HIGH-VALENT Cr, Mn, AND Fe SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 313

porphyrine, and carrole with Mn(III), Mn(V), and Mn(VI) have been synthe-
sized and characterized to understand their role in the generation of reactive
intermediates in catalytic atom- or group-transfer reactions for several biologi-
cal and synthetic systems [204-208]. For example, Mn(III)-corrole protects rat
pancreatic beta cells against intracellular nitration by peroxynitrite, which
causes subsequent cell death. The structure of corrole is in the form of the
corrin and the positive charged Mn(III)-corrole rapidly decomposes peroxyni-
trite through a mechanism that does not involve the usual nitrating reaction
intermediates [209]. Recently, evidence for the simultaneous generation of
Mn III -OOC(O)R, Mn IV =O, and Mn V =O as active oxidant species in olefin
epoxidation by Mn(III) complexes have been reported [210]. A potential role
of the oxidant-Mn-oxo(imido) intermediate has also been suggested in the
epoxidation of alkenes with a series of iodosylarenes as oxidants catalyzed by
Mn(V) oxo and imido complexes [198].
The OEC within PSII, containing Mn and Ca ions as well as amino acids
in the structure, catalyzes the oxidation of water to form oxygen [211]. PSII
contains two redoxactive tyrosines, YD and YZ, which performed different
roles in catalysis [212]. An essential role of the redox-active tyrosines, YZ, for
oxygen evolution has been explained. Biophysical and inorganic chemistry
analyses, X-ray crystallography, and theoretical calculations were performed
to comprehend the structures of the Mn and Ca ions, the redox-active tyrosine,
and the surrounding amino acids that are present in the OEC [213, 214]. The
manganese-catalytic site rapidly reduced the YZ. The PSII is useful in studying
proton-coupled electron transfer reactions [11].
6.2.3 Oxidation by Mn(VII)
Permanganate has been used widely in the synthesis of organic compounds
[215-221]. The Mn(VII) ion has also demonstrated its ability to be a versatile
industrial oxidant in the preparation of many organic compounds [215]. Per-
manganate is now considered a green oxidant because of recent success in the
recycling of its byproduct, MnO 2 , back to permanganate.
Examples of selective oxidation carried out by the permanganate ion are
presented in Table 6.3 [215]. Selectivity is generally defined by the conditions
under which oxidations were carried out. Table 6.3 suggests the use of per-
manganate in the synthesis of organic compounds. The application of KMnO 4
adsorbed onto a solid support as a heterogeneous reagent or under solvent-
free conditions has made significant advances in organic synthesis [215]. Other
applications of permanganate include its use in the oxidation of organic
contaminants in water purification [222-224]. Permanganate generally con-
verts organic molecules into carbon dioxide and water. The oxidation of poly-
cyclic aromatic hydrocarbons by permanganate is an example of a wide range
of applications in the remediation of contaminants [225]. Oxidation of the
aromatic ring is usually much slower than that of the side chains in hydrocar-
bons by the permanganate ion in slightly acidic, neutral, or basic conditions.