Oxidation redox cycle enabling

Figure 8 Redox cycle enabling the oxidation of unsaturatedfatty acids.

In this scenario, the bulk electron donor or reductant rapidly reduces an electron carrier or mediator, which in turn transfers electrons to the pollutant of interest. The oxidized electron mediator is then rapidly reduced again by the bulk reductant, which enables the redox cycle to continue. 

TEMPO and other organic nitroxyls have been used as catalysts in combination with numerous stoichiometric oxidants, such as sodium hypochlorite [24], PhI(OAc)2 [25], and sodium chlorite [26]. A number of recent studies have shown that NO -based redox cocatalysts enable these reactions to be conducted with O2 as the terminal oxidant [27]. The general catalytic cycle for these aerobic nitroxyl/NO -catalyzed alcohol oxidation reactions is depicted in Scheme 15.6a. A variation of this approach features halides as additives, in which the X2/HX redox couple is believed to mediate the NO2/NO and oxoammonium/hydroxylamine redox couples (Scheme 15.6b). 

Electron shuttles serve as the intermediate molecule for electron transport between the electrode and the redox enzyme in the microorganism. The key features of these chemical electron shuttles have been well established. First of all, the moleeules should be able to form redox couples. This character is indispensable as it enables them to store and release electrons, which are vital for electron shuttling. Shuttles in the oxidized state can be reduced in the presence of electrons within the cell membrane and then pass through the membrane and release the eleetrons to the anode and return to the oxidized state simultaneously. This redox cycle improves the EET and thus enhances the power output. Seeondly, both of their redueed and oxidized forms should be stable and non-degradable. Shewanella species have been proved to be able to accumulate flavins in the supernatants. External flavins at biologically relevant concentrations primarily act as electron shuttles for S. oneidensis MR-1. Finally, the shuttles should be nontoxic to the microbes. 

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