- Email: [email protected]
A fluorescent sensor based on bicarboxamidoquinoline for highly selective relay recognition of Zn2+ and citrate with ratiometric response
Sensors and Actuators B 221 (2015) 923–929
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A fluorescent sensor based on bicarboxamidoquinoline for highly selective relay recognition of Zn2+ and citrate with ratiometric response Xuhua Tian, Xiangfeng Guo ∗ , Lihua Jia ∗ , Rui Yang, Guangzhou Cao, Chaoyue Liu College of Chemistry and Chemical Engineering, Key Laboratory of Fine Chemicals of College of Heilongjiang Province, Qiqihar University, Qiqihar 161006, China
a r t i c l e
i n f o
Article history: Received 12 March 2015 Received in revised form 10 July 2015 Accepted 13 July 2015 Available online 15 July 2015 Keywords: Relay recognition Ratiometric sensor Zinc Citrate Bicarboxamidoquinoline
a b s t r a c t A novel bicarboxamidoquinoline-based fluorescent sensor 1 was designed and synthesized, which performed ratiometric recognition for Zn2+ without interference from Cd2+ . The sensor 1 bound Zn2+ in 1:1 stoichiometry, with the binding constant of 2.07 × 103 M−1 . Moreover, the in situ generated 1–Zn2+ complex could serve as an excellent ratiometric citrate sensor via a Zn2+ displacement and discriminated citrate from a series of common carboxylates in neutral aqueous solution. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Citrate is an important organic tricarboxylate in the Krebs cycle, its concentration in urine can be served as an indicator of renal metabolism [1]. In addition, citrate has been widely used in foods and pharmaceuticals [2,3]. Various techniques were established for the determination of citrate [4]. Nevertheless, some techniques with higher selectivity and convenience are still needed. Fluorescence detection has been widely implemented in different kinds of analytes as a result of the simplicity, high sensitivity, selectivity and manipulability [5,6]. Especially, ratiometric fluorescence monitoring offers additional advantages in the detection process because it may avert the influences of many analyteindependent factors. Thus, varieties of fluorescent ratiometric sensors have been developed successfully [7]. Up to now, considerable effort has been devoted to the development of fluorescent sensors for citrate [8–10,4,11]. For example, Fabbrizzi et al. developed a metal-containing sensor for citrate based on the fluorescent indicator displacement [10]. Yen et al. designed a symmetrical coumarin-based sensor for citrate [4]. Ghosh et al. synthesized a pyridinium-based sensor for citrate
∗ Corresponding authors. Tel.: +86 0452 2742563; fax: +86 0452 2742563. E-mail addresses: [email protected] (X. Guo), [email protected] (L. Jia). http://dx.doi.org/10.1016/j.snb.2015.07.047 0925-4005/© 2015 Elsevier B.V. All rights reserved.
through indicator displacement assay [11]. All the sensors mentioned above can triumphantly recognize citrate with OFF–ON fluorescent behavior. Furthermore, Parker and Yu [12] successfully developed a citrate sensor by using coordinatively unsaturated Eu-complex to chelate citrate, which performed excellently ratiometric response for citrate. However, literature on the ratiometric sensing of citrate was still very few. Intrigued by relay recognition of metal ions and anions [13–15], we hope a new ratiometric response for citrate could be established through metal ions displacement approach. Based on the strategy, a ratiometric sensor for a metal ion is necessary, and then the metal ion bonded with the sensor can be exactly captured by citrate while a reverse spectrum change appears. In consideration of our previous work about ratiometric zinc sensor [16,17] and some related researches [18–20], a new sensor was designed and synthesized as shown in Scheme 1. The sensor is based on bicarboxamidoquinoline groups which are connected to the binaphthol scaffold through ethylenediamine linkers. The symmetric sensor with intramolecular two carboxamidoquinolines could form a feasible convergent space for Zn2+ . The introduction of ethylenediamine linkers could increase the chelate space of bicarboxamidoquinoline, resulting in weaker binding capacity of the sensor with Zn2+ . And then a particular carboxylate could be recognized via Zn2+ displacement approach. In addition, the ethylenediamine linkers and hydroxyethyl groups are beneficial to the recognition in aqueous solution. As expected, the sensor
924
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
Cl OH
O
O
O
H N
H2N
O
OH
OH
H N
O
N H
O
O
O
O H N
O Binol
O
O
3
OH
OH
N H
2 HO O O NH
N H
N
N
N
O O
O
4
N NH O
Cl
N O
1
NH
N H
HO
Scheme 1. Synthesis route of sensor 1.
recognized Zn2+ with high selectivity and importantly the resultant Zn2+ -sensor complex discriminated citrate with ratiometric emission changes. 2. Experimental 2.1. Chemicals and apparatus All solvents and analytical grade chemicals were obtained commercially and used directly without further purification. NMR spectra were recorded using a Bruker AVANCE-600 spectrometer and referenced to internal tetramethylsilane. Infrared spectral data were measured with Nicolet Avatar-370. A Waters Xevo G2-S QT was used for Mass measurements. Melting points were performed on an X-6 microscopic melting point apparatus. The UV–vis spectra were determined with a Puxi TU-1901 spectrophotometer. Fluorescence measurements were scanned with a Hitachi F-7000. The pH measurements were monitored with a Sartorius basic pH-meter PB-10. 2.2. General procedure for spectroscopic measurements Ultra-pure water and tris–HCl buffer were used for all experiments. The metal ion solutions (0.050 M) were obtained from NaCl, KCl, Mg(ClO4 )2 , Ca(NO3 )2 , Cr(NO3 )2 , Fe2 (SO4 )3 , CoSO4 , NiSO4 , Cu(NO3 )2 , Zn(NO3 )2 , AgNO3 , CdSO4 , HgCl2 , Pb(NO3 )2 , AlCl3 . Carboxylates (as sodium or potassium salts, 0.050 M) in ultra-pure water were used in experiments. The spectra measurements were operated at room temperature and the pH value of all experiments were maintained at pH 7.4. All fluorescence data were recorded under the 320 nm excitation, the slit widths of excitation and emission were 2.5 nm. 1–Zn2+ complex was obtained from mixing 2.0 equiv of Zn2+ with 10 M sensor 1 in solution (methanol/water = 1:1, pH = 7.4).
Preparation of compound 2. To a solution of compound 3 (0.254 g, 0.550 mmol) in ethanol (5.0 mL), ethanolethylene diamine (0.284 g, 2.73 mmol) was added and the mixture was refluxed for 3 h. The cooled reaction mixture was poured into saturated sodium chloride solution and the aqueous phase was extracted with dichloromethane (50 mL). The combined CH2 Cl2 solution was dried over anhydrous MgSO4 , and evaporated to give the crude product 2 as a sticky substance (0.227 g, crude). Then the crude product collected was directly used for the next step without further purification. Preparation of compound 1. Compound 2 (0.227 g, 0.395 mmol), compound 4 (0.192 g, 0.869 mmol), potassium carbonate (0.163 g, 1.185 mmol), and catalytic amount of potassium iodide were dissolved in dry acetonitrile (8.0 mL) and the reaction mixture were refluxed for 9 h. On completion of the reaction, the residue was diluted by water and extracted with 50 mL of dichloromethane. The organic extracts were dried over anhydrous MgSO4 and concentrated in vacuo. The crude products were purified by column chromatography (methanol/dichloromethane = 20/1) on silica gel to give 1 (0.109 g, 27.5%). Mp: 88.2–89.8 ◦ C. 1 H NMR (600 MHz, CDCl3 ) ı 11.09 (s, 2H), 8.72 (dd, J = 7.3, 1.2 Hz, 2H), 8.64 (dd, J = 4.2, 1.2 Hz, 2H), 8.17 (dd, J = 8.2, 1.5 Hz, 2H), 7.85 (d, J = 9.1 Hz, 2H), 7.80 (d, J = 8.1 Hz, 2H), 7.62–7.53 (m, 4H), 7.34 (dd, J = 8.3, 4.2 Hz, 2H), 7.31 (t, J = 7.4 Hz, 2H), 7.24 (d, J = 7.0 Hz, 2H), 7.14 (d, J = 3.4 Hz, 2H), 7.13 (d, J = 4.3 Hz, 2H), 5.67 (br, 2H), 4.25 (s, 4H), 4.12 (br, 2H), 3.61 (br, 4H), 3.26 (br, 4H), 3.06–2.91 (m, 4H), 2.73 (br, 4H), 2.32 (br, 2H), 2.26 (br, 2H). 13 C NMR (150 MHz, CDCl3 ) ı 169.20, 168.03, 152.71, 148.79, 138.66, 136.88, 133.45, 133.26, 130.22, 129.63, 128.24, 128.22, 127.47, 127.36, 124.94, 124.73, 122.21, 121.69, 119.54, 117.38, 114.97, 68.57, 60.57, 59.86, 58.85, 54.48, 36.67. FTIR (cm−l ): 3407, 3060, 1683, 1527, 1270, 1151, 1049. MS (ESI): m/z calcd for C54 H55 N8 O8 + (M + H+ ) 943.4065, found 943.4116. 3. Results and discussion
2.3. Synthesis
3.1. Fluorescence response for Zn2+
The medium product 2-chloro-N-(quinol-8-yl) acetamide 4 was prepared as our previous work [17]. And diethyl 2,2 (1,1 -Binaphthyl-2,2 -diylbis(oxy))diacetate 3 was prepared as previously described [21].
In order to evaluate the selectivity of sensor for Zn2+ , the fluorescence changes of 1 to various metal ions were investigated in aqueous solution (Fig. 1A). Compared to other metal ions examined, only Zn2+ caused a red shift to 500 nm via the 14-fold enhancement
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
925
160
A 2+
120
80 others
B
1 + metal ions (2 eq.) 1 + metal ions (2 eq.) +zinc ion (2 eq.)
3
I500nm/I410nm
2
1
40 Cu
2+
3+
+
3+
Al Fe
Ag + Hg 2 + Cd 2 + Pb 2
2+
2+
2+
Ni Cu
+
3+
Cr Co
+
600
+
450 500 550 Wavelength(nm)
se nt Zn 2
400
ab
350
K+ M 2 g + Ca 2
0
0
Na
Intensity(a.u.)
Zn
Fig. 1. Fluorescence spectra of 10 M sensor 1 in the present of 20 M different metal ions (A). Metal ions competition analysis of 10 M sensor 1 (B). Black bars: the emission of 1 in the presence of 2.0 equiv of metal ions. Red bars: the emission of 1 in the presence of 2.0 equiv of other metal ions followed by 2.0 equiv of Zn2+ . Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
500
12
300 μM
A
B
300 0 μM
200
8 I(500nm)/I(410nm)
Intensity(a.u.)
2+
[Zn ]
I(500nm)/I(410nm)
10
400
6 4
4 2 0
2
100
Y = 0.026 + 0.10X 2 R = 0.997
6
0
25
50
2+
[Zn ]/ μM
0
0 350
400
450
500
550
600
Wavelength(nm)
0
50
100
150
200
250
300
2+
[Zn ]/ μM
Fig. 2. Fluorescence emission spectra of 1 upon addition of Zn2+ . Inset: the intensity ratio (I500 nm /I410 nm ) as functions of Zn2+ concentration. Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm.
of ratio intensity (I500 nm /I410 nm ). And Cu2+ led to a slight fluorescence quenching. Importantly, 1 could distinguish Zn2+ from Cd2+ , which was well known to be a major obstacle [22–24]. The enhancement emission might arise from the occurrence of the chelation-enhanced fluorescence (CHEF) process upon binding to Zn2+ [19,25,26]. And the red-shift might result from the ICT process which was promoted by the deprotonation of amide NH after binding to Zn2+ [17]. To validate the selectivity of 1 in practice, the competition experiments were also conducted by addition of 2.0 equiv Zn2+ to aqueous solutions in the presence of 2.0 equiv other metal ions as shown in Fig. 1B. The fluorescence intensity of the complex was negligibly affected by other coexistent metal ions except Cu2+ , which often acted as a quencher via the high affinity and paramagnetism [27,28]. In an attempt to evaluate the influence of Zn2+ concentration, the fluorescence properties of 1 were studied in aqueous solutions (Fig. 2). Upon addition of Zn2+ , a significant decrease of the fluorescence intensity at 410 nm and an increase of fluorescence emission band centered at 500 nm were observed. As shown in Fig. 2B, the ratio of fluorescence intensity (I500 nm /I410 nm ) increased linearly over the Zn2+ concentration range 0–50 M and a linear relationship (R2 = 0.997) is obtained, which indicates that sensor 1 shown potential use for the quantitative determination of Zn2+ with ratiometric response. When more than 20 equiv Zn2+ was added, the maximum fluorescence intensity was retained, which suggests the sensor 1 had weak binding capacity. The stoichiometry for sensor 1 and Zn2+ was found to be 1:1 based on Job’s plot analysis (Fig. S1 see ESI). Further the binding constant was extracted from the
fluorescence titrations to afford the value of 2.07 × 103 M−1 obtained from the Benesi–Hildebrand equation (Fig. S2 see ESI) [29,30]. The weaker binding capacity compared with some reported sensors provided a displacement possibility by other higher affinity carboxylates [17]. In addition, the stability constant for zinc–citrate complex was in the order of 1011 M−1 , which revealed the citrate had higher affinity toward Zn2+ [31].
3.2. Fluorescence sensing of 1–Zn2+ complex for citrate Considering the weak binding capacity of sensor 1 to Zn2+ , the on-site generated 1–Zn2+ complex was a possible sensor for citrate via Zn2+ displacement approach. To verify this conjecture, the carboxylates-selective experiment was conducted by respective addition of varying carboxylates into 1–Zn2+ solution. As exhibited in Fig. 3, only the addition of citrate led to a strong fluorescence quenching (ratio intensity quenching efficiency, (I0 − I)/I0 × 100% = 79%), which might be attributed to Zn2+ displacement approach. Under the same conditions, 20 M of oxalate caused a slight fluorescence quenching effect, whereas, the addition of other carboxylates induced negligible fluorescence spectral changes. To get further insight into the high selectivity of 1–Zn2+ complex to citrate, the fluorescence competition experiments were implemented subsequently. The results show that coexistence of other carboxylates caused scarce interference on the detection of citrate. These illustrated that 1–Zn2+ complex could serve as a highly selective sensor for citrate.
926
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929 2+
150
500nm 410nm
100
B
2
/I
oxalate
50
I
Intensity(a.u.)
others
1-Zn complex + 2 eq anions 2+ 1-Zn complex + 2 eq anions + 2 eq citrate
3
A
1
citrate 0 400
450
500
550
600
Wavelength(nm)
ab se n ci t tra ac te et a ox te al a ta te rtr a m te al a m te al e fu ate m ar m at al e o su nat cc e in ad ate ip at es
0
350
Fig. 3. Fluorescence spectra of 1–Zn2+ complex with different carboxylates at 20 M concentration (A). The ratio fluorescence intensity changes of 1–Zn2+ complex against various carboxylates (B); red bars: the ratio fluorescence intensity of 1–Zn2+ complex in the presence of miscellaneous carboxylates at 20 M concentration; black bars: the change of the ratio fluorescence intensity upon the subsequent addition of 20 M citrate to the above solution. Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
4
200
5
B
45 μM
3
[citrate]
100
0
I(500nm)/I(410nm)
Intensity(a.u.)
150
2
3 2 1 0
1
50
Y = 3.25 - 0.17X 2 R =0.992
4 I(500nm)/I(410nm)
A
0
4
8 12 [citrate] μM
16
0
0 350
400
450
500
550
600
0
10
20
30
40
50
[citrate] μM
Wavelength(nm) 2+
1-Zn complex + 4.5eq citrate free 1
Intensity(a.u.)
60
C
40
20
0 350
400
450
500
550
600
Wavelength(nm) Fig. 4. Fluorescence titration spectra of 1–Zn2+ complex with increasing amounts of citrate. The ratio intensity (I500 nm /I410 nm ) of 1–Zn2+ complex versus the concentration of citrate (B). The fluorescence spectra overlay (C); red line: free 1; black line: 1–Zn2+ complex treated with 45 M citrate. Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The sensing property of 1–Zn2+ complex to citrate was further evaluated by fluorescence titration experiment (Fig. 4A). Upon gradual introduction of citrate concentration, the emission intensity at 500 nm was gradually decreased, yet the emission band around 410 nm was gradually increased. The ratio of fluorescence intensity (I500 nm /I410 nm ) decreased linearly over the citrate concentration range 0–15 M with a linear relationship (R2 = 0.992), then the ratio fluorescence intensity decreased slowly to minimum with the continued increase of citrate (Fig. 4B). These indicate that the Zn2+ was captured by citrate, which resulted in
fluorescence recovery of sensor 1. To verify our assumption, the fluorescence spectra overlay of free sensor 1 and sensor 1–Zn2+ complex + 4.5 equiv citrate were depicts in Fig. 4C. The high overlap in Fig. 4B supported that citrate acted as a Zn2+ chelator in the second recognition progress. In order to further verify the displacement of Zn2+ and release of the sensor with addition of citrate, the ESI–MS spectra of complex sensor 1 + Zn2+ (5.0 equiv) and the complex sensor 1 + Zn2+ (5.0 equiv) + citrate (5.0 equiv) were measured as shown in Fig. S7 and Fig. S8. Peaks m/z 943.4188 and 1005.3354 values corresponded to [1 + H+ ]+ and
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
2.5
1.0
A
Y = 1.96 X + 9.50 2 R = 0.982 Detection limit = 1.42 μM
Y = 0.922 X + 5.22 2 R = 0.984 Detection limit = 2.19 μM
0.8
(Imax - I)/(Imax - Imin)
2.0
(I - Imin)/(Imax - Imin)
927
1.5
1.0
0.5
B
0.6
0.4
0.2
0.0 -5.0
-4.8
-4.6
-4.4
-4.2
-4.0
-3.8
-3.6
-5.6
-5.4
-5.2
2+
-5.0
-4.8
-4.6
Log[citrate]
Log[Zn ]
Fig. 5. Normalized response of the ratio fluorescence signal (I500 nm /I410 nm ) to changing Zn2+ concentrations (A) and citrate concentrations (B). Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm.
2.5
4
A
B
2.0
I500nm/I410nm
I500nm/I410nm
3 1.5
1.0
2
1 0.5
0
0.0 0
2
4
6
8
10
12
0
1
2
Time/min
3
4
5
6
7
8
Time/min
Fig. 6. Time responses of the sensor 1 in the presence of 2.0 equiv. Zn2+ (A) and 1–Zn2+ complex in the presence of 2.0 equiv. citrate (B). Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm.
[1 + Zn2+ –H+ ]+ , respectively. When 5.0 equiv of citrate was added, the peak of [1 + H+ ]+ increased and the peak of [1 + Zn2+ –H+ ]+ decreased obviously. The [1 + Zn2+ –H+ ]+ complex was calculated at m/z 1005.3189 and measured at m/z 1005.3354 or 1005.3273. This indicated the formation of a 1–Zn2+ complex of 1:1 stoichiometry. After the addition of citrate, the peak at 1005.3237 corresponding to [1 + Zn2+ –H+ ]+ decreased and obviously, indicating that 1–Zn2+ complex lost Zn2+ and the free sensor 1 was released. All these revealed that sensor 1–Zn2+ could quantitatively detect citrate with ratiometric behavior. 3.3. Detection limit To study the sensitivity of sensor 1 and 1–Zn2+ complex, the detection limits of the sensors were obtained based on a reported
method [32–34]. A linear regression curve was then fitted to these normalized ratio fluorescence intensity data in Fig. 5. The detection limit of the sensor 1 was 1.42 M, the 1–Zn2+ complex was 2.19 M. 3.4. Response time Besides the selectivity and selectivity, the response time is an important indicator of evaluation of the sensor. So the response times of sensor 1 with Zn2+ and 1–Zn2+ complex with citrate were investigated (Fig. 6). The ratio intensity of sensor 1 gradually increased when Zn2+ was introduced and then was retained after more than 6 min. The ratio intensity of 1–Zn2+ complex gradually decreased with the addition of citrate and tended to stabilize after 1 min. The results indicated that the sensor had a fast response in the recognition processes.
Table 1 Determination of analyte concentrations in real samples (n = 3). Samples
Analytes
Tap water
Zinc ion
Sprite
Citrate
a
Average value of three determinations.
Added (M)
Founda (M)
Recovery (%)
0.00
20.00 35.00
20.50 ± 0.012 33.40 ± 0.045
102.50 96.68
3.14
1.00 2.00
4.31 ± 0.011 6.14 ± 0.074
104.02 119.46
Content (M)
928
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
3.5. Practical applications In order to verify the practical applicability of the ratio sensors, the determination of Zn2+ in tap water and the determination of citrate in Sprite (drink from Coca-Cola) were evaluated using the standard addition method. The recovery of Zn2+ in tap water from 96.68 to 102.50% and the recovery of citrate in Sprite from 104.02 to 119.46% were obtained, indicating the appreciable practicality of the presented sensors (Table 1). 4. Conclusion A new sensor 1 based on bicarboxamidoquinoline for sequential recognition of Zn2+ and citrate with ratiometric behavior was established. 1 displayed a high selectivity toward Zn2+ over other metal ions especially over Cd2+ via the CHEF mechanism. 1–Zn2+ complex with a 1:1 binding stoichiometry performed a high selectivity in recognizing citrate, which exhibited excellently distinguishing behavior among a series of common carboxylates. The design strategy that the metal-complex with adjustable binding capacity through introduction suitable linker could serve as a sensor for some certain analyte might be helpful in expanding the development of sensors for carboxylates. Acknowledgements This work was supported by the National Natural Science Foundation of China (21176125), the Natural Science Foundation of Heilongjiang Province of China (B201114, B201313, B201419) and the Science Research Project of the Ministry of Education of Heilongjiang Province of China (2012TD012, 12511Z030, 12521594).
[14]
[15]
[16] [17]
[18]
[19]
[20]
[21]
[22]
[23]
[24] [25]
[26]
[27]
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2015.07.047
[28]
References
[29]
[1] L.L. Hamm, Renal handling of citrate, Kidney Int. 38 (1990) 728–735. [2] S¸. Türko˘glu, Genotoxicity of five food preservatives tested on root tips of Allium cepa L., Mutat. Res. 626 (2007) 4–14. [3] T. Pérez-Ruiz, C. Martínez-Lozano, V. Tomás, O. Val, Flow-injection chemiluminometric determination of citrate based on a photochemical reaction, Analyst 120 (1995) 471–475. [4] Z.H. Liu, S. Devaraj, C.R. Yang, Y.P. Yen, A new selective chromogenic and fluorogenic sensor for citrate ion, Sens. Actuators, B: Chem. 174 (2012) 555–562. [5] Z. Liu, W. He, Z. Guo, Metal coordination in photoluminescent sensing, Chem. Soc. Rev. 42 (2013) 1568–1600. [6] J. Wu, W. Liu, J. Ge, H. Zhang, P. Wang, New sensing mechanisms for design of fluorescent chemosensors emerging in recent years, Chem. Soc. Rev. 40 (2011) 3483–3495. [7] M.H. Lee, J.S. Kim, J.L. Sessler, Small molecule-based ratiometric fluorescence probes for cations, anions, and biomolecules, Chem. Soc. Rev. 44 (2015) 4185–4191. [8] C. Schmuck, M. Schwegmann, A naked-eye sensing ensemble for the selective detection of citrate – but not tartrate or malate – in water based on a tris-cationic receptor, Org. Biomol. Chem. 4 (2006) 836–838. [9] M. Isabel Burguete, F. Galindo, S.V. Luis, L. Vigara, A turn-on fluorescent indicator for citrate with micromolar sensitivity, Dalton Trans. 36 (2007) 4027–4033. [10] L. Fabbrizzi, F. Foti, A. Taglietti, Metal-containing trifurcate receptor that recognizes and senses citrate in water, Org. Lett. 7 (2005) 2603–2606. [11] K. Ghosh, A.R. Sarkar, Pyridinium-based symmetrical diamides as chemosensors in visual sensing of citrate through indicator displacement assay (IDA) and gel formation, Org. Biomol. Chem. 9 (2011) 6551–6558. [12] D. Parker, J. Yu, A pH-insensitive, ratiometric chemosensor for citrate using europium luminescence, Chem. Commun. 25 (2005) 3141–3143. [13] L. Tang, M. Cai, P. Zhou, J. Zhao, K. Zhong, S. Hou, Y. Bian, A highly selective and ratiometric fluorescent sensor for relay recognition of zinc(II) and sulfide
[30]
[31] [32]
[33]
[34]
ions based on modulation of excited-state intramolecular proton transfer, RSC Adv. 3 (2013) 16802–16809. Z. Dong, X. Le, P. Zhou, C. Dong, J. Ma, Sequential recognition of zinc ion and hydrogen sulfide by a new quinoline derivative with logic gate behavior, RSC Adv. 4 (2014) 18270–18277. X. Lou, D. Ou, Q. Li, Z. Li, An indirect approach for anion detection: the displacement strategy and its application, Chem. Commun. 48 (2012) 8462–8477. X. Tian, X. Guo, L. Jia, Y. Zhang, Bi-8-carboxamidoquinoline derivatives for the fluorescent recognition of Zn2+ , J. Fluoresc. 25 (2015) 441–449. Y. Zhang, X. Guo, W. Si, L. Jia, X. Qian, Ratiometric and water-soluble fluorescent zinc sensor of carboxamidoquinoline with an alkoxyethylamino chain as receptor, Org. Lett. 10 (2008) 473–476. V.V.S. Mummidivarapu, K. Tabbasum, J.P. Chinta, C.P. Rao, 1,3-Di-amidoquinoline conjugate of calix[4]arene (l) as a ratiometric and colorimetric sensor for Zn2+ : spectroscopy, microscopy and computational studies, Dalton Trans. 41 (2012) 1671–1674. L. Tang, J. Zhao, M. Cai, P. Zhou, K. Zhong, S. Hou, Y. Bian, An efficient sensor for relay recognition of Zn2+ and Cu2+ through fluorescence ‘off–on–off’ functionality, Tetrahedron Lett. 54 (2013) 6105–6109. X. Zhou, Y. Lu, J.F. Zhu, W.H. Chan, A.W.M. Lee, P.S. Chan, R.N.S. Wong, N.K. Mak, Ratiometric fluorescent Zn2+ chemosensor constructed by appending a pair of carboxamidoquinoline on 1,2-diaminocyclohexane scaffold, Tetrahedron 67 (2011) 3412–3419. K. Ghosh, T. Sen, (rac)-1,10-Binaphthyl-based simple receptors designed for fluorometric discrimination of maleic and fumaric acids, J. Phys. Chem. B 115 (2011) 8597–8608. Z. Dong, Y. Guo, X. Tian, J. Ma, Quinoline group based fluorescent sensor for detecting zinc ions in aqueous media and its logic gate behaviour, J. Lumin. 134 (2013) 635–639. C. Gao, X. Jin, X. Yan, P. An, Y. Zhang, L. Liu, H. Tian, W. Liu, X. Yao, Y. Tang, A small molecular fluorescent sensor for highly selectivity of zinc ion, Sens. Actuators, B: Chem. 176 (2013) 775–781. L. Gu, X. Wan, H. Liu, T. Liu, Y. Yao, A novel ratiometric fluorescence sensor for Zn2+ detection, Anal. Methods 6 (2014) 8460–8463. L. Wang, W. Qin, X. Tang, W. Dou, W. Liu, Development and applications of fluorescent indicators for Mg2+ and Zn2+ , J. Phys. Chem. A 115 (2011) 1609–1616. Y. Bao, B. Liu, H. Wang, F. Du, R. Bai, A highly sensitive and selective ratiometric Cd2+ fluorescent sensor for distinguishing Cd2+ from Zn2+ based on both fluorescence intensity and emission shift, Anal. Methods 3 (2011) 1274–1276. S. Anbu, R. Ravishankaran, M.F.C. Guedes da Silva, A.A. Karande, A.J.L. Pombeiro, Differentially selective chemosensor with fluorescence off–on responses on Cu2+ and Zn2+ ions in aqueous media and applications in pyrophosphate sensing, live cell imaging, and cytotoxicity, Inorg. Chem. 53 (2014) 6655–6664. S. Mandal, S. Ghosh, C. Banerjee, J. Kuchlyan, N. Sarkar, Unique photophysical behavior of 2,2 -bipyridine-3,3 -diol in DMSO–water binary mixtures: potential application for fluorescence sensing of Zn2+ based on the inhibition of excited-state intramolecular double proton transfer, J. Phys. Chem. B 117 (2013) 12212–12223. M. Zhu, M. Yuan, X. Liu, J. Xu, J. Lv, C. Huang, H. Liu, Y. Li, S. Wang, D. Zhu, Visible near-infrared chemosensor for mercury ion, Org. Lett. 10 (2008) 1481–1484. H.A. Benesi, J.H. Hildebrand, A spectrophotometric investigation of the interaction of iodine with aromatic hydrocarbons, J. Am. Chem. Soc. 71 (1949) 2703–2707. A. Ringbom, Complexation in Analytical Chemistry, Wiley (Interscience), New York, NY, 1963. W. Lin, L. Yuan, Z. Cao, Y. Feng, L. Long, A sensitive and selective fluorescent thiolprobe in water based on the conjugate 1,4-addition of thiols to ␣,-unsaturated ketones, Chem. Eur. J. 15 (2009) 5096–5103. A. Caballero, R. Martínez, V. Lloveras, I. Ratera, J. Vidal-Gancedo, K. Wurst, A. Tárraga, P. Molina, J. Veciana, Highly selective chromogenic and redox or fluorescent sensors of Hg2+ in aqueous environment based on 1,4-disubstitutedazines, J. Am. Chem. Soc. 127 (2005) 15666–15667. M. Shortreed, R. Kopelman, M. Kuhn, B. Hoyland, Fluorescent fiber-optic calcium sensor for physiological measurements, Anal. Chem. 68 (1996) 1414–1418.
Biographies Xuhua Tian received his B.S. degree from Taiyuan Institute of Technology, PR China, in 2011. He is currently a master candidate at College of Chemistry and Chemical Engineering, Qiqihar University, PR China. His research interests focus on developing fluorescent chemosensors. Xiangfeng Guo received his Ph.D. degree from Dalian University of Technology, PR China, in 2004. He is a professor in College of Chemistry and Chemical Engineering, Qiqihar University. His current research interests are mainly in the development of chemosensors and new surfactant. Lihua Jia received her Ph.D. degree from Dalian University of Technology, PR China, in 2004. She is a professor in College of Chemistry and Chemical Engineering, Qiqihar
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
929
University. Her current research interests include supramolecular chemistry and the development of catalyst.
Qiqihar University, PR China. His research interests focus on developing new surfactant.
Rui Yang received her master degree from Qiqihar University, PR China, in 2012. She is now working in Qiqihar University. Her current research interests focus on chemosensors.
Chaoyue Liu received her B.S. degree from Qiqihar University, PR China, in 2012. She is currently a master candidate at College of Chemistry and Chemical Engineering, Qiqihar University, PR China. Her current research interests focus on molecular recognition.
Guangzhou Cao received his B.S. degree from Binzhou University, PR China, in 2012. He is currently a master candidate at College of Chemistry and Chemical Engineering,
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A fluorescent sensor based on bicarboxamidoquinoline for highly selective relay recognition of Zn2+ and citrate with ratiometric response Xuhua Tian, Xiangfeng Guo ∗ , Lihua Jia ∗ , Rui Yang, Guangzhou Cao, Chaoyue Liu College of Chemistry and Chemical Engineering, Key Laboratory of Fine Chemicals of College of Heilongjiang Province, Qiqihar University, Qiqihar 161006, China
a r t i c l e
i n f o
Article history: Received 12 March 2015 Received in revised form 10 July 2015 Accepted 13 July 2015 Available online 15 July 2015 Keywords: Relay recognition Ratiometric sensor Zinc Citrate Bicarboxamidoquinoline
a b s t r a c t A novel bicarboxamidoquinoline-based fluorescent sensor 1 was designed and synthesized, which performed ratiometric recognition for Zn2+ without interference from Cd2+ . The sensor 1 bound Zn2+ in 1:1 stoichiometry, with the binding constant of 2.07 × 103 M−1 . Moreover, the in situ generated 1–Zn2+ complex could serve as an excellent ratiometric citrate sensor via a Zn2+ displacement and discriminated citrate from a series of common carboxylates in neutral aqueous solution. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Citrate is an important organic tricarboxylate in the Krebs cycle, its concentration in urine can be served as an indicator of renal metabolism [1]. In addition, citrate has been widely used in foods and pharmaceuticals [2,3]. Various techniques were established for the determination of citrate [4]. Nevertheless, some techniques with higher selectivity and convenience are still needed. Fluorescence detection has been widely implemented in different kinds of analytes as a result of the simplicity, high sensitivity, selectivity and manipulability [5,6]. Especially, ratiometric fluorescence monitoring offers additional advantages in the detection process because it may avert the influences of many analyteindependent factors. Thus, varieties of fluorescent ratiometric sensors have been developed successfully [7]. Up to now, considerable effort has been devoted to the development of fluorescent sensors for citrate [8–10,4,11]. For example, Fabbrizzi et al. developed a metal-containing sensor for citrate based on the fluorescent indicator displacement [10]. Yen et al. designed a symmetrical coumarin-based sensor for citrate [4]. Ghosh et al. synthesized a pyridinium-based sensor for citrate
∗ Corresponding authors. Tel.: +86 0452 2742563; fax: +86 0452 2742563. E-mail addresses: [email protected] (X. Guo), [email protected] (L. Jia). http://dx.doi.org/10.1016/j.snb.2015.07.047 0925-4005/© 2015 Elsevier B.V. All rights reserved.
through indicator displacement assay [11]. All the sensors mentioned above can triumphantly recognize citrate with OFF–ON fluorescent behavior. Furthermore, Parker and Yu [12] successfully developed a citrate sensor by using coordinatively unsaturated Eu-complex to chelate citrate, which performed excellently ratiometric response for citrate. However, literature on the ratiometric sensing of citrate was still very few. Intrigued by relay recognition of metal ions and anions [13–15], we hope a new ratiometric response for citrate could be established through metal ions displacement approach. Based on the strategy, a ratiometric sensor for a metal ion is necessary, and then the metal ion bonded with the sensor can be exactly captured by citrate while a reverse spectrum change appears. In consideration of our previous work about ratiometric zinc sensor [16,17] and some related researches [18–20], a new sensor was designed and synthesized as shown in Scheme 1. The sensor is based on bicarboxamidoquinoline groups which are connected to the binaphthol scaffold through ethylenediamine linkers. The symmetric sensor with intramolecular two carboxamidoquinolines could form a feasible convergent space for Zn2+ . The introduction of ethylenediamine linkers could increase the chelate space of bicarboxamidoquinoline, resulting in weaker binding capacity of the sensor with Zn2+ . And then a particular carboxylate could be recognized via Zn2+ displacement approach. In addition, the ethylenediamine linkers and hydroxyethyl groups are beneficial to the recognition in aqueous solution. As expected, the sensor
924
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
Cl OH
O
O
O
H N
H2N
O
OH
OH
H N
O
N H
O
O
O
O H N
O Binol
O
O
3
OH
OH
N H
2 HO O O NH
N H
N
N
N
O O
O
4
N NH O
Cl
N O
1
NH
N H
HO
Scheme 1. Synthesis route of sensor 1.
recognized Zn2+ with high selectivity and importantly the resultant Zn2+ -sensor complex discriminated citrate with ratiometric emission changes. 2. Experimental 2.1. Chemicals and apparatus All solvents and analytical grade chemicals were obtained commercially and used directly without further purification. NMR spectra were recorded using a Bruker AVANCE-600 spectrometer and referenced to internal tetramethylsilane. Infrared spectral data were measured with Nicolet Avatar-370. A Waters Xevo G2-S QT was used for Mass measurements. Melting points were performed on an X-6 microscopic melting point apparatus. The UV–vis spectra were determined with a Puxi TU-1901 spectrophotometer. Fluorescence measurements were scanned with a Hitachi F-7000. The pH measurements were monitored with a Sartorius basic pH-meter PB-10. 2.2. General procedure for spectroscopic measurements Ultra-pure water and tris–HCl buffer were used for all experiments. The metal ion solutions (0.050 M) were obtained from NaCl, KCl, Mg(ClO4 )2 , Ca(NO3 )2 , Cr(NO3 )2 , Fe2 (SO4 )3 , CoSO4 , NiSO4 , Cu(NO3 )2 , Zn(NO3 )2 , AgNO3 , CdSO4 , HgCl2 , Pb(NO3 )2 , AlCl3 . Carboxylates (as sodium or potassium salts, 0.050 M) in ultra-pure water were used in experiments. The spectra measurements were operated at room temperature and the pH value of all experiments were maintained at pH 7.4. All fluorescence data were recorded under the 320 nm excitation, the slit widths of excitation and emission were 2.5 nm. 1–Zn2+ complex was obtained from mixing 2.0 equiv of Zn2+ with 10 M sensor 1 in solution (methanol/water = 1:1, pH = 7.4).
Preparation of compound 2. To a solution of compound 3 (0.254 g, 0.550 mmol) in ethanol (5.0 mL), ethanolethylene diamine (0.284 g, 2.73 mmol) was added and the mixture was refluxed for 3 h. The cooled reaction mixture was poured into saturated sodium chloride solution and the aqueous phase was extracted with dichloromethane (50 mL). The combined CH2 Cl2 solution was dried over anhydrous MgSO4 , and evaporated to give the crude product 2 as a sticky substance (0.227 g, crude). Then the crude product collected was directly used for the next step without further purification. Preparation of compound 1. Compound 2 (0.227 g, 0.395 mmol), compound 4 (0.192 g, 0.869 mmol), potassium carbonate (0.163 g, 1.185 mmol), and catalytic amount of potassium iodide were dissolved in dry acetonitrile (8.0 mL) and the reaction mixture were refluxed for 9 h. On completion of the reaction, the residue was diluted by water and extracted with 50 mL of dichloromethane. The organic extracts were dried over anhydrous MgSO4 and concentrated in vacuo. The crude products were purified by column chromatography (methanol/dichloromethane = 20/1) on silica gel to give 1 (0.109 g, 27.5%). Mp: 88.2–89.8 ◦ C. 1 H NMR (600 MHz, CDCl3 ) ı 11.09 (s, 2H), 8.72 (dd, J = 7.3, 1.2 Hz, 2H), 8.64 (dd, J = 4.2, 1.2 Hz, 2H), 8.17 (dd, J = 8.2, 1.5 Hz, 2H), 7.85 (d, J = 9.1 Hz, 2H), 7.80 (d, J = 8.1 Hz, 2H), 7.62–7.53 (m, 4H), 7.34 (dd, J = 8.3, 4.2 Hz, 2H), 7.31 (t, J = 7.4 Hz, 2H), 7.24 (d, J = 7.0 Hz, 2H), 7.14 (d, J = 3.4 Hz, 2H), 7.13 (d, J = 4.3 Hz, 2H), 5.67 (br, 2H), 4.25 (s, 4H), 4.12 (br, 2H), 3.61 (br, 4H), 3.26 (br, 4H), 3.06–2.91 (m, 4H), 2.73 (br, 4H), 2.32 (br, 2H), 2.26 (br, 2H). 13 C NMR (150 MHz, CDCl3 ) ı 169.20, 168.03, 152.71, 148.79, 138.66, 136.88, 133.45, 133.26, 130.22, 129.63, 128.24, 128.22, 127.47, 127.36, 124.94, 124.73, 122.21, 121.69, 119.54, 117.38, 114.97, 68.57, 60.57, 59.86, 58.85, 54.48, 36.67. FTIR (cm−l ): 3407, 3060, 1683, 1527, 1270, 1151, 1049. MS (ESI): m/z calcd for C54 H55 N8 O8 + (M + H+ ) 943.4065, found 943.4116. 3. Results and discussion
2.3. Synthesis
3.1. Fluorescence response for Zn2+
The medium product 2-chloro-N-(quinol-8-yl) acetamide 4 was prepared as our previous work [17]. And diethyl 2,2 (1,1 -Binaphthyl-2,2 -diylbis(oxy))diacetate 3 was prepared as previously described [21].
In order to evaluate the selectivity of sensor for Zn2+ , the fluorescence changes of 1 to various metal ions were investigated in aqueous solution (Fig. 1A). Compared to other metal ions examined, only Zn2+ caused a red shift to 500 nm via the 14-fold enhancement
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
925
160
A 2+
120
80 others
B
1 + metal ions (2 eq.) 1 + metal ions (2 eq.) +zinc ion (2 eq.)
3
I500nm/I410nm
2
1
40 Cu
2+
3+
+
3+
Al Fe
Ag + Hg 2 + Cd 2 + Pb 2
2+
2+
2+
Ni Cu
+
3+
Cr Co
+
600
+
450 500 550 Wavelength(nm)
se nt Zn 2
400
ab
350
K+ M 2 g + Ca 2
0
0
Na
Intensity(a.u.)
Zn
Fig. 1. Fluorescence spectra of 10 M sensor 1 in the present of 20 M different metal ions (A). Metal ions competition analysis of 10 M sensor 1 (B). Black bars: the emission of 1 in the presence of 2.0 equiv of metal ions. Red bars: the emission of 1 in the presence of 2.0 equiv of other metal ions followed by 2.0 equiv of Zn2+ . Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
500
12
300 μM
A
B
300 0 μM
200
8 I(500nm)/I(410nm)
Intensity(a.u.)
2+
[Zn ]
I(500nm)/I(410nm)
10
400
6 4
4 2 0
2
100
Y = 0.026 + 0.10X 2 R = 0.997
6
0
25
50
2+
[Zn ]/ μM
0
0 350
400
450
500
550
600
Wavelength(nm)
0
50
100
150
200
250
300
2+
[Zn ]/ μM
Fig. 2. Fluorescence emission spectra of 1 upon addition of Zn2+ . Inset: the intensity ratio (I500 nm /I410 nm ) as functions of Zn2+ concentration. Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm.
of ratio intensity (I500 nm /I410 nm ). And Cu2+ led to a slight fluorescence quenching. Importantly, 1 could distinguish Zn2+ from Cd2+ , which was well known to be a major obstacle [22–24]. The enhancement emission might arise from the occurrence of the chelation-enhanced fluorescence (CHEF) process upon binding to Zn2+ [19,25,26]. And the red-shift might result from the ICT process which was promoted by the deprotonation of amide NH after binding to Zn2+ [17]. To validate the selectivity of 1 in practice, the competition experiments were also conducted by addition of 2.0 equiv Zn2+ to aqueous solutions in the presence of 2.0 equiv other metal ions as shown in Fig. 1B. The fluorescence intensity of the complex was negligibly affected by other coexistent metal ions except Cu2+ , which often acted as a quencher via the high affinity and paramagnetism [27,28]. In an attempt to evaluate the influence of Zn2+ concentration, the fluorescence properties of 1 were studied in aqueous solutions (Fig. 2). Upon addition of Zn2+ , a significant decrease of the fluorescence intensity at 410 nm and an increase of fluorescence emission band centered at 500 nm were observed. As shown in Fig. 2B, the ratio of fluorescence intensity (I500 nm /I410 nm ) increased linearly over the Zn2+ concentration range 0–50 M and a linear relationship (R2 = 0.997) is obtained, which indicates that sensor 1 shown potential use for the quantitative determination of Zn2+ with ratiometric response. When more than 20 equiv Zn2+ was added, the maximum fluorescence intensity was retained, which suggests the sensor 1 had weak binding capacity. The stoichiometry for sensor 1 and Zn2+ was found to be 1:1 based on Job’s plot analysis (Fig. S1 see ESI). Further the binding constant was extracted from the
fluorescence titrations to afford the value of 2.07 × 103 M−1 obtained from the Benesi–Hildebrand equation (Fig. S2 see ESI) [29,30]. The weaker binding capacity compared with some reported sensors provided a displacement possibility by other higher affinity carboxylates [17]. In addition, the stability constant for zinc–citrate complex was in the order of 1011 M−1 , which revealed the citrate had higher affinity toward Zn2+ [31].
3.2. Fluorescence sensing of 1–Zn2+ complex for citrate Considering the weak binding capacity of sensor 1 to Zn2+ , the on-site generated 1–Zn2+ complex was a possible sensor for citrate via Zn2+ displacement approach. To verify this conjecture, the carboxylates-selective experiment was conducted by respective addition of varying carboxylates into 1–Zn2+ solution. As exhibited in Fig. 3, only the addition of citrate led to a strong fluorescence quenching (ratio intensity quenching efficiency, (I0 − I)/I0 × 100% = 79%), which might be attributed to Zn2+ displacement approach. Under the same conditions, 20 M of oxalate caused a slight fluorescence quenching effect, whereas, the addition of other carboxylates induced negligible fluorescence spectral changes. To get further insight into the high selectivity of 1–Zn2+ complex to citrate, the fluorescence competition experiments were implemented subsequently. The results show that coexistence of other carboxylates caused scarce interference on the detection of citrate. These illustrated that 1–Zn2+ complex could serve as a highly selective sensor for citrate.
926
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929 2+
150
500nm 410nm
100
B
2
/I
oxalate
50
I
Intensity(a.u.)
others
1-Zn complex + 2 eq anions 2+ 1-Zn complex + 2 eq anions + 2 eq citrate
3
A
1
citrate 0 400
450
500
550
600
Wavelength(nm)
ab se n ci t tra ac te et a ox te al a ta te rtr a m te al a m te al e fu ate m ar m at al e o su nat cc e in ad ate ip at es
0
350
Fig. 3. Fluorescence spectra of 1–Zn2+ complex with different carboxylates at 20 M concentration (A). The ratio fluorescence intensity changes of 1–Zn2+ complex against various carboxylates (B); red bars: the ratio fluorescence intensity of 1–Zn2+ complex in the presence of miscellaneous carboxylates at 20 M concentration; black bars: the change of the ratio fluorescence intensity upon the subsequent addition of 20 M citrate to the above solution. Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
4
200
5
B
45 μM
3
[citrate]
100
0
I(500nm)/I(410nm)
Intensity(a.u.)
150
2
3 2 1 0
1
50
Y = 3.25 - 0.17X 2 R =0.992
4 I(500nm)/I(410nm)
A
0
4
8 12 [citrate] μM
16
0
0 350
400
450
500
550
600
0
10
20
30
40
50
[citrate] μM
Wavelength(nm) 2+
1-Zn complex + 4.5eq citrate free 1
Intensity(a.u.)
60
C
40
20
0 350
400
450
500
550
600
Wavelength(nm) Fig. 4. Fluorescence titration spectra of 1–Zn2+ complex with increasing amounts of citrate. The ratio intensity (I500 nm /I410 nm ) of 1–Zn2+ complex versus the concentration of citrate (B). The fluorescence spectra overlay (C); red line: free 1; black line: 1–Zn2+ complex treated with 45 M citrate. Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The sensing property of 1–Zn2+ complex to citrate was further evaluated by fluorescence titration experiment (Fig. 4A). Upon gradual introduction of citrate concentration, the emission intensity at 500 nm was gradually decreased, yet the emission band around 410 nm was gradually increased. The ratio of fluorescence intensity (I500 nm /I410 nm ) decreased linearly over the citrate concentration range 0–15 M with a linear relationship (R2 = 0.992), then the ratio fluorescence intensity decreased slowly to minimum with the continued increase of citrate (Fig. 4B). These indicate that the Zn2+ was captured by citrate, which resulted in
fluorescence recovery of sensor 1. To verify our assumption, the fluorescence spectra overlay of free sensor 1 and sensor 1–Zn2+ complex + 4.5 equiv citrate were depicts in Fig. 4C. The high overlap in Fig. 4B supported that citrate acted as a Zn2+ chelator in the second recognition progress. In order to further verify the displacement of Zn2+ and release of the sensor with addition of citrate, the ESI–MS spectra of complex sensor 1 + Zn2+ (5.0 equiv) and the complex sensor 1 + Zn2+ (5.0 equiv) + citrate (5.0 equiv) were measured as shown in Fig. S7 and Fig. S8. Peaks m/z 943.4188 and 1005.3354 values corresponded to [1 + H+ ]+ and
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
2.5
1.0
A
Y = 1.96 X + 9.50 2 R = 0.982 Detection limit = 1.42 μM
Y = 0.922 X + 5.22 2 R = 0.984 Detection limit = 2.19 μM
0.8
(Imax - I)/(Imax - Imin)
2.0
(I - Imin)/(Imax - Imin)
927
1.5
1.0
0.5
B
0.6
0.4
0.2
0.0 -5.0
-4.8
-4.6
-4.4
-4.2
-4.0
-3.8
-3.6
-5.6
-5.4
-5.2
2+
-5.0
-4.8
-4.6
Log[citrate]
Log[Zn ]
Fig. 5. Normalized response of the ratio fluorescence signal (I500 nm /I410 nm ) to changing Zn2+ concentrations (A) and citrate concentrations (B). Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm.
2.5
4
A
B
2.0
I500nm/I410nm
I500nm/I410nm
3 1.5
1.0
2
1 0.5
0
0.0 0
2
4
6
8
10
12
0
1
2
Time/min
3
4
5
6
7
8
Time/min
Fig. 6. Time responses of the sensor 1 in the presence of 2.0 equiv. Zn2+ (A) and 1–Zn2+ complex in the presence of 2.0 equiv. citrate (B). Methanol/water = 1/1 (v/v), pH = 7.4, 0.010 M tris–HCl, ex = 320 nm.
[1 + Zn2+ –H+ ]+ , respectively. When 5.0 equiv of citrate was added, the peak of [1 + H+ ]+ increased and the peak of [1 + Zn2+ –H+ ]+ decreased obviously. The [1 + Zn2+ –H+ ]+ complex was calculated at m/z 1005.3189 and measured at m/z 1005.3354 or 1005.3273. This indicated the formation of a 1–Zn2+ complex of 1:1 stoichiometry. After the addition of citrate, the peak at 1005.3237 corresponding to [1 + Zn2+ –H+ ]+ decreased and obviously, indicating that 1–Zn2+ complex lost Zn2+ and the free sensor 1 was released. All these revealed that sensor 1–Zn2+ could quantitatively detect citrate with ratiometric behavior. 3.3. Detection limit To study the sensitivity of sensor 1 and 1–Zn2+ complex, the detection limits of the sensors were obtained based on a reported
method [32–34]. A linear regression curve was then fitted to these normalized ratio fluorescence intensity data in Fig. 5. The detection limit of the sensor 1 was 1.42 M, the 1–Zn2+ complex was 2.19 M. 3.4. Response time Besides the selectivity and selectivity, the response time is an important indicator of evaluation of the sensor. So the response times of sensor 1 with Zn2+ and 1–Zn2+ complex with citrate were investigated (Fig. 6). The ratio intensity of sensor 1 gradually increased when Zn2+ was introduced and then was retained after more than 6 min. The ratio intensity of 1–Zn2+ complex gradually decreased with the addition of citrate and tended to stabilize after 1 min. The results indicated that the sensor had a fast response in the recognition processes.
Table 1 Determination of analyte concentrations in real samples (n = 3). Samples
Analytes
Tap water
Zinc ion
Sprite
Citrate
a
Average value of three determinations.
Added (M)
Founda (M)
Recovery (%)
0.00
20.00 35.00
20.50 ± 0.012 33.40 ± 0.045
102.50 96.68
3.14
1.00 2.00
4.31 ± 0.011 6.14 ± 0.074
104.02 119.46
Content (M)
928
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
3.5. Practical applications In order to verify the practical applicability of the ratio sensors, the determination of Zn2+ in tap water and the determination of citrate in Sprite (drink from Coca-Cola) were evaluated using the standard addition method. The recovery of Zn2+ in tap water from 96.68 to 102.50% and the recovery of citrate in Sprite from 104.02 to 119.46% were obtained, indicating the appreciable practicality of the presented sensors (Table 1). 4. Conclusion A new sensor 1 based on bicarboxamidoquinoline for sequential recognition of Zn2+ and citrate with ratiometric behavior was established. 1 displayed a high selectivity toward Zn2+ over other metal ions especially over Cd2+ via the CHEF mechanism. 1–Zn2+ complex with a 1:1 binding stoichiometry performed a high selectivity in recognizing citrate, which exhibited excellently distinguishing behavior among a series of common carboxylates. The design strategy that the metal-complex with adjustable binding capacity through introduction suitable linker could serve as a sensor for some certain analyte might be helpful in expanding the development of sensors for carboxylates. Acknowledgements This work was supported by the National Natural Science Foundation of China (21176125), the Natural Science Foundation of Heilongjiang Province of China (B201114, B201313, B201419) and the Science Research Project of the Ministry of Education of Heilongjiang Province of China (2012TD012, 12511Z030, 12521594).
[14]
[15]
[16] [17]
[18]
[19]
[20]
[21]
[22]
[23]
[24] [25]
[26]
[27]
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2015.07.047
[28]
References
[29]
[1] L.L. Hamm, Renal handling of citrate, Kidney Int. 38 (1990) 728–735. [2] S¸. Türko˘glu, Genotoxicity of five food preservatives tested on root tips of Allium cepa L., Mutat. Res. 626 (2007) 4–14. [3] T. Pérez-Ruiz, C. Martínez-Lozano, V. Tomás, O. Val, Flow-injection chemiluminometric determination of citrate based on a photochemical reaction, Analyst 120 (1995) 471–475. [4] Z.H. Liu, S. Devaraj, C.R. Yang, Y.P. Yen, A new selective chromogenic and fluorogenic sensor for citrate ion, Sens. Actuators, B: Chem. 174 (2012) 555–562. [5] Z. Liu, W. He, Z. Guo, Metal coordination in photoluminescent sensing, Chem. Soc. Rev. 42 (2013) 1568–1600. [6] J. Wu, W. Liu, J. Ge, H. Zhang, P. Wang, New sensing mechanisms for design of fluorescent chemosensors emerging in recent years, Chem. Soc. Rev. 40 (2011) 3483–3495. [7] M.H. Lee, J.S. Kim, J.L. Sessler, Small molecule-based ratiometric fluorescence probes for cations, anions, and biomolecules, Chem. Soc. Rev. 44 (2015) 4185–4191. [8] C. Schmuck, M. Schwegmann, A naked-eye sensing ensemble for the selective detection of citrate – but not tartrate or malate – in water based on a tris-cationic receptor, Org. Biomol. Chem. 4 (2006) 836–838. [9] M. Isabel Burguete, F. Galindo, S.V. Luis, L. Vigara, A turn-on fluorescent indicator for citrate with micromolar sensitivity, Dalton Trans. 36 (2007) 4027–4033. [10] L. Fabbrizzi, F. Foti, A. Taglietti, Metal-containing trifurcate receptor that recognizes and senses citrate in water, Org. Lett. 7 (2005) 2603–2606. [11] K. Ghosh, A.R. Sarkar, Pyridinium-based symmetrical diamides as chemosensors in visual sensing of citrate through indicator displacement assay (IDA) and gel formation, Org. Biomol. Chem. 9 (2011) 6551–6558. [12] D. Parker, J. Yu, A pH-insensitive, ratiometric chemosensor for citrate using europium luminescence, Chem. Commun. 25 (2005) 3141–3143. [13] L. Tang, M. Cai, P. Zhou, J. Zhao, K. Zhong, S. Hou, Y. Bian, A highly selective and ratiometric fluorescent sensor for relay recognition of zinc(II) and sulfide
[30]
[31] [32]
[33]
[34]
ions based on modulation of excited-state intramolecular proton transfer, RSC Adv. 3 (2013) 16802–16809. Z. Dong, X. Le, P. Zhou, C. Dong, J. Ma, Sequential recognition of zinc ion and hydrogen sulfide by a new quinoline derivative with logic gate behavior, RSC Adv. 4 (2014) 18270–18277. X. Lou, D. Ou, Q. Li, Z. Li, An indirect approach for anion detection: the displacement strategy and its application, Chem. Commun. 48 (2012) 8462–8477. X. Tian, X. Guo, L. Jia, Y. Zhang, Bi-8-carboxamidoquinoline derivatives for the fluorescent recognition of Zn2+ , J. Fluoresc. 25 (2015) 441–449. Y. Zhang, X. Guo, W. Si, L. Jia, X. Qian, Ratiometric and water-soluble fluorescent zinc sensor of carboxamidoquinoline with an alkoxyethylamino chain as receptor, Org. Lett. 10 (2008) 473–476. V.V.S. Mummidivarapu, K. Tabbasum, J.P. Chinta, C.P. Rao, 1,3-Di-amidoquinoline conjugate of calix[4]arene (l) as a ratiometric and colorimetric sensor for Zn2+ : spectroscopy, microscopy and computational studies, Dalton Trans. 41 (2012) 1671–1674. L. Tang, J. Zhao, M. Cai, P. Zhou, K. Zhong, S. Hou, Y. Bian, An efficient sensor for relay recognition of Zn2+ and Cu2+ through fluorescence ‘off–on–off’ functionality, Tetrahedron Lett. 54 (2013) 6105–6109. X. Zhou, Y. Lu, J.F. Zhu, W.H. Chan, A.W.M. Lee, P.S. Chan, R.N.S. Wong, N.K. Mak, Ratiometric fluorescent Zn2+ chemosensor constructed by appending a pair of carboxamidoquinoline on 1,2-diaminocyclohexane scaffold, Tetrahedron 67 (2011) 3412–3419. K. Ghosh, T. Sen, (rac)-1,10-Binaphthyl-based simple receptors designed for fluorometric discrimination of maleic and fumaric acids, J. Phys. Chem. B 115 (2011) 8597–8608. Z. Dong, Y. Guo, X. Tian, J. Ma, Quinoline group based fluorescent sensor for detecting zinc ions in aqueous media and its logic gate behaviour, J. Lumin. 134 (2013) 635–639. C. Gao, X. Jin, X. Yan, P. An, Y. Zhang, L. Liu, H. Tian, W. Liu, X. Yao, Y. Tang, A small molecular fluorescent sensor for highly selectivity of zinc ion, Sens. Actuators, B: Chem. 176 (2013) 775–781. L. Gu, X. Wan, H. Liu, T. Liu, Y. Yao, A novel ratiometric fluorescence sensor for Zn2+ detection, Anal. Methods 6 (2014) 8460–8463. L. Wang, W. Qin, X. Tang, W. Dou, W. Liu, Development and applications of fluorescent indicators for Mg2+ and Zn2+ , J. Phys. Chem. A 115 (2011) 1609–1616. Y. Bao, B. Liu, H. Wang, F. Du, R. Bai, A highly sensitive and selective ratiometric Cd2+ fluorescent sensor for distinguishing Cd2+ from Zn2+ based on both fluorescence intensity and emission shift, Anal. Methods 3 (2011) 1274–1276. S. Anbu, R. Ravishankaran, M.F.C. Guedes da Silva, A.A. Karande, A.J.L. Pombeiro, Differentially selective chemosensor with fluorescence off–on responses on Cu2+ and Zn2+ ions in aqueous media and applications in pyrophosphate sensing, live cell imaging, and cytotoxicity, Inorg. Chem. 53 (2014) 6655–6664. S. Mandal, S. Ghosh, C. Banerjee, J. Kuchlyan, N. Sarkar, Unique photophysical behavior of 2,2 -bipyridine-3,3 -diol in DMSO–water binary mixtures: potential application for fluorescence sensing of Zn2+ based on the inhibition of excited-state intramolecular double proton transfer, J. Phys. Chem. B 117 (2013) 12212–12223. M. Zhu, M. Yuan, X. Liu, J. Xu, J. Lv, C. Huang, H. Liu, Y. Li, S. Wang, D. Zhu, Visible near-infrared chemosensor for mercury ion, Org. Lett. 10 (2008) 1481–1484. H.A. Benesi, J.H. Hildebrand, A spectrophotometric investigation of the interaction of iodine with aromatic hydrocarbons, J. Am. Chem. Soc. 71 (1949) 2703–2707. A. Ringbom, Complexation in Analytical Chemistry, Wiley (Interscience), New York, NY, 1963. W. Lin, L. Yuan, Z. Cao, Y. Feng, L. Long, A sensitive and selective fluorescent thiolprobe in water based on the conjugate 1,4-addition of thiols to ␣,-unsaturated ketones, Chem. Eur. J. 15 (2009) 5096–5103. A. Caballero, R. Martínez, V. Lloveras, I. Ratera, J. Vidal-Gancedo, K. Wurst, A. Tárraga, P. Molina, J. Veciana, Highly selective chromogenic and redox or fluorescent sensors of Hg2+ in aqueous environment based on 1,4-disubstitutedazines, J. Am. Chem. Soc. 127 (2005) 15666–15667. M. Shortreed, R. Kopelman, M. Kuhn, B. Hoyland, Fluorescent fiber-optic calcium sensor for physiological measurements, Anal. Chem. 68 (1996) 1414–1418.
Biographies Xuhua Tian received his B.S. degree from Taiyuan Institute of Technology, PR China, in 2011. He is currently a master candidate at College of Chemistry and Chemical Engineering, Qiqihar University, PR China. His research interests focus on developing fluorescent chemosensors. Xiangfeng Guo received his Ph.D. degree from Dalian University of Technology, PR China, in 2004. He is a professor in College of Chemistry and Chemical Engineering, Qiqihar University. His current research interests are mainly in the development of chemosensors and new surfactant. Lihua Jia received her Ph.D. degree from Dalian University of Technology, PR China, in 2004. She is a professor in College of Chemistry and Chemical Engineering, Qiqihar
X. Tian et al. / Sensors and Actuators B 221 (2015) 923–929
929
University. Her current research interests include supramolecular chemistry and the development of catalyst.
Qiqihar University, PR China. His research interests focus on developing new surfactant.
Rui Yang received her master degree from Qiqihar University, PR China, in 2012. She is now working in Qiqihar University. Her current research interests focus on chemosensors.
Chaoyue Liu received her B.S. degree from Qiqihar University, PR China, in 2012. She is currently a master candidate at College of Chemistry and Chemical Engineering, Qiqihar University, PR China. Her current research interests focus on molecular recognition.
Guangzhou Cao received his B.S. degree from Binzhou University, PR China, in 2012. He is currently a master candidate at College of Chemistry and Chemical Engineering,