Electropolymerization solution-surface

Stejskal that aniline radical cations adsorb on the substrate surface during an induction period before bulk polymerization is observed. The adsorbed species promote the formation of a dense film initially on the substrate surface. Once this film has formed, further growth occurs on the PAn surface in a manner similar to the growth of localized globules during electropolymerization. The surface roughness of in situ PAn films may be further increased by the incorporation of PAn precipitates from the bulk solution. 

Pringle J. M., Fors5d h M., Wallace G. G., and MacFarlane D. R, Solution-surface electropolymerization a route to morphologically novel poly(pyrrole) using an ionic liquid. Macromolecules, 2006, 39, 7193-7195. 

The enzyme can be immobilized on the electrode by several techniques (53). The simplest method, first used in 1962, is to trap an enzyme solution between the electrode surface and a semipermeable membrane. Another technique is to immobilize the enzyme in a polymer gel such as polyacrylamide which is coated on the electrode surface. Very thin-membrane films can be obtained by electropolymerization techniques (49,54,55) using polypyrrole, polyindole, or polyphenylenediamine films, among others. These thin films (qv) offer the advantage of improved diffusion of substrate and product that... 

The [Co(terpy)2]+ ion (terpy = 2,2 6, 2"-terpyridine) has been found to catalyze the reduction of C02 when the divalent precursor is immobilized on electrode surfaces. The vinyl-substituted terpy analog was electropolymerized to give a film that reduced the overpotential for C02 reduction in DMF and MeCN by more than 1V.104 The activity of this surface-confined species was superior to that of the complexes in solution.105 Similarly, in water, the [Co(terpy)2]2+ ion immobilized and reduced in situ within a Nafion film also catalyzes the reduction of C02106 and H+ ions.107... 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

Despite the vast quantity of data on electropolymerization, relatively little is known about the processes involved in the deposition of oligomers (polymers) on the electrode, that is, the heterogeneous phase transition. Research - voltammetric, potential, and current step experiments - has concentrated largely on the induction stage of film formation of PPy [6, 51], PTh [21, 52], and PANI [53]. In all these studies, it has been overlooked that electropolymerization is not comparable with the electrocrystallization of inorganic metallic phases and oxide films [54]. Thus, two-or three-dimensional growth mechanisms have been postulated on the basis that the initial deposition steps involve one- or two-electron transfers of a soluted species and the subsequent formation of ad-molecules at the electrode surface, which may form clusters and nuclei through surface diffusion. These phenomena are still unresolved. 

Examples of surface-immobilized mediators are electropolymerized azines for electro-oxidation of The extreme form of this approach is formation of biocatalytic monolayer, comprising a surface-bound mediator species that is itself bound to a single enzyme molecule. Katz et al. report a complete cell based on novel architecture at both electrodes (Figure 7). On the anode side, the FAD center of glucose oxidase is removed from the enzyme shell and covalently attached to a pyrroloquinoline quinone (PQQ) mediator species previously immobilized on a gold surface. The GOx apoenzyme (enzyme with active center removed) is reintroduced in solution and selectively binds to FAD, resulting in a PQQ-... 

Most suitable for electrically conducting materials such as carbon fibers, the electrochemical processes involve deposition of polymer coatings on the fiber surface through electrodeposition or electropolymerization techniques. The major advantage of these processes is that a uniform layer of controlled thickness and variable polymer structure and properties can be obtained by controlling the current and the solution concentration. 

Formate production has also been reported for electropolymerized films of [Co(4-vinylterpyridine)2] " on glassy carbon electrodes in dimethylformamide solutions [63]. Interestingly, the product of this same catalytic system in aqueous solutions is formaldehyde [81]. Other heterogeneous systems that produce formate include Cd, Sn, Pb, In, and Zn electrodes in aqueous media [12] (see also Vol VII 5.2.3). It is likely that the pathway to formate formation on metal electrodes follows the sequence of M—H bond formation followed by CO2 insertion to form a M—0C(0)H species followed by desorption from the electrode surface. 

Procedure-Electron-Mediated Biosensor. 1,3-DAB was electropolymerized onto the graphite from a 3 mM solution in phosphate buffer using cyclic voltammetry. The potential was cycled from 0.00 V to +0.80 V and back to 0.00 V (vs SCE) at 5 mV/s for twelve scans. l,r-dimethylferrocene (1,1 -DMF) was adsorbed onto an inverted electrode. Three successive drops of a saturated solution (10 pL each) were added to the surface and each was allowed to air dry before applying the next drop. The electrode was rinsed with water after application of each drop. 

The chemical reaction mechanism of electropolymerization can be described as follows. The first step in course of the oxidative electropolymerization is the formation of cation radicals. The further fate of this highly reactive species depends on the experimental conditions (composition of the solution, temperature, potential or the rate of the potential change, galvanostatic current density, material of the electrode, state of the electrode surface, etc.). In favorable case the next step is a dimerization reaction, and then stepwise chain growth proceeds via association of radical ions (RR-route) or that of cation radical with a neutral monomer (RS-route). There might even be parallel dimerization reactions leading to different products or to the polymer of a disordered structure. The inactive ions present in the solution may play a pivotal role in the stabilization of the radical ions. Potential cycling is usually more efficient than the potentiostatic method, i.e., at least a partial reduction... 

The LB film of a conducting polymer was first prepared by Iyoda et al. [82-85] using an amphiphilic pyrrole derivative mixed with octadecane. This precursor LB film is electropolymerized to give a lateral conductivity of 0.1 S/cm, with the conductivity in the perpendicular direction being 10"11 S/cm. The procedure of the electropolymerization is shown in Fig. 9 The precursor film is immersed in an acetonitrile solution of LiC104 by a few millimeters, and the electropolymerization starts near the liquid surface and proceeds upward. 

It was observed that the direct electrodeposition of H2(ETRPyP) from a DMF solution leads to poor quality films, due to the looseness of the presumably low molecular weight polymeric chains. Considering that the supramolecular porphyrin is able to form quite homogeneous films by dip coating (122, 167, 170, 184, 250, 286, 296) and that such films are poorly soluble in acetonitrile, an altenative procedure was devised. This procedure was carried out by an electropolymerization reaction on pre-formed films (53, 172), whose advantages are the high concentration of the monomer on the electrode surface and the presence of suitably preoriented molecules, which keep the n-stacking structure of the dip-coated films. Such characteristics increase the efficiency of the electropolymerization, since only one or two scans in the... 

Figure 39. Morphology of the surface of a dip-coated film before and after electropolymerization (two scans) in TEACIO4 0.2 Af acetonitrile solution, in the -1.3 to 1.2V-range.

A transformation of some synthetic versatility is the oxidation of methyl groups in a methylcobaltocenium salt by Mn04 to give the respective carboxylic acid. In this way, mono- and dicarboxylatocobaltocenium salts have been prepared. These acids can be further functionalized and used as receptors for the selective recognition of anion guest species. A pyrrole-fimctionalized cobaltocenium salt has also been electropolymerized on an electrode surface this system displays anion sensing in solution and when immobilized. ... 

---