Browse Articles

Discovery of a Heme‐Dependent Enzyme Catalyzing Nitrogen–Nitrogen Bond Formation in Kinamycin Biosynthesis

Abstract A nitrogen–nitrogen (N─N) bond is a core feature of diverse natural products with interesting structural and biological properties. Kinamycin and lomaiviticin, featuring a diazobenzo[b]fluorene core, exhibit exceptional potency as chemotherapeutic agents. However, the N─N bond forming step in their biosynthesis has remained elusive. Through extensive mutagenesis and biochemical studies, we herein report that Alp1J, belonging to a new family of heme‐dependent enzymes, catalyzes the N─N bond formation in kinamycin biosynthesis. Interestingly, Alp1J forms a stable complex with its partner ferredoxin Alp1I, which can protect the cofactors and is critical for the N─N bond formation activity. With its partner ferredoxin, Alp1J catalyzes formation of the hydrazine intermediate directly from l ‐aspartate and nitrite by a pathway involving four‐electron reduction. Our findings expand the knowledge of enzymatic N─N bond formation and show the potential for the discovery and development of novel N─N bond containing natural products through genome mining and synthetic biology.

Spatial Confinement of Solution‐Inaccessible Single‐Site Cu(I) in a Molecular Titanium–Oxo Cage for Efficient Photo‐Electrocatalytic Urea Synthesis

Abstract We introduce a precisely engineered molecular titanium‐oxo cage, Ti 16 O 24 Bz 24 (denoted as Ti 16 ; Bz = C 6 H 5 CO 2 ), designed to host a spatially confined Cu + single‐atom site, that enables efficient and selective C─N coupling from CO 2 and NO 3 − under photo‐electrocatalytic (PEC) conditions, providing a molecular‐level blueprint for multi‐reactant coupling catalysis. Ti 16 features a large internal cavity assembled from TiO 6 octahedra shielded by a hydrophobic benzoate shell. Metalation of Ti 16 with CuCl 2 /NaBH 4 incorporates Cu + ions, displacing encapsulated H 3 O + and enabling the synthesis of Ti 16 Cu x ( x = 0.25–8). Among the Ti 16 Cu x series, Ti 16 Cu 2 demonstrates optimal performance under PEC conditions, achieving a high urea yield of 20 mmol g cat −1 h −1 with a Faradaic efficiency of 85% and a selectivity of 62% at −0.6 V versus RHE, outperforming most reported Cu‐based systems. Spectroscopic and structural analyses reveal that C─N bond formation occurs via coupling of *CO and *NO species at the confined Cu sites, highlighting the essential role of the molecular cage in stabilizing reactive species and facilitating their interaction. This work establishes cage‐like metal–oxo clusters as an atomically precise and versatile molecular platform for developing highly selective single‐atom catalysts for challenging multi‐reactant coupling reactions.

High-entropy negative thermal expansion oxide with thermally enhanced upconversion luminescence

High-entropy (HE) materials, renowned for their exceptional chemical and physical properties, have attracted growing interest due to their broad applications across various fields. In this work, we report the synthesis of a compound, (Al0.196Sc0.196In0.196Yb0.196Y0.196)2Mo3O12:0.04Er3+ (HEMO), designed via a high-entropy solid solution strategy based on the A2Mo3O12 framework. The crystal structure, microstructure, elemental valence states, and thermal expansion properties of HEMO were systematically investigated using variable temperature synchrotron X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. HEMO exhibits negative thermal expansion (NTE) in the temperature range of 300–1000 K due to coupled polyhedral rotations. Under 980 nm excitation, its upconversion luminescence (UCL) shows remarkable negative thermal quenching (NTQ), with a 53.4-fold increase in intensity between 300 and 650 K. Based on the fluorescence intensity ratio technique, it shows a max relative sensitivity (Sr) of 0.84% K−1 (300 K) at 300–650 K. This work not only reports a high-entropy NTE phosphor but also opens an avenue for exploring UCL phosphors with NTQ luminescence.

Enhancement of tribological behavior and microhardness of AISI H13 tool steel by electrochemical boriding

Abstract Iron boride coatings were developed on AISI H13 hot work tool steel using the electrochemical boriding method at temperatures of 850, 950, and 1050 °C for durations of 2, 4, and 6 h. The process was conducted at a current density of 200 mA/cm 2 , utilizing a powder mixture containing 22.5 wt.% ferroboron (Fe-B), 70 wt.% borax (Na 2 B 4 O 7 ), and 7.5 wt.% ammonium chloride (NH 4 Cl). The obtained coatings were examined using light microscopy (LM), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), and X-ray diffraction (XRD). Metallographic analysis revealed a distinct saw-tooth shaped interface between the boride layer and the underlying transition zone, which was consistent and uniform across the examined area. XRD results revealed the formation of a dual-phase boride layer (FeB/Fe 2 B) with traces of chromium and vanadium borides. The kinetics of the boriding process were evaluated using the classical parabolic growth law, demonstrating a parabolic relationship between boride layer thickness and treatment time. The activation energy required for boron diffusion throughout the boride layer was determined to be 168.4 kJ/mol. Additionally, the microhardness and wear rate were evaluated. The boride layer reached a thickness up to 252 µm and exhibited a microhardness of 1956 ± 67 HV 0.05 , representing an increase of over 300% compared to the quenched and tempered specimens, which had a microhardness of 543 ± 8 HV 0.05 . The findings demonstrated that the phase composition and thickness of the boride coatings are strongly influenced by the immersion time and processing temperature.

Antisite defect-mediated hot carrier cooling in halide double perovskite Cs2AgBiCl6: Microscopic role of electron–phonon coupling

The intrinsic antisite defects on the B-site (BiAg and AgBi) impose fundamental limits on the performance of silver-bismuth halide perovskite-based optoelectronic and photovoltaic devices. Through combining first-principles calculations and nonadiabatic molecular dynamics simulations, we systematically investigate how these defects modulate hot carrier cooling dynamics in Cs2AgBiCl6. Our results reveal that the BiAg antisite induces a significant octahedral distortion that reduces the degeneracy of the conduction band. The enhanced nonadiabatic couplings (NAC) and strengthened electron–phonon coupling ultimately accelerate electron cooling dynamics. As a donor-type defect, the BiAg antisite has limited influence on valence bands and hot-hole cooling process. Acting as a shallow acceptor, AgBi induces minimal structural distortion. Thus, the AgBi-defective system exhibits a similar hot-hole cooling process to its defect-free counterpart. Paradoxically, despite introducing low-frequency phonon modes (<200 cm−1) that can interact with hot electrons, the preserved energy gap and conduction band degeneracy suppress the NAC and electron–phonon couplings, thereby prolonging electron relaxation time. This study provides atomistic insights into defect-mediated carrier cooling processes and establishes defect-engineering strategies for optimizing hot carrier dynamics in double halide perovskites.

Correction: Impact of resection margins on local recurrence in patients with myxofibrosarcoma

High-performance <b> <i>β</i> </b> -Ga2O3 vertical diodes integrating metal-interlayer-semiconductor architecture and mesa termination

In this Letter, we report on high-performance β-Ga2O3 metal-interlayer-semiconductor (MIS) diodes featuring anode self-aligned mesa terminations and ultra-thin NiO as interlayers. The polycrystalline NiO interlayer was formed by thermal oxidation of a 5-nm Ni film deposited by e-beam evaporation and the mesa termination was fabricated by inductively coupled plasma etching. High-resolution transmission electron microscopy revealed a polycrystalline structure of the NiO and a perpendicular sidewall angle of approximately 84.6° at the mesa region. The 40-μm-radius mesa metal-interlayer-semiconductor Schottky barrier diodes achieves a low turn-on voltage of 1 V and a high breakdown voltage of 2.45 kV, while maintaining a decent specific on-resistance of 4.2 mΩ·cm2, yielding a power figure of merit of 1.43 GW/cm2, which is one of the highest among those reported state-of-the-art Ga2O3 MIS and mesa-termination diodes. Additionally, high on/off ratio of 1011, negligible C–V and I–V hysteresis curves, ideality factor of 1.2, and subthreshold swing of 74 mV/dec are demonstrated, all attributable to the well-defined NiO/Ga2O3 interface and the high crystal quality. The fabricated β-Ga2O3 MIS diodes with mesa termination show good switching performance, further promoting Ga2O3 technology for next-generation power electronics.

Evolving trends in cardiogenic shock management in acute myocardial infarction: mortality, discharge outcomes, and economic implications

Plasmonic coupling driven spectral and sensitivity evolution in TIR-excited discrete AuNP arrays

Localized surface plasmon resonance (LSPR) in discrete nanoparticle monolayers is difficult to control because disorder and aggregation obscure the link between microscale coupling and macroscopic spectra. We demonstrate that surface coverage (SC) and incidence angle (θ) provide a coordinated control under total internal reflection. A compact finite element method and an effective-medium theory framework, supported by a dipole-oscillator picture, predict that tightening gaps strengthens dipole–dipole coupling, redshifts, deepens the resonance, and increases intensity sensitivity (SI) until multipolar modes emerge and reduce SI. Increasing θ reconditions the evanescent field and shifts the SC threshold for strong coupling to higher values. Using pH-responsive self-assembly to tune SC from 8.07% to 23.62% and a prism-based angle-resolved setup under unpolarized illumination, we experimentally verify a nonmonotonic SI and a θ-dependent right-shift of the optimum. These results provide actionable design rules and a scalable route to high-sensitivity, self-assembled LSPR sensors.

Motion/force transmission performance analysis and optimal design of closed-chain end-effector for steel arch splicing robot

Laminar-flow-based sound absorption with a single Hilbert curve surpassing the Rozanov bound

Advances in metamaterials, additive manufacturing, and computational design have enabled significant progress in airborne sound absorption. However, most absorbers still rely on two conventional mechanisms, i.e., friction-induced viscous loss and pressure-fluctuation-induced thermal loss, leaving their thickness constrained by the Rozanov bound. Here, we investigate an acoustic metamaterial based on a single three-dimensional Hilbert curve, designed to achieve sound absorption beyond this theoretical limit. The Hilbert curve forms continuous, tightly spaced winding channels whose geometry enables laminar flow-like shear dissipation. Experimental, numerical, and theoretical results demonstrate that with an optimal slit width close to the viscous boundary layer thickness, the actual thickness can be approximately 86% of the calculated Rozanov bound. This finding suggests a dissipation mechanism distinct from classical porous and resonator-based absorbers, opening different avenues for ultra-thin broadband sound absorbers.

Dose‒response relationship between physical activity and all-cause mortality in Chinese adults

Abstract To determine the dose-response association between physical activity (PA) and all-cause mortality to identify minimum PA thresholds for significant mortality risk reduction by using a nationally representative sample of Chinese adults. This population-based cohort study included 109,407 Chinese participants from the Kailuan study with linkage to national death records up to December 31, 2022. Baseline data were derived from self-reported surveys among participants aged 53.32 ± 13.55 years. During a median follow-up of 6.99 (IQR 5.99–6.99) years, 4571 participants died from all causes. Performing at least 75 min per week of physical activity contributed to significantly reduced all-cause mortality. Compared with physical inactivity, total physical activity was inversely associated with the risk of mortality in the very low (HR: 1.08; 95% CI: 0.98–1.19), low (HR: 0.89; 95% CI: 0.81–0.98), medium (HR: 0.88; 95% CI: 0.79–0.96) and high (HR: 0.77; 95% CI: 0.69–0.85) quartiles. The dose‒response curve revealed a steady decline in HRs with more minutes of physical activity per week with all-cause mortality. Our study demonstrated an inverse nonlinear dose‒response relationship between physical activity and all-cause mortality in elderly adults, with as little as 75 min of weekly activity showing clinically meaningful risk reduction compared with inactivity. These findings suggest that mortality benefits at lower thresholds for elderly adults. The results provide evidence-based justification for health policies that promote graduated physical activity targets to improve population-level adherence among aging communities.

Outside Front Cover: Deciphering Ball Milling Mechanochemistry via Molecular Simulations of Collision‐Driven and Liquid‐Assisted Reactivity (Angew. Chem. Int. Ed. 50/2025)

Probing the features of electron dispersion by tunneling between slightly twisted bilayer graphene sheets

Tunneling conductance between two bilayer graphene (BLG) sheets separated by 2 nm-thick insulating barrier was measured in two devices with the twist angles between BLGs less than 1°. At small bias voltages, tunneling occurs with conservation of energy and momentum at the points of intersection between two relatively shifted Fermi circles. Here, we experimentally found and theoretically described signatures of electron–hole asymmetric band structure of BLG: since holes are heavier, the tunneling conductance is enhanced at the hole doping due to the higher density of states. Another key feature of BLG that we explore is gap opening in a vertical electric field with a strong polarization of electron wave function at van Hove singularities near the gap edges. This polarization, by shifting electron wave function in one BLG closer to or father from the other BLG, gives rise to asymmetric tunneling resonances in the conductance around charge neutrality points, which result in strong sensitivity of the tunneling current to minor changes of the gate voltages. The observed phenomena are reproduced by our theoretical model taking into account electrostatics of the dual-gated structure, quantum capacitance effects, and self-consistent gap openings in both BLGs.

The hybrid protection method for copper alloy against electrochemical attack using benzotriazole and Sb₂O₃ nanoparticles synergy

Ultrahigh-efficiency solar-blind ultraviolet detection with a <b> <i>β</i> </b> -Ga2O3/Si heterojunction

To overcome the limitations of low responsivity (R) and suboptimal spectral selectivity inherent in silicon (Si)-based solar-blind ultraviolet (SBUV) photodetectors (PDs), as well as the challenges posed by the low electron mobility and polycrystalline structure of heteroepitaxial β gallium oxide (β-Ga2O3), a high-electron-mobility PD utilizing a β-Ga2O3/Si heterojunction is developed. In this PD, β-Ga2O3 serves as the SBUV absorption layer, capitalizing on its high responsivity and spectral selectivity, while Si acts as the photogenerated electron transport layer, leveraging its superior crystalline quality and electron mobility to form a complementary system. The resulting PD achieves a remarkable R of 6.67 × 105 A/W and an external quantum efficiency of 3.25 × 108%, coupled with exceptional spectral selectivity. This study provides valuable guidance for SBUV applications of both Si and β-Ga2O3.

Optimized ANN–RF hybrid model with optuna for fault detection and classification in power transmission systems

A hydrogen-bonding anchoring strategy for buried interface passivation toward enhanced efficiency and stability of inverted perovskite solar cells

Buried interface defects in perovskite solar cells (PSCs) remain one of the key factors limiting the efficiency and stability of the devices. Various passivation strategies for reducing buried interface defects have been explored. However, the strong solvation capability of perovskite precursor solvents (e.g., DMF/DMSO) often causes passivation molecules to diffuse the into perovskite bulk. This adversely affects perovskite film crystallization or degrades the passivation layer, ultimately undermining the passivation efficacy. Herein, we developed an effective anchoring strategy for buried interface passivation in inverted PSCs by leveraging the hydrogen bonding between a cross-linked P-TSPA [3-(triethoxysilyl)propylamine] polymer and thenoyltrifluoroacetone (TTFA) passivation molecules. The P-TSPA layer, stabilized by “Si–O” bonding with NiOx, resists solvent dissolution, while TTFA forms multiple hydrogen bonds with P-TSPA and passivates undercoordinated Pb2+ defects at the buried interface. Characterizations confirmed that TTFA passivation remains localized at the buried interface without perturbing the perovskite lattice structure. This approach enhances grain growth, reduces defect density, and prolongs carrier lifetime, enabling inverted PSCs (ITO/NiOx/P-TSPA/TTFA/MAPbClxI3−x/PEAI/C60/BCP/Ag) to achieve a champion efficiency of 20.07% (vs 16.21% for controls) via suppressed interfacial recombination. Further optimization with FA+ doping improves efficiencies to 20.30% (FA0.1MA0.9PbClxI3−x) and 20.83% (FA0.2MA0.8PbClxI3−x). The modified devices also exhibit exceptional stability, retaining 85.3% of their initial performance after 50 days (12% humidity, low O2), compared to 53.1% for controls, due to enhanced hydrophobicity and strong Pb coordination at the buried interfaces. This work demonstrates a scalable interface engineering strategy for high-performance, industrially viable PSCs.

Factors associated with unplanned pregnancy among pregnant women in Uganda

Solvent Channels and Electric Fields Guide Proton Delivery to the Active Site of Heme Peroxidases

Abstract The active sites of heme enzymes have evolved to control the formation of highly reactive intermediates in oxidative catalysis. Proton delivery to the heme is essential, yet the mechanisms of proton delivery remain poorly understood. Here, we identify routes and drivers of proton delivery in a heme peroxidase (ascorbate peroxidase) using computational approaches that combine classical, quantum, and hybrid methods with enhanced sampling and local electric field (LEF) analyses. Our results show that networks of active‐site water molecules facilitate proton exchange with Arg38, which may act as a transient proton carrier at the γ‐heme edge where the substrate binds. The distal His42 residue aids proton transfer into the active site via solvent at the δ‐edge. Molecular dynamics simulations of three heme peroxidases identify hydrated channels leading to both γ‐ and δ‐edges, allowing solvent protons to reach the active site. Comparison with eight other heme peroxidases shows that these channels are conserved. LEF analyses reveal a continuous electrostatic funnel drawing protons toward the heme from the γ‐ and δ‐edges, a feature that is broadly conserved across other peroxidases. These results suggest that nature pre‐organizes electrostatic funnels and solvent channels to provide multiple well‐defined routes for proton delivery in peroxidase catalysis.