This review provides an overview of the current state-of-the-art and major trends in the application of protic ionic liquids (PILs) to sustainable chemistry.

Polymers containing TEMPO moieties are effective catalysts for the electrochemical oxidation of alcohols. Such polymers, almost exclusively, are non-commercial and are prepared using multi-step synthetic procedures. Here we show that a commercially available TEMPO bearing polymer, Polyamine Immobilised Piperidinyl Oxyl (PIPO), is an effective homogeneous and surface-confined polymeric catalyst for electrochemical alcohol oxidation at carbonaceous electrodes. We probe electrolytic conditions for effective and stable electrocatalytic alcohol oxidation showing that dichloromethane (DCM), containing tetrabutylammonium perchlorate (TBAP) and N-methyl imidazole (NMI), is a suitable medium for homogeneous catalysis whilst carbonate buffer (pH 9.5) is better suited when PIPO is adsorbed at the electrode surface. These findings demonstrate the viability of PIPO as an effective and accessible catalyst for electrochemical alcohol oxidations. image

Significant differences in performance between the two prevalent cell configurations in all-soluble, all-iron redox flow batteries are presented, demonstrating the critical role of cell architecture in the pursuit of novel chemistries in non-vanadium systems. Using a ferrocyanide-based posolyte, and a negolyte containing a hydroxylamine-based iron complex, higher maximum power density, energy efficiency, and electrolyte utilisation were observed with a flow-over cell that incorporated a carbon paper, compared with a flow-through configuration that used a graphite felt. Capacity fade was lower in the flow-over case, likely the result of a set-up with lower overpotentials, as indicated by polarisation curve analysis. Capacity fade in the flow-through case increased upon lowering current density, suggesting a different degradation pathway, dominated instead by electrolyte cross-over. These findings highlight the potential of novel non-vanadium chemistries in both flow-through and flow-over cells, prompting further research exploration of cell architectures. All-soluble, all-iron flow battery performance is critically dependent upon cell configuration. Flow-through and flow-over designs exhibit stark differences in efficiency, maximum power density, capacity retention, and self-discharge.

Electron/proton transfers in water proceeding from ground/excited states are the elementary reactions of chemistry. These reactions of an iconic class of molecules─polypyridineRu(II)─are now controlled by capturing or releasing three of them with hosts that are shape-switchable. Reversible erection or collapse of the host walls allows such switchability. Some reaction rates are suppressed by factors of up to 120 by inclusive binding of the metal complexes. This puts nanometric coordination chemistry in a box that can be open or shut as necessary. Such second-sphere complexation can allow considerable control to be exerted on photocatalysis, electrocatalysis, and luminescent sensing involving polypyridineRu(II) compounds. The capturing states of hosts are symmetry-matched to guests for selective binding and display submicromolar affinities. A perching complex, which is an intermediate state between capturing and releasing states, is also demonstrated.

Fuel cells have the potential to provide sustainable clean energy but are hampered by the reliance on Pt as an electrocatalyst for half-cell reactions. Bio-inspired molecular catalysts, composed of Earth-abundant elements, have shown promise as alternative electrocatalysts for fuel oxidation and oxygen reduction reactions. This article provides a concise overview of recent progress in this area with particular focus on (i) electrodes modified with molecular catalysts for fuel oxidation and O2 reduction and (ii) fuel cells incorporating surfaceconfined molecular catalysts for both anodic and cathodic reactions. Finally, the prospect and challenges of using molecular catalysts in fuel cell assemblies are discussed.

Nitroxide radical polymers (NRPs) are widely used as electroactive materials in a range of electrochemical applications, however, their preparation can be complex. Polyamine Immobilised Piperidinyl Oxyl (PIPO) is a commercially available, well-defined, NRP whose electrochemical properties have not been explored to date. Cyclic voltammetric (CV) studies demonstrate the electroactivity of PIPO in a range of organic electrolytes, displaying quasi-reversible redox waves, characteristic of a nitroxide radical / oxoammonium couple, with midpoint potentials in the range of 0.2 to 0.3 V vs. Fc(+)/Fc. When immobilised at a graphite electrode surface, PIPO maintains its electroactivity, forming stable, swellable films in acetonitrile-based electrolyte. Voltammetric and potentiometric analyses indicate that films can undergo repeated charge / discharge cycling, possibly facilitated by a diffusional controlled 'electron hopping' process. Furthermore, CV studies indicate that PIPO is an effective surface confined electrocatalyst for oxidation reactions of relevance to organic electrosynthesis and to lithium-air battery development. Such insights establish the basis for further investigations of PIPO as an accessible, cost-effective, and adaptable electroactive material for electrocatalytic and energy storage applications. (C) 2021 Elsevier Ltd. All rights reserved.

Surface chemistry is known to influence the formation, composition, and electroactivity of electron-conducting biofilms. However, understanding of the evolution of microbial composition during biofilm development and its impact on the electrochemical response is limited. Here we present voltammetric, microscopic and microbial community analysis of biofilms formed under fixed applied potential for modified graphite electrodes during early (90 h) and mature (340 h) growth phases. Electrodes modified to introduce hydrophilic groups (-NH2, -COOH and -OH) enhance early-stage biofilm formation compared to unmodified or electrodes modified with hydrophobic groups (-C2H5). In addition, early-stage films formed on hydrophilic electrodes are dominated by the gram-negative sulfur-reducing bacterium Desulfuromonas acetexigens while Geobacter sp. dominates on -C2H5 and unmodified electrodes. As biofilms mature, current generation becomes similar, and D. acetexigens dominates in all biofilms irrespective of surface chemistry. Electrochemistry of pure culture D. acetexigens biofilms reveal that this microbe is capable of forming electroactive biofilms producing considerable current density of > 9 A/m2 in a short period of potential-induced growth (~19 h following inoculation) using acetate as an electron donor. The inability of D. acetexigens biofilms to use H2 as a sole source electron donor for current generation shows promise for maximizing H2 recovery in single-chambered microbial electrolysis cell systems treating wastewaters.

Functional materials have the potential to significantly impact on the development of neural implants designed to promote regeneration or to interface bi-directionally the signals between the brain and an external device. Physicochemical functionaliziation of a neural implant to present an electrochemically or biologically active interface, as decribed by Catalina Vallejo Giraldo, Manus Biggs, and co-workers in article number 1605035, represents a particularly rapidly expanding research field.

Physicochemical modification of implantable electrode systems is recognized as a viable strategy to enhance tissue/electrode integration and electrode performance in situ. In this work, a bench‐top electrochemical process to formulate anodized indium tin oxide (ITO) films with altered roughness, conducting profiles, and thickness is explored. In addition, the influence of these anodized films on neural cell adhesion, proliferation, and function indicates that anodized ITO film cytocompatibility can be altered by varying the anodization current density. Furthermore, ITO‐anodized films formed with a current density of 0.4 mA cm −2 show important primary neural cell survival, modulation of glial scar formation, and promotion of neural network activity.

The inhibition of water and glycerol permeation via human aquaglyceroporin-3 (AQP3) by gold(iii) complexes has been studied by stopped-flow spectroscopy and, for the first time, its mechanism has been described using molecular dynamics (MD), combined with density functional theory (DFT) and electrochemical studies. The obtained MD results showed that the most effective gold-based inhibitor, anchored to Cys40 in AQP3, is able to induce shrinkage of pores preventing glycerol and water permeation. Moreover, the good correlation between the affinity of the Au(iii) complex to Cys binding and AQP3 inhibition effects was highlighted, while no influence of the different oxidative character of the complexes could be observed.

Electron transfer between microorganisms and an electrode — even across long distances — enables the former to live by coupling to an electronic circuit. Such a system integrates biological metabolism with artificial electronics; studying these systems adds to our knowledge of charge transport in the chemical species involved, as well as, perhaps most importantly, to our knowledge of charge transport and chemistry at the cell–electrode interfaces. This understanding may lead to microbial electrochemical systems finding widespread application, particularly in the energy sector. Bioelectrochemical systems have already shown promise for electricity generation, as well as for the production of biochemical and chemical feedstocks, and with improvement are likely to give rise to viable applications. Electrodes colonized by microbial electrocatalysts can serve as useful components in the electrosynthesis of valuable chemical products. This Review outlines the mechanisms by which electrons are transferred between microorganisms and electrodes, and describes the challenges involved in designing robust and efficient systems.

The thioredoxin (Trx)-thioredoxin reductase (TrxR) system plays a key role in maintaining the cellular redox balance with Trx being over-expressed in a number of cancers. Inhibition of TrxR is an important strategy for anti-cancer drug discovery. The natural product pleurotin is a well-known irreversible inhibitor of TrxR. The cytotoxicity data for benzo[1,2,4]triazin-7-ones showed very strong correlation (Pearson correlation coefficients ∼0.8) to pleurotin using National Cancer Institute COMPARE analysis. A new 3-CF3 substituted benzo[1,2,4]triazin-7-one gave submicromolar inhibition of TrxR, although the parent compound 1,3-diphenylbenzo[1,2,4]triazin-7-one was more cytotoxic against cancer cell lines. Benzo[1,2,4]triazin-7-ones exhibited different types of reversible inhibition of TrxR, and cyclic voltammetry showed characteristic quasi-reversible redox processes. Cell viability studies indicated strong dependence of cytotoxicity on substitution at the 6-position of the 1,3-diphenylbenzo[1,2,4]triazin-7-one ring.

A novel bimetallic Fe(III) complex with the bis(triaza-cyclononane) ligand 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)-4-methylphenol (bcmp) is reported. [Fe2{bcmp(-H)}(μ-OH)Cl2]Cl2 (2) contains two octahedral Fe(III) centers bound to the two triaza-cyclononane rings of bcmp. The coordination sphere is completed by one chlorine, one bridging phenolate oxygen and one bridging hydroxide group. The complex has been characterized by elemental analysis, Mössbauer spectroscopy, UV–Vis spectroscopy, pH potentiometric titration, ESI mass spectrometry and cyclic voltammetry. The complex hydrolyzes the DNA model bis(2,4-dinitrophenyl) phosphate (BDNPP) with a maximum activity a pH 7. Michaelis–Menten behavior is observed with kcat=3.56×10−4s−1 and Km=0.56mM (pH 7.0, 40°C). The interaction of 2 with CT DNA was studied by electronic absorption spectroscopy and gel electrophoresis. Notably, the complex relaxes supercoiled pUC19 DNA into the nicked form at low micromolar concentration (10μM) in the presence of an external reducing agent (ascorbic acid). Finally, the in vitro antiproliferative activity of 2 was assessed on a panel of human cancer cell lines and results revealed that the complex exhibited a significant cytotoxic effects in particular versus colon LoVo cancer cells, wih IC50 value 2.5 times lower than that shown by the reference metallodrug cisplatin (3.54 versus 8.53μM).

A series of new heterodinuclear luminescent complexes with two different organic ligands have been synthesized and characterized. A luminescent Ru-II(polypyridine) moiety and a metal-based anticancer fragment (AuCl, (p-cymene)RuCl2, (p-cymene)OsCl2, (Cp*)RhCl2, or Au-thioglucose) are the two general features of these complexes. All of the bimetallic compounds have been evaluated for their antiproliferative properties in vitro in human cancer cell lines. Only the complexes containing an Au(I) fragment exhibit antiproliferative activity in the range of cisplatin or higher. The photophysical and electrochemical properties of the bimetallic species have been investigated, and fluorescence microscopy experiments have been performed successfully. The most promising bimetallic cytotoxic complexes (i.e., with the Au-thioglucose scaffold) have shown to be easily taken up by cancer cells at 37 degrees C in the cytoplasm or in specific organelles. Interestingly, experiments repeated at 4 degrees C showed no uptake of the bimetallic species inside cells, which confirms involvement of active transport processes. To evaluate the role of glucose transporters in the cell uptake of the gold complexes, inhibition of the GluT-1 (glucose transporter isoform with high level of expression in cancer cells) was achieved, showing only scarce influence on the compounds' uptake. Finally, the observed absence of interactions with nucleic acid model structures suggests that the gold compounds may have different intracellular targets with respect to cisplatin.

Geobacter sulfurreducens is a dissimilatory metal-reducing bacterium capable of forming thick electron-conducting biofilms on solid electrodes. Here, we employ for the first time comparative proteomics to identify key physiological changes involved in G. sulfurreducens adaptation from fumarate-respiring planktonic cells to electron-conducting biofilms. Increased levels of proteins involved in outer membrane biogenesis, cell motility and secretion are expressed in biofilms. Of particular importance to the electron-conducting biofilms are proteins associated with secretion systems of Type I, II, V and Type IV pili. Furthermore, enzymes involved in lipopolysaccharide and peptidoglycan biosynthesis show increased levels of expression in electron-conducting biofilms compared to planktonic cells. These observations point to similarities in long-range electron transfer mechanisms between G. sulfurreducens and Shewanella oneidensis, while highlighting the wider significance of secretion systems beyond that of Type IV pili identified to date in the adaptation of G. sulfurreducens to electrode respiration.

This presentation focuses on response of films prepared using osmium redox polymers, glucose-oxidising enzymes and carbon nanotubes to glucose oxidation for application to membrane-less enzymatic fuel cells.

Graphite electrodes modified with a redox polymer, [Os(4,4′- dimethoxy-2,2′-bipyridine)2(polyvinyl imidazole)10Cl]Cl (E°′=−0.02V vs Ag/AgCl), crosslinked with glucose oxidising enzymes and various amounts of multi-walled carbon nanotubes are investigated for current generation in the presence of glucose in physiological buffer solutions. Enzyme electrodes based on glucose oxidase and FAD-dependent glucose dehydrogenase are compared in the presence and absence of oxygen. The highest glucose oxidation currents are produced from enzyme electrodes containing 68% w/w multi-walled carbon nanotubes in the deposition matrix. The FAD-dependent glucose dehydrogenase and glucose oxidase enzyme electrodes provide similar current density of ∼0.8mA cm−2 in de-oxygenated 50mM phosphate-buffered saline at 37°C containing 5mM glucose concentration. Current densities under the same conditions, but in the presence of oxygen are 0.50mAcm−2 and 0.27mAcm−2, for glucose dehydrogenase and glucose oxidase enzyme electrodes, respectively, with decreased currents a result of oxygen reduction by the redox polymer in both cases, and oxygen acting as a co-substrate for the glucose oxidase-based electrodes. Application of the anodes in membrane-less enzymatic fuel cells is demonstrated by connection to cathodes prepared by co-immobilisation of [Os(2,2′-bipyridine)2(polyvinyl imidazole)10Cl]Cl redox polymer, Myrothecium verrucaria bilirubin oxidase and multi-walled carbon nanotubes on graphite electrodes. Power densities of up to 270μWcm−2 are achieved, showing promise for in vivo or ex vivo power generation under these conditions.

Harnessing, and understanding the mechanisms of growth and activity of, biofilms of electroactive bacteria (EAB) on solid electrodes is of increasing interest, for application to microbial fuel and electrolysis cells. Microbial electrochemical cell technology can be used to generate electricity, or higher value chemicals, from organic waste. The capability of biofilms of electroactive bacteria to transfer electrons to solid anodes is a key feature of this emerging technology, yet the electron transfer mechanism is not fully characterized as yet. Acetate oxidation current generated from biofilms of an EAB, Geobacter sulfurreducens, on graphite electrodes as a function of time does not correlate with film thickness. Values of film thickness, and the number and local concentration of electrically connected redox sites within Geobacter sulfurreducens biofilms as well as a charge transport diffusion co-efficient for the biofilm can be estimated from non-turnover voltammetry. The thicker biofilms, of 50 ± 9 μm, display higher charge transport diffusion co-efficient than that in thinner films, as increased film porosity of these films improves ion transport, required to maintain electro-neutrality upon electrolysis.

Co-immobilisation of three separate multiple blue copper oxygenases, a Myceliophthora thermophila laccase, a Streptomyces coelicolor laccase and a Myrothecium verrucaria bilirubin oxidase, with an [Os(2,2-bipyridine)(2)(polyvinylimidazole)(10)Cl](+/2+) redox polymer in the presence of multi-walled carbon nanotubes (MWCN (-2) for oxygen reduction at an applied potential of 0 V versus Ag/AgCl. Fully enzymatic membraneless fuel cells are assembled with the oxygen-reducing enzyme electrodes connected to glucose-oxidising anodes based on co-immobilisation of glucose oxidase or a flavin adenine dinucleotide-dependent glucose dehydrogenase with an [Os(4,4-dimethyl-2,2-bipyridine)(2)(polyvinylimidazole)(10)Cl](+/2+) redox polymer in the presence of MWCN (-2) on operation in pH 7.4 phosphate buffer solution at 37 degrees C containing 150 mM NaCl, 5 mM glucose and 0.12 mM O-2. Myceliophthora thermophila laccase enzyme electrodes produce the highest power density if combined with glucose oxidase-based anodes. Although the maximum power density of a fuel cell of glucose dehydrogenase and Myceliophthora thermophila laccase enzyme electrodes decreases from 110 Wcm(-2) in buffer to 60 Wcm(-2) on testing in artificial plasma, it provides the highest power output reported to date for a fully enzymatic glucose-oxidising, oxygen-reducing fuel cell in artificial plasma.