Iron porphyrins electron-transfer reactions

In the case of iron porphyrins, ligand exchange reactions also accompany electron transfer. However, in the passage from iron(III) to iron(II), hexacoordination remains intact. Scheme 2.28 summarizes the reduction... 

Reorganization Energies for Electron-transfer Reactions of High-valent Iron Porphyrins... 

Electron-transfer reactions between cytochrome c and cytochrome c peroxidase have been studied extensively because of the well-characterized structures and biophysical properties of the reactants [146-150]. It is well known that the resting ferric form of cytochrome c peroxidase is oxidized by hydrogen peroxide to compound I, which contains an oxyferryl heme moiety in which the iron atom has a formal oxidation state of 4-1- [146-150]. The other is a porphyrin n radical cation or organic radical (R +) localized on an amino acid residue of Trp-191 [151-154] this is formed by transfer of the oxidized equivalent to the amino acid side chain [150]. The site of electron transfer in the reduction of compound I has been controversial and two forms of compound II have been identified, (P)Fe =0 containing the oxyferryl heme Fe(IV) [155-158] and [(P)Fe ] + containing Fe(III) and the porphyrin % radical cation which oxidizes the amino acid side-chain to produce an organic radical [(P)Fe +, R" ] [159 165] as shown in Scheme 10. 

Table 3-12 Bonding, Electron-Transfer Reactions, and Valence-Electronics for Iron-Porphyrin...

Manganese compounds are used as oxidant and catalyst in the various electron-transfer reactions in vivo involving the Mn(II), Mn(III), or Mn(IV) oxidation states. In particular, manganese complexes play an important role as oxygen carrier, similar to iron and copper porphyrins such as hemoglobin and hemocyanin. Manganese compounds have a pecuhar nature for the reaction with molecular oxygen. 

In general, most synthetic iron porphyrins are able to undergo three or four electron-transfer reactions in a variety of nonaqueous solvents, with the exact number of redox reactions depending on the type of porphyrin macrocycle, the type of axial Kgands, and the sol-vent/supporting electrolyte mixture used... 

Schemes Electron-transfer reactions of iron(lll) porphyrins.

Electron transfer between the porphyrin radical and the substrate is readily achieved, while the aromatic substrate is unable to transfer directly an electron to the iron because of steric hindrance within the active site pocket, thus slowing down the third electrode reaction described in Sch. 7. Further details on the electron-transfer reactions of peroxidases, including cytochrome and... 

The reduction ofsec-, and /-butyl bromide, of tnins-1,2-dibromocyclohexane and other vicinal dibromides by low oxidation state iron porphyrins has been used as a mechanistic probe for investigating specific details of electron transfer I .v. 5n2 mechanisms, redox catalysis v.v chemical catalysis and inner sphere v.v outer sphere electron transfer processes7 The reaction of reduced iron porphyrins with alkyl-containing supporting electrolytes used in electrochemistry has also been observed, in which the electrolyte (tetraalkyl ammonium ions) can act as the source of the R group in electrogenerated Fe(Por)R. ... 

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