Properties of Carotenoid Radicals and Excited States and Their Potential Role in Biological Systems - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 288

100% MeOD
95% MeOD
90% MeOD
85% MeOD
80% MeOD
77.5% MeOD
75% MeOD
72.5% MeOD
70% MeOD
67.5% MeOD
65% MeOD
62.7% MeOD
60% MeOD
55% MeOD
50% MeOD

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

200 300 400 500 600

Wavelength (nm)

FIGURE 14.3 (See color insert following page 336.) Ground state absorption spectra of 1 × 10 −5 M
zeaxanthin in various MeOD/D 2 O mixtures.

TABLE 14.3
Second-Order Quenching Rate Constants for the Quenching of
1 O 2 by Carotenoids in Unilamellar DPPC Liposomes, Benzene, and
Triton X-100/405 Micelles

k q (×10 8 M −1 s −1 )

DPPC Liposomes

RB
Sensitization

PBA
Sensitization Carotenoid n Benzene Micelles

LYC 11 24.0 23 170 20

11 23 25 130 24

β-CAR

CAN 11 23 16 120 30

ASTA 11 5.9 — 110 29

ZEA * 11 2.3 1.7 160 25

β-CRYP 11 1.8 1.4 130 —

LUT 10 1.1 0.82 66 33

Note: RB, rose bengal and PBA, 4-(1-pyrene)butyric acid.
*

Values obtained at low concentrations from linear portion of curve.

-CRYP (like all carotenoids in homogeneous solution and all except
ZEA in liposomes) exhibits a linear plot with the quenching of 1 O 2 increasing as the concentration
of the carotenoid increases. While ZEA shows a bell-shaped plot and zero singlet oxygen quench-
ing at concentrations >70

Figure 14.4 shows that β

μ M (see Figure 14.5). Such behavior of ZEA is symptomatic of its unique