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Azaphenalenes are nitrogen substituted analogues of the phenalene ring system, and their radicals have attracted significant attention because of the novel electronic and magnetic properties. In the previous study, the neutral tris(tert-butyl) 1,3-diazaphenalenyl radical has been synthesized by chemical oxidation of the parent compound with PbO 2. In this study, we focused on electrochemical proton-coupled electron transfer (PCET) process leading to the formation of neutral unsubstituted 1,3-diazaphenalenyl radical from 1,3-diazaphenalene (DAP) in solution. Additionally, this electrochemical approach was extended to study the redox behavior of newly synthesized 1,4,7-triazaphenalene (TAP) giving the access to the 1,4,7-triazaphenalenyl radical. Electrochemical oxidation potentials vs. pH plots (Pourbaix diagram) for DAP and TAP revealed that their one-electron oxidation to the corresponding neutral radicals occurred by a PCET process over a wide pH range. From the analysis of Pourbaix diagrams, the p K a values of the protonated radicals were determined to be p K a = 2.57 and 2.39 for the DAP and TAP radicals, respectively. Cyclic voltammograms of azaphenalenes in MeCN and MeCN/buffer solutions showed a characteristic ECE process, in which electrochemical oxidative dimerization took place following the electron transfer. The dimerization reaction pathway was rationalized by the digital simulations, DFT calculations and crystallization of a DAP dimer after chemical oxidation with PbO 2. The spectroscopic properties of azaphenalenes and their dimerized products were characterized by in-situ UV–Vis and EPR spectroelectrochemistry techniques. The fundamental information about the p K a and redox potentials for a series of azaphenalenes (DAP, TAP, as well as 1,3,4,6,7,9-hexaazaphenalene, HAP) could be fed back into the molecular design of redox-active conductive coordination networks based on multi-interactive ligands. [Display omitted] [ABSTRACT FROM AUTHOR]

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 O 2 , 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). [ABSTRACT FROM AUTHOR]

• Electrochemical characterizations of an Aquifex aeolicus McoA multicopper oxidase. • The enzyme adsorbed over the electrode exhibits direct electron transfer. • Reductive activation is required for maximum O 2 reduction activity. • The redox potential shifts with pH under catalysis and non-turnover conditions. • Remarkable KCl influence on catalytic response is observed at pH 4 but not at pH 7. The study of redox proteins confined over an electrode surface is a powerful approach enabling precise modulation of the driving force for interfacial electron transfer through the control of the electrode potential. In this work, we present the investigation of a protein variant of the multicopper oxidase from Aquifex aeolicus obtained by directed evolution. Motivated by the enhanced performance of the protein variant for the oxidation of organic compounds in solution, the enzyme is studied under direct electron transfer with the electrode. A marked dependence of the redox potential with the pH of the electrolyte solution is observed, which is further confirmed by studies under non-turnover conditions. Further investigations show the need for an initial reductive activation to attain maximum bioelectrocatalytic activity for O 2 reduction, in agreement with similar observations made for other multicopper oxidases (MCOs). Moreover, the influence of chloride ions on the bioelectrocatalytic reaction is described. The O 2 -reduction activity is barely affected at KCl concentrations as high as 100 mM. However, a shift in the O 2 -reduction potential towards more negative values is observed at low pH, explaining the apparent loss in activity for the oxidation of organic substrates in the presence of KCl. The obtained results contribute to a more detailed understanding of the electrochemical properties of metallo-oxidases and other MCOs. [ABSTRACT FROM AUTHOR]

Among several non-covalent weak interaction(s), hydrogen bonding is predominantly considered as a key factor in some biological events i.e. information transfer at intra cellular and/or intra/inter organelle level. Dinitroaromatics contain –NO 2 group(s) which strongly facilities electron and/or proton transfer, could be envisaged to be used as an active group in a drug molecule. We have decided to investigate dinitroaromatics as model substances for the following reasons (a) low reduction potential, (b) multi-electron accepting ability of NO 2 groups, (c) formation of stable anion radicals and dianions. Linear scan and cyclic voltammetry were used for study. It was found that DNBs in the presence of HB-agents exhibit switchable H-bonding via electro-reduction steps and formation of DNB −./2- ⋯(HB) n or m . HB strength significantly perturbs chemical equilibrium and/or kinetic process, hence, an array of strong, intermediate and weak type interactions was considered for investigation. Experimental values of stability constant, K eq , rate constant of formation of H-bond, k , and number of bonds formed were evaluated for corresponding process(es) (i) D N B − . + n [ H B ] ⇄ D N B − . ( H B ) n and (ii) D N B 2 − + ( m − n ) [ H B ] ⇄ D N B 2 − ( H B ) m − n . Values of K eq for processes (i) and (ii) were found to be within the range of 1.9–9.0 M -n and 7.0–9.4 × 10 4  M -m , whereas, k values were moderate to high as 0.23–26.1 M -n .s −1 and 3.3–6.5 × 10 6  M -m .s −1 , respectively. A more plausible assumption is the existence of 1:1 or 1:2 associates between (X)DNB 2− (where, X = 1,2-,1,3-,1,4-) and HB-agents. Quantum chemical calculations were carried out for (X)DNB −./2- ⋯(HB) n or m , vis-a-vis geometry optimization leading to better understanding of structural array in three dimensional space. [ABSTRACT FROM AUTHOR]

The redox properties of some alkyl radicals, which are important in atom transfer radical polymerization both as initiators and mimics of the propagating radical chains, have been investigated in CH3CN by an indirect electrochemical method based on homogeneous redox catalysis involving alkyl halides (RX) and electrogenerated aromatic or heteroaromatic radical anions (D᛫-). Dissociative electron transfer between RX and D᛫- yields an intermediate radical (R᛫), which further reacts with D᛫-either by radical coupling or by electron transfer. Examination of the competition between these reactions, which depends on ED/D᛫-, allows determination of the standard reduction potential of R᛫ as well as the self-exchange reorganization energy λR᛫/R-᛫.The standard reduction potentials obtained for the radicals CH2CN, CH2CO2Et and CH(CH3)CO2Me are−0.72 ± 0.06,−0.63 ± 0.07 and −0.66 ± 0.07 V vs. SCE, respectively. Quite high values of λR᛫/R-᛫ (from 122 to 164 kJ mol−1) were found for all radicals, indicating that a significant change of structure accompanies electron transfer to R. [ABSTRACT FROM AUTHOR]

Although the electrocatalytic hydrogen evolution reaction (HER) has great potential in energy conversion, the efficiency is limited by the reaction overpotential. Herein, the origin of thermodynamic overpotential in HER is studied systemically based on the proton-coupled electron transfer (PCET) theory. Metal clusters with different elements or sizes are combined with monolayer black phosphorus (BP@M n) as model catalysts. The thermodynamic overpotentials in HER on BP@M n originate from mainly electron transfer or concerted proton and electron transfer, which also constitutes the rate determining step. The redox potential of the rate determining step determines the efficiency of HER rather than the adsorption energy of H atoms, which also scales linearly with the LUMO state of the catalysts. In subsequent experiments, the turnover frequencies are observed to be in line with the activity trends derived theoretically. Among the different models, BP@Co n exhibits the highest activity and smaller cluster exhibits higher catalytic ability. The results provide insights into the origin of thermodynamic overpotentials in HER and valuable guidance pertaining to the design of highly efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

Electricigenic respiration is a new microbial metabolism discovered recently in an anaerobic environment lacking common electron receptors such as oxygen and others, in which some bacteria utilize extracellular electron transfer system. One electricigen, Klebsiella oxytoca d7, was isolated and confirmed its ability of electricigenic respiration in previous study, but its process and mechanism from intracellular respiratory chain to extracellular electron acceptors were not clear. In this paper, a microbial fuel cell (MFC) of this pure bacterium was constructed, and the main mechanism of electron transfer via the electron transfer mediators (ETMs) during electricity generation process of the bacterium was explored. The results show the ETMs can only be generated with the circuit on, and its contribution to the total electricity generation was much greater than that when the carbon source was insufficient. The redox potential of the ETMs of the K. oxytoca d7 was about −250 mV. The electrons were intercepted during the transfer from NADH to coenzyme Q and flow to the extracellular electron acceptors. The site of electron interception in the ETMs was only dependent on the redox potential of the ETMs secreted by the electricigens. Electrons were transferred from carriers in intracellular respiratory chain and with slightly higher redox potential than ETMs to ETMs. Normally the contribution of extracellular electron transfer mediated by ETMs to the total electricity generation amounted to more than 60%, indicating the process directly affected the conversion of organic substance in anode chamber and the electricity generation performance of the MFC. [ABSTRACT FROM AUTHOR]