Glutamine-containing "turn-on" fluorescence sensor for the highly sensitive and selective detection of chromium (III) ion in water

Article abstract of DOI:10.1016/j.saa.2013.07.069

(Chemical Equation Presented) In this study, we reported a new fluorescence sensor for chromium (III) ion, dansyl-L-glutamine (1). The sensor displayed a unique selective fluorescence "turn-on" response to Cr³⁺ over other common metal ions in w

Full text of DOI:10.1016/j.saa.2013.07.069

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 460–465
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Glutamine-containing ‘‘turn-on’’ fluorescence sensor for the highly
sensitive and selective detection of chromium (III) ion in water
Meili Zhao a,1, Liguo Ma b,2, Min Zhang a,1, Weiguang Cao a,1, Liting Yang a,1, Li-Jun Ma a,
⇑
a
School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China
b
College of Chemical Engineering, China University of Petroleum, Beijing 102200, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
A new fluorescence sensor (1) for Cr3+
was synthesized.
The sensor exhibits a specific
3
+
selectivity for Cr in aqueous
solution.
ꢀ
ꢀ
The sensor showed the ‘‘turn-on’’
fluorescence response to Cr3 in pure
water.
+
The sensor shows a ratiometric
3
+
response to Cr in UV–vis absorption
spectra.
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, we reported a new fluorescence sensor for chromium (III) ion, dansyl-L-glutamine (1). The
Received 1 March 2013
Received in revised form 3 July 2013
Accepted 22 July 2013
3+
sensor displayed a unique selective fluorescence ‘‘turn-on’’ response to Cr over other common metal
3+
ions in water. Notably, 1 still showed a ratiometric response to Cr in UV–vis absorption spectra. The
3+
binding mechanism of 1 to Cr was further clarified by using NMR and ESI-MS spectra. The experiment
Available online 3 August 2013
3
+
results indicated that the dual-responses of 1 to Cr should attribute to the coordination of deprotonated
3
+
sulfonamide group with Cr and the protonation of the dimethylamino group due to the coordination of
Keywords:
Chromium (III) ion
3+
Cr for 1. In addition, two chloride ions also coordinated to the complex of sensor-chromium (III) ion,
3
+
which further strengthened the conformation of 1–Cr
.
‘
‘turn-on’’ Fluorescence sensor
Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved.
Glutamine
Dansyl group
Introduction
heavy and transition metal ions, Cr3+ is a known environment
pollutant. As itself or its compounds are widely used in industry
such as metallurgy, chrome plating, leather tanning, and batteries
[5–7] and its industrial sewage enters into environment and
drinking water, but the threshold limit for chromium uptake is
Development of chemosensors for recognition and sensing of
environmentally and biologically important heavy and transition
metal ions, for example, Pb2 , Hg , Cu , and Cr , have attracted
+
2+
2+
3+
3
3
considerable attention of current researchers [1–4]. Among the
0.1 mg/m in air and 0.05 mg/dm in water [8]. In addition, chro-
mium is an essential trace element in human nutrition, it plays
an important role in the maintenance of an effective carbohy-
3
+
drates, lipid and protein metabolism [9]. Excessive intake of Cr
3
+
causes genotoxic effects [10]. But if one lacks Cr , sugar metabolic
disorder can be easily caused, resulting in engendering diabetes
and cardiovascular disease risk, even cataract, blindness, uremia
⇑
Corresponding author. Tel.: +86 20 39310251; fax: +86 20 39310187.
E-mail address: mlj898021@yahoo.com.cn (L.-J. Ma).
Tel.: +86 20 39310251; fax: +86 20 39310187.
Tel./fax: +86 10 89733089.
1
2
1
386-1425/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.07.069

M. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 460–465
1200
461
and so on [8,11]. So it is important to develop selective fluores-
3
+
cence sensors for Cr in biological or environmental samples.
Recently, Saluja et al. developed a fluorescence sensor based on
benzimidazole to recognized Cr3 [12]. Another chemosensors,
rhodamine derivatives, were reported by Das et al. in presence of
large excess of other competing ions with associated changes in
their optical and fluorescence spectral behavior [13]. Guha et al.
once reported thiophene-counmarin hybrid molecule that can
1
000
+
8
00
(
b) (a)
600
3+
selectively monitoring Cr in CH
3
CNÀHEPES buffer [14]. However,
3
+
Cr as one of the most efficient fluorescence quenchers among the
transition metal ions and it is paramagnetic, so there is a lack of
selective ligand systems for Cr3+ [15,16]. As a result, only very
few reports were available regarding the fluorescent detection of
4
00
00
0
2
3
+
Cr in environment and biological samples or live-cell imaging.
Herein, we designed and synthesized a hypersensitive water-
soluble fluorescence sensor based on glutamine with dansyl
groups; it shows very good selectivity as well as sensitivity for
400
440
480
520
560
600
Wavelength / nm
3
+
Cr . The method is simple, rapid and effective.
Fig. 2. Fluorescence intensity of 1 (5.0 lM) in NaAc/HAc buffer solution (pH 5.5)
upon addition of various amounts of Cr (0.0, 0.5, 1.0, 2.5, 5.0, 10.0, 15.0, 20.0, 30.0,
5.0, 60.0
illumination with 254 nm light.
3+
4
l
M). Inset: fluorescence photographs of 1 (a) and 1–Cr3+ (b) under
Experimental
Materials and apparatus
and was shook with ethyl acetate. The organic layer was separated
and distilled under reduced pressure to give a crude residue. The
product was further purified by column chromatography; finally
the tawny solid product of 1 was obtained with a 64.8% yield.
All chemicals were obtained from commercial suppliers and
were used without further purification. Stock solutions of 1
(
(
5.0
lM) were prepared in distilled water. Stock solutions
5.0 mM) of the chlorate salts of Na , K , Mg ,Ca , Cu2+, Co
+
+
2+
2+
2+
,
2
+
2+
2+
3+
2+
2+
3+
3+
3 5
ESI-MS (m/z): 378.73; calcd for C17H21N O S, 379.43.
Ni , Cd , Fe , Cr , Hg , Pb , Fe , Al in distilled water were
prepared. For all measurements, excitation was at 320 nm.
NMR measurements were performed on a Varian NMR Systems
Results and discussion
4
00 MHz spectrometer. Mass spectra were measured on a
3
+
LCQDACAXPMAX mass spectrometer (Finnigan). Fluorescence
spectra were measured on a Hitachi F-2500 fluorescence spectro-
photometer. UV–vis absorption spectra were obtained on a Shima-
dzu UV-1700 spectrophotometer at room temperature.
Fluorescence response of 1 to Cr
The fluorescence sensor 1 itself has a strong emission band at
543 nm in 5.0 M buffer aqueous solutions. Upon the addition of
l
3
+
increasing concentration of Cr , as shown in Fig. 2, a significant
enhancement of the emission band at 500 nm occurred, resulting
in a 43 nm blue-shift and a significant increase in the intensity of
the emission was observed. Meanwhile, the fluorescence color
apparently changes from yellow to green under a UV lamp excited
at 254 nm (inset in Fig. 2). The blue-shift and the enhancement of
the maximum emission can be tentatively explained in terms of
the internal charge transfer (ICT) between imino group and dansyl
moiety was inhibited [17–21].
Synthesis and characterization of 1
The fluorescence sensor 1 was easily synthesized by two steps
in the reaction of dansyl chloride and glutamine (see Fig. 1).
0
.12 g Glutamine (0.821 mmol) in flasks was dissolved in
sodium bicarbonate solution (15.0 ml, 0.10 M). The mixed solution
was cooled at 0 °C ice-water bath for 10 min. Then the solution of
dansyl chloride (0.225 g, 0.835 mmol) in 15.0 mL acetone was
added dropwise to the above stirred glutamine solution. The
reaction was stirred at 0 °C ice-water bath for 30 min, and then
under room temperature for 3 h [17,18]. After the completion of
reaction, the acetone in the mixture was evaporated under reduced
Fluorescence response of 1 to metal ions and pH
2
+
The additions of other 13 common metal ions including Ca
,
2+
+
+
2+
3+
2+
2+
2+
3+
2+
2+
pressure. Then, the residue liquid was washed with Et
2
O for three
Cu2+, Hg , K , Na , Pb , Al , Cd , Co , Fe , Fe , Mg or Ni
times (3 Â 20.0 mL). The aqueous layer was added HCl to pH 4.5,
was examined in the identical conditions did not have similar
Fig. 1. The synthetic route and atomic number sequences of 1.

4
62
M. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 460–465
1
1
200
000
(
a)
Cr3+
None, Pb , Cd , Co2+,
2
+
2+
Ca , Na , K , Ni , Mg2+,
2
+
+
+
2+
8
6
4
2
00
00
00
00
0
Cu2+, Fe , Al
2+
3+
(b)
Hg2+
Fe3+
4
00
440
480
520
560
600
Wavelength / nm
Fig. 3. (a) The fluorescence intensity of 1 (5.0
l
M) in NaAc/HAc buffer solution (pH 5.5) in the presence of 30.0
l
M of various metal ions; (b) the mix system of 1–Cr3+ and
common foreign metal ions. [1] = 5.0 lM, [Cr ] = 10.0 lM, [M ] = 50.0 lM. In pH = 5.5 NaAc/HAc buffer solution.
3
+
n+
4
3
2
1
00
00
00
00
0
1000
1
+ Cr3+
8
6
4
2
00
00
00
00
0
1
+ Cr3+ + EDTA
1
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
420
450
480
510
540
570
600
pH
Wavelength / nm
Fig. 4. Variation of fluorescence intensity difference at 500 nm of 1 (5.0
l
M) in
Fig. 6. Fluorescence spectra of 1 (5.0
upon addition of Cr (30.0 lM) and EDTA (90.0 lM).
l
M, pH 5.5) in NaAc/HAc buffered solution
3
+
aqueous solution in the presence and absence of Cr (10.0
em = 500 nm).
lM) as a function of pH
3+
(k
To explore further the utility of 1 as a Cr3+ selective fluorescence
sensor, competition experiments were performed (Fig. 3b) by
observing the fluorescence spectra of 1 in the presence of Cr at
2
2
2
1
1
0
0
.8
.4
.0
.6
.2
.8
.4
3+
0
0
0
0
0
0
0
.30
.25
.20
.15
.10
.05
.00
M mixed with Cd , Hg , Ca , Co , Na , K , Fe , Fe2+
2+
2+
2+
2+
+
+
3+
1
0.0
l
,
3+
2+
2+
2+
2+
Al , Ni , Cu , Mg and Pb at 50.0
strated that the presence of Hg and Fe reduces its sensitivity,
l
M. The results demon-
2+
3+
2+
2+
while no obvious interference of other metal ions as Cd , Fe
,
3+
2+
2+
Al , Ni , Cu , etc. can be observed. It was clear that 1 can be uti-
3+
0
50
100
-6
150
200
lized as a Cr selective fluorescence sensor even in the presence of
200.0 µM
Cr3+
3+
[
Cr ] / 10 M
0
.0 µM
5 equiv of background of other metal ions.
Cr3+
The effect of pH influence on the fluorescence response of 1 to
0.0 µM
Cr3+ was tested in buffer aqueous solution, however, the complex
2
00.0 µM
3
+
of 1–Cr had a strong pH-dependence (see Fig. 4). The enhance-
ment of fluorescent intensity at 500 nm of 1 in the presence of
3
+
Cr was observed when the pH during the range of 4.5–6.0, the
largest enhancement was observed at pH 5.5, implying the possible
3
+
interaction of 1 and Cr under weakly acidic conditions. Finally, in
2
40
260
280
300
320
340
360
380
400
the current study, pH value of 5.5 was chosen for the detection of
Wavelength/nm
3
+
Cr and other common metal ions in aqueous solutions.
Fig. 5. UV–vis absorption spectra of 1 (20.0
l
M) in NaAc/HAc buffer solution (pH
.5), upon gradual additions of Cr (0.0, 10.0, 20.0, 40.0, 60.0, 80.0, 100.0, 120.0,
60.0, 200.0 M). Inset: the ratio of absorption intensity, A289/A327, for 1 with
3
+
5
1
3
+
l
UV–vis spectral response of 1 to Cr
3+
gradient amount of Cr (0.0–200.0 lM), respectively.
The UV–vis absorption spectroscopy of 1 to different metal ions
was also studied (Fig. 5). The absorption spectra of 1 had two
absorption bands at 247 and 327 nm, which represented the
results as Cr3+, even at high concentrations as 30.0
lM (see Fig. 3a).
The results indicated a high selectivity of 1 toward Cr over these
common metal ions in aqueous solutions.
3+
absorption bands of dansyl group [22]. With the addition of Cr3+
,

M. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 460–465
463
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0.00005
(
a)
(b)
0.00004
0.00003
0
0
0
.00002
.00001
.00000
0
.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.0
0.2
0.4
0.6
0.8
1.0
3
+
3+
I-I0 / Imax-I0
[
Cr ] / ( [Dasn]+[Cr ] )
3
+
Fig. 7. (a) Fluorescent intensity ratio at 500 nm of 1 and Cr with a total concentration of 5.0 lM in NaAc/HAc buffer solution (pH 5.5), indicating a 2:1 stoichiometric ratio of
3+
3+
2
1
:Cr (kem = 500 nm); (b) estimation of association constant for 1 and Cr , the plot was calculated based on the equation and a 2:1 binding model (R = 0.9799).
DGLN_130115163913 #5 RT: 0.10 AV:1 NL: 1.80E7
T: - c ESI Full ms [ 400.00-2000.00]
880.18
100
9
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
5
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
1
174.38
1
037.23
1263.33
1303.79
1673.73 1775.96
8
93.84
1517.10 1617.62
1
134.03
1912.59
1900
1
377.74
9
00
1000
1100
1200
1300
1400
1500
1600
1700
1800
2000
m/z
Fig. 8. ESI-MS spectra of 1–Cr3+ complex in CH
OH.
3
the UV–vis absorption spectroscopy had a 39 nm blue-shift, indi-
effect to 1. To demonstrate whether the nitrogen atom of the
dimethylamino group caused the protonation, we specifically add
the relatively strong acid as HCl, acetic acid or trifluoroacetic acid.
Similar results were obtained in UV–vis absorption spectra, so the
nitrogen atom of the dimethylamino group indeed caused the pro-
tonation. Meanwhile, the ratios of absorption intensities at 289 and
3+
cated the interactions between the 1 and Cr . When the concen-
3
+
tration of Cr reached 200.0
lM, the bands at 327 nm decreased
and a new significant enhancement of the absorption bands at
2
3
88 nm occurred, resulting in two isosbestic points (264 and
05 nm) in the absorption spectra of 1. However, the new absorp-
3
+
tion band at 288 nm was the characteristic band for the protonated
form of the dimethylamino group of the dansyl moiety [22–24]. So
the reason of the change in absorption spectroscopy of 1 was the
protonation of nitrogen atom in dimethylamino group when 1
327 nm, A289/A327, for 1 with Cr , were shown in inset of Fig. 5.
This result illustrated a ratiometric response in UV–vis absorption
3
+
spectra for 1 to Cr in aqueous solution.
3
+
3+
interactes with Cr , which consequently decreased the electron
density of nitrogen atom and reduced the charge-transfer between
electron-rich and electron-deficient moieties and finally resulted in
a band shift [25]. In addition, we also examined the UV–vis spectral
response of 1 to other metal ions, which showed no conspicuous
The reversibility of 1 to Cr
We investigated whether 1 reversibly detected Cr3+ in aqueous
solution or not. (Fig. 6) Addition of 3 equiv EDTA (Ethylene diamine
3
+
tetraacetic acid) to 1–Cr
complex caused reduced emission

4
64
M. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 460–465
a unique peak at m/z 880.18 corresponding to [2 Ã 1 + Cr3+–
+
À
3+
+
À
2
H +2Cl ] (calcd for 2 Ã 1 + Cr –2H + 2Cl = 879.75) was clearly
observed. Moreover, considering the electronegative property of
the chloride ion, it may bonding with Cr to further strengthen
3
+
3
+
the special conformation of 1–Cr
.
1
H NMR experiments were carried out in D
addition of CrCl , the obvious downfield shift of H(7) (
ppm) demonstrated the nitrogen atom of dimethylamino group is
protonated [24] and the chemical shift of H(8) ( H8 = 0.03 ppm) in
the chiral carbon atom indicated the coordination between car-
2
O (Fig. 9). Upon the
3
DdH7 = 0.06 -
(
d)
(
(
c)
Dd
b)
3
+
boxyl group and Cr . The obvious chemical shifts of hydrogen on
the naphthalene ring were due to the fact that the electron density
in the naphthalene ring was decreased as the protonation of nitro-
3
1
6
2
5(4
)
8
7
(
a)
3
+
gen atom and the chelation of Cr with 1. However, the proton
peak of H(10) show almost no chemical shift, which indicated that
the terminal amino group of probe did not coordinate to Cr . Fi-
8
.6
8.4
8.2
8.0
ppm
7.8
7.6
3.4
3.2
3+
nally, we proposed a potential coordination model between 1
3
+
Fig. 9. Partial 1H NMR spectra of (a) 1 (4.98 mM), (b) 1–Cr3+ (10:1), (c) 1–Cr3+ (4:1),
d) 1–Cr3+ (2:1) in D
O.
and Cr (Fig. 10).
(
2
3
+
intensity because EDTA has a potent binding affinity to Cr in
aqueous solution. Thus, the detection of Cr3 by 1 is good
reversible.
Conclusion
+
In conclusion, a new glutamine-based derivative had been syn-
3
+
thesized for the detection of Cr at pH 5.5 via a ‘‘turn-on’’ response
in the fluorescent spectra and a ratiometric response in UV–vis
absorption spectra, which were attributed to the protonation of
the dimethylamino group and the deprotonation of imino group
Binding stoichiometry and binding affinity
The Job’s plot [26,27] (Fig. 7a) manifested a 2:1 stoichiometry
3
+
complex forms between 1 and Cr3+. It was assumed that the fluo-
rescence change was induced by 2:1 complex formation between
on 1. Moreover, two chloride ions may bond with Cr to further
3
+
strengthen the special conformation of 1–Cr . The readily syn-
thetic route of 1 and its high selectivity were both the superiorities
of 1 for chemosensor.
3
+
1
and Cr . A mathematical treatment [28,29] based on the depen-
dence of (I À I )/(Imax À I ) at 500 nm in emission spectra on the
resulted in an association constant of
(see Fig. 7b), revealing a strong complexa-
0
0
3
+
concentration of Cr
1
1
3
À2
K
21 = 5.23 Â 10
M
.
Acknowledgments
+
tion of 1 and Cr
The authors are grateful to the Natural Science Foundation of
China (No. 20903041) for project funding, the project of science
3
+
Binding mode of 1 with Cr
&
technology new star of Zhu Jiang in Guangzhou city (No.
To further investigate the binding mode of 1 with Cr3+, we used
2012J2200026), Open Project of State Key Laboratory of Supramo-
lecular Structure and Materials (SKLSSM201312), and the ‘‘Exhibi-
tion Base of Production, Study & Research on New Polymer
Materials and Postgraduate Students’’ Innovation Training of
Guangdong Higher Education Institutes.
organic spectroscopy techniques such as NMR and mass
3+
spectroscopy. ESI-MS studies offered the evidence of 1–Cr inter-
actions directly, as showed in Fig. 8. It was also supported 1 and
Cr complex was combined 2:1. In the ESI-MS of 1–Cr3+ complex,
3
+
Fig. 10. Proposed coordination model for 1–Cr3+
.

M. Zhao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 460–465
465
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14] S. Guha, S. Lohar, A. Banerjee, A. Sahana, I. Hauli, S.K. Mukherjee, J.S. Matalobos,
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