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4΄
5΄
15΄
13΄
11΄
9΄
7΄
7
11
9
13
15
5
4
β-carotene (I)
8΄
13΄
11΄
9΄
15΄
7
13
15
9
11
O
5
4
8΄-apo-β-carotene-8΄-al (II)
O
4΄
5΄
15΄
13΄
7΄
11΄
9΄
7
9
11
13
15
5
4
Canthaxanthin (III)
O
8΄
15΄
13΄
11΄
9΄
CN
7΄
9
7
11
13
15
5
4
CN
7΄-apo-7΄,7΄-dicyano-β-carotene (IV)
O
15΄
11΄
13΄
9΄
13
8΄
7
9
11
15
OEt
5
4
Ethyl 8΄-apo-β-caroten-8΄-oate (V)
5΄
4΄
13΄
11΄
9΄
15΄
7΄
7
9
11
13
15
5
4
7,7΄-diphenylcarotenen (VI)
SCHEME 9.3
Carotenoid structures.
It has been found (Polyakov et al. 2001c) that when carotenoids are involved in a reaction cycle
with the participation of iron as Fe
2+
, an increase of the total radical yield or a prooxidant effect will
occur and will increase with decreasing carotenoid oxidation potential and its scavenging activity.
The mechanism of the participating carotenoid is shown in Scheme 9.4 (Polyakov et al. 2001c).
Fe
2+
+ H
2
O
2
Fe
3+
+
•
OH +
-
OH
Car
Car
•+
•
R
Car
•
Car-R
Pro-oxidant/Antioxidant activity
SCHEME 9.4
The formation of Car
•+
is the prooxidant activity and
•
Car-R is the antioxidant activity (From
Polyakov, N.E.,
Free Rad. Biol. Med
., 31, 398, 2001. With permission.)
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