Basal Plane Graphite Electrode Research Articles

Electrochemical and structural characterization of Azotobacter vinelandii flavodoxin II.

Azotobacter vinelandii flavodoxin II serves as a physiological reductant of nitrogenase, the enzyme system mediating biological nitrogen fixation. Wildtype A. vinelandii flavodoxin II was electrochemically and crystallographically characterized to better understand the molecular basis for this functional role. The redox properties were monitored on surfactant‐modified basal plane graphite electrodes, with two distinct redox couples measured by cyclic voltammetry corresponding to reduction potentials of −483 ± 1 mV and −187 ± 9 mV (vs. NHE) in 50 mM potassium phosphate, 150 mM NaCl, pH 7.5. These redox potentials were assigned as the semiquinone/hydroquinone couple and the quinone/semiquinone couple, respectively. This study constitutes one of the first applications of surfactant‐modified basal plane graphite electrodes to characterize the redox properties of a flavodoxin, thus providing a novel electrochemical method to study this class of protein. The X‐ray crystal structure of the flavodoxin purified from A. vinelandii was solved at 1.17 Å resolution. With this structure, the native nitrogenase electron transfer proteins have all been structurally characterized. Docking studies indicate that a common binding site surrounding the Fe‐protein [4Fe:4S] cluster mediates complex formation with the redox partners Mo‐Fe protein, ferredoxin I, and flavodoxin II. This model supports a mechanistic hypothesis that electron transfer reactions between the Fe‐protein and its redox partners are mutually exclusive.

Thin-Film Voltammetry of a Lutetium Bisphthalocyanine at Ionic Liquid|Water Interface

At room temperature, tetraoctylphosphonium bromide is a viscous ionic liquid, this gel-like organic phase can be cast over a basal-plane graphite electrode (BPGE). Cyclic voltammetry at such a modified electrode, in contact with an aqueous solution have revealed one reversible oxidation and five reversible reduction steps for a LuIII bisphthalocyanine dissolved in the ionic liquid film, a proof that the highly reactive reduced species were protected from interaction with water in this highly lipophilic phase. It has also been shown that the redox properties are influenced by the ions in the aqueous phase, a property which has been attributed to ion-pairing effects; obviously, the ion transfers at the organic|aqueous interface has been ignored. Electrochemistry of Lu(III)[(tBu)4Pc]2 (cyclic voltammetry and square wave voltammetry) under similar conditions shows that the nature and concentration of the anion in the aqueous solution in contact with the ionic liquid film influences the potential of the electrode reaction. This can be attributed to variations of the interfacial potential and also because the organic phase is an anion exchanger. Moreover, SWV experiments suggest that the rate of the overall reaction varies with the nature and concentration of the anion of the aqueous electrolyte, which implies that the ion transfer through the organic|aqueous interface is slower than the electron exchange rate of the molecule at the surface of graphite.

10.1007/s11175-008-3012-3

Using 1-ethyl-2-methylimidazolium trifluoroacetate (EMImTfa) as the supporting electrolyte, a couple of well-defined and reversible redox peaks of Myb could be observed at the basal plane graphite (BPG) electrode through direct electron transfer between the protein and the BPG electrode, whose anodic and cathodic peak potentials were at −0.098 V and −0.144 V vs. Ag | AgCl, respectively. Both anodic and cathodic peak currents increased linearly with the potential scan rates. Compared with the supporting electrolyte of phosphate buffer solution, EMImTfa played an important role for the direct electron transfer between Myb and the BPG electrode. Further investigation suggested that Myb was adsorbed tightly on the surface of the BPG electrode in the presence of EMImTfa to form a stable, approximate monolayer Myb film. Myb adsorbed on the BPG electrode surface could retain its biological activity and showed a remarkable electrocatalytic activity for the reduction of H2O2 in an EMImTfa aqueous solution. Based on these, a third-generation biosensor could be constructed to directly detect the concentration of H2O2 in EMImTfa aqueous solution with a limit of detection of 3.24 × 10−8 M.

DC and AC voltammetry of a free-base porphyrin adsorbed onto basal-plane graphite under acidic conditions: An example of a close to ideal reversible two-electron surface-confined redox process at sub-monolayer coverages

The free-base porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21 H,23 H-porphine (H 2TMPyP), adsorbs onto a basal-plane graphite electrode. Under DC cyclic voltammetric conditions, the fully protonated dication, [H 4TMPyP(0)] 2+, undergoes an apparently close to ideal surface-confined two-electron reduction to the neutral [H 4TMPyP(-II)] species when the supporting electrolyte consists of aqueous 1 M HCl and 1 M NaCl and coverages are sub-monolayer. The reversible potential calculated from the average of the oxidation and reduction peak potentials is 0.138 ± 0.002 V (vs Ag/AgCl, 3 M NaCl) whilst their separation Δ E p, approaches 0 mV at slow scan rates, as expected theoretically for an ideal surface-confined electron transfer process. Comparisons of simulated and experimental data imply that the increase in Δ E p observed at scan rates above 10 V s −1 is consistent with uncompensated Ohmic IR u drop effects, and not limitations imposed by electron transfer kinetics. Analysis of fundamental and higher harmonic components derived from large-amplitude sine-wave AC voltammetry is consistent with a very fast electron transfer rate constant, k 0, in excess of 10 6 s −1 for the overall two-electron process. However, careful comparison with AC theory highlights minor levels of non-ideality not attributable to purely capacitative background or uncompensated resistance effects. These are particularly evident when greater than monolayer surface coverages are employed. It is likely that subtle contributions from heterogeneity in the adsorbed layer and complexities in the reaction mechanism are present in this close to ideal surface-confined process, but they are more readily detected under conditions of large-amplitude Fourier transformed AC cyclic voltammetry than with the conventionally used DC cyclic format.

Direct Electrochemistry of Cytochrome c on a Silica Sol‐Gel Film Modified Electrode

AbstractDilute silica sol‐gel was simply dropped on the surface of a basal plane graphite electrode (BPGE) to form a silica sol‐gel film modified electrode. Direct electrochemical response of cytochrome c (Cyt c) on the modified electrode was observed by cyclic voltammetry (CV). The results suggested that Cyt c could be tightly adsorbed on the surface of the silica sol‐gel film modified electrode. A couple of well‐defined and nearly reversible redox peaks can be observed in a phosphate buffer solution (pH 7.0), which anodic and cathodic peak potentials were at −0.243 and −0.306 V (vs. Ag/AgCl), respectively. Cyt c adsorbed on the surface of silica sol‐gel film shows a remarkable electrocatalytic activity for the reduction of oxygen. Based on these, a third‐generation biosensor could be constructed to detect the concentration of oxygen in aqueous solution.

Direct Electrochemistry of Myoglobin on a Room Temperature Ionic Liquid Modified Electrode and Its Application to Nitric Oxide Biosensing

AbstractMyoglobin (Myb) was successfully immobilized on a room temperature ionic liquid (RTIL), 1‐ethyl‐3‐methyl imidazolium tetrafluoroborate ([EMIM][BF4]) modified basal plane graphite (BPG) electrode. The electrochemical behavior of Myb on RTIL modified BPG electrode was explored and the results from cyclic voltammetry (CV) showed a well‐defined and quasi‐reversible CV peaks with a formal potential of −0.379 V (versus Ag/AgCl) in a phosphate buffer solution (pH 7.0). RTIL shows an obvious promotion for the direct electron‐transfer between Myb and BPG electrode. Myb adsorbed on electrode surface exhibits an obvious electrocatalytic activity for the reduction of nitric oxide (NO). The catalytic current is corresponding linearly to the NO concentration in the range of 7.0×10−7 to 7.0×10−6 M with a limit of detection of 2.0×10−7 M (three times the ratio of signal to noise, S/N=3).

Direct electrochemistry of myoglobin in a room temperature ionic liquid aqueous solution and its catalysis to H2O2

Using 1-ethyl-2-methylimidazolium trifluoroacetate (EMImTfa) as the supporting electrolyte, a couple of well-defined and reversible redox peaks of Myb could be observed at the basal plane graphite (BPG) electrode through direct electron transfer between the protein and the BPG electrode, whose anodic and cathodic peak potentials were at −0.098 V and −0.144 V vs. Ag | AgCl, respectively. Both anodic and cathodic peak currents increased linearly with the potential scan rates. Compared with the supporting electrolyte of phosphate buffer solution, EMImTfa played an important role for the direct electron transfer between Myb and the BPG electrode. Further investigation suggested that Myb was adsorbed tightly on the surface of the BPG electrode in the presence of EMImTfa to form a stable, approximate monolayer Myb film. Myb adsorbed on the BPG electrode surface could retain its biological activity and showed a remarkable electrocatalytic activity for the reduction of H2O2 in an EMImTfa aqueous solution. Based on these, a third-generation biosensor could be constructed to directly detect the concentration of H2O2 in EMImTfa aqueous solution with a limit of detection of 3.24 × 10−8 M.

Detailed Analysis of the Electron-Transfer Properties of Azurin Adsorbed on Graphite Electrodes Using dc and Large-Amplitude Fourier Transformed ac Voltammetry

The analysis of dc cyclic voltammograms of surface-confined metalloproteins is complicated by large background currents, significant ohmic iRu drop, and frequency dispersion related to protein and electrode surface inhomogeneity. The use of large-amplitude Fourier transform ac voltammetry for the quantification of the electron-transfer properties of a thin film of redox-active protein azurin adsorbed onto edge-plane, basal-plane, and highly oriented pyrolytic graphite electrode surfaces has been evaluated and compared to results obtained by dc cyclic voltammetry. In principle, it has been established that fourth and higher harmonic sine-wave data are ideally suited for analysis of electron-transfer processes as they are almost completely devoid of background capacitance current contributions. However, uncompensated resistance has a higher impact on these components, as is the case with fast scan rate dc techniques, so strategies to include this term in the simulations have been investigated. Application of recommended strategies for the evaluation of the electron-transfer properties of azurin adsorbed onto three forms of graphite, each having different background or uncompensated resistance values, is described and compared to results obtained by traditionally used forms of cyclic voltammetry. The electron-transfer rate constant, k0', of azurin at a highly oriented pyrolytic graphite electrode surface was approximately 250 s(-1), compared with > or =1000 s(-1) at edge-plane and basal-plane graphite electrodes. The significantly lower k0' value found at the highly oriented pyrolytic graphite electrode was related to the relatively low level of edge-plane defect sites present at the surface of this electrode. However, analysis of high ac harmonics suggests that frequency dispersion is substantial at all electrode surfaces. Such effects in these diffusionless situations are significantly enhanced relative to solution-phase voltammetry, where overlay of diffusion layers minimizes the impact of heterogeneity.

Direct electrochemical response of cytochrome c on a room temperature ionic liquid, N-butylpyridinium tetrafluoroborate, modified electrode

Cytochrome c (Cyt c) and a room temperature ionic liquid (RTIL), 2-methyl- N-butylpyridinium tetrafluoroborate ([2-MBPy][BF 4]), were immobilized on the surface of a basal plane graphite (BPG) electrode. Direct electron transfer from Cyt c to BPG electrode was clearly observed. A pair of well-defined and reversible redox peaks could be obtained in a 0.13 M [2-MBPy][BF 4] aqueous solution. The anodic and cathodic peak potentials of Cyt c were at −0.064 and −0.020 V (vs. Ag/AgCl), respectively. The results showed that [2-MBPy][BF 4] promoted the direct electron transfer between Cyt c and the BPG electrode. Cyt c immobilized on BPGE can catalyze the reduction of hydrogen peroxide. Based on this, a biosensor can be constructed to detect quantitatively hydrogen peroxide.

Direct electrochemical response of Myoglobin using a room temperature ionic liquid, 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate, as supporting electrolyte

Direct electrochemical response of Myoglobin (Myb) at the basal plane graphite (BPG) electrode was observed when a room temperature ionic liquid (RTIL), 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate ([HEMIm][BF 4]), was used as the supporting electrolyte. In a 0.17 M [HEMIm]BF 4 aqueous solution, a couple of well-defined redox peaks of Myb could be obtained, whose anodic and cathodic peak potentials were at −0.158 and −0.224 V (vs. Ag/AgCl), respectively. Both anodic and cathodic peak currents increased linearly with the potential scan rate. Compared with the supporting electrolyte of phosphate buffer, [HEMIm][BF 4] played an obvious promotion for the direct electron transfer between Myb and the BPG electrode. Further investigation suggested that Myb was adsorbed tightly on the surface of the BPG electrode in the presence of [HEMIm][BF 4] to form a stable, approximate monolayer Myb film. Myb adsorbed on the BPG electrode surface showed a remarkable electrocatalytic activity for the reduction of oxygen in a [HEMIm][BF 4] aqueous solution. Based on these, a third-generation biosensor could be constructed to directly detect the concentration of oxygen in aqueous solution with a limit of detection of 2.3 × 10 −8 M.

Chemical adsorption of phenothiazine dyes onto carbon nanotubes: Toward the low potential detection of NADH

The cyclic voltammetric responses for phenothiazine dyes, adsorbed onto CNT have been assessed as a means of promoting the low potential, sensitive and stable determination of NADH. The analytical signal of the toluidine blue modified carbon nanotubes (TB-CNT) has been evaluated and compared with those of the bare carbon nanotubes and toluidine blue coated basal plane graphite electrodes; significant improvements in both the sensitivity and stability are demonstrated when using amperometic detection. The bulk modification of the CNT has allowed for the development of an inexpensive and facile electrode design, in which the CNT are packed into a small cavity. The electrode was found to be stable and gave greatly improved signals over its toluidine blue coated graphite powder counterpart.

Redox Couples of Inducible Nitric Oxide Synthase

We report direct electrochemistry of the iNOS heme domain in a DDAB film on the surface of a basal plane graphite electrode. Cyclic voltammetry reveals FeIII/II and FeII/I couples at -191 and -1049 mV (vs Ag/AgCl). Imidazole and carbon monoxide in solution shift the FeIII/II potential by +20 and +62 mV, while the addition of dioxygen results in large catalytic waves at the onset of FeIII reduction. Voltammetry at higher scan rates (with pH variations) reveals that the FeIII/II cathodic peak can be resolved into two components, which are attributable to FeIII/II couples of five- and six-coordinate hemes. Digital simulation of our experimental data implicates water dissociation from the heme as a gating mechanism for ET in iNOS.

Electrooxidation of methanol on ruthenium oxide layer supported by basal plane graphite in acid media

The electrooxidation of methanol on ruthenium oxide layer supported by basal plane graphite (BPG) in acid media was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy. A simple electrodeposition method of ruthenium oxide layer on BPG electrode was established in this study. Ruthenium oxide layer, which was prepared by a simple electrodeposition method in acidic ruthenium chloride solution, stable in the potential range between −0.3 and 0.9 V vs. saturated calomel electrode (SCE) but stripped at high potential range between 1.0 and 1.7 V . According to XPS analysis, the layer presented more than two different peaks, which showed the oxidation states of ruthenium between Ru (2+) and Ru (4+). A peak current of 260 μA at 1.0 V was observed for the electrooxidation of methanol on ruthenium oxide layer.

Mediated reduction of oxygen at poly(phenosafranine) modified electrodes

The immobilization of catalytic molecules on electrodes is advantageous due to their ready separation from the solution medium and the small amount of catalyst necessary for the reaction [1±4]. Di€erent methods are available to immobilize catalysts on electrode surfaces. The most frequently used method is the adsorption of catalytic molecules on a polyelectrolyte or clay or zeolite ®lm coated electrode [1, 3, 4]. Another method is the immobilization of catalysts through electropolymerization of monomers on the surface [1, 5]. This type of electrode modi®cation allows the electrocatalyst to be dispersed at the molecular level with good activity towards many electrocatalytic reactions [1, 2, 5, 6]. Electrocatalytic reduction of dioxygen has been studied extensively because of its relevance to fuel cell technology [7]. Dioxygen reduction to hydrogen peroxide is a two-electron reaction and the four-electron reduction leads to the formation of water [8]. The kinetics and mechanisms of oxygen reduction have been investigated using a wide range of cathode materials and electrolytes [9±13]. In this work phenosafranine (PS‡) (Figure 1(a)), a phenazine dye, was electropolymerized on a basal plane graphite (BPG) electrode and zeolite-L coated BPG electrode to give poly(phenosafranine) (BPG/poly(phenosafranine)) and zeolite±poly(phenosafranine) (BPG/zeolite-L/poly(phenosafranine)) modi®ed electrodes. The oxygen electroreduction was then studied at such electrodes in 0.1 M NaH2PO4.

Aqueous Electrochemistry of a C60-Bearing Artificial Lipid Bilayer Membrane Film Immobilized on an Electrode Surface: Thermodynamics for the Binding of Tetraalkylammonium Ion to the Fullerene Anion

Thermodynamics for the binding of electrolyte cations, in particular, tetraalkylammonium ions, to the electrogenerated radical anion and the dianion of the fullerene moieties in a molecular-bilayer membrane film of C60-bearing artificial lipid, 1, cast on an electrode surface was described. The theoretical treatment predicts a linear relationship between the half-wave potential (E1/2) for the electrode reaction and electrolyte concentration in the film (c) at higher concentrations and enables us to obtain the number of bound cation and binding constant, respectively, from the slope and intercept of the E1/2−ln c plot. We measured differential pulse voltammograms for a cast film of 1 on a basal plane graphite electrode in aqueous solution containing tetraethylammonium chloride (or tetra-n-butylammonium chloride) + KCl = 0. 5 M and found that E1/2−ln cs plots for the modified electrodes are linear in a concentration range of ca. 0.002−0.14 M, where cs is the concentration of ammonium electrolytes in the sol...

In situ fourier transform infrared reflection spectroscopic studies of ferricyanide/ferrocyanide on graphite electrode

AbstractThe electrochemical reactions of Fe(CN) and Fe(CN) on basal plane graphite electrode were studied using cyclic voltammetry and in situ Fourier transform infrared (FTIR) reflection spectroelectrochemistry. The IR band near 2080 to 2067 cm−1 was found to be an intermediate for Fe(CN) reduction and the band near 2058 to 2067 cm−1 for Fe(CN) oxidation. The possible mechanisms of reduction and oxidation and structure of intermediate are discussed.

Direct electrical communication of cytochrome c and ytochrome b5 at basal plane graphite electrodes modified with lauric acid or laurylamine

Herein we report two examples of the direct electrochemistry of cytochrome c and cytochrome b 5 to BPG electrodes, modified with lauric acid and laurylamine, respectively. Presumably the hydrophobic chain of modifier is bound to the graphite electrode, allowing the hydrophilic groups to interact with the charged residues carried by cytochrome c or cytochrome b 5

Electrochemistry of cytochrome c, plastocyanin, and ferredoxin at edge- and basal-plane graphite electrodes interpreted via a model based on electron transfer at electroactive sites of microscopic dimensions in size

The electrochemistry of a range of electron-transfer proteins at edge- and basal-plane graphite electrodes has been reconsidered using a microscopic model, which involves fast electron transfer at very small oxygen-containing electroactive surface sites. This model assumes that mass transport to the electrode occurs by radial diffusion when the density of the surface active sites is low (as is generally true in the case of the basal-plane graphite electrode) and by linear diffusion when the density of the active sites is increased sufficiently to cause overlap of the diffusion layers. With this model it is now proposed that the electrochemistry of cytochrome c, plastocyanin, and ferredoxin occurs with a very fast rate of charge transfer (≥1 cm s-1) at both edge- and basal-plane graphite electrodes. Critical factors, such as the mode of surface preparation (including covalent derivatization), the pH, and the presence in the electrolyte of cations such as Mg2+ or Cr(NH3)63+, control the density of surface sites, which result in the electrochemistry of a specific protein. This contrasts with the conclusion that has been reached previously based upon a conventional macroscopic model, which supposes that the rate of electron transfer is subject to enhancement or depression through these factors. The proposal that the electron-transfer process at the protein-graphite electrode interface is very fast over a wide range of conditions is now consistent with homogeneous kinetic studies where electron-transfer reactions of proteins, particularly amongst physiological partners, are also known to be fast. © 1989 American Chemical Society.