Polymeric redox mediators

Polymeric redox mediators have been used for the transport of electrons between active sites of redox enzymes and electrodes 1-11). In complexes between high molecular weight redox polymers and redox en mes, electrons are transfer] efficiently from the substrate reduced redox active site of tihie enzyme to redox centers of the polymers (7,72)... 

A new crosslinkable polymer was synthesized by the SBP-catalyzed polymerization of cardanol. When HRP was used as catalyst for the cardanol polymerization, the reaction took place in the presence of a redox mediator (phe-nothiazine derivative) to give the polymer. Fe-salen efficiently catalyzed the polymerization of cardanol in organic solvents (Scheme 29). " The polymerization proceeded in 1,4-dioxane to give the soluble polymer with molecular weight of several thousands in good yields. The curing of the polymer took place in the presence of cobalt naphthenate catalyst at room temperature or thermal treatment (150°C for 30 min) to form yellowish transparent films ( artificial urushi ... 

Rau J, Maris B, Kinget R et al (2002) Enhanced anaerobic degradation of polymeric azo compounds by Escherichia coli in the presence of low-molecular-weight redox mediators. J Pharm Pharmacol 54 1471-1479... 

The effect of concentration of the redox mediator on the formation of PEDOT/PSSNa was studied by these researchers by varying the concentration of terthiophene (0.025-1%) in a series of reactions. At least 0.5% (by weight of monomer concentration) of the terthiophene was observed to be required to initiate the polymerization of EDOT using SBP (Fig. 8). PEDOT/PSSNa was not formed when the concentration of terthiophene was 0.025%. The polymerization was also performed at various pH conditions, and the concentration of the final polymer was monitored spectroscopically, as shown in Fig. 8b. It could also be observed that the... 

Scheme 5 Above Polymerization of EDOT catalyzed by SBP using terthiophene as a redox mediator. Below Proposed mechanism for the reaction. (Reprinted with permission from Nagarajan et al. [44]. 2008, American Chemical Society)...

The amino acid residues at the environment of the catalytic tryptophan described above (Fig. 3.6) could be responsible for the differences observed in the oxidation of high redox-potential aromatic substrates by VP and LiP. In this regard, LiP needs redox mediators for oxidation of some compounds that are directly oxidized by VP, such as Reactive Black 5 (RB5) and even polymeric lignin (although model dimers are directly oxidized) [10]. In contrast, VP exhibits a lower efficiency oxidizing VA than LiP. 

Relevant issues still to be addressed in constructing amperometric enzyme sensors either using the electrical wiring of enzymes with redox polymers or with flexible polymeric electron mediators are sensor efficiency, accuracy, reproducibility, selectivity, insensitivity to partial pressure of oxygen, detectivity (signal-to-noise ratio) as well as sensor hfetime and biocompatibility [47]. Then we can address manufacturability and the cost of use of either in vitro or in vivo sensors. 

Ferrocene modified flexible polymeric electron transfer systems Ferrocene and its derivatives are readily available and commonly used organometalUc redox mediators, so it is quite natural that they were selected first to synthesize mediator modified polymeric electron transfer systems. Siloxane pol5uners are flexible but aqueous insoluble pol3nmers. As previously indicated, a flexible polymer backbone allows close contact between the redox center(s) of the enzyme and the mediator, and the water insoluble property of the polymer prevents not only redox polymer from leaching into bulk media but also prevents enzyme diffusion away fi-om the electrode surface by entrapping it in the polymer/carbon paste matrix. Therefore, ferrocene and... 

Quinone modified polymeric electron transfer systems The redox mechanism of quinone (two electron-proton acceptor/donor) is pH dependent and somewhat more complicated than for ferrocene or osmium (one electron accepter/donor). However, quinones are naturally occurring redox mediators and therefore, many researchers have studied their application to biosensors [107-109]. 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Monomeric and polymeric A-alkylpyridine-4-carboxylates serve as redox mediators for the indirect electroreduction of z /c-dihalides to PYWj -olefins [219,220]. 

The electrolytic oxidation was found to proceed much faster in the presence of Cu-pyridine as a redox mediator in the electrolytic cell divided with a membrane. The electrode coated with Cu/poly(4-vinylpyridine) was also effective for the oxidative polymerization, and what was more, without a partition membrane (Figure 8). Polymer-Cu complex film coated on the electrode prevented formation of the insulating film of the product polymer on the electrode surface and decreased the electrolytic potential. The oxidation using the electrode coated with a macromolecular Cu complex provides a facile method for forming poly(phenylene oxide)s. 

A new crosslinkable polymer was synthesized by the SBP-catalyzed polymerization of cardanol [103]. When HRP was used as catalyst for cardanol polymerization, the reaction took place in the presence of a redox mediator (phenothiazine derivative) to give the polymer [104]. 

Figure 8.10 PEDOT enzymatic polymerization by using terthiophene as substrate/redox mediator (Reproduced with permission from [86]. Copyright (2008) American Chemical Society).

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