Electropolymerization functional molecules

In addition to catalysis of small molecule transformations and biocatalysis, non-functionalized LLC phases used as reaction media have also been found to accelerate polymerization reactions as well. For example, the L and Hi phases of the sodium dodecylsulfate/n-pentanol/sulfuric acid system have been found to lower the electric potential needed to electropolymerize aniline to form the conducting polymer, polyaniline [110]. In this system, it was also found that the catalytic efficiency of the L phase was superior to that of the Hi phase. In addition to this work, the Ii, Hi, Qi, and L phases of non-charged Brij surfactants (i.e., oligo(ethylene oxide)-alkyl ether surfactants) have been observed to accelerate the rate of photo-initiated radical polymerization of acrylate monomers dissolved in the hydrophobic domains [111, 112]. The extent of polymerization rate acceleration was found to depend on the geometry of the LLC phase in these systems. Collectively, this body of work on catalysis with non-functionalized LLC phases indicates that LLC phase geometry and system composition have a large influence on reaction rate. 

Different examples of hydrogenation of organic molecules with conducting polymer modified electrodes have been described rather recently in the literature. Two different kinds of modification have been considered for this application insertion of metallic particles, and functionalization of pyrrole with transition metal complexes leading, after electropolymerization, to active electrodes. 

Pyrrole electropolymerization on noninert metallic substrates has been specially optimized for aluminum [33,34] and stainless steel [35,36]. In the case of aluminum electrodes, highly conductive polypyrrole films are obtained from solutions of t-butylammonium p-toluenesulfonate in acetonitrile [37]. Their conductivities range between 10 and 350 S cm", as a function of the electrical and chemical variables of synthesis. On stainless steel, highly conductive polypyrrole films can be obtained by means of square waves of potential [36]. In this case, charging of the electrical double layers, oxidation of pyrrole molecules, and formation of a porous oxide layer occur during the application of the anodic step and promote the polymerization process. The application of the cathodic potential seems to avoid corrosion... 

Controlled electrochemical synthesis of conductive polymer nanotubes in a porous alumina template has been studied as a function of monomer concentration and potential in the case of PEDOT the electropolymerization leads either to solid nanowires or to hollow nanotubes depending on the template pore diameter, the applied oxidation potential and the monomer concentration [265], Nanowires are formed at slow reaction rate and high concentration monomer supply in fact monomeric molecules should have enough time to diffuse into and fill the pores, from the bulk solution. On the other hand, nanotubes are predominantly formed with fast reaction rate and low monomer concentration, because the monomers that diffuse from the bulk solution can be deposited along the pore wall thanks to the interaction of the polymer with the wall surface. 

It is not surprising that electropolymerization has been used to make functional layers for biosensors. A fruitful development of fimctional layers started with this appHcation. The method was used preferably to immobilize enzymes, either by embedding in polymer layers or by linking with polymer surfaces which had been fimctionalized before by attachment of amino groups. The stability of embedded molecules has been further improved by crossUnking with glutaraldehyde. 

Another approach is to occlude into the electroconductive polymer film a second polymer that contains functionalities to which indicator molecules may be conveniently covalently attached. Guiseppi-Elie and Wilson [180] coelectropolymerized pyrrole and 3-(l-pyrrolyl)-propionic acid in the presence of poly(styrenesuIfonic acid) and polyvinylamine (PVAm). Incorporation of the PV Am into the polymer film confers free primary amines on the surface of the film. Using aqueous cross-linking chemistry Guiseppi-Elie and Wilson conjugated the suc-cinamide ester of NHS-LC-biotin to the primary amine sites of the polymer surface. A simple variation on this theme can produce a wide variety of chemical and biological sensors. The occlusion of human serum albumin (HSA) [154] or bovine serum albumin (BSA) by electropolymerization in electroconductive polymer can also provide —COOH, —NH2, and —SH sites for the convenient attachment of indicator molecules. Likewise, macromolecular counteranions may be functionalized prior to or following occlusion into the CEP membrane. 

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