Applications in Redox Cofactor Electrochemistry

In this section we review applications of electroactive polymers as electrode materials for use with redox cofactors, primarily NAD/NADH, and with components of redox proteins and redox enzymes, such as iron-sulphur clusters or flavins. We begin by considering the NAD/NADH couple. 

Oxidation of NADH at both poly(3-methylthiophene) and poly(pyrrole) has been studied. Using poly(3-methylthiophene) Atta et observed some 

FIGURE 9.19. Structures of poly(pyrroles) modified by chloroanil and 2,3-dichloro-1,4-naphthoquinone (see Ref. 129). 

In the study of NADH oxidation at poly(pyrrole), Schuhmann and colleagues used poly(pyrrole) and modified poly(pyrrole) films. For poly(pyrrole) itself and poly(pyrrole) containing electrostatically bound ferricyanide, vanadate, or molybdate anions, they observed no NADH oxidation, although these electroactive anions are known to oxidize the NADH in homogeneous solution. By using pyrrole modified by covalent attachment of chloranil or 2,3-dichloro-1,4-naphthoquinone (Fig. 9.19) structures, they were able to obtain catalytic oxidation of NADH and reasonable stability. It this case quinone functionalities are presumed to act as catalytic sites for oxidation, since they are known to be efficient homogeneous oxidants for NADH.  

Electropolymerized films of mediator species, such as mercaptoquinone, N-methyl phenazinium ion, and thionine (a redox dye), were also shown to mediate NADH oxidation, although in these latter cases, the structure of the electropolymerized film is not well-established. 

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