Electro/Ni Dual-Catalyzed Decarboxylative C(sp3)-C(sp2) Cross-Coupling Reactions of Carboxylates and Aryl Bromide

Paired redox-neutral electrolysis offers an attractive green platform for organic synthesis by avoiding sacrificial oxidants and reductants. Carboxylates are non-toxic, stable, inexpensive, and widely available, making them ideal nucleophiles for C-C cross-coupling reactions. Here, we report the electro/Ni dual-catalyzed redox-neutral decarboxylative C(sp3)-C(sp2) cross-coupling reactions of pristine carboxylates with aryl bromides. At a cathode, a NiII(Ar)(Br) intermediate is formed through the activation of Ar-Br bond by a NiI-bipyridine catalyst and subsequent reduction. At an anode, the carboxylates, including amino acid, benzyl carboxylic acid, and 2-phenoxy propionic acid, undergo oxidative decarboxylation to form carbon-based free radicals. The combination of NiII(Ar)(Br) intermediate and carbon radical results in the formation of C(sp3)-C(sp2) cross-coupling products. The adaptation of this electrosynthesis method to flow synthesis and valuable molecule synthesis was demonstrated. The reaction mechanism was systematically studied through electrochemical voltammetry and density functional theory (DFT) computational studies. The relationships between the electrochemical properties of carboxylates and the reaction selectivity were revealed. The electro/Ni dual-catalyzed cross-coupling reactions described herein expand the chemical space of paired electrochemical C(sp3)-C(sp2) cross-coupling and represent a promising method for the construction of the C(sp3)-C(sp2) bonds because of the ubiquitous carboxylate nucleophiles and the innate scalability and flexibility of electrochemical flow-synthesis technology.

Boosting Electrocatalytic Ethylene Epoxidation by Single Atom Modulation

The electrochemical synthesis of ethylene oxide (EO) using ethylene and water under ambient conditions presents a low-carbon alternative to existing industrial production process. Yet, the electrocatalytic ethylene epoxidation route is currently hindered by largely insufficient activity, EO selectivity, and long-term stability. Here we report a single atom Ru-doped hollandite structure KIr4O8 (KIrRuO) nanowire catalyst for efficient EO production via a chloride-mediated ethylene epoxidation process. The KIrRuO catalyst exhibits an EO partial current density up to 0.7 A cm-2 and an EO yield as high as 92.0 %. The impressive electrocatalytic performance towards ethylene epoxidation is ascribed to the modulation of electronic structures of adjacent Ir sites by single Ru atoms, which stabilizes the *CH2CH2OH intermediate and facilitates the formation of active Cl2 species during the generation of 2-chloroethanol, the precursor of EO. This work provides a single atom modulation strategy for improving the reactivity of adjacent metal sites in heterogeneous electrocatalysts.

Electroreduction of divanillin to polyvanillin in an electrochemical flow reactor

The electrochemical conversion of biobased intermediates offers an attractive and sustainable process for the production of green chemicals. One promising synthesis route is the production of the total vanillin-based polymer polyvanillin, which can be produced by electrochemical pinacolization of divanillin (5-5´bisvanillyl). Divanillin can be easily enzymatically generated from vanillin, a renewable intermediate accessible from lignin on an industrial scale. This study investigates systematically the electrochemical production of polyvanillin in a divided plane parallel flow reactor in recirculation mode. Several analytic methods, such as online UV-VIS spectroscopy, size exclusion chromatography (SEC), 2D-NMR (HSQC, 13C/1H), TGA and DSC were used to monitor the reaction progress and to characterize the reaction products under different galvanostatic reaction conditions revealing new insights into the reaction mechanism and structural features of the polymer. Further, by using an electrochemical engineering-based approach determining the limiting current densities, we readily achieved high current densities over 50 mA cm-2 for the polyvanillin synthesis and reached averaged molecular weights up to Mw = 4100 g mol-1 and Mn = 2700 g mol-1. The cathodic polymerization to polyvanillin offers an innovative approach for the electrochemical production of biobased polymers presented on flow cell level.

Single-Atom Manganese-Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol

The oxygen evolution reaction (OER), characterized by a four-electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single-atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn-N-C single-atom catalyst (Mn-SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate' s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn-SA@NC drives the entire reaction, establishing a practical Mn SAC-catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Anodic Oxidation of Methanol to Formaldehyde Synergizing with a Br- /Br2 Redox-Mediated Chemical Route to Produce Methyl Formate

Methyl formate (MF) is one of the most important chemical commodities, which has a wide range of applications. Due to environmental friendliness, mild reaction conditions, and easy operations, electrosynthesis of MF has garnered increasing attention in recent years. In this work, we reported an electrosynthesis route toward MF in a halide-containing methanol solution. The thorough mechanistic investigations point out that electrosynthesis of MF is accomplished by instant reaction between aldehyde from anodic methanol oxidation, and methoxy bromide (CH3 OBr) that is in-situ generated by reaction of Br2 from anodic oxidation of Br- with methoxide (CH3 O- ) from cathodic reduction of methanol. This method features high atomic economy only producing valuable MF and hydrogen gas, and shows distinct advantages compared to the reported MF electrosynthesis methods. Even at 200 mA/cm2 , the faradaic efficiency (FE) of MF remains consistently around 60 % at the anode while a 100 % FE hydrogen gas is produced at the cathode.

Cobalt-Catalyzed Electroreductive Alkylation of Unactivated Alkyl Chlorides with Conjugated Olefins

Reactions of unactivated alkyl chlorides under mild and sustainable conditions are rare compared to those of alkyl bromides or iodides. As a result, synthetic methods capable of modifying the vast chemical space of chloroalkane reagents, wastes, and materials are limited. We report the cobalt-catalyzed reductive addition of unactivated alkyl chlorides to conjugated alkenes. Co-catalyzed activation of alkyl chlorides is performed under electroreductive conditions, and the resulting reactions constitute formal alkyl-alkyl bond formation. In addition to developing an operationally simple methodology, detailed mechanistic studies provide insights into the elementary steps of a proposed catalytic cycle. In particular, we propose a switch in the mechanism of C-Cl bond activation from nucleophilic substitution to halogen atom abstraction, which is critical for efficiently generating alkyl radicals. These mechanistic insights were leveraged in designing ligands that enable couplings of primary, secondary, and tertiary alkyl chlorides.

Electrochemical H2O2 - stat mode as reaction concept to improve the process performance of an unspecific peroxygenase

The electroenzymatic hydroxylation of 4-ethylbenzoic acid catalyzed by the recombinant unspecific peroxygenase from the fungus Agrocybe aegerita (rAaeUPO) was performed in a gas diffusion electrode (GDE)-based system. Enzyme stability and productivity are significantly affected by the way the co-substrate hydrogen peroxide (H2O2) is supplied. In this study, two in-situ electrogeneration modes of H2O2 were established and compared. Experiments under galvanostatic conditions (constant productivity of H2O2) were conducted at current densities spanning from 0.8 mA cm-2 to 6.4 mA cm-2. For comparison, experiments under H2O2-stat mode (constant H2O2 concentration) were performed. Here, four H2O2 concentrations between 0.06 mM and 0.28 mM were tested. A maximum H2O2 productivity of 5.5 µM min-1 cm-2 and productivity of 10.5 g L-1 d-1 were achieved under the galvanostatic condition at 6.4 mA cm-2. Meanwhile, the highest total turnover number (TTN) of 710,000 mol mol-1 and turnover frequency (TOF) of 87.5 s-1 were obtained under the H2O2-stat mode at concentration limits of 0.15 mM and 0.28 mM, respectively. The most favorable outcome in terms of maximum achievable TTN, TOF and productivity was found under the H2O2-stat mode at concentration limit of 0.2 mM. Here, a TTN of 655,000 mol mol-1, a TOF of 80.3 s-1 and a productivity of 6.1 g L-1 d-1 were achieved. The electrochemical H2O2-stat mode not only offers a promising alternative reaction concept to the well-established galvanostatic mode but also enhances the process performance of unspecific peroxygenases.

Comprehensive Comparisons between Directing and Alternating Current Electrolysis in Organic Synthesis

Organic electrosynthesis has consistently aroused significant interest within both academic and industrial spheres. Despite the considerable progress achieved in this field, the majority of electrochemical transformations have been conducted through the utilization of direct-current (DC) electricity. In contrast, the application of alternating current (AC), characterized by its polarity-alternating nature, remains in its infancy within the sphere of organic synthesis, primarily due to the absence of a comprehensive theoretical framework. This minireview offers an overview of recent advancements in AC-driven organic transformations and seeks to elucidate the differences between DC and AC electrolytic methodologies by probing into their underlying physical principles. These differences encompass the ability of AC to preclude the deposition of metal catalysts, the precision in modulating oxidation and reduction intensities, and the mitigation of mass transfer processes.

Nanoarchitectonics on Electrosynthesis and Assembly of Conjugated Metallopolymers

In contrast to edge-on and face-on orientations, end-on uniaxial conjugated polymers have the theoretical possibility of providing a macroscopic crystalline film. However, their fabrication is insurmountable due to sluggishly thermodynamic equilibrium states. Herein, we report the programmatic pathway to fabricate nanoarchitectonics on end-on uniaxial conjugated metallopolymers by surface-initiated simultaneous electrosynthesis and assembly. Self-assembled monolayer (SAM) with bottom-up oriented electroactive molecules as a temple allows orientation, stacking, and reactive addition of monomers triggered by switching alternative redox reactions as well as crystallization of small molecules. Repeating the same reaction can repair the unreactive site on the SAM and dynamically and statistically ensure maximum iterative coverage with ideal linear coefficients between optical or electrical responses and iterative times. The resulting nanoarchitectonics on uniaxially assembled end-on polymers over centimeter-sized areas have a subnanometer-uniform morphology and exhibit ultrahigh modulus as well as an inorganic indium tin oxides and the highest conductance among conjugated molecular monolayers. Their memristive devices provide quantitative electrical and optical responses as a function of molecular length, bias, and iterative junctions. Precise processing of nanoarchitectonics as an electrically assisted assembly or printing technique can present sophisticated optoelectric functions and dimensional batch-to-batch consistency for micro-sized organic materials and electronics.

Bioelectrocatalytic Synthesis: Concepts and Applications

Bioelectrocatalytic synthesis is the conversion of electrical energy into value-added products using biocatalysts. These methods merge the specificity and selectivity of biocatalysis and energy-related electrocatalysis to address challenges in the sustainable synthesis of pharmaceuticals, commodity chemicals, fuels, feedstocks and fertilizers. However, the specialized experimental setups and domain knowledge for bioelectrocatalysis pose a significant barrier to adoption. This review introduces key concepts of bioelectrosynthetic systems. We provide a tutorial on the methods of biocatalyst utilization, the setup of bioelectrosynthetic cells, and the analytical methods for assessing bioelectrocatalysts. Key applications of bioelectrosynthesis in ammonia production and small-molecule synthesis are outlined for both enzymatic and microbial systems. This review serves as a necessary introduction and resource for the non-specialist interested in bioelectrosynthetic research.

Electrosynthesis and Microanalysis in Thin Layer: An Electrochemical Pipette for Rapid Electrolysis and Mechanistic Study of Electrochemical Reactions

Electrochemistry represents unique approaches for the promotion and mechanistic study of chemical reactions and has garnered increasing attention in different areas of chemistry. This expansion necessitates the enhancement of the traditional electrochemical cells that are intrinsically constrained by mass transport limitations. Herein, we present an approach for designing an electrochemical cell by limiting the reaction chamber to a thin layer of solution, comparable to the thickness of the diffusion layer. This thin layer electrode (TLE) provides a modular platform to bypass the constraints of traditional electrolysis cells and perform electrolysis reactions in the timescale of electroanalytical techniques. The utility of the TLE for electrosynthetic applications benchmarked using NHPI-mediated electrochemical C-H functionalization. The application of microscale electrolysis for the study of drug metabolites was showcased by elucidating the oxidation pathways of the paracetamol drug. Moreover, hosting a microelectrode in the TLE, was shown to enable real-time probing of the profiles of redox-active components of these rapid electrosynthesis reactions.

Electroreductive Desulfurative Transformations with Thioethers as Alkyl Radical Precursors

Thioethers are highly prevalent functional groups in organic compounds of natural and synthetic origin but remain remarkably underexplored as starting materials in desulfurative transformations. As such, new synthetic methods are highly desirable to unlock the potential of the compound class. In this vein, electrochemistry is an ideal tool to enable new reactivity and selectivity under mild conditions. Herein, we demonstrate the efficient use of aryl alkyl thioethers as alkyl radical precursors in electroreductive transformations, along with mechanistic details. The transformations proceed with complete selectivity for C(sp3 )-S bond cleavage, orthogonal to that of established transition metal-catalyzed two-electron routes. We showcase a hydrodesulfurization protocol with broad functional group tolerance, the first example of desulfurative C(sp3 )-C(sp3 ) bond formation in Giese-type cross-coupling and the first protocol for electrocarboxylation of synthetic relevance with thioethers as starting materials. Finally, the compound class is shown to outcompete their well-established sulfone analogues as alkyl radical precursors, demonstrating their synthetic potential for future desulfurative transformations in a one-electron manifold.

Simultaneous Generation of H2O2 and Formate by Co-Electrolysis of Water and CO2 over Bifunctional Zn/SnO2 Nanodots

Hydrogen peroxide (H2O2) and formate are important chemicals used in various chemical manufacturing industries. One promising approach for the simultaneous production of these chemicals is coupling anodic two-electron water oxidation with cathodic CO2 reduction in an electrolyzer using nonprecious bifunctional electrocatalysts. Herein, we report an innovative hybrid electrosynthesis strategy using Zn-doped SnO2 (Zn/SnO2) nanodots as bifunctional redox electrocatalysts to achieve Faradaic efficiencies of 80.6% and 92.2% for H2O2 and formate coproduction, respectively, along with excellent stability for at least 60 h at a current density of ~ 150 mA cm-2. Through a combination of physicochemical characterizations, including operando attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), isotope labeling mass spectrometry (MS)/1H NMR and quasi-in-situ electron paramagnetic resonance (EPR), with density functional theory (DFT) calculations, we discovered that the Zn dopant facilitates the coupling of *OH intermediates to promote H2O2 production and optimizes the adsorption of *OCHO intermediates to accelerate formate formation. Our findings offer new insights into designing more efficient bifunctional electrocatalyst-based pair-electrosynthesis system for the coproduction of H2O2 and formate feedstocks.

Deuterodehalogenation Under Net Reductive or Redox-Neutral Conditions Enabled by Paired Electrolysis

Interest in deuterated active pharmaceutical ingredients (APIs) is increasing as deuteration holds promise for kinetic isotope effect (KIE) regulated fine-tuning of API performance. Moreover, deuterium isotope labeling is frequently carried out to study organic and bioorganic reaction mechanisms and to facilitate complex target synthesis. As such, methods for highly selective deuteration of organic molecules are highly desirable. Herein, we present an electrochemical method for the selective deuterodehalogenation of benzylic halides via a radical-polar crossover mechanism, using inexpensive deuterium oxide (D2 O) as the deuterium source. We demonstrate broad functional group compatibility across a range of aryl and heteroaryl benzylic halides. Furthermore, we uncover a sequential paired electrolysis regime, which permits switching between net reductive and overall redox-neutral reactions of sulfur-containing substrates simply by changing the identity of the sacrificial reductant employed.

Enabling Direct Photoelectrochemical H₂ Production using Alternative Oxidation Reactions on WO₃

The efficient and inexpensive conversion of solar energy into chemical bonds, such as in H2 via the photoelectrochemical splitting of H2O, is a promising route to produce green industrial feedstocks and renewable fuels, which is a key goal of the NCCR Catalysis. However, the oxidation product of the water splitting reaction, O2, has little economic or industrial value. Thus, upgrading key chemical species using alternative oxidation reactions is an emerging trend. WO3 has been identified as a unique photoanode material for this purpose since it performs poorly in the oxygen evolution reaction in H2O. Herein we highlight a collaboration in the NCCR Catalysis that has gained insights at the atomic level of the WO3 surface with ab initio computational methods that help to explain its unique catalytic activity. These computational efforts give new context to experimental results employing WO3 photoanodes for the direct photoelectrochemical oxidation of biomass-derived 5-(hydroxymethyl) furfural. While yield for the desired product, 2,5-furandicarboxylic acid is low, insights into the reaction rate constants using kinetic modelling and an electrochemical technique called derivative voltammetry, give indications on how to improve the system.

Electrooxidative Activation of B-B Bond in B2 cat2 : Access to gem-Diborylalkanes via Paired Electrolysis

This report describes the unprecedented electrooxidation of a solvent (e.g., DMF)-ligated B₂ cat₂ complex, whereby a solvent-stabilized boryl radical is formed via quasi-homolytic cleavage of the B-B bond in a DMF-ligated B₂ cat₂ radical cation. Cyclic voltammetry and density functional theory provide evidence to support this novel B-B bond activation strategy. Furthermore, a strategy for the electrochemical gem-diborylation of gem-bromides via paired electrolysis is developed for the first time, affording a range of versatile gem-diborylalkanes, which are widely used in synthetic society. Notably, this reaction approach is scalable, transition-metal-free, and requires no external activator.

Preferential Adsorption of Ethylene Oxide on Fe and Chlorine on Ni Enabled Scalable Electrosynthesis of Ethylene Chlorohydrin

Industrial manufacturing of ethylene chlorohydrin (ECH) critically requires excess corrosive hydrochloric acid or hypochlorous acid with dealing with massive by-products and wastes. Here we report a green and efficient electrosynthesis of ECH from ethylene oxide (EO) with NaCl over a NiFe₂ O₄ nanosheet anode. Theoretical results suggest that EO and Cl preferentially adsorb on Fe and Ni sites, respectively, collaboratively promoting the ECH synthesis. A Cl radical-mediated ring-opening process is proposed and confirmed, and the key Cl and carbon radical species are identified by high-resolution mass spectrometry. This strategy can enable scalable electrosynthesis of 185.1 mmol of ECH in 1 h with 92.5 % yield at a 55 mA cm^-2 current density. Furthermore, a series of other chloro- and bromoethanols with good to high yields and paired synthesis of ECH and 4-amino-3,6-dichloropyridine-2-carboxylicacid via respectively loading and unloading Cl are achieved, showing the promising potential of this strategy.

C-H Fluoromethoxylation of Arenes by Photoredox Catalysis

Redox-active N-(fluoromethoxy)benzotriazoles were made accessible from fluoroacetic acid and hydroxybenzotriazoles via electrodecarboxylative coupling. After alkylation, they become effective monofluoromethoxylation reagents, enabling the photocatalytic C-H functionalization of arenes. Thus, irradiation of 1-(OCH₂ F)-3-Me-6-(CF₃ )benzotriazolium triflate with blue LED light in the presence of [Ru(bpy)₃ (PF₆ )₂ ] promotes the synthesis of diversely functionalized aryl monofluoromethyl ethers. This method allows the late-stage functionalization of biologically relevant structures without relying on ecologically problematic halofluorocarbons.

Electrosynthetic C-O Bond Activation in Alcohols and Alcohol Derivatives

Alcohols and their derivatives are ubiquitous and versatile motifs in organic synthesis. Deoxygenative transformations of these compounds are often challenging due to the thermodynamic penalty associated with the cleavage of the C-O bond. However, electrochemically driven redox events have been shown to facilitate the C-O bond cleavage in alcohols and their derivatives either through direct electron transfer or through the use of electron transfer mediators and electroactive catalysts. Herein, a comprehensive overview of preparative electrochemically mediated protocols for C-O bond activation and functionalization is detailed, including direct and indirect electrosynthetic methods, as well as photoelectrochemical strategies.

The Use of Redox Mediators in Electrocatalysis and Electrosynthesis

Electrocatalysis and electrosynthesis, which convert the electrical energy and store them in the chemical forms, have been considered as promising technologies to utilize green renewable energy sources. Most of the studies focused on developing novel active molecules or advanced electrodes to improve the performance. However, the direct acquisition and electron transferring will be limited by the intrinsic characters of the electrodes. The introduce of redox mediators, which are served as the intermediate electron carriers or reservoirs without changing the final products, provide a unique approach to accelerate the electrochemical performance of these energy conversions. This review provides an overview of the recent development of electrocatalysis and electrosynthesis by using redox mediators, and provides a comprehensive discussion toward focusing on the principles and construction of these systems.

Silver-Free C-H Activation: Strategic Approaches towards Realizing the Full Potential of C-H Activation in Sustainable Organic Synthesis

The activation of carbon-hydrogen bonds is considered as one of the most attractive techniques in synthetic organic chemistry because it bears the potential to shorten synthetic routes as well as to produce complementary product scopes compared to traditional synthetic strategies. However, many current methods employ silver salts as additives, leading to stoichiometric metal waste and thereby preventing the full potential of C-H activation to be exploited. Therefore, the development of silver-free protocols has recently received increasing attention. Mechanistically, silver can serve various roles in C-H activation and thus, avoiding the use of silver requires different approaches based on the role it serves in a given process. In this Review, we present the comparison of silver-based and silver-free methods. Focusing on the strategic approaches to develop silver-free C-H activation, we provide the reader with the means to develop sustainable methods for C-H activation.

Electrochemical Reactors for Continuous Decentralized H2 O2 Production

The global utilization of H₂ O₂ is currently around 4 million tons per year and is expected to continue to increase in the future. H₂ O₂ is mainly produced by the anthraquinone process, which involves multiple steps in terms of alkylanthraquinone hydrogenation/oxidation in organic solvents and liquid-liquid extraction of H₂ O₂ . The energy-intensive and environmentally unfriendly anthraquinone process does not meet the requirements of sustainable and low-carbon development. The electrocatalytic two-electron (2 e^- ) oxygen reduction reaction (ORR) driven by renewable energy (e.g. solar and wind power) offers a more economical, low-carbon, and greener route to produce H₂ O₂ . However, continuous and decentralized H₂ O₂ electrosynthesis still poses many challenges. This Minireview first summarizes the development of devices for H₂ O₂ electrosynthesis, and then introduces each component, the assembly process, and some optimization strategies.

Distal Ruthenaelectro-Catalyzed meta-C-H Bromination with Aqueous HBr

While electrochemical ortho‐selective C−H activations are well established, distal C−H activations continue to be underdeveloped. In contrast, we herein describe the electrochemical meta‐C−H functionalization. The remote C−H bromination was accomplished in an undivided cell by RuCl₃⋅3 H₂O with aqueous HBr. The electrohalogenation proceeded under exogenous ligand‐ and electrolyte‐free conditions. Notably, pyrazolylarenes were meta‐selectively brominated at the benzenoid moiety, rather than on the electron‐rich pyrazole ring for the first time. Mechanistic studies were suggestive of an initial ruthenacycle formation, and a subsequent ligand‐to‐ligand hydrogen transfer (LLHT) process to liberate the brominated product.

Transform electrocatalytic biomass upgrading and hydrogen production from electricity input to electricity output

Integrating biomass upgrading and hydrogen production in an electrocatalytic system is attractive both environmentally and sustainably. Conventional electrolyzer systems coupling anodic bio-substrate electrooxidation with hydrogen evolution reaction usually require electricity input. In this work, we develop a fuel cell electrocatalytic system achieve the biomass upgrading and hydrogen production as well as electricity generation. Different with conventional furfural electrooxidation, the employed low-potential furfural oxidation enables the hydrogen atom of the aldehyde group to be released as gaseous hydrogen at the anode under a low potential of ~0 VRHE (vs. reversible hydrogen electrode). The integrated fuel cell system could generate electricity of ~2 kWh for per cubic meter of hydrogen produced. This work may provide a transformative technology that turns the electrocatalytic biomass upgrading and hydrogen production from electricity input to electricity output.

Highly Diastereoselective Synthesis of Dihydro-benzoimidazo-[1,3]-thiazines via Electro-oxidative Selenocyclization of Thioallyl Benzoimidazoles

The current methodology reveals a green and proficient electro-oxidative tandem selenocyclization of thioallyl benzoimidazoles manufacturing selenylated dihydro-benzoimidazo-thiazine derivatives. Both C-Se and C-N bond formation were achieved via this mild protocol which exhibits good functional group tolerability affording an extensive range of substrate scope up to 96% isolated yields. Complete control over the regioselective formation of the six-membered heterocycle and stereoselective construction of the contiguous stereocenters was established. The practical electrochemical method operates in an undivided cell at ambient temperature without using any metal and external chemical oxidant.

The Longer Route can be Better: Electrosynthesis in Extended Path Flow Cells

This personal account provides an overview of work conducted in my research group, and through collaborations with other chemists and engineers, to develop flow electrolysis cells and apply these cells in organic electrosynthesis. First, a brief summary of my training and background in organic synthesis is provided, leading in to the start of flow electrosynthesis in my lab in collaboration with Derek Pletcher. Our work on the development of extended path electrolysis flow reactors is described from a synthetic organic chemist's perspective, including laboratory scale-up to give several moles of an anodic methoxylation product in one day. The importance of cell design is emphasised with regards to achieving good performance in laboratory electrosynthesis with productivities from hundreds of mg h^-1 to many g h^-1 , at high conversion in a selective fashion. A simple design of recycle flow cell that can be readily constructed in a small University workshop is also discussed, including simple modifications to improve cell performance. Some examples of flow electrosyntheses are provided, including Shono-type oxidation, anodic cleavage of protecting groups, Hofer-Moest reaction of cubane carboxylic acids, oxidative esterification and amidation of aldehydes, and reduction of aryl halides.

A facile and fast strategy for cathodic electroactive-biofilm assembly via magnetic nanoparticle bioconjugation

Microbial electrosynthesis is a promising electricity-driven technology for converting carbon dioxide into value-added compounds, but the formation of cathodic electroactive-biofilms (CEBs) is challenging. Herein, we have demonstrated an innovative strategy for CEBs assembly via magnetic nanoparticle bioconjugation, which lies in the synergistic interactions among a bonder (Streptavidin, SA), conductive nanomaterials (Fe₃O₄), and a methanogen (M. barkeri). The results showed that the bioconjugated M. barkeri-SA-Fe₃O₄ biohybrids significantly enhanced both methane yield (33.2-fold) and faradaic efficiency (5.6-fold), compared with that of bare M. barkeri. Such an enhancement was attributed to the improved viability of CEBs with a higher biomass density. Particularly, more live cells were presented in the inner biofilms and promoted the long-distance electron exchange between the live outer-layer biofilm and the cathode electrode. Meanwhile, the higher redox activity of CEBs with the M. barkeri-SA-Fe₃O₄ biohybrids resulted in an improved transient charge storage capability, which was beneficial for the biological CO₂-to-CH₄ conversion via acting as an additional electron donor. This work has provided a new approach to accelerate the formation of CEBs and subsequent electron transfer, which holds a great potential for accomplishing electrosynthesis and CO₂ fixation.

Electrochemical Generation and Use in Organic Synthesis of C-, O-, and N-Centered Radicals

During the last decade several research groups have been developing electrochemical procedures to access highly functionalized organic molecules. Among the most exciting advances, the possibility of using free radical chemistry has attracted the attention of the most important synthetic groups. Nowadays, electrochemical strategies based on these species with a synthetic purpose are published continuously in scientific journals, increasing the alternatives for the synthetic organic chemistry laboratories. Free radicals can be obtained in organic electrochemical reactions; thus, this review reassembles the last decade's (2010-2020) efforts of the electrosynthetic community to generate and take advantage of the C-, O-, and N-centered radicals' reactivity. The electrochemical reactions that occur, as well as the proposed mechanism, are discussed, trying to give clear information about the used conditions and reactivity of these reactive intermediate species.

An innovative and simple all electrochemical approach to functionalize electrodes with a carbon nanotubes/polypyrrole molecularly imprinted nanocomposite and its application for sulfamethoxazole analysis

Sulfamethoxazole (SMX) is a commonly used antibiotic which accumulation can favor the development of antimicrobial resistance. Therefore, easy and cheap system to monitor the presence of SMX are needed for human health protection. Herein we present a straightforward all electrochemical approach to fabricate a sensor based on a nanocomposite molecularly imprinted polymer (nanoMIP) for the determination of SMX. Firstly, oxidized multiwalled carbon nanotubes (oxMWCNTs) were electrochemically deposited on a polarized electrode to increase electrodic surface area up to 350%. Then, ultrathin overoxidized polypyrrole MIP in presence of SMX was electropolymerized on oxMWCNTs surface (nanoMIP). Finally, antibiotic was electrochemically removed. The obtained nanoMIP was characterized by atomic force microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The nanoMIP was used for the electrochemical detection of SMX evidencing a lower limit of detection (413 nM) and a wider linear range (1.99-10.88 μM) with respect a non-nanostructured film. The nanoMIP evidenced also good affinity and a highly reproducible response (RSD = 1.2%). The sensor was able to determine SMX in milk samples evidencing good recovery values. The proposed approach can be also used in future to easily prepare different nanoMIP based sensors with improved performances for different target molecules thus overcoming current fabrication limits.

Manganese-catalyzed Electro-oxidative Azidation-annulation Cascade to Access Oxindoles and Quinolinones

An environmentally benign and proficient electro-oxidative tandem azidation-radical cyclization strategy is reported. Manganese-catalyzed electrochemical reaction in an undivided cell at room temperature and the use of NaN₃ as the cheapest azide source are the key features of this protocol. Using this approach, a series of oxindole and quinolinone derivatives are synthesized in high yields. The synthesized azide functionality was efficiently converted to various valuable derivatives.

Electrosynthesis in Laminar Flow Using a Flow Microreactor

Electrosynthesis and microflow synthesis have become essential tools in their own rights in modern organic synthesis. In this personal account, we summarize our works on the integrated use of these techniques, i. e., electrosynthesis in a flow microreactor. Our group has developed an electrochemical microflow system composed of a pair of electrodes that face each other to form a micrometer-scale gap for the flow path, through which solution passes in laminar flow. By the aid of laminar flow, unprecedented chemo- and electrochemical selectivity has been observed, which is not achievable with conventional batch-type electrochemical cells. In addition, we showcase various unique electrochemical systems and reactions achieved with the flow microreactor, including self-supported electrolysis, efficient paired electrolysis, in situ generation of active species and its flash use, the spaciotemporal control of electropolymerization, and combinatorial screening of the reaction conditions.

Electrochemical Insight into Mechanisms and Metallocyclic Intermediates of C-H Functionalization

Transition metal-catalyzed C-H activation has emerged as a powerful tool in organic synthesis and electrosynthesis as well as in the development of new methodologies for producing fine chemicals. In order to achieve efficient and selective C-H functionalization, different strategies have been used to accelerate the C-H activation step, including the incorporation of directing groups in the substrate that facilitate coordination to the catalyst. In this review, we try to underscore that the understanding the mechanisms of the catalytic cycle and the reactivity or redox activity of the key metal cyclic intermediates in these reactions is the basis for controlling the selectivity of synthesis and electrosynthesis. Combination of the electrosynthesis and voltammetry with traditional synthetic and physico-chemical methods allows one to achieve selective transformation of C-H bonds to functionalized C-C or C-X (X=heteroatom or halogen) bonds which may encourage organic chemists to use it in the future more often. The possibilities and the benefits of electrochemical techniques are analyzed and summarized.

Electrochemically synthesized NiFe layered double hydroxide modified Cu(OH)2 needle-shaped nanoarrays: A novel sorbent for thin-film solid phase microextraction of antifungal drugs

Herein, we applied a simple electrosynthesis process to deposit nickel-iron layered double hydroxides (NiFe LDH) on the surface of copper hydroxide (Cu(OH)₂) needle-shaped nanoarrays and introduce a new sorbent for thin-film solid phase microextraction (TF-SPME). For this purpose, the nanoarrays were grown via electrochemical anodization on a copper foil's surface and then modified with NiFe LDH. The synthesized sorbent was characterized by field emission-scanning electron microscopy, Brunauer-Emmett-Teller (BET), and Barrett-Joiner-Halenda (BJH) analysis, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The Cu(OH)₂-NiFe LDH based TF-SPME method was used to measure antifungal drugs in veterinary plasma samples followed by HPLC-UV analysis. The effects of various parameters in the extraction efficiency, including pH (5.0), extraction time (20 min), stirring rate (500 rpm), and salt effect (5.0%), type of eluent (acetonitrile), eluent volume (100 μL) and desorption time (5 min) were thoroughly optimized. Under the optimum conditions, limits of detection for ketoconazole, clotrimazole, and miconazole were obtained below 10 ng mL^-1. Intra-day, inter-day and film-to-film RSDs% were obtained less than 6.2%, 7.3% and 7.0%, respectively. Moreover, calibration plots were linear from 30 to 5000 ng mL^-1 for ketoconazole, 8.0-1000 ng mL^-1 for clotrimazole, and 15-1000 ng mL^-1 for miconazole, with determination coefficients between 0.9937 and 0.9971. Finally, good relative recoveries (%) in the range of 85-97% were obtained for measuring trace amounts of antifungal drugs in dogs' plasma samples. As a result, the method can be considered as an appropriate alternative to the conventional sample preparation methods for measuring trace amounts of antifungal drugs in biological samples.

Electrochemically Induced Diels-Alder Reaction: An Overview

One of the most important name reactions in organic chemistry, is the Diels-Alder cycloaddition reaction. It is a chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile to construct a substituted cyclohexene derivative. It is the stereotypical example of a pericyclic reaction with a concerted mechanism. In synthesis, the use of electricity instead of stoichiometric amounts of oxidant or reducing agents is definitely appealing for economic, ecological and selective, reasons. In this review, we try to underscore the combination of the electrosynthesis with Diels-Alder cycloaddition reaction to establish of a powerful synthetic tool which may encourage synthetic organic chemists to use it in the future.

Polypyrrole nanotubes for electrochemically controlled extraction of atrazine, caffeine and progesterone

Polypyrrole (PPy) was electrochemically synthesized with charge control on the surface of a steel mesh. Two different morphologies (globular and nanotubular) were created and characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The modified electrodes were used as extraction phases in solid-phase extraction (SPE) and electrochemically controlled solid-phase extraction (EC-SPE) of atrazine, caffeine and progesterone. Raman spectroscopy was employed for the structural characterization of PPy after long exposure to the analytes. The electrochemical behavior was studied by cyclic voltammetry which revealed the higher capacitive behavior of polypyrrole nanotubes because of the huge superficial area, also no electrocatalytical behavior was observed evidencing the strong adsorption of the analytes on the PPy surface. The effects of the PPy oxidation state on the extraction performance were evaluated by in-situ electrochemical sorption experiments. The sorption capacity was evaluated by gas chromatography coupled to mass spectrometry (GC-MS). The method displays good stability, repeatability and reproducibility. The limits of detection range between 1.7-16.7 μg L^-1. Following the extraction of river water samples, it was possible to identify the presence of other endogenous organic compounds besides the analytes of interest. This indicates the potential of the method and material developed in this work. Graphical abstract Schematic representation of a steel mesh electrode covered with polypyrrole nanotubes used as extraction phase for separation of contaminants from aqueous samples. The oxidation level of polypyrrole was electrochemically tuned by which the adsorption of analytes is deeply affected.

Electrical energy storage with engineered biological systems

The availability of renewable energy technologies is increasing dramatically across the globe thanks to their growing maturity. However, large scale electrical energy storage and retrieval will almost certainly be a required in order to raise the penetration of renewable sources into the grid. No present energy storage technology has the perfect combination of high power and energy density, low financial and environmental cost, lack of site restrictions, long cycle and calendar lifespan, easy materials availability, and fast response time. Engineered electroactive microbes could address many of the limitations of current energy storage technologies by enabling rewired carbon fixation, a process that spatially separates reactions that are normally carried out together in a photosynthetic cell and replaces the least efficient with non-biological equivalents. If successful, this could allow storage of renewable electricity through electrochemical or enzymatic fixation of carbon dioxide and subsequent storage as carbon-based energy storage molecules including hydrocarbons and non-volatile polymers at high efficiency. In this article we compile performance data on biological and non-biological component choices for rewired carbon fixation systems and identify pressing research and engineering challenges.

Synthesis and biological evaluation of 3-amino-, 3-alkoxy- and 3-aryloxy-6-(hetero)arylpyridazines as potent antitumor agents

Various 3-amino-, 3-aryloxy- and alkoxy-6-arylpyridazines have been synthesized by an electrochemical reductive cross-coupling between 3-amino-, 3-aryloxy- or 3-alkoxy-6-chloropyridazines and aryl or heteroaryl halides. In vitro antiproliferative activity of these products was evaluated against a representative panel of cancer cell lines (HuH7, CaCo-2, MDA-MB-231, HCT116, PC3, NCI-H727, HaCaT) and oncogenicity prevention of the more efficient derivatives was highlighted on human breast cancer cell line MDA-MB 468-Luc prior establishing their interaction with p44/42 and Akt-dependent signaling pathways.

Electrochemically enhanced microbial CO conversion to volatile fatty acids using neutral red as an electron mediator

Conversion of C1 gas feedstock, including carbon monoxide (CO), into useful platform chemicals has attracted considerable interest in industrial biotechnology. Nevertheless, the low conversion yield and/or growth rate of CO-utilizing microbes make it difficult to develop a C1 gas biorefinery process. The Wood-Ljungdahl pathway which utilize CO is a pathway suffered from insufficient electron supply, in which the conversion can be increased further when an additional electron source like carbohydrate or hydrogen is provided. In this study, electrode-based electron transference using a bioelectrochemical system (BES) was examined to compensate for the insufficient reducing equivalent and increase the production of volatile fatty acids. The BES including neutral red (BES-NR), which facilitated electron transfer between bacteria and electrode, was compared with BES without neutral red and open circuit control. The coulombic efficiency based on the current input to the system and the electrons recovered into VFAs, was significantly higher in BES-NR than the control. These results suggest that the carbon electrode provides a platform to regulate the redox balance for improving the bioconversion of CO, and amending the conventional C1 gas fermentation.

Electrosynthesis of bismuth nanodendrites/gallium nitride electrode for non-enzymatic hydrogen peroxide detection

Bismuth nanodendrites (BiNDs) were electrodeposited on planar gallium nitride (GaN) electrode via a differential pulse voltammetric technique to fabricate the non-enzymatic hydrogen peroxide (H₂O₂) sensor. SEM images revealed that the as-obtained BiNDs had numerous dendrite sub-branches, whose diameters ranged from 136 to 152nm. The BiNDs/GaN electrode showed linear amperometric responses for H₂O₂ in the concentration range from 10µM to 1mM with the sensitivity of 60.0μAmM^-1cm^-2. Another linear range was from 1 to 10mM with the sensitivity of 23.3μAmM^-1cm^-2. The limit of detection (LOD) was 5µM with the signal-to-noise ratio of 3. The applicability of the sensor was investigated to the H₂O₂ detection in real samples such as fetal bovine serum and milk, and the sensor exhibited excellent anti-interference capacity. The achieved results indicate that the as-prepared BiNDs/GaN sensor with good reproducibility and long-term stability was promising for detecting H₂O₂ in practical environments.

Neutral red-mediated microbial electrosynthesis by Escherichia coli, Klebsiella pneumoniae, and Zymomonas mobilis

The aim of this work was to compare the effects of electrosynthesis on different bacterial species. The effects of neutral red-mediated electrosynthesis on the metabolite profiles of three microorganisms: Escherichia coli, Klebsiella pneumoniae, and Zymomonas mobilis, were measured and compared and contrasted. A statistically comprehensive analysis of neutral red-mediated electrosynthesis is presented using the analysis of end-product profiles, current delivered, and changes in cellular protein expression. K. pneumoniae displayed the most dramatic response to electrosynthesis of the three bacteria, producing 93% more ethanol and 76% more lactate vs. control fermentation with no neutral red and no electron delivery. Z. mobilis showed no response to electrosynthesis except elevated acetate titers. Stoichiometric comparison showed that NAD(+) reduction by neutral red could not account for changes in metabolites during electrosynthesis. Neutral red-mediated electrosynthesis was shown to have multifarious effects on the three species.

Metabolic engineering in chemolithoautotrophic hosts for the production of fuels and chemicals

The ability of autotrophic organisms to fix CO2 presents an opportunity to utilize this 'greenhouse gas' as an inexpensive substrate for biochemical production. Unlike conventional heterotrophic microorganisms that consume carbohydrates and amino acids, prokaryotic chemolithoautotrophs have evolved the capacity to utilize reduced chemical compounds to fix CO2 and drive metabolic processes. The use of chemolithoautotrophic hosts as production platforms has been renewed by the prospect of metabolically engineered commodity chemicals and fuels. Efforts such as the ARPA-E electrofuels program highlight both the potential and obstacles that chemolithoautotrophic biosynthetic platforms provide. This review surveys the numerous advances that have been made in chemolithoautotrophic metabolic engineering with a focus on hydrogen oxidizing bacteria such as the model chemolithoautotrophic organism (Ralstonia), the purple photosynthetic bacteria (Rhodobacter), and anaerobic acetogens. Two alternative strategies of microbial chassis development are considered: (1) introducing or enhancing autotrophic capabilities (carbon fixation, hydrogen utilization) in model heterotrophic organisms, or (2) improving tools for pathway engineering (transformation methods, promoters, vectors etc.) in native autotrophic organisms. Unique characteristics of autotrophic growth as they relate to bioreactor design and process development are also discussed in the context of challenges and opportunities for genetic manipulation of organisms as production platforms.

Synthesis, solution and crystal structure of the coenzyme B(12) analogue Co(β)-2'-fluoro-2',5'-dideoxyadenosylcobalamin

Crystal structure analyses have helped to decipher the mode of binding of coenzyme B12 (AdoCbl) in the active site of AdoCbl-dependent enzymes. However, the question of how such enzymes perform their radical reactions is still incompletely answered. A pioneering study by Gruber and Kratky of AdoCbl-dependent glutamate mutase (GLM) laid out a path for the movement of the catalytically active 5'-deoxyadenosyl radical, in which H-bonds between the protein and the 2'- and 3'-OH groups of the protein bound AdoCbl would play a decisive role. Studies with correspondingly modified coenzyme B12-analogues are of interest to gain insights into cofactor binding and enzyme mechanism. Here we report the preparation of Coβ-2'-fluoro-2',5'-dideoxyadenosylcobalamin (2'FAdoCbl), which lacks the 2'-OH group critical for the interaction in enzymes. 2'FAdoCbl was prepared by alkylation of cob(I)alamin, obtained from the electrochemical reduction of aquocobalamin. Spectroscopic data and a single crystal X-ray analysis of 2'FAdoCbl established its structure, which was very similar to that one of coenzyme B12. 2'FAdoCbl is a (19)F NMR active mimic of coenzyme B12 that may help to gain insights into binding interactions of coenzyme B12 with AdoCbl-dependent enzymes, proteins of B12 transport and of AdoCbl-biosynthesis, as well as with B12-riboswitches.

Design and analysis of metabolic pathways supporting formatotrophic growth for electricity-dependent cultivation of microbes

Electrosynthesis is a promising approach that enables the biological production of commodities, like fuels and fine chemicals, using renewably produced electricity. Several techniques have been proposed to mediate the transfer of electrons from the cathode to living cells. Of these, the electroproduction of formate as a mediator seems especially promising: formate is readily soluble, of low toxicity and can be produced at relatively high efficiency and at reasonable current density. While organisms that are capable of formatotrophic growth, i.e. growth on formate, exist naturally, they are generally less suitable for bulk cultivation and industrial needs. Hence, it may be helpful to engineer a model organism of industrial relevance, such as E. coli, for growth on formate. There are numerous metabolic pathways that can potentially support formatotrophic growth. Here we analyze these diverse pathways according to various criteria including biomass yield, thermodynamic favorability, chemical motive force, kinetics and the practical challenges posed by their expression. We find that the reductive glycine pathway, composed of the tetrahydrofolate system, the glycine cleavage system, serine hydroxymethyltransferase and serine deaminase, is a promising candidate to support electrosynthesis in E. coli. The approach presented here exemplifies how combining different computational approaches into a systematic analysis methodology provides assistance in redesigning metabolism. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.