Chemistry Reference
In-Depth Information
ca. 40%
a
Bromamines/
bromamides
Protein + HOBr
Radicals
Major
process
ca. 30%
a
ca. 3%
a
Fragmentation
Further
oxidation
of Tyr
Di-Tyr
Br-Tyr/
diBr-Tyr
Carbonyl
groups
Minor
process
?
?
Minor
process
Aggregation
Figure 3.9.
Summary of proposed reactions of HOBr with proteins such as BSA.
a
With
a 50-fold molar excess HOBr (adapted from Hawkins and Davies [68] with the permis-
sion of Elsevier Inc.).
3,4,-dihydroxyphenylalanine (DOPA), and di-Tyr. A scheme for the formation
of products is presented in Figure 3.9 [68]. Major products were Br-Tyr and
diBr-Tyr, while other products were minor.
Several studies on the kinetics and mechanisms of the oxidation of organo-
sulfur compounds by aqueous bromine and bromate in acidic solutions have
also been performed [73-76]. Elementary steps within reactions of the mecha-
nisms were modeled to explain the kinetic traces of oxidation. Oxidations
occurred through S-oxygenation pathways. Final products were formed with
and without cleavage of the C-S bond of the compound, and hence, products
were sulfenic, sulfinic, and cysteic acids as well as the sulfate ion.
3.1.3 Hypothiocyanous
HOSCN/OSCN
−
decomposes rapidly at physiological pH to form oxyacids
such as cyanosulfurous acid (HO
2
SCN) and cyanosulfuric acid (HO
3
SCN)
(Eqs. 3.5 and 3.6) [77, 78]:
2
HOSCN HO SCN H SCN
→
+
+
+
−
(3.5)
2
−
+
.
(3.6)
HOSCN HO SCN HO SCN SCN H
+
→
+
+
2
3
Oxyacid may also be formed from the reaction of H
2
O
2
with HOSCN (Eq.
3.7):
.
(3.7)
HOSCN H O
+
→
HO SCN H O
+
2
2
2
2
The formation of OCN
−
, CN
−
, and thiocaramate-S-oxide has also been sug-
gested in biological systems (Eqs. 3.8-3.10) [52, 79-83]:
HO SCN H O
+
→
OCN H SO H
−
+
+
+
(3.8)
2
2
2
2
3
HO SCN H O CN H SO H
3
+
→
−
+
+
+
(3.9)
2
2
4
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