Anodic Peak Potentials Research Articles

Interesting Electronic Interaction between Polyaniline and Chloranil

Reduced polyaniline (PANI) showed a Nernstian response to dissolved chloranil (CHR), linear electrode potential-log[CHR] relationship. The anodic peak potential (Epa) of PANI in the cyclic voltammogram was directly proportional to log[CHR], i.e. linear Epa-log[CHR] relationship. These linear relationships and the fact that the new absorption shoulder was evident at around 450 nm in the UV-visible absorption spectra implied that PANI incorporated with CHR. The measurements of the electron spin resonance (ESR) spectra and the magnetic susceptibility (χg) of the PANI incorporating CHR revealed that the incorporation magnetized PANI. No magnetic hysteresis loop was observed for the PANI, and it showed no ferromagnetic property. However, it had an unusual paramagnetic property because χg was not inversely pro-portional to temperature. In addition, from the ESR spectra, the polaron species (cation radicals) of PANI are delocalized along the entire polymeric backbones.

Determination Of Procymidone in Apple by Square-Wave Voltammetry

A low cost electrochemical method was developed for the determination of trace-level of procymidone based on the properties of glassy carbon electrode (GCE). The electrochemical behavior of procymidone studied by cyclic voltammetry (CV) suggests that its oxidation occurs via a one irreversible electron transfer vs. Ag|AgCl, KCl 3 M reference electrode. The anodic peak potential for procymidone oxidation at GCE is about +1.38 V in a supporting electrolyte solution composed of NaOH 0.5 mol L-1. A combination of GCE with square-wave voltammetric analysis resulted in a sensitive and selective electrochemical method for determination of procymidone pesticide in apple.

Voltammetric behavior of theophylline and its determination at multi-wall carbon nanotube paste electrode

The voltammetric behavior of theophylline was investigated using cyclic and differential-pulse voltammetric techniques. The cyclic voltammetric results indicate that multi-wall carbon nanotube paste electrode can remarkably enhance electrocatalytic activity toward the oxidation of theophylline in pH 3.0 phosphate buffer solution than the carbon paste electrode. The oxidation of theophylline was observed to be a two-electron process, irreversible with diffusion character. Effects of anodic peak potential (Ep), anodic peak current (Ip) and heterogeneous rate constant (ko) have been discussed. Under optimal conditions, the anodic peak current was proportional to theophylline concentration in the range of 2.0×10−6 to 1.5×10−4M with a detection limit of 1.97×10−8M using differential pulse voltammetry. The proposed method was employed to determine theophylline in pharmaceutical formulations and urine as a real sample.

Gold nanoparticles on a thiol-functionalized silica network for ascorbic acid electrochemical detection in presence of dopamine and uric acid

A simple preparation methodology able to stabilize gold nanoparticles and to obtain an electrode which detects ascorbic acid, uric acid, and dopamine by different techniques is presented. A 3-mercaptopropyl-functionalized silica network was synthesized using the sol–gel method. Gold nanoparticles (nAu) were immobilized on the material at synthesis by adding a sol of these previously prepared particles to the reaction mixture. The electrochemical behavior of the SiO2/MPTS/Au carbon paste electrode was studied using cyclic voltammetry in the presence of a hexacyanoferrate probe molecule. The presence of nAu in the functionalized silica network changes the electrochemical characteristics of the material, favoring the electron transfer process of this complex ion. The SiO2/MPTS/Au electrode was proven to be an efficient tool in the simultaneous determination of ascorbic acid (H2AA), dopamine (DA), and uric acid (UA) using square wave voltammetry techniques. With the nAu on the electrode, an increase in the peak current related to the redox process of the H2AA, DA, and UA was observed. The separations of the anodic peak potentials between DA/H2AA and UA/H2AA were 310 and 442 mV, respectively. The results obtained show that the SiO2/MPTS/Au electrode can be used in the simultaneous determination of H2AA, DA, and UA.

Iodide-induced adsorption of lead(II) ion on a glassy carbon electrode modified with ferroferric oxide nanoparticles

Spherical Fe3O4 nanoparticles (NPs) were prepared by hydrothermal synthesis and characterized by scanning electron microscopy and X-ray diffraction. A glassy carbon electrode was modified with such NPs to result in a sensor for Pb(II) that is based on the strong inducing adsorption ability of iodide. The electrode gives a pair of well-defined redox peaks for Pb(II) in pH 5.0 buffer containing 10 mM concentrations of potassium iodide, with anodic and cathodic peak potentials at −487 mV and −622 mV (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.10 to 44 nM, and the detection limit is 40 pM at an SNR of 3. The sensor exhibits high selectivity and reproducibility.

Simultaneous Voltammetric Determination of Ascorbic Acid and Sulfite in Beverages Employing a Glassy Carbon Electrode Modified with Carbon Nanotubes within a Poly(Allylamine Hydrochloride) Film

AbstractA glassy carbon electrode modified with functionalized multiwalled carbon nanotubes within a poly(allylamine hydrochloride) film was used for the simultaneous voltammetric determination of ascorbic acid and sulfite. The anodic peak potentials of ascorbic acid and sulfite oxidation at a MWCNTs‐PAH/GCE were found to be 0.005 V and 0.327 V (vs. Ag/AgCl (3.0 M KCl)), respectively by cyclic voltammetry, whereas at a GCE were 0.278 V and 0.722 V. Using linear sweep voltammetric technique, the obtained analytical curves were linear in the ascorbic acid and sulfite concentration range from 5.0 to 200.0 µM, with detection limits of 3.0 and 3.5 µM for ascorbic acid and sulfite, respectively. The proposed method was successfully used for the simultaneous determination of ascorbic acid and sulfite in fruit juices.

Synthesis, crystal structure, antibacterial activities, and electrochemical studies of new N,N′-polymethylene bis-sulfonamides

Abstract Four disulfonamide derivatives (C 2 H 5 ·SO 2 ·NH) 2 (CH 2 ) n ( n = 2, 3, 4, 5) were synthesized and characterized by FTIR, 1 H NMR, 13 C NMR, HETCOR, LCMS and elemental analysis. Ethanesulfonamide-N,N′-pentamethylene bis was also characterized by X-ray single crystal diffraction measurement. The electrochemical characteristics of the disulfonamide derivatives were performed by cyclic voltammetry and chronoamperometry. 1 H and 13 C NMR chemical shifts of the compounds were calculated by using DFT/B3LYP methods with a 6-311++G (d,p) basis set. Antibacterial activity and the structural relationship of the compounds showed that activity decreases proportionately to the increasing length of the carbon chain between NH groups, log P values, hydration energy and molecular volumes. Anodic peak potentials and HOMO values do not correlate with the activity, but reduction potential and LUMO decrease weakly with increasing activity.

Voltammetric oxidation and determination of loop diuretic furosemide at a multi-walled carbon nanotubes paste electrode

Electrochemical oxidation of loop diuretic furosemide (4-chloro-2-(furan-2-ylmethylamino)-5-sulfamoylbenzoic acid) was studied in 5.0 pH with 0.04 M Britton–Robinson buffer as supporting electrolyte at 25 ± 0.1 °C at a multi-walled carbon nanotubes-paraffin oil paste electrode (CNTPE) using cyclic and differential-pulse voltammetric (DPV) techniques. The electrochemical process was observed to be adsorption controlled, irreversible and involving two-electron oxidation. Effects of anodic peak potential ( E pa), anodic peak current ( I pa) and heterogeneous rate constant ( k 0) have been discussed. Under optimal conditions, the peak current was proportional to furosemide concentration in the range of 8.0 × 10 −6 to 2.0 × 10 −4 M with a detection limit of 2.9 × 10 −7 M by differential pulse voltammetry. A differential pulse voltammetric method with good precision and accuracy was developed for the determination of furosemide in pharmaceutical formulations and urine as a real sample.

Electrocatalytic Oxidation of Ascorbic Acid Using a Poly(aniline-co-m-ferrocenylaniline) Modified Glassy Carbon Electrode

A poly(aniline-co-m-ferrocenylaniline) was successfully synthesized on a glassy carbon electrode (GCE) by electrochemical copolymerization using a scan potential range from −0.3 to +0.9 V (vs. Ag/AgCl) in 0.5 M H2SO4 containing 30% acetonitrile (ACN), 0.1 M aniline (Ani) and 0.005 M m-ferrocenyaniline (m-FcAni). The field emission scanning electron microscope (FESEM) and electrochemical methods were used to characterize the poly(Ani-co-m-FcAni) modified electrode. The poly(Ani-co-m-FcAni)/GCE exhibited excellent electrocatalytic oxidation of ascorbic acid (AA) in citrate buffer solution (CBS, pH 5.0). The anodic peak potential of AA was shifted from +0.55 V at the bare GCE to +0.25 V at the poly(Ani-co-m-FcAni)/GCE with higher current responses than those seen on the bare GCE. The scan number at the 10th cycle was selected as the maximum scan cycle in electrochemical polymerization. The limit of detection (LOD) was estimated to be 2.0 μM based on the signal-to-noise ratio (S/N = 3). The amperometric responses demonstrated an excellent selectivity for AA determination over glucose (Glu) and dopamine (DA).

Thermodynamic and structural study of phenanthroline derivative ruthenium complex/DNA interactions: Probing partial intercalation and binding properties

The binding of [Ru(PDTA-H 2)(phen)]Cl (PDTA = propylene-1,2-diaminetetra-acetic acid; phen = 1,10 phenanthroline) with ctDNA (=calf thymus DNA) has been investigated through intrinsic and induced circular dichroism, UV–visible absorption and fluorescence spectroscopies, steady-state fluorescence, thermal denaturation technique, viscosity and electrochemical measurements. The latter indicate that the cathodic and anodic peak potentials of the ruthenium complex shift to more positive values on increasing the DNA concentration, this behavior being a direct consequence of the interaction of both the reduced and oxidized form with DNA binding. From spectrophotometric titration experiments, the equilibrium binding constant and the number of monomer units of the polymer involved in the binding of one ruthenium molecule (site size) have been quantified. The intrinsic circular dichroism (CD) spectra show an unwinding and a conformational change of the DNA helix upon interaction of the ruthenium complex. Quenching process, thermal denaturation experiments and induced circular dichroism (ICD) are consistent with a partial intercalative binding mode.

Ferrocene-modified pyrimidinyl acyl-thiourea derivatives: Synthesis, structures and electrochemistry

Two ferrocene-modified pyrimidinyl acyl-thiourea derivatives, N-ferrocenoyl- N′-(2-pyrimidinyl) thiourea 1 and N-ferrocenoyl- N′-(5-pyrimidinyl) thiourea 2 were prepared from the reactions of ferrocenoyl isothiocyanate with 2-aminopyrimidine or 5-aminopyrimidine, respectively. Both of the new compounds were characterized by 1H NMR, 13C NMR, IR, elemental analyses and single-crystal X-ray diffraction. Comparing with ferrocene, compounds 1 and 2 show red-shift in the absorption peaks and increasing anodic peak potentials ( E pa ) values in the cyclic voltammetry studies. Furthermore, the electrochemical data of compounds 1 and 2 correspondingly exhibit one-electron quasi-reversible and reversible electrochemical redox behaviors. In the solid-state, compound 1 forms a ladder-like assembly by hydrogen-bonding, whereas, compound 2 is assembled into two-dimensional network structure through hydrogen-bonding and unusual intermolecular O⋯π interactions between O-atoms of the carbonyl units and the cyclopentadienyl rings.

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.

Chiral conducting surfaces based on the electropolymerization of 3,4-ethylenedioxythiophene

The synthesis and electrochemical characterization of d- and l-proline functionalized monothiophenes are reported. Both monomers 2L and 2D showed anodic peak potentials of 1.86 V vs. Fc +/Fc and their electropolymerization affords polymers that exhibit poor stability on platinum electrodes. However, the electrochemical copolymerization using cyclic voltammetry of 2L or 2D in the presence of EDOT gives polymeric films at the surface of the electrode with specific chirality. The E 1/2 of the copolymers was found to be 0.38 V vs. Fc +/Fc. The copolymers display excellent electrochemical stability and adhesion properties on the surface of platinum and ITO electrodes. Moreover, the films also undergo a reversible color change between their doped (blue-green) and undoped (blue-brown) states. Incorporation of the chiral pendant group was confirmed through the appearance of characteristic C O stretching absorptions in the IR spectra of the copolymers.

Electrochemical investigation of a glassy carbon electrode modified with carbon nanotubes decorated with (poly)crystalline gold

Multiwalled carbon nanotubes with nanosized sputtered gold were used to modify a glassy carbon electrode (GCE). The substrate was characterized by scanning electron microscopy (SEM), X-ray diffraction, cyclic voltammetry and amperometry. SEM micrographs indicated an uniform coverage of the carbon nanotubes with nanosized (poly)crystalline gold. Cyclic voltammetry reveals that peak separation of the unmodified GCE in the presence of 1 mM ferricyanide is 131 mV, but 60 mV only for the modified GCE. In addition, the oxidation of NADH (1 mmol L−1 solution) begins at negative potentials (around −100 mV vs. Ag/AgCl), and the anodic peak potential (corresponding to the irreversible oxidation of NADH) is found at +94 mV. The effect of pH on the electrocatalytic activity was studied in the range from 5.4 to 8.0. The relationship between the anodic peak potential and the pH indicated a variation of −33.5 mV/pH which is in agreement with a two-electron and one-proton reaction mechanism. Amperometry, performed at either −50 or +50 mV vs. an Ag/AgCl reference electrode, indicates that the modified electrode is a viable amperometric sensor for NADH. At a working potential of +50 mV, the response to NADH is linear in the concentration range from 1 to 100 μmol L−1, with an RSD of 6% (n = 4).

Glassy Carbon Electrode Modified with Functionalized Carbon Nanotubes Within a Poly(allylamine hydrochloride) Film for the Voltammetric Determination of Sulfite in Foods

AbstractThe performance of a glassy carbon electrode modified with functionalized multiwalled carbon nanotubes within a poly(allylamine hydrochloride) film (GCE/PAH/MWCNTs) for the voltammetric determination of sulfite in food samples is described. The anodic peak potential for sulfite oxidation at a GCE/PAH/MWCNTs was 0.41 V whereas at GCE/PAH and GCE, the peak potentials were 0.96 and 0.89 V, respectively. Using square‐wave voltammetric technique, the obtained analytical curve was linear in the sulfite concentration range from 1.1×10−5 to 3.9×10−4 M, with a detection limit of 4.2 µM. The electrode was successfully used to determinate sulfite in vinegar, pickle water, coconut water, and shredded coconut.

Spherical clusters of β-Ni(OH) 2 nanosheets supported on nickel foam for nickel metal hydride battery

Spherical clusters of Ni(OH) 2 nanosheets are directly grown on skeletons of nickel foam via a facile template-free spontaneous growth method. The obtained electrode ( β-Ni(OH) 2/Ni-foam) is characterized by X-ray diffractometry, scanning and transmission electron microscopy and thermal analysis. Results show that Ni(OH) 2 has a β-phase structure and presents on the nickel foam skeleton mostly as spherical clusters with a diameter of ∼10 μm. The spheres are composed of nanosheets with thickness of ∼60 nm, width of ∼230 nm and length up to ∼2 μm, and the nanosheets are assembled by nanoparticles with diameter of ∼20 nm. The electrochemical performance of the β-Ni(OH) 2/Ni-foam electrode is evaluated by cyclic voltammetry and galvanostatic charge–discharge tests. The difference between the oxygen evolution reaction onset potential and the anodic peak potential for this electrode (∼100 mV) is larger than that for β-Ni(OH) 2 nanosheets and nanotubes powder electrode (∼65–77 mV) and much larger than that for commercial spherical β-Ni(OH) 2 powder electrode (∼25–47 mV), indicating that the β-Ni(OH) 2/Ni-foam electrode can be fully charged. The specific discharge capacity of β-Ni(OH) 2 in the β-Ni(OH) 2/Ni-foam electrode reaches 275 mAh g −1, which is close to the theoretical value, lower than that of β-Ni(OH) 2 nanotubes (315 mAh g −1), but higher than that of nanosheets (219.5 mAh g −1), commercial micrometer grade spherical powders (265 mAh g −1) and microtubes (232.4 mAh g −1).

Voltammetric Determination of Hemoglobin Using a Pencil Lead Electrode

AbstractIn this paper the electrochemical behavior of hemoglobin (Hb) immobilized on a pencil lead electrode (PLE) was investigated. Immobilization of Hb on the pencil lead electrode was performed by nonelectrochemical and electrochemical methods. In phosphate buffer solution with pH 7.0 Hb showed a pair of well‐defined and nearly reversible redox waves (the anodic and cathodic peak potentials are located at −0.18 V and −0.22 V, respectively). The dependence of the anodic peak potential (Epa) on the pH of the buffer solution indicated that the conversion of HbFe(III)/HbFe(II) is a one‐electron‐transfer reaction process coupled with one‐proton‐transfer. In addition the effect of scan rate on peak currents and peak separation potential was investigated and electrochemical parameters such as α and ks were calculated. In the second part of this work, the ability of the electrode for determination of Hb concentration was investigated. The results showed a linear dynamic range from 0.15 to 2 µM and a detection limit of 0.11 µM. The relative standard deviation is 4.1 % for 4 successive determinations of a 1 µM Hb solution.

Preparation of Polyaniline Nanotubes and its Electrocatalytic Behaviors

In this paper, we have successfully synthesized polyaniline nanotubes by using chemical oxidation polymerization. This synthesis is simple and an effective way to prepare one-dimensional polymer nanotubes. By transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR), the morphology and physical structures of the as-prepared products were characterized. By cyclic voltammetry we studied the electrocatalytic activity of polyaniline nanotube modified glassy carbon electrode on ascorbic acid. The results show that the polyaniline nanotube modified electrode has excellent electrocatalytic activity on ascorbic acid. Compared with those of the bare glassy carbon electrode, the anodic peak potential of ascorbic acid shifts negatively 0.212 V on the modified electrode, and the anodic peak current increases 43 %. And the concentration of ascorbic acid shows a good linear relation at the range of 1.0×10-5~ 0.1 M with the minimum detection limit of 1.0 × 10-6M.

Determination of tryptophan using electrode modified with poly(9-aminoacridine) functionalized multi-walled carbon nanotubes

Two new kinds of electrochemical sensors were prepared using glassy carbon electrodes modified with poly(9-aminoacridine) (PAA) and PAA-functionalized multi-walled carbon nanotubes (PAA-MWCNTs) for the determination of tryptophan (Trp) in the presence of tyrosine (Tyr). The electrocatalytic response of the modified electrodes towards electrooxidation of Trp and Tyr was investigated and compared by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface of the modified electrodes was characterized using CV, scanning electron microscopy, scanning-tunneling microscopy and scanning-tunneling spectroscopy. The anodic peak current of the electrooxidation of Trp on PAA-MWCNTs electrode was 5.5-fold increased comparing to PAA modified electrode. The anodic peak potential of Trp is shifted about 0.12 V to more negative value indicated that PAA-MWCNTs electrode has better electrocatalytic activity for electrooxidation of Trp. Furthermore, the anodic peak current which was attributed to the electrooxidation of Trp did almost not change with the addition of Tyr in buffer solution at pH 3.5. Besides this, at pH 7.4, the anodic peak current obtained at 0.6 V increased as the concentration of Tyr was increased. The results demonstrate that PAA-MWCNTs electrode can be used for the simultaneous determination of Trp and Tyr by adjusting the pH of the solution.

Electrochemical response of ascorbic and uric acids at organoclay film modified glassy carbon electrodes and sensing applications

A naturally occurring Cameroonian smectite clay has been grafted with trimethylpropylammonium groups and the resulting organoclay deposited as thin film onto a glassy carbon electrode (GCE) surface. It was then exploited as a suitable matrix for the accumulation and the electrochemical detection of ascorbic acid (AA) and uric acid (UA). Cyclic voltammetry revealed an increase in oxidation peak responses along with a negative shift of the corresponding anodic peak potential for both AA and UA species when using the organoclay coated GCE in comparison with the bare electrode. The electroanalytical response was improved by coating the electrode surface with a first layer of sublimed ferrocene (FCs), and then overcoating with the organoclay film to avoid the mediator leaching. The resulting bilayer film exhibited good characteristics such as extended linear range and high sensitivities for AA and UA, in cyclic voltammetry and amperometry. Interestingly, the redox mediator FCs was likely to lower overpotentials for AA oxidation (but not for UA), making possible the selective detection of these species in a mixture. The developed method could be used for the determination of AA in a pharmaceutical preparation and for UA in urine.