A Highly efficient and selective turn-on fluorescent sensor for Cu2+ ion

Article abstract of DOI:10.1002/cjoc.201090300

A new fluorescent chemosensor based on an open-chain azacrown bearing a quinoline subunit was conveniently synthesized, which showed a remarkable enhanced fluorescent intensity in the presence of Cu2⁺ ion and a high selectivity toward Cu²⁺ ion over a wide range of tested metal ions in acetonitrile.

Full text of DOI:10.1002/cjoc.201090300

NOTE
A Highly Efficient and Selective Turn-on Fluorescent Sensor
＋
for Cu2 Ion†
Wang, Xuehua(王学花)
Cao, Jing(曹菁)
Chen, Chuanfeng*(陈传峰)
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
A new fluorescent chemosensor based on an open-chain azacrown bearing a quinoline subunit was conveniently
＋
synthesized, which showed a remarkable enhanced fluorescent intensity in the presence of Cu2 ion and a high se-
＋
lectivity toward Cu2 ion over a wide range of tested metal ions in acetonitrile.
＋
Keywords Cu2 recognition, fluorescent chemosensor, turn-on, selective
Introduction
Experimental
1H NMR spectra were recorded on a Bruker 300
(300 MHz) spectrometer. The fluorescence experiments
at room temperature reported in this paper were carried
out in CH3CN. The resolution was set at 1 nm, and λex
was 315－nm. The samples were prepared with a series of
In recent years, the development of fluorescent
＋
chemosensors for the detection of Cu2 ion has drawn
much attention owing to its importance i＋n environ-
mental and biological systems.1 Since Cu2 has effi-
cient fluorescence quenching character,2 it has been
used in many classic and early-reported cation sensors,
which undergo fluorescence quenching upon the bind-
5
－1
1.0× 10 mol•L HPLC acetonitrile solutions of
compound 1. Me－tal perchlorates were performed with
－3
1
＋
ing of Cu2 ion under an electron or energy transfer
1.0× 10－ mol•L . The sample was performed with
5
－1
1.0× 10 mol•L . Starting material and solvents were
purchased from Beijing Chemical Company. Compound
3 was synthesized according to the published proce-
dure.6
mechanism.3 Because of sensitivity reasons, fluoro-
ionophores showing fluorescence enhancement as a re-
sult of metal-ion binding are to be favored over those
exhibiting fluorescence quenching. Recently, some ex-
amples have been ＋reported, which have a selective re-
sponse toward Cu2 ion by a copper-enhanced fluores-
cence emission.4 In most cases, however, the fluores-
cence enhancement is faintish and usually ha＋s high
background. Furthermo＋re, the sel＋ectivity for Cu2 over
other ions, such as Pb2 and Fe3 , is not very satisfa＋c-
tory in some cases. Thus, development of new Cu2 -
selective turn-on fluorescence sensors is still important
and necessary.
Synthesis of compound 1
Under N2 atmosphere, a mixture of 3 (0.6 g, 3.92
mmol) and 2-quinolinecarboxaldehyde (0.62 g, 3.92
mmol) in ethanol (80 mL) was stirred for 4 h. The sol-
vent was removed under the reduced pressure, and the
residue was then recrystallized from methanol to give
the imine as a yellow solid, which was not purified and
used for the further reaction. To the solution of the
imine (0.3 g, 1 mmol) in methanol (150 mL) at 0 ℃
was slowly added NaBH4 (0.8 g, 20 mmol). After the
mixture was stirred at room temperature for 24 h, the
solvent was removed in vacuo. The residue was treated
Recently, we reported a highly efficient and selec-
＋
tive turn-on fluorescent sensor for Cu2 ion based on
calix[4]arene bearing four iminoquinoline subunits on
－1
the upper rim.5 Herein, we report a new easily available
with 1 mol•L aqueous NaOH, and then extracted with
＋
turn-on fluorescent sensor for Cu2 ion based on an
CH2Cl2. The organic layer was dried over anhydrous
Na2SO4, and concentrated to give the residue, which
was purified by recrystallization from methanol to give
the product 1 (0.25 g, 83%) as a yellow solid. m.p.
open-chain azacrown bearing a quinoline subunit, which
shows a remarkable fluorescent enhancement from al-
＋
most zero background in the presence of Cu2 and a
1
107—108 ℃; H NMR (CDCl3, 300 MHz) δ: 8.12 (d,
＋
high selectivity toward Cu2 ion over a wide range of
J＝8.4 Hz, 2H), 7.81 (d, J＝6.8 Hz, 1H), 7.72 (t, J＝7.4
tested metal ions in acetonitrile.
Hz, 1H), 7.52 (d, J＝8.3 Hz, 2H), 6.85 (t, J＝8.3 Hz,
*
E-mail: cchen@iccas.ac.cn; Tel.: 0086-010-62588936; Fax: 0086-010-62554449
Received June 12, 2010; revised July 20, 2010; accepted August 11, 2010.
Project supported by the National Natural Science Foundation of China (No. 20625206) and the National Basic Research Program (No.
2007CB808004).
† Dedicated to the 60th Anniversary of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.
Chin. J. Chem. 2010, 28, 1777— 1779
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Wang, Cao & Chen
NOTE
2H), 6.67—6.56 (m, 2H), 5.72 (brs, 1H), 4.69 (s, 2H),
4.23 (t, J＝4.6 Hz, 2H), 3.83 (t, J＝4.6 Hz, 2H), 3.49 (s,
3H); 13C NMR (CDCl3, 75 MHz) δ: 159.7, 146.2, 138.6,
136.6, 129.5, 128.9, 127.6, 127.4, 126.1, 122.0, 119.5,
116.7, 112.0, 110.6, 71.3, 68.5, 59.2, 49.9.
MALDI-TOF MS m/z: 308 (M＋ ). Anal. calcd for
C19H20N2O2: C 74.00, H 6.54, N 9.08; found C 73.81, H
6.55, N 9.02.
Results and discussion
Synthesis of compound 1 is depicted in Scheme 1.
According to the literature method,6 compound 3 was
first prepared by reaction of o-nitrophenol 2 with
2-methoxyethyl tosylate in 1∶1 (V∶V) CH3CN and
CH2Cl2 in the presence of K2CO3, and then catalytic
hydrogenation in methanol in the presence of Pd/C. Re-
action of 3 with 2-quinolinecarboxaldehyde in ethanol,
and then reduction with sodium borohydride in metha-
nol gave the target molecule 1 in a total 83% yield for
－5
－1
Figure 1 Fluorescent intensity of 1 (1× 10 mol•L ) in
CH3CN upon the addition of 40.0 equiv. metal ions.
the quinoline group becomes the lowest excited state,
which thus resulted in the increase of the fluorescence
intensity.
The fluorescence titration experiments of 1 with
＋
Cu2 ion were then performed. As shown in Figure 2,
1
the fluorescence intensit＋y of 1 is gradually enhanced
the two steps. Compound 1 was characterized by H
upon the addition of Cu2 ion. When the concentration
NMR, 13C NMR, MALDI-TOF MS, and elemental
analysis.
－5
－1
＋
of Cu2 ion is increased up to 40.0× 10 mol•L , the
intensity is increased by about 1000-fold. The nonlinear
Scheme 1 Synthesis of compound 1
fitting of the titration curve assumed a 1∶1 stoichiome-
＋
try for the 1-Cu2 complex, and the association co－n-
stant (Ka) was thus determined to be 4.87× 105 L•mol ,
1
＋
which indicates a high affinity of 1 to Cu2 . Further-
more, it was found that 1 had a detection limit of 2.06×
－6
－
＋
10 mol•L 1 for Cu2 , which is sufficiently low for the
detection of the submillimole concentration range of
＋
Cu2 ions found in many chemical and biological sys-
tems.
Figure 1 shows the fluorescence spectra (λem＝315
－5
nm) of 1 (10 mol•L－１) measured in acetonitrile with
respective metal cations (40 equiv.). Without cations, 1
shows a very weak fluorescence at 412 nm; however,
＋
the addition of Cu2 creates a remarkably enhanced
fluorescence. Under the same conditions, no obvious
fluorescence change was ob＋served＋for other tested tran-
＋
＋
＋
＋
sition-metal ions (Ni2 , Pb2 , Hg2 , Cd2 , Zn2 , Co2 ,
2＋
－5
－1
Figure 2 Fluorescence t＋itration of 1 (－10
mol•L ) with
Mn ), and alkali metal and alkaline earth metal ions
＋
＋
＋
2＋
－5
Cu(ClO4)2 in CH3CN. [Cu2 ]/(10 mol•L 1): 1.0, 4.0, 8.0, 12.0,
(Li , Na , K , Mg ). These observations indicate that
16.0, 20.0, 24.0, 28.0, 32.0, 36.0, 40.0. λex＝315 nm. Inset: plot
compound 1 has high sensitivity and selectivity for
2＋
＋
of F/∆F vs. 1/[Cu2 ].
Cu ion.
＋
The Cu2 induced selective fluorescence enhance-
The Job’s plot shown in Figure 3 was ＋evaluated from
ment of 1 might be mainly attributed to forma＋tion of the
stable complex between compound 1 and Cu2 ion, and
the subsequent block photoinduced electron transfer of
the fluorescence spectra of 1 and Cu2 with a total
concentration of 10.0 µmol/L, which further support the
＋
1∶1 binding mode between 1 and Cu2 ion.
the quinoline group by the lone-pair electron of the
＋
amine nitrogen atom in the presence of Cu2 .5 Conse-
＋
To explore the utility of 1 a＋s an ion-selective fluo-
rescence chemosensor for Cu2 , competition experi-
ments were－further carried out. Consequently, com-
quently, when Cu2 ion coordinates with the amine and
quinoline nitrogen atoms, the energy of the nπ* state
would be raised so that the ππ* state of the emission of
5
－1
pound 1 (10 mol•L ) was treated with 30 equiv. of
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 1777— 1779

＋
A Highly Efficient and Selective Turn-on Fluorescent Sensor for Cu2 Ion
most tested background metal ions showed small or no
＋
interference with the detection of Cu2 , indicat＋ing that
compound 1 could be used as an efficient Cu2 -selec-
tive turn-on fluorescent chemosensor, and subsequently
found practical applications in chemical and biological
systems.
References
1
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lick, L. Chem. Rev. 2004, 104, 419.
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Figure 3 Job plot of 1 vs. Cu(ClO4)2.
2
(a) Varnes, A. W.; Dodson, R. B.; Wehry, E. L. J. Am.
Chem. Soc. 1972, 94, 946.
(b) Kemlo, J. A.; Shepherd, T. M. Chem. Phys. Lett. 1977,
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＋
Cu2 ion in the presence of different background metal
＋
ions (100＋equiv.). As shown in Figure 4, except for Hg2
and Co2 ions, other tested background metal ions
showed small or no interference with the detection of
3
Some recent examples, see:
＋
Cu2 ion, indicating that 1 could be used as a potential
(a) Fernandez, Y. D.; Gramatges, A. P.; Amendola, V.; Foti,
F.; Mangano, C.; Pallavicini, P.; Patroni, S. Chem. Commun.
2004, 1650.
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practical Cu2 -selective turn-on fluorescent sensor.
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Huang, Z. T. Tetrahedron Lett. 2002, 43, 9209.
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－5
－1
Figure 4 Fluorescent in＋tensity of 1 (10 mol•L ) upon the
addition of 30 equiv. Cu2 in the presence of 100 equiv. back-
ground metal ions in CH3CN. λex＝315 nm.
4
Conclusion
In conclusion, we have developed a new easily
available turn-on fluorescent chemosensor 1 based on
an open-chain azacrown bearing a quinoline subunit,
which showed a remarkable enhanced fluore＋scent inten-
sity (about 1000-fold) in the＋presence of Cu2 ion and a
high selectivity toward Cu2 ion over a wide range of
metal io＋ns in acetonitrile. Moreover, the detection limit
5
6
－6
－1
for Cu2 was found to be 2.06× 10 mol•L , and
(E1006122 Ding, W.; Lu, Y.)
Chin. J. Chem. 2010, 28, 1777— 1779
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
1779