Pyrolytic graphite electrode, cyclic

Figure 7 shows the cyclic voltammetric responses of cytochrome c obtained at pyrolytic graphite electrodes treated in various ways. 

This method involves electrochemical deposition of the MPc onto CNT-modified electrode surface by repetitive cycling in a concentrated MPc solution (1 mM) within a specific potential window. The first cyclic voltammetric scan is usually similar to subsequent scans, indicating the formation of monomeric species only. Ozoemena et al [11] found that on certain occasions, as reported recently [11] during the electro-deposition of CoTAPc onto a basal plane pyrolytic graphite electrode (BPPGE) pre-modified with SWCNT, both cathodic and anodic waves may decrease continually and then stabilizes at a certain scan (a process known as electrochemical adsorption or simply called electrosorption ). 

Figure 3. Cyclic voltammograms of a pyrolytic graphite electrode in pH 7 phosphate buffer following the listed reaction steps. Traces A-D correspond to the reaction steps cited in Fig. 2 and trace G corresponds to a control electrode produced by omitting step D before reacting with hydroxymethyl ferrocene. The potential scale is referenced to Ag/AgCl (saturated KCl). All traces were recorded with a 50 mV/s scan rate. (Reproduced from Ref. 64. Copyright 1978, American...

Fig. 5.4. Left Anaerobic cyclic voltammogram of 2.5 pmol (= one monolayer) P. versicolor laccase on pyrolytic graphite electrode.

Cyclic voltammetric data at a pyrolytic graphite electrode of 2,6-dimercaptopurine show three anodic peaks. The first and second correspond to a disulfide formation from the 6- and 2-mercapto groups, respectively, whereas the third peak is due to an oxidation to purine-2,6-disulfonic acid. Some disulfinic acid was obtained on preparative oxidation [476]. Oxidation of 6-thioguanine gives at low potential the disulfide, whereas oxidation at more positive potentials involves both the sulfur group and the purine ring [477]. 

Fig. 2. Cyclic voltammograms of horse heart cytochrome c at pyrolytic graphite electrodes 0,15 mM protein in 5 mM Tricine/100 mM NaCl, pH 8.0. Scan rate 20 mV sec. ...

Figure 5.8 Cyclic voltammogram (5mVs , 2500rpm) recorded for laccase adsorbed to (a) anthracene-modified and (b) unmodified pyrolytic graphite electrodes immediately following laccase deposition (black) and upon exchange of electrolyte (red). The inset shows...

Figure 14.3.3 Experimental and theoretical cyclic voltammograms for reduction and reoxidation of 9,10-phenanthrenequinone irreversibly adsorbed on a pyrolytic graphite electrode. Fq = 1.9 X 10 mol/cm i = 50 mV/s in 1 M HCIO4. (—) experimental...

An attempt to follow by direct electrochemistry the red-ox reactions involving the cofk tors of the RC embedded in lipid films on pyrolytic graphite electrodes has been recendy carried out, allovdng the evaluation of the peaks relative to quinones and the primary donor. Direct electrochemistry of cofactors was also realized for RC in a lipid film on graphite and ITO or sandvdched between polycation layers on gold, permitting the determination of their midpoint potentials by cyclic and square wave voltammetry. In this case evidence of the presence of peaks relative to the bacteriopheophytin was reported for the first time. ... 

Figure 23. Cyclic voltammogram of 1 mM uric acid in phosphate buffer, pH 7, at a pyrolytic graphite electrode. Sweep rate 200 mV s" ...

Figure 28. Cyclic voltammograms at a rough pyrolytic graphite electrode of (A) 200 fj,M uric acid in a solution contining 200 fiM H2O2, 0.5 M NaCl puls 5 mM Na2HP04, pH 7.5. Curve 1 shows initial sweep towards negative potentials. (B) Cyclic voltammogram of solution in (A) except 0.7 fiM type VIII peroxidase enzyme added. (C) Same as (B) except several minutes later. Sweep rate 200 mV s- ...

There have been few direct electrochemical studies of peroxidase and catalase due to the highly irreversible nature of these electrode reactions. Horseradish peroxidase was found to be electroinactive at the dropping mercury electrode. Tarasevich and co-workers observed a cyclic voltam-metric response for the electron transfer of horseradish peroxidase at an amalgamated gold electrode. However, this response was ascribed to the disulfide bonds of the protein at neutral pH and not to the heme group. No response was detected at pyrolytic graphite electrodes. ... 

Fig. II.1.26 (a) Cyclic voltammogram [123] obtained in aqueous (0.1 M NaC104) media at 20°C for solid rran -[Cr(CO)2(dpe)2l mechanically attached to a polished basal plane pyrolytic graphite electrode (scan rate = 50 mV s ). (b) Schematic representation of redox processes at the interface between solid, electrode surface, and liquid electrolyte system...

Ironically, although XO/XDH is surely the most intensively studied Mo enzyme, its electrochemistry has proven to be quite challenging. An initial unmediated electrochemical study of bacterial [Rhodobacter capsulatus) XDH reported the redox potentials of all centres using a combination of EPR monitored redox potentiometry and cyclic voltammetry. Several non-tumover responses were identified by cyclic voltammetry of XDH adsorbed on an edge-oriented pyrolytic graphite electrode. In the absence of any mediators, but in the presence of xanthine, a pronounced catalytic anodic (oxidation) wave emerged at +400 mV vs. NHE (pH 8). The catalytic current was dependent... 

Figure 5.18 Cyclic voltammetry of E. coli DMSO reductase adsorbed on a pyrolytic graphite electrode (A) at pH 8.9 in the presence of 20 mM DMSO (sweep rate 5 mV s" ) and (B) at pH 9.0 in the presence of 10 mM PMej (sweep rate 20 mV s" ). Reprinted with permission from ref. 112. Copyright 2001 American Chemical Society.

Fig. 6. Cyclic voltammograms (fourth scan, 20 mVs" ) of horse cytochrome c at various types of pyrolytic graphite electrode. Protein is 0.15 mM in 5 mM Tricine and 0.10 M NaCI at pH 8. Temperature 20 °C. In each case the corresponding X-ray photo-electron spectrum of the graphite surface is shown. The scale enlargement for the O, peak is x 3...

Figure 1. A. Cyclic voltammograms recorded with a Nafion-coated pyrolytic graphite electrode containing 1.1 x 10" mole cm of sulfonate groups. The solid line was obtained witn the Nation coating alone the dashed line resulted after incorporation of 2.2 x 10" ° mole cm of CoP(py)4 in the coating.

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