Copper Redox Research Articles

Mechanosynthesis of a Copper complex for redox initiating systems with a unique near infrared light activation

ABSTRACTThe first use of a new mechanosynthesized copper complex (Cu(acac)(2dppba)) as a initiator for the redox and redox photoactivated polymerization of methacrylates under air is proposed. This paper (i) describes the mechanosynthesis of this complex, (ii) outlines the relative efficiency of the complex for redox polymerization (mechanosynthesized product vs. solvent synthesized product), (iii) follows the polymerization enhancement under a 405 nm light, and (iv) demonstrates the high performance of this complex in near infrared photoactivated redox polymerization where a completely colorless polymer is obtained (unprecedented under NIR irradiations, 785 nm, here). The light activated polymerization exhibit higher conversions, better time controls (activation control) and higher surface conversions than redox polymerization. The mechanosynthesis is well characterized by two solvent‐free methods (visual color change and Electron Spin Resonance) and two solvent‐based methods (high resolution‐electrospray ionization‐mass spectrometry (HR‐ESI‐MS) and UV–vis spectrometry). The involved mechanisms are discussed. Mechanosynthesis of copper complexes opens new perspectives for copper (photo)redox polymerization catalysts as the environmental impact and economical costs of the complex synthesis are significantly reduced. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3646–3655

Copper (Photo)redox Catalyst for Radical Photopolymerization in Shadowed Areas and Access to Thick and Filled Samples

The free radical polymerization of low viscosity methacrylate blends upon a LED irradiation at 405 nm under air is carried out using Cu(I)/iodonium salt/tin(II) organic derivative as photoinitiating systems. The system exhibits a high reactivity; where tin derivative plays a crucial role. It operates through a catalytic cycle in which Cu(I) is regenerated and can be used at low concentrations (0.1–0.3 wt %). Remarkable performances are achieved. At first, a final methacrylate conversion of 82% after 40 s in 1.4 mm thick samples is obtained for an irradiance of 35 mW/cm2 whereas such a conversion is only reached only when using a Cu(I)/iodonium salt system under a 200 mW/cm2 light exposure. Second, a 55% conversion is still obtained after 150 s under a very low irradiance (2.5 mW/cm2). Third, almost tack-free thick samples (1.4 mm) under air are produced upon sunlight exposure (65% of conversion for the 1.4 mm thick sample after 90 s of irradiation). Fourth, the photocuring of clear samples as thick as 9 c...

Impact of copper ligand mutations on a cupredoxin with a green copper center

Mononuclear cupredoxins contain a type 1 copper center with a trigonal or tetragonal geometry usually maintained by four ligands, a cystein, two histidines and a methionine. The recent discovery of new members of this family with unusual properties demonstrates, however, the versatility of this class of proteins. Changes in their ligand set lead to drastic variation in their metal site geometry and in the resulting spectroscopic and redox features. In our work, we report the identification of the copper ligands in the recently discovered cupredoxin AcoP. We show that even though AcoP possesses a classical copper ligand set, it has a highly perturbed copper center. In depth studies of mutant's properties suggest a high degree of constraint existing in the copper center of the wild type protein and even the addition of exogenous ligands does not lead to the reconstitution of the initial copper center. Not only the chemical nature of the axial ligand but also constraints brought by its covalent binding to the protein backbone might be critical to maintain a green copper site with high redox potential. This work illustrates the importance of experimentally dissecting the molecular diversity of cupredoxins to determine the molecular determinants responsible for their copper center geometry and redox potential.

Copper binding and redox chemistry of the Aβ16 peptide and its variants: insights into determinants of copper-dependent reactivity.

The metal-binding sites of Aβ peptides are dictated primarily by the coordination preferences of the metal ion. Consequently, Cu(i) is typically bound with two His ligands in a linear mode while Cu(ii) forms a pseudo-square planar stereochemistry with the N-terminal amine nitrogen acting as an anchoring ligand. Several distinct combinations of other groups can act as co-ligands for Cu(ii). A population of multiple binding modes is possible with the equilibrium position shifting sensitively with solution pH and the nature of the residues in the N-terminal region. This work examined the Cu(ii) chemistry of the Aβ16 peptide and several variants that targeted these binding modes. The results are consistent with: (i) at pH < 7.8, the square planar site in CuII-Aβ16 consists primarily of a bidentate ligand provided by the carboxylate sidechain of Asp1 and the N-terminal amine supported by the imidazole sidechains of two His residues (designated here as component IA); it is in equilibrium with a less stable component IB in which the carboxylate ligand is substituted by the Asp1-Ala2 carbonyl oxygen. (ii) Both IA and IB convert to a common component II (apparent transition pKa ∼7.8 for IA and ∼6.5 for IB, respectively) featuring a tridentate ligand consisting of the N-terminal amine, the Asp1-Ala2 amide and the Ala2-Pro3 carbonyl; this stereochemistry is stabilized by two five-membered chelate rings. (iii) Component IA is stabilized for variant Aβ16-D1H, components I (both IA and IB) are imposed on Aβ16-A2P while the less stable IB is enforced on Aβ16-D1A (which is converted to component II at pH ∼6.5); (iv) components IA and IB share two His ligands with Cu(i) and are more reactive in redox catalysis than component II that features a highly covalent and less reactive amide N- ligand. The redox activity of IA is further enhanced for peptides with a His1 N-terminus that may act as a ligand for either Cu(i) or Cu(ii) with lower re-organization energy required for redox-shuttling. This study provided insights into the determinants that regulate the reactivity of Cu-Aβ complexes.

Electro-Engineered Polymeric Films for the Development of Sensitive Aptasensors for Prostate Cancer Marker Detection

We report the development of a simple surface chemistry strategy for the construction of sensitive aptasensors on a polypyrrole (PPy)–polyethylene glycol (PEG) platform in order to provide enhanced antifouling properties. We report the covalent modification of a PPy film formed on a gold electrode by PEG molecules, without prior chemical functionalization of the pyrrole monomer. This process was mediated by electro-oxidation of amine groups present on the one of the PEG end chains. Polyhistidine modified aptamers were immobilized to this surface via a Nα,Nα-Bis(carboxymethyl)-l-lysine ANTA/Cu2+ redox complex covalently attached to the PPy-PEG adduct. The fabricated aptasensor was then utilized for the detection of α-methylacyl-CoA racemase (AMACR; P504S), an emerging biomarker for prostate cancer. Protein/aptamer interactions were monitored through variation of the copper redox signal, using the square wave voltammetry (SWV) technique. We demonstrate that the PPy-PEG-ANTA/Cu2+ hybrid material is characterized by enhanced antifouling properties and sensitivity. The aptasensor was able to detect AMACR down to 5 fM in both buffer and spiked human plasma with a limit of detection (LOD) of 0.15 fM and 1.4 fM, respectively. The developed aptasensor can be generalized for use with any type of aptamer-based sensor.

Iron Complex Facilitated Copper Redox Cycling for Nitric Oxide Generation as Nontoxic Nitrifying Biofilm Inhibitor.

In this study, we developed poly(vinyl chloride) (PVC)-solvent casted mixed metal copper and iron complexes capable of catalytic generation of the antibiofilm nitric oxide (NO) from endogenous nitrite. In the absence of additional reducing agent, we demonstrated that the presence of iron complex facilitates a redox cycling, converting the copper(II) complex to active copper(I) species, which catalyzes the generation of NO from nitrite. Assessed by protein assay and surface coverage analyses, the presence of the mixed metal complexes in systems containing water industry-relevant nitrite-producing nitrifying biofilms was shown to result in a "nontoxic mode" of biofilm suppression, while confining the bacterial growth to the free-floating planktonic phase. Addition of an NO scavenger into the mixed metal system eliminated the antibiofilm effects, therefore validating first, the capability of the mixed metal complexes to catalytically generate NO from the endogenously produced nitrite and second, the antibiofilm effects of the generated NO. The work highlights the development of self-sustained antibiofilm materials that features potential for industrial applications. The novel NO-generating antibiofilm technology diverts from the unfavorable requirement of adding a reducing agent and importantly, the less tendency for development of bacterial resistance.

Copper-Aβ Peptides and Oxidation of Catecholic Substrates: Reactivity and Endogenous Peptide Damage.

The oxidative reactivity of copper complexes with Aβ peptides 1-16 and 1-28 (Aβ16 and Aβ28) against dopamine and related catechols under physiological conditions has been investigated in parallel with the competitive oxidative modification undergone by the peptides. It was found that both Aβ16 and Aβ28 markedly increase the oxidative reactivity of copper(II) towards the catechol compounds, up to a molar ratio of about 4:1 of peptide/copper(II). Copper redox cycling during the catalytic activity induces the competitive modification of the peptide at selected amino acid residues. The main modifications consist of oxidation of His13/14 to 2-oxohistidine and Phe19/20 to ortho-tyrosine, and the formation of a covalent His6-catechol adduct. Competition by the endogenous peptide is rather efficient, as approximately one peptide molecule is oxidized every 10 molecules of 4-methylcatechol.

Development of Multifunctional Pyrimidinylthiourea Derivatives as Potential Anti-Alzheimer Agents.

Starting from a screening-hit compound, via structure modifications and optimizations, a series of nonfused and nonassembly pyrimidinylthiourea derivatives (2-5) was designed, synthesized, and evaluated as novel multifunctional agents against Alzheimer's disease. Biological activity results demonstrated that compounds 5r and 5t exhibited potent inhibition and excellent selectivity toward acetylcholinesterase (AChE, 5r, IC50 = 0.204 μM, SI > 196; 5t, IC50 = 0.067 μM, SI > 597), specific metal-chelating ability, significant antioxidant effects, modulation of metal-induced Aβ aggregation, inhibition of ROS production by copper redox cycle, low cytotoxicity, and moderate neuroprotection to human neuroblastoma SH-SY5Y cells. Moreover, compound 5r displayed appropriate blood-brain barrier (BBB) permeability both in vitro and in vivo and could improve memory and cognitive function of scopolamine-induced amnesia mice. The multifunctional profiles of 5r and its effectivity in AD mice highlight these structurally distinct pyrimidinylthiourea derivatives as prospective prototypes in the research of innovative multifunctional drugs for Alzheimer's disease.

Electrochemistry and STM Observation of a Copper Complex-Based Molecular Rotor on Gold

Molecular rotors demonstrate that switching and mechanical work can be achieved at the nanoscale. The development of a system whereby the switching behavior is controllable at room temperature is one of the ultimate goals in this research field. Further research in this area could lead to the development of methods of detecting or visualizing the motion of individual molecules, which would greatly aid the functionality of future single molecular machines and memory devices. Our group has recently developed a pyridylpyrimidine-ligated copper(I) complex system that acts as a molecular switch through the redox-driven rotation of a coordinated pyrimidine ring (Figure 1).1 Asymmetric substitution at the 4-position of the pyrimidine ring leads to the two switching isomers, in which different degrees of steric congestion result in distinct oxidation potentials. The rotation of this system can be driven by temperature and light, and furthermore, the motion can be detected as various kinds of outputs; for example, changes of rest potential, magnetic and optical properties. Note that it is the correlation between redox potential and structure that enables these functionalities within a simple and small molecular design. In this research, a new molecular switch, a copper complex (1•PF6 ), was synthesized. Cyclic voltammograms of 1•PF6 in solution taken at room temperature had two redox couples. Based on the electrochemistry of Cu complexes, these signals were assigned to the redox reactions of the o- and i-isomer from the negative to the positive potential. This complex was immobilized on the Au surface by immersing an Au-coated mica substrate in a CH2Cl2 solution of 1•PF6 ; the modified substrate is designated as SAM-1. Cyclic voltammetry of SAM-1 at room temperature shows two reversible copper(II/I) redox waves at potentials similar to those of 1•PF6 in solution. From the deconvolution of peak areas, the ratio of the two isomers functionalized on the Au surface was calculated. Different scan rates measurements of oxidation waves suggested that the ratio of the isomers is constant and does not deviate from the equilibrium molar ratio (i : o = 8 : 2). We next carried out scanning tunneling microscopy to observe the isomerization behavior of individual molecules. A mixed self-assembled monolayer (SAM) of 1•PF6 and 1-hexanethiol (mSAM-1) was used for STM observation at room temperature. The brightness of spots are measured as the apparent height. It was found that apparent heights of the complex molecules varied with time as they switched between the two states. Aggregated apparent height data show two Gaussian components. Least squares fitting of the two components indicates that 1 has two conformations which have an area ratio of 8 : 2. This ratio seems consistent with the Cu(I) equilibrium ratio of the i- and o-isomers (i : o = 8 : 2), which suggests a successful observation of the switching behavior of individual molecules. Reference M. Nishikawa, S. Kume, H. Nishihara, Phys. Chem. Chem. Phys. 2013, 15, 10549-10565. Figure 1

Copper Bromide Chemistry Analysis for Use in Large Scale Energy Storage and Beyond

Copper redox flow batteries have been recently studied in a high halide environment [1, 2]. The halide chemistry allows for the stabilization of the copper I oxidation state and the complexation also prevents the disproportionation reaction from taking place [3]. Historically, the copper halide chemistry has been used for electrowinning. Although the chemistry has been used for many years, little has been done to characterize the diffusion of bromide ion in the presence of high concentrations of bromide, the diffusion of the copper bromide complexes, and the kinetic parameters of electrodeposition from the copper I bromide complex. We have conducted charge and discharge experiments on the copper redox flow battery in a bromide electrolyte. It was observed that the battery is able to charge at higher current densities than it can discharge. During charging experiments, the battery was able to achieve a geometric current density over 200mA/cm2. However, during discharging experiments the battery was not able to achieve 125mA/cm2as shown in Figure 1. This is most likely due to an intermediate insoluble complex formed during discharge that passivates the surface. In this study, bromide ion diffusion, copper I diffusion, and copper I kinetics have been explored. A preliminary model, based on these precepts, has been developed and the applicability of these results to redox flow batteries and other systems are discussed. [1] L. Sanz, D. Lloyd, E. Magdalena, J. Palma, K. Kontturi, Journal of Power Sources, 268 (2014) 121-128. [2] D. Lloyd, E. Magdalena, L. Sanz, L. Murtomäki, K. Kontturi, Journal of Power Sources, 292 (2015) 87-94. [3] H. Zhao, J. Chang, A. Boika, A.J. Bard, Analytical Chemistry, 85 (2013) 7696-7703. Figure 1

Direct Hydroxylation and Amination of Arenes via Deprotonative Cupration.

Deprotonative directed ortho cupration of aromatic/heteroaromatic C-H bond and subsequent oxidation with t-BuOOH furnished functionalized phenols in high yields with high regio- and chemoselectivity. DFT calculations revealed that this hydroxylation reaction proceeds via a copper (I → III → I) redox mechanism. Application of this reaction to aromatic C-H amination using BnONH2 efficiently afforded the corresponding primary anilines. These reactions show broad scope and good functional group compatibility. Catalytic versions of these transformations are also demonstrated.

Copper Exchange and Redox Activity of a Prototypical 8-Hydroxyquinoline: Implications for Therapeutic Chelation.

The N-truncated β-amyloid (Aβ) isoform Aβ4-x is known to bind Cu(2+) via a redox-silent ATCUN motif with a conditional Kd = 30 fM at pH 7.4. This study characterizes the Cu(2+) interactions and redox activity of Aβx-16 (x = 1, 4) and 2-[(dimethylamino)-methyl-8-hydroxyquinoline, a terdentate 8-hydroxyquinoline (8HQ) with a conditional Kd(CuL) = 35 pM at pH 7.4. Metal transfer between Cu(Aβ1-16), CuL, CuL2, and ternary CuL(NIm(Aβ)) was rapid, while the corresponding equilibrium between L and Aβ4-16 occurred slowly via a metastable CuL(NIm(Aβ)) intermediate. Both CuL and CuL2 were redox-silent in the presence of ascorbate, but a CuL(NIm) complex can generate reactive oxygen species. Because the NIm(Aβ) ligand will be readily exchangeable with NIm ligands of ubiquitous protein His side chains in vivo, this class of 8HQ ligand could transfer Cu(2+) from inert Cu(Aβ4-x) to redox-active CuL(NIm). These findings have implications for the use of terdentate 8HQs as therapeutic chelators to treat neurodegenerative disease.

Intramolecular Electron Transfer in the Bacterial Two-Domain Multicopper Oxidase mgLAC.

The kinetics of the intramolecular electron transfer process in mgLAC, a bacterial two-domain multicopper oxidase (MCO), were investigated by pulse radiolysis. The reaction is initiated by CO2(-) radicals produced in anaerobic, aqueous solutions of the enzyme by microsecond pulses of radiation. A sequence of pulses of CO2(-) radicals enables examination of the reductive half-cycle of the MCO catalysis. This is done by titrations of the Type 1 (T1) Cu(II) site and monitoring of the time course and amplitude of its reoxidation by internal electron transfer (ET) to the Type 3 site. Comparison of the internal ET kinetics observed for mgLAC with those of other MCOs studied by pulse radiolysis shows that they exhibit distinct reactivities. One main cause for the different reactivities is the broad range of T1 copper redox potentials, from the moderate potential of bacterial enzymes to the high potential of fungal laccases, and this possibly also reflects evolutionary quaternary structural adaptation of the MCO family to the wide range of reducing substrates that they oxidize while maintaining efficient reduction of the common substrate, molecular oxygen.

Cadmium binding mechanisms of isolated domains of human MT isoform 1a: Non-cooperative terminal sites and cooperative cluster sites

A number of biological functions have been ascribed to mammalian metallothioneins (MTs) including zinc and copper homeostatic regulation, redox activity and detoxification of heavy metals like cadmium and mercury. It is unclear how these small, fluxional, cysteine rich proteins manage to play each of these vital roles. Using a combination of cadmium and pH titrations of the isolated domains of human MT isoform 1a monitored by electrospray ionization mass spectrometry and circular dichroism spectroscopy, we report the pH dependencies that control metal binding mechanisms of these domains. We report that the α-domain mechanism is driven by the cooperative formation of the Cd4MT cluster at slightly acidic pH (≤6.9) switching binding mechanisms over a physiologically relevant pH range, whereas the β-domain metalation mechanism is dominated by terminal coordination of cadmium in a non-cooperative manner above pH5.5. These results suggest that, in some acidic sub-cellular compartments, cadmium could be sequestered in the α-domain, leaving zinc or copper bound in the β-domain and available for donation to other metalloproteins. We propose that these results can be explained by the intrinsic nature of the two domains, the four-metal α-cluster being more resistant to proton attack due to its lower charge-to-metal ratio, compared with the three-metal β-domain.

Discovery of novel PDE9 inhibitors capable of inhibiting Aβ aggregation as potential candidates for the treatment of Alzheimer's disease.

Recently, phosphodiesterase-9 (PDE9) inhibitors and biometal-chelators have received much attention as potential therapeutics for the treatment of Alzheimer’s disease (AD). Here, we designed, synthesized, and evaluated a novel series of PDE9 inhibitors with the ability to chelate metal ions. The bioassay results showed that most of these molecules strongly inhibited PDE9 activity. Compound 16 showed an IC50 of 34 nM against PDE9 and more than 55-fold selectivity against other PDEs. In addition, this compound displayed remarkable metal-chelating capacity and a considerable ability to halt copper redox cycling. Notably, in comparison to the reference compound clioquinol, it inhibited metal-induced Aβ1-42 aggregation more effectively and promoted greater disassembly of the highly structured Aβ fibrils generated through Cu2+-induced Aβ aggregation. These activities of 16, together with its favorable blood-brain barrier permeability, suggest that 16 may be a promising compound for treatment of AD.

One Electron Changes Everything. A Multispecies Copper Redox Shuttle for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) are an established alternative photovoltaic technology that offers numerous potential advantages in solar energy applications. However, this technology has been limited by the availability of molecular redox couples that are both noncorrosive/nontoxic and do not diminish the performance of the device. In an effort to overcome these shortcomings, a copper-containing redox shuttle derived from 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (PDTO) ligand and the common DSC additive 4-tert-butylpyridine (TBP) was investigated. Electrochemical measurements, single-crystal X-ray diffraction, and absorption and electron paramagnetic resonance spectroscopies reveal that, upon removal of one metal-centered electron, PDTO-enshrouded copper ions completely shed the tetradentate PDTO ligand and replace it with four or more TBP ligands. Thus, the Cu(I) and Cu(II) forms of the electron shuttle have completely different coordination spheres and are characterized by widely differing Cu(II/I) forma...

Copper Oxidation/Reduction in Water and Protein: Studies with DFTB3/MM and VALBOND Molecular Dynamics Simulations.

We apply two recently developed computational methods, DFTB3 and VALBOND, to study copper oxidation/reduction processes in solution and protein. The properties of interest include the coordination structure of copper in different oxidation states in water or in a protein (plastocyanin) active site, the reduction potential of the copper ion in different environments, and the environmental response to copper oxidation. The DFTB3/MM and VALBOND simulation results are compared to DFT/MM simulations and experimental results whenever possible. For a copper ion in aqueous solution, DFTB3/MM results are generally close to B3LYP/MM with a medium basis, including both solvation structure and reduction potential for Cu(II); for Cu(I), however, DFTB3/MM finds a two-water coordination, similar to previous Born-Oppenheimer molecular dynamics simulations using BLYP and HSE, whereas B3LYP/MM leads to a tetrahedron coordination. For a tetraammonia copper complex in aqueous solution, VALBOND and DFTB3/MM are consistent in terms of both structural and dynamical properties of solvent near copper for both oxidation states. For copper reduction in plastocyanin, DFTB3/MM simulations capture the key properties of the active site, and the computed reduction potential and reorganization energy are in fair agreement with experiment, especially when the periodic boundary condition is used. Overall, the study supports the value of VALBOND and DFTB3(/MM) for the analysis of fundamental copper redox chemistry in water and protein, and the results also help highlight areas where further improvements in these methods are desirable.

Theory and Experiments for Generalization of the Scanning Bipolar Cell for Patterning of Diverse Metals

The Scanning Bipolar Cell (SBC) is a novel system using bipolar electrochemistry for micro-scale patterning without needing to connect the power supply to the substrate. Bipolar electrochemistry, defined as spatially segregated, equal and opposite reduction and oxidation on an electrically-floating conductor, has been understood for several decades but has recently seen a renaissance for many new electrochemical applications (1). The main driving force for bipolar electrochemistry is the ohmic potential drop through the electrolyte solution during the passage of current in an electrochemical cell. The scanning bipolar cell was modified from an electrodeposition tool we call “Electrochemical Printing” (EcP). EcP jets electrolyte through a microcapillary nozzle with an upstream anode onto a conductive substrate that is cathodically polarized using an electrical connection. In this system, the ohmic potential drop beneath the microcapillary wall is designed to be large compared to charge transfer overpotential (small Wagner number), creating a localized current on the macroscopically polarized substrate. The large ohmic potentials typical of EcP make this system ideal for bipolar electrochemical applications and is easily modified when, instead of using the substrate as a cathode, it is allowed to float, and a new “feeder” cathode is placed distant from the microjet (Figure 1a attached) (2). In this configuration localized and controllable electrodeposition occurs on the macroscopic conductive substrate without direct electrical contact. The concept for the scanning bipolar cell was first validated experimentally and computationally using the reversible copper redox couple, where copper deposits were patterned on a sacrificial copper substrate while copper in the far-field oxidized (2). The equal and opposite nature of bipolar electrochemistry provided a restructuring of the copper substrate, where the amount of material etched in the far-field was also locally deposited beneath the nozzle. Secondary current distribution computations evaluated the coupling between the ohmic and charge transfer resistances and determined relative current pathways through the system. We have further generalized the design guidelines for operating the SBC to include a wide range of electrodepositable materials such as nickel, gold, and silver. The design guidelines for the SBC depend on the nobility and electrochemical reversibility of the material. Tailoring the far-field electrochemical reaction to that of the local reduction is also essential for successful bipolar electrodeposition. Nickel is ideal for patterning with the SBC because it behaves irreversibly by forming a passivating oxide film, protecting the deposit from subsequent electrochemical oxidation. For reversible materials, such as copper, any previously patterned material can be electrochemically oxidized during subsequent deposition. This creates an added challenge for electrolyte design in order to create systems where the undesired copper oxidation is secondary to the far-field oxidation chemistry. To overcome this challenge we design pseudo-stable baths, where the equilibrium potential of the reducing agent (ascorbic acid) is slightly lower than that of the material being deposited. Figure 1b shows an optical micrograph of copper patterned on a gold substrate with ascorbic acid providing the bipolar oxidation in the far-field. Essentially, this is an electroless deposition bath that does not function well because of the low thermodynamic driving force. Nonetheless, the ascorbic acid oxidation is thermodynamically preferential to copper etching, so there is a window for the desired chemistry (ascorbic acid oxidation) to occur without the undesired chemistry (copper oxidation) occurring. This window also determines how fast we can drive the electrochemical reactions. Figure 1c shows an optical micrograph where the applied current is 10x larger than in 1b for the same electrolyte formulation, providing enough substrate polarization to do both undesired copper etching and ascorbic acid oxidation. Scaling relationships for the SBC have been studied via simulations, and scale-down limitations center around nozzle fabrication and motion control. However, the SBC functions similarly to scanning ion conductance microscopy (SICM), which has pipette dimensions and motion-control with nanometer resolutions. We are confident that electrolyte design characteristics at the micron-scale can be applied to sub-micron systems with smaller resolution and control (3). We have shown how modifying our pre-existing EcP technology for bipolar electrochemistry provides a platform for patterning without electrical connections to the substrate. Co-design of the electrochemical cell, electrolyte, and substrate is critical to engineering effective bipolar electrochemical systems.

Feasibility of All-Copper Hybrid Redox Flow Battery for Large Scale Energy Storage

Copper redox flow batteries have been newly studied and offer many advantages over other redox flow battery chemistries [1-3]. There is little hydrogen evolution, no dendrite formation has been observed, and it is an all copper system which indicates no crossover contamination. Preliminary analysis indicates an open circuit voltage of 0.81 volts as shown in Figure 1.Although the all copper redox flow battery has a relatively low open circuit voltage, the all copper redox flow batter provides a platform for a simple and cost-effective flow battery system. In this research, the all copper redox flow battery in bromide electrolyte has been studied in a prototype 6.45 cm2electrode single cell. Charge-discharge cycling achieved coulombic efficiencies over 85% and voltaic efficiencies greater than 75%. However, capacity fade was observed and preliminary results suggest this is due to metallic copper loss at the negative electrode. This is most likely due to non-ideal plating morphologies which have been studied independently as a function of current density and electrolyte composition. We will report on our cell testing and single electrode experiments for this promising flow battery chemistry. Figure 1: Cyclic voltammogram of 0.5M Cu1+ in 4M NaBr, 1M HBr, and 0.5M Br-. This is the last of 5 cycles at a scan rate of 10 mV/s, on a graphite working electrode, and using a silver-silver chloride reference electrode. The Cu0/1+ and Cu1+/2+ standard potentials are approximately -0.26 and 0.55 volts, respectively indicating the all copper redox flow battery has an open circuit potential of 0.81 volts.

An electrochemical study of the dissolution of chalcopyrite in ammonia–ammonium sulphate solutions

Ammoniacal solutions are an effective lixiviant for the oxidative dissolution of some mineral sulphides. A study of the anodic dissolution of chalcopyrite in ammonium sulphate-ammonium hydroxide solutions has been carried out using cyclic voltammetry, chrono-amperometry and rest-potential measurements. The role of the copper(II)/copper(I) redox couple in the oxidation process has been evaluated. Rest potentials have been found not to be affected by oxygen but to increase with an increase in initial copper(II) concentration. This trend remains more or less unchanged with increasing total ammonia (NH3+NH4+) concentration. Cyclic voltammetry analysis shows an oxidation peak/shoulder when anodically polarising the chalcopyrite after attaining rest potential in the presence of copper(II) ions. All reverse sweep curves are more or less identical, but the Tafel slope decreases from around 150 mV/decade at 1M total ammonia concentration to around 120 mV/decade at higher ammonia concentrations. Pseudo-steady-state anodic current densities measured in the absence of copper(II) ions at the rest potentials obtained in the presence of copper(II) ions increase with increasing concentration of copper(II) ions, confirming the positive effect of copper(II) ions on the rate of dissolution of the mineral. Cyclic voltametric and chrono-amperometric data show that in the absence of initial copper(II) ions, the rate of dissolution in the presence of dissolved oxygen is significantly lower. These results confirm that the effective oxidant for the mineral under the conditions of the study is copper(II) and not dissolved oxygen. Coulometric measurements have been used to establish the stoichiometry of the anodic reaction at different potentials as involving approximately seven electrons per mole of chalcopyrite, suggesting the formation of thiosulphate, although thiosulphate ions have not been tested for or identified in solution. SEM and energy dispersive X-ray (EDX) analysis of the mineral surface left to equilibrate over time shows a copper-depleted surface, rich in iron but relatively low in sulphur. The iron in the surface layer can easily be removed by short contact with concentrated acid, which is consistent with the formation of a secondary iron-based precipitation layer rather than an altered mineral phase.