Ferrocene polymers polythiophenes

Another method for the analysis of aptamer-protein complexes involved the use of a positively charged ferrocene-tethered polythiophene, (19), as redox label reporting unit (Fig. 12.19). The antithrombin aptamer was immobilized on an electrode surface, and the electrostatic binding of the redox polymer (19) to the aptamer monolayer resulted in a supramolecular complex that revealed electrical contact between the polymer and the electrode.74 The formation of the aptamer-thrombin complex removed the polymer from the surface and blocked the electrical contact between the polymer label and the electrode. As a result, higher concentrations of thrombin increased the surface coverage of the aptamer-thrombin complex on the electrode, and this decreased the amperometric responses of the sensing device. 

Le Floch and co-workers isolated ferrocene-containing polythiophenes for use in deoxyribonucleic acid (DNA) detection.230 The reaction between thiophene 160 and the functionalized ferrocene 161 gave the ferrocene functionalized polythiophene in a quantitative yield (Scheme 2.43). Polymerization in the presence of FeCl3 led to a water-soluble polymer containing a cationic side chain and an electroactive ferrocene moeity. These polymers showed a DNA detection limit of 5 X10-10M. 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

The electropolymerization of metallocene-functionalized pyrrole and thiophene has been utilized for the creation of organometallic polypyrroles and polythiophenes.181 241 242 243 Zotti et al. reported the electrochemical homo- and copolymerization of ferrocene-functionalized pyrrole, 177.242 Polymer 179 was prepared via the copolymerization of monomer 177 with pyrrole (Scheme 2.48). This polymer possessed an electrical conductivity of 1.5 X 10-2 S/cm. 

Ferrocene is an attractive and convenient organometallic species to incorporate into conjugated polymers—it is stable, easy to functionalize, has reversible electrochemistry, and its derivatives (both monomeric and polymeric) can be easily characterized [e.g., by nuclear magnetic resonance (NMR) spectroscopy]. Ferrocene has been incorporated into the backbone and side chains of polythiophene 45 In 1999, both Higgins and Wolf independently reported the synthesis of polythiophenes with ferrocene in the backbone.46,47 Electropolymerization of ferrocene substituted... 

Polythiophenes with ferrocenes in the main chain 41 have been prepared by electropolymerization of bis-substituted ferrocene monomers, but only for the n = 2 and n = 3 monomers [78,79]. The resulting film of the n = 2 monomer showed a thiophene > Fe(III) LMCT band at 1395 nm. A soluble derivative of the n = 3 polymer has been prepared. The oxidized form is blue with a thiophene > Fe(III) LMCT band at 590 nm [80], In general, it has been found that these systems show greater delocalization, the longer the thiophene chain and the better is the matching of the ferrocene and thiophene redox potentials [81,82],... 

Polypyrroles and polythiophenes with pendant ferrocene groups (e.g., 23) have also been prepared using electropolymerization techniques.Studies of these materials using in situ conductivity measurements revealed that the redox conduction, due to hole hopping between the ferrocene units, was enhanced by a decrease of the Fc-backbone distance and by conjugation of the organometallic group with the polymer backbone (as in polymer 23 which possesses a redox conductivity of ca. 8 x 10 Scm ). 

Redox reactions this polymer exhibits the redox transitions of both the ferrocene unit and the polythiophene backbone. 

G. Zotti, S. Zecchin, G. Schiavon, A. Berlin, G. Pagani and A. Canavesi, Conductivity in redox modified conducting polymers. 2. Enhanced redox conductivity in ferrocene-substituted polypyrroles and polythiophenes, Chem. Mater., 1, 2309 - 2315 (1995). 

Polythiophenes, 3-substituted by bipyridyl [268], benzoquinone [269], viologen [270], ferrocene [271], and tetrathiafulvalene [272], have been reported. The redox group is generally apparent in the voltammetric response of the polymers obtained, while the response of the polyconjugated chain is not, an indication of degradation of the backbone. Polymers of better quality with ferrocene and viologen pendants were later electrodeposited from bi- and terthiophenes [273]. 

The electrochemical polymerization of monomers 41-43 resulted in the isolation of polythiophenes with ferrocene groups pendent to the backbone. It was noted that the redox potential of the polymer from the ferrocene-ftmctionaUzed monomer 41 was the same as from n-hexylferrocene. However, increases of about... 

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