Anodic Peak Potentials Research Articles

Synthesis of 3-O-methylgallic acid a powerful antioxidant by electrochemical conversion of syringic acid

BackgroundA kinetic study of the electrochemical oxidation of syringic acid (3,5-dimethoxy-4-hydroxybenzoic acid) by cyclic voltammetry at treated gold disk was combined with results of electrolyses at Ta/PbO2 anode in order to convert it into potentially high-added-value product. MethodsThe electrochemical oxidation of syringic acid was carried out in order to convert this compound to 3-O-methylgallic acid. This latter was identified by mass spectrophotometry using LC-MS/MS apparatus. The 3-O-methylgallic acid synthesis was controlled by cyclic volammetry, Ortho-diphenolicdeterminations and DPPH radical-scavenging activity. ResultsThe proposed mechanism is based on the hypothesis of a bielectronic discharge of syringic acid molecule under free and adsorbed form involving two intermediate cation mesomers. Hydrolysis of the more stable of this last one leads to the formation of the 3,4-dihydroxy-5-methoxybenzoic acid (3-O-methylgallic acid) as a major product. The latter aromatic compound was synthesized by anodic oxidation of syringic acid at PbO2 electrode. The cyclic voltammogram of the electrolysis bath of syringic acid shows that the anodic peak potential of 3-O-methylgallic acid was lower (Epa=128mV) than that of SA (Epa=320mV). And the strongest antiradical activity was detected when the 3-O-methylgallic acid concentration was higher". ConclusionThe electrochemical oxidation using PbO2 anode is a rapid, simple and efficient method tool for a conversion of SA into 3-O-methylgallic acid, a potent antioxidant derivative General SignificanceThe electrochemical process consists in a simple transformation of the syringic acid into 3-O-methylgallic acid having a better antioxidant capacity. This result has been justified by cyclic voltametry which shows that anodic peak of 3-O-methylgallic acid is reversible. Furthermore, its potential is lower than that of the irreversible anodic peak of syringic acid to 3-O-methylgallic acid.

Preparation and properties of coke powder activated carbon/α-Co(OH)2 composite electrode materials

Coke powder activated carbon (CPAC) was prepared by dipping-calcined KOH activation method. Using CPAC as the raw material a series of composite electrode materials of CPAC/α-Co(OH)2 with different mass fractions of cobalt were synthesized by the Sol–gel method. The physical properties of the resulting samples were characterized by the field emission scanning electron microscopy and the X-ray diffraction. The results show that composite materials, CPAC/α-Co(OH)2, have a flower-like structure. The results of electrochemical performances show that the composite material has a good electrochemical capacity of 472.3 F g−1 with a cobalt doping amount of 30 wt %. By the cyclic voltammetry testing, we found that the anodic peak potential of the redox peaks in composite electrode materials shifted positively when the scan rate increased, while the cathodic peak potential shifted negatively, and that would cause a gradual increase of the peak potential difference of redox peaks. In contrast, the lower of the scan rate, the smaller of the peak potential difference and the better of the reversibility of composite material. The results of impedance testing show that CPAC/α-Co(OH)2 has a lower electrochemical impedance than that of CPAC.

Preparation of gold decorated SiO2@polyaniline core–shell microspheres and application as a sensor for ascorbic acid

The gold decorated SiO2@polyaniline (PANI) core–shell microspheres (GDSP) were synthesized by using silica spheres as core, polyaniline as shell, and HAuCl4 as oxidizing agent. Morphology, electroactivity, and conductivity of GDSP can be controlled by varying the HAuCl4 concentration. By increasing the concentration of HAuCl4, a large quantity of GDSP with raspberry-like morphology was fabricated. TEM images indicated that the resulting core–shell microspheres were composed of a SiO2 core with an average diameter of 800nm and a polyaniline shell with an average thickness of 200nm. It was also found that the electrical conductivity of the GDSP was more than 6-fold higher than that of the SiO2@PANI core–shell microspheres (SP) using ammonium persulfate (APS) as oxidizing agent. The electrochemical behavior and electro-catalytic activity of GDSP modified carbon paste electrode (CPE) was characterized by cyclic voltammetry. The GDSP modified CPE is shown to be a better surface for the electrooxidation of ascorbic acid (AA) than SP modified CPE in phosphate buffer solution of pH 7. The anodic peak potential of AA shifts obviously from 610mV at bare CPE to 380mV at the GDSP-modified CPE with greatly enhanced current response. Amperometry was carried out to determine the concentration of AA at 400mV, and a good linear concentration range from 0.15 to 8mM was found.

Influence of Surface Adsorption on the Interfacial Electron Transfer of Flavin Adenine Dinucleotide and Glucose Oxidase at Carbon Nanotube and Nitrogen-Doped Carbon Nanotube Electrodes

The adsorption of flavin adenine dinucleotide (FAD) and glucose oxidase (GOx) onto carbon nanotube (CNT) and nitrogen-doped CNT (N-CNT) electrodes was investigated and found to obey Langmuir adsorption isotherm characteristics. The amount adsorbed and adsorption maximum are dependent on exposure time, the concentration of adsorbate, and the ionic strength of the solution. The formal potentials measured for FAD and GOx are identical, indicating that the observed electroactivity is from FAD, the redox reaction center of GOx. When glucose is added to GOx adsorbed onto CNT/N-CNT electrodes, direct electron transfer (DET) from enzyme-active FAD is not observed. However, efficient mediated electron transfer (MET) occurs if an appropriate electron mediator is placed in solution, or the natural electron mediator oxygen is used, indicating that GOx is adsorbed and active on CNT/N-CNT electrodes. The observed surface-confined redox reaction at both CNT and N-CNT electrodes is from FAD that either specifically adsorbs from solution or adsorbs from the holoprotein subsequently inactivating the enzyme. The splitting of cathodic and anodic peak potentials as a function of scan rate provides a way to measure the heterogeneous electron-transfer rate constant (k(s)) using Laviron's method. However, the measured k(s) was found to be under ohmic control, not under the kinetic control of an electron-transfer reaction, suggesting that k(s) for FAD on CNTs is faster than the measured value of 7.6 s(-1).

Thermoresponsive and Redox Behaviors of Poly(N-isopropylacrylamide)-Based Block Copolymers Having TEMPO Groups as Their Side Chains

Thermoresponsive and redox-active block copolymers having 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties have been synthesized by using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique.N-Isopropylacrylamide (NIPAAm) and 2,2,6,6-tetramethylpiperidyl methacrylate (TEMPMA) monomers were copolymerized stepwise under RAFT polymerization conditions to afford the thermoresponsive block copolymers, PNIPAAm-block-PTEMPMA and PNIPAAm-block-PTEMPMA-block-PNIPAAm. Oxidation of tetramethylpiperidine groups in the copolymers successfully afforded the corresponding TEMPO-containing block copolymers. The resulting triblock copolymer was found to be thermoresponsive showing lower critical solution temperature (LCST) at 34∘C in its aqueous solution. Redox behavior of the resulting copolymer was observed by cyclic voltammetry. The potential of anodic current peak changed below and above the LCST of the block copolymer. These results indicate that the phase transition of thermoresponsive polymer influences the redox potential of TEMPO moieties.

Electrochemical studies of two diphenols isomers at graphene nanosheet–poly(4-vinyl pyridine) composite modified electrode

Abstract A voltammetric sensor for hydroquinone (HQ) and catechol (CC) was developed. This was realized by modifying a glassy carbon electrode with composite film of graphene nanosheet and poly(4–vinylpyridine) (GR–P4VP/GCE). The smaller peak potential separation (ΔEp) of the GR-P4VP/GCE indicates the electrode process is very reversible as a result of increase in kinetics of electron transfer as and when P4VP was present in the modified electrode as compared to the GR/GCE and bare GCE. The proposed electrode has displayed a synergistic effect of P4VP and GR on the electrocatalytic oxidation of CC and HQ in sodium sulphate buffer solution (pH 2.5). The anodic peak potential, Epa, of both were clearly resolved in either cyclic voltammetry or differential pulse voltammetry which made simultaneous determination of both compounds possible. The GR–P4VP/GCE has exhibited excellent sensitivities in the measurement of HQ and CC with detection limits of 8.1 nM and 26 nM, respectively. The GR–P4VP/GCE developed was not interfered by traditional interferences, viz. phenol, nitrophenol, aminophenols, bisphenol A and chlorophenols. The GR–P4VP/GCE was successfully applied for simultaneous detection of spikes HQ and CC in tap water and lake water with encouraging results.

Nano-Cu/PSA III modified glassy carbon electrode for simultaneous determination of ascorbic acid, dopamine and uric acid

Cu nanoparticles (nano-Cu)–poly(sulfonazo III) (PSA III) modified glassy carbon electrode (nano-Cu–PSA III/GCE) had been fabricated and successfully used for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The performance of the nano-Cu–PSA III/GCE towards the electrooxidation of AA, DA and UA had been investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results showed that the modified electrode not only exhibited excellent electrocatalytic activity toward the electrooxidation of AA, DA and UA in a phosphate buffer solution (PBS, pH 4.0), but also could separate the overlapped oxidation waves of these species at the bare GCE into three sharp and strong oxidation peaks at 0.23V, 0.37V and 0.54V using CV and 0.16V, 0.33V and 0.49V using DPV, corresponding to the electrooxidation of AA, DA and UA, respectively. The separations of anodic peak potentials for AA–DA, DA–UA and AA–UA at nano-Cu–PSA III/GCE are large enough for the simultaneous detection of AA, DA and UA. Under the optimum conditions, the linear calibration curves were obtained over the range of 0.30–730, 0.02–65 and 0.25–107μmolL−1 with detection limits of 0.15, 0.01 and 0.10μmolL−1 for AA, DA and UA (S/N=3), respectively. Due to the good selectivity and high sensitivity, nano-Cu–PSA III/GCE had been used for the simultaneous determination of AA and UA in urine samples and DA in human serum samples with satisfactory results.

Electrochemical determination of calcium channel blocker drugs using multiwall carbon nanotube-modified glassy carbon electrode

Abstract Background Calcium channel blockers belonging to the dihydropyridine family have been used as a potent arterial vasodilator in the management of angina and cardiovascular diseases. In the design of glassy carbon electrode coatings for the study of the same, multiwall carbon nanotubes (MWCNT) are favored. They are known for the reduction and oxidation of electroactive species towards cathodic and anodic direction with the simultaneous enhancement of the peak current. Results The MWCNT-modified glassy carbon electrode exhibited a sharp anodic peak potential at around at 0.5 V for amlodipine (AMLD) andnimodipine (NIMD), and 0.4 V for felodipine (FELD) in the cyclic voltammograms. The antihypertensive drugs were determined using a simple two-step procedure developed which comprised a preconcentration step followed by the differential pulse stripping voltammetric quantification. Concentration calibrations were linear within the range from 0.01 to 0.3 μg/mL for AMLD and FELD, and 0.025 to 0.3 μg/mL for NIMD. Conclusion The lower limit detection (LOD) was found to be very low on modified electrode. The LOD is 0.005 μg/mL for AMLD and FELD, and 0.01 μg/mL for NIMD. The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of antihypertensive drugs leading to a remarked improvement in sensitivity. An electrochemical sensor featuring the MWCNT-modified electrode was applied successfully as the result for the calcium channel blocker determination in pharmaceutical samples.

Electrochemical characterization of bioactive hydroxyxanthones by cyclic voltammetry

The present study reports the electrochemical behavior of several phenolic and catecholic-substituted 2,3-diarylxanthones on a glassy carbon electrode, challenged by cyclic voltammetry at different pH values (4.0, 7.4, and 11.0). Higher pH values required lower anodic and cathodic peak voltages. The oxidation of catecholic groups occurred at lower peak potentials in a reversible and pH dependent manner. Anodic peak potentials appeared at higher pH values and were attributed to the electrochemically irreversible oxidation of the phenolic groups. The number and position of hydroxyl substituents were the determinants for the electrochemical behavior and found to correlate with the scavenging activity for reactive oxygen (ROS) and nitrogen species (RNS). A xanthone with two catechol units presented the lowest anodic potential voltage (Epa=0.15V) and proved to be the most effective ROS and RNS scavenger.

Novel nanostructured electrochemical sensor for voltammetric determination of N-acetylcysteine in the presence of high concentrations of tryptophan

A carbon paste electrode chemically modified with multiwall nanotubes and ethynylferrocene (ETFc) was used as a selective and sensitive electrochemical sensor for the determination of minor amounts of N-acetylcysteine (N-AC) in the presence of a high concentration of tryptophan (Trp). Square wave voltammetry (SWV) of N-AC at the modified electrode exhibited linear dynamic range with a detection limit (3 s) of 0.08 μmol L−1. The separations of anodic peak potentials of N-AC and Trp reached 400 mV using SWV. With good selectivity and sensitivity, the present method provides a simple method for selective detection of N-AC in real samples such as drug and urine.

Highly sensitive and simultaneous determination of ascorbic acid and rutin at an acetylene black paste electrode coated with cetyltrimethyl ammonium bromide film

A simple and highly sensitive electrochemical method for the simultaneous and quantitative detection of ascorbic acid (AA) and rutin was developed, based on an acetylene black paste electrode coated with cetyltrimethyl ammonium bromide film (denoted as CTAB/ABPE). In 0.1molL−1 HCl aqueous solution, the prepared modified electrode showed higher accumulation efficiency toward AA and rutin compared with bare ABPE, and significantly enhanced the peak currents of AA and rutin. The difference of the anodic peak potentials between AA and rutin was about 350mV, which is large enough to determine AA and rutin individually and simultaneously. The electrochemical behaviors of AA and rutin were carefully investigated with the electrochemical parameters calculated. Under optimized conditions, the linear calibration ranges were 2.0×10−6M to 1.0×10−3M for AA and 6.0×10−9M to 1.0×10−5M for rutin, and the detection limits (S/N=3) were 1.0×10−6M and 4.0×10−9M, respectively. This modified electrode was applied to direct simultaneous determination of AA and rutin in the selected pharmaceutical samples without previous chemical or physical separations. Moreover, the CTAB/ABPE offers some advantages including low cost, facility of construction, good reproducibility and high stability.

An electrochemical ascorbic acid sensor based on palladium nanoparticles supported on graphene oxide

In this study, an electrochemical ascorbic acid (AA) sensor was constructed based on a glassy carbon electrode modified with palladium nanoparticles supported on graphene oxide (PdNPs-GO). PdNPs with a mean diameter of 2.6nm were homogeneously deposited on GO sheets by the redox reaction between PdCl42− and GO. Cyclic voltammetry and amperometric methods were used to evaluate the electrocatalytic activity towards the oxidation of AA in neutral media. Compared to a bare GC or a Pd electrode, the anodic peak potential of AA (0.006V) at PdNPs-GO modified electrode was shifted negatively, and the large anodic peak potential separation (0.172V) of AA and dopamine (DA), which could contribute to the synergistic effect of GO and PdNPs, was investigated. A further amperometric experiment proved that the proposed sensor was capable of sensitive and selective sensing of AA even in the presence of DA and uric acid. The modified electrode exhibited a rapid response to AA within 5s and the amperometric signal showed a good linear correlation to AA concentration in a broad range from 20μM to 2.28mM with a correlation coefficient of R=0.9991. Moreover, the proposed sensor was applied to the determination of AA in vitamin C tablet samples. The satisfactory results obtained indicated that the proposed sensor was promising for the development of novel electrochemical sensing for AA determination.

Electrochemical oxidation of hydantoins at glassy carbon electrode

The electrochemical behavior of three new hydantoin derivatives; 5-benzylideneimidazolidine-2,4-dione (NBI), 5-(2hydroxybenzylidene)imidazolidine-2,4-dione (HBI), and 5-(4methoxybenzylidene)imidazolidine-2,4-dione (MBI) has been examined over the pH range 1.2–12.8 via cyclic, differential pulse and square wave voltammetry at the surface of glassy carbon electrode. The results of anodic peak potential shift as a function of pH revealed that NH moiety is oxidized by a 1e−, 1H+ diffusion controlled process. The quasi-reversible nature of the redox process was evidenced by Epa−Epa/2 values, scan rate variation of peak potential, heterogenous electron transfer rate constant and inequality of the components of total current. The pKa values of the studied hydantoins were found in good agreement with the reported related structures and varied in the sequence: MBI>NBI>HBI. The variation of diffusion coefficients also followed the same order. Based upon the results obtained, oxidation mechanisms were proposed with the objective of highlighting important aspects of structure–activity relationships and understanding the unexplored pathways by which this class of compounds exert its biochemical actions.

Synthesis and Electrochemical Properties of a Novel Aniline-Based Polyorganodisulfide

From facile preparation method and available low-cost raw materials, we have synthesized a novel kind of aniline-based organodisulfide bis(2-aminobenzyl) disulfide (OABD) and its homopolymer (POABD). The polymer POABD was characterized by Fourier transform infrared spectroscopy (FT-IR) and cyclic voltammetry. The cyclic voltammetry tests reveal that the redox of the S-S bonds behavior in the anodic and cathodic peak potentials differences for poly(bis(2-aminobenzyl) disulfide) is 70 mV. The results indicated that poly(bis(2-aminobenzyl) disulfide) has an excellent electrochemical reversibility.

Magnetization of conductive polymer polyaniline during the electro-oxidation in the presence of chloranil

In the cyclic voltammogram measured using a polyaniline (PANI) coated electrode in the presence of chloranil (CHR), the anodic peak potential of PANI was directly proportional to log[CHR]. A new absorption shoulder was evident at around 450nm in the UV–visible absorption spectrum of PANI after the electro-oxidation. These facts implied that PANI incorporated CHR. The measurements of the ESR spectra and the magnetic susceptibility (χg) of the PANI incorporating CHR revealed that the incorporation magnetized PANI. Although no ferromagnetic property was observed for the PANI, it had an unusual paramagnetic property because χg was not inversely proportional to temperature.

Electrochemical behavior of an antiviral drug acyclovir at fullerene-C60-modified glassy carbon electrode

Electrochemical oxidation of acyclovir at fullerene-C60-modified glassy carbon electrode has been investigated using cyclic and differential pulse voltammetry. In pH 7.4 phosphate buffer, acyclovir showed an irreversible oxidation peak at about 0.96V. The cyclic voltammetric results showed that fullerene-C60-modified glassy carbon electrode can remarkably enhance electrocatalytic activity towards the oxidation of acyclovir. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the acyclovir determination by differential pulse voltammetry. Effects of anodic peak potential (Ep/V), anodic peak current (Ip/μA) and heterogeneous rate constant (k0) have been discussed. Under optimized conditions, the concentration range and detection limit were 9.0×10−8 to 6.0×10−6M and 1.48×10−8M, respectively. The proposed method was applied to acyclovir determination in pharmaceutical samples and human biological fluids such as urine and blood plasma as a real sample. This method can also be employed in quality control and routine determination of drugs in pharmaceutical formulations.

Proton-Coupled Electron-Transfer Mechanism for the Radical Scavenging Activity of Cardiovascular Drug Dipyridamole

Dipyridamole (DIP) is a well-known pharmaceutical drug used as a coronary vasodilator and anti-platelet agent in clinics for treating several cardiovascular diseases. Primarily, the therapeutic effects of the drug are attributed to its antioxidant potency. In this research, we aim to declare the unknown antioxidant mechanism of DIP as well as its potent chain-breaking antioxidant activity in polar aqueous medium inside the cells, using different experimental methods and theoretical quantum calculations. Data demonstrated the higher antioxidant capacity of DIP against ROS and free radicals in polar cell's interior. DIP is capable of generating long living and noninvasive DIP• radicals in oxidant condition that leads to an effective “chain-breaking antioxidant” activity. Quantum computational data indicated that DIP antioxidant has more favorable ionization potential than trolox which means DIP has higher antioxidant activity. Also, data showed that the direct hydrogen-transfer is not a favorable process to construct DIP• because of high barrier energy, though electron-transfer process can more easily to produce DIP•+ with the lowest barrier energy. Altogether, the electron donating potency of DIP to reduce ferric ion, having the low anodic oxidation peak potential, producing long lived stable DIP• radicals and protecting myoblast cells from oxidation, proposed the excellent “chain-breaking antioxidant” potency via electron-transfer mechanism of this vasodilator DIP drug in polar aqueous medium.

A symmetric oxo-centered trinuclear chloroacetato bridged iron(III) complex: Structural, spectroscopic and electrochemical studies

An oxo-centred, carboxylate bridged trinuclear iron(III) complex [Fe3(μ3-O)(O2CCH2Cl)6(H2O)3]ClO4·9H2O (1·9H2O) has been synthesized and characterized on the basis of X-ray crystallography, elemental analysis, cyclic voltammetric, UV–vis and IR spectroscopic techniques. Molecular structure has been established by X-ray diffraction analysis and reveals that the complex 1·9H2O crystallizes in the rhombohedral space group R3 with a=18.0070(6)Å, b=18.0070(6)Å, c=9.7962(5)Å, α=β=90.00° and γ=120.00°. In the highly symmetric trinuclear structure, three iron(III) atoms occupy vertices of equilateral triangle and exhibits a quasi-reversible one-electron reduction at E½=+0.337V vs Ag/AgCl (ΔEp=0.079V) due to the [Fe3(μ3-O)(O2CCH2Cl)6(H2O)3]+/[Fe3(μ3-O)(O2CCH2Cl)6(H2O)3] couple. In addition, ascending difference between cathodic and anodic peak potentials (ΔEp) with the increasing scan rate confirmed the reduction wave to be quasi-reversible.

UV-photoelectron spectroscopy of 1,2- and 1,3-azaborines: a combined experimental and computational electronic structure analysis.

We present a comprehensive electronic structure analysis of structurally simple BN heterocycles using a combined UV-photoelectron spectroscopy (UV-PES)/computational chemistry approach. Gas-phase He I photoelectron spectra of 1,2-dihydro-1,2-azaborine 1, N-Me-1,2-BN-toluene 2, and N-Me-1,3-BN-toluene 3 have been recorded, assessed by density functional theory calculations, and compared with their corresponding carbonaceous analogues benzene and toluene. The first ionization energies of these BN heterocycles are in the order N-Me-1,3-BN-toluene 3 (8.0 eV) < N-Me-1,2-BN-toluene 2 (8.45 eV) < 1,2-dihydro-1,2-azaborine 1 (8.6 eV) < toluene (8.83 eV) < benzene (9.25 eV). The computationally determined molecular dipole moments are in the order 3 (4.577 D) > 2 (2.209 D) > 1 (2.154 D) > toluene (0.349 D) > benzene (0 D) and are consistent with experimental observations. The λ(max) in the UV-vis absorption spectra are in the order 3 (297 nm) > 2 (278 nm) > 1 (269 nm) > toluene (262 nm) > benzene (255 nm). We also establish that the measured anodic peak potentials and electrophilic aromatic substitution (EAS) reactivity of BN heterocycles 1-3 are consistent with the electronic structure description determined by the combined UV-PES/computational chemistry approach.

Electrochemistry of carboxylated nanodiamond films

The electrochemical behavior of nanodiamond (ND) film functionalized with carboxylic acid groups was studied systematically on a glassy carbon (GC) electrode. One stable redox couple corresponding to the carboxylic acid group was observed. At the scan rate of 0.1 V/s, the cathodic and anodic peak potentials were ∼0.093 V and 0.088 V (vs. Ag/AgCl), respectively. The carboxylic acid groups on the ND surface were reduced to CH2OH via a four electron redox process. The ND film modified electrode showed favorable electrocatalytic behavior toward the oxidation as well as the reduction of biomolecules, such as tryptophan and nicotinamide adenine dinucleotide.