Redox Flexibility Research Articles

High performance MnNbS@MXene hybrid electrode for battery-supercapacitor hybrid device and biomedical applications

Hybrid energy storage devices have obtained a lot of interest because of their remarkable capacitance, high stability and multiple applications. The energy-storage capabilities of transition metal sulfides, such as MnNbS, have expanded beyond the domain of oxide-based materials. Transition metal sulfides and the MXene-based nano-architecture materials have been praised because of their synergistically enhanced conductivity and redox flexibility. Manganese niobium sulfide (MnNbS) binary electrode material was synthesized using the hydrothermal method. The MnNbS-MXene nanocomposite electrode was designed to improve the electrochemical characteristics. It exhibited a superior specific capacity (Qs) of 1094 C/g or 1562.85F/g at 1.5 A/g. The hybrid material (MnNbS-MXene) and activated carbon (AC) were used to make the asymmetric hybrid supercapacitors (MNS-MXene//AC). The hybrid device delivered extraordinary Qs of 153.23 C/g, energy density of 35.77 Wh/kg, and power density of 2800 W/kg. To estimate the capacity retention (CR), the device was measured up to 6000 cycles. It also revealed an astonishing CR of 91 %, which is much greater than that of pure MXene//AC and MnNbS//AC. Besides, the MnNbS-MXene//AC nanocomposite electrode is used as a chemical sensor to detect hydrogen peroxide (H2O2). The MnNbS-MXene showed high sensitivity against the H2O2. The device showed the response up to a wide range of H2O2 (1 mM-5mM). Our research presents a perspective and practical application for producing high-performance electrode material based on transition metal sulfide composites and chemical sensors to detect cancerous cells in the body.

Redox flexibility in a germanium hydride manifold: hydrogen shuttling via oxidative addition and reductive elimination.

We report the synthesis of a trimetallic mixed-valence Ge(I)/Ge(II)/Ge(III) trihydride, which presents a structural novel motif among systems of the type (XMH)n (M = group 14 metal). In terms of reactivity (ArNiPr2)GeGe(ArNiPr2)(H)Ge(ArNiPr2)(H)2 can act as a source of both the Ge(II) and Ge(IV) hydrides via Ge-H reductive elimination from the central metal centre involving two different regiochemistries.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe ^III ₄ Fe ^II ₄ } Cubes

Electrocatalytic Water Oxidation by a Trinuclear Copper(II) Complex

Considering the ongoing decrease in the cost of electricity, the development of electrocatalytic processes will gain increasingly more importance in the future. Moreover, with the dwindling of the primary energy source that drives our society, fossil fuels, and the consequences that their utilization has on the environment, it is pivotal to find alternative sustainable energy sources from renewable and carbon free resources. Artificial photosynthesis is a promising strategy for meeting the growing energy demands, where a crucial half-reaction in both natural and artificial photosynthesis is water oxidn. (2H₂O --> O₂ + 4H+ + 4e-), using water as a source of electrons and protons. Inspired by nature, where water oxidn. occurs at the Mn4CaO5 active site of the oxygen evolving complex (OEC) of photosystem II, there has been growing interest in synthetic multinuclear catalysts for promoting intramol. O-O bond formation, with an advantageous redox flexibility for multi-electron transfer arising from the multinuclear core. Here, we employ a mol. trinuclear copper(II) complex, [(DAM)Cu₃(µ³-O)]Cl₄ (DAM = dodecaaza macrotetracycle), as catalyst precursor for electrocatalytic water oxidn. Based on electrochem. studies, we show that this complex is likely an active homogeneous electrocatalyst for water oxidn. in aq. phosphate buffer soln. enabling oxygen evolution with a turnover frequency of approx. 6.0 s⁻¹ at pH =7.

Predicting Spinel Disorder and Its Effect on Oxygen Transport Kinetics in Hercynite.

The iron aluminate spinel hercynite (FeAl2O4) is a promising redox material for solar thermochemical hydrogen production (STCH). Although it has a high H2 production capacity, the kinetics of its oxidation and reduction may be too slow to be practical for STCH. However, our results suggest that Fe-rich hercynite may have substantially faster redox kinetics, which could make hercynite competitive with other materials for STCH. We used density functional theory to investigate the origin of hercynite's slow kinetic behavior and show that it arises from the high activation barrier of 2.46 eV for oxygen vacancy (VO) diffusion in normal hercynite. To model the effect of disorder caused by spinel inversion, we examined 11 of the most common cation arrangements and found a near 1:1 correlation between the diffusion barrier and VO formation energy, both of which decrease by 0.6 eV for each additional nearest-neighbor Fe atom. To examine this trend, we used integrated crystal orbital Hamilton population (ICOHP) analysis to estimate the difference in the metal-oxygen bond strengths of cations neighboring VO and the diffusion transition state. The ICOHP predicted bond strengths correlate to both the diffusion barrier and VO formation energy. We also computed the effect of the charge state of the oxygen vacancy and found that positively charged vacancies are stable at low Fermi energies and have a diffusion barrier of only 0.79 eV, 1.67 eV lower than that of the neutral vacancy, demonstrating that stabilizing these charged vacancies may enable faster oxidation and reduction kinetics in hercynite. We show that uncompensated Fe antisite defects, which are present in Fe-rich hercynite, provide redox flexibility that stabilizes the charged VO and thereby increase the rate of VO diffusion. Finally, we predict that at higher VO concentrations the diffusion barrier depends on the relative positions of the vacancies and decreases when they are next-nearest neighbors.

A Disposable Paper-Based Urea Sensor Using Metal Oxides

The level of urea in urine can be a crucial biomarker to detect kidney failure, dehydration, renal function, and hepatic failure. [1] Thus, rapid and accurate sensing of urea is essential in a diagnostic clinic, especially for point-of-care testing devices (POCT). Paper-based analytical devices have been demonstrated as POCT due to its disposability, portability, low cost, and environmental-friendly quality. [2] In order to measure urea, electrochemical biosensors based on the enzyme were explored, but the application of enzyme has its limitations due to low shelf-life, complicated immobilization procedure, high cost, and complicate operating condition which is not fit to POCT application. [3] To overcome the limitations of enzyme, non-enzymatic urea sensor have attracted from researchers due to advantages such as good stability, re-usability, high sensitivity, redox flexibility, simplicity, and low cost. [4]As a non-enzymatic catalyst, nano metal oxides such as NiO, SnO2, and Fe2O3, exhibited catalytic activity on urea by the formation of the redox couple on the sensor surface.[5] [6] [7] To utilize non-enzymatic catalysts with comparable properties of enzyme, the development to increase reaction surface area has been emphasized by using nanomaterial, hierarchical structure, and support matrix.[8] [9] However, those processes involve complicate fabrication steps and often need additional post-process to remove the template leading to poisoning of the catalyst. As a potential approach for template-free process, paper can be used for an electrochemical sensor substrate. Paper has a complex fiber matrix that can provide pore pathways for the electrolyte to infiltrate inside, and by distributing catalyst uniformly within the paper, which formsmore reaction sites. Therefore, enhancement of performance and simplification of the fabrication can be achieved with the use of paper.In this study, the simple, disposable paper-based device was developed for urea electro-oxidation by using paper matrix as support. The paper-based electrode was fabricated by a screen printing method with filter paper, and different combinations of nano-metal oxides, NiO, SnO2, and Fe2O3. The metal oxide catalysts were loaded on the working electrode area and compared the performance. Structure and morphology of paper-based electrode were characterized by XRD and SEM. Investigation of selectivity and LOD was conducted by potentiostat. A detailed description of the fabrication of paper-based electrode and sensing performances will be presented.

Synergistic activation of mitochondrial metabolism and the glutathione redox couple protects HepG2 hepatocarcinoma cells from palmitoylcarnitine-induced stress.

Fatty acid stress can have divergent effects in various cancers. We explored how metabolic and redox flexibility in HepG2 hepatocarcinoma cells mediates protection from palmitoylcarnitine. HepG2 cells, along with HCT 116 and HT29 colorectal cancer cells were incubated with 100 μM palmitoylcarnitine for up to 48 h. Mitochondrial H2O2 emission, glutathione, and cell survival were assessed in HT29 and HepG2 cells. 100 μM palmitoylcarnitine promoted early growth in HepG2 cells by ~8% after 48 h versus decreased cell survival observed in HT29 and HCT 116 cells. Palmitoylcarnitine increased mitochondrial respiration at physiological and maximal concentrations of ADP, while lowering cellular lactate content in HepG2 cells, suggesting a switch to mitochondrial metabolism. HepG2 cell growth was associated with an early increase in H2O2 emission by 10 min, followed by a decrease in H2O2 at 24 h that corresponded with increased glutathione content, suggesting a redox-based compensatory mechanism. In contrast, abrogation of HT29 cell proliferation was related to decreased mitochondrial respiration (likely due to cell death) and decreased glutathione. Concurrent glutathione depletion with BSO prevented palmitoylcarnitine-induced growth in HepG2 cells, indicating that glutathione was critical for promoting growth following palmitoylcarnitine. Inhibiting UCP2 with genipin sensitized HepG2 cells to palmitoylcarnitine, suggesting that activation of UCP2 may be a 2nd redox-based mechanism conferring protection. These findings suggest that HepG2 cells possess inherent metabolic and redox flexibility relative to HT29 cells that confers protection from palmitoylcarnitine-induced stress via adaptive increases in mitochondrial respiratory control, glutathione buffering, and induction of UCP2.

Non-Enzymatic Electrooxidation of Urea with a Disposable Paper-Based Sensor Using Hierarchical NiO Hollow Sphere

Urea in the urine, protein metabolism, is present in the final product of human. The level of urea is a crucial biomarker that can assess the metabolic activity of humans such as the liver and renal function. [1] A high level of urea in the urine can result in kidney failure, dehydration, and gastrointestinal bleeding, while a low level can lead to nephritic syndrome, hepatic failure, etc. [2] Therefore, accurate and rapid sensing of urea is essential in a diagnostic clinic. Recently, paper-based analytical devices (PAD) are gaining its popularity as a manageable device for point-of-care equipment due to its inexpensive, portable, disposable, and environmentally-friendly qualities.[3] The majority of electrochemical biosensors rely on enzymes, such as urease; yet, utilization of enzyme is limited due to its high cost, poor reproducibility, and most of all, thermal and chemical instability which can influence the duration of sensor that depends on storage conditions such as temperature, pH, and humidity.[4] In addition, non-enzymatic biosensors has been attracted with the advantage of simplicity, redox flexibility, stability, and low cost. As a non-enzymatic metal-based material, Ni-based nanomaterials exhibited excellent catalytic activity over urea originated from catalytic effect for the formation of the redox couple of Ni(II) and Ni(III) on the surface. [5] When compared to enzymatic-based sensors, non-enzymatic catalysts tend to present lower sensitivity and higher limit of detection corresponding to lower performances of urea biosensor. To address this limit, there have been efforts to modify nanostructures with various shapes such as nanofiber, nanoparticle, and nanoflake arrays. Here we investigated a hollow sphere structure with nanosheet building block by using a hydrothermal method. The hollow sphere structure can increase the selectivity and sensitivity for urea biosensor by providing facile transport channels through electrolyte that exploits its inner and outer surfaces as the active site with maintaining the structural stability of the catalyst. Integration of non-enzymatic hierarchical catalyst on disposable PAD will lead to a high potential for the development of point-of-care testing devices. In this study, a non-enzymatic electrochemical paper-based sensor using hollow structure NiO was developed and demonstrated for the determination of urea. PADs were fabricated by sputtering on cotton paper, and hollow NiO was synthesized by hydrothermal method. Structure and morphologies of hierarchical NiO on PAD were characterized by XRD and SEM. Electrochemical properties such as selectivity and LOD were conducted by using a potentiostat with urea solution. A detailed description of the fabrication process and discussion of structure formation and sensing performances of hollow nickel oxide catalyst will be presented.

Enhanced Fe-Centered Redox Flexibility in Fe-Ti Heterobimetallic Complexes.

Previously, we reported the synthesis of Ti[N(o-(NCH2P(iPr)2)C6H4)3] and the Fe–Ti complex, FeTi[N(o-(NCH2P(iPr)2)C6H4)3], abbreviated as TiL (1), and FeTiL (2), respectively. Herein, we describe the synthesis and characterization of the complete redox families of the monometallic Ti and Fe–Ti compounds. Cyclic voltammetry studies on FeTiL reveal both reduction and oxidation processes at −2.16 and −1.36 V (versus Fc/Fc+), respectively. Two isostructural redox members, [FeTiL]+ and [FeTiL]− (2ox and 2red, respectively) were synthesized and characterized, along with BrFeTiL (2-Br) and the monometallic [TiL]+ complex (1ox). The solid-state structures of the [FeTiL]+/0/– series feature short metal–metal bonds, ranging from 1.94–2.38 Å, which are all shorter than the sum of the Ti and Fe single-bond metallic radii (cf. 2.49 Å). To elucidate the bonding and electronic structures, the complexes were characterized with a host of spectroscopic methods, including NMR, EPR, and 57Fe Mössbauer, as well as Ti and Fe K-edge X-ray absorption spectroscopy (XAS). These studies, along with hybrid density functional theory (DFT) and time-dependent DFT calculations, suggest that the redox processes in the isostructural [FeTiL]+,0,– series are primarily Fe-based and that the polarized Fe–Ti π-bonds play a role in delocalizing some of the additional electron density from Fe to Ti (net 13%).

Fatty Acid‐Induced Hepatocellular Carcinoma Growth is Mediated by Decreasing Mitochondrial H2O2 Emission Coupled to Increased Glutathione Levels

Rationale and HypothesisHigh fat diets are associated with increased hepatocellular carcinoma (HCC) risk, as well as increased HCC growth rates. Accelerated HCC growth in response to fatty acid challenges has been attributed to a variety of signalling pathways, but the role of metabolic and redox flexibility in mediating a pro‐growth environment in this context has not been examined. Here we examined the direct effect of fatty acid challenges on HCC growth in relation to altered metabolic and redox homeostasis.Experimental approachThe HCC cell line HepG2 was incubated with 0μM, 50μM and 100μM palmitoylcarnitine (PCarn) for up to 48 hrs. We measured clonogenic survival, mitochondrial H2O2 emission and glutathione following PCarn incubations with and without the glutathione depleting agent buthionine sulfoximine (BSO) and inhibition of uncoupling protein‐2 (UCP2) activity by genipin.Results100μM PCarn increased clonogenic survival in HepG2 by 8% more than control (p<0.05) at 48 hrs which represents a marked early effect considering the population doubling time of HepG2 cells is ~48 hrs. This was associated with an increase in both reduced and oxidized glutathione at both 24 and 48 hrs (p<0.05). Depleting glutathione with BSO prevented PCarn‐stimulated growth (p<0.05). In a separate experiment, acute incubations of 100μM PCarn increased H2O2 emission within the first 10 minutes (p<0.05) followed by a decrease in H2O2 at 1 hr that remained lower at 24 hrs (p<0.05). The acute increase in H2O2 followed by a more chronic depression in H2O2 suggested PCarn might have triggered a compensatory mechanism. In support of this notion, inhibition of UCP2 with genipin sensitized HepG2 cells to PCarn‐induced decreases in clonogenic survival (p<0.05) without a change in UCP2 protein content.ConclusionCollectively, this data suggests that PCarn‐induced HCC growth is in part attributed to elevated glutathione. Increases in glutathione may be a result of UCP2 rapidly attenuating PCarn‐induced H2O2 emission which may permit greater glutathione synthetic rates and creation of a pro‐growth redox environment.Support or Funding InformationFunding was provided to C.G.R.P. by National Science and Engineering Research Council (#436138‐2013) with infrastructure supported by Canada Foundation for Innovation, Ontario Research Fund and the James H. Cummings Foundation. P. C. T. was supported by an NSERC CGS‐D scholarship.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Modeling Protein S-Aromatic Motifs Reveals Their Structural and Redox Flexibility.

S-aromatic motifs are important noncovalent forces for protein stability and function but remain poorly understood. Hence, we performed quantum calculations at the MP2(full)/6-311++G(d,p) level on complexes between Cys (H2S, MeSH) and Met (Me2S) models with models of Phe (benzene, toluene), Trp (indole, 3-methylindole), Tyr (phenol, 4-methylphenol), and His (imidazole, 4-methylimidazole). The most stable gas-phase conformers exhibit binding energies of -2 to -6 kcal/mol, and the S atom lies perpendicular to the ring plane. This reveals preferential interaction with the ring π-system, except in the imidazoles where S binds edge-on to an N atom. Complexation tunes the gas-phase vertical ionization potentials of the ligands over as much as 1 eV, and strong σ- or π-type H-bonding supports charge transfer to the H-bond donor, rendering it more oxidizable. When the S atom acts as an H-bond acceptor (N/O-Har···S), calibration of the CHARMM36 force field (by optimizing pair-specific Lennard-Jones parameters) is required. Implementing the optimized parameters in molecular dynamics simulations in bulk water, we find stable S-aromatic complexes with binding free energies of -0.6 to -1.1 kcal/mol at ligand separations up to 8 Å. The aqueous S-aromatics exhibit flexible binding conformations, but edge-on conformers are less stable in water. Reflecting this, only 0.3 to 10% of the S-indole, S-phenol, and S-imidazole structures are stabilized by N/O-Har···S or S-H···Oar/Nar σ-type H-bonding. The wide range of energies and geometries found for S-aromatic interactions and their tunable redox properties expose the versatility and variability of the S-aromatic motif in proteins and allow us to predict a number of their reported properties.

A soluble cyanide-bridged {Fe4Ni4} box encapsulating a Cs+ ion: synthesis, structure and electronic properties

Cyanide coordination clusters have received attention for their electronic and magnetic properties. Here, we synthesized a new octametallic cyanide box encapsulating a Cs+. The cationic complex Cs⊂[FeIII4(Tp)4NiII4(NMe2Tp)4(μ-CN)12]+ was crystallized as a BF4− salt and its structure reveals that the cesium ion interacts with the twelve cyanide edges. These interactions are likely responsible for the remarkable stability of the supramolecular assembly, which maintains its integrity in solution, as shown by NMR spectroscopy, mass spectrometry, and cyclic voltammetry experiments. The 1H NMR spectrum of 1 shows well-resolved signals, which are strongly shifted due to the paramagnetic nature of the cage. The encapsulated caesium ion is also affected by the paramagnetic cage and shows a strongly shifted 133Cs paramagnetic NMR signal. The {Fe4Ni4} box shows remarkable redox flexibility with five accessible oxidation states, which correspond to the reversible oxidation/reduction of the four FeIII/FeII ions. The separation of the four consecutive redox waves accounts for the occurrence of an efficient electronic communication between the metal ions through the cyanide bridges. The cyanide bridges are also efficient in transmitting a ferromagnetic interaction between the iron and nickel ions as shown by the magnetic properties.

Valence‐Tautomerism‐Driven Aromatic Nucleophilic Substitution in Cobalt‐Bound Tetrabromocatecholate Ligands – Influence of Positive Charge at the Ligand Backbone on Phenoxazinone Synthase Activity

The mononuclear CoIII complex [Co(Br3Cat‐py)2(py)2]Cl·8H2O (1, py = pyridine, Br3pyCatH2 = 3,5,6‐tribromo‐4‐pyridiniumcatechol) was synthesized through the reaction of CoCl2·6H2O with tetrabromocatechol in the presence of an excess of pyridine at elevated temperature. The solid‐state structure was determined by X‐ray crystallography, which disclosed the valence‐tautomerism‐induced aromatic nucleophilic substitution of the tetrabromocatecholate ligands by pyridine. A cyclic voltammetry study revealed the redox flexibility of both the transition‐metal centre and the coordinated redox‐active ligand in this complex. Moreover, 1 exhibits moderately strong catalytic activity and mimics the function of phenoxazinone synthase. A detailed kinetic study disclosed that the extra positive charges at the ligand backbone resulting from the substitution of the Br atoms by pyridyl groups could play an anchoring role for the stabilization of the complex–substrate intermediate. This process resembles those in biological systems, in which the extraordinary catalytic activities of metalloenzymes in various biochemical processes are associated with substrate recognition and the stabilization of the reactive intermediates through diverse supramolecular forces. DFT calculations at the M06‐2X/6‐31+G* level of theory were used to support the mechanistic aspects related to both the redox‐driven aromatic nucleophilic substitution and the biomimetic catalysis.

Advanced aging causes diaphragm functional abnormalities, global proteome remodeling, and loss of mitochondrial cysteine redox flexibility in mice

AimInspiratory muscle (diaphragm) function declines with age, contributing to exercise intolerance and impaired airway clearance. Studies of diaphragm dysfunction in rodents have focused on moderate aging (~24months); thus, the impact of advanced age on the diaphragm and potential mechanisms of dysfunction are less clear. Therefore, we aimed to define the effects of advanced age on the mechanics, morphology, and global and redox proteome of the diaphragm. MethodsWe studied diaphragm from young (6months) and very old male mice (30months). Diaphragm function was evaluated using isolated muscle bundles. Proteome analyses followed LC-MS/MS processing of diaphragm muscle. ResultsAdvanced aging decreased diaphragm peak power by ~35% and maximal isometric specific force by ~15%, and prolonged time to peak twitch tension by ~30% (P<0.05). These changes in contractile properties were accompanied, and might be caused by, decreases in abundance of calsequestrin, sarcoplasmic reticulum Ca2+-ATPase, sarcalumenin, and parvalbumin that were revealed by our label-free proteomics data. Advanced aging also increased passive stiffness (P<0.05), which might be a consequence of an upregulation of cytoskeletal and extracellular matrix proteins identified by proteomics. Analyses of cysteine redox state indicated that the main diaphragm abnormalities with advanced aging are in metabolic enzymes and mitochondrial proteins. ConclusionOur novel findings are that the most pronounced impact of advanced aging on the diaphragm is loss of peak power and disrupted cysteine redox homeostasis in metabolic enzymes and mitochondrial proteins.

A new {Fe4Co4} soluble switchable nanomagnet encapsulating Cs+: enhancing the stability and redox flexibility and tuning the photomagnetic effect.

We report a new cyanide-bridged Cs⊂{Fe4Co4} box, a soluble model of photomagnetic Prussian blue analogues (PBAs). The Cs+ ion has a high affinity for the box and can replace the K+ ion in the preformed K-cube. This exchange is kinetically impeded at room temperature but is accelerated by heating and using the 18-crown-6 ether. The inserted Cs+ ion confers a high robustness to the cube, which withstands boiling, as shown by variable-temperature NMR studies. The stability of this model complex in solution allows the probing of the electronic interaction between the alkali ion and the cyanide cage by using various techniques. These interactions are known to play a role in the photomagnetic behaviour of PBAs. Firstly, the 133Cs NMR spectroscopy proves that there is an electronic communication between the encapsulated alkali ion and the cyanide cage. The measured up-field signal, observed at ca. -200 ppm at 300 K, reveals that a certain amount of spin density is transferred through the bonds from the paramagnetic Co(ii) ion to the encapsulated cation. Secondly, cyclovoltammetric studies show that the nature of the inserted ions affects the redox properties of the cage and influences the electronic communication between the metal ions. However, the differences in the electrochemical properties of the K-cube and the Cs-cube remain moderate. As the switching properties are influenced by the redox potential of the Fe and Co centers, similar photomagnetic behaviour is observed, with both of them being highly photomagnetic. This result contrasts strikingly with previous studies on the 3D polymeric PBAs, where the PBAs with a high amount of Cs+ show poor photomagnetic behaviour. In that case, cooperative behaviour likely influences the switching properties. Finally, EPR spectroscopy shows that the K-cube is more anisotropic than the Cs-cube. This difference is reflected in the changes occurring in the slow magnetic relaxation (single molecule magnet behaviour) observed in the two cubes.

Electrochemical Polymerization of Iron(III) Polypyridyl Complexes through C-C Coupling of Redox Non-innocent Phenolato Ligands.

Phenolato moieties impart redox flexibility to metal complexes due their accessible (oxidative) redox chemistry and have been proposed as functional ligand moieties in redox non-innocent ligand based transition metal catalysis. Here, the electro- and spectroelectrochemistry of phenolato based μ-oxo-diiron(III) complexes [(L1)Fe(μ-O)Fe(L1)]2+ (1) and [(L2)Fe(μ-O)Fe(L2)]2+ (2), where L1 = 2-(((di(pyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenol and L2 = 3,5-di-tert-butyl-2-(((di(pyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenol, is described. The electrochemical oxidation of 1 in dichloromethane results in aryl C-C coupling of phenoxyl radical ligand moieties to form tetra nuclear complexes, which undergo subsequent oxidation to form iron(III) phenolato based polymers (poly-1). The coupling is blocked by placing tert-butyl groups at para and ortho positions of phenol units (i.e., 2). Poly-1 shows two fully reversible redox processes in monomer free solution. Assignment of species observed during the electrochemical and chemical {(NH4)2[CeIV(NO3)6]} oxidation of 1 in acetonitrile is made by comparison with the UV-vis-NIR absorption and resonance micro-Raman spectroelectrochemistry of poly-1, and by DFT calculations, which confirms that oxidative coupling occurs in acetonitrile also. However, in contrast to that observed in dichloromethane, in acetonitrile, the oligomers formed are degraded in terms of a loss of the Fe(III)-O-Fe(III) bridge by protonation. The oxidative redox behavior of 1 and 2 is, therefore, dominated by the formation and reactivity of Fe(III) bound phenoxyl radicals, which considerably holds implications in regard to the design of phenolato based complexes for oxidation catalysis.

Mn(III)‐Salen Protect Against Different ROS Species Generated by the Aβ16‐Cu Complex

AbstractAβ‐Cu complex generates different reactive oxygen species (ROS) which are responsible for oxidative stress in neuronal cells. We studied the effect of Mn(III)‐salen on Aβ‐Cu catalyzed ROS generation using different assays. Mn(III)‐salen reacts with O2•−generated by Aβ‐Cu and delay H2O2production. Mn(III)‐salen significantly inhibits the formation of HO•generated by Aβ‐Cu which is further confirmed using mass spectrometry analysis. Our results indicate that H2O2generated by Aβ‐Cu activates Mn(III)‐salen to oxomanganese which in turn detoxify Aβ‐Cu‐induced NO production in microglial cells. Overall, Mn(III)‐salen complex can efficiently inhibits different ROS generated by Aβ‐Cu due to its redox flexibility.

A pentanuclear iron catalyst designed for water oxidation.

Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth's crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between Fe(II)5 and Fe(III)5; the Fe(III)5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.

Redox flexibility of iron complexes supported by sulfur-based tris(o-methylenethiophenolato)amine relative to its tripodal oxygen-based congener.

Tripodal ligands designed to generate a local C3 symmetry have resulted in novel types of metal complexes that feature unusual bonding and electronic properties. However, most complexes reported to date are characterised by strong field ligands that enforce low or intermediate-spin states for the metal centres. Moreover, anionic sulfur-based tripodal ligands are particularly scarce due to their challenging synthesis. In this context, we herein report the synthesis, spectral characterization, structural, and electronic properties of an iron complex supported by the tripodal, trianionic ligand [N(CH2ArS)3](3-) as the trigonal-bipyramidal complexes [Fe{N(CH2ArS)3}(X)] ((X), X = DMSO, THF). The solid-state structures reveal local C3v symmetry around the Fe(3+) ions, while electron spin resonance measurements established a high-spin state (S = 5/2). Electrochemical studies demonstrate the redox flexibility of the FeS3 fragment by direct comparison with the oxygen-based analogue N(CH2ArOH)3, which displays an irreversible reduction; in contrast, (THF) has a reversible Fe(3+)/Fe(2+) redox process at -0.83 V (relative to the ferrocenium/ferrocene redox couple). The high spin and redox properties of (THF) are attributable to the weak ligand field provided by the NS3 fragment, as confirmed by the electronic structure calculated by density functional theory, which reveals substantial electronic delocalisation and covalency of the Fe-S bonds in (X).

OP37 - Redox proteomic approaches to understanding age-related changes in redox signalling

Redox modifications of regulatory amino acids offers a dynamic and versatile means to rapidly alter the activity or structure of proteins in response to external and internal stimuli. These stimuli often refer to endogenously generated reactive oxygen or reactive nitrogen species (ROS/RNS), which play a role in normal cellular functioning including glycolysis, oxidative phosphorylation, biogenesis, autophagy, transcription, translation. The activities of redox sensitive proteins are often determined by the redox state of specific cysteine (Cys) residues located in catalytic sites or involved in co-factor binding. Disruption or dysregulation of many of these pathways by excessive or diminished levels of ROS/RNS signalling has been suggested to play a crucial role in ageing and many metabolic diseases. Skeletal muscle provides an ideal model to study age related changes in redox signalling, as muscle generates ROS/RNS during contractions and ageing is associated with a loss of skeletal muscle mass and function, with particular muscle types more susceptible than others. In this presentation, I will describe techniques that we have applied to study the effects of age on the redox proteome of a number of different skeletal muscles (Soleus, Gastrocnemius, and Vastus lateralis). Combining global label free proteomics and differential Cys labelling allowed the relative quantification of the redox state of specific Cys residues in the context of the protein’s abundance. Once redox sensitive Cys residues have been identified a targeted redox proteomic approach using parallel reaction monitoring, can accurately quantify the reversible oxidative state of individual Cys residues. Results indicate that muscles from old mice have a reduced redox flexibility and that muscle types respond differently to the effects of ageing. Differences we observed in the redox proteome are a reflection of the age related changes in redox signalling within muscle types.