A new fluorescence chemosensor for selective detection of copper ion in aqueous solution

Article abstract of DOI:10.1016/j.tetlet.2016.04.025

A new fluorescent chemosensor based upon 2,5-diphenylfuran and di(2-picolyl)amine (DPA) was designed and synthesized. Its structure was confirmed by single crystal X-ray diffraction and its photophysical properties were studied by absorption and fluorescence spectra. This compound can be used to determine Cu²⁺ ion with high selectivity among a series of cations in aqueous DMSO. This sensor forms a 1:1 complex with Cu²⁺ and displays fluorescent quenching.

Full text of DOI:10.1016/j.tetlet.2016.04.025

Tetrahedron Letters xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A new fluorescence chemosensor for selective detection of copper
ion in aqueous solution
⇑
Yang Hu, Qian Ke, Chang Yan, Cai-Hua Xu, Xiao-Huan Huang, Sheng-li Hu
Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, Hubei Collaborative Innovation Center for Rare Metal Chemistry, College of Chemistry and Chemical
Engineering, Hubei Normal University, Huangshi 435002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new fluorescent chemosensor based upon 2,5-diphenylfuran and di(2-picolyl)amine (DPA) was
designed and synthesized. Its structure was confirmed by single crystal X-ray diffraction and its photo-
physical properties were studied by absorption and fluorescence spectra. This compound can be used to
Received 28 January 2016
Revised 7 April 2016
Accepted 8 April 2016
Available online xxxx
2+
determine Cu ion with high selectivity among a series of cations in aqueous DMSO. This sensor forms a
2
+
1
:1 complex with Cu and displays fluorescent quenching.
Ó 2016 Elsevier Ltd. All rights reserved.
Keywords:
2
,5-Diphenylfuran
Di(2-picolyl)amine
Fluorescence sensor
2+
Cu
The development of chemosensors for the detection of metal
Moreover, its fluorescent signal can be revived by the addition of
EDTA solution.
ions has received considerable attention because of their important
roles in medicine, living systems, and the environment.1 Among
metals, copper is the third most abundant essential transition
,2
The new sensor 1 was synthesized as outlined in Scheme 1.
3-(Methylthio)-4-bromomethyl-2,5-diphenyl-furan (5) was syn-
3
22
metal ion in the human body. Many proteins use copper ions as
thesized according to the our reported procedure, after reaction
a cofactor for electron transport, or as a catalyst in oxido-reduction
reactions. Copper distribution in the human body is highly
controlled, because of its cellular toxicity. An excess of copper ions
in living cells can damage lipids, nucleic acids, and proteins.
of compound 5 with DPA (6) in refluxing CH
3
CN, the desired
product 1 was obtained in 75.7% yields. The structure of compound
1
13
1 was fully characterized by H NMR, C NMR, ESI-MS (ESI,
2
3
24
Figs. S1–S3), and single crystal X-ray diffraction analysis
(Fig. 1).
4
Several serious diseases, including Alzheimer’s disease, Indian
childhood cirrhosis, prion disease,6 and Menkes and Wilson
5
To examine the binding properties of 1 with metal ions, the
absorption spectra of 1 (10 M) in DMSO/water (95:5, v/v) con-
7
diseases, have been associated with the cellular toxicity of copper
l
ions. Due to its extensive applications in our daily lives, copper is
also a common metal pollutant. For these reasons, much effort
has been devoted to the design of various chemosensors specific
taining HEPES buffer (10 mM, pH = 7.0) were first explored in the
presence of 1 equiv of different metal ions and the results are
depicted in Figure 2. The sensor 1 exhibited broad absorption in
2
+
8–18
+
+
2+
2+
2+
for Cu detection.
In continuing of our study on developing molecular sensors for
326 nm. Upon binding of metal ions (K , Na , Ni , Mg , Mn ,
3
+
2+
2+
2+
2+
2+
3+
2+
Cr , Pb , Zn , Cd , Cu , Co , Fe , and Hg ) (as their chloride
Cu2+ detection,
19–21
herein, we report a new fluorescent chemosen-
salts), it was found that only the Cu ion causes the maximum
2+
sor 1, which is constructed via two functional moieties: 2,5-
diphenylfuran acts as a fluorophore for its excellent photophysical
property, and di(2-picolyl)amine (DPA) linked to 2,5-diphenylfu-
ran provides the recognition and binding site for metal ions.
Sensor1 displays high selectivity for Cu2 ion among the metal ions
examined and exhibits fluorescence quenching upon binding of
absorption peak obvious change with a blue shift from 326 nm to
292 nm, other metal ions did not cause this change under the same
conditions.
The UV/Vis titration of 1 with Cu2+ was shown in Figure 3. With
+
2+
the addition of increasing amounts of Cu to a solution of 1 in
DMSO/water (95:5, v/v), the maximum absorbance at 326 nm
decreased gradually, and concomitantly, a rising new absorbance
that peaked at 292 nm appeared. An isosbestic point was clearly
observed at 314 nm, indicating the formation of a new complex
2
+
Cu ion with an ‘on–off’ type fluoroionophoric switching property.
⇑
Corresponding author. Tel./fax: +86 0714 6515602.
E-mail address: hushengli168@126.com (S.-l. Hu).
2
+
between 1 and Cu
.
http://dx.doi.org/10.1016/j.tetlet.2016.04.025
040-4039/Ó 2016 Elsevier Ltd. All rights reserved.
0
Please cite this article in press as: Hu, Y.; et al. Tetrahedron Lett. (2016), http://dx.doi.org/10.1016/j.tetlet.2016.04.025

2
Y. Hu et al. / Tetrahedron Letters xxx (2016) xxx–xxx
SCH
3
O
O
C
O
C
I
2
, CuO
HAc, HCl
SnCl
C
C
O
DMSO
2
SCH
3
4
2
3
N
Br
N
N
N
H
N
6
CH
3
S
N
3
3%HBr-HAc
3
CH S
(
CH
2
O)n
O
3 2 3
CH CN, K CO , reflux
O
5
1
Scheme 1. Synthesis of chemosensor 1.
excitation at 326 nm. No significant changes of the spectra were
observed for 1 upon addition of most of the metal ions, except
2
+
2+
2+
2+
for Co , Ni , and Cu . Upon addition of 1 equiv of Co and
2
+
Ni , the fluorescence intensity of 1 was reduced to 78.5% and
2.1% of the initial one, respectively. Compared with Co and
Ni , upon addition of 1 equiv of Cu , the fluorescence intensity
2
+
7
2
+
2+
of 1 could be reduced to 22.4% of the initial one. Such a significant
2
+
difference in fluorescence intensity between Cu and other metal
ions indicates that the function group DPA of 1 is more suitable to
2
+
bind Cu than other metal ions observed.
2
+
The fluorescence titration of 1 toward Cu was shown in
Figure 5. The fluorescence intensity of compound 1 gradually
2
+
decreased as Cu was gradually titrated. When the amount of
2
+
Cu added was about 20
lM, the fluorescence intensity almost
reached minimum. The fluorescence quantum yield of compound
2
+
2+
1
in the absence of Cu and in the presence of 20
respect to quinine sulfate in 0.1 N H SO solution (
was calculated to be 0.337 and 0.012, respectively.
To determine the binding stoichiometry of the 1–Cu complex,
l
M Cu with
U
s
= 0.54)25
2
4
2+
2
6
the Job plot for the system was performed in aqueous solution by
keeping the total concentration of 1 and Cu at 10 lM and chang-
ing the molar ration of Cu ([Cu ]/[ Cu + 1]) from 0 to 1. As
2
+
Figure 1. Crystal structure of compound 1.
2
+
2+
2+
shown in Figure 5, the result shows a maximum at a molar fraction
of 0.5, indicating the formation of 1:1 complex of 1 and Cu . The
The selectivity of sensor 1 to Cu2+ was further investigated by
2+
fluorometric detection in DMSO/water (95:5, v/v) containing
HEPES buffer (10 mM, pH = 7.0). As shown in Figure 4, 1 exhibited
ESI mass spectrum of a mixture of 1 and CuCl also revealed the
formation of a 1:1 metal–ligand complex through the metal coor-
2
a
relatively strong fluorescence emission at 381 nm upon
dination interaction where there is a major signal at m/z 575.24
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.30
3
+
Al
292nm
3
26nm
2
+
Cd
326nm
3+
0.25
2
92nm
Cr
1
eq
Cu
2
+
2+
Cu
Cu
Fe
Hg
3
+
0.20
0.15
0.10
0.05
0.00
2+
2
+
+
0
3
14nm
K
2
+
Mg
Na+
2+
Pb
2
+
Zn
2
+
3
62nm
Co
2
+
Ni
250
275
300
325
350
375
400
425
250
275
300
325
350
375
400
425
Wavelength (nm)
Wavelength (nm)
Figure 2. UV–vis spectral changes of compound
95:5, v/v) containing HEPES buffer (10 mM, pH = 7.0) upon additions of various
metal ions (10 M).
1
(10
l
M) in DMSO/water
Figure 3. UV–vis spectral changes of compound
1 (10 lM) in DMSO/water
(
(95:5, v/v) containing HEPES buffer (10 mM, pH = 7.0) with increasing amount of
2+
l
Cu (as its chloride salt).
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Y. Hu et al. / Tetrahedron Letters xxx (2016) xxx–xxx
3
8
7
6
5
4
3
2
1
00
00
00
00
00
00
00
00
0
0.010
1
only,
+
y = 0.00102+ 0.0008x
R = 0.9982
+
2+
2+
3+
2+
K , Na , Mg , Mn ,Cr , Pb ,
Zn , Cd , Fe , Hg , Cu .
2
+
2+
3+
2+
+
0
0
0
0
0
.008
.006
.004
.002
.000
5
-1
K
=1.27×10 M
ass
2
+
Ni
2+
Co
2
+
Cu
0
1
2
3
4
5
6
7
8
9
10 11
350
375
400
425
450
475
500
2+
Wavelength(nm)
1/[Cu ]
Figure 6. Benesi–Hildebrand plot of sensor 1 with Cu2+
.
Figure 4. Emission spectral changes of compound 1 (10
v/v) containing HEPES buffer (10 mM, pH = 7.0) upon additions of various metal
ions (10 M). kex = 326 nm.
l
M) in DMSO/water (95:5,
l
8
00
+
(
calculated value, 575.09) assigned to the species [Cu (1)Cl] with
À
700
600
1
the loss of one Cl anion (ESI, Fig. S4).
The association constant as determined by fluorescence titra-
tion method following the Benesi–Hildebrand equation is found
1
+CuCl2
27
1+Cu(NO3)
2
5
À1
1
+Cu(AcO)2
to be 1.27 Â 10 M (Fig. 6). The detection limit, based on the def-
5
4
00
00
inition of IUPAC (CDL = 3Sb/m),28 was found to be 1.68 Â 10
À7
M
1+ CuSO4
from 10 blank solutions, lower than the limit of copper in drinking
water (ꢀ20
lM). These results suggest that compound 1 has a high
2
+
selectivity to Cu , and could be exploited as a fluorescence sensor
300
2
+
for Cu
.
2
1
00
00
0
Additionally, the effects of anionic counterions on the sensing
behavior of compound 1 to Cu2 were also investigated. The sepa-
rate concomitant additions of different copper salts, such as Cu
+
(
3 2 2 4
NO ) , Cu(AcO) , and CuSO to the receptor 1, gave rise to the
2+
same fluorescence profiles in its response to Cu (Fig. 7) indicating
a negligible effect of the counter anions on the recognition ability
and photo physical properties of receptor 1.
The effect of pH on the emission spectrum of 1 and 1–Cu com-
plex was depicted in Figure 8. At a low (2.0–6.0) pH, decreasing pH
protonates the nitrogen of DPA moiety of 1 and inhibits the PET to
350
375
400
425
450
475
500
Wavelength(nm)
2
+
Figure 7. Emission spectra of 1 (10
HEPES buffer (10 mM, pH = 7.0) in the presence of different copper salts (10
ex = 325 nm.
l
M) in DMSO/water (95:5, v/v) containing
lM).
k
8
7
6
5
4
3
2
1
00
00
00
00
00
00
00
00
0
3
50
00
50
8
00
3
0
2
1
2
2
+
700
600
2+
Cu
1+Cu
200
150
eq
100
500
400
300
200
100
0
5
0
0.0
0.2
0.4
0.6
0.8
1.0
3
50
375
400
425
450
475
500
2
4
6
8
10
12
Wavelength(nm)
pH
Figure 5. Emision spectra of 1 (10
lM) in DMSO/water (95:5, v/v) containing
2
+
HEPES buffer (10 mM, pH = 7.0) upon the addition of Cu (0–2 equiv) at 25 °C.
Figure 8. Fluorescence response (381 nm) of free 1 (10
l
M) and after addition of
Inset: Job’s plot of 1 and Cu2 . The total concentration of 1 and Cu was kept at a
+
2+
Cu (10
2+
l
M) in DMSO /H O (v/v 95:5, 10 mM buffer) solution as a function of
2
fixed 10 M.
l
different pH values.
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4
Y. Hu et al. / Tetrahedron Letters xxx (2016) xxx–xxx
the fluorophore resulting in a decrease in fluorescence of 1. At pH
.0, 1 shows a maximum intensity and it remains unchanged at
800
6
(a) only 1
2+
7
6
5
4
00
00
00
00
higher pH (>6.0). The effect of pH on 1–Cu complex shows that
the increase in pH increases the amount of quenching, reaching
its maximum at pH 6.0 after which it displayed no pH-sensitivity
in the pH range of 6.0–9.0. With a further increase in pH, the fluo-
rescence intensity was gradually restored with the pH increase.
2+
(c) 1+Cu + EDTA
À
This response was due to the stronger complexation of OH with
2
+
2+
Cu than the complexation of 1 with Cu and formation of Cu
OH) . Thus 1 displayed virtually no physiological pH-sensitivity
(
2
300
00
2+
2+
2+
(
b) 1+Cu
(d) 1+Cu + EDTA+ Cu
2+
and fluorescence on–off can be controlled by Cu binding within
the pH range of 6.0–9.0.
2
Competitive binding experiments with different metal ions and
Cu2+ were carried out from fluorescence spectra and the result is
100
0
shown in Figure 9. When 1 (10
l
M) was treated with 1 equiv of
2
+
Cu in the presence of the same concentration of other metal ions,
3
50
375
400
425
450
475
500
2
+
the Cu - induced fluorescence response of 1 was almost unaf-
Wavelength(nm)
fected by the presence of the other metal ions. The results indicate
that the binding of Cu ion to 1 is much stronger than that of other
metal ions.
2
+
Figure 10. Emission spectra in DMSO/water (95:5, v/v) containing HEPES buffer
M) with Cu2 (10
+
l
M); (c) 1
M) with
(10 mM, pH = 7.0). (a) Only 1 (10
l
M); (b) 1 (10
l
To establish the reversibility of 1–Cu2+ complexes, EDTA titra-
tion was conducted as shown in Figure 10. Upon addition of EDTA
to the solution containing 1 and Cu2 mixture, the original fluores-
cence could be reproduced again. When Cu2 was added to the sys-
tem again, the fluorescence intensities of solution decrease again.
The results indicated that sensor 1 could be easily regenerated
for repeating use.
2+
(
10
l
M) with Cu (10
l
M) and then addition of EDTA (20
l
l
M); (d) 1 (10 l
2
+
2+
Cu (10
l
M) and EDTA (20
l
M) then addition of Cu (25
M).
+
+
Cl-
N
N
N
N
Cu2+
N
N
CuCl2
3
CH S
Based on above studies, a proposed binding model for 1 with
Cu2+ is shown in Scheme 2. The complexation of Cu2+ ion requires
the coordination of three N atoms of DPA and one S atom of
3
CH S
EDTA
O
O
2+
methylthio group of 1, which was supported by Cu induced
1
1-Cu2+
1
chemical shift of l changes in the H NMR spectra (ESI, Fig. S5).
In the presence of 1.0 equiv of Cu2 ions, chemical shifts of proton
+
Scheme 2. Proposed binding model for 1 with Cu2+
.
3
NMR signals corresponding to the methylthio-CH was downfield
shifted by 0.0017 ppm. In the same way, obvious change in the
chemical shifts of proton of pyridine-H and three bridged-CH
2
PET process occurred.1,29 Thus, the quenching phenomena of the
fluorescence of 1 by Cu were observed.
groups also can be observed owing to the binding of the Cu +.
2
2+
These results suggest that the DPA and methylthio group are
In conclusion, a new selective fluorescent sensor based on 2,5-
diphenylfuran and di(2-picolyl)amine (DPA) was designed and
2+
involved in the complexation with Cu . When the DPA and
methylthio group coordinated to Cu2 , the electron density of the
DPA and methylthio group would be decreased, lowering their
electrondonating ability. While 1 was excited, the electron was
probably transferred from the fluorophore to the receptor, and a
+
2+
synthesized which was capable to detect Cu ion with high selec-
tivity in aqueous DMSO. This sensor formed a 1:1 complex with
2+
Cu and showed a fluorescent quenching.
Acknowledgments
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
1.15
0.99
This study was supported by the Science Technology Founda-
tion for Creative Research Group of HBDE (Grant No. T201311)
and the National Natural Science Foundation of China (Grant No.
1.13
1.12
1.11
1.07
1
.021.02
1.01
1.0
0.98
0.94
0.97
2
1501055).
0.89
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2016.04.
025.
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27 3
8.80. Found C, 75.23; H, 5.35; N, 8.67.
+
2
2
24. Crystal data for 1.
a = 10.5773(12),
30 27 3
C H N OS, M = 477.61, Triclinic, space group P-1,
b = 11.1121(12),
= 107.317(2)°, V = 1229.6(2) Å , Z = 2, Dc = 1.339 g cm
c = 12.1339(13) Å,
a
= 110.1090(10),
3
À3
b = 98.237(2),
c
,
1
2
2
Reflections collected: 11208, independent reflections: 6970 [R(int) = 0.0215],
Final indices [I > 2 (I)]: = 0.0418, wR = 0.1239. indices (all data):
= 0.0466, wR = 0.1307. CCDC 924966.
R
r
R
1
2
R
R
1
2
1
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2
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(
Please cite this article in press as: Hu, Y.; et al. Tetrahedron Lett. (2016), http://dx.doi.org/10.1016/j.tetlet.2016.04.025