Novel pyrazoline-based selective fluorescent sensor for Zn2+ in aqueous media

Sensors and Actuators B 159 (2011) 148–153

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Novel pyrazoline-based selective fluorescent sensor for Zn2+ in aqueous media Zhong-Liang Gong, Fei Ge, Bao-Xiang Zhao ∗ Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China

a r t i c l e

i n f o

Article history: Received 12 April 2011 Received in revised form 15 June 2011 Accepted 19 June 2011 Available online 24 June 2011 Keywords: Pyrazoline Fluorescent sensor Zinc ion detection Selective

a b s t r a c t This work describes the preparation of a novel pyrazoline compound and the properties of its UV–vis absorption and fluorescence emission. Moreover, this compound can be used to determine Zn2+ ion with high selectivity and a low detection limit in the HEPES (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) buffer solution. This sensor forms a 1:1 complex with Zn2+ and shows a fluorescent enhancement by chelation enhanced fluorescence effect with good tolerance of other metal ions. In addition, this sensor is very sensitive with fluorometric detection limit of 0.12 ␮M. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Transition or heavy metal ion pollution such as Cd2+ , Cr3+ , Cu2+ , Hg2+ , Ni2+ , Pb2+ , and Zn2+ poses severe risks for human health and the environment, due to they tend to accumulate in the food chain and are usually associated with toxicity. Zinc is one of the most important metals widely used in electroplating industries and its toxicity has been found in both acute and chronic forms. In addition, it is well known that zinc ion, the second most abundant transition–metal ion in the human body and its highest concentrations occurring in the brain, plays crucial roles in many important biological processes acting as the structural and catalytic cofactors, neural signal transmitters or modulators, regulators of gene expression, and apoptosis [1–4]. Zinc is also known to have a role in neurological disorders, such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and epileptic seizures [5,6]. Our increased understanding of the deleterious effects of zinc exposure has sparked interest in the development of new tools for detecting Zn2+ in the environment. One major challenge involves creating Zn2+ sensors that function in water and are highly selective for Zn2+ against a background of competing analytes. For example, it is still a challenge to develop chemosensors that can discriminate Zn2+ from Cd2+ because zinc and cadmium are in the same group of the periodic table and have similar properties, which usually cause similar spectral changes after interacting with chemosensors [7–9]. Therefore, the design and development of a fluorescent chemosen-

∗ Corresponding author. Tel.: +86 531 88366425; fax: +86 531 88564464. E-mail addresses: [email protected], [email protected] (B.-X. Zhao). 0925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.06.064

sor selective to zinc are of considerable interest [10]. Although a variety of zinc ion selective fluorescent probes based on quinoline [11–15], fluorescein [16,17], coumarin [18,19], indole [20,21], 1,8-naphthalimide [22], thiazole [23], triazole [24,25], xanthene [26,27], benzoxazole [28], and other fluorophores [29,30] have been developed, chemists still need to design novel ones that are simpler, easier to synthesize, and have better sensitivity, selectivity, and reliability [31]. 1,3,5-Triaryl-2-pyrazolines, with their rigid but only partly unsaturated central pyrazoline ring, are well-known fluorescent compounds widely used in fluorescent dyes emitting blue fluorescence with high fluorescence quantum yield [32,33] and electroluminescence fields [34–36], However, to the best of our knowledge, only a few examples have been reported on the interactions between pyrazoline derivatives and zinc ion [37–39] and most of these systems have their limitations, which include interference from other metal ions, delayed response to Zn2+ , and/or a lack of water solubility. Thus, the development of chemosensors with high sensitivity and selectivity for detecting Zn2+ in aqueous media remains a significant challenge. In our previous papers, we described synthesis of pyrazoline derivatives [40,41] and application of chemosensor based on pyrazoline derivative for the detection of Zn2+ [42]. However, it was used in organic solvent. Hence, in order to detect Zn2+ in aqueous media, we modified the structure of the probe. Herein, we report the synthesis of 4-chloro-2-(5-phenyl-1-(pyridin-2-yl)-4,5dihydro-1H-pyrazol-3-yl)phenol and the properties of its UV–vis and fluorescence. This sensor can be applied in aqueous solution and will have wider applicable scope than the one reported in our previous paper [42].

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2. Materials and methods

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108.5, 60.7, 42.7. HRMS: calcd for [M+H]+ C20 H17 ClN3 O: 350.1060; found: 350.1052.

2.1. Apparatus Thin-layer chromatography (TLC) was conducted on silica gel 60 F254 plates (Merck KGaA). 1 H NMR spectra were recorded on a Bruker Avance 400 (400 MHz) spectrometer, using CDCl3 as solvent and tetramethylsilane (TMS) as internal standard. Melting points were determined on an XD-4 digital micro melting point apparatus. IR spectra were recorded with an IR spectrophotometer VERTEX 70 FT-IR (Bruker Optics). HRMS spectra were recorded on a QTOF6510 spectrograph (Agilent). UV–vis spectra were recorded on a U-4100 (Hitachi). Fluorescent measurements were recorded on a Perkin–Elmer LS-55 luminescence spectrophotometer. All pH measurements were made with a Model PHS-3C pH meter (Shanghai, China) and operated at room temperature about 298 K. 2.2. Reagents Deionized water was used throughout the experiment. All the reagents were purchased from commercial suppliers and used without further purification. The salts used in stock aqueous solutions of metal ions were CoCl2 ·6H2 O, ZnCl2 , CaCl2 , NaCl, CuCl2 ·2H2 O, NiCl2 ·6H2 O, KCl, CdCl2 ·2½H2 O, HgCl2 , FeCl3 ·6H2 O, AgNO3 , Mg(ClO4 )2 . HEPES (4-(2-hydroxyethyl)-1piperazineethanesulfonic acid) buffer solution (pH = 7.2) was prepared using 20 mM HEPES, and proper amount of aqueous sodium hydroxide under adjustment by a pH meter. 2.3. Synthesis of 4-chloro-2-(5-phenyl-1-(pyridin-2-yl)-4,5dihydro-1H-pyrazol-3-yl)phenol 3 The synthetic route of the proposed compound 3 is shown in Scheme 1. Starting materials chalcone (1) and 2-hydrazinylpyridine (2) were prepared according to literatures [43–45]. To a stirred solution of chalcone (1) (0.258 g, 1.0 mmol) in ethanol (15 mL) was added 2-hydrazinylpyridine (2) (0.131 g, 1.2 mmol) and NaOH (0.12 g, 3.0 mmol). The reaction mixture was refluxed for 4 h. The progress of the reaction was monitored by TLC. After completion, the reaction mixture was cooled to room temperature and diluted with chilled water, and then hydrochloric acid was added to neutralize it. The crude product was obtained as yellow precipitates. The precipitates were filtered, washed with water and ethanol, and consequently recrystallized from ethanol to afford 3. Yellow crystal; yield: 36.0%; mp: 172–173 ◦ C; IR (KBr, cm−1 ): 3066.0, 3031.5, 1588.9, 1476.0, 1443.9, 1255.9, 1145.2, 760.4, 692.9; 1 H NMR (400 MHz, CDCl3 ): ı 3.28 (dd, 1H, J = 5.6, 17.4 Hz, 4-Htrans ), 3.89 (dd, 1H, J = 12.4, 17.4 Hz, 4-Hcis ), 5.81 (dd, 1H, J = 5.6, 12.4 Hz, 5-H of pyrazoline), 6.70 (dd, 1H, J = 5.3, 6.7 Hz, pyridine-H), 6.99 (d, 1H, J = 8.8 Hz, Ar-H), 7.12 (d, 1H, J = 2.5 Hz, Ar-H), 7.22 (dd, 1H, J = 2.5, 8.8 Hz, Ar-H), 7.25–7.32 (m, 6H, Ar-H + pyridine-H), 7.56 (m, 1H, pyridine-H), 8.07 (d, 1H, J = 4.2 Hz, pyridine-H), 10.61 (s, 1H, OH); 13 C NMR (100 MHz, CDCl ): 155.8, 154.4, 150.6, 147.9, 142.4, 137.4, 3 130.4, 128.8 (2C), 127.4, 126.9, 125.8 (2C), 124.2, 118.0, 117.5, 115.4,

Scheme 1. Synthesis of compound 3.

2.4. Analytical procedure and Quantum yield A 5.0 × 10−4 M of stock solution of compound 3 was prepared in CH3 CN. The cationic stocks were all in H2 O with a concentration of 10−2 M for UV–vis absorption and fluorescence spectra analysis. For all measurements of fluorescence spectra, excitation was at 350 nm with 10.0 nm of excitation slit width and scan speed was set at 800 nm min−1 . UV–vis and fluorescence titration experiments were performed using 5 × 10−5 M and 10−5 M of compound 3 in the HEPES buffer (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN), respectively. For Zn2+ ion absorption and fluorescence titration experiments, a 3 mL solution of compound 3 (5 × 10−5 M) and a 3 mL solution of compound 3 (10−5 M) were filled in the quartz cell of 1 cm optical path length, and each time 1.5 ␮L solution of Zn2+ (10−2 M) and 1.0 ␮L solution of Zn2+ (3 × 10−3 M) were added into the quartz cell gradually by using a micro-syringe, respectively. After each addition of Zn2+ ion, the solution was stirred for 3 min. The volume of cationic stock solution added was less than 100 ␮L with the purpose of keeping the total volume of testing solution without obvious change. The ability of the molecules to emit the absorbed light energy is characterized quantitatively by the fluorescence quantum yield (˚F ). Quantum yields were determined by the relative comparison procedure, using quinine sulfate dihydrate (≥99.0%) in 0.1 N H2 SO4 as the main standard. The corrected emission spectra were measured for the quinine sulfate dihydrate standard (ex = 380 nm; A (absorption) < 0.01; ˚F = 0.510 [46] and for compound 3 as well as complex of compound 3 with Zn2+ (ex = 380 nm; A < 0.05). The general equation used in the determination of relative quantum yields from earlier research was given in Eq. (1) [47]. ˚Fu =

(˚FS )(FAu )(As )(2u ) (FAs )(Au )(2s )

(1)

where ˚F = fluorescence quantum yield; FA = integrated area under the corrected emission spectrum; A = absorbance at the excitation wavelength;  = the refractive index of the solution; and the subscripts u and s refer to the unknown and the standard, respectively. 3. Results and discussion 3.1. UV–vis studies The absorption spectrum of compound 3 exhibits a broad band at 347 nm at room temperature in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN). Binding affinities of compound 3 toward metal ions, Ag+ , Mg2+ , Hg2+ , Cd2+ , Co2+ , Cu2+ , Ni2+ , Zn2+ and Fe3+ ions were evaluated by UV–vis spectroscopy measurements. Upon addition of these metal ions, the absorption spectrum changes in different manner as shown in Fig. 1. In the case of Ag+ or Mg2+ , absorption curve did not change, whereas in the case of Hg2+ , Fe3+ , Cd2+ , Co2+ , Cu2+ , Ni2+ and Zn2+ ions, the addition of metal ions caused a decrease of absorption intensity to some extent at 347 nm, accompanied by an new absorption peak appeared obviously at the range of 400–420 nm. To investigate the binding property of compound 3 toward Zn2+ , we measured the UV–vis absorption spectra of compound 3 (5 × 10−5 M) in the presence of various concentrations of Zn2+ ion (0–2 × 10−4 M), as shown in Fig. 2. The absorbance of compound 3 at 347 nm gradually decreases with an increasing concentration of Zn2+ ion. Moreover, isobestic point appears at 378 nm and a new absorption peak appears at the range of 400–420 nm, and its absorption intensity gradually increases with the addition of

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Fig. 1. UV–vis spectral changes of compound 3 (5 × 10−5 M) in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) upon additions of various metal ions (5 × 10−5 M).

Zn2+ ion. This absorption peak is likely due to the coordination of compound 3 with Zn2+ ion. Under comparable experimental conditions, the UV–vis spectrum of Zn2+ displayed no appreciable absorption between 220 and 600 nm within the appropriate concentration range. According to the above phenomena, we can observe the transformation from free compound 3 to the Zn2+ coordinated species. In addition, the coordination stoichiometry between 3 and Zn2+ ion was estimated to be 1:1 by a nonlinear curve fitting of the UV–vis titration results (inset) similar to Job’s plot as depicted in Fig. S1. 3.2. Effect of pH on the fluorescence and 1 H NMR spectra studies The effect of pH (6.3–8.5) on the fluorescence of the sensor 3 with Zn2+ ion was also evaluated. As depicted in Fig. S2, the fluorescence intensity slightly increased with increasing pH and reached its maximum at pH around 7.0 and then fluorescence intensity sharply decreased with continuing to increase pH. The 1 H NMR spectra of sensor 3 (Fig. S3) indicate that upon coordination to Zn2+ ion in acetonitrile-d3 the protons of the pyridine slightly shift downfield and the hydroxyl proton shifts upfield. The

Fig. 3. Fluorescence emission spectra of compound 3 (10−5 M) was titrated with Zn2+ (0–5 × 10−5 M) in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN). Emission slit width was 2.5 nm. Inset: variations of fluorescence intensity of compound 3 (10−5 M) at 460 nm vs. equivalents of [Zn2+ ] [3] (I and I0 denote fluorescence intensity of compound 3 at 460 nm in the presence and absence of Zn2+ , respectively).

changes of proton peaks suggested the interaction of nitrogen of pyridine and oxygen of hydroxyl with Zn2+ ion. We also tried to obtain more evidence for the interaction position between Zn2+ ion and sensor 3 by 1 H NMR spectroscopy in the solution of CD3 CN/D2 O (1/1, v/v), but failed due to the low solubility of sensor 3 in the solution of CD3 CN/D2 O (1/1, v/v). 3.3. Fluorescence titration studies The titration of Zn2+ ion was carried out by adding small aliquots of ZnCl2 stock aqueous solution (10−2 M) into the solution of 3 (10−5 M) in the HEPES (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) buffer solution. As shown in Fig. 3, the fluorescence quantum yield of compound 3 in the absence of Zn2+ was calculated to be 0.12. As Zn2+ ion was gradually titrated, the fluorescence intensity of compound 3 gradually enhanced, and when the amount of Zn2+ ion added was about 10 ␮M, the fluorescence intensity almost reached maximum. The quantum yield of 3 was calculated to be 0.53 in the presence of Zn2+ ion (10 ␮M) and almost enhanced 3.5-fold. When more ZnCl2 ethanol solution was titrated, the fluorescence intensity showed negligible changes. The nonlinear curve fitting of the fluorescence titration (inset) also gives a 1:1 stoichiometric ratio between compound 3 and Zn2+ similar to UV–vis spectra as shown in Fig. 2 and the association constant (Ka ) between compound 3 and Zn2+ ion in the HEPES buffer (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) was calculated to be 2.87 × 106 M−1 according to the literature [48]. 3.4. Interference from other ions

Fig. 2. UV–vis titration of compound 3 (5 × 10−5 M) in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) with increasing amount of Zn2+ . Inset: Absorption changes of compound 3 at 400 nm upon the addition of Zn2+ (0–2 × 10−4 M).

The selectivity and tolerance of compound 3 for zinc ion over other metal cations such as Co2+ , Cu2+ , Fe3+ , and Ni2+ ions were investigated by adding metal cations (10−5 M) to the solution of compound 3 (10−5 M). As depicted in Fig. 4, the fluorescence of compound 3 (10−5 M) was either partially or completely quenched by Co2+ , Cu2+ , Fe3+ , and Ni2+ ions; whereas it showed enhancement after additions of Ag+ and Zn2+ ions, especially with 10 ␮M Zn2+ ion, the fluorescence quantum yield increased almost 3.5-fold. This means that sensor 3 has a high selectivity to Zn2+ ion. The fluorescence quenching resulted from the additions of the paramagnetic transition–metal ions Co2+ , Cu2+ , Fe3+ , and Ni2+ suggests

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Fig. 4. Fluorescence intensity changes ((I − I0 )/I0 ) of free compound 3 (10−5 M) at 460 nm in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) upon additions of various metal ions (10−5 M). Emission slit width was 3 nm. (I and I0 denote fluorescence intensity of compound 3 in the presence and absence of Zn2+ , respectively.) Photograph of compound 3 in the HEPES buffer (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) without (left) and with (right) addition of 10 ␮M Zn2+ ion under the irradiation of UV light at 365 nm (inset).

Fig. 6. Fluorescence emission spectra of free compound 3 (10−5 M) in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN) upon additions of various zinc salts (10−5 M). Emission slit width was 2.5 nm.

that these ions occupy open shell d-orbitals and provide a very fast and efficient non-radiative decay of the excited states due to the electron or energy transfer between the metal ions and compound 3 [23]. Whereas Zn2+ ion, which has close shell d-orbitals, does not introduce low-energy metal-centered or charge-separated excited states energy and electron transfer processes cannot take place [10]; at the same time, the fluorescence intensity of compound 3 at 460 nm increased after addition of 10 ␮M Zn2+ ion can be attributed to chelation enhanced fluorescence (CHEF) of compound 3 with Zn2+ ion. And from the photo shown in Fig. 4 (inset), we can see the stronger blue emission of compound 3 with addition of 10 ␮M Zn2+ ion under the irradiation at 365 nm than without addition of Zn2+ ion. To further gauge selectivity for zinc ion over other metal ions, the competition experiments of Zn2+ ion mixed with other metal ions were carried out and the results were shown in Figs. 5 and S4. When 10 ␮M Co2+ , Cu2+ or Ni2+ ion was added, respectively, the fluorescence of compound 3 in the presence of Zn2+ ion was quenched in different degrees, and the fluorescence can be completely quenched when 30 ␮M Co2+ , Cu2+ or Ni2+ ion was added. But Fe3+ ion almost had no influence on the fluorescence even when

30 ␮M Fe3+ ion was added. In addition, the fluorescence intensity of compound 3 with Zn2+ ion in the presence of 30 ␮M Cd2+ ion was slightly enhanced as shown in Fig. S4. Whereas excess other transition metal ions Ag+ and Hg2+ ions, alkali metal ions K+ , Na+ ions as well as alkali earth metal ions Mg2+ , Ca2+ ions and even mixture of them all showed no obvious influence on the fluorescence of compound 3 in the presence of Zn2+ ion. Compound 3 can form complexes with these cations and the complexes possess different association constants. The difference in association constants results in different interference capacity to the fluorescence selectivity of compound 3 to Zn2+ ion. Additionally, in order to explore the effects of anionic counterions on the sensing behavior of compound 3 to Zn2+ ion, fluorescence responses of compound 3 to acetate, chloride, and nitrate salts of zinc were conducted in the HEPES buffer (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN). As can be seen from Fig. 6, there were no obvious changes in the fluorescence responses of compound 3 to Zn(AcO)2 , ZnCl2 , and Zn(NO3 )2 . To gain further insight into the fluorescent signaling behavior of compound 3 toward Zn2+ ion, the effect of EDTA on the fluorescence signaling of the 3–Zn2+ system was investigated. When 10 ␮M EDTA was added into the 3–Zn2+ system, the fluorescence intensity decreased to the fluorescence intensity of compound 3 without Zn2+ ion as shown in Fig. S5. This may be

Fig. 5. Fluorescence emission spectra of compound 3 (10−5 M) and 3–Zn2+ in the presence of Ag+ , Fe3+ , Co2+ , Ni2+ , Cu2+ , Cd2+ and Hg2+ (10−5 M) and Mg2+ , Ca2+ , K+ and Na+ (5 × 10−4 M) in the HEPES buffer solution (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN). Emission slit width was 3 nm.

Fig. 7. Fluorescence intensity of compound 3 (10−5 M) at 460 nm vs. Zn2+ concentrations.

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attributed to the stronger complexation of Zn2+ ion with EDTA than with sensor 3. 3.5. Quantitative studies The quantitative response of compound 3 toward Zn2+ ion was studied by the fluorescence titration and the linear calibration plots as shown in Fig. 7. The dynamic range for the determination of Zn2+ was determined to be linear up to 0–7 ␮M with correlation coefficient (R2 ) of 0.973 [49]. The limit of detection (LOD) is evaluated using 3 bi /m [50], where  bi is the standard deviation of the blank signals and m is the slope of the linear calibration plot. The LOD for determination of Zn2+ was thus calculated to be 0.12 ␮M. 4. Conclusions In summary, a new highly selective fluorescent sensor based on pyrazoline unit was synthesized and used for the determination of Zn2+ ion with high selectivity and a low detection limit in the HEPES buffer (20 mM HEPES, pH = 7.2, 50% (v/v) CH3 CN). This sensor formed a 1:1 complex with Zn2+ and showed a fluorescent enhancement by CHEF effect with good tolerance of other metal ions. Moreover, this sensor is very sensitive with fluorometric detection limit of 0.12 ␮M. Acknowledgements This study was supported by 973 Program (2010CB933504) and the National Natural Science Foundation of China (20972088). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.snb.2011.06.064. References [1] B.L. Vallee, K.H. Falchuk, The biochemical basis of zinc physiology, Physiol. Rev. 73 (1993) 79–118. [2] J.M. Berg, Y. Shi, The galvanization of biology: a growing appreciation for the roles of zinc, Science 271 (1996) 1081–1085. [3] C.J. Frederickson, Neurobiology of zinc and zinc-containing neurons, Int. Rev. Neurobiol. 31 (1989) 145–238. [4] X. Xie, T.G. Smart, A physiological role for endogenous zinc in rat hippocampal synaptic neurotransmission, Nature 349 (1991) 521–524. [5] M.P. Cuajungco, G.J. Lees, The biochemical basis of zinc physiology, Brain Res. 23 (1997) 219–236. [6] A. Takeda, Zinc homeostasis and functions of zinc in the brain, Biometals 14 (2001) 343–351. [7] S. Aoki, D. Kagata, M. Shiro, K. Takeda, E. Kimura, Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions, J. Am. Chem. Soc. 126 (2004) 13377–13390. [8] N.C. Lim, J.V. Schuster, M.C. Porto, M.A. Tanudra, L. Yao, H.C. Freake, C. BrD uckner, Coumarin-based chemosensors for zinc(II): toward the determination of the design algorithm for CHEF-type and ratiometric probes, Inorg. Chem. 44 (2005) 2018–2030. [9] R. Parkesh, T.C. Lee, T. Gunnlaugsson, Highly selective 4-amino-1,8naphthalimide based fluorescent photoinduced electron transfer (PET) chemosensors for Zn(II) under physiological pH conditions, Org. Biomol. Chem. 5 (2007) 310–317. [10] P.J. Jiang, Z.J. Guo, Fluorescent detection of zinc in biological systems: recent development on the design of chemosensors and biosensors, Coord. Chem. Rev. 248 (2004) 205–229. [11] Y. Liu, N. Zhang, Y. Chen, L.H. Wang, Fluorescence sensing and binding behavior of aminobenzenesulfonamidoquinolino-␤-cyclodextrin to Zn2+ , Org. Lett. 9 (2007) 315–318. [12] H.H. Wang, Q. Gan, X.J. Wang, L. Xue, S.H. Liu, H. Jiang, A water-soluble, small molecular fluorescent sensor with femtomolar sensitivity for zinc ion, Org. Lett. 9 (2007) 4995–4998. [13] J.W. Lee, H.S. Jung, P.S. Kwon, J.W. Kim, R.A. Bartsch, Y. Kim, S.J. Kim, J.S. Kim, Chromofluorescent indicator for intracellular Zn2+ /Hg2+ dynamic exchange, Org. Lett. 10 (2008) 3801–3804.

[14] X.Y. Chen, J. Shi, Y.M. Li, F.L. Wang, X. Wu, Q.X. Guo, L. Liu, Two-photon fluorescent probes of biological Zn(II) derived from 7-hydroxyquinoline, Org. Lett. 11 (2009) 4426–4429. [15] L. Xue, C. Liu, H. Jiang, A ratiometric fluorescent sensor with a large stokes shift for imaging zinc ions in living cells, Chem. Commun. (2009) 1061–1063. [16] S.C. Burdette, G.K. Walkup, B. Spingler, R.Y. Tsien, S.J. Lippard, Fluorescent sensors for Zn2+ based on a fluorescein platform: synthesis, properties and intracellular distribution, J. Am. Chem. Soc. 123 (2001) 7831–7841. [17] K.R. Gee, Z.L. Zhou, W.J. Qian, R. Kennedy, Detection and imaging of zinc secretion from pancreatic ␤-cells using a new fluorescent zinc indicator, J. Am. Chem. Soc. 124 (2002) 776–778. [18] N.C. Lim, C. Bruckner, DPA-substituted coumarins as chemosensors for zinc(II): modulation of the chemosensory characteristics by variation of the position of the chelate on the coumarin, Chem. Commun. (2004) 1094–1095. [19] K. Komatsu, Y. Urano, H. Kojima, T. Nagano, Development of an iminocoumarinbased zinc sensor suitable for ratiometric fluorescence imaging of neuronal zinc, J. Am. Chem. Soc. 129 (2007) 13447–13454. [20] K. Hanaoka, K. Kikuchi, H. Kojima, Y. Urano, T. Nagano, Development of a zinc ion-selective luminescent lanthanide chemosensor for biological applications, J. Am. Chem. Soc. 126 (2004) 12470–12476. [21] L. Li, Y.Q. Dang, H.W. Li, B. Wang, Y.Q. Wu, Fluorescent chemosensor based on Schiff base for selective detection of zinc(II) in aqueous solution, Tetrahedron Lett. 51 (2010) 618–621. [22] Z.C. Xu, X.H. Qian, J.N. Cui, R. Zhang, Exploiting the deprotonation mechanism for the design of ratiometric and colorimetric Zn2+ fluorescent chemosensor with a large red-shift in emission, Tetrahedron 62 (2006) 10117– 10122. [23] A. Helal, H.S. Kim, Thiazole-based chemosensor: synthesis and ratiometric fluorescence sensing of zinc, Tetrahedron Lett. 50 (2009) 5510–5515. [24] O. David, S. Maisonneuve, J. Xie, Generation of new fluorophore by Click chemistry: synthesis and properties of ␤-cyclodextrin substituted by 2-pyridyl triazole, Tetrahedron Lett. 48 (2007) 6527–6530. [25] S. Huang, R.J. Clark, L. Zhu, Highly sensitive fluorescent probes for zinc ion based on triazolyl-containing tetradentate coordination motifs, Org. Lett. 9 (2007) 4999–5002. [26] A. Ojida, I. Takashima, T. Kohira, H. Nonaka, I. Hamachi, Turn-on fluorescence sensing of nucleoside polyphosphates using a xanthene-based Zn(II) complex chemosensor, J. Am. Chem. Soc. 130 (2008) 12095–12101. [27] H.A. Michaels, C.S. Murphy, R.J. Clark, M.W.L. Davidson, Zhu, 2-anthryltriazolylcontaining multidentate ligands: zinc-coordination mediated photophysical processes and potential in live-cell imaging applications, Inorg. Chem. 49 (2010) 4278–4287. [28] M. Taki, J.L. Wolford, T.V. O’Halloran, Emission ratiometric imaging of intracellular zinc: design of a benzoxazole fluorescent sensor and its application in two-photon microscopy, J. Am. Chem. Soc. 126 (2004) 712–713. [29] J. Dessingou, R. Joseph, C.P. Rao, A direct fluorescence-on chemo-sensor for selective recognition of Zn(II) by a lower rim 1,3-di-derivative of calix[4]arene possessing bis-{N-(2-hydroxynaphthyl-1-methylimine)} pendants, Tetrahedron Lett. 46 (2005) 7967–7971. [30] J.N. Ngwendson, A. Banerjee, A Zn(II) ion selective fluorescence sensor that is not affected by Cd(II), Tetrahedron Lett. 48 (2007) 7316–7319. [31] Y. Zhang, X.F. Guo, W.X. Si, L.H. Jia, X.H. Qian, Ratiometric and water-soluble fluorescent zinc sensor of carboxamidoquinoline with an alkoxyethylamino chain as receptor, Org. Lett. 10 (2008) 473–476. [32] S.J. Ji, H.B. Shi, Synthesis and fluorescent property of some novel benzothiazoyl pyrazoline derivatives containing aromatic heterocycle, Dyes Pigments 70 (2006) 246–250. [33] B. Bian, S.J. Ji, H.B. Shi, Synthesis and fluorescent property of some novel bischromophore compounds containing pyrazoline and naphthalimide groups, Dyes Pigments 76 (2008) 348–352. [34] X.Q. Wei, G. Yang, J.B. Cheng, Z.Y. Lu, M.G. Xie, Synthesis of novel light-emitting calix[4]arene derivatives and their luminescent properties, Opt. Mater. 29 (2007) 936–940. [35] S. Pramanik, P. Banerjee, A. Sarkar, A. Mukherjee, K.K. Mahalanabis, S.C. Bhattacharya, Spectroscopic investigation of 3-pyrazolyl 2-pyrazoline derivative in homogeneous solvents, Spectrochim. Acta A 71 (2008) 1327– 1332. [36] M. Pokladko, E. Gondek, J. Sanetra, J. Nizioł, A. Danel, I.V. Kityk, A.H. Reshak, Spectral emission properties of 4-aryloxy-3-methyl-1-phenyl-1Hpyrazolo[3,4-b]quinolones, Spectrochim. Acta A 73 (2009) 281–285. [37] P.F. Wang, N. Onozawa-Komatsuzaki, Y. Himeda, H. Sugihara, H. Arakawa, K. Kasuga, 3-(2-Pyridyl)-2-pyrazoline derivatives: novel fluorescent probes for Zn2+ ion, Tetrahedron Lett. 42 (2001) 9199–9201. [38] Q. Peng, X.H. Tang, Synthesis of a novel calix[4]arene-based fluorescent ionophore and its metal ions recognition properties, Chin. Chem. Lett. 2 (2009) 13–16. [39] H.B. Shi, S.J. Ji, B. Bian, Studies on transition metal ions recognition properties of 1-(2-benzothiazole)-3-(2-thiophene)-2-pyrazoline derivatives, Dyes Pigments 73 (2007) 394–396. [40] Z.L. Gong, L.W. Zheng, B.X. Zhao, D.Z. Yang, H.S. Lv, W.Y. Liu, S. Lian, The synthesis, X-ray crystal structure and optical properties of novel 1, 3,5-triaryl pyrazoline derivatives, J. Photochem. Photobiol. A 209 (2010) 49–55. [41] W.Y. Liu, Y.S. Xie, B.X. Zhao, B.S. Wang, H.S. Lv, Z.L. Gong, S. Lian, L.W. Zheng, The synthesis, X-ray crystal structure and optical properties of novel 5-aryl-1arylthiazolyl-3-ferrocenyl-pyrazoline derivatives, J. Photochem. Photobiol. A 214 (2010) 135–144.

Z.-L. Gong et al. / Sensors and Actuators B 159 (2011) 148–153 [42] Z.L. Gong, B.X. Zhao, W.Y. Liu, H.S. Lv, A new highly selective “turn on” fluorescent sensor for zinc ion based on a pyrazoline derivative, J. Photochem. Photobiol. A 218 (2011) 6–10. [43] A. Hasan, K.M. Khan, M. Sher, G.M. Maharvi, S.A. Nawaz, M.I. Choudhary, A.U. Rahman, C.T. Supuran, Synthesis and inhibitory potential towards acetylcholinesterase butyrylcholinesterase and lipoxygenase of some variably substituted chalcones, J. Enzym. Inhib. Med. Chem. 20 (2005) 41–47. [44] I.C. Kogon, R. Minin, C.G. Overberger, 2-Chloropymidine, Org. Synth. Colloid 4 (1963) 182. [45] A.A. Alhaider, M. Atef Abdelkader, E.J. Lien, Design, synthesis, and pharmacological activities of 2-substituted 4-phenylquinolines as potential antidepressant drugs, J. Med. Chem. 28 (1985) 1394–1398. [46] R.A. Velapoldi, K.D. Mielenz, A Fluorescence Standard Reference Material: Quinine Sulfate Dihydrate. National Bureau of Standards (now the National Institute of Standards and Technology, NIST) Special Publication 260-64, U.S. Government Printing Office, Stock No. 003-003-02148-2, Washington, DC, 1980. [47] S.M. Song, D. Ju, J.F. Li, D.X. Li, Y.L. Wei, C. Dong, P.H. Lin, S.M. Shuang, Synthesis and spectral characteristics of two novel intramolecular charge transfer fluorescent dyes, Talanta 77 (2009) 1707–1714. [48] J. Bourson, J. Pouget, B. Valeur, Ion-responsive fluorescent compounds. 4. Effect of cation binding on the photophysical properties of a coumarin linked to monoaza- and diaza-crown ethers, J. Phys. Chem. 97 (1993) 4552– 4557. [49] N. Li, Y. Xiang, X.T. Chen, A.J. Tong, Salicylaldehyde hydrazones as fluorescent probes for zinc ion in aqueous solution of physiological pH, Talanta 79 (2009) 327–332.

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[50] B.P. Joshi, J. Park, W.I. Lee, K.H. Lee, Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor, Talanta 78 (2009) 903–909.

Biographies Zhong-Liang Gong received his B.Sc. in chemistry from Zao Zhuang University (Zaozhuang, China) in 2008. At present, he is a M.Sc. student in Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University (Jinan, China). His current research interest involves the synthesis of the fluorescence materials and the application of fluorescent sensors. Fei Ge received his B.Sc. in chemistry from Shandong University (Jinan, China). At present, he is a M.Sc. student in the Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University (Jinan, China). His current research interest involves the chemosensor and polymer modified magnetic nanoparticles used for the detection or removal of heavy metal ions and organic dyes. Dr. Bao-Xiang Zhao is a professor in organic chemistry at Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University (Jinan, China), since 2000. Currently his research interests include synthesis of fluorescent probe for detecting ions in water and in living cells; preparation of polymer modified magnetic nanoparticles used for the detection and removal of heavy metal ions and organic dyes; design and synthesis of diversity small molecules for chemical biology research.