A highly selective fluorescent probe for Al3+ based on 4-aminoantipyrine

Article abstract of DOI:10.1016/j.saa.2012.12.084

A novel and simple Schiff base based on 2-pyridine formaldehyde and 4-aminoantipyrine was synthesized and characterized as a fluorescent probe. In the presence of Al³⁺, the fluorescent intensity has a dramatic enhancement over other examined metal ions in aqueous solution. The method of Job's plot indicated the formation of 1:1 complex between probe and Al ³⁺, and the possible binding mode of the system was also proposed. Moreover, other examined metal ions had no effect on the detection of Al ³⁺.

Full text of DOI:10.1016/j.saa.2012.12.084

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 68–72
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A highly selective fluorescent probe for Al3+ based on 4-aminoantipyrine
⇑
Yanmei Zhou , Junli Zhang, Hua Zhou, Xiaoyi Hu, Lin Zhang, Min Zhang
Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, PR China
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
We designed and synthesized a new
Schiff base fluorescent probe.
The probe showed high sensitivity
for Al3+ over other metal ions in
aqueous solution.
"
"
The other metal ions have no effect
on the detection of Al3+
.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 August 2012
Received in revised form 4 December 2012
Accepted 31 December 2012
Available online 5 January 2013
A novel and simple Schiff base based on 2-pyridine formaldehyde and 4-aminoantipyrine was synthe-
sized and characterized as a fluorescent probe. In the presence of Al3+, the fluorescent intensity has a dra-
matic enhancement over other examined metal ions in aqueous solution. The method of Job’s plot
indicated the formation of 1:1 complex between probe and Al3+, and the possible binding mode of the
system was also proposed. Moreover, other examined metal ions had no effect on the detection of Al3+
.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Aminoantipyrine
Pyridineformaldehyde
Fluorescence
Al3+
Introduction
equipment. Up till now, a few fluorescent probes have been devel-
oped for the detection of aluminum. However, the poor selectivity
in aqueous solution hinders the practical applications [9–15].
Therefore, it is of great demand to develop new fluorescent sensor
in aqueous solution.
Aluminum is the third most abundant element after oxygen and
silicon in the earth’s crust [1]. In addition, compound derivatives
from aluminum are widely used in food additives, water treatment
and medicine [2]. However, the overload amounts of aluminum to
human being will lead to the malfunction of central nervous sys-
tem because of its ubiquitous distribution in daily life of human
[3]. A number of methods have been developed to determine alu-
minum, such as spectrophotometry, electrochemistry and chroma-
tography [4–8]. Compared to these methods, fluorimetric methods
for detection of aluminum are very popular due to its operational
simplicity, high selectivity, sensitivity, rapidity, low cost of
In recent years, Schiff base as a good ligand for metal ions were
widely used in many areas [16–20], especially in chemosensors
[21–26]. Herein, we reported on the structural and spectroscopic
properties of a new Schiff base derived from 2-pyridine formalde-
hyde and 4-aminoantipryine, which was synthesized in only one
step as shown in Scheme 1. The probe exhibits remarkably en-
hanced intensity in its fluorescence emission in presence of Al3+
in aqueous solution over other metal ions examined. The method
of Job’s plot confirmed the formation of 1:1 between Al3+ and
probe. In addition, other metal ions in aqueous solution have no ef-
⇑
Corresponding author. Tel.: +86 378 2868833 3422; fax: +86 378 3881589.
E-mail address: zhouyanmei@henu.edu.cn (Y. Zhou).
fect on the selectivity to Al3+
.
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.12.084

Y. Zhou et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 68–72
69
Scheme 1. The synthesis of P1.
Experiment
Apparatus
IR spectra were recorded on Nicolet AVATAR360 infrared
spectrometer. The MS spectra were performed on Bruker ESQUTRE
LC-MC. 1H NMR spectra were recorded by Bruker AVANCE-400
spectrometer. The fluorescence spectra were recorded on Hitachi
F-7000FL spectrophotometer.
Fig. 2. UV–Vis absorbance of P1 and P1–Al3+ ([P1] = [M] = 1.0 Â 10À5 mol LÀ1).
9.795 (1H, S), 8.693 (2H, d), 7.989 (1H, d), 7.490 (2H, t), 7.46 (1H,
t), 7.408 (2H, d), 7.335 (1H, t), 3.194 (3H, S), 2.529 (3H, S).
Results and discussion
Materials
The effect of solvents on fluorescent spectra
The solution of metal ions was prepared from their chloride
salts and nitrate salts of analytical grade. The value of pH was
The fluorescent spectra of P1 for kex = 340 nm have been re-
corded in various solvents and were displayed in Fig. 1. P1 exhibits
different fluorescent emission and intensity in different solvents.
The fluorescent emission was fixed at 430 nm in DMF, while it
was fixed at 445 nm in aqueous solution. Taking into account of
the economic cost and practical application, the experiments were
carried out in aqueous media.
adjusted by HCl (0.10 mol LÀ1 and 1.0 mol LÀ1
) and NaOH
(0.10 mol LÀ1 and 1.0 mol LÀ1) at room temperature. All chemicals
were of analytical grade. All measurements of spectra were carried
out in aqueous solution with 1% ethanol as cosolvent.
The synthesis of Schiff base
The selectivity of probe towards metal ions
The synthetic route of Schiff base (P1) is shown in Scheme 1. It
was prepared by refluxing a mixture of 0.50 mL 2-pyridine formal-
dehyde and 10 mmol 4-aminoantipyrine in 30.0 mL absolute etha-
nol for 8 h with HAc (3d). The solvent was rotary evaporated and
then was poured into 2.0 mL absolute ethanol. Pale yellow crystal
was afforded after cooling with a yield of 98%. The structure was
characterized by various spectroscopic analyses. m.p. 163.1–
164.0 °C. IR (KBr pellet, cmÀ1): 3441, 3402, 1635, 1561, 1413,
757. Ms: m/z: 315 ([M + Na]+). 1H NMR (400 MHz, CDCl3): d
The representative absorbance spectra of P1 (5 Â 10À5 mol LÀ1
)
in aqueous media before and after addition of Al3+ were shown in
Fig. 2. The absorption spectra of P1 exhibited only a very weak
band over 350 nm region. When Al3+ was added, a remarkable
enhancement in absorbance at 345 nm was observed. These
observations preliminary indicated that P1 had a response to Al3+
ion in aqueous solution.
Fig. 1. The fluorescent spectra of P1 in different solvents ([P1] = 1.0 Â 10À5 mol LÀ1
kex = 340 nm).
,
Fig. 3. The fluorescent emission of P1 with
([P1] = [M] = 1.0 Â 10À5 mol LÀ1, kex = 340 nm).
1 equiv various metal ions

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Y. Zhou et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 68–72
Fig. 4. The fluorescence emission of different concentrations of Al3+
([P1] = 2.0 Â 10À5 mol LÀ1, kex = 340 nm). Inset: fluorescence intensity at 445 nm
as a function of Al3+ concentration.
Fig. 6. The influence of response time on the fluorescent intensity of P1 in the
absence and presence of Al3+ ([P1] = [Al3+] = 1.0 Â 10À5 mol LÀ1, kex = 340 nm).
As shown in Fig. 3, the fluorescence spectra of P1 with various
metal ions in aqueous solution were conducted to examine the
selectivity. The solution of P1 emits fluorescence very weakly.
The addition of 1 equiv of Al3+ induced a dramatic enhancement
in fluorescent intensity, which was attributed to the formation of
a P1–Al3+ complex. While no significant changes was found with
results showed that P1 exhibited very weak fluorescent emission
between pH 7.0 and 11.9, but the fluorescent intensity increased
when the pH value was smaller than 7.0. In the presence of Al3+
,
fluorescent intensity increased remarkably in the range of pH
2.3–8.5 as shown in Fig. 5. These results indicated that the Al3+ rec-
ognition process is free from pH interference under near neutral
conditions. All the spectral experiments carried out in Tris-HCl
(10 mM, pH = 7.2) aqueous buffer solution.
The effect of reaction time in Tris-HCl (10 mM, pH = 7.2) aque-
ous buffer solution was depicted in Fig. 6. No obvious fluorescence
variation of P1 was observed even over a period of 2 h at 445 nm,
the interaction of P1 with Al3+ was completed in less than 5 min,
and the fluorescence intensity was stable at least 2 h. Thus the
reaction time of 10 min may be used for this system.
the addition of other metal ions, such as Na+, K+, Pb2+, Ag+, Hg2+
,
Cd2+, Ba2+, Mg2+, Ni2+, Zn2+, Ca2+, Cu2+ and Fe3+. To further investi-
gate the interaction of Al3+, a fluorescence titration experiment was
carried out. It can be seen from Fig. 4 that a linear increase of fluo-
rescence intensity of P1 was observed by increasing the amount of
Al3+. The linear equation was determined to be I = 18.7692C +
107.1538 (n = 11, R = 0.9962). While the concentration of Al3+
ranges from 4.0 Â 10À6 mol LÀ1 to 1.6 Â 10À5 mol LÀ1 and the
detection limit is 3.2 Â 10À7 mol LÀ1
.
The effect of ionic strength on the fluorescent spectra of P1–Al3+
in Tris-HCl (10 mM, pH = 7.2) aqueous buffer solution was depicted
in Fig. 7. Various concentrations of KCl were used as the ionic
strength regulator. With the ionic strength increasing, no obvious
fluorescent intensity variation of P1–Al3+ was observed at
445 nm. These observations indicated that the ionic strength had
The influence of pH, response time and ionic strength on fluorescent
spectra
Furthermore, the effect of pH on the fluorescent spectra of P1 in
the absence and presence of Al3+ were investigated. The NaOH–HCl
was used by alkali or acid and Tris-HCl buffer used by neutral. The
no effect on fluorescent response of P1–Al3+
.
Fig. 5. The influence of pH on the fluorescent intensity of P1 in the absence and
presence of Al3+ ([P1] = [Al3+] = 1.0 Â 10À5 mol LÀ1, kex = 340 nm).
Fig. 7. The influence of ionic strength on the fluorescent intensity of P1–Al3+
([P1] = [Al3+] = 1.0 Â 10À5 mol LÀ1, kex = 340 nm).

Y. Zhou et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 68–72
71
Fig. 10. Metal ion selectivity of P1 (1.0 Â 10À5 mol LÀ1) in aqueous solution. The red
bars represent the fluorescent intensity of P1 and Al3+ (1:1, 1.0 Â 10À5 mol LÀ1). The
black bars represent the fluorescence changes that occur upon the addition of
competing ions to the solution containing P1 and Al3+ (1:1, 1.0 Â 10À5 mol LÀ1).
Fig. 8. The Job’s plot for P1 and Al3+
.
0: only P1; 1: blank; 2: Ag+; 3: Pb2+; 4: Na+; 5: K+; 6: Hg2+; 7: Cd2+; 8: Ba2+; 9: Zn2+
;
10: Mg2+; 11: Cu2+; 12: Ni2+; 13: Ca2+; 14: Fe3+; 15: Cr3+, 16: Ga3+, 17: SCNÀ, 18:
SO24À, 19: CrO42À, 20: BrÀ, 21: Cr2O72À, 22: PO34À, 23: ClOÀ3 , 24: FÀ, 25: ClÀ, 26: IÀ, 27:
S2O2À, 28: NOÀ3 , 29: HSO4À, 30: CO32À, 31: HCOÀ3 , 32: H2POÀ, 33: AcOÀ, 34: all the
8
4
metal ions and anions. (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
1.0 Â 10À4 mol LÀ1 [27]. It can be seen clearly from Fig. 8 that the
maximum was at a molar fraction of 0.5, which indicated the for-
mation of 1:1 between P1 and Al3+. According to literature [28–31],
the binding mode of P1 and Al3+ was also proposed as shown in
Scheme 2. It was inferred that Al3+ coordinated with oxygen atom
of C@O, the nitrogen atom of C@N and pyridine, where two five-
number rings formed.
Furthermore, IR spectra of P1 and P1–Al3+ were taken in KBr
disks, respectively, and the results were shown in Fig. 9. The peak
at 1719 cmÀ1, which corresponds to the characteristic carbonyl
absorption of P1, was shifted to 1642 cmÀ1 upon chelating with
Al3+. These results indicate that carbonyl group is involved in
Al3+ coordination [32,33].
Scheme 2. The biding mode of P1 and Al3+
.
The mechanism of the complex coordination
In order to further confirm the P1 coordinating with Al3+, the
EDTA-adding experiments were conducted to examine the revers-
ibility of the probe P1. The results displayed that, the fluorescence
To determine the stoichiometry between P1 and Al3+, the meth-
od of Job’s plot has been carried out with the total concentration of
Fig. 9. IR spectra of P1 (a) and P1–Al3+ complex (b) in KBr disks.

72
Y. Zhou et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 68–72
Table 1
Determination of Al3+ in samples (n = 5).
Sample
Al3+ measured
Al3+ added
Al3+ found
Recovery (%)
R.S.D. (%)
(10À6 mol LÀ1
5.2
)
(10À6 mol LÀ1
)
(10À6 mol LÀ1
)
River water
Tap water
0.5
5
5.68
10.26
99.7
100.6
2.1
3.0
0.5
5
9.25
13.81
99.5
101.5
1.8
2.3
8.6
intensities of solution containing P1 and Al3+ decrease with
increasing EDTA concentration. When Al3+ was added to the sys-
tem again, the fluorescence could be reproduced again. These find-
(122300410260), the International Science Cooperation Project of
Henan Province (124300510012) and the Key Scientific and Tech-
nological Project of Henan Province (112102310360).
ings indicated that P1 reversibly coordinated with Al3+
.
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Under the optical conditions, the influence of other metal ions
and anions were tested by premixing P1 with other ions, such as
Na+, K+, Pb2+, Ag+, Hg2+, Cd2+, Ba2+, Mg2+, Ni2+, Zn2+, Ca2+, ÀCu2+
,
Fe3+, Cr3+, Ga3+, SCNÀ, SO42À, CrO24À, BrÀ, Cr2O2À, PO34À, ClO3 , FÀ,
7
ClÀ, IÀ, S2O2À, NOÀ3 , HSO4À, CO32À, HCOÀ, H2POÀ and AcOÀ. The exper-
8
3
4
imental results were shown in Fig. 10. Basically, these ions did not
induce interference the fluorescent intensity of the sensitivity to-
wards Al3+. As a result, P1 can be seen as a highly selectivity and
sensitivity for Al3+ in aqueous solution.
Preliminary analytical application
In order to examine the applicability of the proposed method in
practical sample analysis, the sensor P1 was applied in the deter-
mination of Al3+ in river water and tap water samples. The river
water samples were obtained from the campus of Henan Univer-
sity and simply filtered. All these samples were adjusted pH by
Tris-HCl (10 mM, pH = 7.2) aqueous buffer solution and spiked
with standard Al3+ solutions, then analyzed with proposed sensor
P1 and recorded with a F-7000FL spectrofluorimeter. The results
were summarized in Table 1, which showed satisfactory recovery
and R.S.D. values for all of the samples. Thus, the present probe
seems useful for the determination of Al3+ in real samples.
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Conclusion
In summary, a highly sensitive chemosensor for Al3+ based on
2-pyridineformaldehyde and 4-aminoantipyrine has been synthe-
sized and structurally characterized. The new sensor displayed an
excellent selectivity towards Al3+, no significant optical interfer-
ences arise from the other examined metal ions and anions such
as Na+, K+, Pb2+, Ag+, Hg2+, Cd2+, Ba2+, Mg2+, Ni2+, Zn2+, Ca2+,ÀCu2+
,
Fe3+, Cr3+, Ga3+, SCNÀ, SO42À, CrO24À, BrÀ, Cr2O2À, PO34À, ClO3 , FÀ,
7
ClÀ, IÀ, S2O2À, NOÀ3 , HSO4À, CO32À, HCOÀ, H2POÀ and AcOÀ. This probe
8
3
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successfully applied to determination of Al3+ in water samples
analysis.
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Acknowledgements
The authors thank the Foundation and Cutting-Edge Technology
Research Project of Henan Science and Technology Department