REACTIVE INORGANIC OXY-SPECIES OF C, N, S, AND P - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 229

in reaction (5.39), did not accumulate; however, it decomposed readily to form
∼33% • NO 2 and CO •− radicals. The radicals in the absence of potentially reduc-
ing substrates yielded nitrate, suggesting nitrate is produced through the for-
mation of an intermediate nitrocarbonate, O 2 NO-C(O)O − (Eq. 5.41):

•

NO CO +

•−

→ O NO-C O O ( )

−

→ NO CO

−

+ . (5.41)

2 3 2 3 2

The rate of diffusion of radicals out of solvent cages decreases with increas-
ing solvent viscosity; therefore, a study was conducted to learn the effect of
solvent viscosity on product yields and rate constants for the decomposition
of free radical initiators [196]. The ∼33% yield of Fe CN ( ) 3− and ABTS •− from

the reactions of ONOO − with Fe C( ) 3− and ABTS 2− in the presence of excess
CO − , respectively, decreased with increasing concentration of added glycerol
[196]. Moreover, yields of the oxidized products were independent of the
initial concentrations of Fe C( ) 3− and ABTS 2− within experimental error, an
indication that the decreased yields in the presence of glycerol were not due
to a competing reaction of glycerol with Fe C( ) 3− and ABTS 2− , but instead, in
the increased viscosity in the reaction mixtures. Thus, oxidizing radicals, • NO 2
and CO •− , were in a water cage and only ∼3% could escape from the cage to
the bulk of the solution.
The changes in gibbs energies for the reactions involving peroxynitrite and
CO 2 have been evaluated [185]. An energy diagram for the reaction of per-
oxynitrite and CO 2 is shown in Figure 5.14. The relative low value of Δ G ° for
reaction (5.39) suggests the O-O bond in ONOOC(O)O − is weak. This conclu-
sion was also supported with theoretical calculations [197]. Therefore, an
adduct, ONOOC(O)O − , is short-lived and a rate constant for the decay of the
adduct was estimated between 10 7 and 10 9 /second [185, 198]. Furthermore, the
lifetime for the decay of the adduct below ca. 0.1 µs clearly indicates an insuf-
ficient time to react with any biological matter prior to homolyzation into • NO 2
and CO •− radicals. Hence, • NO 2 and CO •− radicals are responsible species for
any biological damage related to the simultaneous presence of ONOO − and
CO 2 .

5.2.3.4 Reactivity with Inorganic and Organic Substrates. Peroxynitrite is
a strong oxidant and has a reduction potential of 1.4V at pH 7.0 [199]. The reac-
tivity of peroxynitrite with inorganic species showed a descending order of Sn(
II) > Sb(II) > As(III) > S(IV) >> P(I) > P(III) [200]. This order was not related
to the formal potentials of the reducing centers and reactions involving oxygen
transfer via O-bridged precursor complexes [200]. Other studied inorganic
compounds include NH 2 OH, iodide, cyanide, Fe CN ( ) 4− , and Mo C( ) 3− [164,

200-203]. Among the studied organic substrates were amino polycarboxylates,
1,2-glycols, pyruvate, thioethers, thiols, sulfides, sulfite, dimethylsulfide (dMS),
dimethylselenide (dMSe), carbonyls, and phenols [145, 204-216]. Common
chelators such as desferrioxamine, salicylaldehyde isonicotinoyl hydrazone
(SIH), ethylenediaminetetraacetate (EdTA), diethylenetraminepentaacetate