Ion Activity Research Articles

Real-Time Estimation of CO2 Absorption Capacity Using Ionic Conductivity of Protonated Di-Methyl-Ethanolamine (DMEA) and Electrical Conductivity in Low-Concentration DMEA Aqueous Solutions

The present study investigates the real-time estimation of CO2 absorption capacity (CAC) based on the electrical conductivity (EC) of low-concentration di-methyl-ethanolamine (DMEA) solutions (0.1–0.5 M). CO2 absorption experiments are conducted to measure the variation in CAC and EC during CO2 absorption, revealing a strong correlation between the two properties. The ionic conductivity of DMEAH+ formed during absorption is calculated to be 53.1 S·cm2/(mol·z), which is found to be larger than that of TEAH+ and MDEAH+. This can be attributed to the smaller molar mass and higher ionic mobility of DMEAH+. A significant finding is that the measured EC (ECM) of the DMEA solutions consistently demonstrates a lower value than the theoretically predicted value. This discrepancy is due to the larger ionic size of DMEAH+, which results in a reduction in the real mean ionic activity coefficient. This effect becomes more pronounced with increasing DMEA concentration. Consequently, a higher CAC is required to produce the same change in EC at higher amine concentrations. Based on these findings, an empirical equation is devised to estimate CAC from ECM in solutions of constant DMEA concentration. This equation will be employed as a practical approach for the in situ monitoring of CO2 absorption using DMEA aqueous solution.

Appraisal of Heavy Metal Risk Hazards of Eisenia fetida-Mediated Steel Slag Vermicompost on Oryza sativa L.: Insights from Agro-Scale Inspection and Machine Learning Analytics

The steel industry drives world economic growth, yet it generates heavy metal-rich steel slag, which jeopardizes the environment. The utilization of vermi-technology is essential for the sustainable transformation of toxic steel waste slag (SW) into organic amendments, although field-scale use of vermiprocessed SW remains unexplored. To bridge the gap, this study evaluated the efficacy of vermiprocessed SW as an organic supplement for rice field cultivation, focusing on heavy metal (HM) bioavailability, human health risk, and yield in comparison to raw slag and NPK fertilizer. The results indicated a considerable decrease in the bioavailable fraction of heavy metals in T4 (1:1 SW vermicompost 50% + 50% fertilizer). In treatments, T9 (100% SW) and T10 (50% SW + 50% fertilizer) (FIAM) free ion activity modeling confirmed grain absorption of HMs, and the FIAM HQ values indicated the health risk for the direct application of steel slag waste on the field. The risk factor evaluation of HMs’ presence in treatments T9 and T10 established the possible cancer risk for living beings. Similarly, machine learning models like SOBOL sensitivity analysis and artificial neural networks revealed potential threats associated with HMs on different treatments, respectively. The correlation coefficient revealed the negative effects of bioavailable HMs on various soil microbial and enzymatic properties. Moreover, the abundant yield of rice was attributed to the combination treatment (1:1 50% + NPK 50%), which paved the way for an alternative agronomic approach based on the utilization of vermicomposted steel waste slag.

Anion-induced optimization of non-aqueous zinc-air battery performance: Insights into OTF− selection

Rechargeable non-alkaline zinc-air batteries (ZABs) address the CO₂ incompatibility and instability issues of conventional alkaline batteries. However, the impact of solid discharge products like zinc oxide on discharge capacity at the air cathode remains unexplored. In this study, we investigate how anions influence ion pair solvation structures using Zinc trifluoromethanesulfonate (Zn(OTF)₂)-N, N-dimethylformamide (DMF) and Zinc acetate (Zn(Ac)₂)-DMF electrolytes, and how these structures affect the distribution of discharge product. Our finding shows that anions with lower donor numbers (DNs), like the weaker ligand OTF- (20.5), enhance the zinc ion activity and promote rapid Zn2⁺ reactions with oxygen during discharge, leading to a more than tenfold increase in discharge capacity. In contrast, acetate anions with higher DNs (43.3) form stable complexes, inhibiting zinc ion activity and causing the formation of film-like discharge products, which reduces ZAB performance. The Zn(OTF)₂-DMF electrolyte also enables a battery lifespan of over 200 h, more than fivefold compared to the acetate-based system.

Origin of the Difference in Proton Transport Direction between Inward and Outward Proton-Pumping Rhodopsins.

ConspectusActive transport is a vital and ubiquitous process in biological phenomena. Ion-pumping rhodopsins are light-driven active ion transporters that share a heptahelical transmembrane structural scaffold in which the all-trans retinal chromophore is covalently bonded through a Schiff base to a conserved lysine residue in the seventh transmembrane helix. Bacteriorhodopsin from Halobacterium salinarum was the first ion-pumping rhodopsin to be discovered and was identified as an outward proton-pumping rhodopsin. Since the discovery of bacteriorhodopsin in 1971, many more ion-pumping rhodopsins have been isolated from diverse microorganisms spanning three domains (bacteria, archaea, and eukaryotes) and giant viruses. In addition to proton-pumping rhodopsins, chloride ion- and sodium ion-pumping rhodopsins have also been discovered. Furthermore, diversity of ion-pumping rhodopsins was found in the direction of ion transport; i.e., rhodopsins that pump protons inward have recently been discovered. Very intriguingly, the inward proton-pumping rhodopsins share structural features and many conserved key residues with the outward proton-pumping rhodopsins. However, a central question remains unchanged despite the increasing variety: how and why do the ion-pumping rhodopsins undergo interlocking conformational changes that allow unidirectional ion transfer within proteins? In this regard, it is an effective strategy to compare the structures and their evolutions in the proton-pumping processes of both inward and outward proton-pumping rhodopsins because the comparison sheds light on key elements for the unidirectional proton transport. We elucidated the proton-pumping mechanism of the inward and outward proton-pumping rhodopsins by time-resolved resonance Raman spectroscopy, a powerful technique for tracking the structural evolutions of proteins at work that are otherwise inaccessible.In this Account, we primarily review our endeavors in the elucidation of the proton-pumping mechanisms and determination factors for the transport directions of inward and outward proton-pumping rhodopsins. We begin with a brief summary of previous findings on outward proton-pumping rhodopsins revealed by vibrational spectroscopy. Next, we provide insights into the mechanism of inward proton-pumping rhodopsins, schizorhodopsins, obtained in our studies. Time-resolved resonance Raman spectroscopy provided valuable information about the structures of the retinal chromophore in the unphotolyzed state and intermediates of schizorhodopsins. As we ventured further into our investigations, we succeeded in uncovering the factors determining the directions of proton release and uptake in the retinal Schiff base. While it is intriguing that the proton-pumping rhodopsins actively transport protons against a concentration gradient, it is even more curious that proteins with structural similarities transport protons in opposite directions. Solving the second mystery led to solving the first. When we considered our findings, we realized that we would probably not have been able to elucidate the mechanism if we had studied only the outward pump. Our Account concludes by outlining future opportunities and challenges in the growing research field of ion-pumping rhodopsins, with a particular emphasis on elucidating their sequence-structure-function relationships. We aim to inspire further advances toward the understanding and creation of light-driven active ion transporters.

Overcoming volumetric capacitance-rate performance tradeoff with 0D/2D conductive carbon nitride/phosphorene heterostructure for flexible supercapacitor

Few-layer black phosphorus (FL-BP) is considered a rising star 2D material for flexible supercapacitors (FSCs) due to its exceptional properties, including mechanical flexibility and high active surface area. However, the disordered deposition of FL-BP nanoflakes often leads to face-to-face restacking, which diminishes the effective active area and ion transport channels. This poses a huge challenge in simultaneously achieving high volumetric capacitance and rate capability. To address this, a 3D porous 0D/2D FL-BP/conductive carbon nitride (FL-BP/c-CN) film has been developed. The introduction of 0D c-CN nanoparticles effectively prevents the restacking of FL-BP nanoflakes and expands the nanofluidic channels, thus facilitating charge transport and ions diffusion. Additionally, the highly conductive c-CN nanoparticles embedded into the FL-BP layers significantly improve overall conductivity. As a result, the FL-BP/c-CN film-based FSC demonstrates a remarkable rate performance, retaining 70% capacitance as the scan rate increases from 10 to 100 mV/s. Moreover, the incorporation of 0D c-CN nanoparticles increases the available space for charge accumulation, yielding a volumetric capacitance of 28.5 F/cm3 at a scan rate of 10 mV/s, which is three times higher than that of a pure FL-BP film electrode (9.2 F/cm3). This work presents an innovative approach for developing high-performance FL-BP-based FSCs.

Lithium-containing 45S5 Bioglass-derived glass-ceramics have antioxidant activity and induce new bone formation in a rat preclinical model of type 1 diabetes mellitus

Abstract Diabetes mellitus (DM) has been associated with complications that affect the skeletal system, such as alterations in bone repair, osteoporosis, and an increased risk of fractures. In this context, the use of biomaterials able to promote osteogenic differentiation and, at the same time, limit the oxidative stress induced by DM offers a novel perspective to ensure the repair of diabetic bone tissue. Since lithium (Li) has been recently identified as a biologically active ion with osteogenic and antioxidant properties, the localized and controlled release of Li ions from bioactive glass-ceramic materials represents a promising therapeutic alternative for the treatment of bone lesions in DM. Thus, the aim of this study was to evaluate the potential osteogenic and antioxidant effects of glass-ceramic microparticles derived from a 45S5-type bioactive glass (Bioglass) containing (% by weight) 45% SiO2, 24.5% Na2O, 24.5% CaO, and 6% P2O5, in which Na2O was partially substituted by 5% of Li2O (45S5.5Li), in an experimental model of type 1 DM (DM1). The results obtained demonstrate, for the first time, that both 45S5 and 45S5.5Li glass-ceramic microparticles possess antioxidant activity and stimulate bone formation in vivo both under physiological conditions and under experimental DM1 in rats. In this sense, they would have potential application as inorganic osteogenic agents in different strategies of bone tissue regenerative medicine.

An enhanced electrokinetic system for remediation of Cu-polluted clay soils by integrating purging solutions and intermittent power

This study investigated the effectiveness and underlying mechanisms of purging solutions enhanced by intermittent power in improving electrokinetic (EK) restoration of clay soils even under high levels of heavy metals (HM). In so doing, the artificially contaminated specimens containing a wide range of copper (Cu) were prepared and then subjected to a series of EK tests with various electrolytes and electric regimes. Macro and micro scale examinations revealed that under the unenhanced EK condition (i.e., continuous current without agents), the formation of non-conducting solid phases and/or the clogged fabric in the samples with the high dosages (> 250 mg/kg) of HM could dramatically impede the metal separation from the soil. Hence, increasing the remediation time would not be very effective in facilitating the decontamination process. It was observed that the EDTA-ameliorated treatment accompanied by pentetic acid and acetic acid can mitigate the metal precipitation/encapsulation effects induced by EK actions, resulting in improved rate of HM removal. In this case; however, a high portion of these enhancers would be required to ensure the stable mobility of ions and to achieve successful recovery. Such a limitation has been shown to be overcome by incorporating pulsed power (PP) at an optimal frequency. In fact, as evidenced by SEM-EDX and XRD analyses, the integration of chemical agents with PP could simultaneously retain the solubilized Cu species in the soil mass and modify the matrix tortuosity (i.e., the establishment of well-linked pores), two features that have been found to play essential roles in providing for favorable activity of HM ions during the EK operation. The corresponding refinements in the binary system would cause an almost 8 folds increase in the removal efficiency and a shorter (up to 30 %) time of treatment compared to conventional EK.

Using physicochemical properties to predict the impact of natural dissolved organic carbon on transepithelial potential in the freshwater rainbow trout (Oncorhynchus mykiss) at neutral and acidic pH.

Dissolved organic carbon (DOC) is a complex mixture of molecules that varies in composition based on origin as well as spatial and temporal factors. DOC is an important water quality parameter as it regulates many biological processes in freshwater systems, including the physiological function of the gills in fish. These effects are often beneficial, especially at low pH where DOCs mitigate ion loss and protect active ion uptake. DOCs of different compositions and quality have varied ionoregulatory effects. The molecular variability of DOCs can be characterized using optical and chemical indices, but how these indices relate to the physiological effects exerted by DOCs is not well understood. We tested the effects of five naturally sourced DOCs, at both pH 7 and pH 4, on transepithelial potential (TEP) (a diffusion potential between the blood plasma and the external water) in rainbow trout. The five chosen DOCs have been well characterized and span large differences in physicochemical characteristics. Each of the DOCs significantly influenced TEP, although in a unique manner or magnitude which was likely due to their physicochemical characteristics. These TEP responses were also a function of pH. With the goal of determining which physicochemical indices are predictive of changes in TEP, we evaluated correlations between various indices and TEP at pH 7 and pH 4. The indices included: specific absorbance coefficient at 340nm, molecular weight index, fluorescence index, octanol-water partition coefficient, molecular charge, proton binding index, % humic acid-like, % fulvic acid-like, and % protein-like components by parallel factor analysis on fluorescence data (PARAFAC). Our results demonstrate the novel finding that there are three particularly important indices that are predictors of changes in TEP across pHs in rainbow trout: specific absorbance coefficient at 340nm, octanol-water partition coefficient; and proton binding index.

High-mass loaded redox-active lignin functionalized carbonized wood collector to construct sustainable and high-performance supercapacitors

Traditional electrode materials for supercapacitors often face issues like high toxicity, cost, and non-renewability. To address these drawbacks, biomass-based alternatives are being explored, aligning with green development trends. Herein, carbonized wood (CW) with rich pore structure and redox-active lignin are combined to fabricate an all-wood-based sustainable supercapacitor electrode material. Due to its inherent porous structure, CW provides a larger surface area for accommodating active materials ion, enabling the electrode to achieve a higher lignin loading capacity of 2.82–11.68 mg/cm2. Furthermore, the utilization of lignin as a substitute for conventional transition metal-based pseudocapacitor material functionalized CW endows the electrode with exemplary electrochemical performance while guaranteeing the comprehensive sustainability of the electrode. This synergy confers the electrode with exceptional electrical performance, yielding an areal capacitance of 960.7 mF/cm2 at a current density of 1 mA/cm2. The symmetric supercapacitors (SSC) manufactured by this composite electrode can achieve a notable areal energy density of 0.14 mWh/cm2 and a power density of 15.98 mW/cm2, while maintaining an outstanding capacitance retention rate of 81 % after 50,000 cycles at 20 mA/cm2. The manufacture of CW-lignin electrode underscores the potential of utilizing renewable biomass resources as alternatives for developing high-performance energy storage applications, thereby reducing negative environmental impacts.

Calculations of mean ionic activity coefficients of copper and manganese salts in aqueous solutions

Accurately predicting the activity coefficients of copper and manganese salts in aqueous solutions is crucial for treating industrial wastewater, and it is of practical interest to calculate the activity coefficients of heavy metals in aqueous solutions using the Equation of State because of its high flexibility and wide range of applicability. This work conducts a modeling study on the mean ionic activity coefficients of copper and manganese salts in aqueous solutions. The thermodynamic framework used in this work is an electrolyte version of the Cubic Plus Association Equation of State (e-CPA). The model's ion-water binary interaction parameters are obtained by regressing the osmotic coefficients and mean ionic activity coefficients in aqueous solutions. The modeling results indicate that the electrolyte Equation of State can satisfactorily correlate the water activity, osmotic coefficients, and mean ionic activity coefficients of copper and manganese salts in aqueous solutions over a wide range of salt concentrations. Among all the systems at 298.15 K, the biggest average relative deviation between calculated and experimental values is within 6.7 % and 2.3 % for the mean ionic activity coefficients and water activity, respectively. Furthermore, this work discusses the impact of ion pairs on the phase equilibrium of aqueous systems from a microscopic mechanism perspective and analyzes and discusses the model's adaptability. The model used in this work can accurately predict the activity coefficients of a variety of copper and manganese salts in aqueous solutions over wide concentration ranges and provides an improved interface for improving the calculation accuracy of the model under high concentration or other complex conditions.

Novel Eu3+-Doped Glasses in the MoO3-WO3-La2O3-B2O3 System: Preparation, Structure and Photoluminescent Properties.

Novel multicomponent glasses with nominal compositions of (50-x)MoO3:xWO3:25La2O3:25B2O3, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % Eu2O3 were prepared using a conventional melt-quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. The optical properties of the glasses were investigated by UV-vis absorption spectroscopy and a determination of the refractive index. Physical parameters such as density, molar volume, oxygen molar volume and oxygen packing density were determined. The glasses are characterized by a high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO4)2- and (WO4)2- units providing Raman bands of around 317 cm-1, 341-352 cm-1, 832-820 cm-1 and 928-935 cm-1. At the same time, with the replacement of MoO3 with WO3 some fraction of WO6 octahedra are produced, the number of which increases with the increasing WO3 content. A strong red emission from the 5D0 level of Eu3+ ions was registered under near-UV (397 nm) excitation using the 7F0 → 5L6 transition of Eu3+. Photoluminescence (PL) emission gradually increases with increasing WO3 content, evidencing that WO3 is a more appropriate component than MoO3. The integrated fluorescence intensity ratio R (5D0 → 7F2/5D0 → 7F1) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu3+ in non-centrosymmetric sites. All findings suggest that the investigated glasses are potential candidates for red light-emitting phosphors.

Luminescence performance, temperature sensing characteristics and Judd-Ofelt theory analysis of Y2MoO6:Er3+/Yb3+/Li+ upconversion phosphors

A series of Y2MoO6:0.01Er3+/0.09Yb3+ upconversion phosphors doped with different concentrations of Li+ ions (0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 mol) were prepared by the high temperature solid phase reaction method, and their physical phase structures and upconversion luminescence were analyzed. At the excitation wavelength of 980 nm, the addition of Li+ sharply increased the upconversion luminescence intensity. With the increase of Li+ ion content, the luminescence intensity first increases and then decreases. When the doping amount reaches 0.25 mol, the luminescence intensity reaches the maximum, and the sample emits green light in the two-photon process. Y2MoO6:0.01Er3+/0.09Yb3+/0.25Li+ exhibits excellent temperature sensing properties. Its absolute sensitivity Sa reaches up to 0.012 K-1, the relative sensitivity Sr is 0.017 K-1 and the measurement error δT is less than 0.3 K at room temperature. Its temperature sensing performance is far superior to similar materials. In addition, Judd-Ofelt theory calculations revealed that in comparison with Y2MoO6:0.01Er3+/0.09Yb3+, its Ω2 increased from 0.56×10-20 cm2 to 3.68×10-20 cm2 , and the spectroscopic quality factor Ω4/Ω6 ratio reached 4.09, which is much higher than that of the other fluorescent materials. The main reason is that Li+ replaces the Y3+ ion lattice site, causing lattice distortion and reducing the lattice symmetry around the active ion. The increase in asymmetry increases the possibility of spontaneous radiative transitions. It is shown that the prepared upconversion luminescent materials have potential applications in the field of solid-state lasers and optical sensing.

Research progress on iron metabolism in the occurrence and development of periodontitis

Iron metabolism refers to the process of absorption, transport, excretion and storage of iron in organisms, including the biological activities of iron ions and iron-binding proteins in cells. Clinical research and animal experiments have shown that iron metabolism is associated with the progress of periodontitis. Iron metabolism not only enhances the proliferation and toxicity of periodontal pathogens, but also activate host immune-inflammatory response mediated by macrophages, neutrophils and lymphocytes. In addition, iron metabolism is also involved in regulating cellular death sensitivity of gingival fibroblasts and osteoblasts and promoting the differentiation of osteoclasts, which plays a regulatory role in the regeneration and repair of periodontal tissue. This article reviews the research progress on the pathogenesis of periodontitis from the perspective of iron metabolism, aiming to provide new ideas for the treatment of periodontitis.

Preparation, Characterization and in Vitro Stability of Soy Protein Fibrils Ferrous Delivery System

Iron deficiency is considered widespread globally, and discovering ferrous ion delivery system with better stability is one of the keys to solving this problem. In this paper, a ferrous ion delivery system was prepared from soy isolate protein fibrils (SPNFs). The alterations in infrared spectrum and microstructure before and after loading were compared, and the ionic strength stability, freeze-thaw stability, and oxidative reaction activity of soy isolate protein fibrils loaded with ferrous iron (SPNFs-Fe) were analyzed, simulating the release kinetics of gastrointestinal digestion. The results demonstrated that SPNFs load ferrous ions with carboxyl, carbonyl, and amino groups. SPNFs-Fe had good ionic strength stability and excellent freeze-thaw stability and showed weak pro-oxidation activity. The release kinetics of SPNFs-Fe in simulated gastrointestinal digestion best fit the Ritger-Peppas model, which had a slow-release effect in simulated gastrointestinal digestion. The release of SPNFs-Fe in simulated gastric fluid belonged to Fick diffusion, while in simulated intestinal fluid it belonged to non-Fick diffusion. These results suggest that SPNFs-Fe is a promising ferrous delivery system as a supplementary source of iron.

Antioxidant and Xanthine oxidase inhibitory activities of the tea (Camellia sinensis) flower

The major purpose of this study was to investigate the DPPH radical scavenging activity, hydroxyl radical scavenging activity, superoxide radical scavenging activity, reducing power, ferrous ion chelating activity, and xanthine oxidase activity for research of antioxidant and xanthine oxidase inhibitory activities using a variety of extracts of tea (Camellia sinensis) flower. Among the several extracts, when 800 μg/mL of the ethanol extract was used, the maximum DPPH radical scavenging activity was obtained, 79.2%, which was approximately 80.8% compared to L-ascorbic acid, the maximum hydroxyl radical scavenging activity, 71.3%, which was approximately 73.2% compared to BHA, and the maximum super oxide radical scavenging activity, 89.4%, which was, approximately 90.6% compared to BHT, and the maximum reducing power, 1.94 at an OD of 700 nm, which was approximately 49.2% compared to L-ascorbic acid, respectively. On the other hand, when 800 μg/mL of the hot water extract was used, the maximum activity of ferrous ion chelate was obtained, 28.6%, which was approximately 48.4% compared to EDTA and the maximum xanthine oxidase inhibitory activity, 61.4%, approximately 63.8% compared to catechin, respectively. These results indicated the application potential for industries that can produce new biomaterials that can compensate for the shortcomings of existing synthetic antioxidants and use discarded tea flower as food, pharmaceutical, and cosmetic materials.

Novel sulfonylurea fluorescence probes for antiproliferative activity, detection and imaging of fluoride ions in living cells

In this study, four novel triphenylpyrazoline 4-toluenesulfonylureas (PYSUs) were synthesized to develop potential anticancer drugs and fluorescent probes for the detection of F− ions. The compounds were synthesized via a two-step microwave-assisted method. The antiproliferative activity of the PYSUs was tested against two cancer cell lines: HepG2 and MDA-MB-231. Among the compounds, 3a exhibited strong activity against both cell lines, while 3b showed strong activity against MDA-MB-231 cells but weaker inhibition of HepG2 cells. Furthermore, compound 3b was identified as the best fluorescent probe, with an increase in emission intensity in the presence of F− ions from tetrabutylammonium fluoride (TBAF). In DMSO, the emission wavelength was found to be 518 nm (green) with an excitation wavelength of 469 nm. The limit of detection (LOD) was calculated to be 0.269 mM in the linear range of 5–10 mM. The interaction mechanism between F− ions and compound 3b was further explored via DFT/TDDFT calculations. Additionally, fluorescent imaging of TBAF-incubated MDA-MB-231 and HepG2 cells confirmed the potential of PYSUs as fluorescent sensors for F− ions in living cancer cells.

Ion sensors based on organic semiconductors acting as quasi-reference electrodes

Thin-film devices that transduce the chemical activity of ions into electronic signals are essential components in various applications, including healthcare diagnostics and environmental monitoring. Combinations of organic semiconductors (OSCs) and ion-selective materials have been explored for developing solution-processable ion sensors. However, the necessity of reference electrodes (REs) and operational stability in ion-permeable OSCs have posed questions regarding whether reliable measurements with thin-film components are attainable with OSCs. Herein, we report electric double-layer transistors (EDLTs) with OSCs in single-crystal forms for ion sensing. Our EDLTs demonstrated high operational stability, with a one-to-one relationship between the source electrode potential and device resistance, and served as quasi-REs (qRE). When our EDLT is served as qRE, its drift was as small as 0.5 mV/h and comparable to that of commonly employed REs. In our system, the semiconductor-electrolyte interface is self-passivated by the alkyl chains of OSCs in single-crystal structures, with the two-dimensional transport layer appearing unaltered upon gating. EDLT arrays with ion-selective and nonselective liquid junctions enable ion concentration sensing without a conventional RE. These findings provide opportunities to develop thin-film devices based on OSCs for easy integration and reliable measurements.

Evaporated Copper‐Based Perovskite Dynamic Memristors for Reservoir Computing Systems

AbstractDynamic memristors are considered as the optimal hardware devices for reservoir computing (RC) enabled by their nonlinear conductance variations. This significantly reduces the extensive training workload typically required by traditional neural networks. Lead halide perovskites, with their tunable band structure and active ion migration properties, have emerged as highly promising materials for developing dynamic memristors. However, large‐scale and consistently stable production remains a challenge for perovskite functional films, while lead elements' toxicity and environmental impact also partly restrict their practical device utilization. In this work, lead‐free copper‐based perovskite (i.e., CsCu2I3) films are prepared by thermal evaporation for constructing dynamic memristors. The effective conductivity modulation of CsCu2I3‐based memristor can be utilized in artificial neural networks, achieving a high handwritten digit recognition accuracy of 91.2%. In addition, the RC system is also constructed based on the dynamic behavior of the devices, by which a letter recognition accuracy of 98.2% with simple training is achieved. This technology provides a feasible pathway to construct copper‐based perovskite dynamic memristors for future neural network information processing.

Bidentate Substrate Binding Mode in Oxalate Decarboxylase.

Oxalate decarboxylase is an Mn- and O2-dependent enzyme in the bicupin superfamily that catalyzes the redox-neutral disproportionation of the oxalate monoanion to form carbon dioxide and formate. Its best-studied isozyme is from Bacillus subtilis where it is stress-induced under low pH conditions. Current mechanistic schemes assume a monodentate binding mode of the substrate to the N-terminal active site Mn ion to make space for a presumed O2 molecule, despite the fact that oxalate generally prefers to bind bidentate to Mn. We report on X-band 13C-electron nuclear double resonance (ENDOR) experiments on 13C-labeled oxalate bound to the active-site Mn(II) in wild-type oxalate decarboxylase at high pH, the catalytically impaired W96F mutant enzyme at low pH, and Mn(II) in aqueous solution. The ENDOR spectra of these samples are practically identical, which shows that the substrate binds bidentate (κO, κO') to the active site Mn(II) ion. Domain-based local pair natural orbital coupled cluster singles and doubles (DLPNO-CCSD) calculations of the expected 13C hyperfine coupling constants for bidentate bound oxalate predict ENDOR spectra in good agreement with the experiment, supporting bidentate bound substrate. Geometry optimization of a substrate-bound minimal active site model by density functional theory shows two possible substrate coordination geometries, bidentate and monodentate. The bidentate structure is energetically preferred by ~4.7 kcal/mol. Our results revise a long-standing hypothesis regarding substrate binding in the enzyme and suggest that dioxygen does not bind to the active site Mn ion after substrate binds. The results are in agreement with our recent mechanistic hypothesis of substrate activation via a long-range electron transfer process involving the C-terminal Mn ion.

Dependence of oxygen evolution reaction catalysis at thin cathodically-deposited nickel-iron-selenide on Fe in the alkaline electrolyte vs. codeposited Fe

This study interrogated the role of Fe co-deposited in films versus Fe included from traces in the electrolyte on the electrochemical dynamics and kinetics for the oxygen evolution reaction (OER) in alkaline at a nickel-iron selenide OER pre-catalyst. Iron was co-included in the bulk of nickel selenide (NixSey) during cathodic deposition and is termed bulk-Fe (Febulk), and/or was included on its surface post-deposition by conditioning at anodic bias in alkaline with Fe traces and is termed surface-Fe (Fesurface). The electrochemical dynamics, OER kinetics, and sustainability of catalysis were studied in 1 M KOH stripped of Fe (Fe-free KOH) or containing Fe traces (KOH). The selenides transformed into a selenide/hydroxide with a few monolayers of surface hydroxide during the hours of conditioning and electrokinetic measurements at anodic bias in both solutions. Bulk-Fe did not enhance OER catalysis at nickel selenide, while surface-Fe promoted OER catalysis. Tafel slopes of ca. 40 mV/dec were recorded at (NiFebulk)xSey-Fesurface and NixSey-Fesurface in KOH, while Tafel-slopes of ca. 100 mV/dec were recorded at (NiFebulk)xSey in Fe-free KOH. Tafel slopes of 60–80 mV/dec were recorded in Fe-free KOH at (NiFebulk)xSey-Fesurface and NixSey-Fesurface that had been conditioned in KOH. OER catalysis at Fesurface-activated electrocatalysts was not sustained in alkaline stripped of Fe, neither at anodic bias nor subjected to potential cycling. The electrochemical data is consistent with a mechanism involving a low-coordination surface-Fe in the thin hydroxide layer of not more than few monolayers formed in-situ on the selenide. Surface-Fe is pictured as part of a dynamic catalytic site whose equilibrium density, to ensure sustainable catalysis, requires a greater than a threshold activity of Fe ions and lower than a threshold of activity of Ni, otherwise Fe will be in an inactive high-coordination state.