Chemistry Reference
In-Depth Information
1
O
2
+ CAR
O
2
+
3
CAR
Vibrational relaxation
of
3
CAR
1
O
2
+
1
CAR
3
O
2
+
3
CAR
SCHEME 14.1
14.1. Thus, the carotenoid acts as a catalyst deactivating
1
O
2
. Many different carotenoids have
been studied to investigate the inl uence of different carotenoid structural characteristics on
the ability to quench
1
O
2
. Much of this work has been carried out in organic solvents with some
typical results, taken from Conn et al. (1991), Rodgers and Bates (1980), and Edge et al. (1997) as
shown in Table 14.1.
The three unsymmetrical carotenoids such as asteroidenone, adonixanthin, and adonirubin are
not well known and their structures are shown in Figure 14.1. However, they have been studied in
detail as
1
O
2
quenchers both in benzene and methanol as shown in Table 14.2.
TABLE 14.1
Singlet Oxygen Quenching Rate Constants for
Carotenoids in Benzene
Carotenoid
N
k
q
(×10
9
M
−1
s
−1
)
Dodecapreno-
β
-carotene
19
23.0
15
20.0
Decapreno-β-carotene (DECA)
Tetradehydrolycopene
15
10.7
Rhodoxanthin
12 (+2, C=O)
12.0
Astaxanthin (ASTA)
11 (+2, C=O)
14.0
Canthaxanthin (CAN)
11 (+2, C=O)
12.0
Lycopene (LYC)
11
17.0
Dihydroxylycopene
11
5.1
11
13.0
All-
trans
-β-carotene (β-CAR)
11
11.0
15-
cis
-β-carotene
11
11.0
9-
cis
-β-carotene
Zeaxanthin (ZEA)
11
12.0
10
12.0
α-carotene
10
5.27
β-apo-8′-carotenal (APO)
Lutein (LUT)
10
6.64
Violaxanthin
9
16.0
9
1.38
Septapreno-β-carotene (SEPTA)
8
0.3
7,7′dihydro-β-carotene (77DH)
Note:
N
, Number of conjugated double bonds.
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