Optimal conditions for cell-free synthesis of citrus exocortis viroid and the question of specificity of RNA polymerase activity

Cell-free synthesis of citrus exocortis viroid (CEV) in nuclei-rich preparations from infected Gynura aurantiaca was optimum at 18-24°C. Incubation of reaction mixtures at higher temperatures (30-36°C) resulted in an increase of CEV linear molecules and the recovery of incomplete or nicked newly synthesized RNA species. Although the Mg²⁺ optimum (2.5-5 mM) for CEV synthesis was lower than that for total [³²P]CMP incorporation (10 mM), the response to Mn²⁺ ion was distinctly different. Whereas maximum total activity was observed in 1 mM Mn²⁺ with a pronounced reduction (80%) in 5 mM Mn²⁺, CEV synthesis was maintained in 1-15 mM Mn²⁺. Inhibition of α-amanitin-sensitive CEV synthesis in 200 mM (NH₄)₂SO₄ resembles the reaction of RNA polymerase II on a free nucleic acid template. However, detection of trace levels of α-amanitin-resistant CEV synthesis activity inhibited by low (NH₄)₂SO₄ concentrations (25 mM) suggests the possible involvement of RNA polymerase I- and/or III-like activity.     

Stoichiometry, inhibitor sensitivity, and organization of manganese associated with photosynthetic oxygen evolution

Chloroplast thylakoid membranes isolated in the presence of EDTA retain high rates of O₂ evolution (≥340 μmol·h^-1·mg chlorophyll^-1) but contain no Mn²⁺ that is detectable by electron paramagnetic resonance (EPR) at room temperature. The total Mn²⁺ content of these preparations is 4.6 per 400 chlorophylls; 0.6 Mn²⁺ can be released by addition of Ca²⁺, a treatment that does not affect O₂ evolution. The remaining Mn²⁺ (4 per 400 chlorophylls) appears to be functionally associated with O₂ evolution activity. Inhibition by Tris, NH₂OH, or heat will release a small fraction of Mn²⁺ from these membranes (≈25% with Tris, for example). Addition of Ca²⁺ further enhances Mn²⁺ release so that for Tris and for NH₂OH, 2 and 3, respectively, Mn²⁺ per 400 chlorophylls are extracted from the O₂-evolving complex. Based on the microwave power-saturation properties of the EPR signal IIf, which arises from an intermediate electron carrier in the water splitting process, it appears that one of the four Mn²⁺ associated with photosystem II is uniquely sensitive to Tris. A new model is proposed for the organization and inhibitor sensitivity of manganese in the O₂-evolving complex.     

Structure of Sr-substituted photosystem II at 2.1 ? resolution and its implications in the mechanism of water oxidation

Oxygen-evolving complex of photosystem II (PSII) is a tetra-manganese calcium penta-oxygenic cluster (Mn₄CaO₅) catalyzing light-induced water oxidation through several intermediate states (S-states) by a mechanism that is not fully understood. To elucidate the roles of Ca²⁺ in this cluster and the possible location of water substrates in this process, we crystallized Sr²⁺-substituted PSII from Thermosynechococcus vulcanus, analyzed its crystal structure at a resolution of 2.1 Å, and compared it with the 1.9 Å structure of native PSII. Our analysis showed that the position of Sr was moved toward the outside of the cubane structure of the Mn₄CaO₅-cluster relative to that of Ca²⁺, resulting in a general elongation of the bond distances between Sr and its surrounding atoms compared with the corresponding distances in the Ca-containing cluster. In particular, we identified an apparent elongation in the bond distance between Sr and one of the two terminal water ligands of Ca²⁺, W3, whereas that of the Sr-W4 distance was not much changed. This result may contribute to the decrease of oxygen evolution upon Sr²⁺-substitution, and suggests a weak binding and rather mobile nature of this particular water molecule (W3), which in turn implies the possible involvement of this water molecule as a substrate in the O-O bond formation. In addition, the PsbY subunit, which was absent in the 1.9 Å structure of native PSII, was found in the Sr-PSII structure.     

Structural and mechanistic insights into guanylylation of RNA-splicing ligase RtcB joining RNA between 3′-terminal phosphate and 5′-OH

The RtcB protein has recently been identified as a 3′-phosphate RNA ligase that directly joins an RNA strand ending with a 2′,3′-cyclic phosphate to the 5′-hydroxyl group of another RNA strand in a GTP/Mn²⁺-dependent reaction. Here, we report two crystal structures of Pyrococcus horikoshii RNA-splicing ligase RtcB in complex with Mn²⁺ alone (RtcB/ Mn²⁺) and together with a covalently bound GMP (RtcB-GMP/Mn²⁺). The RtcB/ Mn²⁺ structure (at 1.6 Å resolution) shows two Mn²⁺ ions at the active site, and an array of sulfate ions nearby that indicate the binding sites of the RNA phosphate backbone. The structure of the RtcB-GMP/Mn²⁺ complex (at 2.3 Å resolution) reveals the detailed geometry of guanylylation of histidine 404. The critical roles of the key residues involved in the binding of the two Mn²⁺ ions, the four sulfates, and GMP are validated in extensive mutagenesis and biochemical experiments, which also provide a thorough characterization for the three steps of the RtcB ligation pathway: (i) guanylylation of the enzyme, (ii) guanylyl-transfer to the RNA substrate, and (iii) overall ligation. These results demonstrate that the enzyme’s substrate-induced GTP binding site and the putative reactive RNA ends are in the vicinity of the binuclear Mn²⁺ active center, which provides detailed insight into how the enzyme-bound GMP is tansferred to the 3′-phosphate of the RNA substrate for activation and subsequent nucleophilic attack by the 5′-hydroxyl of the second RNA substrate, resulting in the ligated product and release of GMP.     

Regulation of hormone(PTH and PGE1)-stimulated adenylate cyclase by renal cytosolic factors

Cytosolic factors in a 50–75% (NH₄)₂SO₄ fraction of the 105 000 × g supernatant of the renal cortex modulated adenylate cyclase activity in membrane preparations enriched in renal tubular cell basal-lateral membranes. The crude factor preparation had no effect on basal activity but it contained components that augmented the stimulation of the enzyme by NaF, parathyroid hormone (PTH), prostaglandin e₁ (PGE₁), and inhibited the activation of the enzyme by GMP-PNP. The factor(s) potentiating the stimulation by the hormones was partially purified (13-fold) by DEAE-cellulose and Sephadex G-75 chromatography. During purification, the component(s) that increased hormone-stimulated adenylate cyclase was separated from those affecting the activity in the presence of NaF and GMP-PNP. The factor(s) enhanced the PTH- and PGE₁-stimulated enzyme at all concentrations of hormone, suggesting that the affinity for the hormone was not affected. The factor(s) was heat-stable. Partial proteolysis with chymotrypsin greatly reduced the ability of the factor(s) to enhance hormonal responsive adenylate cyclase. However, the factor(s) was resistant to trypsin digestion. The effect of the factor was not due to GTP, nor was GTP necessary for its action. Ca²⁺ was not needed for the enhancing activity of the factor(s). These findings suggest the presence in the cytosol of the kidney cortex of a protein(s) that regulates the response of renal adenylate cyclase to hormones. The relationship between this kidney cytosolic factor and those reported in other tissues remains to be established.     

Dolichyldiphosphoryloligosaccharide—protein oligosaccharyltransferase: Solubilization, purification, and properties

Dolichyldiphosphoryloligosaccharide—protein oligosaccharyltransferase was solubilized from hen oviduct rough endoplasmic reticulum by extraction with 0.2% Nonidet P40. Oligosaccharyltransferase activity was assayed in an incubation mixture containing Glc_n-Man_x-GlcNAc₂-diphosphoryldolichol as an oligosaccharyl donor and the ¹²⁵I-labeled tryptic peptide consisting of residues 29-58 from bovine α-lactalbumin as acceptor. The transferase was purified approximately 2000-fold by fractionation on a bovine α-lactalbumin-Sepharose column; the active material bound quantitatively to the gel and was eluted by removal of divalent cation from the wash buffer. The product of the transferase activity, ¹²⁵I-glycopeptide, was determined as concanavalin A-agarose-adsorbed radioactivity by a filter disc assay method. ¹²⁵I-Labeled concanavalin A-agarose-bound product was characterized as a glycopeptide as follows: (i) gel filtration behavior on Sephadex G-50; (ii) elution from concanavalin A-agarose with 1% α-methyl mannoside; (iii) absence of affinity for ricin-Sepharose and loss of affinity for concanavalin A-agarose after treatment with endo-β-N-acetylglucosaminidase H; (iv) enzymatic synthesis of identical product upon using [³H]oligosaccharyldiphosphoryldolichol and unlabeled peptide acceptor; and (v) digestion of ³H-labeled peptide with Pronase, resulting in the formation of lower molecular weight glycopeptide. Oligosaccharyltransferase activity exhibited an absolute requirement for divalent cations (3 mM Mn²⁺; Mg²⁺ was 30% as effective), complete dependence on exogenously supplied peptide acceptor (1.33 μg/ml) and oligosaccharyldiphosphoryldolichol (approximately 10 nmol/ml), and an optimum pH between 7 and 7.5.     

Solution Synthesis of Cubic Spinel Mn–Ni–Cu–O Thermistor Powder

Toward the development of NTCR thermistors, nanocrystalline Mn–Ni–Cu–O powder was synthesized from a mixed chloride aqueous solution by a simple co-precipitation method.The introduction of an oxidizing agent (H₂O₂) into the solution led to the partial oxidation of Mn²⁺ ions into Mn³⁺ ions, which enabled the collected powder to be well crystallized at 650 °C. Such a low calcining temperature resulted in fine particles with a mean size of 60 nm, which significantly promoted densification of the resulting ceramics. As a result, a dense and homogenous microstructure with a relative density up to 97.2% was achieved for pellets sintered at 1100 °C. Furthermore, these sintered ceramics exhibited a room temperature resistivity (ρ₂₅) of 67 Ω·cmand a thermistor constant (B_25/85) of 2843 K, which make them suitable for use in industrial thermistors. In addition, electrical stability was greatly improved when the ceramics were prepared by a new two-step sintering method. The results suggest that the co-precipitation route with the introduction of H₂O₂ is suitable for the fabrication of cubic spinel thermistor nanopowders.     

Superionic Solid Electrolyte Li7La3Zr2O12 Synthesis and Thermodynamics for Application in All-Solid-State Lithium-Ion Batteries

Solid-state reaction was used for Li₇La₃Zr₂O₁₂ material synthesis from Li₂CO₃, La₂O₃ and ZrO₂ powders. Phase investigation of Li₇La₃Zr₂O₁₂ was carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) methods. The thermodynamic characteristics were investigated by calorimetry measurements. The molar heat capacity (C_p,m), the standard enthalpy of formation from binary compounds (Δ_oxH_LLZO) and from elements (Δ_fH_LLZO), entropy (S⁰₂₉₈), the Gibbs free energy of the Li₇La₃Zr₂O₁₂ formation (∆_f G⁰₂₉₈) and the Gibbs free energy of the LLZO reaction with metallic Li (∆_rG_LLZO/Li) were determined. The corresponding values are C_p,m = 518.135 + 0.599 × T − 8.339 × T⁻², (temperature range is 298–800 K), Δ_oxH_LLZO = −186.4 kJ·mol⁻¹, Δ_fH_LLZO = −9327.65 ± 7.9 kJ·mol⁻¹, S⁰₂₉₈ = 362.3 J·mol⁻¹·K⁻¹, ∆_f G⁰₂₉₈ = −9435.6 kJ·mol⁻¹, and ∆_rG_LLZO/Li = 8.2 kJ·mol⁻¹, respectively. Thermodynamic performance shows the possibility of Li₇La₃Zr₂O₁₂ usage in lithium-ion batteries.     

Effect of Heat Treatment on Structural,Magnetic and Electrical Properties of La2FeMnO6

In this study, the effect of heat treatment on the structural, magnetic and electrical properties of La₂FeMnO₆ prepared via the sol–gel and sintering method were investigated. The heat-treatment conditions, i.e., the calcination temperature (1023 K and 1173 K), sintering temperature and time (1273 K for 1 and 3 h) were carried out. X-ray diffraction (XRD) revealed orthorhombic pnma (62) symmetry without any impurity phase for all samples. X-ray photoelectron spectroscopy confirmed the presence of Fe²⁺–Fe³⁺–Fe⁴⁺ and Mn³⁺–Mn⁴⁺ mixed states, and lanthanum and oxygen vacancies resulting in various magnetic exchange interactions. Furthermore, the magnetisation hysteresis showed enhanced hysteresis loops accompanied by an increase in magnetisation parameters with calcination temperature. The Raman phonon parameters induced a redshift in the phonon modes, alongside an increase in the intensity and compression of the linewidth, reflecting a decrease in lattice distortion, which was confirmed by XRD. The temperature-dependent conductivity showed that the conduction mechanism is dominated by p-type polaron hopping, and the lowest activation energy was approximately 0.237 ± 0.003 eV for the minimum heat-treatment conditions. These results show that varying heat-treatment conditions can significantly affect the structural, magnetic and electrical properties of the La₂FeMnO₆ system.     

Phytochelatins, the heavy-metal-binding peptides of plants, are synthesized from glutathione by a specific gamma-glutamylcysteine dipeptidyl transpeptidase (phytochelatin synthase)

An enzyme has been discovered and characterized from Silene cucubalus cell suspension cultures that catalyzes the transfer of the γ-glutamylcysteine dipeptide moiety of glutathione to an acceptor glutathione molecule or a growing chain of [Glu(-Cys)]_n-Gly oligomers, thus synthesizing phytochelatins, the metal-binding peptides of higher plants and select fungi. The enzyme was named γ-glutamylcysteine dipeptidyl transpeptidase and given the trivial name phytochelatin synthase. The primary reaction catalyzed is [Glu(-Cys)]-Gly + [Glu(-Cys)]_n-Gly → [Glu(-Cys)]_n+1-Gly + Gly. The enzyme is isoelectric near pH 4.8 and has temperature and pH optima at 35°C and 7.9, respectively. Phytochelatin synthase is constitutively present in cell cultures of various plant species and its formation is not noticeably induced by heavy metal ions in the growth medium. The enzyme (M_r95,000) seems to be composed of four subunits, the dimer (M_r50,000) being also catalytically active. Cd²⁺ is by far the best metal activator of the enzyme followed by Ag⁺, Bi³⁺, Pb²⁺, Zn²⁺, Cu²⁺, Hg²⁺, and Au⁺. The K_m for glutathione is 6.7 mM. The enzyme activity seems to be self-regulated in that the product of the reaction (the phytochelatins) chelates the enzyme-activating metal, thus terminating the enzyme reaction. The molar ratio of the γ-glutamylcysteine dipeptide in phytochelatin to Cd²⁺ in the newly formed complex was 2:1.     

Influence of Isostatic Pressure on the Elastic and Electronic Properties of K2SiF6:Mn4+

Isostatic pressure effects on the elastic and electronic properties of non-doped and Mn⁴⁺-doped K₂SiF₆ (KSF) have been investigated by first-principles calculations within density functional theory (DFT). Bulk modulus was obtained by the Murnaghan’s equation of states (EOS) using the relationship between volume and pressures at pressures between 0 and 40 GPa, and elastic constants were calculated by the stress–strain relationship giving small distortions at each pressure point. The other elastic parameters such as shear modulus, sound velocity and Debye temperature, which can be obtained from the elastic constants, were also estimated. The influence of external isostatic pressure on the electronic properties, such as crystal field strength 10Dq and emission energy of ²E → ⁴A² transition (E_em), of KSF:Mn⁴⁺ was also studied. The results suggest that 10Dq and E_em linearly increase and decrease, respectively, with increasing pressure.     

Low-Temperature Selective Catalytic Reduction DeNOX and Regeneration of Mn–Cu Catalyst Supported by Activated Coke

The activated coke is a promising support for catalysts, and it is important to study the performance of the activated coke catalyst on the removal of NOx. In the current research, a series of the activated coke-supported Mn–Cu catalysts are prepared by the incipient wetness impregnation method. The effects of the molar ration of Mn/Cu, the content of Mn–Cu, the calcination temperature, and reaction space velocity on NO conversion are investigated, and it was found that the 8 wt.% Mn_0.7Cu_0.3/AC had the best catalytic activity when the calcination temperature was 200 °C. The existence of SO₂ caused the catalyst to deactivate, but the activity of the poisoning catalyst could be recovered by different regeneration methods. To uncover the underlying mechanism, BET, XPS, XRD, SEM and FTIR characterizations were performed. These results suggested that the specific surface area and total pore volume of the poisoning catalyst are recovered and the sulfite and sulfate on the surface of the poisoning catalysts are removed after water washing regeneration. More importantly, the water washing regeneration returns the value of Mn³⁺/Mn⁴⁺, Cu²⁺/Cu⁺, and O_α/O_β, related to the activity, basically back to the level of the fresh catalyst. Thus, the effect of water washing regeneration is better than thermal regeneration. These results could provide some helpful information for the design and development of the SCR catalysts.     

Metal ions control product specificity of isoprenyl diphosphate synthases in the insect terpenoid pathway

Isoprenyl diphosphate synthases (IDSs) produce the ubiquitous branched-chain diphosphates of different lengths that are precursors of all major classes of terpenes. Typically, individual short-chain IDSs (scIDSs) make the C₁₀, C₁₅, and C₂₀ isoprenyl diphosphates separately. Here, we report that the product length synthesized by a single scIDS shifts depending on the divalent metal cofactor present. This previously undescribed mechanism of carbon chain-length determination was discovered for a scIDS from juvenile horseradish leaf beetles, Phaedon cochleariae. The recombinant enzyme P. cochleariae isoprenyl diphosphate synthase 1 (PcIDS1) yields 96% C₁₀-geranyl diphosphate (GDP) and only 4% C₁₅-farnesyl diphosphate (FDP) in the presence of Co²⁺ or Mn²⁺ as a cofactor, whereas it yields only 18% C₁₀ GDP but 82% C₁₅ FDP in the presence of Mg²⁺. In reaction with Co²⁺, PcIDS1 has a K_m of 11.6 μM for dimethylallyl diphosphate as a cosubstrate and 24.3 μM for GDP. However, with Mg²⁺, PcIDS1 has a K_m of 1.18 μM for GDP, suggesting that this substrate is favored by the enzyme under such conditions. RNAi targeting PcIDS1 revealed the participation of this enzyme in the de novo synthesis of defensive monoterpenoids in the beetle larvae. As an FDP synthase, PcIDS1 could be associated with the formation of sesquiterpenes, such as juvenile hormones. Detection of Co²⁺, Mn²⁺, or Mg²⁺ in the beetle larvae suggests flux control into C₁₀ vs. C₁₅ isoprenoids could be accomplished by these ions in vivo. The dependence of product chain length of scIDSs on metal cofactor identity introduces an additional regulation for these branch point enzymes of terpene metabolism.     

Removal of Fe2+ and Mn2+ from Polluted Groundwater by Insoluble Humic Acid/Tourmaline Composite Particles

Insoluble humic acid/tourmaline composite particles (IHA/TM) were prepared by combining inorganic tourmaline (TM) with the natural organic polymer humic acid (HA) and carbonizing them at 330 °C to study the removal characteristics and mechanism of Fe²⁺ and Mn²⁺. The results showed that the optimal ratio of TM to IHA is 2:3. When the temperature of the IHA/TM composite particles was 35 °C and the pH was 6, the adsorption of Fe²⁺ and Mn²⁺ by IHA/TM reached equilibrium at 240 min. The optimum dose of the adsorbent was 10 g/L, and the equilibrium adsorption capacities of Fe²⁺ and Mn²⁺ were 5.645 mg/g and 3.574 mg/g, respectively. The process of IHA/TM adsorption of Fe²⁺ and Mn²⁺ in water was spontaneous, endothermic and sustainable, and cooling was not conducive to adsorption. The pseudo-second order kinetic equation can well reflect the adsorption mechanism of IHA/TM on Fe²⁺ and Mn²⁺, and the Langmuir adsorption model better describes the isothermal adsorption behaviour. The material characterisation and adsorption experiments indicate that surface coordination and chemical precipitation are the main mechanisms of Fe²⁺ and Mn²⁺ removal by IHA/TM.     

If and SR Ca release both contribute to pacemaker activity in canine sinoatrial node cells

Increasing evidence suggests that cardiac pacemaking is the result of two sinoatrial node (SAN) cell mechanisms: a ‘voltage clock’ and a Ca²⁺ dependent process, or ‘Ca²⁺ clock.’ The voltage clock initiates action potentials (APs) by SAN cell membrane potential depolarization from inward currents, of which the pacemaker current (I_f) is thought to be particularly important. A Ca²⁺ dependent process triggers APs when sarcoplasmic reticulum (SR) Ca²⁺ release activates inward current carried by the forward mode of the electrogenic Na⁺/Ca²⁺ exchanger (NCX). However, these mechanisms have mostly been defined in rodents or rabbits, but are unexplored in single SAN cells from larger animals. Here, we used patch-clamp and confocal microscope techniques to explore the roles of the voltage and Ca²⁺ clock mechanisms in canine SAN pacemaker cells. We found that ZD7288, a selective I_f antagonist, significantly reduced basal automaticity and induced irregular, arrhythmia-like activity in canine SAN cells. In addition, ZD7288 impaired but did not eliminate the SAN cell rate acceleration by isoproterenol. In contrast, ryanodine significantly reduced the SAN cell acceleration by isoproterenol, while ryanodine reduction of basal automaticity was modest (∼ 14%) and did not reach statistical significance. Importantly, pretreatment with ryanodine eliminated SR Ca²⁺ release, but did not affect basal or isoproterenol-enhanced I_f. Taken together, these results indicate that voltage and Ca²⁺ dependent automaticity mechanisms coexist in canine SAN cells, and suggest that I_f and SR Ca²⁺ release cooperate to determine baseline and catecholamine-dependent automaticity in isolated dog SAN cells.     

A Novel Red-Emitting Na2NbOF5:Mn4+ Phosphor with Ultrahigh Color Purity for Warm White Lighting and Wide-Gamut Backlight Displays

In this work, a novel red-emitting oxyfluoride phosphor Na₂NbOF₅:Mn⁴⁺ with an ultra-intense zero-phonon line (ZPL) was successfully synthesized by hydrothermal method. The phase composition and luminescent properties of Na₂NbOF₅:Mn⁴⁺ were studied in detail. The photoluminescence excitation spectrum contains two intense excitation bands centered at 369 and 470 nm, which match well with commercial UV and blue light-emitting diode (LED) chips. When excited by 470 nm blue light, Na₂NbOF₅:Mn⁴⁺ exhibits red light emission dominated by ZPL. Notably, the color purity of the Na₂NbOF₅:Mn⁴⁺ red phosphor can reach 99.9%. Meanwhile, the Na₂NbOF₅:Mn⁴⁺ phosphor has a shorter fluorescence decay time than commercial K₂SiF₆:Mn⁴⁺, which is conducive to fast switching of images in display applications. Profiting from the intense ZPL, white light-emitting diode (WLED) with high color rendering index of Ra = 86.2 and low correlated color temperature of T_c = 3133 K is realized using yellow YAG:Ce³⁺ and red Na₂NbOF₅:Mn⁴⁺ phosphor. The WLED fabricated using CsPbBr₃ quantum dots (QDs) and red Na₂NbOF₅:Mn⁴⁺ phosphor shows a wide color gamut of 127.56% NTSC (National Television Standard Committee). The results show that red-emitting Na₂NbOF₅:Mn⁴⁺ phosphor has potential application prospects in WLED lighting and display backlight.     

Energy-Resolved Ultrafast Spectroscopic Investigation on the Spin-Coupled Electronic States in Multiferroic Hexagonal HoMnO3

A complete temperature-dependent scheme of the Mn³⁺ on-site d-d transitions in multiferroic hexagonal HoMnO₃ (h-HoMnO₃) thin films was unveiled by energy-resolved ultrafast spectroscopy. The results unambiguously revealed that the ultrafast responses of the e_1g and e_2g states differed significantly in the hexagonal HoMnO₃. We demonstrated that the short-range antiferromagnetic and ferroelectric orderings are more relevant to the e_2g state, whereas the long-range antiferromagnetic ordering is intimately coupled to both the e_2g and e_1g states. Moreover, the primary thermalization times of the e_2g and e_1g states were 0.34 ± 0.08 ps and 0.38 ± 0.08 ps, respectively.     

Oxygen controls on magmatism in rocky exoplanets

Refractory oxygen bound to cations is a key component of the interior of rocky exoplanets. Its abundance controls planetary properties including metallic core fraction, core composition, and mantle and crust mineralogy. Interior oxygen abundance, quantified with the oxygen fugacity (fO₂), also determines the speciation of volatile species during planetary outgassing, affecting the composition of the atmosphere. Although melting drives planetary differentiation into core, mantle, crust, and atmosphere, the effect of fO₂ on rock melting has not been studied directly to date, with prior efforts focusing on fO₂-induced changes in the valence ratio of transition metals (particularly iron) in minerals and magma. Here, melting experiments were performed using a synthetic iron-free basalt at oxygen levels representing reducing (log fO₂ = −11.5 and −7) and oxidizing (log fO₂ = −0.7) interior conditions observed in our solar system. Results show that the liquidus of iron-free basalt at a pressure of 1 atm is lowered by 105 ± 10 °C over an 11 log fO₂ units increase in oxygen abundance. This effect is comparable in size to the well-known enhanced melting of rocks by the addition of H₂O or CO₂. This implies that refractory oxygen abundance can directly control exoplanetary differentiation dynamics by affecting the conditions under which magmatism occurs, even in the absence of iron or volatiles. Exoplanets with a high refractory oxygen abundance exhibit more extensive and longer duration magmatic activity, leading to more efficient and more massive volcanic outgassing of more oxidized gas species than comparable exoplanets with a lower rock fO₂.

Oxygen (∼21% in Earth’s atmosphere) is essential to life on Earth, and is the most abundant element in the rocky outer layers of Earth (1) as well as the other terrestrial planets in our solar system (2–4). Oxygen can be both refractory (bonded to cations—predominantly Si, Mg, Fe, and Ca—in minerals condensing from planetary disks orbiting young stars) and volatile (condensing in ices—for example, H₂O, CO, CO₂—in the colder outer disk parts) (e.g., ref. 5). The abundance and activity of refractory oxygen in a rock is described using the oxygen fugacity (fO₂), commonly quantified relative to mineral redox buffers, for example, the IW (iron–wüstite) or MH (magnetite–hematite) buffer (6).The fO₂ conditions in planetary interiors affect the prevailing redox state of polyvalent cations, particularly transition metals (e.g., Fe⁰ versus Fe²⁺ versus Fe³⁺; Eu²⁺ versus Eu³⁺; Cr²⁺ versus Cr³⁺) (e.g., ref. 7). The oxygen fugacity in the rocky mantles of the terrestrial planets varies widely. Mercury’s rocky outer shell is oxygen depleted, with an fO₂ around 5 log units below that of the iron–wüstite buffer (ρIW−5) (8). As a result, the iron content of Mercury’s mantle and crust is very low, with almost all Fe present at Fe⁰ in the core. In contrast, Earth’s upper mantle today is estimated to contain oxygen levels corresponding to fO₂ of ∼ρIW+3 (6), and parts of the Martian mantle may exhibit fO₂ up to ρIW+5 (e.g., ref. 9), yielding mantles with FeO abundances of 8 wt.% and 18 wt.%, respectively.These current mantle fO₂ values do not necessarily reflect oxygen fugacity conditions during planetary accretion. Mantle oxygen fugacities can change significantly during planetary growth, differentiation, and subsequent evolution. For example, models of accretion and metallic core segregation in Earth (e.g., refs. 10 and 11), based on the observed abundances of siderophile (iron-loving) elements in their mantle, suggest initial fO₂ values during accretion that are Mercury-like, up to 8 log fO₂ units lower than present-day mantle estimates. This suggests significant terrestrial mantle oxidation occurred after the main phase of accretion and core formation, perhaps resulting from late accretion of oxidizing agents such as H₂O (11). Alternatively, in Earth, mantle self-oxidation is proposed to have occurred through the disproportionation reaction 3Fe²⁺O = Fe₂³⁺O₃ + Fe⁰ which can take place in the presence of the high-pressure mineral bridgmanite (e.g., ref. 12) or in a deep magma ocean setting (13). If iron metal can be sequestered to the core, this reaction can increase the redox state of the mantle. In Mars and the Moon, lower interior pressures prevented this process, although the increasing stability of Fe³⁺ over Fe²⁺ with increasing pressure (e.g., ref. 14) could still have resulted in significant vertical oxygen fugacity gradients in their magma oceans. Astronomical observations suggest that both the initial and present-day spreads in terrestrial planet oxygen abundances, masses, and sizes in our solar system are not unusually broad. Many rocky exoplanets have been characterized over the past decade, some with masses and radii far exceeding those of the rocky bodies in our own solar system (e.g., ref. 15). Such planets likely include super-Earths (with compositions perhaps similar to terrestrial planets in our solar system but with significantly higher mass and radius), but also likely include rocky planets with bulk compositions significantly different from compositions found in our solar system. Examples include rocky exoplanets enriched in elements that typically condense at very high temperatures, such as Ca and Al (16); rocky exoplanets rich in water (“ocean worlds”) (17); planets that lack a metallic core altogether (18); and planets with high or low C/O ratios (16, 19, 20). The mantle oxygen fugacity in such exoplanets could span a range similar to that found in rocky bodies in our solar system (e.g., refs. 21 and 22).     

The Effects of Ru4+ Doping on LiNi0.5Mn1.5O4 with Two Crystal Structures

Doping of Ru has been used to enhance the performance of LiNi_0.5Mn_1.5O₄ cathode materials. However, the effects of Ru doping on the two types of LiNi_0.5Mn_1.5O₄ are rarely studied. In this study, Ru⁴⁺ with a stoichiometric ratio of 0.05 is introduced into LiNi_0.5Mn_1.5O₄ with different space groups (Fd3¯m, P4₃32). The influence of Ru doping on the properties of LiNi_0.5Mn_1.5O₄ (Fd3¯m, P4₃32) is comprehensively studied using multiple techniques such as XRD, Raman, and SEM methods. Electrochemical tests show that Ru⁴⁺-doped LiNi_0.5Mn_1.5O₄ (P4₃32) delivers the optimal electrochemical performance. Its initial specific capacity reaches 132.8 mAh g⁻¹, and 97.7% of this is retained after 300 cycles at a 1 C rate at room temperature. Even at a rate of 10 C, the capacity of Ru⁴⁺-LiNi_0.5Mn_1.5O₄ (P4₃32) is still 100.7 mAh g⁻¹. Raman spectroscopy shows that the Ni/Mn arrangement of Ru⁴⁺-LiNi_0.5Mn_1.5O₄ (Fd3¯m) is not significantly affected by Ru⁴⁺ doping. However, LiNi_0.5Mn_1.5O₄ (P4₃32) is transformed to semi-ordered LiNi_0.5Mn_1.5O₄ after the incorporation of Ru⁴⁺. Ru⁴⁺ doping hinders the ordering process of Ni/Mn during the heat treatment process, to an extent.