Anodic Wave Research Articles

Stabilization of oxidovanadium(iv) by organic radicals

o-Imino-p-R'-benzosemiquinone anion radical (L(R')(IS)(˙-)) complexes of oxidovanadium(IV) of type [(L(1)(R-))(VO(2+))(L(R')(IS)(˙-))] (R = H, R' = H, 1; R = H, R' = -CMe(3), 2; R = -CMe(3), R' = H, 3 and R = -CMe(3), R' = -CMe(3), 4) incorporating the redox-innocent tridentate NNO-donor L(1)(R-) ligands (L(1)(R)H = 2,4-di-R-6-{(2-(pyridin-2-yl)hydrazono)methyl}phenol) were isolated and substantiated by elemental analyses, IR, mass, NMR and UV-vis spectra including the single crystal X-ray structure determinations. The V-O(phenolato) (cis to the V=O) lengths spanning 1.905(3)-1.9355(15) Å in 1-4 are consistent with the coordination to the [VO](2+) state. The V-O(IS) (trans to the V=O) lengths, 2.1505(17)-2.1869(15) Å, in 1-4 are longer due to the trans influence of the V=O bond. The V-N(IS) lengths, 1.906(3)-1.924(2) Å, in 1-4 are comparatively shorter due to the higher affinity of the paramagnetic [VO](2+) ion towards the L(R')(IS)(˙-) anion radicals. Density functional theory (DFT) calculations using B3LYP, B3PW91 and PBE1PBE functionals on 1 and 2 authenticated that the closed shell singlet (CSS) solutions (dianionic o-amido-p-R'-phenolates (L(R')(AP)(2-)) coordinated to VO(3+), Type I) of 1-4 are unstable with respect to the open shell singlet (OSS) perturbations. Broken symmetry, BS (1,1) M(s) = 0 (L(R')(IS)(˙-) coordinated to the VO(2+) ion, Type III) solutions of 1-4 are stable and reproduce the experimental bond parameters. Frozen glasses EPR spectra of [1-4](+) ions (e.g. g(||) = 1.948, g(⊥) = 1.978, A(||) = 184 (22 G), A(⊥) = 62(15 G) for [2](+)) and unrestricted DFT calculations on [1](+), [2](+), [1](-) and [2](-) ions using doublet spin state elucidated that the reversible anodic waves at [0.15-0.31] V of 1-4 complexes are due to the oxidation of L(R')(IS)(˙-) generating [(L(1)(R-))(VO(2+))(L(R')(IQ))]+ complexes (L(R')(IQ) = o-imino-p-R'-benzoquinone) coordinated to the [VO](2+) ion (Type V) while the irreversible cathodic waves at -[1.08-1.49] V are due to the formation of unstable [(L(1)(R-))(VO(2+))(L(R')(AP)(2-))](-) complexes (Type II). The second anodic waves at [0.76-0.89] V are assigned to a [VO](3+)-[VO](2+) couple affording diamagnetic [(L(1)(R-))(VO(3+))(L(R')(IQ))](2+), [1-4](2+) complexes (Type VI) which are identified by UV-vis spectra, DFT and time dependent (TD) DFT calculations. Spectro-electrochemical measurements and TD DFT calculations on 1 and 2 disclosed that lower energy electronic absorption bands of 1-4 are due to the LMCT and CSS-OSS perturbation which disappear in [1-4](+) ions. [1-4](+) absorb at 600-650 nm due to d-d transitions and MLCT which are absent in VO(3+) complexes, [1-4](2+).

9,10-Phenanthrenesemiquinone radical complexes of ruthenium(iii), osmium(iii) and rhodium(iii) and redox series

Reactions of 9,10-phenanthrenequinone (PQ) in toluene with [M(II)(PPh3)3X2] at 298 K afford green complexes, trans-[M(PQ)(PPh3)2X2] (M = Ru, X = Cl, 1; M = Os, X = Br, 2) in moderate yields. Reaction of anhydrous RhCl3 with PQ and PPh3 in boiling ethanol affords the dark brown paramagnetic complex, cis-[Rh(PQ)(PPh3)2Cl2] (3) in good yields. Diffusion of iodine solution in n-hexane to the trans-[Os(PQ) (PPh3)2(CO)(Br)] solution in CH2Cl2 generates the crystals of trans-[Os(PQ)(PPh3)2(CO)(Br)](+)I3(-), (4(+))I3(-)), in lower yields. Single crystal X-ray structure determinations of 1·2toluene, 2·CH2Cl2 and 4(+)I3(-), UV-vis/NIR absorption spectra, EPR spectra of 3, electrochemical activities and DFT calculations on 1, 2, trans-[Ru(PQ)(PMe3)2Cl2] (1Me), trans-[Os(PQ)(PMe3)2Br2] (2Me), cis-[Rh(PQ)(PMe3)2Cl2] (3Me) and their oxidized and reduced analogues including trans-[Os(PQ)(PMe3)2(CO)(Br)](+) (4Me(+)) substantiated that 1-3 are the 9,10-phenanthrenesemiquinone radical (PQ(˙-)) complexes of ruthenium(III), osmium(III) and rhodium(III) and are defined as trans/cis-[M(III)(PQ(˙-))(PPh3)2X2] with a minor contribution of the resonance form trans/cis-[M(II)(PQ)(PPh3)2X2]. Two comparatively longer C-O (1.286(4) Å) and the shorter C-C lengths (1.415(7) Å) of the OO-chelate of 1·2toluene and 2·CH2Cl2 and the isotropic fluid solution EPR signal at g = 1.999 of 3 are consistent with the existence of the reduced PQ(˙-) ligand in 1-3 complexes. Anisotropic EPR spectra of the frozen glasses (g11 = g22 = 2.0046 and g33 = 1.9874) and solids (g11 = g22 = 2.005 and g33 = 1.987) instigate the contribution of the resonance form, cis-[Rh(II)(PQ)(PPh3)2Cl2] in 3. DFT calculations established that the closed shell singlet (CSS) solutions of 1Me and 2Me are unstable due to open shell singlet (OSS) perturbation. However, the broken symmetry (BS) (1,1) Ms = 0 solutions of 1Me and 2Me are respectively 22.6 and 24.2 kJ mole(-1) lower in energy and reproduced the experimental bond parameters well prompting the coordination of PQ(˙-) to the M(III) ions. The comparatively shorter C-O lengths, 1.268(4) and 1.266(5) Å and the longer C-C length, 1.466(6) Å, are consistent with the PQ chelation to osmium(II) ion in 4(+). The reversible anodic waves at 0.22, 0.22, and 0.18 V of 1-3, referenced by the Fc(+)/Fc couple, are assigned to the PQ(˙-)/PQ couple forming PQ complexes as trans/cis-[M(III)(PQ)(PPh3)2X2](+) while the cathodic waves at -0.92 and -0.89 V of 2 and 3 are due to formations of PQ(2-) complexes as trans-[M(III)(PQ(2-))(PPh3)2X2](-). 1 displays two overlapping cathodic waves at -0.72(89), -1.0(120) V. EPR spectrum of the frozen glass of 1(-) along with DFT calculations detected the contribution of both the valence tautomers, trans-[Ru(III)(PQ(2-))(PPh3)2Cl2](-) (g1 = g2 = 2.456; g3 = 1.983) and trans-[Ru(II)(PQ(˙-))(PPh3)2X2](-) (g(iso) = 1.999) in the anion. The characteristic lower energy absorption bands of 1 and 2 at 700 nm were assigned to CSS-OSS perturbation MLCT those are absent in paramagnetic 3, 1(+), 2(+), 1(-), 2(-) and 4(+) complexes, investigated by spectro-electrochemical measurements and time dependent (TD) DFT calculations on 1Me, 2Me, 1Me(+) and 1Me(-).

Ferrate(VI) synthesis at boron-doped diamond anode

The oxidation of iron compounds from alkaline 10 M KOH electrolytes on a boron doped diamond electrode is examined by cyclic voltammetry between the potentials of hydrogen evolution reaction and oxygen evolution reaction, due to ferrate(VI) electrochemical synthesis. It is shown that the anodic current peak that appears in iron free electrolyte at a less positive potential than the potential of oxygen evolution probably coincides with oxidation of hydrogen in >CH2 groups and C-sp2 graphite impurities with formation of >C=O groups at C-sp3 diamond structure. Addition of Fe(III) compounds to the electrolyte provoke formation of the anodic wave on cyclic voltammograms in the potential region which correlates with generation of ferrate(VI). It is concluded that the direct electrochemical synthesis of Fe(VI) at the boron doped diamond anode is possible because of the less positive potential of ferrate(VI)FeO2-4 formation in respect to the potential of oxygen evolution reaction. Presence of ferrate(VI) in electrolyte, formed after anodic polarization of boron electrode in 10 M KOH electrolyte saturated with Fe(III) at + 0.9 V against Hg|HgO electrode, has been proven by UV-VIS spectrometry.

Electrochemical and Colorimetric Measurements Show the Dominant Role of FeS in a Permanently Anoxic Lake

Recent publications have shown that the anodic reaction between FeS and Hg can be used for electrochemical detection of colloidal and particulate FeS in natural waters. Anodic waves that were recorded around -0.45 V (vs Ag/AgCl) in model solutions correspond to the electrochemical transformation of nanoparticulate FeS to HgS. Here, as a further step, the proposed approach is tested on anoxic, sulfidic, and iron-rich samples of a meromictic freshwater lake (Lake Pavin, France). Based on new and more comprehensive work on FeS electrochemistry in model and anoxic Lake Pavin samples, a new interpretation is given for previously recorded voltammetric signals in sulfide and iron rich environment, usually designated FeS(aq), and its role in controlling solubility of different FeS phases. A comparison of the depth profiles of S(-II) measured by voltammetry and the methylene blue method showed that the majority of S(-II) is in the form of FeS. In the monimolimnion layer, thermodynamic calculations based on total Fe(II) and S(-II) concentration, measured by ferrozine and the methylene blue method, predict precipitation of FeS with log K(s) values between -3.6 and -3.8, very close to mackinawite's K(s) value. In the upper part of the same layer, precipitation of greigite is predicted. It is shown that modification of a Hg electrode by surface-formed FeS has a significant influence on voltammetric Fe(II) determination, since reduction of Fe(II) under such conditions occurs both on bare (-1.4 V) and on FeS modified Hg surfaces (-1.1 V); Fe(II) may be underdetermined when only the -1.4 V peak is measured.

Synthesis and characterization of a family of Co(II) triphenylamido-amine complexes and catalytic activity in controlled radical polymerization of olefins

The present work reports a new family of tripodal CoII complexes bearing trianionic triphenylamido-amine ligands with a variety of pendant arms (aryl, acyl, alkyl). These complexes have been synthesized by the reaction of anhydrous CoCl2 with the deprotonated ligands and exhibit stoichiometric and structural variation. The solid-state structures of these compounds reveal that in all cases the four nitrogen-atom residues of the ligands are coordinated to the metal center in a distorted trigonal-pyramidal geometry. In two cases, the presence of acetonitrile adds a fifth moiety to the coordination sphere. Among the aryl-armed CoII reagents, [K(L3)CoII–NCMe]n (1), [K(THF)6][(L5)CoII]·1.5THF (2) and [K(NCMe)3(L13)CoII–NCMe] (6), the two five-coordinate structures (1, 6) exhibit distorted trigonal bipyramidal geometries, with that of 6 being the least distorted. The four-coordinate species 2 is the only compound with a distinct anionic [(L5)CoII]− component, since the K+ ion is solely coordinated by solvent molecules. The acyl-armed CoII compounds [K(THF)2(L8)CoII]n (3) and {[K2(DMA)3(L10)2CoII2]·0.5Et2O}n (5) are strictly four-coordinate species, with the carbonyl moieties oriented exo with respect to the cavity of the vacant coordination site. Finally, compound [K2(L9)2CoII2]n (4) is the only example bearing an alkyl-armed ligand, and exhibits a geometry featuring a repeating –[Co(1)–K(1)–Co(2)–K(2)]n– sequence. All compounds have been characterized by spectroscopic and electrochemical techniques. Compounds 1, 2, 4, and 6 show reversible or semi-reversible CoII/CoIII redox couples, whereas the electron-deficient complexes 3 and 5 exhibit irreversible anodic waves. The catalytic reactivity of these complexes towards controlled radical polymerization (CRP) of styrene (St) and methyl methacrylate (MMA) has been studied and preliminary results are presented. Compounds 4 and 5 seem to be the most reactive with both monomers, giving high yields of polymers (60–86%), 3 efficiently induces styrene polymerization (90%), whereas 2 and 6 provide lower yields (12–16% for PS and 30–45% for PMMA). The steric factor seems to play an essential role, since CoII compounds that feature a less hindered fifth coordination site show the highest reactivity and better control over polymerization. The polymers obtained are predominately syndiotactic, consistent with radical polymerization, with two exceptions (1, 2) that exhibit unusually high ratios of isotactic triads. Interestingly, in many cases, the polymers obtained feature bimodal distributions, while the molecular weight distributions are not very broad (1.40–2.00), and this strongly indicates that two parallel mechanisms may be in operation.

Asymmetric Mixed‐Valence Complexes that Consist of Cyclometalated Ruthenium and Ferrocene: Synthesis, Characterization, and Electronic‐Coupling Studies

Three bis-tridentate ferrocene-containing cyclometalated ruthenium complexes, [(Fcdpb)Ru(tpy)](+) (1(+)), [(Fctpy)Ru(dpb)](+) (2(+)), and [(Fcdpb)Ru(Fctpy)](+) (3(+)), have been prepared and characterized, where Fcdpb is the 2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene, tpy is 2,2':6',2"-terpyridine, dpb is the 2-deprotonated form of 1,3-di(2-pyridyl)benzene, and Fctpy is 4'-ferrocenyl-2,2':6',2"-terpyridine. Single crystals of compounds 2(+) and 3(+) have been studied by X-ray analysis. Complexes 1(+) and 2(+) displayed two anodic redox waves, whilst three well-separated redox couples were observed for compound 3(+). A combined experimental and computational study suggested that the ferrocene unit on the Fcdpb moiety in compounds 1(+) and 3(+) was oxidized first. In contrast, the order of the oxidation of ruthenium and ferrocene in complex 2(+) was reversed. Metal-to-metal-charge-transfer transitions (MM'CT) have been observed for the singly oxidized states 1(2+), 2(2+), and 3(2+) in the near-infrared region. Hush analysis showed that the metal-metal electronic couplings in compounds 1(2+) and 3(2+) were much stronger than those in compound 2(2+).

Different interaction of codeine and morphine with DNA: A concept for simultaneous determination

In this study, the interaction between codeine and morphine with dsDNA was assessed at pH 7.0. Poly(diallyldimethylammonium chloride), PDDA, was used as a dispersant of MWCNTs. Using differential pulse voltammetry (DPV) at pencil graphite electrode (PGE) showed that both molecules were electrochemically oxidized due to the presence of phenolic and amino groups in their structures. When DNA was added to the solution, the electrochemical signal of codeine and morphine was decreased and shifted to more negative and positive potentials, respectively. The interaction modes were respectively electrostatic for codeine and intercalation for morphine with two anodic peaks of codeine being merged into them when DNA concentration was increased. At high DNA concentrations, a sharp anodic wave for codeine and a clear discrimination of codeine and morphine oxidation peaks were observed. Finally, a pencil graphite electrode was modified with carbon nanotubes and DNA was tested in order to determine codeine and morphine in solution. Electrochemical oxidation of codeine and morphine bonded on dsDNA/MWCNTs–PDDA/PGE was used to obtain an analytical signal. Allowing five min as an accumulation time, a linear dependence was observed between 0.05 and 40μgmL−1 for codeine and 0.05 and 42μgmL−1 for morphine. Detection limits of 0.041 and 0.043μgmL−1 were obtained for codeine and morphine, respectively. The biosensor was applied to validate its capability for the analysis of codeine and morphine in blood serum, urine samples and pharmaceutical formulations.

Electrochemical Characterization of the Marine Antioxidant Gadusol

The electrochemical properties of gadusol, a metabolite extracted from fish roes, were determined for the first time by cyclic- and square-wave voltammetries on a glassy carbon electrode in buffered aqueous solutions. The aims of the work were characterization of the redox behavior and assessment of the mechanism underlying the antioxidant capacity of the compound. Anodic waves with peak potentials of 710 +/- 5 mV and 601 +/- 9 mV vs. Ag/AgCl were obtained for gadusol and its anion gadusolate, respectively. The voltammograms point to the irreversible nature of the oxidation process and reveal better antioxidant properties for the compound under physiological pH, with a moderate reductive power, but improved stability under atmospheric oxidation in comparison with other natural antioxidants such as ascorbic acid. The presence of direct ionic micelles prepared with sodium dodecyl-sulfate or cetyl-trimethyl-ammonium chloride yielded no significant differences regarding homogeneous medium in the cyclic voltammetry of gadusolate. The results provide evidence of the electron transfer mechanism for the quenching reaction of standard-reactive species by gadusolate and support it as a promising candidate to be tested as an antioxidant additive to food, cosmetic and pharmaceutical formulas. The direct analysis of the metabolite in biological systems and natural extracts by electrochemical methods is also envisaged.

Comparison of the Antioxidant Properties of Commonly Consumed Commercial Teas

The antioxidant properties of various commonly consumed commercial teas were screened and compared to check what the consumers get in commercial tea bags in the range of consume preparation conditions. It includes flavored black teas and green teas, as well as some fruit teas. Electron transfer-based assays, such as phenolic content by Folin-Ciocalteu method and cupric ion reducing antioxidant capacity (CUPRAC), were applied. Higher antioxidant activity values were obtained for green and black tea infusions in comparison to fruit teas. The correlation between FC total phenolic and CUPRAC assay for all studied teas was significant (R2 = 0.871). The antioxidant power of tea infusions were also measured using cyclic voltammetry. The observed anodic waves were broadened in comparison with voltammograms of single flavonoids due to the response of several antioxidants with different oxidation potentials. The values of Trolox equivalents obtained by electrochemical approach were lower than in the CUPRAC assay; however, the increased order of the antioxidant capacity of tea infusions was the same.

Electrochemical behavior of dopamine and ascorbic acid at dendritic Au rod surfaces: Selective detection of dopamine in the presence of high concentration of ascorbic acid

Electrochemical behavior of dopamine (DA) and ascorbic acid (AA) at dendritic Au rod (DAR) surfaces prepared by a simple and fast electrodeposition from sulfite-based Au(I) electrolytes was investigated. The unique DAR structures with sharp edge Au sites differentiated the anodic waves between DA and AA, and the electrooxidation of DA at DAR surfaces was significantly enhanced at lower DA concentration ranges. The DAR surfaces enabled the differential pulse voltammetric determination of DA in the presence of 0.1mM of AA, and the modification of the DAR with Nafion layers enhanced the sensitivity and selectivity against AA. Electrochemical deposition would offer an efficient route for fabricating nanostructured surfaces for electrochemical determination of biologically important species.

Electrochemical studies of quinine in surfactant media using hanging mercury drop electrode: A cyclic voltammetric study

The electrochemical behavior of quinine was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) using surfactant. The reduction peak current of quinine increases remarkably in presence of 1% CTAB. Its electrochemical behavior is quasi-reversible in the Britton–Robinson buffers of pH 10.38 by exhibiting the well-defined single cathodic and anodic waves and the ratio of Ipa/Ipc approaching one at the scan rate of 500mVs−1. On the basis of CV, SWV and Coulometry, electrochemical reduction mechanism of quinine has been proposed which has shown that protonation occurs on the nitrogen of the quinoline moiety. Linearity was obtained when the peak currents (Ip) were plotted against concentrations of quinine in the range of 30.0–230.0ngmL−1 with a detection limit of 0.132ngmL−1 in SWV and 90.0–630.0ngmL−1 with a detection limit of 0.238ngmL−1 in DPV. Fast and sensitive SWV has been applied for the quantitative analysis of quinine in bark of Cinchona sp. and in soft drinks and a good recovery was obtained. The accuracy and precision of the method are determined and validated statistically. No interferences from other food additives were observed. The relative standard deviation for intraday and interday assay was 0.89 and 0.73% (n=3) respectively.

Mechanistic Study on the Electrochemical Reduction of 9,10-Anthraquinone in the Presence of Hydrogen-bond and Proton Donating Additives

The electrochemical reduction of 9,10-anthraquinone (AQ) was investigated in CH(3)CN in both the absence and presence of the hydrogen-bond and proton donating additives, CH(3)OH, CH(CF(3))(2)OH, phenol, 4-methoxyphenol, 4-cyanophenol, 2,4,6-trichlorophenol, and benzoic acid (BA). Three clearly different types of electrochemical behavior were observed with increasing concentrations of the additives, and were simulated to analyze the reaction mechanisms. Type I was observed for weakly interacting additives, such as CH(3)OH, characterized by positive shifts of the two well-separated reduction waves, corresponding to the formation of AQ(•-) and AQ(2-), with no loss of reversibility. The second wave shifted more strongly, and finally merged with the first. These behaviors are explained by the association of AQ(2-) with the additives via strong hydrogen-bonding. Type II is attributed to a reduction mechanism involving quantitative formation of strong hydrogen-bonded complexes of AQ(2-) with additives, such as CH(CF(3))(2)OH, phenol and 4-methoxyphenol, showing a reversible or quasireversible two-electron reduction wave with increasing concentrations of the additives. The behavior of Type III, observed in the presence of strongly interacting additives, such as 2,4,6-trichlorophenol and BA, is characterized by a voltammogram composed of the 2-electorn cathodic and the broad anodic waves without keeping reversibility, facilitated by proton transfer in the hydrogen-bonded complexes, AQ(•-)-BA and AQ(2-)-BA. The effects of hydrogen-bonding and protonation on the electrochemistry of AQ have been systematically demonstrated in terms of the potentials and reaction pathways of the various species, which appear in quinone-hydroquinone systems.

Electroanalysis of Trace Inorganic Arsenic with Gold Nanoelectrode Ensembles

AbstractThe results of a study on the determination of trace levels of arsenic with nanoelectrode ensembles (NEEs) are reported. In order to lower the detection limit and to increase the number of performable analysis for each NEE, the right choice of the supporting electrolyte concentration and electroanalytical parameters were optimized. The electrochemical behavior of As(III) at NEEs was studied at first by cyclic voltammetry, while trace concentrations of As(III) were determined by anodic stripping square wave voltammetry. The method is characterized by a detection limit as low as 5 ng/L (65 pM) after 3 min preconcentration at −0.4 V. Finally, NEEs were applied to trace As analysis in real samples such as certified seawater samples.

Simultaneous voltammetric determination of uric acid and ascorbic acid using carbon paste/cobalt Schiff base composite electrode

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0 × 10−4 to 1.0 × 10−8 and 1.0 × 10−3 to 1.0 × 10−8 M with detection limit of 8.0 × 10−9 and 8.0 × 10−9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.

Octahedral and tetrahedral cobalt species in nanodimensional pores of mordenite zeolite as modified carbon paste electrode for determination of ascorbic acid

A new method is developed for the catalytic oxidation of ascorbic acid (AA) at zeolite-modified carbon paste electrode, doped with cobalt (II) (Co 2+ MOR/ZME). Characterisation of Co 2+ -loaded mordenite zeolite has been carried out by diffuse reflectance spectroscopy (DRS), Fourier transform-infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). FTIR and DRS show octahedral and tetrahedral Co 2+ species into mordenite channels. TEM pictures reveal the formation of cobalt phyllosilicate. Cobalt (II) exchanged in zeolite-type mordenite acts as a catalyst to oxidise AA. The modified electrode lowered the overpotential of the reaction by ~500~mV. The mechanism of electrochemical oxidation of AA using modified electrode was investigated by cyclic voltammetry (CV) study. Results of CV using this modified electrode show one well-resolved anodic wave for the oxidation of AA, which makes it possible for determination of compound.

Synthesis, structure, properties and immobilization on a gold surface of the monoribbed-functionalized tris-dioximate cobalt(ii) clathrochelates and an electrocatalytic hydrogen production from H+ ions

The cycloaddition of the mono- and dichloroglyoximes to the cobalt(II) bis-α-benzyldioximate afforded the cobalt(II) mono- and dichloroclathrochelates in moderate yields (40-60%). These complexes undergo nucleophilic substitution of their reactive chlorine atoms with aliphatic amines, alcohols and thiolate anions. In the case of ethylenediamine and 1,2-ethanedithiol, only the macrobicyclic products with α,α'-N(2)- and α,α'-S(2)-alicyclic six-numbered ribbed fragments were obtained. The cobalt(II) cage complexes with terminal mercapto groups were synthesized using aliphatic dithiols. The crystal and molecular structures of the six cobalt(II) clathrochelates were obtained by X-ray diffraction. Their CoN(6)-coordination polyhedra possess a geometry intermediate between a trigonal prism and a trigonal antiprism, and the encapsulated cobalt(II) ions are shifted from their centres due to the structural Jahn-Teller effect with the Co-N distances varying significantly (by 0.10-0.26 Å). The electrochemistry of the complexes obtained was studied by cyclic voltammetry (CV). The anodic waves correspond to the quasi-reversible Co(2+/3+) oxidations, whereas the cathodic ranges contain the quasi-reversibile waves assigned to the Co(2+/+) reductions; all the cobalt(i)-containing clathrochelate anions formed are stable in the CV time scale. The electrocatalytic properties of the cobalt complexes obtained were studied in the production of hydrogen from H(+) ions: the addition of HClO(4) resulted in the formation of the same catalytic cathodic reduction Co(2+/+) waves. The controlled-potential electrolysis with gas chromatography analysis confirmed the production of H(2) in high Faraday yields. The efficiency of this electrocatalytic process was enhanced by an immobilization of the complexes with terminal mercapto groups on a surface of the working gold electrode.

A Polarographic Study of Chlorogenic Acid and Its Interaction with Some Heavy Metal Ions

AbstractThe behavior of chlorogenic acid (CGA) and its interaction with Hg(II), Pb(II), Cu(II), Cd(II) and Zn(II) has been studied using direct current (DC) and differential‐pulse polarography (DPP). Adsorptive and kinetic/catalytic anodic waves of CGA have been detected at −0.02 and −0.18 V vs. SCE, respectively; Hg(I)‐CGA surface disproportionation has been assumed. Reduction of Hg(II)‐ions, added in the buffered solution of CGA (pH 7.5), occurs rather than complexation, while the complex forming ability of CGA towards Pb(II) and Cu(II) has been observed. Stoichiometry 1 : 1 for Pb(II)‐CGA, and 1 : 1 and 1 : 2 for Cu(II)‐CGA has been established applying Job’s method of continuous variation on DPP data. UV‐vis spectrophotometric measurements additionally confirmed the existence and stoichiometry of Cu(II) complexes.

Electrochemical Synthesis of Ferrate Using Iron with 3.3% Si Anode

A ferrate solution about 236.87mM was obtained under the optimum conditions: 16MNaOH, J=100mAcm-2, 35°C, electrolysis duration (1h), The optimal current efficiency was 45.86%. The cyclic voltammogram of iron with 3.3% Si revealed a new anodic wave between -0.2V and 0.1V versus HgO/Hg corresponding to Fe(V) production.

Electrochemical behavior of gold (III) in cyanide-free bath with 5,5′-dimethylhydantoin as complexing agent

Gold electrodeposits are prepared in a cyanide-free bath with 5,5′-dimethylhydantoin (DMH) as complexing agent. The electrochemical behavior of the electrodeposition is then investigated together with the influence of additive A (pyridyl-compound) as an additive on the nucleation and growth of gold using electrochemical techniques on gold working electrode at different temperatures. Cyclic voltammogram consists of a single cathodic reduction wave at −0.62 V which corresponds to the reduction of Au(III) to Au without anodic oxidation wave observed. The diffusion coefficient of Au(III) in the bath is found to be ∼10 −6 cm 2/s and the energy of activation (43 kJ/mol) is deduced from the cyclic voltammograms at different temperatures. The nucleation and growth of gold on gold working electrode is investigated by chronoamperometry. The progressive nucleation mechanism is found for gold deposition using Scharifker–Hills’ model with three-dimensional (3D) diffusion-controlled growth nucleation. The introduction of the additive A does not influence this mechanism. The gold electrodeposits are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cathodic polarization measurements. Experimental results indicate that additive A increases the cathodic polarization of bath, refines the grains of electrodeposit and changes the preferred orientation of electrodeposit from [1 1 1] direction to [2 0 0] direction.

Analysis of the Antioxidant Capacities of Flavonoids under Different Spectrophotometric Assays Using Cyclic Voltammetry and Density Functional Theory

Flavonoids often show inconsistent antioxidant activities (AAs) depending on the assay used. The electrochemical properties of 14 flavonoid standards in cyclic voltammetry [area under anodic wave (Q) and oxidant peak potentials (Epa)] and the structural parameters [bond dissociation enthalpy (BDE) and ionization potential (IP)] were investigated. They were compared with the results of four spectrophotometric assays, namely, diphenyl-1-picrylhydrazyl (DPPH), Folin-Ciocalteu reagent (FCR), ferric reducing ability of plasma (FRAP), Trolox equivalent antioxidant capacity (TEAC), to analyze the chemical reasons for the varying AAs of flavonoids under different assays. Using the cyclic voltammetry method, the AAs of the flavonoids in the DPPH, FCR, and FRAP assays were mainly determined by the ease of charge transferring in the first oxidation step. Meanwhile, the results of TEAC assays were primarily influenced by the amount of charge transfer in the multiple oxidation steps (MOS) of flavonoids. In the theoretical calculation, the BDE values of the selected flavonoids had considerably higher correlations with the results of the DPPH assay (r2=0.89) compared with the other three assays, which indicates that the oxidant-scavenging reaction of the tested flavonoids in the DPPH assay is closer to a hydrogen atom transfer mechanism. Neither the IP values nor BDE values had satisfactory correlation with the AAs of the flavonoids in the TEAC assay (r2=0.57, r2=0.54, respectively), Therefore, complex reaction mechanisms underlie this method and appropriate structural descriptors for reflecting the AAs of flavonoids based on MOS (e.g., TEAC values) need further investigation.