Highly selective fluorescence turn-on chemosensor based on naphthalimide derivatives for detection of trivalent chromium ions

Article abstract of DOI:10.1002/cjoc.201201070

A new fluorescent probe, NPQ-C, was synthesized. NPQ-C was based on the naphthalimide derivatives and exhibited high selectivity and sensitivity for Cr³⁺ ions. As a Cr³⁺-amplified fluorescent probe, Its fluorescence spectrum showed 5.5-fold enhancement in the intensity of the signal at 500 nm on binding with the Cr³⁺. Based on the fluorescence titration spectra and Job's-plot analysis, binding mode of NPQ-C with Cr ³⁺ was proposed. Fluorescence intensity was linear with concentration of Cr³⁺ cation in a range from 0 to 10 μmol·L ^-1. NPQ-C was also sensitive for Cr³⁺. The detection limit was calculated to be 0.20 μmol·L^-1 which indicated that NPQ-C was sensitive to Cr³⁺. Copyright

Full text of DOI:10.1002/cjoc.201201070

FULL PAPER
DOI: 10.1002/cjoc.201201070
Highly Selective Fluorescence Turn-on Chemosensor Based
on Naphthalimide Derivatives for Detection of Trivalent
Chromium Ions†
Chen, Zhijuna(陈志俊)
Wang, Limin*,a,b(王利民)
Zou, Ganga(邹刚)
Teng, Mingshuanga(滕明爽)
Yu, Jianjuna(余建军)
a Shanghai Key Laboratory of Functional Materials Chemistry and Institute of Fine Chemicals,
East China University of Science and Technology, Shanghai 200237, China
b College of Chemistry & Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325035, China
A new fluorescent probe, NPQ-C, was synthesized. NPQ-C was based on the naphthalimide derivatives and
exhibited high selectivity and sensitivity for Cr3+ ions. As a Cr3+-amplified fluorescent probe, Its fluorescence spec-
trum showed 5.5-fold enhancement in the intensity of the signal at 500 nm on binding with the Cr3+. Based on the
fluorescence titration spectra and Job's-plot analysis, binding mode of NPQ-C with Cr3+ was proposed. Fluores-
－
1
cence intensity was linear with concentration of Cr3+ cation in a range from 0 to 10 μmol•L . NPQ-C was also
－
1
sensitive for Cr3+. The detection limit was calculated to be 0.20 μmol•L which indicated that NPQ-C was sensi-
tive to Cr3+.
Keywords trivalent chromium ions, fluorescent probe, fluorescence enhancement, high selectivity, high sensitiv-
ity
＋
the paramagnetic nature of Cr3 .[10] turn-off sensors
showed bad sensitivity and selectivity for the cations,[11]
compared with turn-on chemosensors. On the other
hand, naphthalimide and its derivatives are widely de-
ployed in the construction of chemosensors.[12] But,
Introduction
Trivalent chromium (Cr3 ) is an essential nutrient
for humans and plays an important role in the metabo-
＋
lism of carbohydrates, lipids, proteins, and nucleic ac-
＋
ids.[1] Insufficient intake of Cr3 increases the risk for
＋
currently, few of fluorescent probes for Cr3 based on
diabetes and cardiovascular diseases,[2-3] whereas exces-
sive intake causes genotoxic effects.[4] Accurate and
the naphthalimide and its derivatives are reported. With
this in mind, herein, we designed and synthesized a new
highly selective and turn-on fluorescent sensor for de-
＋
rapid determination of Cr3 amount in the environment
is therefore necessary. Traditional analytical methods
＋
tection of Cr3 based on naphthalimide derivative. The
＋
for Cr3 employ expensive instruments such as atomic
synthesis of NPQ-C started from 4-bromine naphtha-
lene anhydride, via four steps, NPQ-C was obtained, as
shown in Scheme 1.
absorption spectrometry and inductively-coupled
plasma atomic emission spectrometry.[5-6] Although
these methods enable accurate and selective detection of
Cr3＋, these are usually time-consuming and require
complicated and tedious sample preparation.[7]
Experimental
Fluorescence method has more advantages over all
the other mentioned methods due to its operational sim-
plicity, high selectivity, sensitivity, rapidity, nonde-
structive methodology, high sampling frequency and
low cost of equipment and direct visual perception.[8]
Reagents and solvents were reagent grade, used as
received unless otherwise noted. All solvents used in
water-sensitive reactions were freshly distilled. Reac-
tions were monitored by TLC. Yields were of purified
1
product and were not optimized. H NMR were re-
Thus, construction and design of fluorescent probes
corded at 400 MHz. 13C NMR were recorded at 100
MHz. Fluorescence spectra were measured on a Thermo
Fluorescence spectrophotometer.
＋
for Cr3 always constitute an active area of research.[9]
＋
Although a lot of chemosensors for Cr3 are developed,
＋
most of them are turn-off chemosensors for Cr3 due to
*
E-mail: wanglimin@ecust.edu.cn
Received November 1, 2012; accepted November 21, 2012; published online December 13, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201201070 or from the author.
Dedicated to the 60th Anniversary of East China University of Science and Technology.
†
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Chin. J. Chem. 2012, 30, 2844—2848

Fluorescence Turn-on Chemosensor for Detection of Trivalent Chromium Ions
Scheme 1 The synthetic route of NPQ-C
thalic anhydride (5 g, 18 mmol), 1-aminobutane (1.7 g,
23.3 mmol) in 40 mL acetic acid was stirred under re-
flux in a nitrogen atmosphere for 6 h. After the comple-
tion of reaction, the reaction mixture was then poured
into a mixture of cracked ice and water (200 mL) and
filtered to get a pale yellow solid. The crude product
was recrystallized from chlorobenzene to give 4.6 g
CH2Cl2, r.t.
Br
N
+
Br
HN
N
O
Br
NH2
O
1
1
light gray solid in a yield of 85%. H NMR (CDCl3) δ:
8.64 (d, J＝7.2 Hz, 1H), 8.53—8.55 (m, 1H), 8.39 (d,
J＝7.6 Hz, 1H), 8.02 (d, J＝8.0 Hz, 1H), 7.81—7.85 (m,
1H), 4.17 (t, J＝7.6 Hz, 2H), 1.67—1.75 (m, 2H),
1.40—1.49 (m, 2H), 0.98 (t, J＝7.2 Hz, 3H).
O
O
O
O
N
O
H2N
Compound 3 4-Brom-N-n-buty-1-naphthalimide
(954 mg, 3 mmol) and piperazine (1810 mg, 21 mmol)
were dissolved in 2-methoxyethanol (18 mL), and the
reaction mixture was refluxed for 6 h under N2 atmos-
phere. After removal of 2-methoxyethanol under re-
duced pressure, the product was then chromatographed
on silica gel using dichloromethane/methanol (10∶1,
V/V) as eluant to afford 830 mg (82%) 2 as yellow solid.
1H NMR (CDCl3) δ: 8.57 (d, J＝7.2 Hz, 1H), 8.51 (d,
J＝8.4 Hz, 1H), 8.41 (d, J＝8.4 Hz, 1H), 7.68 (t, J＝7.6
Hz, 1H), 7.21 (d, J＝8.0 Hz, 1H), 4.16 (t, J＝7.6 Hz,
2H), 3.19—3.24 (m, 8H), 1.74—1.79 (m, 3H), 1.67—
1.73 (m, 2H), 1.41—1.47 (m, 2H), 0.97 (t, J＝7.2 Hz,
3H).
CH3COOH, reflux
Br
Br
2
H
N
O
N
O
N
H
CH3OCH2CH2OH, reflux
N
N
H
NPQ-C A mixture of 3 (150 mg, 0.4 mmol), 1
(300 mg, 1.2 mmol), K2CO3 (413 mg, 3 mmol), and KI
(50 mg, 0.3 mmol) in anhydrous CH3CN (15 mL) was
stirred at 60 ℃ for 4 h under an nitrogen atmosphere.
Subsequently, the solvent was removed under reduced
pressure, and the resulting residue was purified by silica
gel chromatography using methanol/CH2Cl2 (1∶100)
3
O
N
O
1
1
K2CO3, KI, CH3CN, reflux
as eluent to afford a yellow solid (110 mg, 25%). H
N
NMR (CDCl3) δ: 11.48 (s, 1H), 8.84—8.86 (m, 1H),
8.78—8.80 (m, 1H), 8.55—8.60 (m, 2H), 8.43 (d, J＝
8.4 Hz, 1H), 8.15—8.18 (m, 1H), 7.69—7.72 (m, 1H),
7.52—7.58 (m, 2H), 7.44—7.47 (m, 1H), 7.30—7.32
(m, 1H), 4.18 (t, J＝7.2 Hz, 2H), 3.46—3.50 (m, 6H),
3.05—3.06 (m, 4H), 1.40—1.50 (m, 2H), 1.25—1.28
(m, 2H), 0.98 (t, J＝7.2 Hz, 3H); 13C NMR (CDCl3) δ:
168.05, 164.47, 164.05, 155.77, 148.61, 139.00, 136.28,
134.19, 132.47, 131.15, 130.15, 129.88, 128.07, 127.34,
126.20, 125.82, 123.35, 121.90, 121.63, 117.05, 116.65,
114.99, 62.42, 53.50, 53.35, 40.13, 30.28, 29.70, 20.42,
13.89. MS m/z: 522.2427 [M＋H]＋ (calcd 522.2430
[M＋H]＋).
N
H
N
O
N
NPQ-C
Compound 1 A solution of 8-aminoquinoline
(0.72 g, 5 mmol) in CH2Cl2 (25 mL) and triethylamine
(0.505 g, 5 mmol) was cooled in an ice bath. Bromo-
acetyl bromide (1.20 g, 5.5 mmol) dissolved in CH2Cl2
(10 mL) was added dropwise over 10 min with stirring.
Upon stirring at ambient temperature for 4 h, the reac-
tion mixture was washed successively with 0.3 mol•L－
1
The metal salts used
HCl (30 mL) and the organic layer was extracted and
rotary-evaporated. The resultant oil was purified by
chromatography on a silica gel column using ethyl ace-
tate-hexanes (V/V＝1∶2) as eluent. The product was
obtained as a yellow solid by removal of the solvent.
Yield: 90% (1.18 g). 1H NMR (CDCl3) δ: 10.91 (s, 1H),
8.74—8.76 (m, 1H), 8.16—8.18 (m, 1H), 7.55—7.56
(m, 2H), 7.46—7.49 (m, 1H), 4.31 (s, 2H).
Fe2(SO4)3•9H2O, ZnSO4•6H2O, Co(ClO4)2•6H2O,
NiSO4•6H2O, Ca(ClO4)2, Cr(ClO4)3•6H2O, CuSO4•
5H2O, Mn(ClO4)2•6H2O, Na2SO4•10H2O, K2SO4,
AgClO4•H2O, Hg(ClO4)2•3H2O, Cd(ClO4)2•6H2O.
Results and Discussion
The interaction of sensor NPQ-C with the cations
Compound 2 A mixture of 4-bromo-1,8-naph-
was investigated through fluorescence spectra. All the
Chin. J. Chem. 2012, 30, 2844—2848
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2845

Chen et al.
FULL PAPER
fluorescence behavior of sensor NPQ-C was studied in
acetonitrile-water (70∶30, V/V) with a buffer solution
of 3-(N-morpholino) propanesulfonic acid (MOPS, 10
－
1
mmol•L , pH＝7.0). The effects of pH were evaluated
in the pH range from 5 to 10 (Figure 1), suggesting that
it was insusceptible to the change of acid-base solution.
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
-2000
－
Figure 2 Fluorescence spectra of NPQ-C (1×10－5 mol•L ) in
1
5
6
7
8
9
10
acetonitrile-water (70 ∶30, V/V) with a buffer solution of
pH
3-(N-morpholino) propanesulfonic acid (MOPS, 10 mmol•L－
,
1
Figure 1 pH-dependent fluorescence spectra of NPQ-C (1×
＋
pH＝7.0) in the presence of different concentrations of Cr3 (0—
10 equiv.), λex＝390 nm. Inset: fluorescence intensity at 500 nm
－
10－5 mol•L )
1
＋
of NPQ-C as a function of Cr3 concentration.
＋
Fluorescence titrations of NPQ-C with Cr3 were
performed and the responding spectra are shown in Fig-
ure 2. Free NPQ-C exhibited very slight fluorescence
response with a maximum at 520 nm, which was due to
efficient photoinduced electron transfer (PET) process
from the electro-rich receptor to the excited NPQ-C
＋
fluorophore (Ф＝0.07). Upon addition of Cr3 , fluo-
rescence enhancement would be observed and a
blue-shifted emission band centered at 500 nm showed
up (Ф＝0.38). The fluorescence enhancement was at-
＋
tributed to the formation of a NPQ-C/Cr3 complex and
PET mechanism was quenched. While the blue-shift to
500 nm was caused by a change of the internal charge
transfer process (ICT). And a continuous increase of
＋
fluorescence intensity could be observed with Cr3
concentration increasing (Figure 2). The increase was
＋
saturated upon the addition of 1 equiv. of Cr3 and the
Figure 3 Curve of fluorescence intensity at 500 nm of NPQ-C
－
＋
(1×10－5 mol•L ) versus increasing concentrations of Cr3 (0—
1
fluorescence peak no longer changed when the concen-
＋
tration of Cr3 increased from 1 to 10 equiv. (Figure 2,
－
1
10 μmol•L ).
inset), implicating a 1∶1 complexation of NPQ-C with
＋
the Cr3 .
(Figure 4). The results also indicated that NPQ-C
＋
formed a 1∶1 stoichiometrical complex with Cr3 .
Figure 3 showed there was a good linearity between
＋
the emission at 500 nm and concentrations of Cr3 in
Figure 5 showed the fluorescence spectra (λex＝390
－
1
nm) of NPQ-C (1×10－ mol•L ) measured in ace-
tonitrile-water (70∶30, V/V) with a buffer solution of
3-(N-morpholino) propanesulfonic acid (MOPS, 10
5
the range from 0 μmol•L－ to 10 μmol•L , indicating
－
1
1
that sensor NPQ-C could detect quantitatively relevant
＋
concentrations of Cr3 . The linear equation was found
－
1
to be y＝9242.1×105x＋2513.4 (R＝0.9841), where y
mmol•L , pH＝7.0), with 10 equiv. of respective metal
＋
＋
＋
＋
＋
cations such as Cr3 , Na＋, Ag＋, Ca2 , Mg2 , Zn2 , Pb2 ,
＋
was the emission at 500 nm measured at a given Cr3
＋
＋
＋
＋
＋
＋
＋
Hg2 , Ni2 , Mn2 , Co2 , Cd2 , K＋, Fe3 and Cu2 .
concentration and x represented the concentration (10－
5
＋
mol/L) of Cr3 added. According to IUPAC, the detec-
Without cations, NPQ-C showed weak fluorescence.
＋
Addition of Cr3 , a strong fluorescence emission en-
tion limit was determined from three times the standard
－
1
hancement with a blue-shift was observed. In contrast,
deviation of the blank signal (3s) as 0.20 μmol•L . The
＋
result indicated that NPQ-C was sensitive to Cr3 .
addition of other metal cations could not cause signifi-
＋
cant enhancement in fluorescence emission. With Cr3 ,
In order to further understand the coordination of
＋
NPQ-C with Cr3 , Job's-plot analysis was carried out
the enhancement factor was determined to be 15212.
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Fluorescence Turn-on Chemosensor for Detection of Trivalent Chromium Ions
Figure 6 Fluorescent emission changes of NPQ-C (1×10－
5
－
1
mol•L ) upon addition of 10 equiv. of each relevant analyte
Figure 4 Job’s plot for determining the stoichiometry of
＋
＋
＋
＋
＋
＋
＋
＋
＋
(Cu2 , Mg2 , Hg2 , Na＋, K＋, Zn2 , Fe3 , Cr3 , Co2 , Ni2 , Ca2 ,
＋
NPQ-C ([NPQ-C]＋[Cr3＋]＝40 μmol•L－1) and Cr3 in aceto-
＋
＋
＋
Ag＋, Cd2 , Ba2 , Mn2 ) in acetonitrile-water (70∶30, V/V) with
nitrile-water (70 ∶ 30, V/V) with
a buffer solution of
3-(N-morpholino) propanesulfonic acid (MOPS, 10 mmol•L－
pH＝7.0). λex＝390 nm.
,
1
a buffer solution of 3-(N-morpholino) propanesulfonic acid
(MOPS, 10 mmol•L , pH＝7.0). λex＝390 nm.
－
1
To examine whether sensor NPQ-C could still retain
＋
the sensing response to Cr3 under the potential com-
petition of relevant analytes, the sensor was treated with
＋
Cr3 in the presence of other metal ions. As displayed
in Figure 7, all the relevant analytes tested had virtually
＋
no influence on the detection of Cr3 . Thus, sensor
＋
NPQ-C seemed to be useful for selectively sensing Cr3 ,
even with these relevant analytes.
－
Figure 5 Fluorescent response of NPQ-C (1×10－5 mol•L ) to
various metal ions at 10 equiv. concentration in acetonitrile-water
(70∶30, V/V) with a buffer solution of 3-(N-morpholino) pro-
1
－
1
panesulfonic acid (MOPS, 10 mmol•L , pH＝7.0). λex＝390 nm.
In contrast, other metal ions quenched fluorescence of
NPQ-C or had a little influence on NPQ-C. This sug-
＋
gested that the factor for Cr3 was more than 5.5 times
larger than that for other metal cations, which was larger
Figure 7 The fluorescent intensity at 500 nm of NPQ-C (1×
＋
than the value obtained with early reported Cr3 probes
－
＋
10－ mol•L ) with 10 equiv. of Cr3 and 10 equiv. of various
metal ions in acetonitrile-water (70∶30, V/V) with a buffer solu-
tion of 3-(N-morpholino) propanesulfonic acid (MOPS, 10
5
1
( ＜ 4 times),[13] as shown in Figure 6. The
above-mentioned findings clearly indicated that NPQ-C
－
1
behaved as a highly selective turn-on fluorescent probe
mmol•L , pH＝7.0). λex＝390 nm.
＋
for Cr3 . In addition, the fluorescence increase took
＋
place immediately after Cr3 addition (within 10 s),
According to the fluorescence titration spectra, the
＋
indicating that NPQ-C enables rapid detection of Cr3 .
＋
＋
Cr3 induced a hypsochromic shift in emission maxi-
As for the high selectivity for Cr3 , we think that the
mum. This phenomenon usually occurs when the nitro-
gen, which is also the donor of push-pull system, che-
lates to metal ions, which eventually induced the change
of the internal charge transfer process (ICT).[15] There-
following two factors might play critical role for high
selectivity of NPQ-C. On one hand, the avoidance of
using sulfur atom in our scaffold will avoid interference
from other metal ions especially mercury.[14] On the
fore, we believed that the pyrazine nitrogen that linked
＋
to the naphthalimide ring did involve in Cr3 chelation.
other hand, the receptor of NPQ-C is relatively rigid
＋
and has a cavity, which probably fitted Cr3 best com-
Based on this factor and Job's-plot analysis, we pro-
pared to other metal ions.
posed a plausible binding mode of the probe NPQ-C
Chin. J. Chem. 2012, 30, 2844—2848
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Chen et al.
FULL PAPER
＋
with Cr3 as shown in Scheme 2.
Funds for the Central Universities, the Opening Foun-
dation of Zhejiang Provincial Top Key Discipline, and
Baihehua Group.
＋
Scheme 2 Proposed binding mode of NPQ-C with Cr3
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－
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＋
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＋
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－
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1
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Acknowledgement
The authors gratefully acknowledge the National
Nature Science Foundation of China (21272069,
20672035), the support from the Fundamental Research
(Pan, B.; Fan, Y.)
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Chin. J. Chem. 2012, 30, 2844—2848