Chronopotentiometric study of laccase-catalysed oxidation of quinhydrone microcrystals immobilised on a gold electrode surface and of the oxidation of a phenol-derivatised graphite electrode surface

Scholz, Fritz; Schädel, Sandra A.; Schultz, Asgard; Schauer, Frieder

doi:10.1016/s0022-0728(99)00469-6

Cited by 11 publications

(7 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…5b; a straight line is obtained with a slope of -2509 K. From the Arrhenius equation, 30,31 this slope is equal to -E a / 2.303R, where E a is the activation energy and R is the universal gas constant. From the above, the activation energy is equal to 48.040 kJ/mol.…”

Section: Effect Of Temperaturementioning

confidence: 99%

Electropolymerization of m‐Toluidin on Platinum Electrode from Aqueous Acidic Solution and Character of the Obtained Polymer

2016

View full text Add to dashboard Cite

ABSTRACT:The electrochemical anodic electropolymerization of m-toluidin on a Pt electrode from a deoxygenated aqueous acid medium is carried out using the cyclic voltammetry technique. The effects of different parameters on the electrochemical polymerization such as the monomer, sulfuric acid, sodium sulfate concentrations, scan rate, and temperature are investigated using a conventional three-electrode cell. The results show the presence of an oxidation peak (anodic current peak) at approximately +1110 mV vs. saturated calomel electrode in all cases of the investigated parameters. A gradual increase in the anodic current peak density (I p ) is observed with a repeating number of cycles accompanied with the appearance of a new peak at low positive potential from the second repeating cycle. In addition, the effects of m-toluidin, sulfuric acid, sodium sulfate concentrations, scan rate, and temperature values have the same behavior on I p values, in which there is an increase in I p values till certain values (different for each parameter) and then decrease. The experimentally obtained kinetic equation is deduced from values of I p , and a simplified mechanism for the electrochemical anodic polymerization of m-toluidin is proposed. Moreover, the diffusion coefficient, activation energy (E a ), and thermokinetic parameters such as entropy ( S*), enthalpy of reaction ( H*), and free energy change ( G*) are calculated. The prepared polymer is characterized by elemental analysis, UV-visible, IR, 1 H NMR, X-ray diffraction, SEM, and TGA. C

show abstract

Section: Effect Of Temperaturementioning

confidence: 99%

Electropolymerization of m‐Toluidin on Platinum Electrode from Aqueous Acidic Solution and Character of the Obtained Polymer

2016

View full text Add to dashboard Cite

show abstract

“…In the present study multiwall carbon nanotubes were abrasively attached to the basal plane pyrolytic graphite (bppg) electrodes using the approach of Scholz developed for the study of solid electrocatalysts. 19 The resulting films showed very stable electrochemical behaviour and were used to mediate the electrochemical oxidation of epinephrine with the successful elimination of the interference by ascorbic acid in voltammetric detection of the latter.…”

Section: Introductionmentioning

confidence: 99%

Abrasive immobilization of carbon nanotubes on a basal plane pyrolytic graphite electrode: application to the detection of epinephrine

Salimi

Banks

Compton

2004

Analyst

148

View full text Add to dashboard Cite

The performance of a basal plane pyrolytic graphite (bppg) electrode modified with carbon nanotubes is described. Abrasive immobilization of multiwall carbon nanotubes on a bppg electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes. The resulting electrode showed excellent mediation of epinephrine oxidation: a decrease in the overvoltage of the epinephrine electro-oxidation (200-500 mV) was observed as well as a dramatic increase in the peak current (4 times) compared to that seen at a bare bppg electrode. The oxidation peaks of epinephrine and ascorbic acid which overlap on bare bppg electrode were separated successfully (by ca. 220 mV) at the surface of the modified bppg electrode. The modified electrode showed good stability in comparison to most modified carbon nanotubes electrodes prepared by alternative methods.

show abstract

“…The accepted mechanism for laccase activity suggests that the electron entry point is the T1 copper which rapidly transfers the electron to the triangular active site, consisting of the antiferromagnetically coupled T3 copper atoms and the T2 copper atom (7,(16)(17)(18). The in vivo electron donor can be substituted by an artificial electrode, thereby enabling estimates for the reduction potentials, electron transfer rate constants, and thermal and pH stability, in addition to the screening of effective inhibitors (3,12,17,19,20).…”

mentioning

confidence: 99%

“…For example, the T1 reduction potential of Polyporus Versicolor is +785 mV (22) whereas Rv is +420 mV. However, the majority of electrochemical studies of laccases reported to date show a single, poorly defined redox response (6,17,20). Although Armstrong et al (23) identified two distinct redox processes at 10 °C, other workers have since been unable to reproduce this behavior (17).…”

mentioning

confidence: 99%

Electrochemical Characterization of Purified Rhus vernicifera Laccase: Voltammetric Evidence for a Sequential Four-Electron Transfer

et al. 2003

View full text Add to dashboard Cite

Rhus vernicifera (Rv) laccase was purified to electrophoretic homogeneity by hydrophobic interaction chromatography. A comprehensive study of the direct electrochemistry of Rv laccase covalently immobilized at a gold electrode using alkanethiol monolayers was undertaken. The observed midpoint potential was 410 mV versus the normal hydrogen electrode (NHE), consistent with reduction potentials obtained by potentiometric titration for the T1 copper site. Evidence is presented for a concerted 4-electron reversible process at slow scan rates (v) on the basis of peak current ratios (i(pa)/i(pc)). Catalytic currents were observed in the presence of the biological substrate oxygen, indicating that laccase activity is retained throughout the immobilization process. Electrochemical characteristics of the immobilized laccase were essentially invariant across the pH range 5.5-8.5 and the temperature range 5-35 degrees C. The purified enzyme displayed a pH optimum of 9.0, when assayed spectrophotometrically with syringaldazine as a substrate. Inhibition of the laccase activity with azide or fluoride showed an I(50)(NaN(3)) of 2.5 mM and an I(50)(NaF) of 18.5 mM. Electrochemistry in the presence of azide reduces the anodic current by ca. one-half, consistent with the 4-electron process decreasing to a 2-electron process. However, fluoride has no effect on anaerobic electrochemistry. These electrochemical results suggest that the pH dependence of laccase activity is related to the effects of pH on the structure or binding of the substrate.

show abstract

Chronopotentiometric study of laccase-catalysed oxidation of quinhydrone microcrystals immobilised on a gold electrode surface and of the oxidation of a phenol-derivatised graphite electrode surface

Cited by 11 publications

References 5 publications

Electropolymerization of m‐Toluidin on Platinum Electrode from Aqueous Acidic Solution and Character of the Obtained Polymer

Electropolymerization of m‐Toluidin on Platinum Electrode from Aqueous Acidic Solution and Character of the Obtained Polymer

Abrasive immobilization of carbon nanotubes on a basal plane pyrolytic graphite electrode: application to the detection of epinephrine

Electrochemical Characterization of Purified Rhus vernicifera Laccase: Voltammetric Evidence for a Sequential Four-Electron Transfer

Contact Info

Product

Resources

About