Iron hydroxide, electron acceptors

Compared with electron donors, the relative difference in Gibbs energy is much greater for a range of ferric iron electron acceptors in iron reduction, clearly illustrated by comparing the values of AG°r from Qi7.4), (R7.5) and (R7.6) with the following reactions, in which the iron(III) hydroxide electron acceptor has been replaced with hematite [8] and goethite [9], respectively ... 

The reductase in Geobacter sulfurreducens is located in the outer membrane and a soluble Fe(III) reductase has been characterized from cells grown anaerobically with acetate as electron donor and Fe(III) citrate or fumarate as electron acceptor (Kaufmann and Lovley 2001). The enzyme contained Fe, acid-labile S, and FAD. An extracellular c-type cytochrome is distributed in the membranes, the periplasm, and the medium, and functions as a reductase for electron transfer to insoluble iron hydroxides, sulfur, or manganese dioxide (Seeliger et al. 1998). 

Below this zone, iron(III) oxides or iron(III) hydroxides in the solid phase of the sediments act as electron acceptors. For details of these reactions, see Chapter 7. 

Biooxidation is decomposition of organic matter with oxidizing of its carbon. Organic matter in these reactions is donor of electrons, and the acceptors are elements or compounds outside it O, NO3. NO T Fe, iron hydroxide Fe(OH)3>, CO, some chlorinated solvents, etc. There may be aerobic and anaerobic oxidizing. In the former case acceptor of electrons is directly molecular oxygen O, in the latter oxidized forms of nitrogen (NOj", NO3 ), manganese (Mn ), iron (Fe +), sulphur (SO ), etc. 

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