Bioelectrocatalytic CO₂ Reduction by Redox Polymer-Wired Carbon Monoxide Dehydrogenase Gas Diffusion Electrodes

The development of electrodes for efficient CO₂ reduction while forming valuable compounds is critical. The use of enzymes as catalysts provides the advantage of high catalytic activity in combination with highly selective transformations. We describe the electrical wiring of a carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans (ChCODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO₂ to CO over gas diffusion electrodes. High catalytic current densities of up to −5.5 mA cm¯² are achieved, exceeding the performance of previously reported bioelectrodes for CO₂ reduction based on either carbon monoxide dehydrogenases or formate dehydrogenases. The proposed bioelectrode reveals considerable stability with a half-life of more than 20 h of continuous operation. Product quantification using gas chromatography confirmed the selective transformation of CO₂ into CO without any parasitic co-reactions at the applied potentials

Cross-Linkable Polymer-Based Multi-layers for Protecting Electrochemical Glucose Biosensors against Uric Acid, Ascorbic Acid, and Biofouling Interferences

The lifetime of implantable electrochemical glucose monitoring devices is limited due to the foreign body response and detrimental effects from ascorbic acid (AA) and uric acid (UA) interferents that are components of physiological media. Polymer coatings can be used to shield biosensors from these interferences and prolong their functional lifetime. This work explored several approaches to protect redox polymer-based glucose biosensors against such interferences by designing six targeted multi-layer sensor architectures. Biological interferents, like cells and proteins, and UA and AA interferents were found to have individual effects on the current density and operational stability of glucose biosensors, requiring individual protection and treatment. Protection against biofouling can be achieved using a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC) zwitterionic polymer coating. An enzyme-scavenging approach was compared to electrostatic repulsion by negatively charged polymers for protection against AA and UA interferences. A multi-layer novel polymer design (PD) system consisting of a cross-linkable negatively charged polyvinylimidazole-polysulfostyrene co-polymer inner layer and a cross-linkable MPC zwitterionic polymer outer layer showed the best protection against AA, UA, and biological interferences. The sensor protected using the novel PD shield displayed the lowest mean absolute relative difference between the glucose reading without the interferent and the reading value with the interferent present and also displayed the lowest variability in sensor readings in complex media. For sensor measurements in artificial plasma, the novel PD extends the linear range (R2 = 0.99) of the sensor from 0–10 mM for the control to 0–20 mM, shows a smaller decrease in sensitivity, and retains high current densities. The application of PD multi-target coating improves sensor performance in complex media and shows promise for use in sensors operating in real conditions

Electron Transfer Reactions in Chemistry of Di- and Tetrahydropyridines

The mechanism of the electrochemical oxidation of 1,2,3,4-tetrahydropyridines in acetonitrile has been studied. A single reversible one-electron oxidation is registered in the accessible voltage range. The reversibility of the process of tetrahydropyridines is sensitive to the traces of oxygen in solution. The electrochemically generated radical cation of tetrahydropyridine may act as a mediator in an indirect oxidation of dihydropyridines if the difference in oxidation potentials between two compounds is less than 200 mV. During the indirect oxidation of 2,4,6-trimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid diethyl ester to 3,5-bis(ethoxycarbonyl)-2,4,6-trimethylpyridinium perchlorate, some of the starting tetrahydropyridine is protonated thus making it anodically inactive

Photoinduced 1,2,3,4-Tetrahydropyridine Ring Conversions

Stable heterocyclic hydroperoxide can be easily prepared as a product of fast oxidation of a 1,2,3,4-tetrahydropyridine by 3O2 if the solution is exposed to sunlight. The driving force for the photoinduced electron transfer is calculated from electrochemical and spectroscopic data. The outcome of the reaction depends on the light intensity and the concentration of O2. In the solid state the heterocyclic hydroperoxide is stable; in solution it is involved in further reactions

A biophotoelectrode based on boronic acid-modified Chlorella vulgaris\textit {Chlorella vulgaris} cells integrated within a redox polymer

Green microalgae are gaining attention in the renewable energy field due to their ability to convert light into energy in biophotovoltaic (BPV) cells. The poor exogenous electron transfer kinetics of such microorganisms requires the use of redox mediators to improve the performance of related biodevices. Redox polymers are advantageous in the development of subcellular-based BPV devices by providing an improved electron transfer while simultaneously serving as immobilization matrix. However, these surface-confined redox mediators have been rarely used in microorganism-based BPVs. Since electron transfer relies on the proximity between cells and the redox centres at the polymer matrix, the development of molecularly tailored surfaces is of great significance to fabricate more efficient BPV cells. We propose a bioanode integrating $\textit {Chlorella vulgaris}$ embedded in an Os complex-modified redox polymer. $\textit {Chlorella vulgaris}$ cells are functionalized with 3-aminophenylboronic acid that exhibits high affinity to saccharides in the cell wall as a basis for an improved integration with the redox polymer. Maximum photocurrents of (5 $\pm$ 1) $\mu$A $cm^{−2}$ are achieved. The developed bioanode is further coupled to a bilirubin oxidase-based biocathode for a proof-of-concept BPV cell. The obtained results encourage the optimization of electron-transfer pathways toward the development of advanced microalgae-based biophotovoltaic devices

An oxygen-insensitive amperometric galactose biosensor based on galactose oxidase co-immobilized with an Os-complex modified redox polymer

<p>Monitoring <a href="https://www.sciencedirect.com/topics/chemistry/galactose">galactose</a> levels in dairy products can help to prevent severe complications with a hereditary metabolic disease such as galactosemia, a life-threatening disease. The current state of the art requires the development of less expensive, more reliable and specific methods to determine galactose levels in food in a practical way. We report the development and optimization of an <a href="https://www.sciencedirect.com/topics/chemistry/amperometric">amperometric</a> biosensor for determination of galactose in dairy products based on galactose oxidase (GaOx) co-immobilized with an osmium-complex modified redox polymer on glassy carbon electrodes. To attain the maximum catalytic currents based on mediated electron transfer, two Os-complex based polymers with different <a href="https://www.sciencedirect.com/topics/chemistry/redox-potential">redox potentials</a> and different enzyme:redox polymer ratios were studied. The optimized GaOx-modified electrode gave a maximum electrocatalytic response of galactose <a href="https://www.sciencedirect.com/topics/chemical-engineering/oxidation-reaction">oxidation</a> that was not affected by the presence of O2, indicating fast wiring of the enzyme by the Os-complex modified redox polymer. The biosensor that gave the best analytical parameters for galactose detection was further tested for measuring galactose concentration in lactose-containing and lactose-free milk and yogurt samples under aerobic conditions. The results obtained with the amperometric biosensor were validated by high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD).</p&gt

Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia

Electrocatalytic recycling of waste nitrate ($NO_{3}$$^-$) to valuable ammonia ($NH_3$) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate $NH_3$ synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade $NO_{3}$$^-$-to-$NH_3$ conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell $Cu/CuO_x$ and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner $Cu/CuO_x$ phases preferentially catalyze $NO_{3}$$^-$ reduction to $NO_{2}$$^-$, which is rapidly reduced to $NH_3$ at the nearby Co/CoO shell. This unique tandem catalyst system leads to a $NO_{3}$$^-$-to-$NH_3$ Faradaic efficiency of 93.3 $\pm$ 2.1% in a wide range of $NO_{3}$$^-$ concentrations at pH 13, a high $NH_3$ yield rate of 1.17 mmol $cm^{−2} h^{−1}$ in 0.1 M $NO_{3}$$^-$ at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports

An oxygen-insensitive amperometric galactose biosensor based on galactose oxidase co-immobilized with an Os-complex modified redox polymer

Monitoring galactose levels in dairy products can help to prevent severe complications with a hereditary metabolic disease such as galactosemia, a life-threatening disease. The current state of the art requires the development of less expensive, more reliable and specific methods to determine galactose levels in food in a practical way. We report the development and optimization of an amperometric biosensor for determination of galactose in dairy products based on galactose oxidase (GaOx) co-immobilized with an osmium-complex modified redox polymer on glassy carbon electrodes. To attain the maximum catalytic currents based on mediated electron transfer, two Os-complex based polymers with different redox potentials and different enzyme:redox polymer ratios were studied. The optimized GaOx-modified electrode gave a maximum electrocatalytic response of galactose oxidation that was not affected by the presence of O2, indicating fast wiring of the enzyme by the Os-complex modified redox polymer. The biosensor that gave the best analytical parameters for galactose detection was further tested for measuring galactose concentration in lactose-containing and lactose-free milk and yogurt samples under aerobic conditions. The results obtained with the amperometric biosensor were validated by high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD).</p