Porphyrins electropolymerization

Anion-Selective Electrodes Based on Electropolymerized Porphyrin Filins... 

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

The high background impedance of the electropolymerized porphyrin films contrasts with the relatively high intrinsic conductivity observed for the electrostatic assembled Co(TRPyP)/Zn(TPPS) bilayer films (296). In this case, a very low... 

Bettelheim, A., L. Soifer, E. Korin (2004). Electropolymerized porphyrin films as methanol barriers in direct methanol fuel cells. J. Electroanal. Chem. 571, 265-272. 

Daunert, S., S. Wallace, A. Hondo, and L.G. Bachas (1991). Anion-selective electrodes based on electropolymerized porphyrin films. Anal. Chem. 63, 1676-1679. 

Presspiich, K.A., S.G. Maybury, R.E. Thomas, R.W Linton, E.A. Irene, and R.W. Murray (1989). Molecular sieving by electropolymerized porphyrin films only a few monolayers thick. J. Phys. Chem. 93, 5568-5574. 

The authors have also reported on the comparison between the electrocatalytic activity of electropolymerized films of cobalt porphyrins and phthalocyanines (cobalt tetrakis(p-hydroxyphenyl)porphyrin cobalt tetrakis(o-aminophenyl)porphyrin and Co(II)-2), with emphasis on the effect of the film thickness on the electro-oxidation of 2-mercaptoethanol [52]. It was shown that, despite the porphyrins modified electrodes exhibit electrocatalytic activity, their activity strongly depends on the film thickness with a decrease of activity as the thickness increases, in contrast to the phthalocyanine-based electrodes. This difference in behavior was attributed to lower electronic conductivity of electropolymerized porphyrin films relative to phthalocyanine-based ones, and to the potential implication of the less reactive Co(III) form of the deposited porphyrin complexes. 

Fiber optic sensors based on electropolymerized porphyrins... 

Fig. 2. Curve A Eleotropolymerization of ImH H2(o-NH2)TPP in 0.1M Et NClO /CH CN by sweeping potential at 200mV/s on Pt electrode. Numbers represent scan number. Curve B Cyclic voltammogram of an electropolymerized film of poly-[H2(o-NH2)TPP] on a Pt electrode, in 0.1M Et NClO /CH CN at 200 mV/s. Integration of the charge under the wave shows that coverage is 3.5X10 9 mol/cm of the porphyrin sites. Curve C Rotated disk electrode voltammetry of the Os(lII,Il) reaction for 0.2 mM...

Dloxygen reduction electrocatalysis by metal macrocycles adsorbed on or bound to electrodes has been an Important area of Investigation (23 ) and has achieved a substantial molecular sophistication in terms of structured design of the macrocyclic catalysts (2A). Since there have been few other electrochemical studies of polymeric porphyrin films, we elected to inspect the dloxygen electrocatalytic efficacy of films of electropolymerized cobalt tetraphenylporphyrins. All the films exhibited some activity, to differing extents, with films of the cobalt tetra(o-aminophenylporphyrin) being the most active (2-4). Curiously, this compound, both as a monomer In solution and as an electropolymerized film, also exhibited two electrochemical waves... 

Extensive work has been carried out on microsensors built from electropolymerized nickel porphyrin films.328,329 Films of Prussian blue (Fe4[Fe(CN)6]3) 345 metal-salen complexes (M = Co, Fe, Cu, Mn)346 or the ferrocene-containing Nin-tetraaza[14] annulene (24),347 also exhibit interesting activity for NO electrooxidation and sensing. 

In contrast to Co-porphyrin complexes, the direct four-electron reduction of 02 has been only very rarely claimed to be catalyzed by a cobalt phthalocyanine 404 407 In particular cofadal binuclear Co-Pc complexes immobilized on pyrolytic graphite catalyze only the two-electron electroreduction of 02 to H202.408,409 However, recent work has established that an electropolymerized Co-Pc derivative provides a stable four-electron reduction pathway over a wide pH range 410... 

N. Diab and W. Schuhmann, Electropolymerized manganese porphyrin/polypyrrole films as catalytic surfaces for the oxidation of nitric oxide. Electrochim. Acta 47, 265-273 (2001). 

An imprinted poly[tetra(o-aminophenyl)porphyrin] film, deposited on a carbon fibre microelectrode by electropolymerization, was used for selective determination of dopamine [208] in the potential range of —0.15 to 1.0 V. This chemosensor has been used successfully for dopamine determination in brain tissue samples. The dopamine linear concentration range extended from 10 6 to 10-4 M with LOD of 0.3 pM. However, this LOD value is very high compared to that of the dopamine voltammetric detection using polyaminophenol MIPs prepared by electropolymerization [209]. Dopamine was determined by CV and DPV at concentrations ranging from 2 x 10 s to 0.25 x 10 6 M with LOD of 1.98 nM. This LOD value is lower than that of PM dopamine detection [133]. 

The incorporation of vitamin B12 derivatives into plasticized poly(vinyl chloride) membranes has resulted in the development of several ion-selective electrodes (ISEs). The response of the electrodes has been related to principles of molecular recognition chemistry. In addition, ISEs have been prepared by electropolymerization of a cobalt porphyrin. These electrodes have selectivity properties that are controlled by both the intrinsic selectivity of the metalloporphyrin and the characteristics of the polymer film (e.g., pore size). 

Co(0-NH2)TPP] was polymerized onto glassy-carbon electrodes from an electrolytic solution containing the monomer and tetraethylammonium perchlorate as the electrolyte by cycling the electrode potential in the oxidative way (26). The polymerization of this monomer appears to proceed through a radical cation of the porphyrin with a mechanism similar to that of the oxidative electropolymerization of aniline (27). 

M thiocyanate solution. The lifetime of these electropolymerized electrodes (at least 2 months) is a significant improvement over that of PVC-based electrodes that use cobalt porphyrins (28, 29). The latter electrodes were selective toward thiocyanate, but the slopes of the calibration curves deteriorated substantially in less than one month. The improved lifetimes of the poly[Co(o-NH2)TPP] electrodes may be attributed to the covalent fixation of the ionophore to the polymeric matrix ... 

It should be noted that, although both the electropolymerized films and the PVC electrodes that use cobalt porphyrins as ionophores respond primarily to thiocyanate, their selectivity properties are quite different. Specifically, the electropolymerized [Co(0-NH2)TPP] films demonstrate a much larger discrimination for thiocyanate... 

Figure 8. Selectivity pattern of an ISE based on an electropolymerized cobalt porphyrin film. The electrode was exposed to the following anions thiocyanate (1), perchlorate (2), iodide (3), nitrite (4), salicylate (5), bromide (6), chloride (7), bicarbonate (8), phosphate (9). The baseline potential was 364 mV. (Adapted from ref. 26.)...

Diffuse reflectance UV-vis spectroscopy was applied in electrocatalysis by El Mouahid et al. (1998), who followed the electropolymerization of a cobalt porphyrin complex on a vitreous carbon electrode. The thin polymer... 

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