Iron redox cycle modifiers

Nitric Oxide Synthase 266 4.5 Iron Redox Cycle Modifiers 272... 

The electron transfer properties of the cytochromes involve cycling of the iron between the +2 and +3 oxidation states (Cytochrome)Fe + e" (Cytochrome)Fe ° = -0.3Vto+ 0.4V Different cytochromes have different side groups attached to the porphyrin ring. These side groups modify the electron density in the delocalized iz system of the porphyrin, which in turn changes the redox potential of the iron cation in the heme. 

Simple redox solutes, ferrocene, N, N, N, JV-tetramethyl-l,4-phenylenediam-ine, decamethylferrocene, bis(i-propylcyclopentadienyl) iron(ll), [Ru(phen)j] (0104)2, [Fe(bpy)3](0104)2, [Co(bpy)3](0104)2, and iodine have been studied at electrodes modified with polymeric fullerene films. FuUerene-modified electrodes were prepared by electropolymerization of Cjq initiated by traces of dioxygen or by simultaneous electroreduction of fullerene and Pd(ll) acetate trimer. For the former films, the electrochemical activity decreases upon potential cycling. The electrochemical activity of the film is stabihzed by the redox solute added to the electropolimerization stage due to the catalytic oxidation of the fullerene film by the oxidized form of the redox system. Similarly, positively charged species can also be incorporated into the structure of the film. The reversible behavior of redox solutes decreases with the increase in the thickness of the Pd/C q film. This film also incorporates ferricinium ion, N, N, N, N-tetramethyl-l,4-phenylenediamine cation, decamethylferricinium ion, and to a smaller degree [Co(bpy)3]"+ [53]. 

Figure 19. Transformations of Fe(II, III) at an oxic anoxic boundary in the water or sediment column (modified from Davidson, 1985). Peaks in the concentration of solid Fe(III) (hydr)oxides and of dissolved Fe II) are observed at locations of maximum Fe(III) and Fe(II) production, respectively. The combination of ligands and Fe(ll) produced in underlying anoxic regions are most efficient in dissolving Fe(III) (hydr)oxides. Redox reactions of iron—oxidation accompanied by precipitation, reduction accompanied by dissolution—constitute an important cycle at the oxic-anoxic boundary which is often coupled with transformations (adsorption and desorption) or reactive elements such as heavy metals, metalloids, and phosphates.

---