HIGH-VALENT Cr, Mn, AND Fe SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 356

FeO

3 −

+ EDTA

4 −

→ products . (6.154)

4

Reactions (6.143) and (6.144) involve proton ambiguity to justify the pH
dependence of the reaction of ferrate(V) with EDTA. Thus, the experimental
values of k fit reasonably well (a solid line in Fig. 6.41) by considering either
reactions (6.151) and (6.152) (model I) or reactions (6.151) and (6.153) (model
II). Reaction (6.154) was not imperative to fit the data.

6.3.3 Conclusions

Extensive research on the synthesis and reactivity of nonheme oxoiron(IV)
complexes is being performed to understand oxidation reactions in enzymes.
The C-H bond activation, oxygen-atom transfer reaction, and electron and
hydride transfer in oxidations have been demonstrated. Recent focus on oxi-
dation studies includes the influence of axial ligands, the topology of ligands,
solvent pH, the spin state of the iron(IV) ion, and redox-inactive metal ions
(e.g., Sc 3+ ). Future work may include the development of generality of such
influences on oxidation reactions carried out by nonheme oxoiron(IV) com-
plexes. Fe(V)-oxo complexes are synthesized and characterized to provide
evidence of their generation in the enzyme-like C-H and C=C oxidation
reactions. Direct evidence of the generation of Fe(V) is forthcoming, and a
technique such as VT-MS would be useful in the investigation of reactive
intermediates of the reactions. The role of Fe(V)-nitrido species in the biologi-
cal production of ammonia has been suggested.
High-valent nonheme iron complexes are capable of modifying side chains
of proteins by the oxidation of the amino acids. Cys, Try, and Trp residues of
trypsin and chymotrypsin can be oxidized by high-valent iron complexes.
However, the potential role of such complexes compared to reactive oxygen
and nitrogen species in modification of proteins in biological systems still need
to be established.
The reactivity of ferryl(IV) ion with inorganic substrates is generally under-
stood. However, similar information of ferryl(IV) ion reactions with organic
constituents of the atmospheric liquid phase (e.g., organic peroxides) is
required to better evaluate the role of iron in the chemistry of the aqueous
atmosphere. Moreover, product studies of known reactivity of the ferryl(IV)
ion with organic constituents of the atmosphere (formic, formaldehyde, and
acetone) are needed in order to understand the importance of such
reactions.
The studies carried out by ferrate(VI) were mostly related to industrial and
remediation processes. Oxidation reactions carried out by ferrate(VI) were
completed in shorter time periods than oxidations carried out by permanga-
nate and chromate [387, 388]. These results have implications in organic syn-
theses performed using transition metal oxidants. Iron, unlike chromium and
manganese, is considered almost nontoxic; therefore, ferrate(VI) can make