A general and effective method for the synthesis of amides through decarboxylative amidation of α-keto acids with amines has been developed. The reaction proceeded smoothly to afford the ...corresponding amide products in good yield under air and shows excellent functional group tolerance. In addition, the protocol can be further applied in the synthesis of heterocyclic compounds like benzimidazoles.
► Solid carbon paste coated with PAMT film as a new support of platinum catalyst. ► Pt particles show chestnut-bur-like morphology with numerous nanothorns. ► Pt particles on the PAMT are found in ...two size fractions. ► The sCPE-supported PAMT film facilitates electron transfer kinetics for methanol oxidation. ► The Pt/PAMT/sCPE exhibits excellent electrocatalytic activity.
Electrodeposition of platinum is comparatively performed on four carbon-based supports: bare glassy carbon electrode (GCE), bare solid carbon paste electrode (sCPE), and a conducting polymer film coated GCE and sCPE. Both the sCPE and poly(2-amino-5-mercapto-1,3,4-thiadiazole) (PAMT) are first used to deposit Pt, with an aim of improving electrocatalytic activity of Pt toward methanol oxidation. Scanning electron microscopy shows that chestnut bur-like Pt particles with numerous nanothorns are deposited on all the supports by controlling deposition potential and time, and the particles on the PAMT film supported on the both substrates are found in two size fractions (<1μm and 2–3μm). Voltammetric data indicate that both the sCPE and the PAMT contribute to increase electrochemical active area of Pt catalyst and therefore have a positive effect on Pt's electrocatalytic activity, in comparison with the GCE and the uncoated supports, respectively. Moreover, impedance spectroscopy reveals that the sCPE-supported PAMT facilitates the electron transfer kinetics of methanol oxidation, whereas the GCE-supported PAMT gives an opposite effect on the electron transfer. This work shows that the solid carbon paste is superior to glassy carbon for use in combination with a conducting polymer as a support of Pt electrocatalyst.
The phytic acid-coated titanium (IP6/Ti) electrode was prepared through a simple drop-drying process, with an aim of improving electrocatalytic activity toward the hydrogen evolution reaction (HER). ...Scanning electron microscope and X-ray photoelectron spectroscopy showed that the IP6 coated the substrate surface uniformly and completely. Evaluation of the electrode activity was carried out in 1.0 M NaOH by linear polarization, electrochemical impedance spectroscopy (EIS) and chronopotentiometry. The kinetic parameters obtained from Tafel curves reveal that the IP6 coating can enhance the exchange current density of the HER by 489 times compared to the bare Ti, and reduce the HER activation energy by nearly 50%. The EIS data prove that the charge transfer resistance of the HER was considerably reduced due to the IP6 coating, with a decrease in real surface area of the electrode. The catalytic effect of IP6 is due to an improvement in the charge transfer kinetics of the HER. This work indicates that IP6 may be a potent candidate as a catalyst for hydrogen energy production.
► A naturally occurring phosphorus compound was used as electrocatalyst of HER. ► Phytic acid coated Ti electrode was prepared through a simple drop-drying process. ► The prepared electrode shows excellent electrocatalytic activity toward HER. ► The catalytic effect is due to intrinsic electrocatalytic properties of phytic acid.
The redox processes of quercetin in acidic medium (pH 1.8) were investigated on a graphite-wax electrode by cyclic voltammetry, potential-controlled UV/Vis spectra and derivative cyclic ...voltabsorptometry. A long-optical-path thin-layer cell was used for the spectroelectrochemical measurements. A stable quinonic product with a united conjugated structure was found to form at the first anodic peak or higher potentials via an EC mechanism, and was non-electroactive unless oxygen evolution potential was reached. Quercetin both in the free solution and pre-adsorbed on electrodes participated in the reaction at the first anodic peak, and the contribution of species in solution to total current was estimated. The subsequent anodic peaks as well as all the cathodic peaks were adsorption waves corresponding to the further redox of the adsorbed intermediates. The results demonstrate that cyclic voltabsorptometry in a long-optical-path cell is a feasible method for the analysis of electrochemical processes coupled with adsorption and homogeneous chemical transitions.
An amperometric sensor with attractive sensing behavior was prepared by using solid carbon paste as substrate for electropolymerization of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT). Morphology, ...polymerization mechanism and charge-transfer performance of the poly-AMT (PAMT) film on the composite substrate surface were investigated by using SEM, in situ UV–vis spectroelectrochemistry and electrochemical impedance spectrum methods. The results indicate that the PAMT film covered the wax portion prior to the graphite grains on the substrate surface, and the resulting sensor showed remarkable decrease in charge-transfer resistance with the increase in the amount of deposited PAMT. At the physiological pH the sensor gave sensitive and well separated voltammetric signals for two bioflavonoid isomers with the same electro-active moiety, luteolin and fisetin. The sensor achieved amperometric sensitivities of 1.41
nA
nM
−1
cm
−2 to luteolin and 0.648
nA
nM
−1
cm
−2 to fisetin in a linear range of 10–700
nM, with the lowest detection limits of 3
nM luteolin and 5
nM fisetin, respectively. The study demonstrates that the solid carbon paste is a superior substrate material for PAMT film sensor.
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•In situ monitoring of radical intermediate in redox of chlorpromazine.•High anodic current responses of chlorpromazine at physiological pH.•A positive and a negative ...voltabsorptometric peak due to formation and conversion of intermediate.•A pH-dependent mechanism proposed for oxidation of chlorpromazine.
Chlorpromazine has been used widely as an antipsychotic agent and its major metabolic pathways include 7-hydroxylation, N-dealkylation, N-oxidation and S-oxidation. The present work focuses on in situ monitoring of the radical intermediate, for clarifying the mechanism diversity in anodic oxidation of chlorpromazine at acidic and physiological pH’s. Only in acidic media the colored cation radical was detected by UV–vis spectroelectrochemistry and cyclic voltabsorptometry. The radical was formed at the first anodic peak, followed by a further one-electron oxidation at the second peak to generate the sulfoxide. At physiological pH, the sulfoxide was generated at the first anodic peak through a one-step two-electron oxidation, resulting in much higher current response than at acidic pH’s. This work provides an example of a positive and a negative voltabsorptometric peak indicating the formation and conversion of a radical intermediate.
•Phytate greatly inhibits corrosion of brass in NaOH.•Eight cyclic voltabsorptometry peaks correspond to reactions of various ions.•Phytate can suppress formation of various zinc and cupric ions.•A ...spectroelectrochemical cell allows its light path length to be changed.
Corrosion inhibition of brass by phytate in alkaline media was evaluated by cyclic voltammetry, UV–vis spectra, derivative cyclic voltabsorptometry (DCVA) and scanning electron microscopy. A thin-layer electrochemical cell was fabricated with an appropriate light-path-length. A high corrosion inhibition efficiency of phytate on brass was achieved in 0.1moldm−3 NaOH. Soluble ions such as Zn(OH)42-, Cu(I) intermediate ion, Cu(OH)42- and another Cu(II)–O complex, were monitored in situ under potentiostatic and potentiodynamic conditions. The DCVA curves at given wavelengths show five positive and three negative peaks corresponding to the potential-resolved formation and reduction of various soluble corrosion products.
► Application and analysis of in situ thin-layer spectroelectrochemistry. ► Cyclic voltabsorptometry used for a drug study. ► Highly pH-dependent oxidative metabolism of raloxifene. ► A complex ...parallel-consecutive mechanism proposed for oxidation of raloxifene.
Raloxifene is a selective estrogen receptor modulator that may produce toxic oxidative species in metabolism. The oxidation mechanism of raloxifene with different pH values was studied by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), in situ UV–vis spectral analysis and cyclic voltabsorptometry based on a long optical-path thin-layer electrochemical cell. Time-derivative cyclic voltabsorptograms were obtained for comparative discussion with the corresponding cyclic voltammograms. Raloxifene was initially oxidized to reactive phenoxyl radicals, followed by a series of transformation steps leading to different final products in different pH media. A parallel-consecutive reaction mechanism was proposed for the pH-dependent formation of 7-hydroxyraloxifene, raloxifene 6,7-o-quinone and two raloxifene dimers, each pathway following a complex electrochemical-chemical mechanism. Both raloxifene diquinone methide and its N-oxides were not detected by in situ UV–vis spectroscopy and XPS analysis. This work provides an electrochemical viewpoint and comparable information for better understanding of the oxidative metabolism and chemical toxicology of raloxifene under physiological conditions in vivo or in vitro.
A novel electrochemical sensor based on multi-wall carbon nanotubes (MWCNTs) has been developed for the determination of carbon monoxide (CO). The catalytic activation of multi-wall carbon nanotubes ...microelectrode (MWCNTME) with Pt micro-disk as substrate was investigated in different supporting electrolyte solutions by cyclic voltammetry and constant potential transient method. The result shows that MWCNTME exhibited strong catalytic effect toward the electrochemical oxidation of carbon monoxide in 0.5
mol
l
−1 HClO
4. As compared with the bare Pt disk electrode, MWCNTME can greatly decrease the overpotential and obviously increase the current of CO oxidation. The current–time curve recorded under conditions of constant potential and various CO concentrations suggests that current response depend linearly on CO concentration. A linear equation
I
(
μA)=0.00624c
(
μg
ml
−1)+0.2299
with a correlation coefficient of 0.9957 was obtained over the concentration range 0.72–52
μg
ml
−1 at potential +700
mV relative to Ag/AgCl reference electrode. The detection limit was 0.60
μg
ml
−1 and the relative standard deviation was 4.8% (
n=5) at room temperature.
Acquisition of data from both in situ spectroscopy detection and online chromatography-like separation is important for studying complex electrochemical reactions. The present work provides an ...example of combination of thin-layer spectral and electrophoretic electrochemistry, both based on thin-layer electrolysis. Two thin-layer electrochemical cells were used to investigate the electro-oxidation of solid ellagic acid at different potentials, in acidic, physiological, and alkaline buffer media. UV–vis spectra and cyclic voltabsorptograms of the oxidation products were recorded in situ without interference from the solid reactant. Four oxidation products, depending upon the buffer pH and the applied potential, were separated and detected by electrophoretic electrochemistry. The major products possess redox stability, possibly with a diquinonemethide structure. The minor product is considered as an o-quinone derivative with a lactone-ring-opening, which can be reduced or further oxidized at appropriate potentials. A consecutive-parallel reaction mechanism is proposed for the formation of four products of ellagic acid in different pH media, which enriches the knowledge about the oxidation pathway and antioxidant property of this biologically active polyphenol compound.
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