Polypyrrole coated electrodes

Komori and Nonaka132,133 electrochemically oxidized methyl, isopropyl, n-butyl, isobutyl, r-butyl and cyclohexyl phenyl sulfides (108) and cyclohexyl p-tolyl sulfide (109) to their sulfoxides using a variety of polyamino acid-coated electrodes to obtain the range of e.e. values shown in parentheses. The highest enantiomeric purities were obtained using an electrode doubly coated with polypyrrole and poly(L-valine), an electrode which also proved the most durable of those prepared. 

Several alkyl aryl sulfides were electrochemically oxidized into the corresponding chiral sulfoxides using poly(amino acid)-coated electrodes448. Although the levels of enan-tioselection were quite variable, the best result involved t-butyl phenyl sulfoxide which was formed in 93% e.e. on a platinum electrode doubly coated with polypyrrole and poly(L-valine). Cyclodextrin-mediated m-chloroperbenzoic acid oxidation of sulfides proceeds with modest enantioselectivity44b. 

An electron transfer type of enzyme sensor was thus fabricated by a electrochemical process. Although no appreciable leakage of ADH and MB from the membrane matrix was detected, NAD leaked slightly. To prevent this leakage, the ADH-MB-NAD/polypyrrole electrode was coated with Nation. A calibration curve is presented in Fig.25 for ethanol determination in an aquous solution with the enzyme sensor. Ethanol is selectively and sensitively determined in the concentration range from 0.1 nM to 10 mM. 

In order to determine whether the new nanotubule electrode shows improved performance, a control electrode composed of the same material but prepared via a more conventional method is required. This control LiMn204 electrode was prepared by applying the precursor solutions described above directly onto a 1 cm Pt plate and thermally processing as before. Scanning electron micrographs showed that these films consisted of LiMn204 particles with diameters of —500 nm [124]. Spectrophotomet-ric assay showed that this control electrode also contained 0.75 mg of LiMn204 per cml A polypyrrole coat identical to that applied to the tubular electrode (0.065 mg) was also applied to this control electrode. 

Photoinduced Changes in Phase Boundary Potentials. The photoinduced membrane potentials were measured by using PVC matrix liquid membranes in contact with a polypyrrole-coated Pt electrode [dibutyl phthalate (DBP) as the membrane solvent]. The polypyrrole layer allows to obtain a stable and sample-in-dependent potential drop between Pt and the PVC membrane. The phase boundary potential at the interface of a membrane containing ionophore and an aqueous RbCl or KCl solution could be reversibly altered by UV and visible light irradiation, as shown for ionophore 89 in Figure 23a,b. The values of the photoinduced potential... 

H. Shinohara, G. F. Khan, and M. Aizawa, Electrochemical oxidation and reduction of PQQ using a conducting polypyrrole-coated electrode, J. Electroanal. Chem. 304, 74-84 (1991). 

Alkyl aryl sulfides electrochemically oxidized on electrodes whose surfaces were modified by coating them with optically active compounds like camphoric acid [89] and poly(amino acids) [90, 91] afford mixtures of sulfoxides with variable enantiomeric excess. An optical yield of 93% is claimed when f-butyl phenyl sulfide is oxidized at a Pt electrode doubly coated with polypyrrole and poly(L-valine) [91]. 

H. Yoneyama, K. Wakamoto, and H. Tamura, Photoelectrochemical properties of polypyrrole-coated silicon electrodes, J. Electrochem. Soc. 132 2414, 1985. 

R. E. Malpas and B. Rushby, The stability of two-layer ferrocene/polypyrrole-coated n-Si electrodes in aqueous photoelectrochemical photovoltaic cells, J. Electroanal. Chem. 157, 387, 1983. 

R. A. Bull, F.-R. F. Fan and A. J. Bard, Polymer films on electrodes VII. Electrochemical behavior at polypyrrole-coated platinum and tantalum electrodes, J. Electrochem. Soc. 129 (1982) 1009-1015. 

The recent work of Albano et aL illustrates a particularly innovative ap-phcation of molecular imprinting [148]. In the presence of sodium dodecyl sulfate (SDS), a thin layer of polypyrrole was electrodeposited onto the surface of a quartz crystal Removal of the SDS by washing with water afforded a molecularly imprinted sensor element which could be used to monitor levels of pollutant siuTactants in river water. Thus, the piezoelectric quartz sensor was contained within a flow cell so that the MlP-coated side of the crystal remained in contact with analyte solution while the electrodes of the sensor were connected to an oscillator circuit. A significant drop in the quartz crystal oscillation frequency occmred when the sensor was in contact with SDS. This is consistent with an increase in mass on the surface of the sensor, suggesting that SDS molecules had bound to the layer of imprinted polypyrrole. A reference polypyrrole-coated sensor, prepared in parallel to the MlP-sensor but in the absence of SDS, showed only a minimal response to the target analyte. 

Figure 16.10 OCP curves of coated PPy zinc electrodes cured In air for 1 h at 180 °C and immersed in 3.5% NaCI solution. PPy films (Ri2iim thick) were synthesized in 2 M NaSac+ 0.5 M Py at pH 5 and 1.9 M NaSac + 0.1 M DISacH + 0.5 M Py at pH 5.4. (Reprinted with permission from Chemistry of Materials, Ultrafast electrosynthesis of high hydrophobic polypyrrole coatings on a Zinc electrode Applications to the protection against Corrosion by E. Hermelin,]. Petitjean, P.C. Lacaze et al., 20, 13, 4447—4456. Copyright (2008) Elsevier Ltd)...

E. Hermelin, J. Petitjean, J.-C. Lacroix, K.I. Chane-Ching, J. Tanguy, and P.C. Lacaze, Ultrafast electrosynthesis of high hydrophobic polypyrrole coatings on a Zinc electrode Applications to the protection against Corrosion, Chem. Mater., 20, 4447 1456 (2008). 

Wadhwa, R., Lagenaur, C.F., Cui, X.T., 2006. ElectrochemicaUy controlled release of dexamethasone from conducting polymer polypyrrole coated electrode. J. Controlled Release 110,531-541. 

All of the above modes of operation serve to increase sensitivity, and to some degree selectivity. They do, however, have some disadvantages when compared to conventional electrodes. With CMEs, the electrode preparation stage is obviously more detailed and time-consuming. Preparation of a conventional substrate is usually the first, and most important, step. For example, we have found that the analytical performance of polypyrrole coated on platinum substrate depends critically on the substrate preparation. Furthermore, the method of attaching the modifier, whether by chemisorption, covalent bonding or electropolymerisation, must also be carefully controlled if reproducible electrode surfaces are to be obtained. There is no doubt, however, that these time consuming procedures can be tolerated if the elect roan alyti cal chemist is provided with a surface which displays improved performance, reproducibility and stability over an extended time period. 

The use of polymer modified electrodes for the FIA determination of electroinactive anions has been reported by Ikariyama and Heineman. This method is based on repetitive doping-undoping of the polypyrrole coating due to influx/regress of anions such as PO and COg , and could determine concentration of these ions between 10 fiM to 1 mM. The coating was found to be stable for two weeks in an anaerobic atmosphere. 

FIGURE 16.8 (a) Stainless steel electrode partially coated with an electrogenerated polypyrrole film, (b) adhesion... 

Aoki T, Tanino M, Sanui K, Ogata N, Kumakura K, Okano T, et al. Culture of mammalian cells on polypyrrole-coated TTO as a biocompatible electrode. Synth Met 1995 71. 

Skotheim, T., Photoelectrochemical cells based on polypyrrole coated n Si electrodes, Polym. Prepr, 23, 136 (1982). 

Jackowska, K., and Tien, H. T., Electrochemical solar cells with polypyrrole coated CdBe sintered electrodes, J. Appl. Electrochem., 18, 357-362 (1988). 

Finally, two reports have appeared in which polypyrrole-modified electrodes have shown electrochemical selectivity. In one report, polypyrrole coated electrodes are reported to selectively permit the reaction to occur in the presence of the... 

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