Chemistry Reference
In-Depth Information
R S R S-OO
+
−
→
2
R S O
=
.
(4.39)
2
2
2
The zwitterionic-peroxy species was also observed in the reaction of free
Met with
1
O
2
, which also reacted with another molecule of Met to produce
2 mol of sulfoxides [172]. However, the stoichiometry of
1
O
2
to Met was
complex and varied with pH. The stoichiometries were 1 : 2 and 1 : 1 below pH 5
and above pH 7, respectively. Several other intermediates such as nitrogen-
sulfur cyclic species have been reported, which, on subsequent hydrolysis,
formed sulfoxide [172].
The chemiluminescence in protein oxidation by
1
O
2
, generated by the irra-
diation of rose bengal (RB), was observed [166, 176]. The examination of che-
miluminescence in the presence of several amino acids (cys, Met, Trp, Tyr, and
His) demonstrated the peroxides (and/or hydroperoxides) of the Trp residue
of proteins were mainly responsible for chemiluminescence [166]. There is a
significant amount of evidence for the formation of multiple endohydroperox-
ides in the reaction of tryptophan with
1
O
2
has been provided by using different
analytical techniques such as high-performance liquid chromatography
(HPLc)/mass spectrometry (MS) and
18
O-labeled NMR [13, 133, 160, 166].
Scheme 4.1 in Figure 4.10 displays the pathway for the production of hydroper-
oxides.The initial reaction of
1
O
2
withTrp yielded 3α-hydroperoxypyrroloindole
(
1
) through the postulated precursor species. The subsequent decomposition of
species produced N-formylkynurenine (NFK), whereas ring closure formed
O
O
O
OOH
OOH
O
-
1
O
2
O
-
O
-
NH
3
+
NH
3
+
NH
H
N
H
N
1
?
1
O
2
?
?
Reduction
?
O
O
O
OH
O
?
O
-
?
O
-
O
O
-
O
NH
NH
3
+
NH
3
+
O
H
H
N
H
H
N-Formylkynurenine
2
O
O
O
-
NH
3
+
NH
2
Kynurenine
Scheme 4.1
Figure 4.10.
Oxidation of Trp by
1
O
2
(adapted from Davies [13] with the permission
of the Royal Society of chemistry).
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