Positive Redox Research Articles

A Unique Ceruloplasmin Shows Distinct Redox Potentials for the Catalytic and Electron‐Transfer Metal Sites

ABSTRACTCeruloplasmin, a multicopper oxidase essential for copper metabolism and oxidative defense, from blood serum of domestic goats (Capra aegagrus hircus) has been purified to homogeneity by using three steps of column chromatography. The purified goat ceruloplasmin (gCP) protein has an estimated molecular weight of approximately 141 kDa as determined by SDS‐PAGE. ICP‐AES analysis indicates that each molecule of the protein contains 5.6 ± 0.2 atoms of copper. The optimum pH of catalysis for gCP was found to be pH 5.5. Using the Hill equation, the Km and Vmax values for gCP are estimated to be 0.41 ± 0.01 mM and 0.35 ± 0.01 μmol/min/mg, respectively. The enzyme has an average of 3.3 ± 0.33 substrate binding sites per molecule. Both, circular dichroism (CD) spectroscopy studies and computational analysis using PDBsum reveals that gCP is primarily composed of β‐strands distinguishing it from the α‐helix‐rich human ceruloplasmin. Also, computational analysis of gCP reveals six copper‐binding sites, composed of histidine (his), methionine (Met), and cysteine (cys). Cyclic voltammetry studies of gCP immobilized on a glassy carbon electrode indicate the presence of Type 1 and Type 2/3 copper centers within the protein identified by two unique redox potential values of +294 mV and −250 mV versus the normal hydrogen electrode (NHE), respectively. The positive redox potential site that probably acts as the electron‐transfer center had a slightly lower redox potential compared to that reported in other ceruloplasmin. The negative redox potential site of the protein possibly corresponds to the catalytic site containing trinuclear copper center proposed earlier. The redox potential of the Type 1 center aligns closely with azurin, suggesting evolutionary homology and suitability for direct electron transfer (DET). The distinct electrochemical properties of gCP may enhance applications in biofuel cells, biosensors, and other bioelectronic devices due to its efficient electron‐transfer capabilities. This study provides valuable insights into the functional versatility of ceruloplasmin across species and highlights the biotechnological potential of this unique variant.

Charge-Selective Electrochemical Detection through Electrolyte Adsorption on Indium Tin Oxide Electrodes

In the field of electroanalytical methods, selective sensing of target analytes is as crucial as sensitive detections, as interfering substances coexist in real samples. Therefore, various strategies have been developed to enhance the selectivity of electrochemical sensors, including molecularly imprinted polymers, enzymes, or nanostructured electrodes. Modifying the charge of electrode have been also developed, which leads to charge-based discrimination, and eventually resulting in selective electrochemical sensing of charged species. For example, the introduction of negatively charged functional groups (e.g., carboxyl groups) on electrodes has shown selective detection towards positively charged species (e.g., dopamine). However, such approaches require complex materials that are customized for specific target redox species, which limits their wide applicability. In this work, we utilized the adsorption of electrolyte anions on bare indium tin oxide (ITO) electrodes to control the surface charge of the electrode and thus enable charge-based discrimination of redox species. By using polyprotic acid anions as electrolytes and varying the solution pH to determine their protonation states, we could systematically assess the electrochemical response of adsorbed charge density towards negative, positive, and neutral redox species. Furthermore, the anion effect was applied to the selective detection of dopamine in the presence of the two representative interfering species in blood, ascorbic acid and uric acid. We expect that the electrolyte-derived surface charging of the ITO electrode could be a widely applicable strategy for the selective detection of charged analytes.

Ion Beam Implantation of Graphite Felt for Redox Flow Batteries: Role of Defects Versus Nitrogen Groups

Vanadium flow batteries (VFBs) are a promising solution to the growing demand for large-scale energy storage [1] . A critical component of VFBs are the electrodes, commonly manufactured from highly porous, carbon materials [2] . Carbon-based electrodes have good conductivity, high surface area, and are low-cost, however, they often exhibit poor activity for the vanadium redox reactions. The reactivity of electrode materials is of great interest, with previous research on carbon felt ascribing enhanced electrode reaction kinetics to the presence of oxygen functional groups (OFGs), nitrogen functional groups (NFGs), and/or carbon defects [3–6].In this study, catalytic sites were introduced into graphite felt using ion beam implantation to probe the effectiveness of specific active sites for the VFB. Specifically, N2 +- and Ne+-ion implantation are used to investigate the influence of introducing both NFGs and carbon defects versus carbon defects only. Polarisation curves and impedance measurements revealed that defects and edges sites introduced onto the electrode surface appear to be the relevant catalytic sites for facilitating the positive vanadium redox reaction. Raman spectroscopy and XPS helped to establish correlations between the surface chemistry and structure of graphite felt to electrode activity. Lower implantation fluences (< 1016 ion cm-2) were found to improve performance compared to pristine electrodes. In contrast, implantation at higher fluences resulted in the formation of amorphous carbon at the electrode surface, which was thought to result in a lower density of active defect sites and lower conductivity. Furthermore, this electrode modification technique was investigated on a scaled-up electrode geometry to assess its effectiveness for larger electrodes. Full- and half-cell measurements allowed for full-cell, positive half-cell, and negative half-cell performance to be independently investigated, whilst providing insight into performance-limiting factors. References K. Lourenssen, J. Williams, F. Ahmadpour, R. Clemmer, S. Tasnim. Vanadium redox flow batteries: A comprehensive review. J. Energy Storage 25 (2019) 100844.M.-S. Park, J. Ho Kim, M. Skyllas-Kazacos, K. Jae Kim, Y.-J. Kim. A technology review of electrodes and reaction mechanisms in vanadium redox flow batteries. J. Mater. Chem. A 3 (2015) 16913–16933.M. E. Lee, H.-J. Jin, Y. S. Yun. Synergistic catalytic effects of oxygen and nitrogen functional groups on active carbon electrodes for all-vanadium redox flow batteries. RSC Adv. 7 (2017) 43227–43232.L. Zeng, T. Zhao, L. Wei. Revealing the Performance Enhancement of Oxygenated Carbonaceous Materials for Vanadium Redox Flow Batteries: Functional Groups or Specific Surface Area? Adv. Sustainable Syst. 2 (2018) 1700148.H. Radinger, A. Ghamlouche, H. Ehrenberg, F. Scheiba. Origin of the catalytic activity at graphite electrodes in vanadium flow batteries. J. Mater. Chem. A 9 (2021) 18280–18293.S. C. Kim, J. Paick, J. S. Yi, D. Lee. Marked importance of surface defects rather than oxygen functionalities of carbon electrodes for the intrinsic vanadium redox kinetics in flow batteries. J. Power Sources 520 (2022) 230813.

Enhanced anodic performance of CTF0 monolayer for Li-ion batteries through F and Si co-doping: A DFT insight

Covalent triazine frameworks (CTFs) have been identified as promising electrode materials for Li-ion batteries (LIBs) because of their high surface area, adjustable conjugated structures, and good chemical/thermal stability. However, their low electrical conductivity limits electron and ion conduction, leading to poor electrochemical performance. In this work, a novel CTF-based monolayer, namely F and Si co-doped CTF0 (F,Si-CTF0), was designed using density functional theory (DFT) calculations. The results demonstrated that the co-doping of F and Si atoms on the CTF0 surface creates more accessible adsorption sites for Li-ion adsorption. The energy analysis confirmed the stability of the F,Si-CTF0 monolayer, which exhibits a notable adsorption energy of −3.53 eV for Li-ion. The F,Si-CTF0 monolayer can accommodate five Li-ions, providing a theoretical specific capacity of 462 mAh g−1 and a positive redox potential of 2.57 V. adsorption of Li ions on the F,Si-CTF0 monolayer leads to a transition from a semiconducting to a metallic state, resulting in a notable enhancement in electronic conductivity. Moreover, the monolayer undergoes minor lattice variations (1.3 %) throughout the lithiation/delithiation process, demonstrating excellent cycling performance. Finally, Li-ion diffuses rapidly on the monolayer surface with a very small diffusion energy barrier of 0.078 eV. The findings suggest that the F,Si-CTF0 monolayer can be used as a viable anode material in next-generation LIBs. This research shows that F and Si co-doping is an effective and viable strategy for designing two-dimensional CTF-based materials as efficient electrodes for LIBs.

High-Valent Thiosulfate Redox Electrochemistry for Advanced Sulfur-Based Aqueous Batteries.

Sulfur-based aqueous batteries (SABs) are promising for safe, low-cost, and high-capacity energy storage. However, the low output voltage of sulfur cannot meet the demands of high-energy cathode applications due to its intrinsic negative potential (E0 = -0.51 V vs SHE) of low-valent polysulfide redox (S2-/S0). Here, instead of relying on traditional aqueous polysulfide redox, for the first time, we demonstrate a high-valent thiosulfate redox (S2O32-/S4O62-) electrochemistry, exhibiting positive redox potential (E0 > 0 V vs SHE) and reversible cation storage in aqueous environment. Operando X-ray absorption fine structure spectroscopy, in situ Raman spectroscopy, and density functional theory calculations reveal the high reversibility and dynamic charge transfer process of high-valent thiosulfate redox. Significantly, the aqueous thiosulfate redox exhibits a high operating voltage of approximately 1.4 V, a reversible capacity of 193 Ah L-1, and a long cycling life of over 1000 cycles (99.6% capacity retention). This work provides new insights into the high-valent S-based electrochemistry and opens a new pathway to achieve energetic aqueous batteries.

Developing Terpyridine-Based Metal Complexes for Non-Aqueous Redox Flow Batteries

Redox flow batteries (RFBs) that utilize dissolved electroactive materials have shown great potential in storing intermittent solar and wind energy. The unique technological advantages of decoupled energy and power lead to high flexibility and scalability in RFB design, making it possible to satisfy a wide range of energy and power applications.[1,2] In traditional RFBs, inorganic transition-metal salts like all-vanadium, iron-chromium, and zinc-bromine RFBs are commonly used.[3,4] However, the narrow electrochemical stability window of water limits the attainable cell voltages in these aqueous systems. [5,6] To overcome these limitations, recent research has shifted towards non-aqueous RFBs (NARFBs) that use non-aqueous solvents, which can offer a wider electrochemical window up to 5 V.[7,8] Here, we introduce our research efforts on the design and synthesis of a series of terpyridine-based complexes of the first-row transition metals Cr, Mn, Fe, and Co for non-aqueous redox flow batteries (NARFBs). Electrochemical studies reveal that these complexes can undergo multi-electron transfer redox reactions. Notably, the Mn and Fe-based complexes exhibit both low negative redox potentials and high positive redox potential, enabling them to serve as a bipolar electrolyte for symmetric RFBs with a cell voltage of over 2 V. The assembled iron-based symmetric NARFB demonstrates a high cell voltage of 2.3 V, columbic efficiency of 97%, energy efficiency as high as 88%, and stable charge-discharge capacity retention of 60% after 160 cycles, corresponding to 99.75 % capacity retention per cycle. Figure 1

Novel ion beam implantation of felt electrodes for the vanadium flow battery: Role of defects versus nitrogen groups for the VO2+/VO2+ redox reaction

A novel approach to introduce catalytic sites to carbon and graphite felts in order to improve electrode activity and investigate the effectiveness of specific active sites for the vanadium flow battery (VFB) has been achieved via ion beam implantation. Here, both N2+ and Ne+ implantation is used to show that the positive vanadium (VO2+/VO2+) redox reaction preferentially occurs at the introduced defect sites, and not nitrogen-containing groups. This is shown through short charge and discharge tests and electrochemical impedance spectroscopy, with the electrodes characterised via X-ray photoelectron and Raman spectroscopies. Lower implantation fluences (1 × 1014–4 × 1015 ion cm−2) were shown to improve the pristine electrodes due to the formation of defect sites. However, implantation at higher fluences (above 4 × 1015 ion cm−2) resulted in a decrease in defect density, and a layer of amorphous carbon at the electrode surface was thought to hinder the redox reaction due to lower surface conductivity and less available active sites. This new approach of felt electrode modification shows that nitrogen-containing groups are not necessary for the positive vanadium redox reaction and shows the importance of defect engineering of electrodes for the VFB.

A green and cost-effective zinc-biphenol hybrid flow battery with eutectic electrolyte

Eutectic electrolytes have been widely used in redox flow batteries (RFBs) due to their unique features such as abundant availability, biodegradability, and low cost, as well as their excellent dissolution ability for redox-active substances. Despite these advantages, eutectic electrolytes still have some limitations in important aspects such as reaction kinetics, mass transport and ionic conductivity due to their relatively high intrinsic viscosity. In this work, we explore a green and cost-effective zinc-based eutectic electrolyte containing small molecules additives, which not only has elevated ionic conductivity, but also can dissolve organic cathode materials 3,3′,5,5′-tetramethylaminemethylene-4,4′-biphenol (TABP) at high concentrations. In this zinc-based eutectic electrolyte, TABP exhibits a highly positive redox potential (1.50 V versus Zn/Zn2+), quasi-reversible redox reaction kinetics and good redox stability. When operated in a practical hybrid flow battery, the Zn-TABP cell based on this eutectic electrolyte exhibits excellent rate performance, high capacity utilization, and low capacity decay rate (0.119 % per cycle). Post-analysis for the TABP catholyte suggests that the Michael side reaction rate of TABP in electrochemical cycling appears to depend upon its concentration.

X-ray chemical imaging for assessing redox microsites within soils and sediments

Redox reactions underlie several biogeochemical processes and are typically spatiotemporally heterogeneous in soils and sediments. However, redox heterogeneity has yet to be incorporated into mainstream conceptualizations and modeling of soil biogeochemistry. Anoxic microsites, a defining feature of soil redox heterogeneity, are non-majority oxygen depleted zones in otherwise oxic environments. Neglecting to account for anoxic microsites can generate major uncertainties in quantitative assessments of greenhouse gas emissions, C sequestration, as well as nutrient and contaminant cycling at the ecosystem to global scales. However, only a few studies have observed/characterized anoxic microsites in undisturbed soils, primarily, because soil is opaque and microsites require µm-cm scale resolution over cm-m scales. Consequently, our current understanding of microsite characteristics does not support model parameterization. To resolve this knowledge gap, we demonstrate through this proof-of-concept study that X-ray fluorescence (XRF) 2D mapping can reliably detect, quantify, and provide basic redox characterization of anoxic microsites using solid phase “forensic” evidence. First, we tested and developed a systematic data processing approach to eliminate false positive redox microsites, i.e., artefacts, detected from synchrotron-based multiple-energy XRF 2D mapping of Fe (as a proxy of redox-sensitive elements) in Fe-“rich” sediment cores with artificially injected microsites. Then, spatial distribution of FeII and FeIII species from full, natural soil core slices (over cm-m lengths/widths) were mapped at 1–100 µm resolution. These investigations revealed direct evidence of anoxic microsites in predominantly oxic soils such as from an oak savanna and toeslope soil of a mountainous watershed, where anaerobicity would typically not be expected. We also revealed preferential spatial distribution of redox microsites inside aggregates from oak savanna soils. We anticipate that this approach will advance our understanding of soil biogeochemistry and help resolve “anomalous” occurrences of reduced products in nominally oxic soils.

Electrochemical and structural characterization of recombinant respiratory proteins of the acidophilic iron oxidizer Ferrovum sp. PN-J47-F6 suggests adaptations to the acidic pH at protein level.

The tendency of the periplasmic redox proteins in acidophiles to have more positive redox potentials (Em) than their homologous counterparts in neutrophiles suggests an adaptation to acidic pH at protein level, since thermodynamics of electron transfer processes are also affected by acidic pH. Since this conclusion is mainly based on the electrochemical characterization of redox proteins from extreme acidophiles of the genus Acidithiobacillus, we aimed to characterize three recombinant redox proteins of the more moderate acidophile Ferrovum sp. PN-J47-F6. We applied protein film voltammetry and linear sweep voltammetry coupled to UV/Vis spectroscopy to characterize the redox behavior of HiPIP-41, CytC-18, and CytC-78, respectively. The Em-values of HiPIP-41 (571 ± 16 mV), CytC-18 (276 ± 8 mV, 416 ± 2 mV), and CytC-78 (308 ± 7 mV, 399 ± 7 mV) were indeed more positive than those of homologous redox proteins in neutrophiles. Moreover, our findings suggest that the adaptation of redox proteins with respect to their Em occurs more gradually in response to the pH, since there are also differences between moderate and more extreme acidophiles. In order to address structure function correlations in these redox proteins with respect to structural features affecting the Em, we conducted a comparative structural analysis of the Ferrovum-derived redox proteins and homologs of Acidithiobacillus spp. and neutrophilic proteobacteria. Hydrophobic contacts in the redox cofactor binding pockets resulting in a low solvent accessibility appear to be the major factor contributing to the more positive Em-values in acidophile-derived redox proteins. While additional cysteines in HiPIPs of acidophiles might increase the effective shielding of the [4Fe-4S]-cofactor, the tight shielding of the heme centers in acidophile-derived cytochromes is achieved by a drastic increase in hydrophobic contacts (A.f. Cyc41), and by a larger fraction of aromatic residues in the binding pockets (CytC-18, CytC-78).

Electrochemical and spectroscopic characterisation of organic molecules with high positive redox potentials for energy storage in aqueous flow cells

Electrochemical and spectroscopic characterisation of organic molecules with high positive redox potentials for energy storage in aqueous flow cells

Kinetics of Charge Transfer at Carbon-Based Counter Electrodes for Dye-Sensitized Solar Cells with Aqueous Electrolytes

Dye-sensitized solar cells (DSSCs) might provide a highly sustainable alternative for next generation photovoltaics. This is due to their low-energy production from abundant materials, short energy payback time, high efficiency under low illumination intensities (i.e., diffuse light or indoor conditions), and versatile concepts of applications. However, some commonly used electrolyte components are environmentally problematic. Acetonitrile or other volatile organic solvents, e.g., as well as carcinogenic cobalt complexes should not leak from DSSCs. Sealing foils, however, which are typically used to prevent such leakage, carry a risk of long-term failure.Replacing the organic solvent by water offers several advantages, as it is environmentally benign, less volatile and the cell function, further, cannot be damaged by the intrusion of water vapor. Instead of Co-complexes, e.g., the stable organic radical TEMPO (2,2,6,6-tretramethylpiperidine-1-oxyl) can serve as an alternative redox mediator with a highly positive redox potential (0.71 V vs. NHE). Using TEMPO, power conversion efficiencies (PCE) of up to 4.3% and high open-circuit voltages (V oc = 0.955 V) have been reported.[1] However, the use of TEMPO is limited by its solubility in water (C max < 0.15 M). Its derivative 4-hydroxy-TEMPO (OH-TEMPO) possesses a significantly higher solubility in water (C max > 2 M) and a more positive redox potential (0.81 V vs. NHE), making it a promising candidate as a redox mediator.In this work, we built DSSCs with TEMPO and OH-TEMPO based aqueous electrolytes, Y123-sensitized TiO2 photoanodes, and counter electrodes coated with poly(3,4-ethylenedioxythiphene) (PEDOT). For OH-TEMPO, the short-circuit current density (j sc) and open-circuit voltage were higher than with TEMPO, but the fill factor (FF) and the PCE were significantly lower. By impedance studies, large charge transfer resistances at the counter electrode (R CE) were obtained for OH-TEMPO in combination with additives such as 1-methylbenzimidazole (MBI), indicating a strong kinetic limitation of the OH-TEMPO+ reduction. However, we found that such additives as MBI or other organic compounds, are necessary to suppress recombination at the photoanode/electrolyte interface. Thus, we subsequently studied different counter electrode materials, such as platinum (reference), conducting polymers, and carbon materials, in contact to OH-TEMPO electrolytes with MBI to determine R CE and find suitable materials for the application in DSSCs.[1] Yang, W., Söderberg, M., Eriksson, A. I. K. & Boschloo, G. Efficient aqueous dye-sensitized solar cell electrolytes based on a TEMPO/TEMPO+ redox couple. RSC Advances 5, 26706–26709 (2015).

Intercalated Redox-Active Anions in Layered Double Hydroxides: Toward New Electrode Designs

Layered Double Hydroxides (LDHs) are a versatile class of 2D materials, which consist of layered di- and trivalent metal cation hydroxides with intercalated anions (1). They are used in many applications including energy storage electrodes, water purification or drug delivery (2, 3).In this new study, Anthraquinone-2-sulfonate (AQS) intercalated in the LDH structure of Mg2Al(OH)6, has been investigated and a charge capacity of 100 mAh g-1 has been measured. However, the dissolution of reduced AQS into the aqueous electrolyte occurs from the first reduction leading to a drastic capacity fade upon cycling.To get around the dissolution issue, we synthesize a new intercalated LDH using ferrocene as the redox active moiety. Electrodes with this new LDH material Mg2Al(OH)6-Fc (Figure 1A) showed more stable cycling when used in combination with aqueous or organic electrolytes. However, the most significant increase in cycle life was achieved by operating this electrode in highly concentrated, highly viscous ionic liquid based electrolytes such as Pyr13TFSI. Over 97 % capacity retention was achieved after 200 cycles with a coulombic efficiency close to 100 % (Figure 1B). The higher stability of redox active anions working at positive redox potentials like ferrocene in the LDH structure is a key parameter to improve cycling ability. Moreover, the limited solubility of the intercalated redox anions into the high concentrated ionic liquid electrolyte is also a key factor for improving cycle life of this new electrode.Figure 1: A) Schematic structure of Mg2Al(OH)6-Fc, C) Improved cycling stability of Mg2Al(OH)6-Fc based electrodes in ionic liquid electrolyte Pyr13TFSI. Figure 1

Asymmetric Supercapacitors based on 1,10-phenanthroline-5,6-dione Molecular Electrodes Paired with MXene.

An efficient approach to increase the energy density of supercapacitors is to prepare electrode materials with larger specific capacitance and increase the potential difference between the positive and negative electrodes in the device. Herein, an organic molecular electrode (OME) is prepared by anchoring 1,10-phenanthroline-5,6-dione (PD), which possesses two pyridine rings and an electron-deficient conjugated system, onto reduced graphene oxide (rGO). Because of the electron-deficient conjugated structure of PD molecule, PD/rGOs exhibit a more positive redox peak potential along with the advantages of high capacitance-controlled behaviour and fast reaction kinetics. Additionally, the small energy gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) leads to increased conductivity in PD/rGO. To assemble the asymmetric supercapacitor (ASC), a two-dimensional metal carbide, as known as MXene, with a chemical composition of Ti3C2Tx is selected as the negative electrode due to its exceptional performance, and PD/rGO-0.5 is employed as the positive electrode. Consequently, the working voltage is expanded up to 1.8 V. Through further electrochemical measurements, the assembled ASC (PD/rGO-0.5//Ti3C2Tx) achieves a remarkable energy density of 36.8 Wh kg-1. Remarkably, connecting two ASCs in series can power 73 LEDs, showcasing its promising potential for energy storage applications.

A redox effect on the viscosity of molten pyrolite

The viscosity of molten Earth mantle has been determined for various redox states using very high temperature viscometry at 1 bar. The viscosity-temperature relationship of the most oxidised pyrolite studied here is comparable to that of a previous determination of the viscosity of a peridotite melt. For the first time, the effect of iron redox state on molten mantle viscosity has been determined by calorimetric analysis of the glass transition on extremely carefully characterised glassy samples quenched from conditions of variable fO2 using gas-mixing levitation. There is a clear trend of decreasing viscosity with increasing redox state over the range of Fe3+/ΣFe. = 0.07–0.29. We also observe an increase in glass transition temperatures with increasing melt depolymerisation (i.e., higher NBO/T ratios). Both the negative oxidation dependence of viscosity and glass transition behaviour upon depolymerisation are contradictory to the trends observed from redox viscometry of more silica-rich melts but may be consistent with the broadly diminishing positive redox viscometry trends of melts with increasing basicity.

Glutathione Transferases Are Involved in the Genotype-Specific Salt-Stress Response of Tomato Plants.

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (EGSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between EGSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

Iron Complex Posolyte Species Possessing Low Capacity Fade Rate Combined with Large Positive Redox Potential for Aqueous Organic Flow Batteries

Redox flow batteries are promising technologies for energy storage and conversion applications. Among different types of flow batteries, iron-based redox-active materials can have cost and environmental advantages. We introduce a high-potential tris(2,2'-bipyridine-4,4'-diyldimethanol) iron dichloride compound as a posolyte species with a redox potential more than 0.5 V more positive than that of ferro/ferricyanide. The new species, abbreviated Fe(Bhmbp)3, operating at near-neutral pH, was paired with bis(3-trimethylammonio)propyl viologen tetrachloride as the negolyte species. The resulting aqueous flow battery exhibits an open-circuit voltage of 1.36 V and it shows excellent cycling stability with a capacity fade rate of 0.0007% per cycle or 0.07% per day. In comparison with previously reported organic and metalorganic compounds, Fe(Bhmbpy)3 exhibits a superior combination of high positive redox potential and low capacity fade rate. We investigated the decomposition pathways during cell cycling to an unprecedented level of depth for an aqueous posolyte. We found that the compound degrades through self-discharge, dimerization and ligand dissociation. The proposed decomposition pathways explain the capacity fade phenomena and offer opportunities for future improvement of metalorganic posolytes with high redox potential and good cycling stability

Characterization of an Aqueous Flow Battery Utilizing a Hydroxylated Tetracationic Viologen and a Simple Cationic Ferrocene Derivative

Herein, a new semi‐organic aqueous flow battery based on a hydroxylated tetracationic viologen, 1,1′‐bis(3‐((2‐hydroxyethyl)dimethylammonio)propyl)‐[4,4′‐bipyridine]‐1,1′‐diium tetrachloride ([(DMAE‐Pr)2‐Vi]Cl4), and the ferrocene derivative, (ferrocenylmethyl)trimethylammonium chloride (FcNCl), is demonstrated. Efficiency, accessible capacity, and capacity retention of the battery are investigated at two concentrations of the active redox species: 0.1 and 0.5 mol dm−3 in 1 mol dm−3 KCl near‐neutral electrolytes. The implementation of the ferrocene‐derivative posolyte decreases the capacity fade rate by a factor of ≈4 with respect to previous work using 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPOL) as posolyte. Capacity loss is driven by crossover of the positive redox couple into the negolyte, in particular at high concentrations, indicating the need for more selective membranes and less permeable ferrocene derivatives. Discussions are supported by conductivity measurements, cell resistance, and postmortem analysis of the electrolytes using cyclic voltammetry and nuclear magnetic resonance (NMR) spectroscopy. The characterization of [(DMAE‐Pr)2‐Vi]Cl4 is expanded as a high‐energy negolyte and future scaleup requirements for aqueous organic flow batteries are informed.

Shedding light on the electron transfer chain of a moderately acidophilic iron oxidizer: characterization of recombinant HiPIP-41, CytC-18 and CytC-78 derived from Ferrovum sp. PN-J47-F6

Efficient electron transfer from the donor to the acceptor couple presents a necessary requirement for acidophilic and neutrophilic iron oxidizers due to the low energy yield of aerobic ferrous iron oxidation. Involved periplasmic electron carriers are very diverse in these bacteria and show adaptations to the respective thermodynamic constraints such as a more positive redox potential reported for extreme acidophilic Acidithiobacillus spp. Respiratory chain candidates of moderately acidophilic members of the genus Ferrovum share similarities with both their neutrophilic iron oxidizing relatives and the more distantly related Acidithiobacillus spp. We examined our previous omics-based conclusions on the potential electron transfer chain in Ferrovum spp. by characterizing the three redox protein candidates CytC-18, CytC-78 and HiPIP-41 of strain PN-J47-F6 which were produced as recombinant proteins in Eschericha coli. UV/Vis-based redox assays suggested that HiPIP-41 has a very positive redox potential while redox potentials of CytC-18 and CytC-78 are more negative than their counterparts in Acidithiobacillus spp. Far Western dot blotting demonstrated interactions between all three recombinant redox proteins while redox assays showed the electron transfer from HiPIP-41 to either of the cytochromes. Altogether, CytC-18, CytC-78 and HiPIP-41 indeed represent very likely candidates of the electron transfer in Ferrovum sp. PN-J4-F6.

Microbiological assessment of wastewater of milk processing enterprise

Recently, microbiological methods of wastewater treatment have been increasingly used. Microbiological destruction of a wide range of polycarbon organic compounds occurs due to the formation of a microbial sequence. The sequence consists in the fact that the end products (exometabolites) of “primary” destructive microorganisms are the primary substrates for “secondary” destructive microorganisms. The purpose of the work was to conduct a microbiological assessment of industrial wastewater from the fi ltration pond of a dairy processing enterprise using a biological purifi cation system. The proposed concept is a spatial sequence for the treatment of wastewater containing a wide range of organic substances of high concentration. The essence of the biological purifi cation system was the introduction of microbiological preparations into wastewater according to an individually developed technology. At the same time, air was additionally injected into the water column by an aerator. Wastewater sampling was carried out in accordance with the general requirements for surface waters according to National State Standard 31861-2012. Sample preparation and research were carried out using standard techniques. The wastewater of milk processing enterprises contains a signifi cant amount of proteins. During the decomposition of the protein the process of ammonifi cation occurs, i.e. the splitting of amino groups and their accumulation in the medium in the form of NH4 or NH3, these compounds alkalize the medium, which explains the increase in pH. The conducted sanitary and microbiological studies of wastewater and biofi lm using a biological wastewater treatment system of the milk processing enterprise indicate that a decrease in the concentration of organic matter is a consequence of the positive redox potential of the medium. The increased value of the redox potential means the decrease in the concentration of organic compounds in wastewater, which is an indicator of the effectiveness of treatment.