Cyclic Voltammetric Behavior Research Articles

Three-dimensional mesoporous gold film to enhance the sensitivity of electrochemicaldetection

Cell–cell and cell–extracellular matrix (ECM) adhesion are fundamental andimportant in the development of a cell-based chip. In this study, a novel, simple,rapid, and one-step technique was developed for the fabrication of a uniformthree-dimensional mesoporous gold thin film (MPGF) onto a gold (Au) coatedglass plate based on an electrochemical deposition method. Scanning electronmicroscopy images demonstrated that the resulting MPGF electrode had uniformlydistributed pores with diameters of about 20 nm. The cyclic voltammetric behavior of[Fe(CN)6]4 − /3 − coupled onto MPGF and Au electrodes demonstrated that the MPGF electrode had ahigher electrocatalytic sensitivity and reversibility than the bare Au electrode. TheArg–Gly–Asp (RGD) sequence containing the peptide was immobilized on theMPGF and bare Au substrates. HeLa cancer cells were then cultured on theRGD peptide layer. The successful immobilization of the peptide and cells wasconfirmed by atomic force microscopy. The cell proliferation and viability wereevaluated by cyclic voltammetry and Trypan blue dyeing assay. These resultsindicated that the RGD/MPGF modified electrodes showed an electrochemicalsensitivity in the detection of cancer cells which is approximately three times higher,especially at low cell density, than RGD/Au electrodes. This much improvedsensitivity of the MPGF modified electrode demonstrates the potential for thefabrication of a highly sensitive and low-cost cell-based chip for rapid cancer detection.

Synthesis, Structure and Cyclic Voltammetry Studies of a 2D Sheet-like μ3-Hydroxyl- and μ2-, μ4-Oxamidato-Bridged Copper(II) Complex

A novel 2D sheet-like copper(II) complex formulated [Cu6(trans-oxen)3(μ3-OH)2(H2O)2]n-(ClO4) 4n . 2nH2O (1), where H2oxen is N,N’-bis(2-aminoethyl)oxamide, has been synthesized and characterized by elemental analysis, IR and UV–visible spectroscopy, and single-crystal X-ray diffraction. 1 crystallizes in triclinic space group P-1 with crystallographic data: a = 10.299(2) A, b = 10.833(2) A, c = 11.781(2) A, α = 69.95(3)°, β = 81.10(3)°, γ = 62.44(3)°, and Z = 2. In the crystal structure, the cation [Cu6(trans-oxen)3(μ3-OH)2(H2O)2] n 4n+ exhibits a two-dimensional sheet-like structure for Cu(II) ions bridged both by trans-oxen and hydroxyl groups. Each Cu(II) ion is located in a slightly distorted square-pyramidal environment. The hydroxyl group bridges three [Cu(oxen)Cu]2+ dications in which one oxen2− is μ2-bridge while the other two act as never before reported μ4-bridge. Perchlorate anions and H2O molecules are inserted between the sheets and bridge the 2D cations via N–H···O and O–H···O hydrogen bonds to form an infinite three-dimensional system. The cyclic voltammetric behavior of 1 and the influence of counter ions on structure are preliminarily investigated.

Electrochemical behavior of anthraquinone in aqueous solution in presence of a non-ionic surfactant

Cyclic voltammetric behavior of anthraquinone in aqueous medium has been studied in presence of a non-ionic surfactant, Triton X-100 (TX-100) using sodium salt of anthraquinone-2-sulphonic acid (AQS) as the electro-active species. When cathodic potential is applied, the anthraquinone (AQ) group of AQS is reduced to its dianion. In the reverse scan, the oxidation of AQ2− gives AQ. The electrochemical behavior shows a profound influence from the dissolved state of TX-100 in aqueous media. Spectrophotometric results indicate interaction between AQ and TX-100. A CEC (chemical–electrochemical–chemical) mechanism with the electrochemical reaction coupled with preceding interaction of AQS with TX-100 and following protonation reaction of reduced AQ has been proposed.

Crystal Structure and Electrochemical Properties of Ferrocenyl Aminophosphonic Esters

A series of novel compounds of aminophosphonates bearing the ferrocenyl moiety are obtained. X-ray Crystallography of 2c reveals that it belongs to monoclinic system with space group P2(1)/c, R1 = 0.0620, wR2 = 0.1516. The cyclic voltammetric behavior of these compounds show one pair of quasi-reversible and redox waves in the potential range of 0.0–1.0 V and it is controlled by diffusion. The diffusion coefficient decrease with increasing in the molecular weight of the compounds and the size of the molecules. CCDC: 679937

Formic Acid Oxidation on Bi-modified Pt Nanoparticles of Various Sizes

This work presents oxidation of formic acid on Bi-modified Pt nanoparticles of various sizes. The sizes of the studied Pt nanoparticles range from 1.5 to 5.6 nm (detailed in Rhee, C. K.; Kim, B.-J.; Ham, C.; Kim, Y.-J.; Song, K.; Kwon, K. Langmuir 2009, 25, 7140-7147), and the surfaces of the Pt nanoparticles are modified with irreversibly adsorbed Bi. The investigated coverages of Bi on the Pt nanoparticles are 0.12 and 0.25 as determined by coulometry of the oxidation of adsorbed hydrogen and Bi, and X-ray photoelectron spectroscopy. The cyclic voltammetric behavior of formic acid oxidation reveals that the adsorbed Bi enhances the catalytic activity of Pt nanoparticles by impeding a poison-forming dehydration path with a concomitant promotion of a dehydrogenation path. The chronoamperometric results indicate that elemental Bi and partially oxidized Bi are responsible for the catalytic enhancement, when the Bi coverages on Pt nanoparticles are 0.12 and 0.25, respectively. The size effect of Bi-modified Pt nanoparticles in formic acid oxidation is discussed in terms of specific activity (current per unit surface area) and mass activity (current per unit mass).

A simple electrochemical lectin-probe for in situ homogeneous cytosensing and facile evaluation of cell surface glycan

This work constructed a novel electrochemical lectin-probe, ferrocene–concanavalin A (Fc-ConA), for in situ monitoring of cell surface glycan by incorporating the specific recognition ability of lectin to glycan and favorable electrochemical property of ferrocenyl group. The covalent conjugation of ConA with ferrocenyl group was achieved by a carbodiimide coupling reaction and proved with UV–vis absorption spectroscopy and infrared spectroscopy. Cyclic voltammetric behavior of Fc-ConA at glassy carbon electrode demonstrated a reversible diffusion-controlled process. A facile homogeneous cytosensing strategy was then developed using Fc-ConA probe for detection of K562 cells. The suspending cells specifically captured Fc-ConA via membrane mannosyl groups and decreased the concentration of free Fc-ConA, producing a response correlative with cell number and the content of cell surface glycan. A wide linear response to cells ranging from 1 × 10 4 to 1 × 10 7 cells mL −1 with a calculated detection limit of 3000 cells mL −1 was obtained. The lectin-probe could be conveniently used to in situ evaluate cell surface glycan. The average number of mannose moieties on single living K562 cell was detected to be 3.0 × 10 10, while this value increased by 81% on drug-treated cells. These results agreed with those from flow cytometric detection. This strategy presented a promising platform for homogeneous sensitive cytosensing and facile monitoring of carbohydrate expression on living cells in response to drugs.

Electrochemistry of substituted salen complexes of nickel(II): Nickel(I)-catalyzed reduction of alkyl and acetylenic halides

Dimethyl-, diethyl-, and diphenyl-substituted analogues of nickel(II) salen have been synthesized, and the cyclic voltammetric behavior of each compound at a glassy carbon electrode in dimethylformamide (DMF) containing tetra- n-butylammonium tetrafluoroborate (TBABF 4) has been compared with that of nickel(II) salen itself. Differences in the cathodic peak potentials for these species have been rationalized with the aid of theoretical computations based on density functional theory. Cyclic voltammograms for reduction of dimethylated nickel(II) salen reveal that placing a methyl group on the carbon atom of each imino (C N) bond of the ligand improves the performance of electrogenerated dimethylated nickel(I) salen as a catalyst for reduction of 1-iodobutane. This conclusion is supported by experiments that combine controlled-potential electrolysis with high-performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) to detect and analyze the post-electrolysis nickel-containing species arising from the bulk catalytic reduction of 1-iodooctane. Additional studies have been made of the use of electrogenerated dimethylated nickel(I) salen for the catalytic reduction of alkyl halides and for the reductive intramolecular cyclization of acetylenic halides.

Electrochemiluminescent Functionalizable Cyclometalated Thiophene-Based Iridium(III) Complexes

A family of new functional bis-cyclometalated thiophene-based cationic iridium complexes have been prepared and fully characterized. The introduction of formyl groups into the thienyl-based cyclometalating ligand (thpy-CHO) allows one to perform further functionalizability and to confer to the whole species potentially interesting perspectives as functional materials. The X-ray crystal structures of three complexes, namely, [Ir(thpy)(2)bpy]PF(6), [Ir(thpy-CHO)(2)bpy]PF(6), and [Ir(thpy-CHO)(2)phen]PF(6), are reported. A rich reduction voltammetric pattern of the complexes is outlined, and the effect of the substituents on the cyclic voltammetric behavior is fully elucidated. Finally, the electrochemiluminescence spectra of all of the species have been obtained in acetonitrile by annihilation of the one-electron-oxidized and -reduced forms, showing very similar features with respect to the luminescence (as both the shape and energy of the emission bands).

Diffusion regimes at nanoelectrode ensembles in different ionic liquids

The electrochemical and diffusion behaviour of different redox probes in different ionic liquids is studied at gold nanoelectrode ensembles (NEEs) in comparison with millimetre sized gold (Au-macro) and glassy carbon (GC) disk electrodes. The redox probes are neutral ferrocene (Fc), the ferrocenylmethyltrimetylammonium cation (FA +) and the ferrocenylmonocarboxylate anion (FcCOO −). The ILs are the dicyanamide, [N(CN) 2] or bis(trifluoromethylsulfonyl)amide), [N(Tf) 2] salts of the following cations: 1-butyl-3-methylimidazolium, [BMIm], 1-butyl-3-methylpyrrolidonium, [BMPy], or tris(n-hexyl)tetradecylphosphonium [P 14,666]. These ILs are characterized by different viscosities, ranging from 32 to 277 cP. The cyclic voltammetric behaviour of the redox probes is reversible and diffusion controlled at GC electrodes. Diffusion coefficients ( D) calculated by the Randles–Sevcik equation scales inversely with the IL viscosity, ranging from 2 × 10 −8 to 3 × 10 −7 cm 2 s −1. Ionic solutes, namely FA + and FcCOO −, present slightly lower D values than neutral Fc. At the Au-macro the electrochemical behaviour of the redox probes is diffusion controlled in the ILs containing the [N(Tf) 2] anion, while it involves relevant adsorption processes in the [N(CN) 2] containing electrolyte. For this reason the diffusion at gold NEEs is studied only in the former ILs. The CVs of the redox probes at the NEEs are peak shaped at low scan rate ( v ), while they are sigmoidally shaped at high v , but with some shift between forward and backward patterns. This is indicative of the occurrence of a total overlap (TO) diffusion condition when v is low which becomes a mixed diffusion layers (MDL) regime, with only a partial overlapping of individual diffusion layers, at high v values. In the most viscous IL, namely [P 14,666] [N(Tf) 2], at v higher than 0.8 V s −1, a plateau current independent on the scan rate is achieved, indicating the tendency to reach the pure radial regime in this IL. The v values at which the transition between TO and MDL is observed scales directly with D and inversely with the IL viscosity. This behaviour is interpreted on the basis of the dependence of individual diffusion layers at each nanoelectrode on redox probe/IL interaction which fits with existing theoretical models very recently developed for nanoelectrode arrays.

Synthesis and electrochemical behavior of triazole-containing nicotinamide adenine dinucleotide analogs

The coupling of 2′,3′-di-O-acetyl nicotinamide mononucleotide with 3-butyn-1-ol in the presence of 2,4,6-triisopropylbenzenesulfonyl chloride quantitatively afforded a terminal alkyne-containing intermediate. Furthermore, copper(I)-mediated Huisgen [3 + 2] cycloaddition with a series of azido compounds in a two-phase solvent system gave eight triazole-containing nicotinamide adenine dinucleotide analogs with yields over 88%. The cyclic voltammetric behaviors of these novel analogs were investigated with a glassy carbon electrode, and structural features of these analogs on their electrochemical properties were briefly discussed.

Comparison of Kinetics of Hemoglobin Electron Transfer in Solution and Immobilized on Electrode Surface

The electron transfer properties of horse heart hemoglobin are compared using a hydrophilic indium tin oxide electrode and a dilaurydimethylammonium bromide (DDAB) polymer modified PG electrodes. A clear, stable and quasi-reversible redox curve of hemoglobin (Hb) was obtained in the absence of electron transfer mediators or promoters. The formal redox potential of -0.17 vs. Ag/AgCl of Hb was determined. The effects of the sixth axial binding ligands including cyanoand azido binding ligands on the redox properties of Hb were investigated. There are no significant impacts of these ligands on the redox properties of Hb, whereas big effects of the binding ligand on the electrochemical properties of myoglobin were reported. The cyclic voltammetric behavior of hemoglobin was also studied in a DDAB film coated on a pyrolytic graphite electrode. Surface immobilized Hb in DDAB film gave direct, quasi-reversible, nondiffusion-kinetic-controlled electron transfer on the electrode surface. The formal redox potential for Hb in the DDAB film negatively shifted about 140 mV as compared to the diffusion-controlled redox reaction of Hb.

The Electrochemical Behavior of Nitrazepam at a Screen‐Printed Carbon Electrode and Its Determination in Beverages by Adsorptive Stripping Voltammetry

AbstractThe cyclic voltammetric behavior of nitrazepam was investigated at screen‐printed carbon electrodes over the range −1.5 V to +1.5 V. Two reduction peaks were observable on the negative scan, at −0.7 V, and −1.2 V using pH 6 buffer. On the return scan a single oxidation peak was obtained at −0.05 V. For quantitative analysis of beverages, we developed an anodic adsorptive stripping voltammetric method which required only dilution with buffer. The identification of nitrazepam and flunitrazepam could be achieved using cyclic voltammetry.

Amperometric enzyme electrode for glucose determination based on poly(pyrrole-2-aminobenzoic acid)

Polymerization of pyrrole and 2-aminobenzoic acid has been investigated, and a functionalized stable film of poly(pyrrole-2-aminobenzoic acid) (PP2ABA) has been obtained electrochemically onto platinum electrode. Different cyclic voltammetric behavior is obtained for polypyrrole and PP2ABA during electrosynthesis. Fourier-transformed infrared spectrometry and surface-enhanced Raman spectrometry measurements on the two films have confirmed the presence of carboxylate group in the films. The enzyme, glucose oxidase, was covalently immobilized on a conducting PP2ABA film, and amperometric response was measured as a function of concentration of glucose at a potential of 0.7 V vs Ag/AgCl in 0.1 M phosphate buffer at pH 6.2. The effect of polymeric film thickness, pH, and possible interferents were investigated. The linear range of the calibration curve is from 3 to 40 mM with a sensitivity of 0.058 µA mM−1 cm−2 and a limit of detection of 0.5 mM. The apperent Mishaelis–Menten constant K M is calculated to be 1 × 10−2 mM, and the response time is 5 s.

Characterization of the Electron Transfer of a Ferrocene Redox Probe and a Histidine-Tagged Hemoprotein Specifically Bound to a Nitrilotriacetic-Terminated Self-Assembled Monolayer

We report the selective, controlled binding of a model redox probe, 1,1'-bis(N-imidazolylmethyl)ferrocene (Fc-Im2), and a small redox hemoprotein, histidine-tagged recombinant human neuroglobin (hNb), at the surface of metal electrodes (gold and SER-active silver) modified by a self-assembled monolayer (SAM) of a nitrilotriacetic (NTA)-terminated thiol. The resulting SAMs were characterized by cyclic voltammetry and surface-enhanced resonance Raman (SERR) spectroscopy coupled to electrochemistry. Once specifically bounded to the Ni(II)-NTA-modified gold electrode, nearly ideal cyclic voltammetric behavior with relatively fast electron-transfer (ET) communication through the SAM was determined for the Fc-Im2 redox probe. However, no direct electron transfer could be evidenced for the hNb redox protein under the same conditions. This outcome was different from the result obtained during SERR experiments coupled to electrochemistry in which a direct electrochemical conversion of hNb immobilized on a Ni(II)-NTA-modified SER-active Ag electrode was observed. The SERR spectra of the immobilized hNb was the same as the resonance Raman spectra of the protein in homogeneous solution, allowing us to conclude that the native structure of hNb was retained upon immobilization and that the direct ET was not the result of some partial or complete protein denaturation. The long-range ET rate constant (kET) through the SAM was determined by time-resolved SERR spectroscopy. A value of kET=0.12 s(-1) was obtained, which is within the predicted range of a fully nonadiabatic ET through a SAM thickness of approximately 26 A and close to the values previously determined for analogous small redox proteins at similar long-range ET distances. A SERR spectroelectrochemical titration of the immobilized hNb was also carried out, showing both an apparent standard potential (E0') negatively shifted by 100 mV compared with hNb in solution and a gentle slope in the titration curve. These results suggest a range of chemical environments in the surroundings of the redox protein and a variety of interactions with the NTA-terminated SAM. The influence of protein immobilization on E0' is discussed together with the long-range ET rate constant and molecular orientation of the surface-immobilized hNb.

Voltammetry of an Anti-cancer Drug

Voltammetric oxidation of vinblastine sulfate was studied at the platinum semi-micro electrode, by cyclic and pulsed voltammetric techniques, in 9:1 acetonitrile-water mixture containing 0.2 M sodium perchlorate. A plausible scheme of sequential electrochemical and chemical reactions is suggested for the cyclic voltammetric behavior of vinblastine.

Lanthanide nitrate complexes of the redox active ligand (η 5C 5H 4P(O)Ph 2) 2Fe

The synthesis of complexes of (η 5C 5H 4P(O)Ph 2) 2Fe = L with lanthanide nitrates is described. The single crystal X-ray structures for La(NO 3) 3L(μ-L)La(NO 3) 3L ( 1), [Eu(NO 3) 2L 2] 2[Eu(NO 3) 5] ( 2), [Ho(NO 3) 2L 2] 2[Ho(NO 3) 5] ( 3) and [Lu(NO 3) 2L 2] NO 3 ( 4) are reported. Trends in Ln–O bond distances cannot be explained by the lanthanide contraction alone. The cyclic-voltammetric (CV) oxidation–reduction behaviour of 1, 2, 4 and Dy(NO 3) 3L 2 · 2H 2O is described. This was reversible on a timescale of a few seconds in all cases. In our hands the CV behaviour of L also seemed reversible on this timescale, although attempted chemical oxidation of L led to the isolation of [FeL 2(NO 3) 2]NO 3 ( 5) which was characterised by X-ray crystallography.

Determination of analgesics in pharmaceutical formulations and urine samples using nano polypyrrole modified glassy carbon electrode

Three analgesics (acetaminophen, acetylsalicylic acid, and dipyrone) were determined electrochemically using nano polypyrrole modified glassy carbon electrode. The cyclic voltammetric behavior of the three analgesics was studied in aqueous acid, neutral, and alkaline conditions. One well-defined oxidation peak each for acetaminophen and acetylsalicylic acid and three oxidation peaks for dipyrone were observed in the cyclic voltammograms. The influence of pH, scan rate, and concentration reveal the irreversible diffusion controlled loss of 4e− in acid and neutral media and 2e−/1H+ in basic medium for acetaminophen. In the case of acetylsalicylic acid, 2e− and 1H+ loss in acidic and neutral pH and 2e− and 2H+ loss in basic pH were observed and the oxidation was irreversible and controlled by adsorption. Irreversible removal of 2e− and 1H+ in all pH media was observed for dipyrone and the oxidation was controlled by diffusion. A systematic study of the experimental parameters that affect the differential pulse stripping voltammetric response was carried out and optimized conditions which yield maximum peak current were arrived at. Scanning electron microscopy (SEM) analysis confirms good accumulation of the drugs on the electrode surface. The calibration was made under optimum conditions. The range of study for acetaminophen, acetylsalicylic acid, and dipyrone was 50–250, 40–300, and 100–400 ng/mL and the lower limit of determination was 45, 25, and 70 ng/mL respectively. The suitability of the method for the determination of the three analgesics in pharmaceutical preparations and urine samples was also ascertained.

EQCM Investigation of the Electrodeposition of MnO[sub 2] and Its Capacitance Behavior

Electro-oxidation of Mn2+ to MnO2 by cyclic voltammetry on gold in acidic (0.1 M H2SO4) and neutral (0.1 M Na2SO4) media was studied using electrochemical quartz-crystal microbalance (EQCM). The cyclic voltammetric behavior of Au is different in these electrolytes. From EQCM data of mass variation during cycling, the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from the acidic medium owing to different crystallographic structures.

Cyclic voltammetric studies of oxovanadium(IV) complex with 2,6-pyridinedicarboxylic acid in aqueous medium

The cyclic voltammetric behaviour of mononuclear oxovanadium(IV) complex with 2,6-pyridinedicarboxylic acid (H 2 dipic), [VO(dipic)(H 2 O) 2 ] has been studied at GCE working electrode in aqueous 0.2 M NaClO 4 and 0.2 M KCI as supporting electrolytes at initial pH 4.25. [VO(dipic)(H 2 O) 2 ] complex undergoes diffusion-controlled irreversible one electron oxidation reaction in the potential range +0.865 to +1160 mV vs Ag/AgCI for scan rate 25 to 500 mV s -1 .

Electrochemical characterisation of gold on Pt{ h k l} for ethanol electrocatalysis

The cyclic voltammetric (CV) behaviour of gold adsorbed on Pt{ h k l} electrodes is reported. It is found that stepped surfaces vicinal to Pt{1 1 1} exhibit preferential adsorption of gold at step sites. However, for stepped surfaces containing Pt{1 0 0} terraces, adsorption of gold at step and terrace site occurs with equal probability, although for Pt{ n 1 1} electrodes with n < 7 (i.e. electrodes containing short Pt{1 0 0} terraces), slight preference for step site adsorption is still observed. This behaviour is similar to that reported previously for Bi adsorption on Pt{ h k l} and is interpreted in terms of slower rates of gold atom surface diffusion across Pt{1 0 0} vs. Pt{1 1 1} terraces. By comparing the electrochemical response of gold adlayers on Pt{ h k l} with previously published bulk Au{ h k l} voltammetry, it is deduced that the gold overlayers on Pt{ h k l} are pseudomorphic in nature. This finding is in agreement with previous UHV and electrochemical results for gold deposition on platinum. Using such gold modified Pt{ h k l} electrodes as model surfaces, we also report, for the first time, the electrooxidation of ethanol on Au/Pt{ h k l} in alkaline aqueous solution. The ethanol oxidation reaction (EOR) is shown to be structure sensitive for submonolayer gold coverages. In fact, a maximum in the rate of EOR at platinum sites adjacent to gold islands is observed between approximately 0.4–0.6 monolayers of gold on Pt{1 0 0}, Pt{1 1 1} and Pt{1 1 0} in 0.1 M NaOH(aq). A second electrooxidation state at more positive potentials for 0 < θ Au < 1 ascribed to EOR at pure gold sites is also observed, at least for Pt{1 1 1} and Pt{1 0 0}. On Pt{1 1 1}, the potential range and activity of EOR in this second process is similar to bulk gold whereas for submonolayer gold films on Pt{1 0 0}, the peak is shifted to more negative potentials.