Chemistry Reference
In-Depth Information
10
−
3
mol dm
−
3
; product: 2,3-dihydroxyben-
zoic acid, 2,3-DHB; 2.13
×
10
−
5
mol dm
−
3
in the absence of a scavenger) and phenylalanine
(5
×
10
−
3
mol dm
−
3
; product:
p
-tyrosine, 7.3
×
10
−
6
mol dm
−
3
in the absence of a scaven-
ger, total tyrosines 2.21
×
10
−
5
mol dm
−
3
by the Fenton reagent (Fe(III) 5
×
10
−
6
mol dm
−
3
,
EDTA 1.5
×
10
−
5
mol dm
−
3
, H
2
O
2
5
×
10
−
5
mol dm
−
3
, ascorbate 5
×
10
−
5
mol dm
−
3
, phos-
phate buffer pH 7.4) (Kaur et al. 1997). Calculations are based on competition kinetics using
established rate constants. (Buxton et al. 1988)
Table 3.7.
Hydroxylation of salicylic acid (5
×
Scavenger
2,3-DHB
measured
(%)
2,3-DHB
calculated
(%)
p-Tyrosine
measured
(%)
p-Tyrosine
calculated
(%)
None
100
100
100
100
2-Deoxyribose (0.1 mol dm
−
3
)
98
25
69
8
Mannitol (0.1 mol dm
−
3
)
28
33
31
11
Formate (0.1 mol dm
−
3
)
3
25
46
8
Deoxyribose gives rise to TBA-reactive products (Halliwell 1990; Aruoma
1994; Loft and Poulsen 1999) which can be detected spectrophotometrically or
by their fluorescence (Biaglow et al. 1997). However, the test is not specific [the
reaction is also given by base propenals in the case of BLM action on DNA which
is not
•
OH-induced (Chap. 12) and can give misleading results (Gutteridge 1986);
see also Draper et al. (1993)].
Moreover, the oxidation of methional to ethylene has been proposed (Beau-
champ and Fridovich 1970; Biaglow et al. 1997), and the formation of allantoin
(Grootveld and Halliwell 1987; Halliwell et al. 1988) from uric acid as well as the
imidazolone derivative from histamine (Ching et al. 1995) have been suggested
as an index of
•
OH action in vivo (Halliwell et al. 1988).
3.5.4
References for OH-Radical Probes
For setting up a probe system for use in biological systems, it is required that it
provides
•
OH but also adequately behaves with respect to competition kinetics.
The Fenton system seems to fulfill the first criterion in that it produces the re-
quired products in good yields but certainly not the second one. As can be seen
from Table 3.7, the measured yields and the calculated ones [based on compe-
tition kinetics, Eq. (43), and established rate constants] dramatically disagree.
The reason for this is not yet known, but it is evident that this system cannot be
used with advantage as a reference for
•
OH production.
Similar effects have been observed when
•
OH was generated using the xan-
thine/xanthine oxidase system in the presence of EDTA-complexed iron, a
similar Fenton-type system (Owen et al. 1996). The efficiency of suppression of
the formation of the dihydroxybenzoic acids by
•
OH scavengers increases from
Search WWH ::
Custom Search