Electrochemistry

High-level composite, ab initio and density functional theory (DFT) procedures have been employed to study O–H bond dissociation energies (BDEs), as well as radical stabilization energies (RSEs) in the oxygen-centred radicals that are formed in the dissociation of the O–H bonds. Benchmark values are provided by Wn results up to W3.2 and W4.x. We are able to recommend revised BDE values for FO–H (415.6 ± 3 kJ mol–1), MeC(O)O–H (459.8 ± 6 kJ mol–1) and CF3CH2O–H (461.9 ± 6 kJ mol–1) on the basis of high-level calculations. We find that Gn-type procedures are generally reliable and cost-effective, and that some contemporary functionals and double-hybrid DFT procedures also provide adequate O–H BDEs/RSEs. We note that the variations in the O–H BDEs are associated with variations in the stabilities of not only the radicals but also the closed-shell precursor molecules. Most substituents destabilize both species, with σ-electron-withdrawing groups having larger destabilizing effects, whil...

Plane parallel electrodes are favoured, in laboratory studies and industry, for electrosynthesis, environmental treatment and energy conversion. This electrode geometry offers uniform current distribution, while a flow channel ensures a controlled reaction environment. Performance can be enhanced by the use of tailored electrode surfaces, porous, three-dimensional (3D) electrodes and bipolar electrical connections. Scale-up can be achieved by increasing the electrode size, the number of electrodes in a stack, or the number of stacks in a system. Recent trends include (a) 3D printing of fast prototype cell components, (b) use of porous 3D electrode supports and their decoration, (c) development of microflow cells for electrosyn-thesis, (d) anodic Fenton oxidations for wastewater treatment and (e) computational models to simulate and rationalise reaction environment and performance. Future research needs are highlighted. Addresses

Synthesis of metallic and semiconductor nanoparticles through physical and chemical routes has been extensively reported. However, green synthesized metal nanoparticles are currently in the limelight due to the simplicity, cost-effectiveness and eco-friendliness of their synthesis. This study explored the use of aqueous leaf extract of Costus afer in the synthesis of silver nanoparticles (CA-AgNPs). The optical and structural properties of the resulting silver nanoparticles were studied using UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red spectrophotometer (FTIR). TEM images of the silver nanoparticles confirmed the existence of monodispersed spherical nanoparticles with a mean size of 20 nm. The FTIR spectra affirmed the presence of phytochemicals from the Costus afer leaf extract on the surface of the silver nanoparticles. The electrochemical characterization of a CA-AgNPs/multiwalled carbon nanot...

We describe an isocratic, reversed-phase high-performance liquid chromatographic method for the simultaneous measurement of fully oxidised, dihydro- and tetrahydropterins in cerebrospinal fluid. Tetrahydrobiopterin is detected electrochemically using an ESA Coulochem ...

The effect of six different preservatives on the production process and stability of resveratrol nanosuspensions was investigated. Nanosuspensions of the anti-oxidant resveratrol were prepared by high pressure homogenization (1,500 bar, 20 homogenization cycles). The preservatives used were: caprylyl glycol (0.75%), Euxyl PE 9010 (1.0%), Hydrolite-5 (2.0), Phenonip (0.75%), Rokonsal PB-5 (0.5%) and MultiEx Naturotics (2.0%). Preservation is essential for oral and dermal nanosuspensions, but can impair the stability. The effect of the preservatives on stability as a function of cycle numbers was determined by size measurements (photon correlation spectroscopy (PCS), laser diffraction (LD) and light microscopy). Zeta potential measurements were performed for determination of the Stern potential (measurements in water) and as stability criterion (measurements in original dispersion medium), to elucidate the mechanism of destabilization. The preservatives could be placed into three grou...

A controllable composition and morphology AuAg/ZnO catalyst, prepared by an easily scalable method, was, for the first time, explored for the electrocatalytic reduction of CO 2. It was found that the composition of the bimetallic alloy contributes to the overall CO 2 reduction performance. In particular, as also demonstrated by density functional theory calculations, CO production increases, decreasing the Au content in the catalyst alloy. The experimental investigation reveals that the products are H 2 and CO, which production rate increases in the presence of ZnO, up to a Faradic efficiency of 94.7 % at 0.4 V. On the other hand, controlling the oleic acid covering it is possible to modulate the surface properties allowing to obtain, at 0.6 V, H 2 /CO ratios equal to 1.1 and 1.9 for nanocatalysts thermally treated for 2 and 5 h, respectively.

In this work, a methodological approach is reported, aimed at assessing the electrochemical response of some model gluco-oligosaccharides (dextrans). Such strategy is based on the complementary use of both anion-exchange chromatography with pulsed amperometric detection (HPAEC–PAD) and capillary zone electrophoresis coupled with UV detection (CZE–UV). Unlike HPAEC–PAD, CZE–UV required derivatization with a chromophoric dye (i.e., 8-aminonaphtalene-1,3,6-trisulphonic acid, ANTS) to enhance UV response and separation selectivity. From the comparison between chromophore response and PAD signal, the reliability of HPAEC–PAD for quantitative evaluation of dextran mixtures containing mainly oligomers with polymerization degree (DP) up to 18 could be proved, due to the fairly constant molar response. For higher DPs (up to 41), a maximum in the trend of the molar responses was observed followed by a steep decrease for DPs higher than about 30–35; indeed, an underestimation of weight-average...

Rapid, sequence-specific DNA detection is essential for applications in medical diagnostics and genetic screening. Electrical biosensors that use immobilized nucleic acids are especially promising in these applications because of their potential for miniaturization and automation. Current DNA detection methods based on sequencing by synthesis rely on optical readouts; however, a direct electrical detection method for this technique is not available.