An effective Cu(ii) quenching fluorescence sensor in aqueous solution and 1D chain coordination polymer framework

Article abstract of DOI:10.1039/c1dt10987a

In the article, a novel fluorescent probe for the copper cation based on fluorescence quenching mechanism was designed. It exhibited high selectivity for Cu(ii) over other common metal ions in aqueous media. Furthermore the coordination between Cu(ii) and the organic molecule sensor fabricated an interesting 1D chain coordination polymer framework.

Full text of DOI:10.1039/c1dt10987a

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COMMUNICATION
An effective Cu(II) quenching fluorescence sensor in aqueous solution and 1D
chain coordination polymer framework†
Zeng-chen Liu, Zheng-yin Yang,* Tian-rong Li, Bao-dui Wang, Yong Li, Dong-dong Qin, Ming-fang Wang and
Mi-hui Yan
Received 26th May 2011, Accepted 1st August 2011
DOI: 10.1039/c1dt10987a
In the article, a novel fluorescent probe for the copper cation
based on fluorescence quenching mechanism was designed.
It exhibited high selectivity for Cu(II) over other common
metal ions in aqueous media. Furthermore the coordination
between Cu(II) and the organic molecule sensor fabricated an
interesting 1D chain coordination polymer framework.
selective quenching fluorescent probe toward Cu(II) in aqueous
media, which acts by way of a photo-induced electron transfer
(PET) mechanism.
On account of their excellent luminescence properties, quinoline
derivatives have been widely used as fluorophores in fluorescence
chemosensors. In recent years, many fluorescent chemosensors
7
based on quinoline derivatives have been reported. In addition,
acyl hydrazone groups have also been developed due to their
powerful chelating activities. In the present work, the quench-
In the present years, the development of highly selective and
sensitive fluorescent probes toward metal ions has attracted
considerable interest. A large number of fluorescent chemosensors
8
ing fluorescent chemosensor for Cu(II) is 3-formylquinoline-
2(1H)one, bearing 1H-benzotriazol-1-acetic acid hydrazide (L).
The procedure used for its synthesis is shown in Scheme S1†, and
is also described in the ESI.† The structure was determined by
1
based on an off–on mechanism have been designed. Among the
fluorescent probes toward metal ions, the study of chemosensors
for Cu(II) is a very meaningful and challenging work. The copper
ion is the third in abundance after iron and zinc ions among
the essential heavy metal ions in organisms, for example many
enzymes and proteins, and it plays a vital role in several biological
processes. The inadequate and excessive uptake of Cu(II) in
biological systems can cause oxidation and disorders associated
with neurodegenerative diseases, such as Alzheimer’s disease,
1
H-NMR (ESI†). According to our original design, the organic
molecule could chelate metal ions via two carbonyl O atoms and
one imino N atom, but by X-ray crystal structure analysis, the
coordination of L with Cu(II) exhibited an interesting 1D chain
n
polymer framework ([CuL] ). By analyzing the crystal structure,
one nitrogen atom from 1H-benzotriazol-1-acetic acid hydrazide
acted as a bridge to connect with Cu(II), which coordinated with
two carbonyl O and one imino N from the other ligand (Fig. 1).
2
Menke’s disease and Wilson’s disease. Moreover, in the natural
environment, copper is also considered as a significant pollutant
3
To characterize [CuL]
As shown in Fig. S1,† the peaks at 409.2, 754.3, 815.2, 1162.9 and
225.0 were assigned as the fragment ion peaks of ([Cu(II) + L],
Cu(II) + L + Cu(II)], [Cu(II) + L + Cu(II) +L], [Cu(II) + L + Cu(II) +
n
more intensively, its ESI-MS was analyzed.
owing to its high toxicity. So it is very necessary to synthesize
new fluorescent chemosensors to detect copper in biological
systems and the environment. On the other hand, upon binding of
target ions with organic molecules, different sensing mechanisms
including photo-induced electron transfer (PET), internal charge
transfer (ICT) and fluorescence resonance energy transfer (FRET)
1
[
4
have been researched for Cu(II) fluorescent probes. These turn-
on fluorescent chemosensors, which can enhance effectively the
fluorescence intensity of sensors upon binding Cu(II), have been
5
reported extensively. However, effective fluorescent probes based
on the photo-induced electron transfer fluorescence quenching
6
mechanism (PET) are relatively rare. Herein, we report a highly
College of Chemistry and Chemical Engineering and State Key Laboratory of
Applied Organic Chemistry, Key Laboratory of Nonferrous Metal Chemistry
and Resources Utilization of Gansu Province, Lanzhou University, Lanzhou,
7
30000, P.R. China. E-mail: yangzy@lzu.edu.cn; Fax: +86 931 891 2582;
Tel: +86 931 891 3515
Electronic supplementary information (ESI) available: experiment in-
†
struments, the synthetic procedure for the fluorescence probe and X-ray
crystal structure description. CCDC reference number 774747. For ESI
and crystallographic data in CIF or other electronic format see DOI:
Fig. 1 The coordination mechanism and 1D chain coordination polymer
framework ([CuL] ) of sensor L with Cu(II).
1
0.1039/c1dt10987a
n
9
370 | Dalton Trans., 2011, 40, 9370–9373
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L + Cu(II)] and [Cu(II) + L + Cu(II) + L+ Cu(II) + L]) from [CuL]
indicating apparently the formation of [CuL] in MeOH–H
media. Moreover, the elemental analysis and IR spectra (Fig. S2†)
were also tested to characterize [CuL] . The elemental analysis
data (anal. calcd (%): C, 44.81; H, 3.25; N, 19.77. Found (%): C,
n
,
n
2
O
n
4
4.25; H, 3.58; N, 19.21) suggested that the empirical formula was
-
Cu(II)
2
·L
2
·H
2
O·CH
3
OH·(NO
3
) without free solvent molecules.
2
-
1
In the FT-IR spectrum of L, the observed IR bands at 1681.25 cm
and 1648.52 cm- were attributed to the carbonyl stretching vibra-
1
tions from quinoline-2(1H)one and 1H-benzotriazol-1-acetic acid
hydrazide, respectively. Analysizing the IR spectrum of [CuL]
n
, the
-
1
band at 1681.25 cm had been replaced by the characteristic band
-
1
at 1640.94 cm , and that the characteristic band of carbonyl at
1
1
648.52 cm- from 1H-benzotriazol-1-acetic acid hydrazide had
disappeared, which was a convincing proof of an enolic carbonyl.
-
1
Simultaneously, the vibration band at 1603.28 cm for L was
Fig. 2 The electronic absorption spectrum of L (10 mM) upon addition
-
1
of Cu(II) (0–2 equivalent) in MeOH–H O (9 : 1) solution.
assigned to the n (C N) stretch, which shifted to 1588.35 cm
upon coordination of nitrogen atom. Compared with the nitrogen–
nitrogen vibration (589.75 cm ) from the benzotriazol section
of L, the IR band of [CuL] exhibited an apparent change (to
63.11 cm ). Additionally, the intense absorption band in the
IR spectrum associated with the asymmetric stretching appeared
at 1383.95 cm , clearly establishing that there are free nitrate
groups (C2v) in [CuL] . All the results confirmed completely that
the structure was [CuL]
The electronic absorption spectrum (UV-vis spectrum, Fig. 2)
of sensor L in MeOH–H O media exhibited a strong band at
85 nm. Addition of Cu(II) (0.2 mM) to L resulted in a red-shift of
nm to 389 nm in the absorption spectrum, then the absorption
2
-
1
Cr(III), Ni(II), Mn(II), Co(II), Fe(III) and Cu(II) in MeOH–H O
2
n
solution (Fig. 3). It was observed that the metal ions such as Zn(II),
-
1
5
Cd(II), Hg(II) and Mg(II) could enhance weakly the fluorescence
of L. K(I), Na(I), Ca(II), Al(III) and Pb(II) did not interfere with
-
1
10
the fluorescence of L. However, d transition metal ions Ni(II),
n
Mn(II), Co(II), Fe(III) and Cu(II) quench the emission intensity of
L. Interestingly, Cu(II) exhibited very distinct quenching activity
over other metal ions, as it could quench the fluorescence of L
completely. Thus L could be used as a highly selective fluorescence
probe for Cu(II) in the presence of most metal ions.
n
.
2
3
4
The fluorescence titration spectrum of L (10 mM) in MeOH–
band intensity at 389 nm dropped gradually with increased Cu(II)
concentration, which implied a typical PET process. In the fluores-
cence quenching system based on a PET process, the receptor is the
Cu(II) chelating domain, the fluorescence motifs are the quinoline-
H O solution was also investigated (Fig. 4). L showed a strong
emission band at 460 nm when excited at 380 nm. Upon addition
2
of Cu(II) ion (0–20 mM), remarkable fluorescence quenching
of L was observed. Moreover, through fitting the fluorescence
titration curve, the 1 : 1 stoichiometry between L and Cu(II) was
estimated, which was in accordance with the result from the X-ray
crystal structure analysis. Furthermore, the association constant
2
(1H)one and the 1H-benzotriazol fluorophores from the sensor.
The very effective fluorescence quenching phenomenon really
happened when the receptor (Cu(II) chelating domain) integrated
into the fluorescence motifs.
4
-1
for Cu(II) was estimated to be 4.31 ¥ 10 M in MeOH–H O
2
The photophysical properties of L were investigated by exam-
ining its fluorescence behavior upon addition of several ions such
as K(I), Na(I), Mg(II), Ca(II), Zn(II), Cd(II), Hg(II), Al(III), Pb(II),
solution by the linear Benesi–Hildebrand expression I /(I - I ) =
0
0
9
I /[L] + I /[L] ¥ K ¥ [M]. I is the change in the fluorescence
0
0
s
intensity at 460 nm, K is the stability constant, and [L] and
s
Fig. 3 a. Fluorescence spectrum of L (10 mM) upon addition of K(I), Na(I), Mg(II), Ca(II), Zn(II), Cd(II), Hg(II), Al(III), Pb(II), Cr(III), Ni(II), Mn(II),
Co(II), Fe(III) and Cu(II) (10 mM) in MeOH–H O (9 : 1) solution. b. Histogram of fluorescence selectivity experiment.
2
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Fig. 4 a. Fluorescence titration of L (10 mM) upon addition of Cu(II) (0–2 equivalents) in MeOH–H
2
O (9 : 1) solution. Inset: the fluorescence intensity
2
curve of L at 460 nm. b. Benesi–Hildebrand expression fitting of fluorescence titration curve of L in MeOH–H O (9 : 1) solution.
Fig. 5 a. Fluorescence intensity of L (10 mM) upon addition of various metal ions in MeOH–H
response of L to the various metal ions (10 mM). Red bars represent the addition of Cu(II) (10 mM) to the solution. b. The fluorescence images of L and
L with addition of Cu(II) under UV light in MeOH–H O (9 : 1) solution.
2
O (9 : 1) solution. Black bars represent the fluorescence
2
[
M] are the concentration of L and Cu(II), respectively. I
0
is the
Cu(II) is at the 0.1 parts per million level. Under the conditions,
the fluorescence intensity of the solution of sensor L was still
proportional to the amount of added Cu(II) (Fig. S5†).
In summary, we have developed a novel Cu(II) fluorescent
chemosensor based on a photo-induced electron transfer (PET)
mechanism. It exhibits high selectivity and sensitivity toward
fluorescence intensity of L in the absence of Cu(II). On the basis
of the plot of 1/[I] versus 1/[Cu], the stability constant can be
obtained.
To validate the practical selectivity of sensor L with Cu(II)
over other competitive metal ions, the fluorescence competitive
experiment was tested. As shown in Fig. 5a, while Cu(II) elicited
a prominent fluorescence quenching of L, the addition of other
metal ions did not cause any discernible changes. All the results
indicated that the fluorescence probe exhibited higher selectivity
over other metal ions. Moreover, a more complex real sample was
simulated to demonstrate the high selectivity of L with Cu(II).
Fig. S3† illustrated the complex system; it was clear that the
coexistence metal ions system (10 mM) did not effectively quench
the fluorescence of senor L, nevertheless an apparent fluorescence
quenching phenomenon occurred with addition of Cu(II) (10 mM),
which further indicated the excellent selectivity of L with Cu(II) in
Cu(II) over other metal ions in MeOH–H
cence emission of L can be effectively quenched upon addition of
Cu(II) in MeOH–H O solution. Moreover, according to the theory
2
O media. The fluores-
2
investigation and X-ray crystal diffraction, a 1 : 1 stoichiometry
between L and Cu(II) is formed, and they construct an interesting
1D chain coordination polymer framework ([CuL] ). The excellent
n
selectivity and sensitivity of sensor L for Cu(II) in aqueous
media indicates its potential application value in the biological
monitoring and tracking of copper.
MeOH–H O solution. Additionally, to evaluate visually the high
selectivity for Cu(II), the fluorescence images of L (1 mM) and
L (1 mM) upon addition of Cu(II) (1 mM) was also investigated
2
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (20975046). We would also like to thank
Yong-liang Shao (Lanzhou University) and Prof. Zhong-ning
Chen (Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences) for their help with crystal structure
refinement.
(
Fig. 5b), indicating the blue fluorescence of L could be quenched
effectively upon addition of 1 equivalent Cu(II) in MeOH–H
solution. The sensitivity of senor L with Cu(II) in MeOH–H
solution was also tested. The fluorescence titration profile of sensor
2
O
O
2
-
6
L (10 M) with Cu(II) (Fig. S4†) demonstrated the detection of
9
372 | Dalton Trans., 2011, 40, 9370–9373
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Dalton Trans., 2011, 40, 9370–9373 | 9373