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The high-pressure melting curve of FeO controls key aspects of Earth’s deep interior and the evolution of rocky planets more broadly. However, existing melting studies on wüstite were conducted across a limited pressure range and exhibit substantial disagreement. Here we use an in-situ dual-technique approach that combines a suite of >1000 x-ray diffraction and synchrotron Mössbauer measurements to report the melting curve for Fe 1- x O wüstite to pressures of Earth’s lowermost mantle. We further observe features in the data suggesting an order-disorder transition in the iron defect structure several hundred kelvin below melting. This solid-solid transition, suggested by decades of ambient pressure research, is detected across the full pressure range of the study (30 to 140 GPa). At 136 GPa, our results constrain a relatively high melting temperature of 4140 ± 110 K, which falls above recent temperature estimates for Earth’s present-day core-mantle boundary and supports the viability of solid FeO-rich structures at the roots of mantle plumes. The coincidence of the defect order-disorder transition with pressure-temperature conditions of Earth’s mantle base raises broad questions about its possible influence on key physical properties of the region, including rheology and conductivity. Multi-technique synchrotron measurements support the viability of solid FeO-rich structures at Earth’s mantle base. An order-disorder transition identified in the iron defect structure of FeO may lead to unique physical properties in the region.

The +0.1‰ elevated 56 Fe/ 54 Fe ratio of terrestrial basalts relative to chondrites was proposed to be a fingerprint of core-mantle segregation. However, the extent of iron isotopic fractionation between molten metal and silicate under high pressure–temperature conditions is poorly known. Here we show that iron forms chemical bonds of similar strengths in basaltic glasses and iron-rich alloys, even at high pressure. From the measured mean force constants of iron bonds, we calculate an equilibrium iron isotope fractionation between silicate and iron under core formation conditions in Earth of ∼0–0.02‰, which is small relative to the +0.1‰ shift of terrestrial basalts. This result is unaffected by small amounts of nickel and candidate core-forming light elements, as the isotopic shifts associated with such alloying are small. This study suggests that the variability in iron isotopic composition in planetary objects cannot be due to core formation. Terrestrial basalts have a unique iron isotopic signature taken as fingerprints of core formation. Here, high pressure studies show that force constants of iron bonds increase with pressure similarly for silicate and metals suggesting interplanetary isotopic variability is not due to core formation.

SignificanceSeismic studies revealed that shear wave (S wave) travels through the inner core at an anomalously low speed, thus challenging the notion of its solidity. Here we show that for the candidate inner core component Fe7C3, shear softening associated with a pressure-induced spin-pairing transition leads to exceptionally low S-wave velocity (vS) in its low-spin and nonmagnetic phase. An Fe7C3-dominant inner core would match seismic observations and imply a major carbon reservoir in Earth’s deepest interior. Earth’s inner core is known to consist of crystalline iron alloyed with a small amount of nickel and lighter elements, but the shear wave (S wave) travels through the inner core at about half the speed expected for most iron-rich alloys under relevant pressures. The anomalously low S-wave velocity (vS) has been attributed to the presence of liquid, hence questioning the solidity of the inner core. Here we report new experimental data up to core pressures on iron carbide Fe7C3, a candidate component of the inner core, showing that its sound velocities dropped significantly near the end of a pressure-induced spin-pairing transition, which took place gradually between 10 GPa and 53 GPa. Following the transition, the sound velocities increased with density at an exceptionally low rate. Extrapolating the data to the inner core pressure and accounting for the temperature effect, we found that low-spin Fe7C3 can reproduce the observed vS of the inner core, thus eliminating the need to invoke partial melting or a postulated large temperature effect. The model of a carbon-rich inner core may be consistent with existing constraints on the Earth's carbon budget and would imply that as much as two thirds of the planet's carbon is hidden in its center sphere.

The spin state transition from low spin to high spin upon substrate addition is one of the key steps in cytochrome P450 catalysis. External perturbations such as pH and hydrogen bonding can also trigger the spin state transition of hemes through deprotonated histidine (e.g. Cytochrome c ). In this work, we report the isolated 2-methylimidazole Cobalt(II) [Co(TPP)(2-MeHIm)] and [Co(TTP)(2-MeHIm)], and the corresponding 2-methylimidazolate derivatives where the N−H proton of axial 2-MeHIm is removed. Interestingly, various spectroscopies including EPR and XAFS determine a high-spin state ( S  = 3/2) for the imidazolate derivatives, in contrast to the low-spin state ( S  = 1/2) of all known imidazole analogs. DFT assisted stereoelectronic investigations are applied to understand the metal-ligand interactions, which suggest that the dramatically displaced metal center allowing a promotion e g (d π ) →  b 1g ( d x 2 - y 2 ) is crucial for the occurrence of the spin state transition. Studying the electronic structures and spin transitions of synthetic heme analogs is crucial to advancing our understanding of heme enzyme mechanisms. Here the authors show that a Co(II) porphyrin complex undergoes an unexpected spin state transition upon deprotonation of its axial imidazole ligand.

The Martian mantle is considered to have a higher Fe/Mg ratio than the Earth's mantle. Ringwoodite, γ‐(Mg,Fe)2SiO4, is likely the dominant polymorph of olivine in the core‐mantle boundary (CMB) region of Mars. We synthesized anhydrous iron‐rich ringwoodite with molar Mg/(Mg + Fe) = 0.44 and determined its thermal equation of state up to 35 GPa and 750 K by synchrotron X‐ray diffraction. Using a third order Birch‐Murnaghan equation of state, we obtain KT0 = 182 (3) GPa, K′ = 4.6 (2), and α0 = 3.18 (6) × 10−5 K−1. Using these results and an updated mineralogical model with an iron‐rich composition of Mg/(Mg + Fe) = 0.75 for the Martian mantle, we estimate ∼1900 K for the temperature of the D1000 seismic discontinuity inside Mars. The resulting adiabat predicts a warm aerotherm, which could explain the presence of partial melt at the CMB of Mars recently detected with seismic data from the 2019 InSight mission. Plain Language Summary Ringwoodite is an abundant silicate mineral inside Earth and Mars, which can incorporate variable amounts of magnesium, iron and water. Mars is thought to be more iron rich and dry compared with Earth, and so Martian ringwoodite is expected to be anhydrous and have elevated Fe/Mg. We synthesized dry, iron‐rich ringwoodite at the pressure‐temperature conditions of the Martian interior, and then determined its density and compressibility at high temperatures and pressures of the Martian mantle. The results are used to predict the temperature inside Mars by anchoring our measured physical properties to an observed seismic discontinuity at 1,000 km depth. With that, we calculated a temperature curve for inside Mars that may explain why seismic data from the InSight mission show the possibility of partial melt at the base of the Martian mantle. Key Points Iron has little effect on the thermoelastic properties of anhydrous ringwoodite The temperature of the D1000 discontinuity in the mantle of Mars is estimated to be 1,900 K An updated mineralogical model for the Martian mantle is presented

The Advanced Photon Source (APS) has been upgraded with a multi‐bend achromat lattice, achieving significantly reduced electron beam emittance and enhanced X‐ray coherence. Precise characterization of these properties is essential for optimizing beamline performance and enabling new experiments that take full advantage of the upgraded source. We report on measurements of source size and transverse coherence properties using grating interferometry at two beamlines: the APS 3‐ID‐B undulator beamline and the 1‐BM‐B bending magnet beamline. The results confirm the world‐record horizontal emittance of the upgraded APS below 30 pm rad and validate the theoretical design parameters. We further investigate the impact of optical aberrations and mechanical vibrations at the 12‐ID‐C beamline on coherence preservation. These measurements establish a benchmark for future beamline enhancements and demonstrate the effectiveness of grating interferometry for high‐precision beam characterization. Our findings provide critical insights into synchrotron beam dynamics, coherence degradation mechanisms, and strategies for optimizing beamline X‐ray optics at next‐generation light sources. This study presents source emittance and beam coherence measurements at the upgraded Advanced Photon Source using grating interferometry. The results confirm world‐record emittance values, validate design parameters, and offer key insights into coherence preservation and beamline optimization.

The increase in superconducting transition temperature (T C ) of Sn nanostructures in comparison to bulk, was studied. Changes in the phonon density of states (PDOS) of the weakly coupled superconductor Sn were analyzed and correlated with the increase in T C measured by magnetometry. The PDOS of all nanostructured samples shows a slightly increased number of low-energy phonon modes and a strong decrease in the number of high-energy phonon modes in comparison to the bulk Sn PDOS. The phonon densities of states, which were determined previously using nuclear resonant inelastic X-ray scattering, were used to calculate the superconducting transition temperature using the Allen-Dynes-McMillan (ADMM) formalism. Both the calculated as well as the experimentally determined values of T C show an increase compared to the bulk superconducting transition temperature. The good agreement between these values indicates that phonon softening has a major influence on the superconducting transition temperature of Sn nanostructures. The influence of electron confinement effects appears to be minor in these systems.

Synchrotron-based nuclear resonance vibrational spectroscopy is used to characterize the reactive Fe( iv )=O intermediate of the halogenase SyrB2; the substrate directs the orientation of this intermediate, presenting specific frontier molecular orbitals that can activate the selective halogenation. Structure of a halogenase SyrB2 reactive intermediate A key reactive intermediate in the oxidative reactions catalysed by mononuclear non-haem iron (NHFe) enzymes is the high-spin species S = 2 Fe( IV ) = O. In this manuscript the authors use synchrotron-based nuclear resonance vibrational spectroscopy (NRVS), a sensitive method that defines the dependence of the vibrational modes of Fe on the nature of the Fe( IV ) = O active site, to determine the structure of the reactive intermediate of the halogenase SyrB2 from the plant pathogen Pseudomonas syringae . This intermediate reacts via an initial hydrogen-atom abstraction step, with its subsequent halogenation (native) or hydroxylation (non-native) rebound reactivity being dependent on the substrate. The substrate directs the orientation of the oxo intermediate, presenting specific frontier molecular orbitals that can activate the selective halogenation versus hydroxylation reactivity. Mononuclear non-haem iron (NHFe) enzymes catalyse a broad range of oxidative reactions, including halogenation, hydroxylation, ring closure, desaturation and aromatic ring cleavage reactions. They are involved in a number of biological processes, including phenylalanine metabolism, the production of neurotransmitters, the hypoxic response and the biosynthesis of secondary metabolites 1 , 2 , 3 . The reactive intermediate in the catalytic cycles of these enzymes is a high-spin S = 2 Fe( iv )=O species, which has been trapped for a number of NHFe enzymes 4 , 5 , 6 , 7 , 8 , including the halogenase SyrB2 (syringomycin biosynthesis enzyme 2). Computational studies aimed at understanding the reactivity of this Fe( iv )=O intermediate 9 , 10 , 11 , 12 , 13 are limited in applicability owing to the paucity of experimental knowledge about its geometric and electronic structure. Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) is a sensitive and effective method that defines the dependence of the vibrational modes involving Fe on the nature of the Fe( iv )=O active site 14 , 15 , 16 . Here we present NRVS structural characterization of the reactive Fe( iv )=O intermediate of a NHFe enzyme, namely the halogenase SyrB2 from the bacterium Pseudomonas syringae pv. syringae . This intermediate reacts via an initial hydrogen-atom abstraction step, performing subsequent halogenation of the native substrate or hydroxylation of non-native substrates 17 . A correlation of the experimental NRVS data to electronic structure calculations indicates that the substrate directs the orientation of the Fe( iv )=O intermediate, presenting specific frontier molecular orbitals that can activate either selective halogenation or hydroxylation.

Compressional wave velocity-density (V P - ρ) relations of candidate Fe alloys at relevant pressure-temperature conditions of the Earth’s core are critically needed to evaluate the composition, seismic signatures, and geodynamics of the planet’s remotest region. Specifically, comparison between seismic V P - ρ profiles of the core and candidate Fe alloys provides first-order information on the amount and type of potential light elements—including H, C, O, Si, and/or S—needed to compensate the density deficit of the core. To address this issue, here we have surveyed and analyzed the literature results in conjunction with newly measured V P - ρ results of hexagonal closest-packed (hcp) Fe and hcp-Fe ₀.₈₅Si ₀.₁₅ alloy using in situ high-energy resolution inelastic X-ray scattering and X-ray diffraction. The nature of the Fe-Si alloy where Si is readily soluble in Fe represents an ideal solid-solution case to better understand the light-element alloying effects. Our results show that high temperature significantly decreases the V P of hcp-Fe at high pressures, and the Fe-Si alloy exhibits similar high-pressure V P - ρ behavior to hcp-Fe via a constant density offset. These V P - ρ data at a given temperature can be better described by an empirical power-law function with a concave behavior at higher densities than with a linear approximation. Our new datasets, together with literature results, allow us to build new V P - ρ models of Fe alloys in order to determine the chemical composition of the core. Our models show that the V P - ρ profile of Fe with 8 wt % Si at 6,000 K matches well with the Preliminary Reference Earth Model of the inner core.

For a large number of network attacks, feature selection is used to improve intrusion detection efficiency. A new mutual information algorithm of the redundant penalty between features (RPFMI) algorithm with the ability to select optimal features is proposed in this paper. Three factors are considered in this new algorithm: the redundancy between features, the impact between selected features and classes and the relationship between candidate features and classes. An experiment is conducted using the proposed algorithm for intrusion detection on the KDD Cup 99 intrusion dataset and the Kyoto 2006+ dataset. Compared with other algorithms, the proposed algorithm has a much higher accuracy rate (i.e., 99.772%) on the DOS data and can achieve better performance on remote-to-login (R2L) data and user-to-root (U2R) data. For the Kyoto 2006+ dataset, the proposed algorithm possesses the highest accuracy rate (i.e., 97.749%) among the other algorithms. The experiment results demonstrate that the proposed algorithm is a highly effective feature selection method in the intrusion detection.