Chemistry Reference
In-Depth Information
trypsin reacted in a similar manner to the oxidation of invertase by O
3
(Fig.
4.18c). It appears the thiol group, −SH, from cysteine, is enhanced by its inter-
action with a histidine group of another branch of the folded protein in papain,
which was rapidly oxidized to disulfide (Fig. 4.18c). The gelatin molecule does
not contain Trp and also had a low content of Phe and Tyr. This may result
from a low intensity at 275 nm for gelatin (Fig. 4.18d). Similarly, a peak at
275 nm in gelatin disappeared with limited variation in the peak intensity at
222 nm. Other features at the 250- and 295-nm bands of the spectra were also
similar to the O
3
-treated protein samples. The polarimetric measurements of
this study indicated the oxidation by O
3
treatment resulted in the denaturation
of proteins by causing changes in their secondary and tertiary structures [237].
Interfacial reactions of O
3
with pulmonary surfactant protein B (SP-B) in
a model surfactant (1-palmitoyl-2-oleoyl-
sn
-glycerol [POg]) system have
been studied using field-induced droplet ionization (FIDI)/MS [259]. This
study showed the structurally specific oxidative changes of SP-B
1-25
(a short-
ened version of human SP-B) at the air-liquid interface. The heterogeneous
reaction of SP-B
1-25
at the interface was quite different from that in the solu-
tion phase. The homogeneous oxidation of SP-B
1-25
was nearly complete, while
only a subset of the amino acids, which generally reacts with O
3
, was oxidized
in the hydrophobic interfacial environment, both with and without a surfactant
layer [259]. A similar experimental approach was used to study the interfacial
reactions of O
3
with pulmonary phospholipid surfactants [260]. Results of the
interfacial studies may clarify the effect of smoking and airborne particles on
the lung surfactant system.
4.4 HYDROXYL RADICAL
4.4.1 Generation
The production methods of
•
OH include radiolysis, pulsed electron beams,
photochemistry, electrochemistry, corona discharge, sonolysis, and Fenton
chemistry [261-267]. In pulse radiolysis, the interaction of water with radiation
initially produced H
2
O
•+
, dry electron
e
dr
−
, and excited water H
2
O* (Eq. 4.48),
which were then converted into highly reactive primary radical species,
•
OH,
e
a
−
, and H
•
, within 10
−12
seconds [268]:
H O
+ →
h
ν
H O e
•
+
−
+
H O
*
.
(4.48)
2
2
dry
2
The overall ionization produces freely diffusing species with the following
stoichiometry [262]:
100
eV
4 14
.
H O
→
2 87
.
•
OH
+
2 7
.
e
−
+
0 61
.
H
•
+
0 03
.
HO
•
2
aq
2
(4.49)
+
+
0 61
.
H O
+
0
.
43
H
+
2 7
.
H
.
2
2
2
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