Electron Transfer Reactions Research Articles

Structure and fragmentation chemistry of the peptide radical cations of glycylphenylalanylglycine (GFG).

Herein, we explore the generation and characterization of the radical cations of glycylphenylalanylglycine, or [GFG]•+, formed via dissociative electron-transfer reaction from the tripeptide to copper(II) within a ternary complex. A comprehensive investigation employing isotopic labeling, infrared multiple-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations elucidated the details and energetics in formation of the peptide radical cations as well as their dissociation products. Unlike conventional aromatic-containing peptide radical cations that primarily form canonical π-radicals, our findings reveal that 75% of the population of the experimentally produced [GFG]•+ precursors are [GFα•G]+, where the radical resides on the middle α-carbon of the phenylalanyl residue. This unexpected isomeric ion has an enthalpy of 6.8 kcal/mol above the global minimum, which has an N-terminal captodative structure, [Gα•FG]+, comprising 25% of the population. The [b₂-H]•+ product ions are also present in a ratio of 75/25 from [GFα•G]+/ [Gα•FG]+, the results of which are obtained from matches between the IRMPD action spectrum and predicted IR absorption spectra of the [b₂-H]•+ candidate structures, as well as from IRMPD isomer population analyses.

Theoretical insights into the HO●-induced oxidation of chlorpyrifos pesticide: Mechanism, kinetics, ecotoxicity, and cholinesterase inhibition of degradants

The oxidation of the common pesticide chlorpyrifos (CPF) initiated by HO● radical and the risks of its degradation products were studied in the gaseous and aqueous phases via computational approaches. Oxidation mechanisms were investigated, including H-, Cl-, CH3- abstraction, HO●-addition, and single electron transfer. In both phases, HO●-addition at the C of the pyridyl ring is the most energetically favorable and spontaneous reaction, followed by H-abstraction reactions at methylene groups (i.e., at H19/H21 in the gas phase and H22/H28 in water). In contrast, other abstractions and electron transfer reactions are unfavorable. However, regarding the kinetics, the significant contribution to the oxidation of CPF is made from H-abstraction channels, mostly at the hydrogens of the methylene groups. CPF can be decomposed in a short time (5–8 h) in the gas phase, and it is more persistent in natural water with a lifetime between 24 days and 66 years, depending on the temperature and HO● concentration. Subsequent oxidation of the essential radical products with other oxidizing reagents, i.e., HO●, NO2●, NO●, and 3O2, gave primary neutral products P1–P15. Acute and chronic toxicity calculations estimate very toxic levels for CPF and two degradation products, P7w and P12w, in aquatic systems. The neurotoxicity of these products was investigated by docking and molecular dynamics. P7w and P12w show the most significant binding scores with acetylcholinesterases, while P8w and P13w are with butyrylcholinesterase enzyme. Finally, molecular dynamics illustrate stable interactions between CPF degradants and cholinesterase enzyme over a 100 ns time frame and determine P7w as the riskiest degradant to the neural developmental system.

Boosting Photon Emission from the Chemiluminescence of Luminol Based on Host-Guest Recognition for the Determination of Dopamine.

Modulating the photon emission of the luminophore for boosting chemiluminescence (CL) response is very crucial for the construction of highly sensitive sensors via the introduction of functionalized materials. Herein, the integration of the emitter and coreactant accelerator into one entity is realized by simply assembling cucurbit[7]uril (CB[7]) on the surface of gold nanoparticles (AuNPs) through simple assembly via a Au-O bond. The loaded CB[7] on the AuNPs improves their catalytic capacity for the generation of hydroxyl radicals(•OH). Moreover, the host-guest recognition interaction between luminol and CB[7] enables the capture of luminol on AuNPs efficiently. Also, the intramolecular electron-transfer reaction between the luminol and •OH enables the CL response more effectively in the entity, which greatly boosts photon emission ca 100 folds compared with the individual luminol/H2O2. The host-guest recognition between luminol and CB[7] is revealed by Fourier transform infrared spectroscopy, electrochemical, and thermogravimetric characterization. Moreover, the proposed CL system is successfully used for the sensitive and selective determination of dopamine (DA) based on a synergistic quenching mechanism including the competition quenching and radical-scavenging effect from DA. The present amplified strategy by integrating recognized and amplified elements within one entity simplifies the sensing process and holds great potential for sensitive analysis based on the self-enhanced strategies.

Single-Entity Bioelectrochemistry

Interfacing biological catalytic entities, such as whole cells or enzymes, with electrodes, has a wide range of applications, ranging from fundamental studies of the entities themselves to power generation, bioremediation, chemical synthesis, and biosensing. In all cases, the operation of these bioelectrocatalytic systems is based on electron transfer phenomena within protein molecules, whether isolated or residing inside cells or parts of cells, as well as between proteins and electronics. Typically, the electron transfer and catalytic properties of proteins are studied using ensemble averaging methods, which obscure any heterogeneity and dynamics of individual molecules. This information, however, is especially important for understanding electron transfer and catalytic processes within a living cell where only one or a few protein molecules are present. While single-entity electrochemical measurements are particularly useful for studying electron transfer reactions at the nanoscale level, they have limited applications for investigating biological entities due to the experimental challenges associated with direct measurements of small electrical currents. 1,2 Here we will discuss our recent progress in investigating biological electron transfer reactions at the single-entity level, from bacterial cells to single redox proteins, using nano-impact (collision) single-entity electrochemistry. 3 We demonstrate how advances in electrode fabrication methods and detection setups enable current detection in the fA range. When combined with the developed data processing algorithm based on unsupervised learning and template matching techniques, this enabled unprecedented insight into electron transfer processes at the nanoscale. We will talk about insights provided by the method in the study of several important bioelectrocatalytic systems: single E.coli cells with overexpressed Fe-Fe hydrogenases, single bilirubin oxidase molecules, and single catalase molecules. In addition, we will discuss models that we developed for understanding the single bioentity electrode interactions for diffusion-controlled enzymes when the product of the catalytic reaction is detected on the electrode, as well as systems based on direct electron transfer between the bioentity and the electrode. Overall, we show how single-entity bioelectrochemistry can shed light on biological electron transfer and catalysis processes and discuss the challenges it currently faces. Zhang, J.-H.; Zhou, Y.-G. Nano-Impact Electrochemistry: Analysis of Single Bioentities. TrAC Trends Anal. Chem. 2019, 115768.Davis, C.; Wang, S. X.; Sepunaru, L. What Can Electrochemistry Tell Us About Individual Enzymes? Curr. Opin. Electrochem. 2020, 100643.Sekretaryova, A. N.; Vagin, M. Yu.; Turner, A. P. F.; Eriksson, M. Electrocatalytic Currents from Single Enzyme Molecules. J. Am. Chem. Soc. 2016, 138 (8), 2504–250

Ammonium nanochelators in conjunction with arginine-specific enzymes in amperometric biosensors for arginine assay

Amino acid L-arginine (Arg), usually presented in food products and biological liquids, can serve both as a useful indicator of food quality and an important biomarker in medicine. The biosensors based on Arg-selective enzymes are the most promising devices for Arg assay. In this research, three types of amperometric biosensors have been fabricated. They exploit arginine oxidase (ArgO), recombinant arginase I (ARG)/urease, and arginine deiminase (ADI) coupled with the ammonium-chelating redox-active nanoparticles. Cadmium-copper nanoparticles (nCdCu) as the most effective nanochelators were used for the development of ammonium chemosensors and enzyme-coupled Arg biosensors. The fabricated enzyme/nCdCu-containing bioelectrodes show wide linear ranges (up to 200 µM), satisfactory storage stabilities (14 days), and high sensitivities (A⋅M−1⋅m−2) to Arg: 1650, 1700, and 4500 for ADI-, ArgO- and ARG/urease-based sensors, respectively. All biosensors have been exploited to estimate Arg content in commercial juices. The obtained data correlate well with the values obtained by the reference method. A hypothetic scheme for mechanism of action of ammonium nanochelators in electron transfer reaction on the arginine-sensing electrodes has been proposed.Graphical abstract

Accelerating Electrocatalyst Innovation: High-Throughput Automated Microkinetic Modeling

To reduce energy-related emissions, we must create chemicals from carbon dioxide with renewable energy, instead of from petroleum. Designing such a process needs computer models that can describe all the chemical reactions that are happening, including those driven by electrochemistry. There may be thousands of such reactions, so we must build a tool to find them automatically. Our reaction mechanism generator for electrocatalysis will create detailed kinetic models for many electrochemical processes, but for this initial project we are targeting the reduction of carbon dioxide to produce propanol, a useful hydrocarbon product. The kinetic models will be used to simulate an electrochemical reactor, then analyzed both technically and economically to determine which catalyst materials and reactor designs are best. This will allow new catalyst materials to be discovered using powerful computers, instead of using very time-consuming and expensive experiments.Building on the state-of-the-art open-source Reaction Mechanism Generator (RMG) software [1,2], we are creating the first automated mechanism generator for electrochemical reactions on a catalyst. Supplied with a feedstock, catalyst, and conditions, it will propose a detailed kinetic model comprising hundreds of intermediate species and reactions. Reactor simulations will predict product yields as a function of feed, concentrations, and potential, allowing conditions to be optimized and the trade-off between conversion and selectivity to be investigated. In turn this could inform a detailed technoeconomic analysis, enabling catalyst materials to be screened in silico on an economic basis. Meanwhile sensitivity analysis of the simulations will select estimated parameters for refinement with DFT calculations.We must first extend RMG to allow charged species, and implement proton coupled electron transfer (PCET) reactions. We will at first use the computational hydrogen electrode model to determine the Gibbs energy of a species (and hence reaction) as a function of chemical potential. Potential-dependent kinetics will be estimated using a charge transfer coefficient model. In preliminary work with a framework like this we have constructed a reaction mechanism for carbon dioxide reduction on Cu(111) with 37 species and 292 reactions (23 of them electrochemical) [3]. The model discovered many key electrochemical pathways to reduce CO2 to experimentally observed products such as methane, methanol, formic acid, ethylene, and ethanol. Acknowledgements The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0001786. The authors thank Dr. David Farina Jr. for his significant contributions to the proof-of-concept.

Transient Short Circuit-Based Degradation of Lithium and Sodium Anode-Free Batteries

The demand for an extended range of electric vehicles has created a renaissance of interest in replacing the common lithium-ion with a higher energy-density metal anode (e.g., Li or Na). However, alkali metal cells suffer from capacity fading and potential safety issues. The uneven metal electrodeposition often results in dendrite formation and potentially hazardous situations such as cell short-circuiting and thermal runaway.Though lithium plating has been studied widely, a better understanding of the short-circuiting mechanisms and metal battery failure is required. Moreover, a considerable performance gap exists between symmetric metal cells and realistic metal batteries."Soft shorts" are small localised electrical connections between two electrodes that allow the co-existence of direct electron transfer and interfacial reaction. Although soft shorts were identified as a major safety issue in the early nineties, their detection and prevention were not widely studied. Therefore, a fundamental understanding of passivated metals' plating and a reliable testing method for soft short circuits is critical for realising metal batteries, such as Li-Air, Li-S, and anode-free batteries.Here we compared short circuit formation mechanisms and degradation in symmetric cells and anode-free lithium and sodium batteries using coupled galvanostatic impedance spectroscopy (GEIS) and in-situ nuclear magnetic resonance spectroscopy (NMR) for the first time.The coupling of in-situ NMR and EIS allows the observation of metal batteries' electrochemical and chemical dynamics and degradation in real time without affecting the cells' operation.We demonstrated that lithium and sodium short circuit formation mechanisms fundamentally differ and strongly depend on electrolyte composition and SEI stability. This new understanding of the metal plating mechanism is crucial to develop the next generation of rechargeable batteries with high energy density, prolonged cycling life and improved sustainability.

Theoretical Study on the Multiple Free Radical Scavenging Reactions of Pyranoanthocyanins.

The free radical trapping capacities of multiple pyranoanthocyanins in wine storage and ageing were theoretically explored by density functional theory (DFT) methods. Intramolecular hydrogen bonds were detected in all pyranoanthocyanins, and the planarity of the compounds worsened with an increasing dielectric constant in the environment. Solvents significantly influenced the reaction enthalpies; thus, the preferred thermodynamic mechanisms of the free radical scavenging reactions were modified in different phases. This study incorporates hydrogen atom transfer (HAT), proton loss (PL), electron transfer (ET) reactions, and demethylation (De) of methoxy group mechanisms. The three pyranoanthocyanins have the capacity to capture n1+1 free radicals, where n1 represents the number of methoxy groups. In the gas phase, they prefer employing the n1-De-HAT mechanism on the guaiacyl moiety of the B ring, resulting in the formation of a stable quinone or a quinone radical to scavenge free radicals. In the benzene phase, pyranoanthocyanins trap free radicals via a PL-n1-De-HAT mechanism. In the water phase, the targeted pyranoanthocyanins may dissociate in the form of carboxylate and tend to utilize the n2-PL-n1-De-ET mechanism, where n2 and n1 represent the number of phenolic groups and methoxy groups, respectively, facilitating multiple H+/e- reactions.

(Invited) Composite Electrodes – the Challenge of Characterizing Ionic Transport on the Liquid Side of the Solid-Liquid Interface

Composite electrodes are at the hart of modern batteries, since they overcome critical limitations of the solid active materials including volume changes as well as poor electronic and ionic conduction. Due to the very nature of the composite electrodes the solid-liquid interface of electron transfer reaction become buried within the bulk. Moreover, the bulk of the electrode has a complex internal structure, which is exceeding difficult to characterize using even advanced electron and X-ray techniques. This is in part due the nanometric size of the carbon black used to improve electron transport. In this talk, we will present some of our latest development based on scanning electrochemical microscopy and synchrotron radiation to characterize the electrolyte side of the composite electrode. Specifically, we will present data to suggest that the canonical electrolyte transport can be determined in a single sided measurement, greatly simplifying analysis in quality control and providing experimental data for this critical parameter in battery modeling. Moreover, we will present operando measurements of the electrolyte concentration gradient within the composite electrode. This matrix is particularly changeling due to its paramagnetic, conducting and opaque nature. The talk will conclude with an outlook on opportunities and challenges related to these techniques.

Understanding the Reaction Mechanism and Kinetics of Mediated Li-O2 Batteries Using Flow Set-Ups and Cyclic Voltammetry

Li-O2 batteries are very promising candidates for electromobility because of their very high theoretical energy density. Moreover, they are composed of abundant materials, as opposed to Li-ion batteries, which would make them a greener and cheaper alternative. The principal reaction in Li-O2 batteries is the formation of lithium peroxide during discharge via the oxygen reduction reaction (ORR), that is then oxidised during the charge by the oxygen evolution reaction (OER). One of the major challenges of Li-O2 batteries is related to the insulating nature of their discharge product, that significantly limits the capacity and hinders performance. A strategy to overcome this is by using redox mediators (RMs), which shuttle electrons from the electrode surface to the solution and thus facilitate a solution-based mechanism for the formation of large crystals. Understanding the reaction kinetics of these RMs can therefore aid in increasing the battery performance.Quinones, specifically 2,5-Di-tert-butyl-1,4-benzoquinone (DBBQ),is a commonly used discharge RM in this type of batteries. However, their reaction kinetics and how these vary with different electrolyte conditions are not yet well understood. DBBQ undergoes two single electron reductions, whose potentials and kinetics vary with salt concentrations and solvent having a direct effect on its ability to mediate the ORR.In this work, we have developed a Li-O2 flow cell to study the reaction mechanism and kinetics of DBBQ, and performed cyclic voltammetry (CV) studies to better understand how these vary with changing solvent and salt conditions. In the Li-O2 flow set-up the battery is positioned outside the nuclear magnetic resonance (NMR) magnet and plastic tubing then runs through the NMR and electron paramagnetic resonance (EPR) spectrometers. In this way, the reduction of the DBBQ can be monitored while the battery is cycling. In the proton NMR, the neutral DBBQ signals disappear on discharge as the singly reduced DBBQ semiquinone monoanion is a radical. The fast electron exchange between the neutral and radical species broaden out the NMR signals on discharge as the EPR signal grows. On charge, the neutral DBBQ signal reappears and the EPR signal disappears. The Li-O2 flow set-up is very sensitive to air and moisture exposure as the tubing is not perfectly impermeable to them. Therefore, having the CVs as a complementary method to study the reaction mechanisms and kinetics is very useful.We have developed a theoretical framework of Li-coupled electron transfer reactions that can predict the electrochemical kinetics in the presence of high and low donor number solvents and used to quantify thermodynamic and kinetic parameters. We define E0 app and k0 app as the apparent thermodynamic and kinetic parameters that describe the overall system and can be derived from the Nernst equation and Butler Volmer kinetics. These overall descriptors depend on the pathway the reaction takes (Figure 1). The different pathways in different solvents/salts are due to changes in the Li+ solvation strength as well as the competing ionic association of the counter anion.Experimentally, we have shown that in three different solvents, DME, tetraglyme and DMSO the behaviour of DBBQ can be explained by this theoretical framework. In DME, the DBBQ behaviour is most reminiscent of pathway 1 where the kinetics slow down with increasing Li+ concentration. In DMSO the kinetics present a maximum at Li+ concentrations around 1M. Simulations and fitting of the CV experiments in DMSO for the first reduction are in good agreement with pathways 2 and 3, while in tetraglyme it is harder to explain the trends as they do not fit into just one of the pathways.In conclusion we have studied the mechanism and kinetics of DBBQ as a RM for Li-O2 batteries with an in-situ flow set up and CVs and build a theoretical framework to understand how these vary in different electrolyte conditions. This method can be extended to study both the second reduction of DBBQ and other discharge and charge RMs for Li-O2 batteries. Figure 1

(Europe Section Heinz Gerischer Award) Endeavours in the Electro-Solar World of Schottky, Mott and Gerischer

The origins of semiconductor electrochemistry lies in the early 20th century with the pioneering work of scientists like Walter H. Schottky, Nevill Mott, and Heinz Gerischer. Schottky and Mott made significant contributions to the understanding of semiconductor physics, while Gerischer is often credited with laying the groundwork for the field of semiconductor electrochemistry. Particularly Gerischer's studies on the kinetics of electron transfer reactions at semiconductor-electrolyte interfaces have been fundamental to our understanding of semiconductor chemistry and photoelectrochemistry. His early work has conceptually created strong links between electrochemistry and solid state physics, has created a close connection to photochemistry, and has profoundly improved the understanding of interfacial reactions. It allowed to exploit the feature of semiconductors to conduct electricity under certain conditions and their conductivity being strongly altered by doping or by the application of an electric field or a photon flux.These findings have stimulated a work in a wide range of science and led to the foundations towards tremendous success of applications across diverse fields such as Photovoltaics (Solar Cells), Photoelectrochemical Cells, Sensors, Catalysis, Batteries and Fuel Cells, Corrosion Protection, Electrochromic Devices or Water Treatment.The presentation will give a personal perception of the principles, their use in the last 20 years. It is focused on TiO2 based semiconductor electrochemistry and its applications. It involves the growth and use of titania nanotubes their properties and applications, as well as – in recent years – the use of single atoms as co-catalysts in the field of semiconductor electrochemistry.

Unveiling favorable synergy of tubules-like NiMoSe2 with defect-rich borocarbonitride over graphene or MXene for efficient hydrogen evolution reaction electrocatalysis

Hydrogen generation through water splitting has emerged as a promising avenue for green hydrogen fuel production. In this study, we introduce a novel strategy for enhancing hydrogen evolution reaction (HER) activity by combining tubules-like NiMoSe2 with the 2D basal planes of MXene (Ti3C2Tx), borocarbonitride (BCN) and reduced graphene oxide (RGO). A facile one-step hydrothermal approach is employed to achieve the in-situ growth of NiMoSe2 nanotubules on the surfaces of 2D Ti3C2Tx and BCN materials. Characterization techniques confirm the successful integration of these components, highlighting the role of residual functional groups in facilitating nucleation and growth. This unique hybrid structure harnesses the conductive properties of the 2D materials, while providing abundant active sites on the NiMoSe2 nanotubules. Notably, the NiMoSe2/BCN composite outperformed other materials, achieving an overpotential of 215.0 mV to reach a current density of 10 mA cm−2 with a Tafel slope of 88.0 mV dec−1, accompanied by long term stability in acidic electrolyte. This enhanced electrocatalytic performance is attributed to the synergy between NiMoSe2 and BCN, where BCN's defect sites can also act as nucleophiles for H+ ions, promoting electron transfer reactions. Comparative analysis with other state-of-the-art catalysts underscores the competitive performance of the NiMoSe2/BCN nanocomposites towards HER.

Expanding the Scanning Electrochemical Microscopy Toolset for Evaluating Electron Transfer Kinetics of Concentrated and Specialized Redox Electrolytes on Carbon Surfaces

Performing quantitative measurements of heterogeneous electron transfer reactions at electrodes (e.g., determining k0 and a) under conditions of high redox active molecule concentration in solution, such as those encountered in electrolytes for redox flow batteries (RFBs), presents significant technical challenges. For example, attempting to use transient voltammetry methodology quickly leads to limitations imposed by iR drop, as currents can be large and resistance, especially in non-aqueous systems, can be high. Additionally, using steady-state techniques based on convective principles, such as the rotating disk electrode (RDE), involve the use of relatively large equipment, with moving parts, and usually with requirements of tens to hundreds of mL of solution, which may be limiting for exploring new compounds at high concentration.To address these issues, here we introduce the use of scanning electrochemical microscopy (SECM) for the determining the rates of electron transfer of redox active species at high concentration in non-aqueous [1] and other unconventional systems, such as deep eutectic solvents. SECM enables the resolution of higher rates of electron transfer compared to transient voltammetry and RDE, and it also enables experiments with spatial resolution, enabling the exploration of reactivity on various sites of a heterogeneous electrode. In this presentation, we will describe theoretical and practical aspects of these measurements, and we will demonstrate their utility using two model systems. The first one consists on the observation of inherent rate asymmetries observed for ferrocene derivatives, ubiquitous redox probes, at the graphite/carbonate solvent interface. These asymmetries are not present on aqueous systems or metallic electrodes, demonstrating the ability of the SECM technique to capture unique behaviors. In the second case, we will discuss how SECM measurements can be used on deep eutectic solvents such as ethaline to address how interactions between redox actives and the electrode or the solvent systems modulate the rate of electron transfer. By systematically modifying the strength of interactions by means of molecule choice, solvent composition, and electrode type and structure, we can gain insight into the processes that determine reactivity at redox flow battery electrodes. This insight is critical for exploring the interfacial aspects such as adsorption, passivation, and double-layer effects on kinetics of electron transfer.[1] Gaddam, R.; Sarbapalli, D.; Howard, J.; Curtiss, L.A.; Assary, R.S.; Rodríguez-López, J. An SECM-Based Spot Analysis for Redoxmer-Electrode Kinetics: Identifying Redox Asymmetries on Model Graphitic Carbon Interfaces Chem: Asian J., 2023, 18, 2, e202201120. Figure 1

Corrosion Protection of Galvanised Steel Using Organic Coatings Containing Inhibitive Additives Based on Benzothiazoyl Succinic Acid

It is increasingly apparent that the replacement of highly effective, but environmentally unacceptable chromium (VI)- based inhibitive pigment technologies within protective coatings requires the use of combinations of anti-corrosion additives. There is currently significant interest in using organic inhibitors containing hetero-atoms of nitrogen and/or sulphur in conjunction with conventional Cr(vi)-free inorganic pigments as a means of providing equivalent corrosion protection. One such organic inhibitor is benzothiazoyl succinic acid (BTSA), which is presently commercially available as an in-coating anti-corrosion additive, which can improve the protection capability in existing chromate free formulations. In this work we investigate the ability of BTSA to mitigate corrosion-driven organic coating failure within model coatings applied to hot-dip galvanised steel. In addition, the ability of BTSA to inhibit localised corrosion on bare zinc surfaces when released from a protective coating into corrosive electrolyte within a penetrative defect is also evaluated. A combination of time-lapse imaging and in-situ scanning Kelvin probe (SKP) potentiometry is employed to quantify cathodic delamination rates of model poly-vinyl butyral (PVB) coatings containing varying levels of BTSA additions. It is demonstrated that in-coating BTSA, both added directly to PVB or stored as an exchangeable anion in a layered double hydroxide “smart-release” pigment reduce rates of cathodic disbondment by up to a factor of 20. For both methods of incorporating in-coating BTSA, an increasing loading produces a progressive decrease in delamination rates and a transition from linear to parabolic coating failure kinetics. In addition, it is also demonstrated that BTSA dissolved in the aqueous NaCl (aq) electrolyte applied to a defect can also significantly reduce the rate of cathodic disbondment observed for an unpigmented PVB coating. Highly effective inhibition of localised corrosion of bare HDG surfaces by BTSA additions made to NaCl (aq) electrolyte is demonstrated by a combination on SVET and potentiodynamic studies. Linear polarisation resistance experiments demonstrate an inhibition efficiency of 95% for a 10 mM BTSA addition made to 1% w/v NaCl (aq) at pH 7, while SVET-derived, area averaged current density value are shown to decrease by over an order of magnitude compared with an un-inhibited case over a 6 h immersion period. Using polarisation curves obtained for HDG surfaces in the presence and absence of varying concentrations of dissolved BTSA, a mixed inhibition mechanism is proposed. At intermediate concentrations (1 – 10 mM), BTSA strongly adsorbs on the oxide covered Zn surface via its two carboxylate functional groups, thus hindering electron transfer reactions and providing net cathodic inhibition. At higher concentrations (> 10 mM) an additional reinforcement of any weak points in the adsorbed layer is achieved by virtue of the formation of an insoluble salt formed by reaction with Zn(ii) cations, producing a positive shift in free corrosion potential. In-coating BTSA appears to stifle cathodic disbondment by adsorbing strongly on the intact organic-coated metal, which in turn hinders underfilm oxygen reduction and the dissolution of the amphoteric zinc(hydr)oxide layer at the metal-polymer interface.

Scrutinizing the redox chemistry of group 10 complexes supported by a redox-active bis-phenolate mesoionic carbene

We present the synthesis of an isostructural series of group 10 mesoionic carbene complexes with the general formula [M(MIC)Py] (with M = Ni (1), Pd (2) and Pt (3), Py = pyridine and MIC = bis-phenolate triazolylidene). Their electrochemical properties are investigated, revealing two quasi-reversible oxidations for all compounds, while no reductions are observed. Isolation of the oxidized species has been achieved using either silver triflate or nitrosonium tetrafluoroborate for the nickel and the platinum complex yielding the corresponding mono-cationic complexes [1]X and [3]X (X = OTf or BF4). For the palladium complex, oxidation reactions yielded different products 4 and 5 in which the pyridine and/or the phenol(oxy) donors were found to be labile compared to Ni and Pt. Additionally, for Pt the electron transfer reaction was found to be quite slow and short reaction times led to the isolation of an unusual heterobimetallic silver-platinum complex 6. The location of the redox event has been investigated using EPR spectroscopy and computational methods, which suggest, that the oxidation is mostly centered on one of the phenolate anchors.

Bridging the Coordination Chemistry of Small Compounds and Metalloproteins Using Machine Learning.

Metalloproteins require metal ions as cofactors to catalyze specific reactions with remarkable efficiency and specificity. In various electron transfer reactions, metals in the active sites change their oxidation states to facilitate the biochemical reactions. Cryogenic electron microscopy, X-ray, and X-ray free electron laser (XFEL) crystallography are used to image metalloproteins to understand the reaction mechanisms. However, radiation damage in cryoEM and X-ray crystallography, and the challenge of generating homogeneous crystals and keeping the appropriate experimental conditions for all the crystals in XFEL crystallography, may alter the oxidation states. Here, we build machine learning models trained on a large data set from the Cambridge Crystallographic Data Center to evaluate the metal oxidation states. The models yield high accuracy scores (from 82% to 94%) for all metals in the small molecules. Then, they were used to predict the oxidation states of more than 30 000 metal clusters in metalloproteins with Fe, Mn, Co, and Cu in their active sites. We found that most of the metals exist in the lower oxidation states (Fe2+ 77%, Mn2+ 85%, Co2+ 65%, and Cu+ 64%), and these populations correlate with the standard reduction potentials of the metal ions. Furthermore, we found no clear correlation between these populations and the resolution of the structures, which suggests no significant dependence of these predictions on the resolution. Our models represent a valuable tool for evaluating the oxidation states of the metals in metalloproteins imaged with different techniques. The data files and the machine learning code are available in a public GitHub repository: https://github.com/mamin03/OxitationStatesMetalloprotein.git.

Small Papillae Regulated by SPD25 are Critical for Balancing Photosynthetic CO2 Assimilation and Water Loss in Rice

BackgroundThe leaf epidermis plays an important role in the transmission of light and the regulation of water and gas exchange, which influences the photosynthesis of mesophyll cells. Small papillae (SP) are one of the important structural elements of the leaf epidermis. The mechanism of the effect that small papillae have on rice leaf photosynthetic performance remains unclear.ResultsIn this study, a small papilla deficient 25 (spd25) mutant was isolated from japonica rice Longjin1. Small papillae were absent on the adaxial and abaxial leaf surfaces of the spd25 mutant and the silicon and cuticular wax content in the spd25 mutant leaves decreased. Map-based cloning and functional analysis revealed that SPD25, encoding a guanine nucleotide exchange factor for Rop, is a novel allele of OsRopGEF10. The spd25 mutant showed an increased water loss rate and reduced relative water content. The lower stomatal conductance in the spd25 mutant prevented water loss but decreased the intercellular CO2 concentration and net assimilation rate. The fluorescence parameters showed that the inhibited CO2 assimilation reaction feedback regulated the photochemical electron-transfer reaction, but the performance of Photosystem II was stable. Further analysis indicated that the excess light energy absorbed by the spd25 mutant was dissipated in the form of non-photochemical quenching to avoid photodamage through the optical properties of small papillae.ConclusionsSPD25 regulates the development of small papillae on the surface of rice leaves, which play an important role in balancing photosynthetic gas exchange and water loss. This study deepens our understanding of the physiological mechanisms by which small papillae affect photosynthetic performance.

Insight into the Role of Entropy in Promoting Electrochemical CO2 Reduction by Imidazolium Cations.

The electroreduction of CO2 plays an important role in achieving a net-zero carbon economy. Imidazolium cations can be used to enhance the rate of CO2 reduction reactions, but the origin of this promotion remains poorly understood. In this work, we show that in the presence of 1-ethyl-3-methylimidazolium (EMIM+), CO2 reduction on Ag electrodes occurs with an apparent activation energy near zero, while the applied potential influences the rate through the pre-exponential factor. Our findings suggest that the CO2 reduction rate is controlled by the initial state entropy, which depends on the applied potential through the organization of cations at the electrochemical interface. Further characterization shows that the C2-proton of EMIM+ is consumed during the reaction, leading to the collapse of the cation organization and a decrease in the catalytic performance. Our results have important implications for understanding the effect of potential on reaction rates, as they indicate that the common picture based on vibrational activation of electron transfer reactions is insufficient for describing the impact of potential in complex systems, such as CO2 reduction in the presence of imidazolium cations.

Bio-Coated Graphitic Carbon Nitrides for Enhanced Nitrobenzene Degradation: Roles of Extracellular Electron Transfer

Graphitic carbon nitrides (g-C3N4) and microorganisms could collaboratively enhance photocatalytic properties or facilitate environmental depollution through coupled photocatalytic and biological reactions, which prevented the destruction of photocatalytic stresses to ecological systems and resulted in a sustainable technology for water remediation in rivers and lakes. However, the roles of bio-substances as well as electronic interactions between inorganic and organic systems were still unclear. Herein, g-C3N4, nitrogen-deficient g-C3N4 (ND-g-C3N4), and fluorinated g-C3N4 (F-g-C3N4) were coated with representative bacteria, i.e., Escherichia coli MG 1655, and characterized using integrated spectroscopic techniques. Photocatalytic activities were then evaluated through nitrobenzene degradation performance in an aqueous solution under visible light illumination. Nano-photocatalysts were observed to be adsorbed onto bio-aggregates, and surface hydrophilicity was convinced to be determined in the toxicity of photocatalysts in dark environments. Layered structures of ND-g-C3N4 and F-g-C3N4 were revealed in XRD spectra, and surface coverage of the Luria–Bertani medium was eliminated during E. coli cultivation. Hetero-junctions between photocatalysts and bio-substances were indicated in XPS results. Red-shifts for g-C3N4 and F-g-C3N4 materials as well as a slight blue-shift for ND-g-C3N4 were demonstrated in UV-vis spectra, which might be attributed to the destruction of nitrogen defects on ND-g-C3N4. Owing to the attached bio-substances, nitrobenzene removal could reach twice that with pristine photocatalysts, and ROS quantitative analysis confirmed that hydroxyl radicals were the determined reactive species degrading nitrobenzene in the water solution. The observation of more OH species generation indicated that extracellular electron transfer of E. coli reduced electron–hole recombination and provided reduction sites during photocatalytic degradation of nitrobenzene. This work proved additional electron-transfer paths and reaction mechanisms in hybridized photocatalytic and biological processes, which indicated that bio-activities could be a great promoter of material modification and the incorporation between inorganic and organic systems successfully showed an eco-friendly and sustainable pathway to utilize photocatalysts in natural water.

Construction of Sugar-Gourd-Shaped Carbon Nanofibers Embedded with Heterostructured Zinc-Cobalt Selenide Nanocages for Superior Potassium-Ion Storage.

Transition metal selenides are considered as promising anode materials for potassium-ion batteries (PIBs) due to their high theoretical capacities. However, their applications are limited by low conductivity and large volume expansion. Herein, sugar-gourd-shaped carbon nanofibers embedded with heterostructured ZnCo-Se nanocages are prepared via a facile template-engaged method combined with electrospinning and selenization process. In this hierarchical ZnCo-Se@NC/CNF, abundant phase boundaries of CoSe2/ZnSe heterostructure can promote interfacial electron transfer and chemical reactivity. The interior porous ZnCo-Se@NC nanocage structure relieves volume expansion and maintains structural integrity during K+ intercalation and deintercalation. The exterior spinning carbon nanofibers connect the granular nanocages in series, which prevents the agglomeration, shortens the electron transport distance and enhances the reaction kinetics. As a self-supporting anode material, ZnCo-Se@NC/CNF delivers a high capacity (362mAhg-1 at 0.1Ag-1 after 100 cycles) with long-term stability (95.9% capacity retention after 1000 cycles) and shows superior reaction kinetics with high-rate K-storage. Energy level analysis and DFT calculations illustrate heterostructure facilitates the adsorption of K+ and interfacial electron transfer. The K+ storage mechanism is revealed by ex situ XRD and EIS analyses. This work opens a novel avenue in designing high-performance heterostructured anode materials with ingenious structure for PIBs.