Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

A series of [Re(N^N)(CO)3(Cl)] (N^N = diimine) complexes based on 4-(pyrid-2-yl)-1,2,3-triazole (1), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2), and 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3) diimine ligands were prepared and their photophysical and electrochemical properties were characterized. The ligand-based reduction wave is shown to be highly sensitive to the nature of the triazole-based ligand, with the peak potential shifting by up to 600 mV toward more positive potential from 1 to 3. All three complexes are phosphorescent in solution at room temperature with λmax ranging from 540 nm (1) to 638 nm (3). Interestingly, the complexes appear to show inverted energy-gap law behaviour (τ = 43 ns for 1 versus 92 ns for 3), which is tentatively interpreted as reduced thermal accessibility of metal-centred (3MC) states from photoexcited metal to ligand charge transfer (3MLCT) states upon stabilisation of the N^N-centred lowest unoccupied molecular orbital (LUMO). The photophysical characterisation, supported by computational data, demonstrated a progressive stabilization of the LUMO from complex 1 to 3, which results in a narrowing of the HOMO–LUMO energy gap (HOMO = highest occupied molecular orbital) across the series and, correspondingly, red-shifted electronic absorption and photoluminescence spectra. The two complexes bearing pyridyl (1) and pyrimidyl (2) moieties, respectively, showed a modest ability to catalyse the electroreduction of CO2, with a peak potential at ca. −2.3 V versus Fc/Fc+. The catalytic wave that is observed in the cyclic voltammograms is slightly enhanced by the addition of water as a proton source.

A Sensitive Catalytic Wave Formed by Electrochemical Reduction of Morin in the Presence of an Oxidant KIO3

The investigation of the electrogenerated free radical of morin reacting with an oxidant is helpful in understanding its antioxidant pharmacology. In phosphate buffer (pH 5.6 ± 0.1), the reduction of morin proceeds with a one-electron transfer of the C=O double bond into a free radical intermediate, which then delivers the final primary alcohol via a one-electron reduction. When an oxidant KIO3 is present, the free radical intermediate of morin is oxidized to regenerate the original ‘C=O’ bond. Further reduction processes are effectively inhibited, resulting in a sensitive catalytic peak, with the peak current enhanced 70 times.

Catalytic Voltammetric Determination of Vanadium in Crude Oil at Carbon Nanotube Paste Electrode

A catalytic voltammetric method for the determination of vanadium(V) at a multi-wall carbon nanotube paste electrode (MWCNT-PE) in a 4-(2-pyridylazo)-resorcinol(PAR)-bromate system is proposed. The voltammetric response of V(V)-PAR complex at MWCNT-PE was significantly enhanced because of a catalytic cycle consisting of electrochemical reduction of V(V) ion in the complex and subsequent chemical oxidation of the reduction product of V(V) by bromate. In pH 2.70 H2SO4 solution containing 5.0×10-6 mol•L-1 PAR and 3.0×10-2 mol•L-1 KBrO3 without any preconcentration, the linear sweep voltammetric peak current of the catalytic wave was proportional to the vanadium concentration in the range of 8.0×10-9 to 3.0×10-6 mol•L-1. The detection limit was 2.5×10-9 mol•L-1. Using the proposed method, the vanadium concentration in crude oil was evaluated and the results were compared with those of atomic absorption spectrometry.

Electrosynthesis of Commodity Chemicals by an Autotrophic Microbial Community

ABSTRACTA microbial community originating from brewery waste produced methane, acetate, and hydrogen when selected on a granular graphite cathode poised at −590 mV versus the standard hydrogen electrode (SHE) with CO2as the only carbon source. This is the first report on the simultaneous electrosynthesis of these commodity chemicals and the first description of electroacetogenesis by a microbial community. Deep sequencing of the active community 16S rRNA revealed a dynamic microbial community composed of an invariantArchaeapopulation ofMethanobacteriumspp. and a shiftingBacteriapopulation.Acetobacteriumspp. were the most abundantBacteriaon the cathode when acetogenesis dominated. Methane was generally the dominant product with rates increasing from <1 to 7 mM day−1(per cathode liquid volume) and was concomitantly produced with acetate and hydrogen. Acetogenesis increased to >4 mM day−1(accumulated to 28.5 mM over 12 days), and methanogenesis ceased following the addition of 2-bromoethanesulfonic acid. Traces of hydrogen accumulated during initial selection and subsequently accelerated to >11 mM day−1(versus 0.045 mM day−1abiotic production). The hypothesis of electrosynthetic biocatalysis occurring at the microbe-electrode interface was supported by a catalytic wave (midpoint potential of −460 mV versus SHE) in cyclic voltammetry scans of the biocathode, the lack of redox active components in the medium, and the generation of comparatively high amounts of products (even after medium exchange). In addition, the volumetric production rates of these three commodity chemicals are marked improvements for electrosynthesis, advancing the process toward economic feasibility.

Catalytic Wave of Chlorate Ions in the Prezence of the Molybdenum (VI) - 2,3-Dihydroxybenzaldehyde Complex

The polarographic catalytic current in acid solutions of Mo(VI), 2,3-dihydroxybenzaldehyde (2,3-DHBA) and chlorate ions has been investigated. The scheme of reactions taking place in the solutions and on the electrode has been elaborated. The increase of the catalytic current is explained by the formation of the active intermediate complex [Mo(V)×2,3-DHBA (ClO3-)]. The rate constant of formation for the active intermediate complex K = 2.5 × 106 mol-1 × dm3 × s-1, the activation energy of reaction Ea=14.0 kcal×mol-1 and the activation entropy ∆Sa¹= -28.3 e.u. have also been determined.