Fluorescence PET (photo-induced electron transfer) sensor for water based on anthracene-amino acid

Article abstract of DOI:10.1016/j.jphotochem.2011.04.035

An anthracene-amino acid system with two carboxyl groups has been designed and synthesized as a new class of fluorescence PET (photo-induced electron transfer) sensor for detection of water in organic solvents. An enhancement in fluorescence is observed with increasing water content in 1,4-dioxane, THF, acetonitrile and ethanol, which is attributable to the suppression of PET by the intramolecular proton transfer of the carboxyl proton to the amino group. The detection limit and quantitation limit are, respectively, 0.1 and 0.3 wt% for 1,4-dioxane, 0.4 and 1.2 wt% for THF, 0.1 and 0.3 wt% for acetonitrile and 0.1 and 0.3 wt% for ethanol.

Full text of DOI:10.1016/j.jphotochem.2011.04.035

Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 52–55
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Fluorescence PET (photo-induced electron transfer) sensor for water based on
anthracene-amino acid
Yousuke Ooyama, Ai Matsugasako, Tomoya Nagano, Kazuyuki Oka, Kohei Kushimoto,
∗
Kenji Komaguchi, Ichiro Imae, Yutaka Harima
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
An anthracene-amino acid system with two carboxyl groups has been designed and synthesized as a
new class of fluorescence PET (photo-induced electron transfer) sensor for detection of water in organic
solvents. An enhancement in fluorescence is observed with increasing water content in 1,4-dioxane,
THF, acetonitrile and ethanol, which is attributable to the suppression of PET by the intramolecular
proton transfer of the carboxyl proton to the amino group. The detection limit and quantitation limit are,
respectively, 0.1 and 0.3 wt% for 1,4-dioxane, 0.4 and 1.2 wt% for THF, 0.1 and 0.3 wt% for acetonitrile and
Received 14 March 2011
Received in revised form 5 April 2011
Accepted 22 April 2011
Available online 7 May 2011
Keywords:
Anthracene-amino acid
Fluorescence
0
.1 and 0.3 wt% for ethanol.
©
2011 Elsevier B.V. All rights reserved.
Photo-induced electron transfer
Water
1
. Introduction
Fluorescence sensors have received a considerable attention for
linked to a cation binding site such as an amino moiety via a methy-
lene spacer (fluorophore–spacer–receptor structure). The PET takes
place from the nitrogen atom of amino moiety to fluorophore skele-
ton, leading to fluorescence quenching of the fluorophore. When
the nitrogen atom is protonated or strongly interacts with a cation,
the PET is inhibited and a drastic enhancement of fluorescence is
observed. In our fluorescence PET sensor 1, on the other hand, addi-
tion of water to organic solvents containing 1 promotes dissociation
of the carboxyl proton of 1, followed by the formation of fluorescent
zwitterionic structure 1a by the protonation of the amino group.
As a result, the intramolecular proton transfer of the carboxyl pro-
ton to the amino group suppresses PET and thus an enhancement
in fluorescence is observed with increasing water content in polar
and less polar organic solvents. This provides a new concept of the
molecular design for a fluorescence water sensor based on PET. The
detection limit (DL) and quantitation limit (QL) are, respectively, 0.1
and 0.4 wt% for acetonitrile and 0.1 and 0.2 wt% for ethanol. How-
ever, the DL and QL in less polar organic solvents are lower than
those in polar organic solvents.
In order to further improve sensing abilities, we have designed
and synthesized a new fluorescence PET sensor for water based on
anthracene-amino acid 4 having two carboxyl groups (Scheme 1b).
We expected that the addition of water to organic solvents con-
taining 4 causes an efficient formation of fluorescent zwitterionic
compounds 4a, because of a more acidic nature of 4 having two
carboxyl groups than 1 which has one carboxyl group. Herein we
report the high-sensitive detection of a trace amount of water
in a various organic solvents based on the PET characteristics of
anthracene-amino acid 4.
their potential applications to biochemical and medical analyses
and optoelectronic devises [1–8]. Among them, fluorescence sen-
sors for detection and quantification of water in organic solvents
and in the atmosphere are of a major importance in the construction
of environmental monitoring system in industry as well as in the
fundamental analytical chemistry [9–20]. In most of these fluores-
cence water sensors developed so far, however, the fluorescence
intensity decreases with an increase of water in organic solvents
and a significant fluorescence quenching occurs in polar solvents,
in particular [15–20]. Thus, it is difficult to detect a trace amount
of water in polar solvents by using these fluorescence sensors. In
order to improve detection limits of fluorescence water sensors, a
new detection principle is required.
Recently, we have designed and synthesized an anthracene-
amino acid 1 to create a new class of fluorescence PET (photo-
induced electron transfer) sensor for detection of water in organic
solvents (Scheme 1a) [21]. Fluorescence PET sensors, in general,
have been developed as pH sensor or cation sensors for detecting
cations such as H , Na , K , Ca , Mg , Cu , Zn , Pb , and Cd as
well as neutral organic species such as saccharides in biochemical
analyses [5–8,22–29]. They are composed of a fluorophore skeleton
+
+
+
2+
2+
2+
2+
2+
2+
∗ Corresponding author. Tel.: +81 82 424 6534; fax: +81 82 424 5494.
E-mail addresses: harima@mls.ias.hiroshima-u.ac.jp,
harima@minerva.ias.hiroshima-u.ac.jp (Y. Harima).
1
010-6030/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2011.04.035

Y. Ooyama et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 52–55
53
8
00
a
OH
O
0.20
wt%
00
80
wt%
100
80
(
a
a)
(bb )
1
O
O
0.15
60
600
400
200
0
60
4
2
0
0
40
20
10
5
N
H O
N
H
10
5
2
0.1
1
0
0
.1
1.1
0.83
.83
.61
0.61
0.45
0.25
0.051
-
H O
2
0.05
0
0.45
0
.25
0
.051
1
1a
3
30
380
430
380
430
480
530
Non Fluorescence
Fluorescence
Wavelength/nm
Wavelength/nm
0
.20
800
wt%
wt%
100
82
(
c)
(dd )
1
00
8
2
b
OH
O
O
0.15
.1
61
600
400
200
0
61
4
2
0
0
40
20
O
1
0
10
0
5
1
5
1
O
O
0
.83
0.83
0.64
0.44
0.23
0.031
N
H O
2
N
H
0.64
0.44
0.05
0
OH
OH
0
.23
0
.031
-
H O
2
3
30
380
430
380
430
480
530
4
4a
Wavelength/nm
Wavelength/nm
Non Fluorescence
Fluorescence
Fig. 1. (a) Absorption and (b) fluorescence spectra (ꢁex = 366 nm) of
4
−
5
(
c = 2.0 × 10 M) in 1,4-dioxane containing water (0.051–100 wt%). (c) Absorption
Scheme 1. Mechanism of fluorescence PET sensor (a) 1 and (b) 4 for detection of
water in organic solvents.
−5
and (d) fluorescence spectra (ꢁex = 366 nm) of 4 (c = 2.0 × 10 M) in acetonitrile
containing water (0.031–100 wt%).
2
. Experimental
2
.2. Synthesis of 4-anthracen-9-ylmethyl-(3-ethoxycarbonyl-
propyl)-amino-butyric acid ethyl ester
3)
Melting points were measured with a Yanaco micro melt-
(
ing point apparatus MP model. IR spectra were recorded on a
Perkin Elmer Spectrum One FT-IR spectrometer by ATR method.
Absorption spectra were observed with a Shimadzu UV-3150 spec-
trophotometer and fluorescence spectra were measured with a
Hitachi F-4500 spectrophotometer. High resolution mass spectral
data by ESI were acquired on a Thermo Fisher Scientific LTQ Orbi-
A solution of 2 (3.5 g, 10.9 mmol) in acetonitrile (50 ml) was
treated with sodium hydride (60%, 1.7 g, 43.6 mmol) and stirred
for 1 h at room temperature. Ethyl 4-bromobutyrate (10.6 g,
5
was stirred at room temperature for 1 h. After concentrating
under reduced pressure, the resulting residue was dissolved in
dichloromethane, and washed with water. The residue was chro-
matographed on silica gel (CH Cl /ethyl acetate = 3:1 as eluent) to
give 3 (4.0 g, yield 84%) as a yellow oil; H NMR (400 MHz, DMSO-d ,
TMS) ı = 1.18 (t, J = 6.3 Hz, 6H), 1.80–1.86 (m, 4H), 2.10 (t, J = 5.8 Hz,
4
4.4 mmol) was added dropwise over 20 min and the solution
1
trap XL. H NMR spectra were recorded on a JNM-LA-400 (400 MHz)
FT NMR spectrometer with tetramethylsilane as an internal stan-
dard. Column chromatography was performed on silica gel (KANTO
CHEMICAL, 60 N, spherical, neutral). The determination of water
in 1,4-dioxane, THF, acetonitrile and ethanol solution was done
with a MKC-610 and MKA-610 Karl Fischer moisture titrator (Kyoto
Electronics manufucturing Co., Ltd.) based on Karl Fischer coulo-
metric titration for below 1.5 wt% and volumetric titration for above
2
2
1
6
H), 2.36 (t, J = 5.8 Hz, 4H), 4.03 (q, 4H), 4.48 (s, 2H), 7.49–7.55 (m,
H), 8.07 (d, J = 6.1 Hz, 2H), 8.47 (d, J = 7.1 Hz, 2H), 8.55 (s, 1H); IR
4
−
1
+
(ATR): ꢀ = 1726 cm ; HRMS (ESI, m/z) 436.2473 [M+H] .
1
.5 wt%, respectively.
2
4
.3. Synthesis of
2
.1. Synthesis of 4-(anthracen-9-ylmethyl)-amino-butyric acid
-anthracen-9-ylmethyl-(3-carboxy-propyl)-amino-butyric acid
ethyl ester (2)
(
4)
To
a
solution of 9-anthracenecarboxyaldehyde (8.0 g,
3
8.8 mmol) in 25% MeOH/CH Cl2 (100 ml) was added a CH Cl2
A solution of 3 (3.0 g, 6.9 mmol) in ethanol (100 ml) was added
2
2
solution (100 ml) of ethyl 4-aminobutanoate hydrochloride (7.8 g,
6.5 mmol) pretreated with Na CO3 solution (30% aq, 100 ml). The
dropwise aqueous NaOH (3 g, 75 mmol, 50 mL) with stirring at
60 C. After further stirring for 8 h under reflux, the solution
◦
4
2
mixture was stirred at room temperature for 43 h under an argon
atmosphere. The solution cooled to 0 C, and then NaBH4 (4.4 g,
was acidified to pH 4 with 2 N HCl, and concentrated under
reduced pressure. The residue was dissolved in dichloromethane,
and washed with water. The residue was chromatographed on
silica gel (CH Cl /MeOH = 5:2 as eluent) to give 4 (1.15 g, yield
◦
0.12 mol) was added in small portions to the solution. The mixture
was stirred at room temperature for 5 h. The solvent was removed
2
2
◦
1
in vacuo and the solid residue dissolved in CH Cl2 (300 ml) and
44%) as a white solid; mp 169–171 C; H NMR (400 MHz, D O)
2
2
washed with Na CO3 solution (10% aq, 3 × 100 ml). The CH Cl
ı = 1.85–2.08 (br, 4H), 2.20–2.33 (br, 4H), 3.15–3.38 (br, 4H), 5.13
2
2
2
layer was dried over anhydrous Na SO and filtered, and the
(s, 2H), 7.62–7.65 (m, 2H), 7.72–7.76 (m, 2H), 8.10–8.15 (m, 4H),
2
4
−
1
solvent was removed in vacuo to give an oily residue. The residue
was chromatographed on silica gel (CH Cl /MeOH = 9:1 as eluent)
8.65 (s, 1H); IR (ATR): ꢀ = 1721 cm ; HRMS (ESI, m/z) 380.1859
[M+H] .
+
2
2
1
to give 2 (3.7 g, yield 29%) as a light yellow oil; H NMR (400 MHz,
acetone-d , TMS) ı = 1.17 (t, J = 7.2 Hz, 3H), 1.83–1.90 (m, 2H), 2.41
6
3. Results and discussion
(
7
t, J = 7.4 Hz, 2H), 2.93 (t, J = 6.8 Hz, 2H), 4.05 (q, 2H), 4.71 (s, 2H),
.47–7.57 (m, 4H), 8.06 (d, J = 8.2 Hz, 2H), 8.45 (d, J = 9.0 Hz, 2H), 8.54
The synthetic pathway of
a
fluorescence PET sensor
−1
+
(
s, 1H); IR (ATR): ꢀ = 1726 cm ; HRMS (ESI, m/z) 322.1797 [M+H] .
4
is shown in Scheme 2. The reductive amination of 9-

5
4
Y. Ooyama et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 52–55
Fig. 2. Fluorescence peak intensity at around 418 nm (ꢁex = 366 nm) of 4 as a function of water content in (a) 1,4-dioxane, (b) THF, (c) acetonitrile, and (d) ethanol. (e)
Fluorescence peak intensity of 4 in 1,4-dioxane, THF, acetonitrile, and ethanol solutions in the low water content region below 1.2 wt%.
anthracenecarboxyaldehyde with ethyl 4-aminobutanoate gave
a monoester derivative 2 [30,31]. The reaction of monoester
derivative 2 with ethyl 4-bromobutyrate in the presence of sodium
hydride yielded a diester derivative 3. Anthracene-amino acid 4
was obtained by hydrolysis of 3.
The detection of water in 1,4-dioxane, THF, acetonitrile and
ethanol was attempted by measuring absorption and fluorescence
spectra of 4. As are shown typically in Fig. 1a and c for 1,4-dioxane
and acetonitrile, in all the four solvents the absorption spectra of
spectra exhibit significant changes in intensity with a negligible
change in their spectral shapes (Fig. 1b and d). The changes in the
fluorescence peak intensity are plotted in Fig. 2a–d against water
fraction in these four organic solvents. It is seen in the low water
content limit below 1.2 wt% that the fluorescence intensities are
increased linearly in 1,4-dioxane, acetonitrile and ethanol, while
that in THF exhibits only a slight increase (Fig. 2e). When the water
content ranges between 5 and 20 wt%, the fluorescence intensity
is increased dramatically in acetonitrile and ethanol, but gradu-
ally in 1,4-dioxane and THF. The fluorescence intensity in the range
between 20 and 60 wt% is increased dramatically in 1,4-dioxane
4
undergo only small changes in intensity and shape by increasing
water content. On the other hand, the corresponding fluorescence
OEt
O
OEt
O
OH
O
O
O
O
O
NH
N
N
CHO
H N
2
Br
OEt
OH
OEt
NaOH aq.
ethanol
OEt
NaBH4
5%MeOH/CH Cl2
NaH
acetonitrile
2
3
4
2
2
29%
84%
44%
Scheme 2. Synthesis of fluorescence PET sensor 4.

Y. Ooyama et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 52–55
55
ment in fluorescence is observed with increasing water content in
organic solvents, which is attributable to the suppression of PET
by the intramolecular proton transfer of the carboxyl proton to
the amino group. The DL and QL of 4 are higher than those of an
anthracene-amino acid 1 having one carboxyl group. We demon-
strate that the anthracene-amino acid system is one of the most
promising classes of fluorescence PET sensor for detection of a trace
amount of water.
Acknowledgements
This work was supported by A Research for Promoting Tech-
nological Seeds from Japan Science and Technology Agency (JST)
and by the Ogasawara Foundation for the Promotion of Science &
Engineering.
Fig. 3. Fluorescence peak intensity at around 418 nm (ꢁex = 366 nm) of 4 plotted
against ET(30) of solvents. The numbers 1–10 correspond to 1,4-dioxane, THF, DMSO,
acetonitrile, 2-propanol, ethyl acetoacetate, 2-ethoxyethanol, ethanol, methanol,
and water, respectively.
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2
4
. Conclusions
As a new class of fluorescence PET sensor for detection of
water in organic solvents, we have designed and synthesized an
anthracene-amino acid 4 having two carboxyl groups. An enhance-
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