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Colorimetric and fluorescent chemosensor for highly selective and sensitive relay detection of Cu2 + and H2PO4− in aqueous media
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 182 (2017) 67–72
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Colorimetric and fluorescent chemosensor for highly selective and sensitive relay detection of Cu2 + and H2PO− 4 in aqueous media Jun-Xia Su, Xiao-Ting Wang, Jing Chang, Gui-Yuan Wu, Hai-Ming Wang, Hong Yao, Qi Lin, You-Ming Zhang ⁎, Tai-Bao Wei ⁎ Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, PR China
a r t i c l e
i n f o
Article history: Received 8 September 2016 Received in revised form 27 March 2017 Accepted 30 March 2017 Available online 31 March 2017 Keywords: Colorimetric Fluorescence Chemosensor Copper (II) complex H2PO− 4 Aqueous media
a b s t r a c t In this manuscript, a new colorimetric and fluorescent chemosensor (T) was designed and synthesized, it could successively detect Cu2+ and H2PO− 4 in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution with high selectivity and sensitivity. When added Cu2+ ions into the solution of T, it showed a color changes from yellow to colorless, meanwhile, the green fluorescence of sensor T quenched. This recognition behavior was not affected in the presence of other cations, including Hg2+, Ag+, Ca2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, and Mg2+ ions. More interestingly, the Cu2+ ions contain sensor T solution could recover the color and fluorescence upon the addition of − − − − − − − H2PO− 4 anions in the same medium. And other surveyed anions (including F , Cl , Br , I , AcO , HSO4 , ClO4 , − − 2+ CN and SCN ) had nearly no influence on the recognition behavior. The detection limits of T to Cu and T−8 M and 0.994 × 10−7 M, respectively. In addition, the sensor Cu2+ to H2PO− 4 were evaluated to be 1.609 × 10 T also could be served as a recyclable component and the logic gate output was also defined in sensing materials. The test strips based on sensor T were fabricated, which acted as a convenient and efficient Cu2+ and H2PO− 4 test kits. © 2017 Published by Elsevier B.V.
1. Introduction In recent years, the role of ions, especially the transition-metal ions and some poisonous anions in environment and organism, had attracted increasing attention. In addition to zinc and iron ions, cupric ion was the third most abundant essential trace element in humans [1], which played an irreplaceable role in cellular processes, such as functional and structural strengthening of proteins and gene expression, even nervous system [2]. Cupric ion can disrupt normal activity of the life system and lead to various diseases if the concentration of detected is higher or lower than the desire demand of cells, for instance, Alzheimer's disease, Menkes Wilson disease and Prion diseases [3]. From the U.S. Environmental Protection Agency (EPA) it could be known, in drinking water, the maximum concentration of Cu2+ ion is 1.3 ppm (about 20 M) [4]. As one of in major equilibrium with two and PO3− at physiological pH, H2PO− other basic anions HPO2− 4 4 4 anion has become a research target as well as challenging for sensing anions, also owing to the key role in biological significance [5], such as energy storage, signal transduction and gene constructs and so forth [6]. So,
⁎ Corresponding authors. E-mail addresses: [email protected] (Y.-M. Zhang), [email protected] (T.-B. Wei).
http://dx.doi.org/10.1016/j.saa.2017.03.071 1386-1425/© 2017 Published by Elsevier B.V.
the design and synthesis of chemosensors for selectively and sensitively detecting phosphates anions has attracted lively interest. The design and development of optical sensing approaches for the detection of various transition metal ions and toxic anion are significant because of their vital roles in different biological and environmental field [7]. As a consequence, various analytical techniques have been proposed to determine cupric ion such as atomic absorption spectrometry (AAS) [8], inductively coupled plasma emission spectrometry [9], gravimetric, chromatography, anodic stripping voltammetry [10], ion selective electrodes [11] and so on, but most of these methods require time consuming, well-controlled experimental conditions, complicated sample pretreatment and inherent high cost [12]. As an alternative to these methods, due to the advantages of cheap, simple, highly sensitivity, selectivity and low detection concentration [13], colorimetric and fluorescent chemosensor have received considerable attention detection of various ions. And a multitude of fluorescent sensors with singleness of ions have also been synthesized [14]. In the process of detecting the transition metal ions, Cu is an essential element for all living systems, however, the copper chemosensors reported have drawbacks, such as fussy synthesize steps, requirement of anhydrous solvents for sensing, and the interferences from other metal ions, therefore, there is a need chemosensor for easy to synthesize and also highly selectively detection of Cu2+ in aqueous medium [15]. Our research group had a long standing interest in molecular and
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ionic recognition [16]. Herein, we reported a new chemosensor T, which could successively detect Cu2+ and H2PO− 4 in DMSO/H2O (v/v = 9:1, pH = 7.2) with high selectivity. Due to the capable of forming coordinate bonds between Schiff-bases and metal ions through phenolic group and azomethine groups, then we designed the imine-bound as the recognize side and the N,N-diethyl as the fluorescence signal report group, respectively. Consequently, we obtained a great dual-channel sensor for Cu2+ ions, meanwhile, the Cu2+ complex of the sensor also can selectively detect H2PO− 4 by colorimetric and fluorescent method in the aqueous media. 2. Experimental 2.1. Synthesis of Sensor T The synthesis process was shown in Scheme 1, N,N-diethyl salicylaldehyde (4 mmol, 0.77 g), 1,5-naphthalenediamine (1.5 mmol, 0.24 g), and acetic acid (AcOH) as a catalytic, which was stirred under reflux condition for 8 h in DMF (30 mL), after cooling to room temperature, the yellow product was filtrated, washed with hot absolute ethanol three times, then recrystallized with DMF-CH3CH2OH to get yellow powdery T (1 mmol, 0.63 g) in 83% yield (m.p. N 300 °C). 1 H NMR (CDCl3, 600 MHz, Fig. S18) δ 13.90 (s, 2H, –OH), 8.51 (s, 2H, C\\H), 8.18–8.17 (d, 2H), 7.51–7.49 (m, 2H), 7.24–7.23 (d, 2H), 7.19– 7.18 (d, 2H), 6.30–6.26 (m, 4H), 3.45–3.42 (q, 8H, –CH2), 1.25–1.22 (t, 12H, –CH3). ESI-MS (Fig. S16): m/z (M + H)+, calcd for [C32H36N4O2] 508.28, found: 509.26. IR (KBr, cm−1, Fig. S15), v/cm− 1: 3435 (OH), 1244–1582 (C_C), 1620 (C_N). 3. Results and Discussion 3.1. Solvent Effect of Sensor T and T-Cu2+ As showed in Figs. S1 and S2, solvent effect of sensor T and T-Cu2+ were be done to find the suitable solvent. From these two pictures we knew that host T had fluorescence in THF, DMSO, DMF solution. Only in THF solution, T-Cu2+ had weak fluorescence, and the fluorescence was quenched in DMSO solution. In the basis of these properties, in consideration of the harmfulness of other solutions, DMSO solution was chose the best solution to complete this recognition experiment. 3.2. UV/Vis and Flourescent Signaling of Cu2+ The recognition profiles of the chemosensor T toward various metal cations, including Hg2 +, Ag+, Ca2 +, Cu2 +, Co2 +, Ni2 +, Cd2 +, Pb2 +, Zn2+, Cr3+, and Mg2+ were primarily investigated by UV/Vis spectroscopy and fluorescence spectroscopy in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. Interaction of T with 20 equivalents of various metal ions as its perchlorate salt did not result in any significant changes in the absorption spectrum except Cu2+. As shown in Fig. S3, The absorption spectrum of compound T and other ions except Cu2 + in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution exhibits absorption band at 418 nm, the color of T was change from yellow to colorless, and realized the naked eye recognition to Cu2+ ions. To further investigate the interaction between T and Cu2 +, UV/Vis absorption spectral variation of sensor T in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution was monitored during titration with different concentrations of Cu2+ from 0 to 9.2 equivalents. As shown in Fig. S4, upon addition of Cu2+
ions, the absorption band at 418 nm was blue-shifted to 386 nm and at 290 nm appeared a new absorption band, indicating formation of TCu complex (Fig. S4). In the fluorescence spectrum, sensor T emitted very intensively. At 418 nm, the maximum emission wavelength of T was 498 nm in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. The DMSO solution of 20 equivalents of Cu2+ ions were added to the T to a final concentration of 20 μM, leading to a strong green fluorescence decrease rapidly, meanwhile, the fluorescence emission band at 498 nm was blue-shifted to 480 nm (Fig. S5). The fluorescence change was attributed to the formation of the T-Cu complex that the interaction between Cu2+ ions and the hydrogen atom of hydroxyl groups and the nitrogen atom of amino groups. For a better understanding of the binding mode, the fluorescence titration experiments were carried out in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution and a maximum excitation wavelength of 418 nm was selected. As shown in Fig. S6(a), it could cause fluorescence quenching with about 20 nm blue-shift in their emission maxima spectrum when adding 2.1 equivalents Cu2+ ions. Furthermore, the result in the color change from yellow to colorless detected could be clearly observed by the naked eye under UV-lamp/day light at room temperature. Upon addition of Cu2+, chemosensor T showed a apparent change in its UV/Vis spectrum (Fig. S4) and the appearance of new band at 386 nm and increase at 290 nm in their absorbance. On the other hand, the bands observed at 418 nm exhibit a decrease. The blue-shift of 38 nm was attributed to the coordination effect of Cu2+ with T via O from – OH and N by the deprotonation of Schiff-base NH proton. This phenomenon can be interpreted as the broken conjugated structure of T. The detection limit of chemosensor T was evaluated to be 1.609 × 10−8 M (Fig. S12) and the determination of association constant was 1.19 × 109 M−2, the job plot of UV/Vis, fluorescence and MS showed that binding between T and Cu2+ were 1:1 stoichiometry (Fig. S7, Fig. S8 and Fig. S9). As showed in Fig. S8, when the stoichiometry reached to 1:1, the most weak fluorescence could be observable, this situation was also showed in UV/Vis absorbance (Fig. S7). In addition, the ES-MS in the Fig. S9, 568 [T + Cu2 +] + H+ (z = 1) and 633 [T + Cu2 +] + Cu2 + (z = 2) could be received. An important aspect of many prospective metal ion sensors is their ability to detect Cu2+ (target metal ion) selectively over other competing metal ions. To establish the selectivity of T toward Cu2+ over a range of various metallic cations (Hg2+, Ag+, Ca2+, Co2+, Ni2+,Cd2+, Pb2+, Zn2 +, Cr3 + and Mg2 +). We carried out the competitive recognition studies during which the other cations were used in higher concentrations (4 × 10−3 M). From the bar diagram, we could easily understand that the effects on emission intensity of T upon the addition of higher concentrations (4 × 10− 3 M) of various ions were almost negligible. Therefore, it was clear that other ions' interference was negligibly small during the process of detection of Cu2+ ions (Fig. S10). These results further suggested that T could be used as a chemosensor for Cu2+ over a wide range of cations. 3.3. UV/Vis and Flourescent Signaling of H2PO− 4 2+ Considering the possible stability constant of H2PO− , T4 and Cu Cu complex was expected to act as a chemosensing ensemble for H2PO− 4 recognition. So we introduced the anions selectively recognition by adding various anions into the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution of sensor T-Cu2+. Thus, the sensor T-Cu was prepared 2+
Scheme 1. Synthesis route of benzindo indolium croconine.
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in situ by addition of 20 equivalents of Cu2+ to T solution (2 × 10−5 M). The response of T-Cu solution to a variety of anions (including H2PO− 4 , − − − F−, Cl−, Br−, I−, AcO−, HSO− 4 , ClO4 , SCN and CN ) were subsequently investigated in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. Amazingly, upon addition of H2PO− 4 (tetra-butyl ammonium salt 50 equiv. to T) to the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution of T-Cu, it responded with a dramatic color change, the apparent color change from colorless to yellow could be distinguished by naked eye (Fig. 1). To further investigate the interaction between T-Cu and H2PO− 4 , UV/ Vis absorption spectral variation of sensor T-Cu was monitored during titration with different concentrations of H2PO− 4 from 0 to 8.8 equivalents. As shown in Fig. 2(a), with increasing concentrations of H2PO− 4 , the gradually decreased absorbance band at 386 nm and the gradually increased absorbance band at 418 nm were clearly observed, respectively. As showed in Fig. 3, When 50 equivalents of anions (including − − − − − − − − and CN−) was H2PO− 4 , F , Cl , Br , I , AcO , HSO4 , ClO4 , SCN added to the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution of sensors T-Cu, the fluorescence was recovered by H2PO− 4 and none of other anions induced any significant changes in the fluorescent spectrum of the sensor. The H2PO− 4 sensing property of T-Cu was then evaluated by fluorescence titration experiments and the results were depicted in Fig. 4(a), upon incremental addition of H2PO− 4 into T-Cu the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution, the fluorescence intensity increased gradually and reached saturation when 6.16
Fig. 2. (a) Absorbance spectra of T-Cu in the presence of different concentration of H2PO− 4 (0–8.8 equiv.) in DMSO/H2O (v/v = 9:1, pH = 7.2). (b) A plot of absorbance depending on − the concentration of H2PO4 in the range from 0 to 8.8 equivalents, the detection wavelength was 418 nm.
equivalents of H2PO− 4 (relative to T) was introduced. During the titration process, the emission band maximum of the solution was gradually red shifted from 480 nm to 498 nm with the increasing concentration of
Fig. 1. (a) Absorbance data for a mixture of T-Cu and each of the various anions in the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. Inset: color changes observed for T− − − − − − − − − Cu upon the addition of H2PO− 4 , F , Cl , Br , I , AcO , HSO4 , ClO4 , SCN and CN (50 equiv., respectively); (b) Absorbance data for T, T + Cu2+ and T-Cu + H2PO− 4 .
Fig. 3. Visual fluorescence emissions of sensor T-Cu after the addition of different anions in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution (λex = 418 nm). Inset: visual − − − − fluorescence photograph of sensor T-Cu after the addition of H2PO− 4 , F , Cl , Br , I , − − − , ClO , SCN and CN on excitation at 418 nm using UV-lamp at room AcO−, HSO− 4 4 temperature.
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Fig. 6. The Job's plot of fluorescence examined between T-Cu2+ and H2PO− 4 , indicating the 1:2 stoichiometric.
H2PO− 4 anions, which indicated that the form of T-Cu was changed after the H2PO− 4 anions addition. The detection limit of the sensor toward −7 M (Fig. S13), which indicated that this sensor H2PO− 4 was 0.994 × 10 can potentially be used as a probe for H2PO− 4 monitoring.
Subsequently, fluorescence competition experiments were conducted to further evaluate the tolerance of T-Cu to other anions. The results showed that coexistence of equal amount of other anions didn't induce any significant interference on the H2PO− 4 recognition (Fig. 5). The results of these competition experiments also revealed that the H2PO− 4 recognition by sensor T-Cu had an excellent anti-jamming ability. The Job's plot of fluorescence examined between T-Cu2+ and H2PO− 4 (Fig. 6), indicating the 1:2 stoichiometric. As shown in Fig.7, as a crucial aspect for chemical sensor, the reversibility in the response of T has been verified during its five cycles of titrations carried out with Cu2+ followed by H2PO− 4 exhibited alternating enhancing and quenching processes in a sequence, In addition, the Cu2+ exhibited a remarkable fluorescence quenching by showing OFF behavior through complex formation. The addition of an excess amount of TBAH2PO4 to the complex of T and Cu2+ resulted in changing of the fluorescence intensity and acted as an ON switch. This “ON-OFF-ON” switching process could be repeated several times with little fluorescence efficiency loss. Since the fluorescence intensity of sensor T could be controlled by alternative addition of Cu2+ and H2PO− 4 ions, the fluorescence emission of T can be defined as the logic gate output. Here, the actual results from an experiment are shown in Scheme 2, using the Cu2+ and H2PO− 4 ions as inputs while the emission intensity at 498 nm (I = 498) acts as the
Fig. 5. The fluorescence spectra changes of T-Cu to various anions. The black bars represent the fluorescence intensity of T-Cu in the presence of various anions, the red bars represent the fluorescence intensity of the above solution upon addition of H2PO− 4 (λem = 498 nm). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Emission spectra showing the reversible complexation between T and Cu2+ by introduction of H2PO− 4 ions.
Fig. 4. (a) Fluorescence spectra of T-Cu in the presence of different concentrations of Cu2+ (0–6.16 equiv.) in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. (b) A plot of fluorescence intensity depending on the concentration of H2PO− 4 in the range from 0 to 6.16 equivalents, the detection wavelength was 498 nm.
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Fig. 9. Photographs of T-Cu on test papers after immersion into DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution under irradiation at 365 nm (a) only T, (b) T-Cu, (c) T-Cu + H2PO− 4 . (d) T-Cu + other anions.
Scheme 2. (a) The sequential logic circuit of the memory machine and its truth table. (b) Feedback loop showing the reversible logic operations for the memory element with “Writing–Reading–Erasing–Reading” functions.
− H2PO− 4 . Therefore, the test strips could conveniently detect H2PO4 in solutions.
3.4. Possible Sensing Mechanism output. Based on the reversible switch, the sensor T can switch between “ON” (strong fluorescence) and “OFF” (quenched fluorescence) different fluorescence emission states, which display “Read-Erase-WriteRead” behavior. In this particular system (scheme 2), the OFF state (Output 2 = 0) was defined as the weak fluorescence, and the ON state (Output 2 = 1) corresponds to as the strong fluorescence at 498 nm. The two 2+ ) and (In inputs of Cu2+ and H2PO− 4 ions were designated as (In Cu H2PO− 4 ) for the Set (S) and Reset (R) inputs, respectively. The operation of this memory unit is as follows: whenever the Set input is high (S = 1), the system writes and memorizes the binary state 1; whereas, when the Reset input is high (R = 1), the 1 state is erased and the 0 state is written and memorized. For this logic device, There are a great advantages over early reported in the reversibility and reproducibility. Though the pH response trials of T, T + Cu and T-Cu + H2PO− 4 , we found that the selectivity of T to Cu2+ and T-Cu to H2PO− 4 were examined over a wide range of pH values. The detection of Cu2+ can work well in the range of pH 2.0–13.0 and apparent changes of the fluorescence spectra were not observed. The fluorescence properties of T-Cu + H2PO− 4 remain unchanged in buffer solutions with pH up to 4.0– 10.0 values (Fig. 8). To investigate the practical application of sensor, test trips were prepared by immersing filter paper into the DMSO solution of T-Cu. The test strips containing T-Cu was utilized to sense H2PO− 4 and other anions. As shown in Fig. 9, when H2PO− 4 and the other anions were added on the test kits, respectively, the obvious color change was observed only with H2PO− 4 solution under the 365 nm UV lamp. And potentially competitive anions exerted no influence on the detection of
The Stern-Volmer plot's determined the dynamic or static quenching process by providing emission quenched data. For a static process, plotting relative emission intensities (F0/F) against quencher concentration [Q] should yield a linear Stern–Volmer plot. The static quenching constant Ksv can be obtained using the following equation:
F0 F
¼ 1 þ K sv ½Q
from Fig. S14, the linear of the Stern–Volmer analysis could be observed, which indicated that, the static and the dynamic quenching process was not significant in the presence of host T. Thus, the fluorescence quenching mechanism between T-Cu2 + complexation was analyzed and proposed to be a static quenching. The planar fluorescent sensor T is highly conjugated to π-electron systems. Upon addition of Cu2+ to T in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution, the fluorescence of T was quenching. Furthermore, we also revealed T/T + Cu in this complex was 1:1 through job plot of UV/Vis, fluorescence and MS (Fig. S7, Fig. S8 and Fig. S9). According to this information, we put forward the possible mechanism of T with Cu2 + and T-Cu with H2PO− 4 , as shown in Scheme 3. The planarity of this compound prevents the coordination of metal ions to phenolic oxygen atoms of two aromatic moieties in this ligand. However, in case of T: the IR data of this complex clearly indicate the metal ion (Cu2+) coordinate to two phenolic oxygen atoms on T (1237 cm−1) (Fig. S15). The color changes observed in the ligand solution of T upon binding to Cu2 + was because of deprotonation of phenolic-OH. In other words, for the host T, proton transfer occurred in the solution, and the H proton of the phenol-OH was transferred to the N atom of C_N, resulting in C_N cleavage into C\\N, the addition of copper ions destroyed the planarity structure of T, which was responsible for fluorescence quenching behavior of T upon metal complexation. The C_N stretching frequencies of T (1608 cm−1) was also vanished upon binding with Cu2 + ions, indicating change in the molecular planarity. These results clearly suggested that the molecular planarity plays a predominant role. Thus, the ligand T sense Cu2+ based on twisted plane induced proton transfer mechanism. The metal ion coordinates to ligand through two phenolate oxygen atoms and two nitrogens atom of amino groups. After TBAH2PO4 were added to the buffer solution of T-Cu, T-Cu complex was decomposed and inorganic copper phosphate was formed. 4. Conclusion
Fig. 8. Influence of pH on the fluorescence of T-Cu + H2PO− 4 in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution.
In summary, a simple reversible fluorescent chemosensor T was synthesized. It displayed a color changing and fluorescence quenching effect with Cu2 + to form T-Cu, which could be fast dissociated by the
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Scheme 3. Possible mechanism for the T-Cu and H2PO− 4 .
addition of H2PO− 4 in this system so that “ON-OFF-ON” type fluorescence change can be achieved. The reactivity of H2PO− 4 on T-Cu has been demonstrated based on NMR, ESI-MS, fluorescence emission and UV/Vis absorption. Sensor T displays high sensitivity (1.609 × 10− 8 M), good highly selective (1.19 × 109 M−2), for recognizing Cu2+ in the aqueous system, and the T-Cu metal complex could also respond to H2PO− 4 anion. This “ON-OFF-ON” switching process could be repeated at several times with little fluorescence loss. Therefore, the sensor has potential applications in biological and environmental systems for Cu2+ and H2PO− 4 anion detection.
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Acknowledgement This work was supported by the National Natural Science Foundation of China (Nos. 21662031; 21661028; 21574104; 21262032), the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China (IRT 15R56).
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Appendix A. Supplementary data
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Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.saa.2017.03.071.
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References [1] Y. Yang, Q. Zhao, W. Feng, F. Li, Chem. Rev. 113 (2013) 192–270. [2] (a) S. Erdemir, B. Tabakci, M. Tabakci, Sensors Actuators B 228 (2016) 109–116; (b) Y. Fu, C. Ding, A. Zhu, Z. Deng, Y. Tian, M. Jin, Anal. Chem. 85 (2013) 11936–11943; (c) S.K. Sahoo, D. Sharma, A. Moirangthem, A. Kuba, R. Thomas, R. Kumar, A. Basu, J. Lumin. 172 (2016) 297–303. [3] (a) D.M. Townsend, K.D. Tew, H. Tapiero, Biomed. Pharmacother. 57 (2003) 145–155; (b) K.J. Barnham, C.L. Masters, A.I. Bush, Nat. Rev. Drug Discov. 3 (2004) 205–214; (c) D.R. Brown, H. Kozlowski, Dalton Trans. 13 (2004) 1907–1917; (d) D. Sharma, A. Kuba, R. Thomas, R. Kumar, H.J. Choi, S.K. Sahoo, Spectrochim. Acta A Mol. Biomol. Spectrosc. 153 (2016) 393–396. [4] (a) M.H. Mashhadizadeh, M. Pesteh, M. Talakesh, I. Sheikhshoaie, M.M. Ardakani, M.A. Karimi, Spectrochim. Acta B At. Spectrosc. 63 (2008) 885–888; (b) S. Goswami, S. Chakraborty, S. Paul, S. Halder, S. Panja, S.K. Mukhopadhyay, Org. Biomol. Chem. 12 (2014) 3037–3044. [5] (a) D. Zhang, J.R. Cochrane, A. Martinez, G. Gao, RSC Adv. 4 (2014) 29735–29749; (b) W. Gong, D. Na, L. Fang, H. Mehdi, G.L. Ning, Org. Biomol. Chem. 13 (2015) 1979–1982. [6] (a) D. Aldakov, P. Anzenbacher, J. Am. Chem. Soc. 126 (2004) 4752–4753; (b) L.N. Johnson, R.J. Lewis, Chem. Rev. 101 (2001) 2209–2242; (c) X. Zhao, K.S. Schanze, Chem Commun. 46 (2010) 6075–6077; (d) A. Hens, P. Mondal, K.K. Rajak, Polyhedron 85 (2015) 255–266. [7] (a) U. Fegade, S.K. Sahoo, S. Attarde, N. Singh, A. Kuwar, Sensors Actuators B Chem. 202 (2014) 924–928;
[14]
[15]
[16]
(b) S.R. Patil, J.P. Nandre, D. Jadhav, S. Bothra, S.K. Sahoo, M. Devi, U.D. Patil, Dalton Trans. 43 (2014) 13299–13306. (a) L. Zong, Y. Song, Q. Li, Z. Li, Sensors Actuators B Chem. 226 (2016) 239–244; (b) R.J. Cassella, O.I. Magalhães, M.T. Couto, E.L.S. Lima, M.A.F. Neves, F.M.B. Coutinho, Talanta 67 (2005) 121–128. (a) A.S. Queiroz, M.S. Fernandes, H.C. dos Santos, Spectrochim. Acta B At. Spectrosc. 57 (2002) 1939–1950; (b) Z. Jin, Y. Su, Y. Duan, Anal. Chem. 73 (2001) 360–365. (a) K.D. Kreuer, E. Schönherr, J. Maier, Solid State Ionics 70 (1994) 278–284; (b) L.M. McInnes, P.K. Quinn, D.S. Covert, T.L. Anderson, Atmos. Environ. 30 (1996) 869–884; (c) A. Ali, H. Shen, X. Yin, Anal. Chim. Acta 369 (1998) 215–223; (d) K. Saito, A. Sjödin, C.D. Sandau, M.D. Davis, H. Nakazawa, Y. Matsuki, D.G. Patterson, Chemosphere 57 (2004) 373–381; (e) A. Mohadesi, M.A. Taher, Talanta 72 (2007) 95–100; (f) X. Dai, O. Nekrassova, M.E. Hyde, R.G. Compton, Anal. Chem. 76 (2004) 5924–5929. (a) R.N. Goyal, M. Oyama, V.K. Gupta, S.P. Singh, R.A. Sharma, Sensors Actuators B Chem. 134 (2008) 816–821; (b) V.K. Gupta, R. Jain, S. Agarwal, R. Mishra, A. Dwivedi, Anal. Biochem. 410 (2011) 266–271; (c) H.W. Gao, F.F. Chen, L. Chen, T. Zeng, L.T. Pan, J.H. Li, H.F. Luo, Anal. Chim. Acta 587 (2007) 52–59; (d) X.T. Zhao, H.P. Zhao, Y.Q. Le, T. Zeng, H.W. Gao, Ann. Chim. 97 (2007) 251–263. (a) C. Liu, X. Lei, X. Liang, J. Jia, L. Wang, RSC Adv. 7 (2017) 9744–9753; (b) Y. Zhu, Z. Bai, W. Luo, B. Wang, L. Zhai, J. Chem. Technol. Biotechnol. (2017) http://dx.doi.org/10.1002/jctb.5193; (c) A.S. Murugan, M. Pandi, J. Annaraj, ChemistrySelect 2 (2017) 375–383. (a) J. Li, Y. Guo, H. Yao, Q. Lin, Y. Xie, T. Wei, Y. Zhang, Chin. J. Chem. 31 (2013) 271–276; (b) D. Zhang, X. Jiang, H. Yang, Z. Su, E. Gao, A. Martinez, G. Gao, Chem. Commun. 49 (2013) 6149–6151; (c) A. Kuwar, R. Patil, A. Singh, S.K. Sahoo, J. Marek, N. Singh, J. Mater. Chem. C 3 (2015) 453–460. (a) M. Kumar, N. Kumar, V. Bhalla, H. Singh, P.R. Sharma, T. Kaur, Org. Lett. 13 (2011) 1422; (b) L. He, Q. Jiang, R. Gao, X. Yang, W. Feng, S. Luo, L. Yuan, Sci. China: Chem. 57 (2014) 1246–1256; (c) P. Yang, X.J. Yang, B. Wu, Eur. J. Inorg. Chem. (2009) 2951–2958. (a) U.N. Yadav, P. Pant, S.K. Sahoo, G.S. Shankarling, RSC Advances 4 (2014) 42647–42653; (b) V. Uahengo, Y. Zhang, B. Xiong, P. Zhao, P. Cai, L. Rhyman, G. Cheng, J. Fluoresc. (2016) 1–7; (c) V. Kumar, A. Kumar, U. Diwan, M.K. Singh, K.K. Upadhyay, Bull. Chem. Soc. Jpn. 89 (2016) 754–761. (a) W. Li, G. Wu, W. Qu, Q. Li, J. Lou, Q. Lin, H. Yao, Y. Zhang, T. Wei, Sensors and Actuators B Chem. 239 (2017) 671–678; (b) Q. Lin, T. Lu, X. Zhu, T. Wei, H. Li, Y. Zhang, Chem. Sci. 7 (2016) 5341–5346; (c) G. Gao, W. Qu, B. Shi, Q. Lin, H. Yao, Y. Zhang, J. Chang, Y. Cai, T. Wei, Sensors Actuators B 213 (2015) 501–507; (d) W. Qu, G. Gao, B. Shi, T. Wei, Y. Zhang, Q. Lin, H. Yao, Sensors Actuators B Chem. 204 (2014) 368–374; (e) H. Yao, X. You, Q. Lin, H. Wu, T. Wei, Y. Zhang, Chin. J. Chem. 32 (2014) 607–612; (f) B. Shi, P. Zhang, T. Wei, H. Yao, Q. Lin, Y. Zhang, Chem. Commun. 49 (2013) 7812–7814; (g) Y. Zhang, Q. Lin, T. Wei, X. Qin, Y. Li, Chem. Commun. (2009) 6074–6076.
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Colorimetric and fluorescent chemosensor for highly selective and sensitive relay detection of Cu2 + and H2PO− 4 in aqueous media Jun-Xia Su, Xiao-Ting Wang, Jing Chang, Gui-Yuan Wu, Hai-Ming Wang, Hong Yao, Qi Lin, You-Ming Zhang ⁎, Tai-Bao Wei ⁎ Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, PR China
a r t i c l e
i n f o
Article history: Received 8 September 2016 Received in revised form 27 March 2017 Accepted 30 March 2017 Available online 31 March 2017 Keywords: Colorimetric Fluorescence Chemosensor Copper (II) complex H2PO− 4 Aqueous media
a b s t r a c t In this manuscript, a new colorimetric and fluorescent chemosensor (T) was designed and synthesized, it could successively detect Cu2+ and H2PO− 4 in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution with high selectivity and sensitivity. When added Cu2+ ions into the solution of T, it showed a color changes from yellow to colorless, meanwhile, the green fluorescence of sensor T quenched. This recognition behavior was not affected in the presence of other cations, including Hg2+, Ag+, Ca2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, and Mg2+ ions. More interestingly, the Cu2+ ions contain sensor T solution could recover the color and fluorescence upon the addition of − − − − − − − H2PO− 4 anions in the same medium. And other surveyed anions (including F , Cl , Br , I , AcO , HSO4 , ClO4 , − − 2+ CN and SCN ) had nearly no influence on the recognition behavior. The detection limits of T to Cu and T−8 M and 0.994 × 10−7 M, respectively. In addition, the sensor Cu2+ to H2PO− 4 were evaluated to be 1.609 × 10 T also could be served as a recyclable component and the logic gate output was also defined in sensing materials. The test strips based on sensor T were fabricated, which acted as a convenient and efficient Cu2+ and H2PO− 4 test kits. © 2017 Published by Elsevier B.V.
1. Introduction In recent years, the role of ions, especially the transition-metal ions and some poisonous anions in environment and organism, had attracted increasing attention. In addition to zinc and iron ions, cupric ion was the third most abundant essential trace element in humans [1], which played an irreplaceable role in cellular processes, such as functional and structural strengthening of proteins and gene expression, even nervous system [2]. Cupric ion can disrupt normal activity of the life system and lead to various diseases if the concentration of detected is higher or lower than the desire demand of cells, for instance, Alzheimer's disease, Menkes Wilson disease and Prion diseases [3]. From the U.S. Environmental Protection Agency (EPA) it could be known, in drinking water, the maximum concentration of Cu2+ ion is 1.3 ppm (about 20 M) [4]. As one of in major equilibrium with two and PO3− at physiological pH, H2PO− other basic anions HPO2− 4 4 4 anion has become a research target as well as challenging for sensing anions, also owing to the key role in biological significance [5], such as energy storage, signal transduction and gene constructs and so forth [6]. So,
⁎ Corresponding authors. E-mail addresses: [email protected] (Y.-M. Zhang), [email protected] (T.-B. Wei).
http://dx.doi.org/10.1016/j.saa.2017.03.071 1386-1425/© 2017 Published by Elsevier B.V.
the design and synthesis of chemosensors for selectively and sensitively detecting phosphates anions has attracted lively interest. The design and development of optical sensing approaches for the detection of various transition metal ions and toxic anion are significant because of their vital roles in different biological and environmental field [7]. As a consequence, various analytical techniques have been proposed to determine cupric ion such as atomic absorption spectrometry (AAS) [8], inductively coupled plasma emission spectrometry [9], gravimetric, chromatography, anodic stripping voltammetry [10], ion selective electrodes [11] and so on, but most of these methods require time consuming, well-controlled experimental conditions, complicated sample pretreatment and inherent high cost [12]. As an alternative to these methods, due to the advantages of cheap, simple, highly sensitivity, selectivity and low detection concentration [13], colorimetric and fluorescent chemosensor have received considerable attention detection of various ions. And a multitude of fluorescent sensors with singleness of ions have also been synthesized [14]. In the process of detecting the transition metal ions, Cu is an essential element for all living systems, however, the copper chemosensors reported have drawbacks, such as fussy synthesize steps, requirement of anhydrous solvents for sensing, and the interferences from other metal ions, therefore, there is a need chemosensor for easy to synthesize and also highly selectively detection of Cu2+ in aqueous medium [15]. Our research group had a long standing interest in molecular and
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ionic recognition [16]. Herein, we reported a new chemosensor T, which could successively detect Cu2+ and H2PO− 4 in DMSO/H2O (v/v = 9:1, pH = 7.2) with high selectivity. Due to the capable of forming coordinate bonds between Schiff-bases and metal ions through phenolic group and azomethine groups, then we designed the imine-bound as the recognize side and the N,N-diethyl as the fluorescence signal report group, respectively. Consequently, we obtained a great dual-channel sensor for Cu2+ ions, meanwhile, the Cu2+ complex of the sensor also can selectively detect H2PO− 4 by colorimetric and fluorescent method in the aqueous media. 2. Experimental 2.1. Synthesis of Sensor T The synthesis process was shown in Scheme 1, N,N-diethyl salicylaldehyde (4 mmol, 0.77 g), 1,5-naphthalenediamine (1.5 mmol, 0.24 g), and acetic acid (AcOH) as a catalytic, which was stirred under reflux condition for 8 h in DMF (30 mL), after cooling to room temperature, the yellow product was filtrated, washed with hot absolute ethanol three times, then recrystallized with DMF-CH3CH2OH to get yellow powdery T (1 mmol, 0.63 g) in 83% yield (m.p. N 300 °C). 1 H NMR (CDCl3, 600 MHz, Fig. S18) δ 13.90 (s, 2H, –OH), 8.51 (s, 2H, C\\H), 8.18–8.17 (d, 2H), 7.51–7.49 (m, 2H), 7.24–7.23 (d, 2H), 7.19– 7.18 (d, 2H), 6.30–6.26 (m, 4H), 3.45–3.42 (q, 8H, –CH2), 1.25–1.22 (t, 12H, –CH3). ESI-MS (Fig. S16): m/z (M + H)+, calcd for [C32H36N4O2] 508.28, found: 509.26. IR (KBr, cm−1, Fig. S15), v/cm− 1: 3435 (OH), 1244–1582 (C_C), 1620 (C_N). 3. Results and Discussion 3.1. Solvent Effect of Sensor T and T-Cu2+ As showed in Figs. S1 and S2, solvent effect of sensor T and T-Cu2+ were be done to find the suitable solvent. From these two pictures we knew that host T had fluorescence in THF, DMSO, DMF solution. Only in THF solution, T-Cu2+ had weak fluorescence, and the fluorescence was quenched in DMSO solution. In the basis of these properties, in consideration of the harmfulness of other solutions, DMSO solution was chose the best solution to complete this recognition experiment. 3.2. UV/Vis and Flourescent Signaling of Cu2+ The recognition profiles of the chemosensor T toward various metal cations, including Hg2 +, Ag+, Ca2 +, Cu2 +, Co2 +, Ni2 +, Cd2 +, Pb2 +, Zn2+, Cr3+, and Mg2+ were primarily investigated by UV/Vis spectroscopy and fluorescence spectroscopy in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. Interaction of T with 20 equivalents of various metal ions as its perchlorate salt did not result in any significant changes in the absorption spectrum except Cu2+. As shown in Fig. S3, The absorption spectrum of compound T and other ions except Cu2 + in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution exhibits absorption band at 418 nm, the color of T was change from yellow to colorless, and realized the naked eye recognition to Cu2+ ions. To further investigate the interaction between T and Cu2 +, UV/Vis absorption spectral variation of sensor T in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution was monitored during titration with different concentrations of Cu2+ from 0 to 9.2 equivalents. As shown in Fig. S4, upon addition of Cu2+
ions, the absorption band at 418 nm was blue-shifted to 386 nm and at 290 nm appeared a new absorption band, indicating formation of TCu complex (Fig. S4). In the fluorescence spectrum, sensor T emitted very intensively. At 418 nm, the maximum emission wavelength of T was 498 nm in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. The DMSO solution of 20 equivalents of Cu2+ ions were added to the T to a final concentration of 20 μM, leading to a strong green fluorescence decrease rapidly, meanwhile, the fluorescence emission band at 498 nm was blue-shifted to 480 nm (Fig. S5). The fluorescence change was attributed to the formation of the T-Cu complex that the interaction between Cu2+ ions and the hydrogen atom of hydroxyl groups and the nitrogen atom of amino groups. For a better understanding of the binding mode, the fluorescence titration experiments were carried out in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution and a maximum excitation wavelength of 418 nm was selected. As shown in Fig. S6(a), it could cause fluorescence quenching with about 20 nm blue-shift in their emission maxima spectrum when adding 2.1 equivalents Cu2+ ions. Furthermore, the result in the color change from yellow to colorless detected could be clearly observed by the naked eye under UV-lamp/day light at room temperature. Upon addition of Cu2+, chemosensor T showed a apparent change in its UV/Vis spectrum (Fig. S4) and the appearance of new band at 386 nm and increase at 290 nm in their absorbance. On the other hand, the bands observed at 418 nm exhibit a decrease. The blue-shift of 38 nm was attributed to the coordination effect of Cu2+ with T via O from – OH and N by the deprotonation of Schiff-base NH proton. This phenomenon can be interpreted as the broken conjugated structure of T. The detection limit of chemosensor T was evaluated to be 1.609 × 10−8 M (Fig. S12) and the determination of association constant was 1.19 × 109 M−2, the job plot of UV/Vis, fluorescence and MS showed that binding between T and Cu2+ were 1:1 stoichiometry (Fig. S7, Fig. S8 and Fig. S9). As showed in Fig. S8, when the stoichiometry reached to 1:1, the most weak fluorescence could be observable, this situation was also showed in UV/Vis absorbance (Fig. S7). In addition, the ES-MS in the Fig. S9, 568 [T + Cu2 +] + H+ (z = 1) and 633 [T + Cu2 +] + Cu2 + (z = 2) could be received. An important aspect of many prospective metal ion sensors is their ability to detect Cu2+ (target metal ion) selectively over other competing metal ions. To establish the selectivity of T toward Cu2+ over a range of various metallic cations (Hg2+, Ag+, Ca2+, Co2+, Ni2+,Cd2+, Pb2+, Zn2 +, Cr3 + and Mg2 +). We carried out the competitive recognition studies during which the other cations were used in higher concentrations (4 × 10−3 M). From the bar diagram, we could easily understand that the effects on emission intensity of T upon the addition of higher concentrations (4 × 10− 3 M) of various ions were almost negligible. Therefore, it was clear that other ions' interference was negligibly small during the process of detection of Cu2+ ions (Fig. S10). These results further suggested that T could be used as a chemosensor for Cu2+ over a wide range of cations. 3.3. UV/Vis and Flourescent Signaling of H2PO− 4 2+ Considering the possible stability constant of H2PO− , T4 and Cu Cu complex was expected to act as a chemosensing ensemble for H2PO− 4 recognition. So we introduced the anions selectively recognition by adding various anions into the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution of sensor T-Cu2+. Thus, the sensor T-Cu was prepared 2+
Scheme 1. Synthesis route of benzindo indolium croconine.
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in situ by addition of 20 equivalents of Cu2+ to T solution (2 × 10−5 M). The response of T-Cu solution to a variety of anions (including H2PO− 4 , − − − F−, Cl−, Br−, I−, AcO−, HSO− 4 , ClO4 , SCN and CN ) were subsequently investigated in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. Amazingly, upon addition of H2PO− 4 (tetra-butyl ammonium salt 50 equiv. to T) to the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution of T-Cu, it responded with a dramatic color change, the apparent color change from colorless to yellow could be distinguished by naked eye (Fig. 1). To further investigate the interaction between T-Cu and H2PO− 4 , UV/ Vis absorption spectral variation of sensor T-Cu was monitored during titration with different concentrations of H2PO− 4 from 0 to 8.8 equivalents. As shown in Fig. 2(a), with increasing concentrations of H2PO− 4 , the gradually decreased absorbance band at 386 nm and the gradually increased absorbance band at 418 nm were clearly observed, respectively. As showed in Fig. 3, When 50 equivalents of anions (including − − − − − − − − and CN−) was H2PO− 4 , F , Cl , Br , I , AcO , HSO4 , ClO4 , SCN added to the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution of sensors T-Cu, the fluorescence was recovered by H2PO− 4 and none of other anions induced any significant changes in the fluorescent spectrum of the sensor. The H2PO− 4 sensing property of T-Cu was then evaluated by fluorescence titration experiments and the results were depicted in Fig. 4(a), upon incremental addition of H2PO− 4 into T-Cu the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution, the fluorescence intensity increased gradually and reached saturation when 6.16
Fig. 2. (a) Absorbance spectra of T-Cu in the presence of different concentration of H2PO− 4 (0–8.8 equiv.) in DMSO/H2O (v/v = 9:1, pH = 7.2). (b) A plot of absorbance depending on − the concentration of H2PO4 in the range from 0 to 8.8 equivalents, the detection wavelength was 418 nm.
equivalents of H2PO− 4 (relative to T) was introduced. During the titration process, the emission band maximum of the solution was gradually red shifted from 480 nm to 498 nm with the increasing concentration of
Fig. 1. (a) Absorbance data for a mixture of T-Cu and each of the various anions in the DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. Inset: color changes observed for T− − − − − − − − − Cu upon the addition of H2PO− 4 , F , Cl , Br , I , AcO , HSO4 , ClO4 , SCN and CN (50 equiv., respectively); (b) Absorbance data for T, T + Cu2+ and T-Cu + H2PO− 4 .
Fig. 3. Visual fluorescence emissions of sensor T-Cu after the addition of different anions in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution (λex = 418 nm). Inset: visual − − − − fluorescence photograph of sensor T-Cu after the addition of H2PO− 4 , F , Cl , Br , I , − − − , ClO , SCN and CN on excitation at 418 nm using UV-lamp at room AcO−, HSO− 4 4 temperature.
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Fig. 6. The Job's plot of fluorescence examined between T-Cu2+ and H2PO− 4 , indicating the 1:2 stoichiometric.
H2PO− 4 anions, which indicated that the form of T-Cu was changed after the H2PO− 4 anions addition. The detection limit of the sensor toward −7 M (Fig. S13), which indicated that this sensor H2PO− 4 was 0.994 × 10 can potentially be used as a probe for H2PO− 4 monitoring.
Subsequently, fluorescence competition experiments were conducted to further evaluate the tolerance of T-Cu to other anions. The results showed that coexistence of equal amount of other anions didn't induce any significant interference on the H2PO− 4 recognition (Fig. 5). The results of these competition experiments also revealed that the H2PO− 4 recognition by sensor T-Cu had an excellent anti-jamming ability. The Job's plot of fluorescence examined between T-Cu2+ and H2PO− 4 (Fig. 6), indicating the 1:2 stoichiometric. As shown in Fig.7, as a crucial aspect for chemical sensor, the reversibility in the response of T has been verified during its five cycles of titrations carried out with Cu2+ followed by H2PO− 4 exhibited alternating enhancing and quenching processes in a sequence, In addition, the Cu2+ exhibited a remarkable fluorescence quenching by showing OFF behavior through complex formation. The addition of an excess amount of TBAH2PO4 to the complex of T and Cu2+ resulted in changing of the fluorescence intensity and acted as an ON switch. This “ON-OFF-ON” switching process could be repeated several times with little fluorescence efficiency loss. Since the fluorescence intensity of sensor T could be controlled by alternative addition of Cu2+ and H2PO− 4 ions, the fluorescence emission of T can be defined as the logic gate output. Here, the actual results from an experiment are shown in Scheme 2, using the Cu2+ and H2PO− 4 ions as inputs while the emission intensity at 498 nm (I = 498) acts as the
Fig. 5. The fluorescence spectra changes of T-Cu to various anions. The black bars represent the fluorescence intensity of T-Cu in the presence of various anions, the red bars represent the fluorescence intensity of the above solution upon addition of H2PO− 4 (λem = 498 nm). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Emission spectra showing the reversible complexation between T and Cu2+ by introduction of H2PO− 4 ions.
Fig. 4. (a) Fluorescence spectra of T-Cu in the presence of different concentrations of Cu2+ (0–6.16 equiv.) in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution. (b) A plot of fluorescence intensity depending on the concentration of H2PO− 4 in the range from 0 to 6.16 equivalents, the detection wavelength was 498 nm.
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Fig. 9. Photographs of T-Cu on test papers after immersion into DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution under irradiation at 365 nm (a) only T, (b) T-Cu, (c) T-Cu + H2PO− 4 . (d) T-Cu + other anions.
Scheme 2. (a) The sequential logic circuit of the memory machine and its truth table. (b) Feedback loop showing the reversible logic operations for the memory element with “Writing–Reading–Erasing–Reading” functions.
− H2PO− 4 . Therefore, the test strips could conveniently detect H2PO4 in solutions.
3.4. Possible Sensing Mechanism output. Based on the reversible switch, the sensor T can switch between “ON” (strong fluorescence) and “OFF” (quenched fluorescence) different fluorescence emission states, which display “Read-Erase-WriteRead” behavior. In this particular system (scheme 2), the OFF state (Output 2 = 0) was defined as the weak fluorescence, and the ON state (Output 2 = 1) corresponds to as the strong fluorescence at 498 nm. The two 2+ ) and (In inputs of Cu2+ and H2PO− 4 ions were designated as (In Cu H2PO− 4 ) for the Set (S) and Reset (R) inputs, respectively. The operation of this memory unit is as follows: whenever the Set input is high (S = 1), the system writes and memorizes the binary state 1; whereas, when the Reset input is high (R = 1), the 1 state is erased and the 0 state is written and memorized. For this logic device, There are a great advantages over early reported in the reversibility and reproducibility. Though the pH response trials of T, T + Cu and T-Cu + H2PO− 4 , we found that the selectivity of T to Cu2+ and T-Cu to H2PO− 4 were examined over a wide range of pH values. The detection of Cu2+ can work well in the range of pH 2.0–13.0 and apparent changes of the fluorescence spectra were not observed. The fluorescence properties of T-Cu + H2PO− 4 remain unchanged in buffer solutions with pH up to 4.0– 10.0 values (Fig. 8). To investigate the practical application of sensor, test trips were prepared by immersing filter paper into the DMSO solution of T-Cu. The test strips containing T-Cu was utilized to sense H2PO− 4 and other anions. As shown in Fig. 9, when H2PO− 4 and the other anions were added on the test kits, respectively, the obvious color change was observed only with H2PO− 4 solution under the 365 nm UV lamp. And potentially competitive anions exerted no influence on the detection of
The Stern-Volmer plot's determined the dynamic or static quenching process by providing emission quenched data. For a static process, plotting relative emission intensities (F0/F) against quencher concentration [Q] should yield a linear Stern–Volmer plot. The static quenching constant Ksv can be obtained using the following equation:
F0 F
¼ 1 þ K sv ½Q
from Fig. S14, the linear of the Stern–Volmer analysis could be observed, which indicated that, the static and the dynamic quenching process was not significant in the presence of host T. Thus, the fluorescence quenching mechanism between T-Cu2 + complexation was analyzed and proposed to be a static quenching. The planar fluorescent sensor T is highly conjugated to π-electron systems. Upon addition of Cu2+ to T in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution, the fluorescence of T was quenching. Furthermore, we also revealed T/T + Cu in this complex was 1:1 through job plot of UV/Vis, fluorescence and MS (Fig. S7, Fig. S8 and Fig. S9). According to this information, we put forward the possible mechanism of T with Cu2 + and T-Cu with H2PO− 4 , as shown in Scheme 3. The planarity of this compound prevents the coordination of metal ions to phenolic oxygen atoms of two aromatic moieties in this ligand. However, in case of T: the IR data of this complex clearly indicate the metal ion (Cu2+) coordinate to two phenolic oxygen atoms on T (1237 cm−1) (Fig. S15). The color changes observed in the ligand solution of T upon binding to Cu2 + was because of deprotonation of phenolic-OH. In other words, for the host T, proton transfer occurred in the solution, and the H proton of the phenol-OH was transferred to the N atom of C_N, resulting in C_N cleavage into C\\N, the addition of copper ions destroyed the planarity structure of T, which was responsible for fluorescence quenching behavior of T upon metal complexation. The C_N stretching frequencies of T (1608 cm−1) was also vanished upon binding with Cu2 + ions, indicating change in the molecular planarity. These results clearly suggested that the molecular planarity plays a predominant role. Thus, the ligand T sense Cu2+ based on twisted plane induced proton transfer mechanism. The metal ion coordinates to ligand through two phenolate oxygen atoms and two nitrogens atom of amino groups. After TBAH2PO4 were added to the buffer solution of T-Cu, T-Cu complex was decomposed and inorganic copper phosphate was formed. 4. Conclusion
Fig. 8. Influence of pH on the fluorescence of T-Cu + H2PO− 4 in DMSO/H2O (v/v = 9:1, pH = 7.2) buffer solution.
In summary, a simple reversible fluorescent chemosensor T was synthesized. It displayed a color changing and fluorescence quenching effect with Cu2 + to form T-Cu, which could be fast dissociated by the
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Scheme 3. Possible mechanism for the T-Cu and H2PO− 4 .
addition of H2PO− 4 in this system so that “ON-OFF-ON” type fluorescence change can be achieved. The reactivity of H2PO− 4 on T-Cu has been demonstrated based on NMR, ESI-MS, fluorescence emission and UV/Vis absorption. Sensor T displays high sensitivity (1.609 × 10− 8 M), good highly selective (1.19 × 109 M−2), for recognizing Cu2+ in the aqueous system, and the T-Cu metal complex could also respond to H2PO− 4 anion. This “ON-OFF-ON” switching process could be repeated at several times with little fluorescence loss. Therefore, the sensor has potential applications in biological and environmental systems for Cu2+ and H2PO− 4 anion detection.
[8]
[9]
[10]
Acknowledgement This work was supported by the National Natural Science Foundation of China (Nos. 21662031; 21661028; 21574104; 21262032), the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China (IRT 15R56).
[11]
Appendix A. Supplementary data
[12]
Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.saa.2017.03.071.
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References [1] Y. Yang, Q. Zhao, W. Feng, F. Li, Chem. Rev. 113 (2013) 192–270. [2] (a) S. Erdemir, B. Tabakci, M. Tabakci, Sensors Actuators B 228 (2016) 109–116; (b) Y. Fu, C. Ding, A. Zhu, Z. Deng, Y. Tian, M. Jin, Anal. Chem. 85 (2013) 11936–11943; (c) S.K. Sahoo, D. Sharma, A. Moirangthem, A. Kuba, R. Thomas, R. Kumar, A. Basu, J. Lumin. 172 (2016) 297–303. [3] (a) D.M. Townsend, K.D. Tew, H. Tapiero, Biomed. Pharmacother. 57 (2003) 145–155; (b) K.J. Barnham, C.L. Masters, A.I. Bush, Nat. Rev. Drug Discov. 3 (2004) 205–214; (c) D.R. Brown, H. Kozlowski, Dalton Trans. 13 (2004) 1907–1917; (d) D. Sharma, A. Kuba, R. Thomas, R. Kumar, H.J. Choi, S.K. Sahoo, Spectrochim. Acta A Mol. Biomol. Spectrosc. 153 (2016) 393–396. [4] (a) M.H. Mashhadizadeh, M. Pesteh, M. Talakesh, I. Sheikhshoaie, M.M. Ardakani, M.A. Karimi, Spectrochim. Acta B At. Spectrosc. 63 (2008) 885–888; (b) S. Goswami, S. Chakraborty, S. Paul, S. Halder, S. Panja, S.K. Mukhopadhyay, Org. Biomol. Chem. 12 (2014) 3037–3044. [5] (a) D. Zhang, J.R. Cochrane, A. Martinez, G. Gao, RSC Adv. 4 (2014) 29735–29749; (b) W. Gong, D. Na, L. Fang, H. Mehdi, G.L. Ning, Org. Biomol. Chem. 13 (2015) 1979–1982. [6] (a) D. Aldakov, P. Anzenbacher, J. Am. Chem. Soc. 126 (2004) 4752–4753; (b) L.N. Johnson, R.J. Lewis, Chem. Rev. 101 (2001) 2209–2242; (c) X. Zhao, K.S. Schanze, Chem Commun. 46 (2010) 6075–6077; (d) A. Hens, P. Mondal, K.K. Rajak, Polyhedron 85 (2015) 255–266. [7] (a) U. Fegade, S.K. Sahoo, S. Attarde, N. Singh, A. Kuwar, Sensors Actuators B Chem. 202 (2014) 924–928;
[14]
[15]
[16]
(b) S.R. Patil, J.P. Nandre, D. Jadhav, S. Bothra, S.K. Sahoo, M. Devi, U.D. Patil, Dalton Trans. 43 (2014) 13299–13306. (a) L. Zong, Y. Song, Q. Li, Z. Li, Sensors Actuators B Chem. 226 (2016) 239–244; (b) R.J. Cassella, O.I. Magalhães, M.T. Couto, E.L.S. Lima, M.A.F. Neves, F.M.B. Coutinho, Talanta 67 (2005) 121–128. (a) A.S. Queiroz, M.S. Fernandes, H.C. dos Santos, Spectrochim. Acta B At. Spectrosc. 57 (2002) 1939–1950; (b) Z. Jin, Y. Su, Y. Duan, Anal. Chem. 73 (2001) 360–365. (a) K.D. Kreuer, E. Schönherr, J. Maier, Solid State Ionics 70 (1994) 278–284; (b) L.M. McInnes, P.K. Quinn, D.S. Covert, T.L. Anderson, Atmos. Environ. 30 (1996) 869–884; (c) A. Ali, H. Shen, X. Yin, Anal. Chim. Acta 369 (1998) 215–223; (d) K. Saito, A. Sjödin, C.D. Sandau, M.D. Davis, H. Nakazawa, Y. Matsuki, D.G. Patterson, Chemosphere 57 (2004) 373–381; (e) A. Mohadesi, M.A. Taher, Talanta 72 (2007) 95–100; (f) X. Dai, O. Nekrassova, M.E. Hyde, R.G. Compton, Anal. Chem. 76 (2004) 5924–5929. (a) R.N. Goyal, M. Oyama, V.K. Gupta, S.P. Singh, R.A. Sharma, Sensors Actuators B Chem. 134 (2008) 816–821; (b) V.K. Gupta, R. Jain, S. Agarwal, R. Mishra, A. Dwivedi, Anal. Biochem. 410 (2011) 266–271; (c) H.W. Gao, F.F. Chen, L. Chen, T. Zeng, L.T. Pan, J.H. Li, H.F. Luo, Anal. Chim. Acta 587 (2007) 52–59; (d) X.T. Zhao, H.P. Zhao, Y.Q. Le, T. Zeng, H.W. Gao, Ann. Chim. 97 (2007) 251–263. (a) C. Liu, X. Lei, X. Liang, J. Jia, L. Wang, RSC Adv. 7 (2017) 9744–9753; (b) Y. Zhu, Z. Bai, W. Luo, B. Wang, L. Zhai, J. Chem. Technol. Biotechnol. (2017) http://dx.doi.org/10.1002/jctb.5193; (c) A.S. Murugan, M. Pandi, J. Annaraj, ChemistrySelect 2 (2017) 375–383. (a) J. Li, Y. Guo, H. Yao, Q. Lin, Y. Xie, T. Wei, Y. Zhang, Chin. J. Chem. 31 (2013) 271–276; (b) D. Zhang, X. Jiang, H. Yang, Z. Su, E. Gao, A. Martinez, G. Gao, Chem. Commun. 49 (2013) 6149–6151; (c) A. Kuwar, R. Patil, A. Singh, S.K. Sahoo, J. Marek, N. Singh, J. Mater. Chem. C 3 (2015) 453–460. (a) M. Kumar, N. Kumar, V. Bhalla, H. Singh, P.R. Sharma, T. Kaur, Org. Lett. 13 (2011) 1422; (b) L. He, Q. Jiang, R. Gao, X. Yang, W. Feng, S. Luo, L. Yuan, Sci. China: Chem. 57 (2014) 1246–1256; (c) P. Yang, X.J. Yang, B. Wu, Eur. J. Inorg. Chem. (2009) 2951–2958. (a) U.N. Yadav, P. Pant, S.K. Sahoo, G.S. Shankarling, RSC Advances 4 (2014) 42647–42653; (b) V. Uahengo, Y. Zhang, B. Xiong, P. Zhao, P. Cai, L. Rhyman, G. Cheng, J. Fluoresc. (2016) 1–7; (c) V. Kumar, A. Kumar, U. Diwan, M.K. Singh, K.K. Upadhyay, Bull. Chem. Soc. Jpn. 89 (2016) 754–761. (a) W. Li, G. Wu, W. Qu, Q. Li, J. Lou, Q. Lin, H. Yao, Y. Zhang, T. Wei, Sensors and Actuators B Chem. 239 (2017) 671–678; (b) Q. Lin, T. Lu, X. Zhu, T. Wei, H. Li, Y. Zhang, Chem. Sci. 7 (2016) 5341–5346; (c) G. Gao, W. Qu, B. Shi, Q. Lin, H. Yao, Y. Zhang, J. Chang, Y. Cai, T. Wei, Sensors Actuators B 213 (2015) 501–507; (d) W. Qu, G. Gao, B. Shi, T. Wei, Y. Zhang, Q. Lin, H. Yao, Sensors Actuators B Chem. 204 (2014) 368–374; (e) H. Yao, X. You, Q. Lin, H. Wu, T. Wei, Y. Zhang, Chin. J. Chem. 32 (2014) 607–612; (f) B. Shi, P. Zhang, T. Wei, H. Yao, Q. Lin, Y. Zhang, Chem. Commun. 49 (2013) 7812–7814; (g) Y. Zhang, Q. Lin, T. Wei, X. Qin, Y. Li, Chem. Commun. (2009) 6074–6076.