Edge-oriented Pyrolytic Graphite Research Articles

Electrochemical properties of oxygenated cup-stacked carbon nanofiber-modified electrodes.

Oxygenated cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were investigated as electrode materials by using typical redox species in electrochemistry, Fe(2+/3+), [Fe(CN)6](3-/4-), and dopamine. The electron transfer rates for these redox species at oxygenated CSCNF electrodes were higher than those at edge-oriented pyrolytic graphite and glassy carbon electrodes. In addition, the oxygen-containing functional groups also contributed to the electron transfer kinetics at the oxygenated CSCNF surface. The electron transfer rate of Fe(2+/3+) was accelerated and that of [Fe(CN)6](3-/4-) was decelerated by the oxygen-containing groups, mainly due to the electrostatic attraction and repulsion, respectively. The electrochemical reaction selectivities at the oxygenated CSCNF surface were tunable by controlling the amount of nanofibers and the oxygen/carbon atomic ratio at the nanofiber surface. Thus, the oxygenated CSCNFs would be useful electrode materials for energy-conversion, biosensing, and other electrochemical devices.

Electrocatalytic reduction of oxygen with phenanthroline-strapped porphyrins

The electrochemical behavior of three cytochrome c oxidase models has been investigated. All the models are derived from a phenanthroline-strapped, porphyrin framework that binds zinc(II) or iron(III) chloride in the porphyrin subunit, and copper(I) in the phenanthroline site. The iron complex and the bimetallic zinc(II) copper(I) complex of the parent ligand have been characterized by X-ray diffraction. One model consists of the parent structure on which C 12 alkyl chains have been added. This soluble model achieves electrochemical 2-electron reduction of oxygen in organic solvents without the addition of an exogenous axial base, and in the presence of an organic or inorganic source of protons. The two other models comprise the parent phenanthroline-strapped porphyrin framework, on which two pendant imidazoles have been incorporated. These models adsorbed on ring-disk electrodes with an edge-oriented, pyrolytic graphite (EOPG) disk and a platinum ring, efficiently catalyze the 4-electron reduction of oxygen in dioxygen saturated water at neutral pH.

Direct electrochemistry of human, bovine and porcine cytochrome P450c17

The direct electrochemistry of human, bovine and porcine cytochrome P450c17 (CYP17) has been examined on an edge-oriented pyrolytic graphite electrode. The recombinant protein was immobilized on an electrode modified with a surfactant to simulate the environment of a biological membrane, and hence physiological electron-transfer conditions. The P450 enzymes all retained 'electron-transfer' activity while immobilized at the electrode surface as assessed by the presence of catalytic signals under aerobic conditions. The redox potentials for porcine P450c17 were more positive (anodic) than both the human and bovine forms, perhaps reflecting the differences in substrate specificity for these species. In addition, these enzymes were all influenced by pH, consistent with a single proton associated with the single electron-transfer event. Ionic strength of the buffer medium also shifted the redox potentials towards positive, suggesting that electrostatic forces contribute to the protein environment required for the electron-transfer process. The effect of substrate on the redox potential for each P450c17 was measured in the presence of pregnenolone, progesterone, 17alpha-hydroxypregnenolone and 17alpha-hydroxyprogesterone. However, no influence on the redox parameters was observed.

The influence of promoter and of electrode material on the cyclic voltammetry of Pisum sativum plastocyanin

The reversible cyclic voltammetry of pea plastocyanin ( Pisum sativum) was studied with a wide range of electrodes: edge-oriented pyrolytic graphite (PGE), glassy carbon (GCE), gold (Au) and platinum (Pt) electrodes. Plastocyanin was coated onto the electrode surface by exploiting the electrostatic interaction between the negatively charged protein and a wide range of positively charged promoters. The effect of the redox response with an extended range of promoters, including poly- l-lysine, polymyxin B, neomycin, tobramycin, geneticin, spermine and spermidine, were included in this study. The resulting cyclic voltammograms reveal that the observed midpoint potential for plastocyanin can be shifted significantly depending on the choice of promoter. The stability of the negatively charged plastocyanin–promoter layer on an electrode was gauged by the rate of bulk diffusion of the protein from the immobilised film into the solution. Reversible cyclic voltammograms were obtained using edge-oriented pyrolytic graphite (PGE) and glassy carbon electrodes (GCE) with all promoters; however, platinum and gold electrodes were unable to sustain a defined redox response. The combination of pyrolytic graphite electrode/poly- l-lysine/plastocyanin was found to be the most stable combination, with a redox response which remained well defined in solution for more than 1 h at pH 7.0. The midpoint potentials obtained in this manner differed between the two graphite electrodes PGE and GCE using poly- l-lysine as the promoter. This effect was in addition to the expected pH dependence of the midpoint potential for plastocyanin and the results indicated that the p K a for plastocyanin on PGE was 4.94 compared to that on GCE of 4.66. It is concluded that both the electrode material and the nature of the promoter can influence the position of the redox potentials for proteins measured in vitro. This study extends the range of biogenic promoters used in combination with electrode materials. Thus, we can begin to develop a more comprehensive understanding of electrode–protein interactions and draw conclusions as to metalloprotein function, in vivo. To support these studies, we have sought information as to the nature of the electrode/promoter/protein interaction using scanning tunneling microscopy (STM) to study both the promoter and the plastocyanin protein on a gold surface.

Electron transfer from diamond electrodes to heme peptide and peroxidase.

Direct electron transfer from boron-doped diamond electrodes to heme undecapeptide and horseradish peroxidase (HRP) was examined and evaluated for the application to H2O2 biosensors. As-grown and oxygen plasma-treated diamond electrodes on which heme peptide is adsorbed exhibited cathodic current responses to H2O2 on the basis of the direct electron transfer. In a comparative study of carbon electrodes on which heme peptide was adsorbed, an oxygen plasma-treated diamond electrode exhibited responses comparable with those of an edge-oriented pyrolytic graphite (EOPG) electrode, despite much smaller roughness. However, electron transfer to compounds I and II of HRP from the diamond electrodes was much slower than that from EOPG or glassy carbon, suggesting that the pi electrons of an sp2 carbon may play an important role in the direct electron transfer to the heme moiety of HRP. To examine the applicability of heme peptide-modified diamond electrodes to oxidase-based biosensors, anodic current responses of the oxygen plasma-treated diamond electrode to possible interfering agents, ascorbic acid and uric acid, were examined and compared with those of EOPG. Since the diamond electrode exhibited much less sensitivity to those interfering agents, the heme peptide-modified diamond electrode should be a promising H2O2 biosensor for the application to oxidase-based biosensors.

Enzyme-Substrate Kinetics of Adsorbed Cytochrome c Peroxidase on Pyrolytic Graphite Electrodes

Cytochrome c peroxidase (CCP) adsorbed at (sub)monolager surface coverage on edge-oriented pyrolytic graphite (EPG) is being used as a model system for determining the effects of immobilization on the kinetic properties of an enzyme and for developing molecular insight into enzymatic electrocatalysis. Evidence indicating that the catalytic reduction of H 2 O 2 at the CCP/EPG electrode occurs via the intact enzyme and not via some form of «free» heme is discussed. Rotating disk electrode (RDE) voltammetry has been used to determine a Michaelis constant of 48 μM and a minimum turnover number of 110 s -1 for the adsorbed enzyme at 3 o C

Reversible electrochemistry of fumarate reductase immobilized on an electrode surface. Direct voltammetric observations of redox centers and their participation in rapid catalytic electron transport

Fumarate reductase (Escherichia coli) can be immobilized in an extremely electroactive state at an electrode, with retention of native catalytic properties. The membrane-extrinsic FrdAB component adsorbs to monolayer coverage at edge-oriented pyrolytic graphite and catalyzes reduction of fumarate or oxidation of succinate, depending upon the electrode potential. In the absence of substrates, reversible redox transformations of centers in the enzyme are observed by cyclic voltammetry. The major component of the voltammograms is a pair of narrow reduction and oxidation signals corresponding to a pH-sensitive couple with formal reduction potential E degree' = -48 mV vs SHE at pH 7.0 (25 degrees C). This is assigned to two-electron reduction and oxidation of the active-site FAD. A redox couple with E degree' = -311 mV at pH 7 is assigned to center 2 ([4Fe-4S]2+/1+). Voltammograms for fumarate reduction at 25 degrees C, measured with a rotating-disk electrode, show high catalytic activity without the low-potential switch-off that is observed for the related enzyme succinate dehydrogenase. The catalytic electrochemistry is interpreted in terms of a basic model incorporating mass transport of substrate, interfacial electron transfer, and intrinsic kinetic properties of the enzyme, each of these becoming a rate-determining factor under certain conditions. Electrochemical reversibility is approached under conditions of low turnover rate, for example, as the supply of substrate to the active site is limited. In this situation, electrocatalytic half-wave potentials, E1/2, are similar for oxidation of bulk succinate and reduction of bulk fumarate and coincide closely with the E degree' value assigned to the FAD. At 25 degrees C and pH 7, the apparent KM for fumarate reduction is 0.16 mM, and kcat is 840 s-1. Accordingly the second-order rate constant, kcat/KM, is 5.3 x 10(6) M-1 s-1. Under the same conditions, oxidation of succinate is much slower. As the supply of fumarate to the enzyme is raised to increase turnover, the electrochemical reaction eventually becomes limited by the rate of electron transfer from the electrode. Under these conditions a second catalytic wave becomes evident, the E1/2 value of which corresponds to the reduction potential of the redox couple suggested to be center 2. This small boost to the catalytic current indicates that the low-potential [4Fe-4S] cluster can function as a second center for relaying electrons to the FAD.

The electrocatalytic enzyme function of adsorbed cytochrome c peroxidase on pyrolytic graphite

Cytochrome c peroxidase (CCP) is a well characterized redox enzyme which can serve as a model for understanding the electrocatalytic function of adsorbed enzymes. Rotating disk electrode (RDE) voltammetry and cyclic voltammetry were used to show that CCP adsorbed on edge-oriented pyrolytic graphite reduces H 2O 2 electrocatalytically in a manner similar but not identical to solution CCP. Bulk electrolysis and Koutecky—Levich analysis of RDE data proved that the observed amperometric signal corresponds to the unmediated 2e − reduction of H 2O 2 to water. The pH dependence of the enzyme—substrate kinetics of adsorbed CCP were similar to those for solution CCP at pH ≤ 6 but showed some differences at pH > 6. RDE studies in solutions of varying ionic strength show that CCP remains strongly adsorbed to pyrolytic graphite even at high ionic strength. Preliminary cyclic voltammetry experiments revealed that adsorbed CCP is reversibly inhibited by inhibitors of solution CCP.

Proton-coupled electron transfer in[(bpy) 2Mn(O) 2Mn(bpy) 2] 3+: Role of the electrode surface

In this paper we report the electrochemistry of 1 [(bpy) 2 Mn(O) 2 Mn(bpy) 2 ] 3+ (1, bpy=2,2'-bipyridyl) at edge-oriented pyrolytic graphite (EOPG) and tin-doped indium oxide. These surfaces appear to mediate proton-coupled electron transfer; it is also clear that both forms of 1 adsorb at these surfaces under certain conditions

Electrocatalytic reduction of hydrogen peroxide via direct electron transfer from pyrolytic graphite electrodes to irreversibly adsorbed cytochrome c peroxidase

where E is the enzyme, S is the substrate, and P is the product. Various immobilization strategies such as adsorption, entrapment, and covalent attachment have been described. Surface coverage can range from submonolayers to trapped enzyme layers many pm thick. Reaction (2), the net electrode reaction, may involve direct electron transfer between the enzyme and the electrode [l-3], or it may be mediated ]1,2,41. We are interested in the direct electron transfer reactions of redox proteins and enzymes which have been immobilized on electrode surfaces by adsorption. In previous work, we have described the voltammetry of irreversibly adsorbed cytochrome c, an electron carrier protein, on tin oxide electrodes [5,6]. In the present paper, initial results are reported for direct electron transfer to an irreversibly adsorbed heme enzyme, cytochrome c peroxidase (CCP), on edge-oriented pyrolytic graphite (EOPG). This 34.1 kDa (kg mol-‘) enzyme catalyzes the 2 e-/2 H+

The electrode reaction of Euglenagracilis cytochrome c-552 at edge-oriented pyrolytic graphite

The direct electron transfer reaction of Euglena gracilis cytochrome c-552 at edge-oriented pyrolytic graphite electrodes was determined by cyclic voltammetry to be quasi-reversible, stable and reproducible. The presence of a persistent layer of irreversibly adsorbed cytochrome c-552 on the electrode surface was detected in these experiments. Heterogeneous electron transfer rate constants for both the diffusing and adsorbed forms of the protein are reported, and mechanistic aspects are addressed. The applicability of cytochrome c-552 as a complementarily charged analog of eucaryotic cytochrome c in interfacial bioelectrochemical studies is discussed.

Direct electrochemistry of the photosynthetic blue copper protein plastocyanin. Electrostatic promotion of rapid charge transfer at an edge-oriented pyrolytic graphite electrode

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDirect electrochemistry of the photosynthetic blue copper protein plastocyanin. Electrostatic promotion of rapid charge transfer at an edge-oriented pyrolytic graphite electrodeFraser A. Armstrong, H. Allen, O. Hill, B. Nigel Oliver, and David WhitfordCite this: J. Am. Chem. Soc. 1985, 107, 6, 1473–1476Publication Date (Print):March 1, 1985Publication History Published online1 May 2002Published inissue 1 March 1985https://doi.org/10.1021/ja00292a004RIGHTS & PERMISSIONSArticle Views229Altmetric-Citations83LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (509 KB) Get e-Alerts Get e-Alerts

Retention, re-emission and thermal desorption of He implanted into pyrolytic graphite

8 keV 3He ions have been implanted into edge-oriented pyrolytic graphite at temperatures of 120 K and 295 K. The retention behavior observed by nuclear reaction and residual gas analyses differs markedly from that observed in metals. Despite the negligible reflection coefficient, the mean re-emission coefficient at low fluence amounts to ~30% at room temperature, with a relative maximum at a fluence of 1.5 × 10 17 cm −2. Saturation is observed at fluences above 5 × 10 17 cm 12. The implanted He is completely removed by annealing to 750 K. Reimplantation at room temperature shows an enhanced retention (~90%) at low fluences. The experimental results are discussed in terms of He diffusion, trapping at damage sites and possible structural changes of the material.