Antipyrine based Schiff bases as Turn-on Fluorescent sensors for Al (III) ion

Article abstract of DOI:10.1016/j.electacta.2013.11.143

Two new fluorescent sensors C1 and C2 with 4-aminoantipyrine unit have been prepared and characterized. Their complexation behaviour and binding mode towards Al³⁺ and other metal ions have been studied by UV-vis, fluorescence spectrometric and

Full text of DOI:10.1016/j.electacta.2013.11.143

Electrochimica Acta 117 (2014) 405–412
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Antipyrine based Schiff bases as Turn-on Fluorescent sensors for Al
(
III) ion
∗
Vinod Kumar Gupta , Ashok Kumar Singh, Naveen Mergu
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247 667, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 October 2013
Received in revised form
Two new fluorescent sensors C1 and C2 with 4-aminoantipyrine unit have been prepared and charac-
3+
terized. Their complexation behaviour and binding mode towards Al and other metal ions have been
1
studied by UV–vis, fluorescence spectrometric and HRMS methods. The H NMR titrations were carried
1
8 November 2013
out to explore the nature of interaction between receptor and aluminum ion. These sensors are suc-
cessfully applied in highly acidic and neutral pH medium with the fastest response time (<5 sec). The
fluorescence color change could be easily detected by the naked eye under a UV lamp.
Accepted 23 November 2013
Available online 11 December 2013
©
2013 Elsevier Ltd. All rights reserved.
Keywords:
Fluorescent sensor
Schiff base receptor
Aluminum ion recognition
Naked-eye detection.
1
. Introduction
In this paper, we designed and synthesized 4-aminoantipyrine
based compounds (C1 and C2) in a simple approach as fluorescent
sensors for Al3+ ion. The fluorescence intensities of the two sen-
sors C1 and C2 are enhanced by mixing Al , and show bright blue
and bright green color respectively, which can be easily detected
by the naked eye under UV lamp. The results indicated that the pre-
pared 4-aminoantipyrine based sensors can show high sensitivity
and selectivity towards Al3+ over other metal ions.
Aluminum is the most abundant element in the earth’s crust
3+
after oxygen and silicon and is the second most widely used metal
after iron for the manufacture of electrical equipments, automo-
biles, packaging materials, water purification, clinical drug and
building construction etc. [1,2]. Recent studies are shown that the
deposition of aluminum in bone and the nervous system in human
body can cause neurotoxicity in high dosage [3]. It plays an impor-
tant role in the pathology of Parkinson’s, Alzheimer’s and dialysis
diseases [4–7]. In plants, higher concentration of aluminum affects
the growth of root and seed [8,9]. Thus, the monitoring of aluminum
is essential in environment, medicine, foodstuff, etc.
2. Experimental
2.1. Reagents and apparatus
In recent years, many analytical methods have played a role
in the detection of Al3+ ion and others, including ion selective
electrodes [10–22], voltammetric [23–33] and colorimetric sensors
4-aminoantipyrine, salicylaldehyde, 2-hydroxy-1-naphthal-
dehyde and metal salts (from Merck and Aldrich, India). The IR
spectra were recorded on a Nexus FT-IR (Illinois, USA) spectrom-
−
1
[
34–38]. Recently, the fluorescent method has become popular due
eter in the range 4000–400 cm
with KBr. The NMR spectra
to its operational simplicity, high selectivity and sensitivity, real-
time response and naked eye detection [39–48]. Due to its poor
coordination ability compared to transition metals [49], only a few
fluorescent sensors have been reported and on the other hand, most
of the Al sensors are difficult to synthesis and insoluble in aque-
ous solvents. Some of the antipyrine derivatives are detected as a
fluorescent chemosensor towards ions [50].
were recorded on a Bruker 500 MHz (USA), TMS as an internal
standard, CDCl3 and CD OD are taken as solvents. The mass spec-
3
tra were recorded using Bruker-micrOTOF II (USA). The UV–vis
absorption spectra were measured on a Shimadzu UV-2450
spectrophotometer (Japan) and the Fluorescent spectra were
recorded on a Shimadzu RF-5301PC spectrofluorophotometer
(Japan) instruments.
3
+
2.2. Synthesis and characterisation
∗ Corresponding author. Fax: +911332273560.
E-mail addresses: vinodfcy@iitr.ac.in, vinodfcy@gmail.com (V.K. Gupta).
The Schiff base ligands (C1 and C2) were prepared by the
reported method [51–64] with some modifications (Scheme 1). The
0
013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.electacta.2013.11.143

4
06
V.K. Gupta et al. / Electrochimica Acta 117 (2014) 405–412
N
O
N
2
H N
CHO
OH
CHO
OH
OH
HO
O
O
N
N
N
N
N
N
C1
C2
Scheme 1. Synthetic routes to C1 and C2.
Fig. 1. FT-IR Spectrum of C1 and C2.
Fig. 2. 1H NMR Spectrum of C1 and C2.

V.K. Gupta et al. / Electrochimica Acta 117 (2014) 405–412
407
Fig. 3. 13C NMR Spectrum of C1 and C2.
Fig. 4. HRMS Spectrum of C1 and C2.
2+
2+ 2+ 3+
+
2+ 3+ 2+
Blank, Ba ,Ca ,Cd ,Cr ,Cs ,Fe ,Fe ,Hg
,
+
+ 2+ 2+ + 3+ 2+ 2+ 2+
K
,Li ,Mg ,Mn ,Na ,Nd ,Pb ,Sr ,Zn
a
b
1
.0
2+
2+
2+
2+ 3+
+
2+ 3+
2+
,
Cu
1.0
0.5
0.0
Blank, Ba ,Ca ,Cd ,Cr ,Cs ,Fe ,Fe ,Hg
+
+ 2+ 2+ + 3+ 2+ 2+ 2+
K
,Li ,Mg ,Mn ,Na ,Nd ,Pb ,Sr ,Zn
2
+
Ni
2
+
Co
2
+
2+
+
Cu ,Ni
3+
Al
2
Co
0.5
0.0
3+
Al
300
400
Wavelength (nm)
500
400
Wavelength (nm)
500
Fig. 5. UV–vis absorbance spectra of C1 (50 ␮M) (a) and C2 (50 ␮M) (b) in the presence of different metal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cs , Cu2+, Fe2+, Fe3+, Hg2+, K+,
+
+
2+
2+
+
3+
2+
2+
2+
2+
Li , Mg , Mn , Na , Nd , Ni , Pb , Sr , Zn ) (50 ␮M) in methanol solvent.

4
08
V.K. Gupta et al. / Electrochimica Acta 117 (2014) 405–412
7
6
5
4
3
2
1
00
00
00
00
00
00
00
0
a
b
7
6
5
4
3
2
00
00
00
00
00
00
100
0
400
450
500
550
600
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 6. Fluorescence emission spectra of C1 (20 ␮M) (a) and C2 (20 ␮M) (b) in the presence of different metal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cs , Cu2+, Fe2+, Fe3+, Hg2+
K , Li , Mg , Mn , Na , Nd , Ni , Pb , Sr , Zn ) (20 ␮M) in methanol solvent.
+
,
+
+
2+
2+
+
3+
2+
2+
2+
2+
ethanol containing the mixture of 4-aminoantipyrine (10 mmol)
and aldehyde (10 mmol) was stirred at room temperature about
3.1. UV–vis spectral studies
2
–3 hours, the obtained solid was filtered, washed with cold
The chemosensors (C1 and C2) were investigated by UV–vis
absorption spectral behaviour in the presence of various metals in
the 50 ␮M concentration of each component in methanol solvent.
The free ligands C1 and C2 exhibited a main absorption band at
about 345 nm and 380 nm, respectively. On the addition of metal
ethanol, dried under vacuum and characterised by FT-IR, NMR and
HRMS (Figs. 1–4).
1
-phenyl-2,3-dimethyl-4-(N-2-hydroxybenzylidene)-3-
pyrazolin-5-one (C1): Yield: 2.76 g (90%); color: light yellow solid;
◦
−1
2+
2+
m.p. 218-220 C; FT-IR (KBr), ꢀ, cm : 3448 (O − H), 2929, 759
ions to sensors, a new broad absorption band (mainly for Cu , Ni ,
1
2+
3+
(
C − H), 1653 (C = O), 1593 (C = N), 1490 (C = C), 1139 (N − N);
H
Co and Al ions) was observed at 350–480 nm region (Fig. 5). At
the same time the absorption band at 300–390 nm and 340–430 nm
of receptors C1 and C2 respectively, have also been shifted to
low intensity. It means these two sensors are responding to the
above mentioned metal ions, there is no significant changes were
NMR (CDCl ), ı, ppm (J, Hz): 2.42 (s, 3H), 3.18 (s, 3H), 6.89 (t, J = 7.5,
3
1
2
H), 6.96 (d, J = 8.5, 1H), 7.29 (dt, J = 1.5, 7.5, 1H), 7.33 − 7.37 (m,
H), 7.39 (d, J = 2.5, 2H), 7.49 (t, J = 8.0, 2H), 9.82 (s, 1H); 13C NMR
(
CDCl ), ı, ppm: 10.3, 35.7, 116.3, 116.7, 119.1, 120.2, 124.7, 127.3,
3
2
+
2+
2+
1
29.3, 131.9, 132.0, 134.4, 149.9, 160.3, 160.5, 160.7; HRMS calcd
observed when mixed with other metal ions such as Ba , Ca
,
,
+
2+
3+
+
2+
3+
2+
+
+
2+
2+
+
3+
for C18H17N O (M + Na) : 330.1218, found: 330.1211.
Cd , Cr , Cs , Fe , Fe , Hg , K , Li , Mg , Mn , Na , Nd , Pb
3
2
2+
2+
1
-phenyl-2,3-dimethyl-4-(N-2-hydroxynaphthylidene)-3-
Sr and Zn
.
pyrazolin-5-one (C2): Yield: 3.11 g (80%); color: yellow solid; m.p.
◦
−1
2
(
10-212 C; FT-IR (KBr), ꢀ, cm : 3427 (O − H), 3018, 2925, 746
3.2. Fluorescence emission studies
1
C − H), 1638 (C = O), 1588 (C = N), 1479 (C = C), 1145 (N − N);
H
NMR (CHCl ), ı, ppm (J, Hz): 2.46 (s, 3H), 3.20 (s, 3H), 7.17 (d,
The fluorescence response of sensors C1 and C2 (20 ␮M) upon
addition of various metal ions (20 ␮M) have been investigated in
methanol. Receptor C1 and C2 alone displayed a very weak sin-
gle fluorescence emission band at 498 nm and 484 nm respectively,
3
J = 9.0, 1H), 7.34 (m, 2H), 7.43 (d, J = 7.5, 2H), 7.47 (dt, J = 1.0, 7.5,
1
(
1
1
H), 7.51 (t, J = 8.0, 2H), 7.74 (d, J = 8.0, 1H), 7.79 (d, J = 9.0, 1H), 8.25
d, J = 8.5, 1H), 10.84 (s, 1H); 13C NMR (CDCl ), ı, ppm: 10.3, 35.7,
3
2
+
10.6, 116.4, 119.5, 120.6, 123.4, 124.7, 127.4, 127.6, 127.9, 128.8,
29.4, 132.9, 133.8, 134.4, 149.0, 156.8, 160.5, 162.2; HRMS calcd
for C22H19N O (M + Na) : 380.1375, found: 380.1375.
with an excitation of 360 nm. Upon addition of various metals (Ba
,
,
2+
2+
2+
3+
+
2+
2+
3+
2+
+
+
2+
2+
Ca , Cd ,Co , Cr , Cs , Cu , Fe , Fe , Hg , K , Li , Mg , Mn
+
3
2
C1
C2
700
600
500
400
300
200
100
0
2
.3. UV–vis and Fluorescent measurements
UV–vis absorption and fluorescence emission spectra of sensors
measured in 1.0 cm path length quartz cuvettes were measured
using a Shimadzu UV-2450 spectrophotometer and a Shimadzu
RF-5301PC spectrofluorophotometer. Absorption and emission
spectra of the sensor (C1 and C2) in the presence of various metal
3
+
2+
2+
2+
2+
3+
+
2+
2+
3+
2+
+
ions (Al , Ba , Ca , Cd , Co , Cr , Cs , Cu , Fe , Fe , Hg , K ,
Li , Mg ,Mn , Na , Nd3+, Ni2+, Pb2+,Sr and Zn ) were measured
in methanol solvent in the concentration of 50 ␮M and 20 ␮M,
respectively.
+
2+
2+
+
2+
2+
3
. Results and discussion
2
4
6
8
10
The binding ability and mode of sensors (C1 and C2) towards
Al3+ and other metal ions was measured through UV–vis, fluo-
pH
1
rescent spectrometry, naked-eye observation, HRMS and H NMR
Fig. 7. The variation in fluorescence intensity with the pH of receptor (C1 and C2)
20 ␮M) in the presence of Al (1.0 eq.) at 466 nm.
experiments.
3+
(

V.K. Gupta et al. / Electrochimica Acta 117 (2014) 405–412
000
409
1
a
b
8
6
4
2
00
00
00
00
0
8
6
4
2
00
00
00
00
0
1
0 eq.
1
0 eq.
0
.0 eq.
0
.0 eq.
400
450
500
550
600
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 8. Fluorescence emission spectra of (a) C1 (20 ␮M) and (b) C2 (20 ␮M) in methanol upon the addition of Al3+ ion (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 5.0
3
+
and 10.0 eq.) with an excitation of 360 nm. Inset shows the fluorescence change at 466 nm as a function of the amount of Al ions.
a
b
7
6
5
4
3
2
1
00
00
00
00
00
00
00
0
700
6
5
4
3
2
1
00
00
00
00
00
00
0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
3+
3+
[
Host]/([Host]+[Al ])
[Host]/([Host]+[Al ])
Fig. 9. Job’s plot for C1 (a) and C2 (b) by fluorescence method. Total concentration of receptor and metal is 20 ␮M.
Fig. 10. HRMS spectrum of (a) C1 and (b) C2 upon addition of Al(N03)3.9H2O (1 eq.) in MeOH.

4
10
V.K. Gupta et al. / Electrochimica Acta 117 (2014) 405–412
C1+M
C1+M +Al
C2+M
C2+M +Al
7
6
5
4
3
2
1
00
00
00
00
00
00
00
0
a
7
6
5
00
00
00
b
400
300
200
100
0
Fig. 11. Selectivity of the C1 (a) and C2 (b) toward Al3+ and other metal ions. In these experiments, the fluorescence measurement was taken for 20 ␮M concentration of C1
(
a) and C2 (b) at ꢁex = 360 nm in methanol at room temperature with various metal ions (1.0 eq.) and in the absence (black bars) and presence (red bars) of 1.0 eq. Al3+ ion.
Na , Nd3+, Ni2+, Pb2+, Sr2+ and Zn2+) no significant changes were
+
methanol. As shown in Fig. 7, the fluorescence intensity at 466 nm
almost did not change with the pH value at acidic and neutral con-
ditions (pH <7.0). However, the fluorescence intensity decreased
gradually from pH 7.0–10.0, due to the formation of salt. For further
studies, the pH of solvent kept constant at 6.5.
3+
observed (Fig. 6). But on addition of Al , receptors C1 and C2 exhib-
ited a prominent fluorescence enhancement accompanied by a blue
shift of 32 nm from 498 to 466 nm and 18 nm from 484 to 466 nm,
respectively, indicating, that the receptors C1 and C2 exhibit “off-
on” mode with high sensitivity towards Al over other metal ions
which are used. Using a UV lamp, the receptors C1 and C2 in the
3+
Furthermore, the fluorescence response of receptors (C1 and
3+
C2) to various concentrations of Al (0–10 eq.) was investigated.
3
+
3+
presence of Al showed a dramatic colour changes from colour-
less to bright blue and bright green respectively, within 5 seconds,
which could easily be detected by the naked-eye. At the same time,
the addition of other metal ions did not show any significant colour
change.
Upon addition of Al , the fluorescence intensity centred at 466 nm
of receptor gradually increased and remained steady when 1 eq.
3+
Al was added, indicating the formation of a 1:1 bonding mode
3+
between chemosensor and Al (Fig. 8). In addition, a Job plot
obtained from the emission data showed the 1:1 stoichiometric
complexation (Fig. 9). Also, the high resolution mass spectrum of
The interaction between receptor (C1 and C2) and Al3+ ion was
investigated at a pH range from 2.0 to 10.0. This experiment was
carried out at a fixed concentration of receptor-Al3+ is 20 ␮M in
3+
receptors upon addition of 1 eq. of Al indicated the formation of
3+
the receptor-Al complex with 1:1 ratio (Fig. 10).
Fig. 12. The fluorescence emission changes of sensors C1 (a) and C2 (b) (20 ␮M) with 1.0 eq. of Al3+, and in the presence of other metal ions (Cu2+, Ni2+, Co2+) excited by a
commercially available UV lamp (ꢁex = 365 nm).

V.K. Gupta et al. / Electrochimica Acta 117 (2014) 405–412
411
Fig. 13. 1H NMR (500 MHz) spectra of receptor (a) C1 and (b) C2 with Al3+ (0.0–1.0 eq.) in CD3OD.
The selectivity of C1 and C2 (20 ␮M) for Al3+ over other metal
ions (1.0 eq.), was investigated by the competition experiments. As
shown in Fig. 11, the fluorescence response of C1 and C2 toward
reported sensors have the ability to serve as a practical sensor for
detection of Al3+ ion in both environment and biological samples.
3+
Al in the presence of various metal ions was investigated, and
Acknowledgements
2
+
2+
2+
the results indicated that Cu , Ni and Co could interfere in the
3+
interaction between receptor (C1 and C2) and Al . Indicating that
Naveen thanks to the Ministry of Human resource and Develop-
ment (MHRD), New Delhi, India for financial support.
2
+
2+
2+
the binding abilities of Cu , Ni and Co are stronger than that
3
+
3+
of Al toward Schiff bases. Upon addition of 1.0 eq. of Al in the
2
+
2+
2+
3+
+
2+
3+
presence of other metal ions (Ba , Ca , Cd , Cr , Cs , Fe , Fe
,
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enhancement of the fluorescence intensity was observed, which is
large enough to determine Al3+ from other metal ions. We could
2+
+
+
2+
2+
+
3+
2+
[
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3
[
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. Conclusion
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