Biomedical Engineering Reference
In-Depth Information
100
Control
Salicylic
Vanillic
Chlorogenic
Caffeic
Gallic
80
60
40
20
0
0 0.5 1.0 2.0
Concentration (mM)
FIGURE 6.13
The influence of different amounts of phenolic on the relative intensity of
the ESR signal of the spin adduct of the lipid alkoxyl radical. (Adapted from Milic et al.
75
)
O
O
C
CH
CH
OH
HO C
2
OH
HO
OH
OH
FIGURE 6.14
Structure of 5-caffeoylquinic acid.
-
pentahydroxyflavones) produce very potent antioxidants, while
meta
5,7 hydroxyla-
tion of the A ring seems to have little influence.
31,78
Flavonols are also known to chelate metal ions at the 3-hydroxy, 4-keto group
and/or at the 5-hydroxy, 4-keto group (when the A ring is hydroxylated at the
5 position). Chalcones, natural precursors of flavones and flavonones, are readily
cyclized under acid conditions and have been shown to possess more potent anti-
oxidant activity, more so than their corresponding flavonones. The 3,4 dihydroxy-
chalcones are particularly effective as antioxidants. In the isoflavone, hydroxy groups
at both 4
on one ring and
p
-dihydroxy grouping on the other (such as 3,5,8,3
′
,4
′
and 3,7,8,2
′
,5
′
′
and 5 positions are needed for significant antioxidant activity.
31
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