Redox-center-substituted polymers

Glucose Sensors. Siloxane polymers are known to be extremely flexible. This flexibility will, of course, be sensitive to the amount of side-chain substitution present along the polymer backbone. For instance, in the homopolymer used in these studies (polymer A), the presence of a ferrocenylethyl moiety bound to each silicon subunit should provide an additional degree of steric hindrance, and thus a barrier to rotation about the siloxane backbone, in comparison with the copolymers, which have ferrocene relays attached to only a fraction of the Si atoms. Because these siloxane polymers are insoluble in water, their flexibility is an important factor in their ability to facilitate electron transfer from the reduced enzyme. Relays contained within more rigid redox polymers, such as poly(vinylferrocene), cannot achieve close contact with the enzyme s redox centers and are thus less effective as electron transfer mediators (25,34). The importance of this feature can be seen quite clearly by comparing the mediating ability of the homopolymer A with that of copolymers B-D, as shown in Figures 4 and 5. 

The attachment of a redox center to a calkarene-substituted PPy has been achieved by the anodic oxidation of pyrrole-substituted trisbipyridylruthenium(II)-Iinked calixarenes [307]. However, only thin films with a low amount of immobilized [Ru(bpy)3] (bpy = 2,2 -bipyridine) were obtained by homopolymerization. Thicker films could be grown from copolymerization with iV-methylpyrrole. Even if the sensory properties of these polymers have not been investigated yet, it can be predicted that the electrochemical and/or luminescent responses of the ruthenium complex could be changed upon the complexation of a guest cation by the immobilized host calixarene. It must be pointed out that such a recognition event had been already observed with a polypyrrole film N-substituted by an aza crown ether-linked bipyridine ruthenimn (II) complex [271]. 

In order to prepare highly conducting materials, redox-matching of the oxidation potentials of the organic polymer and the metal center has been productively utilized [83, 84]. For example, the thiophene-substituted Schiff-base cobalt com-... 

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