Viologen electrochemically reduced polymers

In the same study, redox polymers (223) were prepared that contained pendant viologens (Scheme 108). An active reducing agent was obtained by chemical reduction with dithionite or zinc, electrochemically, or by exposure to light. Utilization of the reduced poly(viologen) (224) as an electron transfer mediator was demonstrated by addition of a catalytic amount of the polymer to a mixture of zinc powder, ethyl benzoylformate (225) and water-acetonitrile (1 5). A quantitative yield of ethyl mandelate (226) was obtained after two days at room temperature (Scheme 109). Without the polymer, no reaction was observed after a month. 

Glyeoluril-based hosts derivatized with crown ether moieties, such as 8, are known as molecular baskets beeause of their basket- or bowl-like shape (Fig. 2a). In addition to alkali metal ions and diatmnonium salts, these moleeules are excellent receptors for charged aromatic compounds such as viologens (MAT-disubstituted 4,4 -dipyridinium compounds) and polymeric derivatives thereof." Host 8 binds 9 with a of 5.7 x 10" M, which is much stronger than the binding of 9 in the hiXparaphenylene)-[34]-crown-10 macrocycle studied by Stoddart and coworkers. Upon complexation with 8, the redox properties of 9 were modified, i.e., bound 9 is 100 mV more difficult to reduce than uncomplexed 9. Once reduced to its 1+ form, however, 9 is expelled from the cavity. In the case of polymeric derivatives of 9, the electrochemical properties of the polymer are altered by the addition of Host 8. 

Viologen-acrylamide copolymers have been used in a similar manner to entrap enzymes and carry out direct reduction of the active site by bound viologen moieties. In these studies the polymer was reduced chemically rather than electrochemically, but there appears no reason in principle why this same chemistry could not be carried out on an electrode. These viologen-acrylamide copolymers have been shown to reduce nitrate reductase (EC 1.9.6.l/ and glutathione reductase (EC 1.6.4.2). 2 >... 

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