Oxidation State Of Copper Research Articles

Homogeneous oxidative transformations mediated by copper catalyst systems

• State of the art copper-catalysed oxidative transformations is described. • Oxidation and oxygenation, peroxidation and hydroxylation reactions are reviewed. • Key differences in the mechanistic pathways are discussed. Oxidative transformations involve the conversion of organic substrates, through various processes to obtain oxygenates such as alcohols, phenolic and carbonyl compounds which can be used in the pharmaceutical and chemistry industries. Inspired by nature, particularly copper-based enzymes, these reactions include, but are not exclusive to, the radical co-catalyst free oxidation of activated alcohols inspired by copper-based oxidases, the hydroxylation of monophenols which is inspired by tyrosinase, the hydroxylation of benzene, peroxidation of hydrocarbons and oxidative cleavage of polysaccharide model substrates, which draws inspiration from oxygenases. Copper, as an environmentally benign metal pre-catalyst, has received considerable attention during the development of various catalyst systems to generate oxygenates. The mechanistic pathways by which these Cu-based catalyst systems operate has been investigated extensively and the major differences involve the initial oxidation state of copper, the redox lability of these oxidation states and the nature of the Cu-based active species. Herein we provide critical review of developments in copper-catalysed oxidative transformations.

Crystal structure and Cu/Fe K-edge analysis of Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0–0.2) and the influence on conductivity

Ba0.5Sr0.5Fe(1-x) CuxO3-δ (BSFC-x; x = 0–0.2) was synthesized and characterized. A sol-gel self-combustion method with mixed cation nitrate solutions and citric acid was used to synthesize BSFC-x precursors. Calcination was conducted in air at 850 °C for 6 h, followed by sintering in air at 1100 °C for 6 h. The phase, structure, and lattice parameters of the sintered BSFC-x were determined by X-ray diffraction (XRD). X-ray absorption near-edge spectroscopy (XANES) was used to analyze the oxidation state of the cation in the octahedron site (Cu/Fe). It showed that copper's oxidation state was predominantly 3+ due to oxygen octahedron neighbors in the crystalline symmetry and shifted to a lower oxidation state at 800 °C. The oxidation state was thought to be the predominant factor contributing to the overall conductivity through hole creation. The electrical analysis demonstrated semiconductor behavior at up to 500 °C that was influenced by the hole concentration, oxygen vacancies, and hopping distance. Above the maximum conductivity values, oxygen losses dominated the electrical response and disrupted the conductivity. Considering the doping quantity, the optimum doping was x = 0.1 with an electrical conductivity of ≈60 S/cm.

Speciation by XANES of copper migrated into compacted bentonite using electromigration techniques

Copper is a promising overpack material for deep underground nuclear waste disposal, although it is susceptible to corrosion following closure of the repository, and subsequent migration of the corrosion products through the buffer material may affect the migration of redox-sensitive radionuclides. Electromigration experiments were performed in which a copper coupon in contact with compacted bentonite served as the working electrode and was held at a constant potential of + 300 mV vs. Ag/AgCl for up to 48 h. The chemical state of the copper that migrated into the bentonite specimens was investigated by copper K-edge X-ray absorption near-edge structure measurements at the Saga Light Source, Japan. The results confirmed that the oxidation state of copper in the bentonite was copper(II), as indicated by the correlation between the amount of copper migrated into bentonite specimens and the corrosion current. Copper(I) was also observed on the copper coupon, but not in the bentonite samples. The obtained results indicate that the copper initially dissolves as copper(II), which then reacts with the copper metal and precipitates as Cu2O.

Structural characterizations of copper incorporated manganese oxide OMS-2 material and its efficiencies on toluene oxidation

This work aimed to study the excellent properties of the high-valent copper doped into the framework structure of K-OMS-2 catalyst (Cu-K-OMS-2). The physicochemical properties of Cu-K-OMS-2 material were examined by many techniques. The copper dopant can improve the physicochemical properties of the K-OMS-2 catalyst, including the specific surface area, Oads/Olatt ratio, and Cu3+/Cu2+ ratio, resulting in enhanced catalytic activity. The specific surface area of Cu-K-OMS-2 was higher than K-OMS-2 material. The Mn3+/Mn4+ ratio of K-OMS-2 (0.10) was decreased, compared with the Cu-K-OMS-2 (0.08) catalyst. Moreover, the copper dopant can enhance the Oads/Olatt ratio of Cu-K-OMS-2 to 0.62, which higher than K-OMS-2 (0.24). The Cu3+ species were observed in the Cu-K-OMS-2 structure. Besides, the oxidation state of copper on the Cu-K-OMS-2 surface revealed both Cu3+ and Cu2+ species, which affected toluene removal. The existence of the Cu3+/Cu2+ ratio led to enhance toluene removal at the low reaction temperature. Moreover, the Cu K-edge EXAFS spectrum demonstrated that the Cu ions existed in the same site as the Mn ions in the K-OMS-2 framework structure. Consequently, we can propose that Cu3+ existed in the Cu-K-OMS-2 framework structure, which influenced the high toluene oxidation at the low reaction temperature. The H2-TPR results confirmed that the copper dopant could improve the reducibility and enhance oxygen mobility of K-OMS-2 material at the low reaction temperature. Also, the high-valent copper doped into the K-OMS-2 catalyst showed high stability for VOCs oxidation. The activation energy of toluene oxidation over the Cu-K-OMS-2 catalyst was about 91.18 kJ mol−1.

Chemical gradients in automotive Cu-SSZ-13 catalysts for NOx removal revealed by operando X-ray spectrotomography

Nitrogen oxide (NOx) emissions are a major source of pollution, demanding ever-improving performance from catalytic after-treatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model catalysts rather than technical catalysts, and by global rather than spatially resolved characterization tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform three-dimensional chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NOx reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NOx reduction with adsorption–desorption of NH3 and mass transport phenomena, were revealed at micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct three-dimensional visualization of complex reactions on non-model catalysts is feasible only by the use of operando X-ray spectrotomography, which can improve our understanding of structure–activity relationships, including the observation of mass and heat transport effects. Obtaining spatially resolved spectroscopic information for catalysts under working conditions remains challenging. Here, an approach that combines X-ray absorption spectroscopy with microtomography is introduced and showcased for the selective catalytic reduction of NOx with ammonia over a Cu-SSZ-13 washcoated monolith catalyst.

Synthesis and Characterization of a Tetradentate, N-Heterocyclic Carbene Copper(II) Complex and Its Use as a Chan–Evans–Lam Coupling Catalyst

Copper N-heterocyclic carbenes (NHCs) are an emerging area of focus for catalysis and other applications. Using a straightforward methodology, a new and highly modifiable tetradentate copper(II) NHC complex was generated and characterized using X-ray crystallography, UV–vis and EPR spectroscopy, cyclic voltammetry, and ESI-MS. This copper(II) NHC complex adopted a distorted 4-coordinate coordination mode and demonstrates a unique absorption spectrum for a copper(II) species, but more interestingly, its redox properties indicate that it can readily access all three common copper oxidation states under atmospheric conditions. The tetradentate copper(II) NHC complex was used to catalytically generate new C–N bonds from a series of phenylboronic acids and amines. Once this CEL methodology was refined, moderate to high yields were achieved using catalytic amounts of the copper(II) complex to couple phenylboronic acids to a series of aniline derivatives. Substituted phenylboronic acids and anilines had minimal impact on the catalytic capabilities of this copper complex; however, there is some indication that steric interactions between catalyst and substrates may have an impact on efficient catalysis. The straightforward synthesis of this framework and the utilization of an inexpensive, first-row transition metal center in this system highlight the usefulness of copper(II) NHCs as catalyst for cross-coupling reactions.

Phenylacetylene hydrogenation coupled with benzyl alcohol dehydrogenation over Cu/CeO2: A consideration of Cu oxidation state

We have examined the effect of copper oxidation state in the continuous gas phase coupled phenylacetylene hydrogenation (to styrene) with benzyl alcohol dehydrogenation (to benzaldehyde) over Cu/CeO2. Analysis by H2-TPR, XPS, XRD and STEM-EDX analyses demonstrates the generation of a range of Cu oxidation states (Cu0 (13–77%), Cu+ (13–74%), Cu2+ (0–55%)). The stepwise formation of styrene and ethylbenzene was promoted in the stand-alone phenylacetylene hydrogenation. An increase in Cu0/Cu+ (from H2-TPR and XPS) enhanced H2 chemisorption and styrene TOF, but with low hydrogen utilisation efficiency. The formation of benzaldehyde and toluene was promoted in the stand-alone dehydrogenation of benzyl alcohol, where benzaldehyde selectivity and TOF correlate with the concentration of Cu0. Full hydrogen utilisation, exclusive benzaldehyde/styrene formation and a (3-fold) greater styrene TOF (to attain 100% yield) was achieved in the coupled process, where hydrogenation/dehydrogenation activity correlates with Cu+/Cu0. This opens new directions for sustainable “hydrogen free” hydrogenations over non-noble Cu catalysts.

Fabrication and characterization of supercapacitor electrodes using chemically synthesized CuO nanostructure and activated charcoal (AC) based nanocomposite

In this work, the activated charcoal dispersed with copper oxide (CuO) nanoparticles (NPs) electrode materials was proposed as electrode material for supercapacitor that is used as energy storage device. The CuO NPs were synthesized at room temperature using co-precipitation method and the nanocomposite was with activated charcoal (AC) powder for its application in an electrochemical supercapacitor. Synthesis of CuO nanoparticles was carried out at various temperatures. The optimized temperature for synthesis is 600 °C that resulted in better performance of electrode materials. Synchrotron X-ray diffraction confirms the monoclinic structure. The X-ray photoelectron spectroscopy suggests the +2 oxidation state of copper. Electrochemical properties of the prepared nanocomposite electrodes and fabricated supercapacitor cells were characterized using a.c. impedance, cyclic voltammetry, and charge–discharge techniques by using 1 M H2SO4 and 6 M KOH as electrolytes. The optimized composition is 1:1 (mass ratio) of CuO and AC. The specific capacitance of the supercapacitor cells is stable up to 2000 cycles at 100 mV cm−2, which shows that the device has good electrochemical reversibility and cycle life with 6 M KOH and 1 M H2SO4 electrolytes.

Back cover: Investigating the oxidation state of Fe from LiFePO4‐based lithium ion battery cathodes via capillary electrophoresis (elps.202000097) and Accessing copper oxidation states of dissolved negative electrode current collectors in lithium ion batteries (elps.202000155)

Back cover: Investigating the oxidation state of Fe from LiFePO₄‐based lithium ion battery cathodes via capillary electrophoresis (elps.202000097) and Accessing copper oxidation states of dissolved negative electrode current collectors in lithium ion batteries (elps.202000155)

Complex Formation of Phytic Acid With Selected Monovalent and Divalent Metals.

The formation of metal complexes with phytic acid is a complex process that depends strongly on the metal-to-ligand molar ratio, pH value and consequent protonation level of the phytate ligand as well as accompanying side reactions, in particular metal hydrolysis and precipitation of the formed coordination compounds. In the present work, the potentiometric titration technique was used in combination with a detailed analysis of the equivalent point dependencies for selected biologically relevant monovalent and divalent cations from the groups of alkaline earths and transition metals, namely: Mg(II), Zn(II), Fe(II), Cu(I), and Cu(II) ions. The investigation of complex formation mechanism, the evaluation of the species formed, and the identification of other side reactions was based on the examination of three distinct equivalent points, which were detectable by alkalimetric titrations of phytic acid in the presence of selected metal ions. It has been demonstrated that alkaline earth metals interact with different binding site(s) than the transition metals, and experiments with both oxidation states of copper revealed similar complexing characteristics, which depend mainly on the ionic radius (and not on the ionic charge as initially expected). Quantitative data on phytate complexation, hydroxide formation and complex precipitation are presented herein for all metals studied, including Cu(I), which was investigated for the first time by means of alkalimetric titration.

Active copper species of co-precipitated copper-ceria catalysts in the CO-PROX reaction: An in situ XANES and DRIFTS study

Properties of co-precipitated CuO/CeO2 catalysts with nominal content of 1–3 wt.% copper were investigated by EDS, XRD, BET, STEM, EDS map, H2-TPR, in situ DRIFTS and in situ XANES. By comparing results of DRIFTS, XANES and catalytic performance in the CO-PROX reaction, it was evidenced a relationship between the catalytic behavior and the copper oxidation state of the materials. In situ DRIFTS and XANES analyses shed light on the oxidation state of active copper species involved in the CO-PROX reaction between 120 °C and 200 °C. The investigated catalysts present a balance between Cu° and Cu+ species under PROX conditions and the Cu+ is the main species liable to adsorb CO. Furthermore, our studies indicated that the PROX reaction on CuO/CeO2 is impacted by the nature of Cu species, which in turn may vary with reaction temperature, depending on the Cu content. From these results, we propose a new mechanism of PROX reaction on CuCe catalysts, including Cu°/Cu+ and Ce3+/Ce4+ redox pairs and direct CO oxidation on Cu°.

Green and cost-effective synthesis of copper nanoparticles by extracts of non-edible and waste plant materials from Vaccinium species: Characterization and antimicrobial activity

The aim of this work was the green synthesis of copper nanoparticles (Cu-NPs) using aqueous extracts of (i) bilberry (Vaccinium myrtillus L.) waste residues from the production of fruit juices and (ii) non-edible “false bilberry” fruits (Vaccinium uliginosum L. subsp. gaultherioides). Different cupric salts (CuCl2, Cu(CH3COO)2 and Cu(NO3)2) were used for the synthesis. The formation of stable nanoparticles (CuNPs) was assessed by transmission electron microscopy and the oxidation state of copper in these aggregates was followed by X-ray photoelectron spectroscopy. The polyphenol composition of the extracts was characterized, before and after the synthesis, using spectrophotometric methods (i.e. total soluble polyphenols and total monomeric anthocyanins) and high-performance liquid chromatography coupled with tandem mass spectrometry (i.e. individual anthocyanins). Polyphenol concentration in the extracts was found to decrease after the synthesis, indicating their active participation to the processes, which led to the formation of Cu-NPs. The antimicrobial activity of Cu-NPs, berry extracts, and cupric ion solutions were analysed by broth microdilution and time-kill assays, on prokaryotic and eukaryotic models. The antimicrobial activity of Cu-NPs, especially those derived from bilberry waste residues, appeared to be higher for both Gram-negative and Gram-positive bacteria, and for fungi, compared to the ones of its single components (cupric salts and berry extracts). Therefore, Cu-NPs from the green synthesis here proposed can be considered as a cost-effective sanitization tool with a wide spectrum of action.

Economical and Facile Route to Produce Gram-Scale and Phase-Selective Copper Sulfides for Thermoelectric Applications

Producing thermoelectric materials without energy-intensive processes is essential to reduce the production costs and for wide-scale applications. Copper sulfides have recently been identified as new and promising environmentally friendly thermoelectric materials. Here, an economical synthetic route for the gram-scale preparation of copper sulfide is developed that enables selective control of the copper oxidation state, in turn allowing the stoichiometry to be tuned to optimize the thermoelectric characteristics of the product. Through this facile and scalable protocol, CuS, Cu1.75S, Cu1.80S, and Cu2S powders have been synthesized in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy to verify the stoichiometry of each material. The as-prepared compounds were further characterized by thermoelectric measurements and the performance of a test generator module containing ten p-type Cu2S legs was subsequently investigated. Upon heating one side of the module to 70 °C, the device produced an output voltage of 30.9 mV and a corresponding power output of 3.4 μW, which is comparable to the power outputs of many of devices fabricated with expensive and toxic thermoelectric elements. This work presents a novel pathway for the development of low-cost thermoelectric devices by introducing a facile, tunable, and high-yield CuxS synthesis procedure that may be readily adapted to other metal sulfides.

Expression and Purification of Recombinant GHK Tripeptides Are Able to Protect against Acute Cardiotoxicity from Exposure to Waterborne-Copper in Zebrafish.

In this study, an alternative method is developed to replace chemical synthesis to produce glycyl-histidyl-lysine (GHK) tripeptides with a bacterial fermentation system. The target GHK tripeptides are cloned into expression plasmids carrying histidine-glutathione-S-transferase (GST) double tags and TEV (tobacco etch virus) cleavage sites at the N-terminus. After overexpression in Escherichia coli (E. coli) BL21 cells, the recombinant proteins are purified and recovered by high-pressure liquid chromatography (HPLC). UV-vis absorption spectroscopy was used to investigate the chemical and biological properties of the recombinant GHK tripeptides. The results demonstrated that one recombinant GHK tripeptide can bind one copper ion to form a GHK-Cu complex with high affinity, and the recombinant GHK peptide to copper ion ratio is 1:1. X-ray absorption near-edge spectroscopy (XANES) of the copper ions indicated that the oxidation state of copper in the recombinant GHK-Cu complexes here was Cu(II). All of the optical spectrum evidence suggests that the recombinant GHK tripeptide appears to possess the same biophysical and biochemical features as the GHK tripeptide isolated from human plasma. Due to the high binding affinity of GHK tripeptides to copper ions, we used zebrafish as an in vivo model to elucidate whether recombinant GHK tripeptides possess detoxification potential against the cardiotoxicity raised by waterborne Cu(II) exposure. Here, exposure to Cu(II) induced bradycardia and heartbeat irregularity in zebrafish larvae; however, the administration of GHK tripeptides could rescue those experiencing cardiotoxicity, even at the lowest concentration of 1 nM, where the GHK-Cu complex minimized CuSO4-induced cardiotoxicity effects at a GHK:Cu ratio of 1:10. On the other hand, copper and the combination with the GHK tripeptide did not significantly alter other cardiovascular parameters, including stroke volume, ejection fraction, and fractional shortening. Meanwhile, the heart rate and cardiac output were boosted after exposure with 1 nM of GHK peptides. In this study, recombinant GHK tripeptide expression was performed, along with purification and chemical property characterization, which revealed a potent cardiotoxicity protection function in vivo with zebrafish for the first time.

Accessing copper oxidation states of dissolved negative electrode current collectors in lithium ion batteries.

A novel capillary electrophoresis (CE) method with ultraviolet-visible spectroscopy (UV-Vis) detection for the investigation of dissolved Cu+ and Cu2+ in lithium ion battery (LIB) electrolytes was developed. This method is of relevance, as the current collector at the anode of LIBs may dissolve under certain operation conditions. In order to preserve the actual oxidation states of dissolved copper in the electrolytes and to prevent any precipitation during sample preparation and CE measurements, neocuproine (NC) and ethylenediamine tetraacetic (EDTA) were effectively applied as complexing agents for both ionic copper species. However, precipitation and loss of the Cu+ -NC-complex for quantification occurred in presence of the commonly applied conducting salt lithium hexafluorophosphate (LiPF6 ). Therefore, acetonitrile (ACN) was added to the sample in order to suppress this precipitation. Dissolution experiments with copper-based negative electrode current collectors in a LIB electrolyte were conducted at 60°C under non-oxidizing atmosphere. First findings regarding the copper species via CE revealed dissolved Cu+ and mainly Cu2+ . However, primarily Cu+ dissolved from the passivating oxide layer (Cu2 O and CuO) of the current collector due to the formation of acidic electrolyte decomposition products. Due to the instability of Cu+ in the electrolyte a further disproportionation reaction to Cu0 and Cu2+ occurred. The results show the high potential of this CE method for prospective investigations regarding the current collector stability in new battery electrode formulations and correlations of dissolution events with dissolution mechanisms and battery cell operation conditions.

Copper (IV) Stabilization in Macrocyclic Complexes with 3,7,11,15-Tetraazaporphine, Its Di[benzo]- or Tetra[benzo] Derivatives and Oxide Anion: Quantum-Chemical Research.

Using the data of a quantum chemical modeling of molecular structures obtained by the density functional theory (DFT), the possibility of the existence of a copper macrocyclic complexes with 3,7,11,15-tetraazaaporphine, trans-di[benzo] 3,7,11,15-tetraazaaporphine or tetra[benzo] 3,7,11,15-tetraazaaporphine and oxide anion where oxidation state of copper is IV, was shown. The values of the parameters of molecular structures and NBO analysis for such complexes were presented, too.

Effect of Na, Cs and Ca on propylene epoxidation selectivity over CuOx/SiO2 catalysts studied by catalytic tests, in-situ XAS and DFT

This research focuses on epoxidation of propylene over pristine, Na, Ca and Cs modified CuOx/SiO2 catalysts using O2. The selectivity of the reaction is analyzed using a combination of catalytic tests, in-situ XAS and DFT calculations. The initially present subnanometer CuO clusters are present in all catalysts which re-disperse/flatten during reaction. During catalytic reaction, the Cu1+ becomes the predominant oxidation state. There is no correlation between propylene oxide (PO) selectivity and copper oxidation state. DFT analysis of the propylene reaction pathway revealed that Na, Cs, and Ca addition decreases the bonding strength of propylene to CuO and decreases the O2 activation barrier, while simultaneously increase the exothermicity of O2 dissociation. The Na induced Cu–O bond modification decreases the activation barrier from 0.87 to 0.71 eV for the oxametallacycle (OMC) ring closure (first step in the reaction pathway favoring selectivity towards PO) compared to pristine 5Cu catalyst. At the same time, we observed an increase (from 0.45 to 0.72 eV) of the barrier for the abstraction of allylic hydrogen. The opposite effect is achieved by Ca addition: the activation barrier for OMC ring closure increases to 1.08 eV and that for allylic hydrogen stripping decreases to 0.16 eV.

Synthesis and Characterization of Catecholato Copper(II) Complexes with Sterically Hindered Neutral and Anionic N3 Type Ligands: Tris(3,5-diisopropyl-1-pyrazolyl)methane and Hydrotris(3,5-diisopropyl-1-pyrazolyl)borate

Three catecholato copper(II) complexes, [Cu(catCl4)(L1′)], [Cu(catBr4)(L1′)], and [Cu(catCl4)(L1H)], supported by sterically hindered neutral and anionic N3 type ligands: tris(3,5-diisopropyl-1-pyrazolyl)methane (referred to as L1′) and hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (referred to as L1−), are synthesized and characterized in detail. Their X-ray structures reveal that both [Cu(catCl4)(L1′)] and [Cu(catBr4)(L1′)] complexes have a five-coordinate square-pyramidal geometry and [Cu(catCl4)(L1H)] complex has a four-coordinate square-planar geometry. The L1H is unusual protonated ligand that controls its overall charge. For the three catecholato copper(II) complexes, the oxidation state of copper is divalent, and catechol exists in catecholate as two minus anion. This difference in coordination geometry affects their d-d and CT transitions energy and ESR parameters.

One-step synthesis of Cu3N, Cu2S and Cu9S5 and photocatalytic degradation of methyl orange and methylene blue

Herein we report on a novel one-step synthesis of copper-rich Cu3N, Cu2S and Cu9S5 nanoparticles by using the surfactant dodecanethiol as a sulfur source to substitute the nitrogen in Cu3N using the Pearson acid-base concept. The Cu3N nanoparticles are indexed to a cubic anti-ReO3 phase, whilst the Cu2S nanoparticles are indexed to the alpha low cubic phase and Cu9S5 to a rhombohedral phase. The Williamson-Hall method is then used to estimate the sizes from the x-ray diffraction patterns. The estimated sizes are larger than the sizes observed from transmission electron microscopy. X-ray photoelectron spectroscopy confirms the formation of Cu3N, Cu2S and Cu9S5 nanoparticles. The oxidation state of copper in Cu3N and Cu2S is +1 with Cu9S5 having both Cu1+ and Cu2+ present. In addition the S 2p high resolution spectrum for Cu9S5 shows the presence of S2− and (S2)2−. The TEM shows the formation of cubic Cu3N nanoparticles (41 nm) as well as hexagonal Cu2S (27 nm), and elongated Cu9S5 nanoparticles (aspect ratio 1.8). These nanoparticles have direct band-gap transitions of 2.41 eV, 2.75 eV and 2.36 eV respectively. The blue-shifting of photoluminescence spectrum of the Cu3N nanoparticles is indicative of the presence of surface traps while Cu2S and Cu9S5 show near band-edge emission indicative of defect-free samples. The nanoparticles are then used as photocatalysts to degrade methyl orange and methylene blue dyes. The Cu3N photocatalyst degrades 89 % of 20 ppm methyl orange dye in a 1st order reaction with the degradation products being aniline and C5H6N2SO3- fragments whilst the Cu9S5 is the best catalyst at degrading 20 ppm methylene blue (79 %). The methylene blue degradation follows a 2nd order reaction and aniline is the only detectable degradation product.

Complete Charge Regulation by a Redox Enzyme Upon Single Electron Transfer

AbstractThe degree by which metalloproteins partially regulate net charge (Z) upon electron transfer (ET) was recently measured for the first time using “protein charge ladders” of azurin, cytochrome c, and myoglobin [Angew. Chem. Int. Ed. 2018, 57(19), 5364–5368; Angew. Chem. 2018, 130, 5462–5466]. Here, we show that Cu, Zn superoxide dismutase (SOD1) is unique among proteins in its ability to resist changes in net charge upon single ET (e.g., ΔZET(SOD1)=0.05±0.08 per electron, compared to ΔZET(Cyt‐c)=1.19±0.02). This total regulation of net charge by SOD1 is attributed to the protonation of the bridging histidine upon copper reduction, yielding redox centers that are isoelectric at both copper oxidation states. Charge regulation by SOD1 would prevent long range coulombic perturbations to residue pKa’s upon ET at copper, allowing SOD1’s “electrostatic loop” to attract superoxide with equal affinity (at both redox states of copper) during diffusion‐limited reduction and oxidation of superoxide.