Poly electrode coating

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (— )camphoric anhydride or (S)-phenylalanine methyl ester299. Much better results were obtained with the poly(L-valine) coated platinum electrodes300. For example, t-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

ControlW potential electrolyses of dibromostilbenes at poly-7i coated platinum foils gave results similar to those previously observed The electrodes lose... 

A poly(aniline boronic acid)-based conductimetric sensor for dopamine consisting of an interdigitated microarray electrode coated with poly(aniline boronic acid) has also been developed by the Fabre team. The sensor was found to show a reversible chemoresistive response to dopamine without interference by ascorbic acid from their mixtures.42... 

Figure 30. In situ measurements of the time evolution of the Cu K-edge when a platinum electrode coated with a polymeric film of poly (methylthiophene) is cathodically polarized in an aqueous solution containing 50 mM CuCl2. (From Ref. 105, with permission.)... 

Electrocatalytic dehalogenation of organohalides has also been performed in heterogeneous conditions, at a graphite electrode coated by a poly(acrylic acid) film grafted with the nickel(II) tetra-azamacrocyclic complex (20).292... 

J.P. Lowry and R.D. O Neill, Partial characterization in vitro of glucose oxidase modified poly(phenylenediamine)-coated electrodes for neurochemical analysis in vivo. Electroanalysis 6, 369— 379 (1994). 

Figure 2. Cyclic voltammetry as a function of scan rate of a poly(I)-coated Pt electrode with a coverage of 8 x 10-8 mol/cm2 of V2 + centers in CH3CN/0.1 M [Q-Bu4N]PF6.

Figure 3. Cyclic voltammetry of adjacent electrodes of a poly(I)-coated microelectrode array driven individually and together at 200 mV/s in the region of the oxidative potential of polythiophene in CH3CN/O.I II [11-BU4N] PFg.

Figure 5. Generation/collection experiment with poly(I)-coated microelectrodes in CH3CN/O.I M [n-Bu4N]PFg at 10 mV/s. The lower cyclic voltammograms are for the generator electrode as its potential is swept between -0.2 V and -0.9 V vs. Ag+/Ag while the potential of the collector electrodes is held at 0.0 V vs. Ag+/Ag.

A variety of phenol couplings have been described. Those reported before 1991 have been reviewed [66]. 2-Naphthol (27) was oxidized to l,l -binaphthol (28) in high current efficiency on a graphite felt electrode coated with a thin poly(acrylic acid) layer immobilizing 4-amino-2,2, 6,6-tetramethylpiperidinyl-l-oxy (4-amino-TEMPO) (Scheme 10) [67]. 

The electrochemical oxidation of phenols produces quinones that can be used as dienophiles for the Diels-Alder reaction. A typical example is shown in Scheme 14, where a lithium perchlorate/nitromethane system and an electrode coated with a PTFE [poly-(tetrafluoroethylene)] fiber, to create a hydrophobic reaction layer. 

Electrodes coated with thin polymeric films of poly-c -[Ru(vbpy)2(H20)2] " (vbpy = 4-methyl-4 -vinyl-2,2 -bipyridine) or poly-cw-[Ru(pyr-bpy)2(H20)2] (pyr-bpy = 4-(2-pyrrol-l-yl-ethyl)-4 -methyl-2,2 -bipyridine) have been prepared, and cyclic voltammograms of these films are similar to that of c -[Ru (0)2(bpy)2] in solution. ... 

A cell with a small Pt disk working electrode coated with a polyelectrolyte multilayer made of poly(allylamine)-poly(vinyl sulfate), a Pt wire counterelectrode and a reference SCSE may be used for selective amperometric determination of H2O2, in the presence of ascorbic acid (22), uric acid (29) and acetaminophen (148). The latter three compounds show a significant response with the bare working electrode at +0.6 V while a practically nil one with the coated electrode. The reason for this selectivity may be an exclusion effect by the coating. ... 

Fe2+/Fe3+ at the naked n-Si electrode drops to zero in less than 30 s, whereas the poly(pyrrole)coated n-Si gives a stable photocurrent for 5 days. The power conversion efficiency was 3 % corresponding to Isc of 3.2 mA/cm2, Voc of 0.39 V, and a fill factor of... 

One problem for the coated system is that the film is peeled off after prolonged irradiation. In order to have a more adhesive film, the surface of n-Si was modified with N-(3-trimethoxysilyIpropyl)pyrrole (22). Pyrrole was then electrodeposited on this modified electrode as shown in Eq. (24) 85). The durability of the coated poly(pyrrole) was improved by such a treatment of n-Si surface. The n-Si electrode coated only with poly(pyrrole) gave a declined photocurrent from 6.5 to 1.8 mA cm-2 in less than 18 h, while the poly(pyrrole) coated n-Si treated at first with 22 as Eq. (24) gave a stable photocurrent of 7.6 mA cm-2 for 25 h. When an n-Si electrode was coated with Pt layer before the deposition of poly(pyrrole), the stability of the semiconductor was improved remarkably (ca. 19 days)85b). A power conversion efficiency of 5.5% was obtained with iodide/iodine redox electrolytes. 

Further materials that have been evaluated as supports for solid-phase synthesis include phenol-formaldehyde polymers [239,240], platinum electrodes coated with polythiophenes [241], proteins (bovine serum albumin) [242], polylysine [243], soluble poly (vinyl alcohol) [244], various copolymers of vinyl alcohol [4,245,246], and soluble dendrimers [14,247]. 

Mizutani et al. [34] Acetic acid Wines Acetate kinase (AK), pyruvate kinase (PK) and pyruvate oxidase (PyOx)/on a photocross-linkable poly(vinyl alcohol) bearing stilbazolium group membrane Platinum electrode coated with poly (dimethylsilaxane)/-0.4 V vs. Ag/AgCl ... 

Fig. 2.11. Cyclic voltammograms of a poly(aniline)-coated glassy carbon electrode (deposition charge ISO mC, geometric area 0.38 cm2), recorded at 5 mV s 1 in oxygen-free 0.1 mol dm 3 citrate/phosphate buffer at pH 5 in the absence (—), and in the presence (—), of 1 mmol dm-3 NADH. Before each scan the electrode was held at -0.3 V for 3 min to ensure complete reduction of the film.

Fig. 2.12. Plot of the current as a function of time for the oxidation of 4 mmol dm- 1 NADH at 0.2 V at a poly(aniline)-coated rotating disc electrode (area 0.38 cm2, deposition charge ISO mC) in 0.1 mol dm 1 citrate/phosphate buffer, pH 5. The rotation speed of the electrode was increased in the sequence I, 4, 9, 16, 25, 36 and 49Hz and reduced in sequence back to 1 Hz. The broken line connects segments of the curve corresponding to the different rotation speeds. Note The current decays more rapidly at the higher rotation speeds and responds rapidly to changes in rotation speed.

Fig. 2.14. Plots of the first-order decomposition of NADH in pH S buffer measured electro-chemically at a poly(aniline) coated electrode (O), and spectrophotometrically ( ).

Fig. 2.17. Plots of the current at +0.1 V for a poly(aniline)/poly(vinylsulfonate)-coated glassy carbon electrode (deposition charge 150 mC, geometric area 0.38 cm2) rotated at 9 Hz in 0.1 mol dm- 1 citrate/phosphate buffer at pH 7 as a function of the NADH concentration showing the stability of the electrode response. Four replicate calibration curves recorded in succession over 4h using the same electrode are shown ( ) run 1 ( ) run 2 (A) run 3 and (O) run 4. The solid line is drawn as a guide for the eye.

NADH oxidation to function equally well for the oxidation of NADPH. Figure 2.22 shows a direct comparison of the responses of a poly(aniline)-coated electrode to NADH and NADPH. At low concentrations, the currents are identical within experimental error but at higher concentration (in this case above 0.6 mmol dm-3), the currents for NADPH fall below those for NADH. These results clearly show some saturation of the current at high NADPH concentrations. 

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