally, magnetic measurements at room temperature indicate the antiferromagnetic character of the sample.

The surface segregation process and its influence on high-temperature corrosion of five alloys—Fe0.95Al0.05, Fe0.95V0.05, Fe0.90Al0.05V0.05, Fe0.95Ti0.05 and Fe0.95Ge0.05—were studied using X-ray photoelectron spectroscopy (XPS) and 57Fe Transmission Mössbauer Spectroscopy (TMS). To prepare the alloys with the highest surface concentration of solutes, the samples were annealed at elevated temperatures to induce the surface segregation process. After that, they were exposed to air at 870 K for 1 and 5 h. It was found that the Fe0.95Ti0.05 sample annealed at 1073 K had much better anti–corrosion properties than other alloys studied. This finding can be correlated with the extremely high concentration of titanium on the surface, which was more than four times that of iron. In contrast to other alloys studied in this work, the passive layer formed on the surface of Fe0.95Ti0.05 greatly enhanced its resistance to corrosion.

Mössbauer parameters of low-spin six-coordinate [Fe(II)(Por)L 2 ] complexes (where Por is a synthetic porphyrin; L is a nitrogenous aliphatic, an aromatic base or a heterocyclic ligand, a P-bonding ligand, CO or CN) and low-spin [Fe(Por)LX] complexes (where L and X are different ligands) are reported. A known point charge calculation approach was extended to investigate how the axial ligands and the four porphyrinato-N atoms generate the observed quadrupole splittings ( Δ E Q ) for the complexes. Partial quadrupole splitting (p.q.s.) and partial chemical shifts (p.c.s.) values were derived for all the axial ligands, and porphyrins reported in the literature. The values for each porphyrin are different emphasising the importance/uniqueness of the [Fe(PPIX)] moiety, (which is ubiquitous in nature). This new analysis enabled the construction of figures relating p.c.s and p.q.s values. The relationships presented in the figures indicates that strong field ligands such as CO can, and do change the sign of the electric field gradient in the [Fe(II)(Por)L 2 ] complexes. The limiting p.q.s. value a ligand can have and still form a six-coordinate low-spin [Fe(II)(Por)L 2 ] complex is established. It is shown that the control the porphyrin ligands exert on the low-spin Fe(II) atom limits its bonding to a defined range of axial ligands; outside this range the spin state of the iron is unstable and five-coordinate high-spin complexes are favoured. Amongst many conclusions, it was found that oxygen cannot form a stable low-spin [Fe(II)(Por)L(O 2 )] complex and that oxy-haemoglobin is best described as an [Fe(III)(Por)L(O 2 − )] complex, the iron is ferric bound to the superoxide molecule. Graphical abstract