Biology Reference
In-Depth Information
4.4. Indicators
In addition to being sensitive to enzymes and light, coumarins can serve as
environmental indicators. Attachment of groups that are removed by spe-
cific ions constitutes a valuable and general strategy for constructing such
sensors. For example, compound
25
is formed by attachment of a
triisopropylsilyl (TIPS) group to a hydroxycoumarin. Removal of this
blocking group with fluoride ion occurs in a stoichiometric fashion and al-
lows the detection of F
in both aqueous and organic media.
43
Another ex-
ample of a coumarin-based sensor is compound
26
. Here, the phosphine
moiety at the 3-position quenches fluorescence until activation with an
azide in the Staudinger ligation reaction. This fluorescent coumarin be-
comes covalently attached in this reaction, constituting a bioorthogonal
fluorogenic ligation to azide-containing molecules.
44
5. BODIPY DYES
5.1. Overview
The BODIPY dyes, shown in
Fig. 1.3
, are a unique and highly flexible dye
class.
45-47
A simple BODIPY, such as compound
27
,exhibits
505/
511 nm, e
¼
9.1
10
4
M
1
cm
1
,andF
¼
0.94.
2,3
The spectral properties
of these dyes can be red-shifted by extending the conjugated system
through alkenyl or aryl substitution. For example, BODIPY
28
exhibits
l
l
abs
/
l
¼
em
max
/
l
¼
544/570 nm and dye
29
displays even longer wavelengths
em
N
N
N
N
CO
2
H
B
B
N
N
F
F
F
F
B
S
CO
2
H
F
F
CO
2
H
O
29
O
27
28
Enzyme substrates
Indicators
N
N
N
N
O
B
N
NH
HO
2
C
N
CO
2
H
casein
F
F
N
H
O
30
N
O
N
N
HO
2
C
N
CO
2
H
B
N
N
F
F
CO
2
H
B
F
F
N
N
N
N
S
B
HO
2
C
B
O
F
F
F
F
casein
O
H
32
33
34
31
Figure 1.3 Boron dipyrromethene (BODIPY)-based fluorogenic molecules.
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