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A highly selective colorimetric and “turn-on” fluorimetric chemosensor for detecting CN− based on unsymmetrical azine derivatives in aqueous media
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 167 (2016) 101–105
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A highly selective colorimetric and “turn-on” fluorimetric chemosensor for detecting CN− based on unsymmetrical azine derivatives in aqueous media You Sun, Jing-Han Hu ⁎, Jing Qi, Jian-Bin Li 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 18 January 2016 Received in revised form 3 May 2016 Accepted 14 May 2016 Available online 15 May 2016 Keywords: Cyanide anion Colorimetric Deprotonation Test strips
a b s t r a c t A novel highly selective chemosensor S1 for cyanide based on unsymmetrical azine derivative was successfully designed and synthesized, which showed both colorimetric and fluorescence turn-on responses for cyanide ions in aqueous. This structurally simple chemosensor could detect CN− anion over other anions in aqueous solution DMSO/H2O (v/v = 3:2) undergo deprotonation reaction. Results showed that the chemosensor S1 exhibited 50 fold enhancement in fluorescence at 530 nm and showed an obvious change in color from colorless to yellow that could be detected by naked eye under the UV-lamp after the addition of CN− in aqueous solution. Moreover, the detection limit on fluorescence response of the sensor to CN− is down to 6.17 × 10−8 M by titration method. Test strips based on S1 were obtain, which could be used as a convenient and efficient CN− test kit to detect CN− in aqueous solution. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Cyanide is highly toxic to humans and almost all other forms of life [1–2]. A significant proportion of victims among fire victims is due to cyanide poisoning, as blood cyanide concentrations reach a level of 23– 26 μM [3–4]. Despite cyanide toxicity, large quantities of cyanide salts are widely used in synthetic fibers, resins, herbicides, and the gold-extraction process [5]. The Environmental Protection Agency (EPA) has set the MCL (MCL: maximum contaminant level) of 1.9 × 10−6 M for cyanide in order to regulate safe levels for drinking water systems [6]. Rapid and accurate determination of cyanide would facilitate forensic investigation, medical diagnosis, and chronic cyanide monitoring. In this regard, chemosensor can be an important material to monitor these anions [7]. In addition, chemosensor can be simple and convenient with showing its optical change. [8–9] However, many kinds of colorimetric or fluorometric CN− selective receptors have been researched in organic media. Actually, in biological and environmental systems, anion-receptor interactions commonly occur in aqueous media [10]. Most of them suffer the severely interference from coexisting anions such as F−, AcO−, and H2PO− 4 . Few of them exhibit spectral changes in both absorption and emission spectra [11–12]. Therefore, the design of colorimetric and fluorimetric sensors for CN− in aqueous media is therefore currently the focus of attention.
⁎ Corresponding author. E-mail address: [email protected] (J.-H. Hu).
http://dx.doi.org/10.1016/j.saa.2016.05.017 1386-1425/© 2016 Elsevier B.V. All rights reserved.
Azines are attracting the increasing interests for their potential in medical, biological due to their antimicrobial, antibacterial activity [13]. In acyclic chemistry, the products of the reaction between one molecule hydrazine hydrate and two molecules of carbonyl compounds are called azines, among which the symmetrical compounds are widely applied [14]. In the aspect of recognition, numerous works devoted to studying structure of Schiff base complexes, however, the fluorescence properties of azines currently has yet to see the detailed report [15– 16]. As a matter, azine moieties, N-N linked diimines, are very tolerant to hydrolysis and have good ligating ability [17]. Sheng et al. have reported a symmetrical azine chemosensor for Hg2+, but for anion this kind of compound currently has yet to see the detailed report [18–19] (Fig. S6). We have synthesized a new asymmetrical azine chemosensor S1 synthesized with diphenyl diketone and salicylaldehyde hydrazone by one step (Scheme 1). This is a Chromo-fluorogenic anion receptor, which shows fluorescence and UV–vis spectra selectivity for CN− in DMSO/H2O (v/v = 3:2) binary solution over other anions. Chemosensor S1 could form a fine conjugate structure with azine moiety, as a result, the chemosensor has an excellent optical property to achieve nakedeye colorimetric and fluorimetric recognition. Meanwhile, salicylicaldehyde hydrazone provided an active hydrogen atom, which easily combined with strong alkaline ion CN− and allowed the receptors to tolerate a substantial amount of water from the solvent [20]. When CN− was added to the sensor solution, solution color changes from colorless to yellow and shows strong yellow fluorescence. According to the data, this was a deprotonation type reaction based for cyanide ion
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Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 167 (2016) 101–105
Scheme 1. Synthetic procedures for receptor S1.
detection at room temperature. The detection limit in fluorescence response of the sensor to CN− was down to 6.17 × 10−8 M. And the mechanism of this process was verified by spectroscopic methods including 1 H NMR, UV–vis, and mass spectrometry.
2. Experimental 2.1. Materials and physical methods
2.3. General procedure for fluorescence spectra experiments All the fluorescence spectra experiments were carried out in DMSO/ H2O (v/v = 3:2) solution on a Shimadzu RF-5301 spectrometer. Any changes in the fluorescence spectra of the synthesized compound were also recorded upon the addition of tetrabutylammonium anion salts and aqueous solution of NaCN while keeping the ligand concentration constant (2.0 × 10−5 M) in all experiment. The excitation wavelength was 420 nm.
All reagents were purchased from commercial supplies and used without further purification. Solvents and twice-distilled water were purified by standard methods. Fresh double distilled water was used throughout the experiment. All the tetrabutylammonium salts, salicylicaldehyde hydrazone, and diphenyl diketone were purchased from Alfa–Aesar Chemical Reagent Co, and stored in a vacuum desiccator. Chemical shifts are reported in ppm downfield from tetramethylsilane (TMS, δ scale with solvent resonances as internal standards) UV–vis spectra were recorded on a Shimadzu UV-2550 spectrometer. Photoluminescence spectra were recorded on a Shimadzu RF5301 fluorescence spectrophotometer. Melting points were measured on an X-4 digital melting-point apparatus purchased from Beijing Tech Instrument Co. Infrared spectra were recorded on a Digital FTS3000 FT-IR spectrophotometer.
2.4. General procedure for 1H NMR experiments
2.2. General procedure for UV–vis experiments
2.6. Synthesis of S1
All the UV–vis experiments were carried out just after the addition of − tetrabutylammonium anion salt of F−, Cl−, Br−, I−, AcO−, H2PO− 4 , HSO4 − − −2 , ClO− , SCN but CN was prepared in NaCN (1 × 10 M) in DMSO/ 4 H2O (v/v = 3:2) solution, while keeping the ligand concentration constant (2.0 × 10−5 M) in all experiment on a Shimadzu UV-2550 spectrometer.
The synthesis route of sensor S1 is demonstrated in Scheme 1. An ethanol solution (25 mL) of diphenyl diketone (1.1 g, 5 mmol), salicylaldehyde hydrazone (0.68 g, 5 mmol) and catalytic amount of acetic acid (AcOH) were stirred under reflux 6 h. After cooling to room temperature, the yellow precipitate was filtered, washed with hot absolute ethanol three times, then recrystallized with ethyl acetate to get
Fig. 1. Single-crystal X-ray structure of sensor S1.
Fig. 2. Absorbance spectra data for a mixture of S1 and anions: F−, Cl−, Br−, I−, AcO−, − − − − H2PO− 4 , HSO4 , ClO4 , CN , and SCN (50 equiv.) in the DMSO/H2O (v/v = 3:2) solution. − − − Inset: photograph of S1 upon adding of F−, Cl−, Br−, I−, AcO−, H2PO− 4 , HSO4 , ClO4 ,CN , and SCN−.
For 1H NMR titrations, two stock solutions were prepared in DMSOd6, one containing the sensor only and the second containing an appropriate concentration of the anion. Aliquots of the two solutions were mixed directly in NMR tube. 2.5. General procedure for test strips experiments Test strips were prepared by immersing filter papers into a DMSO/ H2O binary solution of S1 (0.01 M) following by exposing it to air to dry it. The test strips containing S1 were utilized to detect CN−. When CN− solution was added on the test kits, the fluorescence turn on response can be obvious observed under UV irradiation.
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 167 (2016) 101–105
Fig. 3. Fluorescence emission data for a mixture of S1 and anions: F−, Cl−, Br−, I−, AcO−, − − − − H2PO− 4 , HSO4 , ClO4 , CN , and SCN (50 equiv.) in the DMSO/H2O (v/v = 3:2) solution (λex = 420 nm). Inset: photograph of S1 upon adding of F−, Cl−, Br−, I−, AcO−, H2PO− 4 , − − − HSO− 4 , ClO4 , CN , and SCN .
yellow product S1. yield 71%, m. p 125 °C–127 °C; 1H NMR (DMSO-d6, 400 MHz) δ:10.32 (s, 1H), 8.95 (s, 1H), 7.87 (d, 2H), 7.75 (d, 3H), 7.71(t, 3H), 7.58 (m, 2H), 7.52 (t, 1H), 7.31 (t, 1H), 6.83 (m, 2H); 13C NMR (DMSO-d6, 100 MHz) δ: 197.19, 163.89, 158.97, 166.87, 135.41, 134.60, 134.18, 132.60, 132.19, 131.40, 130.07, 129.81, 129.30, 127.82, 120.05, 118.33, 116.88. IR (KBr, cm−1) ν: 3460.29, 3057.17, 1610.51, 1478.11, 1445.57, 1271.95, 1224.79, 970.19, 894.97, 750.54, 721.97, 685.06; ESI-MS m/z: (M + H)+ Calcd for C21H17N2O2 329.12; Found 329.17. The structure of sensor S1 was further confirmed by single-crystal X-ray diffraction a single crystal of probe suitable for X-ray crystallography was obtained by solvent diffusion method using ethyl acetate. The O (2)⋯ H (2) bond length in the first molecule was 0.82 nm, and the distance of H (2)⋯N (2) was 1.90 nm (Fig. 1). 3. Results and discussion A series of host-guest recognition experiments were performed to investigate the CN− recognition ability of the S1 in aqueous solution. The colorimetric and fluorimetric sensing abilities were mainly investigated by adding pure water with various anions to the DMSO/H2O (v/ v = 3:2). In the UV–vis spectrum of a solution of S1 in DMSO (2.0 × 10− 5 M), the strong and broad absorption at 355 nm
Fig. 4. Absorbance spectra of S1 in the presence of different concentration of CN− (0.0– 46.8 equiv.) in DMSO/H2O (v/v = 3:2).
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Fig. 5. Fluorescence spectra of S1 in the presence of different concentration of CN− (0.0– 13.2 equiv.) in DMSO/H2O (v/v = 3:2) solution.
disappeared, and at 425 nm a new absorption appeared when 50 equiv. CN− were added (Fig. 2). No significant UV–vis spectra change was observed when solutions of other anions such as F−, Cl−, Br−, I−, − − AcO−, H2PO− 4 , HSO4 , ClO4 , and SCN were added to the host solution. Meanwhile only the addition of cyanide displayed noticeable color changes from colorless to yellow could be distinguished by naked eyes in contrast to other anions and the other anions in the experiment including the more basic ones such as F− AcO− did not cause any obvious color and spectral changes. These results suggested that sensor S1 shows excellent selectivity for CN− over all other. As shown in Fig. 3, compound S1 alone displays a weak, single fluorescence emission band at 480 nm when excited at 420 nm in aqueous media DMSO/H2O (v/v = 3:2) solution. Only when CN− was added to the solution, chemosensor S1 produced a significant enhancement of fluorescence intensity at 528 nm (λex = 420 nm), which responded with a color change from colorless to yellow. However, other anion − − − such as F−, Cl−, Br−, I−, AcO−, H2PO− 4 , HSO4 , ClO4 , and SCN did not cause any significant changes in the fluorescence color and emission intensity. The fluorescence profiles at 528 nm showed a high selectivity for CN− in contrast to other anions. Indeed, such fluorescence enhancement can be distinguished with naked eyes. The binding properties of sensor S1 with CN− (0.01 M) were further studied by UV–vis titration experiments. As shown in Fig. 4, with the increasing concentrations of CN− (0.01 M) from 0.0–48.6 equiv. in DMSO/ H2O (v/v = 3:2) one absorption bands observed at 297 nm was clearly
Fig. 6. Fluorescence detection limit spectra of S1 (2.0 × 10−5 M) in H2O/DMSO (v/v = 3:2) solution upon addition of an increasing concentration of CN− (0.1 M).
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Fig. 7. The job's plot examined between CN− and S1 indicating the 1:1 stoichiometry, which was carried out by fluorescence spectra (λex = 420 nm).
declined and another one at 355 nm gradually showed bathochromic shift in the absorption band with Δλ = 70 nm, which was caused by the break of the hydrogen bonding. As a result, a new peak at 425 nm appeared. In addition, a well-defined isosbestic point was also noted at 383 nm, which indicated an interconversion into single discrete chemical species during the titration process.
Fluorescent titration was carried out to gain more insight into the recognition properties of receptor S1 as a CN− probe (Fig. 5). Due to the hydrogen of hydroxyl group and one nitrogen atoms molecular could form intramolecular hydrogen bond, when the molecules were stimulated, proton migration between oxygen and nitrogen atoms consumed some energy leading S1 fluorescence weak. With increasing addition of CN− (0.1 M), the emission band at 480 nm of chemosensor S1 get red-shifted and steadily increased. About 13.2 equiv. of cyanide ions was required for the complete change of the fluorescent response. The association constant for CN− was estimated to be 1.5 × 104 M− 1 in the same media [21]. In Fig. 6, it was easily seen that the fluorescence intensity change was almost linear with the on concentrations of CN− (0.1 M). The detection limit could be determined to be 6.17 × 10−8 M, as calculated on the basis of 3δ/S (where δ is the standard deviation of the blank solution and S is the slope of the calibration curve), which was much lower than the maximum contaminant level (MCL) of 1.9 × 10− 6 M for cyanide in drinking water by the World Health Organization (WHO). To know the stoichiometry between the guest (CN−) and host S1 molecule in DMSO/H2O (v/v = 3:2) solutions, job's plot has been drawn (Fig. 7). When the molar fraction of CN− (1 × 10−2 M) was 0.55, the intensity at 528 nm reached an extreme value, indicating the formation of a 1:1 complex between S1 and CN−. The pH dependence of sensor S1 in DMSO/H2O (v/v = 3:2) solution was also checked by UV–vis and fluorescence spectroscopy. Cyanide ions were added to the buffer solution of S1 at different pH values. This chemosensor can work in the pH range of 8.0–12.0 (Fig. S5).
Fig. 8. 1H NMR spectra (400 MHz, DMSO-d6) of free S1 and in the presence of CN−.
Scheme 2. The proposed reaction mechanism.
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 167 (2016) 101–105
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(v/v = 3:2) solutions. Moreover, the detection limit on fluorescence response of the sensor to CN− is down to 6.17 × 10−8 M. This sensing system shows many advantages. We believe that these characteristics of S1 make it attractive for further molecular modifications and underlying applications as a colorimetric and fluorimetric sensor for CN−. Acknowledgment This work was supported by the National Nature Science Foundation of China (no. 21467012). Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.saa.2016.05.017. References Fig. 9. Photographs of S1 (0.01 M) on test strips (a) only S1, (b) after immersion into water solutions with CN−, at room temperature and irradiation under UV light at 365 nm.
To explore the sensing mechanism of senor S1 to CN−, the 1H NMR titration was investigated, which illustrated the characteristic structural changes occurring upon interaction with CN−. As shown in the Fig. 8, sensor S1 showed two single peaks at 10.32 and 8.95 ppm in DMSOd6, which corresponded to the protons of –OH and CH_N. After adding 0.1 equiv. of CN− in DMSO, the –OH peak at 10.32 ppm disappeared. It was well logical that the –OH group due to strong acid was readily deprotonated when basic ions existed. Meanwhile with the increase of cyanide, the proton peak of CH_N and aromatic ring both decreased gradually and showed upfield shift. The existence of hydrogen bonding blocked intramolecular energy transfer, which is leading to host molecule could not show fluorescence. The addition of cyanide generated deprotonation causing the break of the hydrogen bonding and releasing energy by radioactive decay. As a result, S1-CN− shows strong yellow fluorescence. Based on the above findings, we propose that the reaction mechanism in this system may proceed through the route depicted in Scheme 2. In order to explore the Na+ whether influence the sensing, we used same anion sodium salts (NaF, NaCl, NaBr, NaI, AcONa, NaH2PO4, NaHSO4, NaClO4, NaCN, and NaSCN) instead of tetrabutylammonium to investigate changes of UV–vis and fluorescence spectroscopy. The experiment demonstrated the Na+ could not influence the sensing (Fig. S7 and Fig. S8). In addition, the interaction mechanism was further confirmed by the control experiments. The OH– acted as a good blank sample for CN−. When the solution of sensor S1 were added 50 equivalents of OH– in DMSO/H2O (v/v = 3:2) solution, changes in the UV–vis and fluorescence spectroscopy were the same as those observed for CN− (Fig. S9 and S10). The experiment demonstrated that the CN− response mechanism involves a deprotonation process in the sensor.
[1] a) b) [2] a) b) c) [3] a) b)
[4]
[5]
[6]
[7]
[8]
[9] [10]
[11]
[12]
4. Application [13]
To facilitate the use of S1 for the detection of cyanide, test strips were prepared by immersing filter papers into a DMSO/H2O (v/v = 3:2) binary solution of S1 (0.01 M) followed by its exposure to air for drying. As shown in the Fig. 9, interestingly, the fluorescence color changed immediately from blue to purple on the test papers were immersed into an aqueous solution (5 mM) of cyanide under UV irradiation. Hence, the test strips could conveniently detect CN− in solutions.
[14]
[15]
[16] [17]
5. Conclusion In conclusion, we have presented an efficient and simple chemosensor S1, which showed special selectivity and high sensitivity UV–vis absorption and fluorescence recognition for CN− in DMSO/H2O
[18] [19] [20] [21]
M.A. Holland, L.M. Kozlowski, Clin. Pharm. 5 (1986) 737–741; H. Khajehsharifi, M.M. Bordbar, Sensors Actuators B 209 (2015) 1015–1022. H.M. Nie, C.B. Gong, Q. Tang, X.B. Ma, Dyes Pigments 106 (2014) 74–80; Y. Sun, Y.L. Liu, M.L. Chen, W. Guo, Talanta 80 (2009) 996–1000; L. Deng, C.G. Chen, M. Zhou, Anal. Chem. 82 (2010) 4283–4287. E. Zeynep, Y.M. Deniz, E.U. Akkaya, Org. Lett. 10 (2008) 461–464; K.W. Kulig, Cyanide Toxicity, U.S. Department of Health and Human Services, Atlanta, GA, 1991; c) P. Singh, L.S. Mittal, S. Kumar, G. Bhargava, S. Kumar, J. Fluoresc. 24 (2014) 909–915. a) B. Sun, B.N. Noller, Water Res. 32 (1998) 3674–3698; b) M. Shahid, S.S. Razi, P. Srivastava, R. Ali, B. Maiti, Tetrahedron 68 (2012) 9076–9084. a) X. Zhou, W. Mu, X. Lv, D. Liu, Adv. 3 (2013) 22150–22154; b) J.H. Hu, N.P. Yan, J.J. Chen, J. Chem. Res. 36 (2012) 619–622; c) X. Liu, Q. Lin, T.B. Wei, Z.Y. Ming, New J. Chem. 38 (2014) 1418–1423. a) I. Jalal, F. Malek, A.E. Achari, Adv. 44 (2013) 22168–22175; b) P.M. Emilio, V.M. Díaz, T. Torres, E. Coronado, Adv. Funct. Mater. 16 (2006) 1166–1170. a) Q. Zhang, N. Maddukuri, M. Gong, J. Chromatogr. A. 1414 (2015) 158–162; b) A.B. Davis, R.E. Lambert, F.R. Fronczek, K.J. Wallace, New J. Chem. 38 (2014) 4678–4683; c) S.Y. Gwon, E.M. Lee, S.H. Kim, Spectrochim. Acta A Mol. Biomol. Spectrosc. 29 (2012) 77–81; d) G. Sivaraman, D. Chellappa, J. Mater. Chem. B 1 (2013) 5768–5772. a) Y.A. Son, S.Y. Gwon, S.H. Kim, Mol. Cryst. Liq. Cryst. 599 (2014) 16–22; b) G. Sivaraman, V. Sathiyaraja, D. Chellappa, J. Lumin. 145 (2014) 480–485; c) G. Sivaraman, T. Anand, ChemPlusChem 79 (2014) 1761–1766; d) R. Balasaravanan, V. Sadhasivam, G. Sivaraman, Asian J. Org. Chem. 5 (2016) 399–410. a) K. Paramjit, S. Divya, S. Kamaljit, Dalton Trans. 41 (2012) 9607–9610; b) H.Y. Xia, J.G. Li, G. Zou, J. Mater. Chem. A 1 (2013) 10713–10719. a) Z.P. Liu, X.Q. Wang, Z.H. Yang, W.J. He, J. Organomet. Chem. 76 (2011) 10286–10290; b) T. Anand, G. Sivaraman, A. Mahesh, D. Chellappa, Anal. Chim. Acta 853 (2015) 596–601; c) C. Arivazhagan, R. Borthakur, R. Jagan, S. Ghosh, Dalton Trans. 45 (2016) 5014–5020. a) Q. Lin, Y. Cai, Q. Li, T.B. Wei, Spectrochim. Acta A Mol. Biomol. Spectrosc. 141 (2015) 113–118; b) L.Y. Wang, G.P. Fang, D.R. Cao, Sensors Actuators B 221 (2015) 63–74; c) T. Anand, G. Sivaraman, Anal. Chim. Acta 853 (2015) 596–601. a) K. Vinod, R. Hemlata, M.P. Kaushik, Analyst 136 (2011) 1873–1880; b) T. Anand, G. Sivaraman, M. Iniya, A. Siva, D. Chellappa, Anal. Chim. Acta 876 (2015) 1–8. a) N.C. Desai, A.H. Makwana, R.D. Senta, J. Saudi Chem. Soc. 1 (2015) 1–9; b) G. Roman, Eur. J. Med. Chem. 89 (2015) 743–744. a) G. Dede, R. Bayrak, M. Er, J. Organomet. Chem. 740 (2013) 70–77; b) I. Alkorta, F. Blanco, J. Elguero, Arkivoc 7 (2008) 48–56; c) P. Zhang, B.B. Shi, T.B. Wei, Tetrahedron 10 (2014) 1889–1894. a) L.Y. Wang, J.J. Ou, G.P. Fang, D.R. Cao, Sensors Actuators B 222 (2015) 1184–1192; b) M.T. Kaczmarek, M. Kubicki, Z. Hnatejko, Polyhedron 102 (2015) 224–232. K. Karaoglu, K. Serbest, M. Emirik, E. Sahin, J. Organomet. Chem. 775 (2015) 80–87. a) M. Emirik, K. Karaoglu, K. Serbest, Polyhedron 88 (2015) 182–189; b) B. Ochiai, Y. Shimada, React. Funct. Polym. 71 (2011) 791–795; c) M. Pošta, J. Cermák, P. Vojtíšek, J. Sykora, I. Císarová, Inorg. Chim. Acta 362 (2009) 208–216. R.L. Sheng, P.F. Wang, W.M. Liu, Sensors Actuators B 128 (2008) 507–511. B. Lee, P. Kang, K.H. Lee, Tetrahedron Lett. 54 (2013) 1384–1388. C.X. Zhang, C.X. Liu, B.Y. Li, New J. Chem. 39 (2015) 1968–1973. Y. Liu, C.C. You, H.Y. Zhang, Supramol. Chem. (2001) 613–620.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A highly selective colorimetric and “turn-on” fluorimetric chemosensor for detecting CN− based on unsymmetrical azine derivatives in aqueous media You Sun, Jing-Han Hu ⁎, Jing Qi, Jian-Bin Li 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 18 January 2016 Received in revised form 3 May 2016 Accepted 14 May 2016 Available online 15 May 2016 Keywords: Cyanide anion Colorimetric Deprotonation Test strips
a b s t r a c t A novel highly selective chemosensor S1 for cyanide based on unsymmetrical azine derivative was successfully designed and synthesized, which showed both colorimetric and fluorescence turn-on responses for cyanide ions in aqueous. This structurally simple chemosensor could detect CN− anion over other anions in aqueous solution DMSO/H2O (v/v = 3:2) undergo deprotonation reaction. Results showed that the chemosensor S1 exhibited 50 fold enhancement in fluorescence at 530 nm and showed an obvious change in color from colorless to yellow that could be detected by naked eye under the UV-lamp after the addition of CN− in aqueous solution. Moreover, the detection limit on fluorescence response of the sensor to CN− is down to 6.17 × 10−8 M by titration method. Test strips based on S1 were obtain, which could be used as a convenient and efficient CN− test kit to detect CN− in aqueous solution. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Cyanide is highly toxic to humans and almost all other forms of life [1–2]. A significant proportion of victims among fire victims is due to cyanide poisoning, as blood cyanide concentrations reach a level of 23– 26 μM [3–4]. Despite cyanide toxicity, large quantities of cyanide salts are widely used in synthetic fibers, resins, herbicides, and the gold-extraction process [5]. The Environmental Protection Agency (EPA) has set the MCL (MCL: maximum contaminant level) of 1.9 × 10−6 M for cyanide in order to regulate safe levels for drinking water systems [6]. Rapid and accurate determination of cyanide would facilitate forensic investigation, medical diagnosis, and chronic cyanide monitoring. In this regard, chemosensor can be an important material to monitor these anions [7]. In addition, chemosensor can be simple and convenient with showing its optical change. [8–9] However, many kinds of colorimetric or fluorometric CN− selective receptors have been researched in organic media. Actually, in biological and environmental systems, anion-receptor interactions commonly occur in aqueous media [10]. Most of them suffer the severely interference from coexisting anions such as F−, AcO−, and H2PO− 4 . Few of them exhibit spectral changes in both absorption and emission spectra [11–12]. Therefore, the design of colorimetric and fluorimetric sensors for CN− in aqueous media is therefore currently the focus of attention.
⁎ Corresponding author. E-mail address: [email protected] (J.-H. Hu).
http://dx.doi.org/10.1016/j.saa.2016.05.017 1386-1425/© 2016 Elsevier B.V. All rights reserved.
Azines are attracting the increasing interests for their potential in medical, biological due to their antimicrobial, antibacterial activity [13]. In acyclic chemistry, the products of the reaction between one molecule hydrazine hydrate and two molecules of carbonyl compounds are called azines, among which the symmetrical compounds are widely applied [14]. In the aspect of recognition, numerous works devoted to studying structure of Schiff base complexes, however, the fluorescence properties of azines currently has yet to see the detailed report [15– 16]. As a matter, azine moieties, N-N linked diimines, are very tolerant to hydrolysis and have good ligating ability [17]. Sheng et al. have reported a symmetrical azine chemosensor for Hg2+, but for anion this kind of compound currently has yet to see the detailed report [18–19] (Fig. S6). We have synthesized a new asymmetrical azine chemosensor S1 synthesized with diphenyl diketone and salicylaldehyde hydrazone by one step (Scheme 1). This is a Chromo-fluorogenic anion receptor, which shows fluorescence and UV–vis spectra selectivity for CN− in DMSO/H2O (v/v = 3:2) binary solution over other anions. Chemosensor S1 could form a fine conjugate structure with azine moiety, as a result, the chemosensor has an excellent optical property to achieve nakedeye colorimetric and fluorimetric recognition. Meanwhile, salicylicaldehyde hydrazone provided an active hydrogen atom, which easily combined with strong alkaline ion CN− and allowed the receptors to tolerate a substantial amount of water from the solvent [20]. When CN− was added to the sensor solution, solution color changes from colorless to yellow and shows strong yellow fluorescence. According to the data, this was a deprotonation type reaction based for cyanide ion
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Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 167 (2016) 101–105
Scheme 1. Synthetic procedures for receptor S1.
detection at room temperature. The detection limit in fluorescence response of the sensor to CN− was down to 6.17 × 10−8 M. And the mechanism of this process was verified by spectroscopic methods including 1 H NMR, UV–vis, and mass spectrometry.
2. Experimental 2.1. Materials and physical methods
2.3. General procedure for fluorescence spectra experiments All the fluorescence spectra experiments were carried out in DMSO/ H2O (v/v = 3:2) solution on a Shimadzu RF-5301 spectrometer. Any changes in the fluorescence spectra of the synthesized compound were also recorded upon the addition of tetrabutylammonium anion salts and aqueous solution of NaCN while keeping the ligand concentration constant (2.0 × 10−5 M) in all experiment. The excitation wavelength was 420 nm.
All reagents were purchased from commercial supplies and used without further purification. Solvents and twice-distilled water were purified by standard methods. Fresh double distilled water was used throughout the experiment. All the tetrabutylammonium salts, salicylicaldehyde hydrazone, and diphenyl diketone were purchased from Alfa–Aesar Chemical Reagent Co, and stored in a vacuum desiccator. Chemical shifts are reported in ppm downfield from tetramethylsilane (TMS, δ scale with solvent resonances as internal standards) UV–vis spectra were recorded on a Shimadzu UV-2550 spectrometer. Photoluminescence spectra were recorded on a Shimadzu RF5301 fluorescence spectrophotometer. Melting points were measured on an X-4 digital melting-point apparatus purchased from Beijing Tech Instrument Co. Infrared spectra were recorded on a Digital FTS3000 FT-IR spectrophotometer.
2.4. General procedure for 1H NMR experiments
2.2. General procedure for UV–vis experiments
2.6. Synthesis of S1
All the UV–vis experiments were carried out just after the addition of − tetrabutylammonium anion salt of F−, Cl−, Br−, I−, AcO−, H2PO− 4 , HSO4 − − −2 , ClO− , SCN but CN was prepared in NaCN (1 × 10 M) in DMSO/ 4 H2O (v/v = 3:2) solution, while keeping the ligand concentration constant (2.0 × 10−5 M) in all experiment on a Shimadzu UV-2550 spectrometer.
The synthesis route of sensor S1 is demonstrated in Scheme 1. An ethanol solution (25 mL) of diphenyl diketone (1.1 g, 5 mmol), salicylaldehyde hydrazone (0.68 g, 5 mmol) and catalytic amount of acetic acid (AcOH) were stirred under reflux 6 h. After cooling to room temperature, the yellow precipitate was filtered, washed with hot absolute ethanol three times, then recrystallized with ethyl acetate to get
Fig. 1. Single-crystal X-ray structure of sensor S1.
Fig. 2. Absorbance spectra data for a mixture of S1 and anions: F−, Cl−, Br−, I−, AcO−, − − − − H2PO− 4 , HSO4 , ClO4 , CN , and SCN (50 equiv.) in the DMSO/H2O (v/v = 3:2) solution. − − − Inset: photograph of S1 upon adding of F−, Cl−, Br−, I−, AcO−, H2PO− 4 , HSO4 , ClO4 ,CN , and SCN−.
For 1H NMR titrations, two stock solutions were prepared in DMSOd6, one containing the sensor only and the second containing an appropriate concentration of the anion. Aliquots of the two solutions were mixed directly in NMR tube. 2.5. General procedure for test strips experiments Test strips were prepared by immersing filter papers into a DMSO/ H2O binary solution of S1 (0.01 M) following by exposing it to air to dry it. The test strips containing S1 were utilized to detect CN−. When CN− solution was added on the test kits, the fluorescence turn on response can be obvious observed under UV irradiation.
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Fig. 3. Fluorescence emission data for a mixture of S1 and anions: F−, Cl−, Br−, I−, AcO−, − − − − H2PO− 4 , HSO4 , ClO4 , CN , and SCN (50 equiv.) in the DMSO/H2O (v/v = 3:2) solution (λex = 420 nm). Inset: photograph of S1 upon adding of F−, Cl−, Br−, I−, AcO−, H2PO− 4 , − − − HSO− 4 , ClO4 , CN , and SCN .
yellow product S1. yield 71%, m. p 125 °C–127 °C; 1H NMR (DMSO-d6, 400 MHz) δ:10.32 (s, 1H), 8.95 (s, 1H), 7.87 (d, 2H), 7.75 (d, 3H), 7.71(t, 3H), 7.58 (m, 2H), 7.52 (t, 1H), 7.31 (t, 1H), 6.83 (m, 2H); 13C NMR (DMSO-d6, 100 MHz) δ: 197.19, 163.89, 158.97, 166.87, 135.41, 134.60, 134.18, 132.60, 132.19, 131.40, 130.07, 129.81, 129.30, 127.82, 120.05, 118.33, 116.88. IR (KBr, cm−1) ν: 3460.29, 3057.17, 1610.51, 1478.11, 1445.57, 1271.95, 1224.79, 970.19, 894.97, 750.54, 721.97, 685.06; ESI-MS m/z: (M + H)+ Calcd for C21H17N2O2 329.12; Found 329.17. The structure of sensor S1 was further confirmed by single-crystal X-ray diffraction a single crystal of probe suitable for X-ray crystallography was obtained by solvent diffusion method using ethyl acetate. The O (2)⋯ H (2) bond length in the first molecule was 0.82 nm, and the distance of H (2)⋯N (2) was 1.90 nm (Fig. 1). 3. Results and discussion A series of host-guest recognition experiments were performed to investigate the CN− recognition ability of the S1 in aqueous solution. The colorimetric and fluorimetric sensing abilities were mainly investigated by adding pure water with various anions to the DMSO/H2O (v/ v = 3:2). In the UV–vis spectrum of a solution of S1 in DMSO (2.0 × 10− 5 M), the strong and broad absorption at 355 nm
Fig. 4. Absorbance spectra of S1 in the presence of different concentration of CN− (0.0– 46.8 equiv.) in DMSO/H2O (v/v = 3:2).
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Fig. 5. Fluorescence spectra of S1 in the presence of different concentration of CN− (0.0– 13.2 equiv.) in DMSO/H2O (v/v = 3:2) solution.
disappeared, and at 425 nm a new absorption appeared when 50 equiv. CN− were added (Fig. 2). No significant UV–vis spectra change was observed when solutions of other anions such as F−, Cl−, Br−, I−, − − AcO−, H2PO− 4 , HSO4 , ClO4 , and SCN were added to the host solution. Meanwhile only the addition of cyanide displayed noticeable color changes from colorless to yellow could be distinguished by naked eyes in contrast to other anions and the other anions in the experiment including the more basic ones such as F− AcO− did not cause any obvious color and spectral changes. These results suggested that sensor S1 shows excellent selectivity for CN− over all other. As shown in Fig. 3, compound S1 alone displays a weak, single fluorescence emission band at 480 nm when excited at 420 nm in aqueous media DMSO/H2O (v/v = 3:2) solution. Only when CN− was added to the solution, chemosensor S1 produced a significant enhancement of fluorescence intensity at 528 nm (λex = 420 nm), which responded with a color change from colorless to yellow. However, other anion − − − such as F−, Cl−, Br−, I−, AcO−, H2PO− 4 , HSO4 , ClO4 , and SCN did not cause any significant changes in the fluorescence color and emission intensity. The fluorescence profiles at 528 nm showed a high selectivity for CN− in contrast to other anions. Indeed, such fluorescence enhancement can be distinguished with naked eyes. The binding properties of sensor S1 with CN− (0.01 M) were further studied by UV–vis titration experiments. As shown in Fig. 4, with the increasing concentrations of CN− (0.01 M) from 0.0–48.6 equiv. in DMSO/ H2O (v/v = 3:2) one absorption bands observed at 297 nm was clearly
Fig. 6. Fluorescence detection limit spectra of S1 (2.0 × 10−5 M) in H2O/DMSO (v/v = 3:2) solution upon addition of an increasing concentration of CN− (0.1 M).
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Fig. 7. The job's plot examined between CN− and S1 indicating the 1:1 stoichiometry, which was carried out by fluorescence spectra (λex = 420 nm).
declined and another one at 355 nm gradually showed bathochromic shift in the absorption band with Δλ = 70 nm, which was caused by the break of the hydrogen bonding. As a result, a new peak at 425 nm appeared. In addition, a well-defined isosbestic point was also noted at 383 nm, which indicated an interconversion into single discrete chemical species during the titration process.
Fluorescent titration was carried out to gain more insight into the recognition properties of receptor S1 as a CN− probe (Fig. 5). Due to the hydrogen of hydroxyl group and one nitrogen atoms molecular could form intramolecular hydrogen bond, when the molecules were stimulated, proton migration between oxygen and nitrogen atoms consumed some energy leading S1 fluorescence weak. With increasing addition of CN− (0.1 M), the emission band at 480 nm of chemosensor S1 get red-shifted and steadily increased. About 13.2 equiv. of cyanide ions was required for the complete change of the fluorescent response. The association constant for CN− was estimated to be 1.5 × 104 M− 1 in the same media [21]. In Fig. 6, it was easily seen that the fluorescence intensity change was almost linear with the on concentrations of CN− (0.1 M). The detection limit could be determined to be 6.17 × 10−8 M, as calculated on the basis of 3δ/S (where δ is the standard deviation of the blank solution and S is the slope of the calibration curve), which was much lower than the maximum contaminant level (MCL) of 1.9 × 10− 6 M for cyanide in drinking water by the World Health Organization (WHO). To know the stoichiometry between the guest (CN−) and host S1 molecule in DMSO/H2O (v/v = 3:2) solutions, job's plot has been drawn (Fig. 7). When the molar fraction of CN− (1 × 10−2 M) was 0.55, the intensity at 528 nm reached an extreme value, indicating the formation of a 1:1 complex between S1 and CN−. The pH dependence of sensor S1 in DMSO/H2O (v/v = 3:2) solution was also checked by UV–vis and fluorescence spectroscopy. Cyanide ions were added to the buffer solution of S1 at different pH values. This chemosensor can work in the pH range of 8.0–12.0 (Fig. S5).
Fig. 8. 1H NMR spectra (400 MHz, DMSO-d6) of free S1 and in the presence of CN−.
Scheme 2. The proposed reaction mechanism.
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(v/v = 3:2) solutions. Moreover, the detection limit on fluorescence response of the sensor to CN− is down to 6.17 × 10−8 M. This sensing system shows many advantages. We believe that these characteristics of S1 make it attractive for further molecular modifications and underlying applications as a colorimetric and fluorimetric sensor for CN−. Acknowledgment This work was supported by the National Nature Science Foundation of China (no. 21467012). Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.saa.2016.05.017. References Fig. 9. Photographs of S1 (0.01 M) on test strips (a) only S1, (b) after immersion into water solutions with CN−, at room temperature and irradiation under UV light at 365 nm.
To explore the sensing mechanism of senor S1 to CN−, the 1H NMR titration was investigated, which illustrated the characteristic structural changes occurring upon interaction with CN−. As shown in the Fig. 8, sensor S1 showed two single peaks at 10.32 and 8.95 ppm in DMSOd6, which corresponded to the protons of –OH and CH_N. After adding 0.1 equiv. of CN− in DMSO, the –OH peak at 10.32 ppm disappeared. It was well logical that the –OH group due to strong acid was readily deprotonated when basic ions existed. Meanwhile with the increase of cyanide, the proton peak of CH_N and aromatic ring both decreased gradually and showed upfield shift. The existence of hydrogen bonding blocked intramolecular energy transfer, which is leading to host molecule could not show fluorescence. The addition of cyanide generated deprotonation causing the break of the hydrogen bonding and releasing energy by radioactive decay. As a result, S1-CN− shows strong yellow fluorescence. Based on the above findings, we propose that the reaction mechanism in this system may proceed through the route depicted in Scheme 2. In order to explore the Na+ whether influence the sensing, we used same anion sodium salts (NaF, NaCl, NaBr, NaI, AcONa, NaH2PO4, NaHSO4, NaClO4, NaCN, and NaSCN) instead of tetrabutylammonium to investigate changes of UV–vis and fluorescence spectroscopy. The experiment demonstrated the Na+ could not influence the sensing (Fig. S7 and Fig. S8). In addition, the interaction mechanism was further confirmed by the control experiments. The OH– acted as a good blank sample for CN−. When the solution of sensor S1 were added 50 equivalents of OH– in DMSO/H2O (v/v = 3:2) solution, changes in the UV–vis and fluorescence spectroscopy were the same as those observed for CN− (Fig. S9 and S10). The experiment demonstrated that the CN− response mechanism involves a deprotonation process in the sensor.
[1] a) b) [2] a) b) c) [3] a) b)
[4]
[5]
[6]
[7]
[8]
[9] [10]
[11]
[12]
4. Application [13]
To facilitate the use of S1 for the detection of cyanide, test strips were prepared by immersing filter papers into a DMSO/H2O (v/v = 3:2) binary solution of S1 (0.01 M) followed by its exposure to air for drying. As shown in the Fig. 9, interestingly, the fluorescence color changed immediately from blue to purple on the test papers were immersed into an aqueous solution (5 mM) of cyanide under UV irradiation. Hence, the test strips could conveniently detect CN− in solutions.
[14]
[15]
[16] [17]
5. Conclusion In conclusion, we have presented an efficient and simple chemosensor S1, which showed special selectivity and high sensitivity UV–vis absorption and fluorescence recognition for CN− in DMSO/H2O
[18] [19] [20] [21]
M.A. Holland, L.M. Kozlowski, Clin. Pharm. 5 (1986) 737–741; H. Khajehsharifi, M.M. Bordbar, Sensors Actuators B 209 (2015) 1015–1022. H.M. Nie, C.B. Gong, Q. Tang, X.B. Ma, Dyes Pigments 106 (2014) 74–80; Y. Sun, Y.L. Liu, M.L. Chen, W. Guo, Talanta 80 (2009) 996–1000; L. Deng, C.G. Chen, M. Zhou, Anal. Chem. 82 (2010) 4283–4287. E. Zeynep, Y.M. Deniz, E.U. Akkaya, Org. Lett. 10 (2008) 461–464; K.W. Kulig, Cyanide Toxicity, U.S. Department of Health and Human Services, Atlanta, GA, 1991; c) P. Singh, L.S. Mittal, S. Kumar, G. Bhargava, S. Kumar, J. Fluoresc. 24 (2014) 909–915. a) B. Sun, B.N. Noller, Water Res. 32 (1998) 3674–3698; b) M. Shahid, S.S. Razi, P. Srivastava, R. Ali, B. Maiti, Tetrahedron 68 (2012) 9076–9084. a) X. Zhou, W. Mu, X. Lv, D. Liu, Adv. 3 (2013) 22150–22154; b) J.H. Hu, N.P. Yan, J.J. Chen, J. Chem. Res. 36 (2012) 619–622; c) X. Liu, Q. Lin, T.B. Wei, Z.Y. Ming, New J. Chem. 38 (2014) 1418–1423. a) I. Jalal, F. Malek, A.E. Achari, Adv. 44 (2013) 22168–22175; b) P.M. Emilio, V.M. Díaz, T. Torres, E. Coronado, Adv. Funct. Mater. 16 (2006) 1166–1170. a) Q. Zhang, N. Maddukuri, M. Gong, J. Chromatogr. A. 1414 (2015) 158–162; b) A.B. Davis, R.E. Lambert, F.R. Fronczek, K.J. Wallace, New J. Chem. 38 (2014) 4678–4683; c) S.Y. Gwon, E.M. Lee, S.H. Kim, Spectrochim. Acta A Mol. Biomol. Spectrosc. 29 (2012) 77–81; d) G. Sivaraman, D. Chellappa, J. Mater. Chem. B 1 (2013) 5768–5772. a) Y.A. Son, S.Y. Gwon, S.H. Kim, Mol. Cryst. Liq. Cryst. 599 (2014) 16–22; b) G. Sivaraman, V. Sathiyaraja, D. Chellappa, J. Lumin. 145 (2014) 480–485; c) G. Sivaraman, T. Anand, ChemPlusChem 79 (2014) 1761–1766; d) R. Balasaravanan, V. Sadhasivam, G. Sivaraman, Asian J. Org. Chem. 5 (2016) 399–410. a) K. Paramjit, S. Divya, S. Kamaljit, Dalton Trans. 41 (2012) 9607–9610; b) H.Y. Xia, J.G. Li, G. Zou, J. Mater. Chem. A 1 (2013) 10713–10719. a) Z.P. Liu, X.Q. Wang, Z.H. Yang, W.J. He, J. Organomet. Chem. 76 (2011) 10286–10290; b) T. Anand, G. Sivaraman, A. Mahesh, D. Chellappa, Anal. Chim. Acta 853 (2015) 596–601; c) C. Arivazhagan, R. Borthakur, R. Jagan, S. Ghosh, Dalton Trans. 45 (2016) 5014–5020. a) Q. Lin, Y. Cai, Q. Li, T.B. Wei, Spectrochim. Acta A Mol. Biomol. Spectrosc. 141 (2015) 113–118; b) L.Y. Wang, G.P. Fang, D.R. Cao, Sensors Actuators B 221 (2015) 63–74; c) T. Anand, G. Sivaraman, Anal. Chim. Acta 853 (2015) 596–601. a) K. Vinod, R. Hemlata, M.P. Kaushik, Analyst 136 (2011) 1873–1880; b) T. Anand, G. Sivaraman, M. Iniya, A. Siva, D. Chellappa, Anal. Chim. Acta 876 (2015) 1–8. a) N.C. Desai, A.H. Makwana, R.D. Senta, J. Saudi Chem. Soc. 1 (2015) 1–9; b) G. Roman, Eur. J. Med. Chem. 89 (2015) 743–744. a) G. Dede, R. Bayrak, M. Er, J. Organomet. Chem. 740 (2013) 70–77; b) I. Alkorta, F. Blanco, J. Elguero, Arkivoc 7 (2008) 48–56; c) P. Zhang, B.B. Shi, T.B. Wei, Tetrahedron 10 (2014) 1889–1894. a) L.Y. Wang, J.J. Ou, G.P. Fang, D.R. Cao, Sensors Actuators B 222 (2015) 1184–1192; b) M.T. Kaczmarek, M. Kubicki, Z. Hnatejko, Polyhedron 102 (2015) 224–232. K. Karaoglu, K. Serbest, M. Emirik, E. Sahin, J. Organomet. Chem. 775 (2015) 80–87. a) M. Emirik, K. Karaoglu, K. Serbest, Polyhedron 88 (2015) 182–189; b) B. Ochiai, Y. Shimada, React. Funct. Polym. 71 (2011) 791–795; c) M. Pošta, J. Cermák, P. Vojtíšek, J. Sykora, I. Císarová, Inorg. Chim. Acta 362 (2009) 208–216. R.L. Sheng, P.F. Wang, W.M. Liu, Sensors Actuators B 128 (2008) 507–511. B. Lee, P. Kang, K.H. Lee, Tetrahedron Lett. 54 (2013) 1384–1388. C.X. Zhang, C.X. Liu, B.Y. Li, New J. Chem. 39 (2015) 1968–1973. Y. Liu, C.C. You, H.Y. Zhang, Supramol. Chem. (2001) 613–620.