Acylhydrazone based fluorescent chemosensor for zinc in aqueous solution with high selectivity and sensitivity

Sensors and Actuators B 208 (2015) 581–587

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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Acylhydrazone based fluorescent chemosensor for zinc in aqueous solution with high selectivity and sensitivity Jing-Han Hu ∗ , Jian-Bin Li, Jing Qi, You Sun College of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, PR China

a r t i c l e

i n f o

Article history: Received 13 September 2014 Received in revised form 3 November 2014 Accepted 6 November 2014 Available online 20 November 2014 Keywords: Zinc (Zn2+ ) Fluorescent sensors Acylhydrazone Test strip

a b s t r a c t A simple chemosensor L bearing an acylhydrazone group as binding site and naphthalene group as the fluorescence signal group was described and synthesized, which showed a fluorescence turn-on response for Zn2+ over other metals ions such as Fe3+ , Hg2+ , Ag+ , Ca2+ , Cu2+ , Co2+ , Ni2+ , Cd2+ , Pb2+ , Cr3+ and Mg2+ in aqueous solutions with specific selectivity and high sensitivity. When zinc is added, the probe L shows an immediate visible change of fluorescence color in aqueous solution; while other cations do not cause obvious color change. In addition, further study demonstrates the detection limit on fluorescence response of the sensor to Zn2+ is down to 9.3 × 10−8 M. Moreover, test strips based on the sensor L were fabricated, which could act as a convenient and efficient Zn2+ test kit. Therefore, the probe should be potential application in both the environment and biological systems for the monitoring of zinc. © 2014 Elsevier B.V. All rights reserved.

1. Introduction The zinc ion (Zn2+ ) is the second most abundant transition metal ion after Fe2+ or Fe3+ in the human body, Zn2+ has drawn considerable interest and plays very important roles in a wide variety of physiological and pathological processes, including modulation of catalytic activity of hundreds of specific enzymes, regulation of gene transcription, structural cofactors in metalloproteins, neural signal transmission, immune function, cellular transport, and involvement in brain pathology [1,2]. Among the 2–3 g of zinc in an average human body, around 90% is tightly bound, while 10% is loosely bound and can be altered. Manipulation of the freely available zinc has been shown to affect a great range of diseases and conditions [3,4]. It is known that disorders of zinc metabolism are closely associated with many severe diseases such as Alzheimer’s disease, Parkinson’s disease, epilepsy, growth failure, immune deficiency, amyotrophic lateral sclerosis, ischemic stroke, infantile diarrhea and Ehlers–Danlos syndrome are all characterized by the accumulation and aggregation of misfolded proteins in the endoplasmic reticulum [5,6]. In addition, with the development of modern industry, the environment pollution caused by transition metals like Zn2+ has become more serious and pose a threat to human heath and the environment [7]. Therefore, it is of essential

∗ Corresponding author. Tel.: +86 931 18109460354. E-mail address: [email protected] (J.-H. Hu). http://dx.doi.org/10.1016/j.snb.2014.11.066 0925-4005/© 2014 Elsevier B.V. All rights reserved.

importance to control the accurate detection of Zn2+ concentrations in both the environment and biological systems. Fluorescence emission spectrometry has emerged as one of the most popular methods for the selective recognition of chemically and biologically important ions because of its high sensitivity, simplicity, and real time monitoring without complicated pretreatment [8–10]. As a result, intensive efforts have been devoted to develop sensitive fluorescence sensors for detection of trace amounts of zinc ions both ‘in vitro’ and ‘in vivo’ and a variety of chemosensors for Zn2+ with apparent dissociation constants in the nanomolar range or higher, based on fluorescein [11], anthracene [12], naphthalimide [13], coumarin [14], quinoline [15], cyanine dyes [16], rhodamine [17], and BODIPY [18] have been reported in the past years. A few fluorescent probes have also been developed and successfully applied to the imaging of Zn2+ in living cells or zebrafish embryos [19]. However, many of the existing Zn2+ probes have poor water solubility, they can only operate in pure or mixed organic solvents for the detection of Zn2+ , which prevents their applications in biological systems. Secondly, it is still a huge challenge for detecting Zn2+ selectively without interference of other transition metal ions, especially Cd2+ , because Zn2+ and Cd2+ display highly similar chemical properties. In addition, to the best of our knowledge, most of these chemosensors for Zn2+ suffer from a turn off response, low detection limit, low water solubility [19a,20a–20c], high energy absorptions, small stokes shifts and suffer from interference from some heavy and transition metal ions [20c]. So far, a number of “turn-on” type fluorescent Zn2+ probes have been developed to date on the basis of various sensing

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Scheme 1. Synthetic procedures for receptor L.

mechanisms, including PET (photoinduced electron transfer) [21], ICT (intramolecular charge transfer) [22], FRET (fluorescence resonance energy transfer) [23], excimer [24], AIE (aggregation induced emission) [19b], and CHEF (chelation enhanced fluorescence) [25]. Among these, a majority of sensors display sophisticated structures [24b,26], requiring a multistep synthesis [24a,10], requiring a high reaction temperature or a long reaction time [21,23], low selectivity and sensitivity [20b] with regard to the zinc ion. Therefore, it remains a challenging task to develop a easily synthesized, water-soluble sensor for Zn2+ ions with fluorescence enhancement exhibiting a high selectivity and sensitivity for Zn2+ over other metal ion and wide applicable pH range [27–30]. In view of this and as part of our research interest in molecular recognition [31], we have made efforts to obtain an efficient optical chemosensor L that could detect Zn2+ with both high selectivity and sensitivity in aqueous solutions. Our strategy for the design of such a sensor has been as follows. Firstly, in order to achieve a good selectivity for Zn2+ , the sensing mode has been adopted and an acylhydrazone group has been introduced into the sensor molecule as a binding site to detect Zn2+ by CHEF mechanism. Secondly, in order to achieve a high sensitivity for Zn2+ , the fluorescent reporter mode has been adopted as fluorescent sensors often provide a higher sensitivity than other optical sensors. Therefore, we introduced naphthalene groups as the fluorescence signal group. In addition, to improve the water solubility of sensor L, the hydrophilic phenol group was introduced into the sensor molecule. Finally, we studied the Zn2+ sensing ability of sensor L in aqueous solution. 2. Experimental 2.1. Materials and physical methods Fresh double distilled water was used throughout the experiment. The inorganic salts Ca(ClO4 )2 ·6H2 O, Mg(ClO4 )2 ·6H2 O, Cd(ClO4 )2 ·6H2 O, Fe(ClO4 )3 ·6H2 O, Hg(ClO4 )3 · 6H2 O, Co(ClO4 )2 ·6H2 O, Ni(ClO4 )2 ·6H2 O, Cu(ClO4 )2 ·6H2 O, Zn(ClO4 )2 ·6H2 O, Pb(ClO4 )2 ·3H2 O, AgClO4 ·H2 O, Cr(ClO4 )3 ·6H2 O and N-2-hydroxyethylpiperazine-N -2-ethanesulfonic acid (HEPES) were purchased from Alfa Aesar Chemical Reagent Co. (Tianjin, China). All reagents and solvents were commercially available at analytical grade and were used without further purification. 1 H NMR and 13 C NMR spectra were recorded on a Mercury-400BB spectrometer at 400 MHz and 100 MHz. Chemical shifts are reported in ppm downfield from tetramethylsilane (TMS, ı scale with solvent resonances as internal standards). Photoluminescence spectra were performed on a Shimadzu RF-5301 fluorescence spectrophotometer. Melting points were measured on an X-4 digital melting-point apparatus (uncorrected). Infrared spectra were performed on a Digilab FTS-3000 FT-IR spectrophotometer. The structure of sensor L and ML (M = Zn2+ ) was further confirmed by mass spectrometer and single-crystal X-ray diffraction.

keeping the ligand concentration constant (2.0 × 10−5 M) on a Shimadzu UV-2550 spectrometer. 2.3. General procedure for fluorescence spectra experiments All fluorescence spectroscopy was carried out just after the addition of hexahydrate perchlorate cation salt in DMSO/H2 O solution, while keeping the ligand concentration constant (2.0 × 10−5 M) on a Shimadzu RF-5301 spectrometer. The solution of cations were prepared from the hexahydrate perchlorate salts of Fe3+ , Hg2+ , Ag+ , Ca2+ , Cu2+ , Co2+ , Ni2+ , Cd2+ , Pb2+ , Zn2+ , Cr3+ and Mg2+ . The excitation wavelength was 378 nm. 2.4. General procedure for 1 H NMR experiments For 1 H NMR titrations, the sensor of stock solutions was prepared in DMSO-d6 , the zinc and magnesium was prepared in D2 O. Aliquots of the two solutions were mixed directly in NMR tubes. 2.5. Synthesis of sensor L The synthesis route of probe molecule L is demonstrated in Scheme 1. 3,4,5-Trihydroxybenzhydrazide (0.386 g, 2 mmol) and 2-hydroxy-1-napthaldehyde (0.344 g, 2 mmol) were dissolved in absolute ethanol (10 mL). The solution was stirred under reflux for 8 h at 353 K. After cooling to room temperature, the yellow precipitate was filtered, washed three times with absolute ethanol, then recrystallized with absolute ethanol to give yellow powder product of L in 40% yield (m.p., 275–278 ◦ C). 1 H NMR (DMSO-d6 , 400 MHz) ı: 12.96 (s, 1H), 11.92 (s, 1H), 9.49 (s, 1H), 9.29 (s, 2H), 9.0 (s, 1H), 8.14 (d, J = 8.5 Hz, 1H), 7.92 (t, J = 8.5 Hz, 2H), 7.62 (t, J = 7.6 Hz, 1H), 7.42 (t, J = 7.5 Hz, 1H), 7.24 (d, J = 8.9 Hz, 1H), 7.0 (s, 2H); 13 C NMR (DMSO-d6 , 100 MHz) ı: 167.57, 162.84, 110.77, 142.42, 137.40, 136.63, 133.98, 132.79, 132.67, 128.49, 127.55, 125.37, 123.96, 113.60, 112.20. IR (KBr) v: 1536 cm−1 (CH N), 1605 cm−1 (C O), 3243 cm−1 (NH), 3447 cm−1 (OH). ESI-MS m/z (M+H+ ): calcd, 339.09; found, 339.08. The structure of sensor L was further confirmed by single-crystal X-ray diffraction (Fig. 1). 3. Results and discussion Receptor was found to have limited solubility in water, and this compelled us to use these sensor in mixed solvent. To evaluate recognition studies of L, Fe3+ , Hg2+ , Ag+ , Ca2+ , Cu2+ , Co2+ , Ni2+ , Cd2+ ,

2.2. General procedure for UV–vis experiments All UV–vis spectroscopy was carried out just after the addition of hexahydrate perchlorate cation salt in DMSO/H2 O solution, while

Fig. 1. Single-crystal X-ray structure of sensor L.

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Fig. 3. Photograph of L (20 ␮M) in the presence of 20 equiv. of various cations, which was taken under a UV-lamp (365 nm).

Fig. 2. Fluorescence spectra response of L (20 ␮M, 80% H2 O) upon addition of 20 equiv. of Zn2+ , Fe3+ , Hg2+ , Ag+ , Ca2+ , Cu2+ , Co2+ , Ni2+ , Cd2+ , Pb2+ , Cr3+ and Mg2+ ions (ex = 378 nm).

Pb2+ , Zn2+ , Cr3+ and Mg2+ ions were used to measure the selectivity and sensitivity of probe L (20 ␮M) in H2 O/DMSO (8:2, v/v), and fluorescence spectra were recorded upon the addition of 20 equiv. of each of these metal ions. Compared to other metal ions examined, changes in spectral pattern were observed only in the presence of Zn2+ (4 × 10−3 M), chemosensor L showed a strong fluorescence response at max = 480 nm in the fluorescence spectrum recorded at a 2 × 10−5 M concentration of the sensors in the aqueous solutions system, responded with a dramatic color change, from colorless to yellow-green. No change in spectral pattern for receptor L in the presence of other cations suggested either a very weak or no interaction between these cations and the compound L (Figs. 2 and 3). For an ideal fluorescent ion probe, only the target ion can induce drastic fluorescence changes, and the coexistence of other competing ions should not disturb the detection of the target ion. As it is well-known, fluorescent Zn2+ probes may encounter interference by other cations, especially Cd2+ and Mg2+ . Thus, competition behavior was checked to further elucidate whether the coexistence of competing metal cations interferes with the detection of Zn2+ . In

Fig. 4. Fluorescence spectra response of L (20 ␮M) in the presence of various cations (4 × 10−5 M) in DMSO/H2 O (2:8, v/v) in response to Zn2+ (4 × 10−4 M); from left to right: free, Zn2+ Ag+ , Cd2+ , Cr3+ , Co2+ , Cu2+ , Ca2+ , Fe3+ , Hg2+ , Mg2+ , Ni2+ and Pb2+ .

the solutions of probe L, upon addition of Zn2+ (4 × 10−4 M) together with other competing cations (4 × 10−5 M) (Fig. 4), similar fluorescence enhancement was clearly observed. Thus, the receptor L displays a good selectivity for Zn2+ over other competing metal ions in aqueous solution. The quantitative nature of the sensing of Zn2+ ion by L was elucidated by fluorescence titration of compound L (20 ␮M) in H2 O/DMSO (8:2, v/v) solution as described in Fig. 5. As the concentration of Zn2+ (0.2 M) increased, a gradual increase in the fluorescence intensity of chemosenor L at 480 nm was observed

Fig. 5. Fluorescence titration spectra (ex = 378 nm) of L (20 ␮M) in DMSO/H2 O (2:8, v/v) upon adding of an increasing concentration of Zn2+ (0.2 M). Inset: plot of fluorescence intensity at 480 nm as a function of [Zn2+ ]/[L].

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Detection limit

Response

References

EtOH/H2 O (99:1, v/v) CH3 OH DMF Aqueous buffer DMSO/H2 O (2:8, v/v)

1.8 ␮M 0.8 ␮M 44 nM 0.44 ␮M 93 nM

Enhancement Enhancement Enhancement Enhancement Enhancement

[30a] [27a] [30b] [29c] Present work

Fig. 6. Fluorescent changes upon the addition of Zn2+ at the indicated concentrations. Images were taken under UV light (365 nm).

as the Zn2+ volume increased from 0 to 3.16 ␮L, when 15 equiv. of Zn2+ was added, the fluorescence intensity of the solution showed almost no enhancement (insert to Fig. 5). We assume that the induction period might demonstrate coordination process: the step is that another Zn2+ might bind to the N atoms of the acylhydrazone and the O atoms of the naphthol group, carbonyl O in sensor L, resulting in fluorescence enhancement. The fluorescence quantum yield (˚f ) of sensor L in DMSO/H2 O (2:8, v/v) solution is 0.06, whereas it reaches 0.41 when sensor L reacts with Zn2+ . In addition, only the aqueous solution containing Zn2+ showed a change of fluorescence color from colorless to yellowish green. These results indicated that L can function as a fluorescent “turn-on” type probe for the Zn2+ ion in aqueous solution. The detection limit is one of the most important parameters in ion sensing. For many practical purposes, it is very important to detect the analytes at low concentrations. The fluorimetric detection limits of sensor L for Zn2+ were also determined. As shown in Fig. 6, the minimum concentration of Zn2+ that could be observed though one order of magnitude lower for fluorescence naked eye detection was 5.0 × 10−7 M, by using a UV lamp at 365 nm. In the meantime, the detection limit of the fluorescence spectra measurements, as calculated on the basis of 3SB /S [32] (where SB is the standard deviation of the blank solution and S is the slope of the calibration curve), Fig. 7 showed a detection limit of approximately 9.3 × 10−8 M for Zn2+ , which is comparable with reported values (Table 1). Thus, L can be applied to detect Zn2+ at an extremely low concentration level of 10−8 M, which may fully meet the requirements in biosensing, as labile Zn2+ in the human body was reported to exist at a millimolar concentration level. These data indicate that probe L show high sensitivity toward Zn2+ and specifically potential ion of biological systems.

Fig. 7. Fluorescence detection limit spectra of L (20 ␮M) in (H2 O/DMSO, 8:2, v/v) solution upon adding of an concentration of Zn2+ (1 × 10−4 M).

Fig. 8. Effect of pH on the fluorescence intensity at 480 nm of L (20 ␮M) in the absence and presence of 4 mM Zn2+ from 1 to 12 in DMSO/H2 O (2:8, v/v, containing 0.01 M HEPES) solution.

The pH dependence of the fluorescence intensity of L and the L–Zn2+ system in HEPES buffer system was examined by fluorescence emission spectroscopy. A solution of Zn2+ was added to a solution of sensor L in DMSO/H2 O (2:8, v/v, containing 0.01 M HEPES) solution at pH values ranging from 1 to 12 range (Fig. 8). Free L was insensitive against H+ and OH− . However, the results of L–Zn2+ system in aqueous media indicated that the reaction of L with the Zn2+ only occurred effectively in the pH range between 5 and 7, the fluorescence intensity at 480 nm was enhanced more significantly. In conclusion, the fluorescence was relatively constant from pH = 5–7, rendering support for applications in biological systems since small changes in the pH values near the physiological pH area were well tolerated. To facilitate the use of L for the detection of zinc, test strips were prepared by immersing filter papers into a DMSO/H2 O binary solution of L (0.01 M) followed by exposure to air until complete drying. Intriguingly, the fluorescence color can be changed immediately from colorless to yellow by naked eye, and to grass green once the test paper was immersed into an aqueous solution (5 ␮M) of Zn2+ under UV irradiation (Fig. 9). Thereby chemosensor L exhibits excellent fluorescence sensing performance, which will be very useful for the fabrication of sensing devices with fast and convenient detection for zinc and ions.

Fig. 9. Photographs of L on test strips (a) only L, (b) after immersion into solutions with Zn2+ , (c) after immersion into DMSO solutions with other cations, (d) after immersion into solutions with Zn2+ and other cations by naked eye (A) and under irradiation at 365 nm (B).

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Fig. 10. Partial 1 H NMR spectra of L (DMSO-d6 ) and in the presence of Zn2+ (D2 O).

Fig. 11. Infrared spectra of L (black line) and its complex L–Zn2+ (red line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

To explore the mechanism underlying the detection of Zn2+ (0.5 M) by sensor L, 1 H NMR titration were carried out. The data showed that characteristic structural changes occurred upon the interaction with Zn2+ . As shown in Fig. 10, the 1 H NMR chemical shifts of the O Ha,d,e , N Hb , and c HC N protons of L were at 12.96, 9.29, 9.0, 11.92, and 9.49 ppm, respectively, before the addition of zinc cation. When 0.5 equiv. of Zn2+ in D2 O was added

Fig. 12. Job’s plot of L with Zn2+ .

to the solution of sensor L (0.01 M) in D6 -DMSO, the N Hb and O Ha protons were quickly exchanged by deuterium, as seen in the gradual disappearance of their resonances, simultaneously, the resonances of c HC N shifted upfield of 0.08 ppm, Hg , Hf shifted upfield of 0.023 ppm and 0.025 ppm, respectively, and other aromatic H scarcely any experienced the change trend, and O Hd ,

Scheme 2. Possible sensing mechanism.

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Fig. 13. UV–vis spectra of L (20 ␮M) in DMSO/H2 O (2:8, v/v) upon adding of an increasing concentration of Zn2+ (0.02 M).

O He also gradually disappeared by deuterium process, when 1.0 equiv. of Zn2+ in D2 O was added to the solution of sensor L in D6 -DMSO. The results show that the N atoms form acylhydrazone part of c HC N and N Hb , O atoms of O Ha , carbonyl O participated in the chelation to zinc ion, it lead to weaken the oxygen of bound ability to three hydroxyl groups on the benzene ring of H, so O Hd , O He also were easily exchanged by deuterium and disappeared. In addition, relative changes in the 1 H NMR spectra were observed until 1.5 equiv. of Zn2+ was added to L, the spectra remained unchanged upon further addition of Zn2+ . These data and fluorescent titrations showed that saturated spectroscopic absorptions could be easily reached while 1.0 equiv. of zinc ion was introduced, indicative of very tight binding and 1:1 stoichiometry for zinc ion and sensor L, as shown in Scheme 2. To further investigate the interaction between sensor L and Zn2+ , the infrared spectra were performed and displayed in Fig. 11. The sensor L of the stretching vibration absorption peaks at 3447 cm−1 ( OH), 3243 cm−1 ( NH), 1536 cm−1 (C N H), 1605 cm−1 ( C O), compared with the L–Zn2+ compound the N H and O H peak disappeared, the peak of (C N H) and ( C O) at 1536 cm−1 , 1605 cm−1 moved to 1522 cm−1 and 1576 cm−1 , respectively, at the same time, the peak at 527 cm−1 and 457 cm−1 clearly produced the v (M N) and v (M O), which demonstrated receptor L combined with Zn2+ and formed the new compound. Moreover, the latter was further confirmed by Job’s plot (Fig. 12). Further evidence for the formation of the adduct L–Zn2+ complex was obtained by ESI-MS. In the ESI-MS spectra of sensor L, the [M+H]+ peak at 339.08 (m/z calcd: 339.09) was observed; however, in the ESI-MS spectra of L–Zn2+ complex, we found a new peak appeared at 402.94, which coincides well with that for the species [M+Zn]2+ (m/z calcd: 402.02). Conclusion, the IR and Job’s plot suggested that the possible binding mode of chemosensor L and zinc. Further evidence for the formation of the L–Zn2+ complex was obtained by UV–vis absorption spectral variation in aqueous solution DMSO/H2 O (2:8, v/v) of sensor L (20 ␮M) was monitored during titration with different concentrations of Zn2+ (0.02 M). As shown in Fig. 13, the strong band with maximum absorbance peak at 363 nm was observed after adding of Zn2+ , and then the absorbance peak at 410 nm increased gradually. The isosbestic points at 386 nm can be clearly observed with increasing concentrations of Zn2+ (0–25 equiv.), indicating a new and stable complexation of L with Zn2+ ion.

4. Conclusion In summary, we have developed a sensor L, which showed a highly selective and a specifically sensitive ratiometric fluorescent response to Zn2+ in aqueous solution based on chelation effect in the weak acid (pH = 5–7) environment. Furthermore, the detection of zinc usually interfere form Mg2+ , especially Cd2+ . Fortunately, the probe L could detect and distinguish zinc individually even in the sample containing Cd2+ and Mg2+ . Moreover, the detection limits was low down 9.3 × 10−8 M of Zn2+ for fluorescence detection by using a spectrofluorometer. Therefore, we have designed and developed a new small molecular fluorescent sensor with extremely high affinity for zinc ion and good selectivity and sensitivity over other metals ions in aqueous solution. The sensor L should be underlying applications and important meaning in both the environment and life sciences for the monitoring of zinc. Acknowledgments We gratefully acknowledge the support of the Nature Science Foundation of China (No. 21467012), the Science and Technology Bureau of Lanzhou, Gansu Province of China (No. 2013-4-63). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2014.11.066. References [1] C.J. Frederickson, J.Y. Koh, A.I. Bush, The neurobiology of zinc in health and disease, Nat. Rev. Neurosci. 6 (2005) 449–462. [2] A.I. Bush, W.H. Pettingell, G. Multhaup, M.D. Paradis, J.P. Vonsattel, J.F. Gusella, K. Beyreuther, C.L. Masters, R.E. Tanzi, Rapid induction of Alzheimer a beta amyloid formation by zinc, Science 265 (1994) 1464–1467. [3] Q.P. Peterson, D.R. Goode, D.C. West, K.N. Ramsey, J.J.Y. Lee, P.J. Hergenrother, PAC-1 activates procaspase-3 in vitro through relief of zinc-mediated inhibition, J. Mol. Biol. 388 (2009) 144–158. [4] R. BarKalifa, M. Hershfinkel, J.E. Friedman, A. Kozak, I. Sekler, The lipophilic zinc chelator DP-b99 prevents zinc induced neuronal death, Eur. J. Pharmacol. 618 (2009) 15–21. [5] C.J. Frederickson, M.D. Hernandez, J.F. McGinty, Translocation of zinc may contribute to seizure-induced death of neurons, Brain Res. 480 (1989) 317–321. [6] (a) M.P. Cuajungco, G.J. Lees, Zinc metabolism in the brain: relevance to human neurodegenerative disorders, Neurobiol. Dis. 4 (1997) 137–169;

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Biographies Jing-Han Hu is a professor of College of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu, China. Jian-Bin Li is currently a graduate student in Lanzhou Jiaotong University. His major is inorganic chemistry. Jing Qi is currently a graduate student in Lanzhou Jiaotong University. His major is inorganic chemistry. You Sun is currently a graduate student in Lanzhou Jiaotong University. Her major is inorganic chemistry.