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A new indazole-based colorimetric chemosensor for sequential detection of Cu2+ and GSH in aqueous solution
Tetrahedron 73 (2017) 4750e4757
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A new indazole-based colorimetric chemosensor for sequential detection of Cu2þ and GSH in aqueous solution Min Seon Kim a, Jae Min Jung a, Ji Hye Kang a, Hye Mi Ahn a, Pan-Gi Kim b, Cheal Kim a, * a
Department of Fine Chemistry and Department of Interdisciplinary Bio IT Materials, Seoul National University of Science and Technology, Seoul 139-743, South Korea b School of Ecology & Environmental Systems, Kyungpook National University, Sangju 37224, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 April 2017 Received in revised form 20 June 2017 Accepted 26 June 2017 Available online 29 June 2017
A new selective and sensitive colorimetric chemosensor 1 was developed for the sequential detection of Cu2þ and glutathione (GSH) in aqueous solution. The sensor 1 detected Cu2þ ion by an obvious color change from colorless to pale yellow. Importantly, 1 could be used to detect and quantify Cu2þ ion in water samples, and the detection limit (0.14 mM) of 1 for Cu2þ was much lower than the guideline (31.5 mM) of WHO in drinking water. Also, Cu2þ-2$1 complex can be used as a colorimetric sensor for GSH via naked-eye. The detection limit for GSH was founded to be 2.98 mM. Moreover, the sensing ability of 1 for Cu2þ was supported by theoretical calculations. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Colorimetric Copper Glutathione Sequential detection Theoretical calculations
1. Introduction The development of selective and sensitive chemosensors is an important assignment for detecting transition metal ions, which play important roles in chemical, biological, and environmental processes.1e7 Among them, copper is one of the most vital metal ions in biological system, because it acts as an essential cofactor correlated with activities of various enzymes, including superoxide dismutase, cytochrome c oxidase, and tyrosinase.8e12 Thus, a steady intake of copper is indispensable for our good health.13 However, an excessive accumulation of copper can cause fatal diseases such as Alzheimer's, Parkinson's, Wilson's and prion diseases.14e18 Moreover, copper is a significant environmental pollutant because of its widespread use in industry and agriculture.19e23 The World Health Organization (WHO) has set the maximum acceptable limit of copper in drinking water at 2 ppm (31.5 mM).24,25 For these reasons, chemosensors with high sensitivity, selectivity and low detection limit capable of rapidly detecting Cu2þ are needed to be urgently developed.26e30 Biological thiols, such as glutathione (GSH) and cysteine (Cys), play important roles in the regulation of various physiological and
* Corresponding author. E-mail address: [email protected] (C. Kim). http://dx.doi.org/10.1016/j.tet.2017.06.051 0040-4020/© 2017 Elsevier Ltd. All rights reserved.
pathological processes, including biological redox homeostasis, biocatalysis, metal binding and post translational modifications.31e35 In particular, GSH is the most abundant cellular thiol with concentration range from 1 to 10 mmol/L,36,37 which plays essential roles in many cellular functions such as antioxidant defense, maintenance of intracellular redox activity and gene regulation.38e40 However, an abnormal level of GSH concentration can induce various diseases including psoriasis, liver damage, cancer, Alzheimer's disease and AIDS.41e43 Accordingly, the development of sensitive and selective sensors for the detection of GSH has become an important subject of current chemical research. Recently, the development of sensors for the sequential detection of diverse cations and amino acids has received a lot of attentions.44e48 Among the different types of chemosensors, the colorimetric sensors based on the sequential color change of metal ions and amino acids have many advantages due to the rapid and convenient detection, and low cost of analysis.49,50 Therefore, we have been interested in the colorimetric sequential recognition of metal ions and amino acids. Herein, we report a new colorimetric chemosensor 1 for the sequential detection Cu2þ and GSH, which was synthesized by the combination of 3-amino-4-methoxy-1H-indazole and 3methoxysalicylaldehyde. The sensor 1 could detect Cu2þ by color change from colorless to pale yellow. In addition, the resulting
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
Cu2þ-2$1 complex could selectively recognize GSH in the presence of other amino acids via naked-eye. 2. Experimental 2.1. Materials and equipment All solvents and reagents (analytical and spectroscopic grade) were obtained commercially and used as received. 1H and 13C NMR spectra were recorded on a Varian 400 MHz and 100 MHz spectrometer and chemical shifts (d) were recorded in ppm. Electro spray ionization mass spectra (ESI-MS) were collected on a Thermo Finnigan (San Jose, CA, USA) LCQ™ Advantage MAX quadrupole ion trap instrument by infusing samples directly into the source using a manual method. Spray voltage was set at 4.2 kV, and the capillary temperature was at 80 C. Absorption spectra were recorded at room temperature using a Perkin Elmer model Lambda 2S UVeVis spectrometer. Elemental analysis for carbon, nitrogen, and hydrogen was carried out by using a MICRO CUBE elemental analyzer (Germany) in Laboratory Center of Seoul National University of Science and Technology, Korea. 2.2. Synthesis of 1 3-Amino-4-methoxy-1H-indazole (0.08 g, 0.5 mmol) was dissolved in 5 mL of methanol and 3-methoxysalicylaldehyde (0.09 g, 0.6 mmol) was added into the solution. The reaction solution was stirred for 12 h at room temperature. The orange powder was filtered and washed with iced methanol and ether. The yield: 0.11 g (73%); 1H NMR (400 MHz DMSO-d6, ppm): d 13.76 (s, 1H), 13.08 (s, 1H), 9.33 (s, 1H), 7.31 (t, J ¼ 8.0 MHz, 1H), 7.28 (d, J ¼ 8.0 MHz, 1H), 7.14 (d, J ¼ 8.0 MHz, 1H), 7.07 (d, J ¼ 8.0 MHz, 1H), 6.91 (t, J ¼ 8.0 MHz, 1H), 6.62 (d, J ¼ 8.0 MHz, 1H), 3.93 (s, 3H), 3.84 (s, 3H); 13 C NMR (100 MHz DMSO-d6, ppm): 162.09, 154.22, 151.36, 148.42, 147.37, 143.76, 128.78, 124.57, 119.68, 118.92, 115.84, 108.78, 103.64, 101.04, 56.18, 55.91. ESI-MS m/z [1þH]þ: calcd, 298.12; found, 298.10. Anal. Calc. for C16H15N3O3: C, 64.64; H, 5.09; N, 14.13. Found: C, 64.79; H, 5.00; N, 13.85%. 2.3. UVevis titration For Cu2þ, 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of this solution (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make a final concentration of 30 mM. Cu(NO3)2 (0.01 mmol) was dissolved in DMSO (1 mL) and 0.45e4.5 mL of the Cu2þ ion solution (10 mM) were transferred to the solution of 1 (30 mM) prepared above. After mixing them for a few seconds, UVevis spectra were taken at room temperature. For GSH, 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of this solution (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make a final concentration of 30 mM. 3.6 mL of Cu2þ solution (10 mM) was transferred to each sensor solution (30 mM) to give 0.4 equiv. Then, GSH (0.01 mmol) was dissolved in bis-tris (10 mM, 1 mL) and 2.25e20.25 mL of this GSH solutions (10 mM) were transferred to Cu2þ-2$1 solution (30 mM) to give 2 equiv. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.4. Job plot measurements For Cu2þ, a stock solution of sensor 1 (10 mM) was prepared in 1 mL of DMSO. Cu2þ solution (10 mM) was prepared by dissolving its nitrate salt in DMSO (1 mL). 13.5, 12.0, 10.5, 9, 7.5, 6, 4.5, 3 and 1.5 mL of the 1 solution were taken and transferred to vials. Each vial
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was diluted with bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make a total volume of 2.985 mL. Then, 1.5, 3, 4.5, 6, 7.5, 9, 10.5, 12 and 13.5 mL of the Cu2þ solution were added to each diluted 1 solution. Each vial had a total volume of 3 mL. After shaking the vials for a minute, UVevis spectra were taken at room temperature. For GSH, a stock solution of sensor 1 (10 mM) was prepared in 1 mL of DMSO. Cu2þ solution (5 mM) was prepared by dissolving its nitrate salt in DMSO (1 mL). The two solutions were mixed to make Cu2þ-2$1 complex. 36, 32, 28, 24, 20, 16, 12, 8 and 4 mL of the Cu2þ2$1 complex solution were taken and transferred to vials. Each vial was diluted with 2.96 mL of bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0). GSH solution (7.5 mM) was dissolved in 10 mM bistris buffer (1 mL). 4, 8, 12, 16, 20, 24, 28, 32 and 36 mL of the GSH solution were added to each diluted Cu2þ-2$1 solution. Each vial had a total volume of 3 mL. After reacting the vials for a few seconds, UVevis spectra were taken at room temperature. 2.5. Competition experiments For Cu2þ ion, sensor 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of the sensor 1 (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make the final concentration of 30 mM. MNO3 (M ¼ Na, K, 0.02 mmol), M(NO3)2 (M ¼ Mn, Ni, Co, Zn, Hg, Ag, Fe, Cd, Mg, Ca, Pb, 0.02 mmol), or M(NO3)3 (M ¼ Al, Ga, In, Fe, Cr, 0.02 mmol) was separately dissolved in 1 mL DMSO. 1.8 mL of each metal-ion solution (20 mM) was taken and added into 3 mL of each sensor 1 solution (30 mM) prepared above to make 0.4 equiv. Then, 3.6 mL of Cu(NO3)2 solution (10 mM) was added into the mixed solution of each metal ion and sensor 1 to make 0.4 equiv. After mixing them for a few seconds, UVevis spectra were taken at room temperature. For GSH, sensor 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of this solution (5 mM) was diluted with 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make the final concentration of 30 mM. Cu(NO3)2$2.5H2O (0.01 mmol) was dissolved in DMSO (1 mL). 3.6 mL of this Cu2þ solution (10 mM) was transferred to the 1 solution (30 mM) to make copper complex. Then, various amino acids and peptide such as Ala, Arg, Asn, Asp, Cys, Gln, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Val and glutathione (GSH) (0.02 mmol) were separately dissolved in bis-tris buffer (10 mM, 1 mL). 9 mL of each amino acid and peptide solution (20 mM) was taken and added into each copper complex solution prepared above to make 2 equiv. Then, 9 mL of the GSH solution (20 mM) was added into the mixed solution of each amino acid or peptide and copper complex to make 2 equiv. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.6. pH effect test For Cu2þ, a series of buffers with pH values ranging from 2 to 12 was prepared by mixing sodium hydroxide solution and hydrochloric acid in bis-tris buffer. After the solution with a desired pH was achieved, sensor 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL), and then 18 mL of the sensor 1 (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 2e12) to make the final concentration of 30 mM. Cu(NO3)2 (0.01 mmol) was dissolved in DMSO (1 mL). 3.6 mL of the Cu2þ solution (10 mM) was transferred to each sensor solution (30 mM) prepared above. After reacting them for a few seconds, fluorescence spectra were taken at room temperature. For GSH, a series of solutions with pH values ranging from 2 to 12 was prepared by mixing sodium hydroxide solution and hydrochloric acid in bis-tris buffer. After the solution with a desired pH was achieved, 18 mL of the 1 solution (30 mM) and 3.6 mL of the
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M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
Scheme 1. Synthesis of 1.
Cu(NO3) 2 solution (10 mM) were added to 2.9784 mL bis-tris buffer/DMSO (7/3, v/v, pH 2e12). Then, 9 mL of the GSH solution (20 mM) was transferred to the Cu2þ-2$1 complex solution prepared above. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.7. Determination of Cu2þ in real samples UVevis spectral measurements of water samples containing Cu2þ were carried out by adding 18 mL solution of the sensor 1 (5 mM) and 0.21 mL of 100 mM bis-tris buffer stock solution to a 1.872 mL sample solution. 0.90 mL of DMSO was taken and added into the sample solution. The sample solution had a total volume of 3 mL. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.8. Theoretical calculations All DFT/TDDFT calculations based on the hybrid exchange correlation functional B3LYP51,52 were carried out using Gaussian 03 program.53 The 6-31G** basis set54,55 was used for the main group elements, whereas the Lanl2DZ effective core potential (ECP)56e58 was employed for copper. In vibrational frequency calculations, there was no imaginary frequency for the optimized geometries of 1 and Cu2þ-2$1, suggesting that these geometries represented local minima. For all calculations, the solvent effect of water was considered by using the Cossi and Barone's CPCM (conductor-like polarizable continuum model).59,60 To investigate the electronic properties of singlet excited states, time-dependent DFT (TDDFT) was performed in the ground state geometries of 1 and Cu2þ-2$1. The 25 singlet-singlet excitations were calculated and analyzed. The GaussSum 2.161 was used to calculate the contributions of molecular orbitals in electronic transitions. 3. Results and discussion The sensor 1 was obtained by the combination of 3-amino-4methoxy-1H-indazole and 3-methoxysalicylaldehyde with 73% yield in methanol (Scheme 1), and characterized by 1H NMR and 13C NMR, ESI-mass spectrometry and elemental analyses. 3.1. Colorimetric and spectral responses of 1 toward Cu2þ The colorimetric sensing ability of 1 was primarily examined with the nitrate salts of various metal ions (Agþ, Al3þ, Ca2þ, Cd2þ, Co2þ, Cr3þ, Cu2þ, Fe2þ, Fe3þ, Ga3þ, Hg2þ, In3þ, Kþ, Mg2þ, Mn2þ, Naþ, Ni2þ, Pb2þ, and Zn2þ) in bis-tris buffer/DMSO (7:3; v/v, 10 mM, pH 7.0). Upon the addition of 0.4 equiv of each metal ion, other metal ions showed no significant change on the color and absorption peak, while only copper complex did both a distinct spectral change (Fig. 1a) and a color change from colorless to pale yellow (Fig. 1b).
c We obtained the copper complex under the sensing condition, and found that its formation yield was 89%.
The formation yield of the copper complex was 89%.c These results indicated that sensor 1 can serve as a “naked-eye” chemosensor for Cu2þ in aqueous solution. To study the binding property of 1 with Cu2þ, UVevis titration experiment was performed (Fig. 2). Upon addition of Cu2þ to a solution of 1, the absorption band at 360 nm significantly decreased, and a new absorption band at 427 nm steadily increased. Two isosbestic points were observed at 407 nm and 470 nm, indicating that the only one product was generated from the interaction of 1 with Cu2þ. The Job plot analysis indicated a 2:1 complexation stoichiometry between 1 and Cu2þ (Fig. S1),62 which was further supported by ESI-mass spectrometry analysis (Fig. 3). The positive-ion mass spectrum showed that the peak at m/z ¼ 656.10 was assigned to [2$1 - Hþ þ Cu2þ]þ (calcd, 656.14). On the basis of the UVevis titration of 1 with Cu2þ, the association constant (K) was calculated to be 5.0 109 M2 by using Li's equation (Fig. S2),63 which was within the range of those (103-1012) reported for Cu2þ chemosensors.64,65 To check interference of other metal ions on Cu2þ-2$1 complexation, the competition experiments were conducted in the presence of Cu2þ (0.4 equiv) mixed with the same concentration of interfering cations such as Agþ, Al3þ, Ca2þ, Cd2þ, Co2þ, Cr3þ, Fe2þ, Fe3þ, Ga3þ, Hg2þ, In3þ, Kþ, Mg2þ, Mn2þ, Naþ, Ni2þ, Pb2þ, and Zn2þ. As shown in Fig. 4, the competing metal ions did not interfere with naked-eye detection of Cu2þ by 1. Thus, 1 could be used as a selective colorimetric sensor for Cu2þ in the presence of competing metal ions. For practical application, the pH dependence of Cu2þ-2$1 complex was investigated in the pH range of 2e12 (Fig. S3). The absorbance intensity of the complex exhibited a strong pH dependence between pH 7 and pH 10, which attests that Cu2þ could be clearly detected by naked-eye or UVevis absorption measurements. We constructed a calibration curve for quantitative determination of Cu2þ by 1 (Fig. 5). Sensor 1 indicated a good linear relationship between the absorbance of 1 and Cu2þ concentration (0.0e2.7 mM) with a correlation coefficient of R2 ¼ 0.9951 (n ¼ 3), which signifies that 1 could be appropriate for quantitative detection of Cu2þ. The detection limit for Cu2þ was calculated as 0.14 mM on the basis of 3s/k,66 which is much lower than guideline (31.5 mM) by the World Health Organization (WHO) in drinking water.24 To examine the practical applicability of 1 with Cu2þ, 1 was applied for the determination of Cu2þ in both tap and drinking water samples. As shown in Table 1, satisfactory recoveries and RSD values were obtained for the water samples. These results suggested that sensor 1 could be practical for the measurement of Cu2þ in chemical and environmental applications. 3.2. Theoretical calculations of 1 with Cu2þ In order to demonstrate the colorimetric sensing mechanism of 1 toward Cu2þ, we conducted density functional theory (DFT) calculations with the B3LYP/6-31G (d, p) method basis set using the Gaussian 03 program. The calculated energy-minimized structures
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
(a)
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0.4 1, 1 + Other metals
Absorbancce
0.3
0.2 1 + Cu
2+
0.1
0.0 300
400
500
600
Wavelength (nm) (b)
Absorbance
0.4
0.3 407 nm
Absorbance at 427 nm
Fig. 1. (a) Absorption spectral changes of 1 (30 mM) in the presence of 0.4 equiv of different metal ions in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0). (b) The color changes of 1 (30 mM) upon addition of various metal ions (0.4 equiv).d
0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.0
0.1
0.2
0.3
0.4
0.5
2+
[Cu ]/[1]
0.2
0.1
470 nm
0.0 300
400
500
600
Wavelength (nm) Fig. 2. Absorption spectral changes of 1 (30 mM) in the presence of different concentrations of Cu2þ (from 0 to 0.5 equiv) at room temperature. Inset: Plot of the absorbance at 427 nm as a function of Cu2þ concentration.
of 1 and Cu2þ-2$1 species are shown in Fig. 6. The energyminimized structure of 1 showed a nearly flat structure with the dihedral angle of 1 N, 2C, 3 N and 4C ¼ 179.846 and the bond length of 3 N and 4C ¼ 1.2705 Å (Fig. 6a). Because ESI-mass spectroscopy and Job plot analyses showed that 1 reacted with Cu2þ in the 2:1 stoichiometric ratio, all theoretical calculations of the copper complex were performed with the 2:1 stoichiometry. Cu2þ2$1 complex exhibited a tetrahedral structure with the dihedral
d
We retook the picture of Fig. 1b, and replaced it with a new one. Although the picture does not look clear, it is clear enough through “naked-eye”.
Fig. 3. Positive-ion electrospray ionization mass spectrum of 1 (0.1 mM) upon addition of Cu(NO3)2 (0.5 equiv).
angle of 1 N, 2C, 3 N, 4C ¼ 140.842 , and Cu2þ was coordinated to 3 N, 30 N, 7O and 70 O. The length of Cu-3N (or 30 N) bond was longer than that of Cu-7O (or 70 O), and these results are well consistent with the crystal structures previously reported for a similar type of copper complexes.67,68 e Then, the copper complex had sp2 hybridized imine groups (bond length ¼ 1.3178 Å (3 N, 4C)) (Fig. 6b). The transition energies and oscillator strengths of 1 and Cu2þ-2$1 complex obtained from TD-SCF calculation and GEN basis set were selected (Figs. S4e6). For 1, the main molecular orbital (MO)
e We tried to get crystals, but it was not successful. Therefore, we made a comparison between the calculated data of the proposed Cu2þ-2$1 complex and some similar crystal structures reported in Refs.67,68
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Absorbance at 427 nm
(a) 0.4 1
0.3
2+
1+Cu 2+ 1+Cu +Other metals
0.2
0.1
0.0 300
400
500
600
Wavelength (nm) (b)
Fig. 4. (a) Competitive selectivity of 1 (30 mM) toward Cu2þ (0.4 equiv) in the presence of other metal ions (0.4 equiv) in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0). (b) The color changes of 1 (30 mM) upon addition of Cu2þ (0.4 equiv) in the absence and presence of 0.4 equiv of various metal ions in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0).
contribution of the 1st lowest excited state was determined for HOMO / LUMO transition (351.91 nm, Fig. S4). In case of Cu2þ-2$1 complex, the main molecular orbital (MO) contributions of the 16th lowest excited state were determined for HOMO / LUMO þ 2 (b), HOMO / LUMO þ 1 (a) and HOMO - 1/ LUMO (a) transitions (418.40, Fig. S5). The calculated HOMO / LUMO þ2 (b) excitation indicated p / p* transition. MO diagrams and excitation energies of 1 and Cu2þ-2$1 are shown in Fig. S6. On the basis of Job plot, ESImass spectroscopy analysis and theoretical calculations, the binding mode of Cu2þ-2$1 complex was proposed in Scheme 2. 3.3. Colorimetric and spectral responses of Cu2þ-2·1 complex toward GSH
Fig. 5. Absorbance (at 427 nm) of 1 as a function of Cu(II) concentration ([1] ¼ 30 mmol/L and [Cu(II)] ¼ 0.3e2.7 mmol/L). Conditions: all samples were conducted in bis-tris buffer/DMSO (7:3; v/v).
Since it has been known that the thiol-containing amino acid and peptide strongly bind to Cu2þ ions D,69e71 we also investigated the selectivity of Cu2þ-2$1 complex toward 20 different amino acids and peptide, Cys, Gly, Ile, Ala, Met, Val, Ser, Thr, Phe, Asp, Gln, Asn, Leu, Arg, Pro, Lys, His, Trp, Glu, and glutathione (GSH) in bistris buffer/DMSO (7:3, v/v). Upon the addition of 2 equiv of each amino acid and peptide to Cu2þ-2$1, only GSH exhibited both an obvious color change from pale yellow to colorless and a spectral
Table 1 Determination of Cu(II) in water samples.a Sample
Cu(II) added (mmol/L)
Cu(II) found (mmol/L)
Recovery (%)
R.S.D (n ¼ 3) (%)
Tap water
0.00 2.70 0.00 2.70
0.00 2.86 0.00 2.82
e 105.9 e 104.4
e 0.67 e 0.12
Drinking water a
Conditions: [1] ¼ 30 mmol/L in 10 Mm bis-tris buffer/DMSO solution (v/v, 7/3, pH 7.0).
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Fig. 6. The energy-minimized structures of (a) 1 and (b) Cu2þ-2$1 complex.
Scheme 2. Proposed binding mode of Cu2þ-2$1 complex.
change (Fig. 7). The final UVevis spectrum was almost similar to the original absorption spectrum of 1 (Fig. S7), which indicates that 1 might be recovered from the Cu2þ-2$1 complex by the chelation of GSH with copper (Scheme 3).72,73 These results suggested that somewhat soft Cu2þ ion might like irreversibly to bind to the soft sulfur atom of GSH.f Importantly, this is the second example for the colorimetric detection of GSH by using copper complex as a sensor. Therefore, these results indicated that Cu2þ-2$1 complex could be a selective chemosensor for detecting GSH over other sulfur-
f We tried to get crystals of Cu-GSH, but it was not successful. Therefore, we proposed the practical structure of Cu-GSH in Scheme 3, based on the structures reported in Refs.72,73 In addition, we found that the reaction in Scheme 3 was irreversible, based on our reversible test.
containing amino acids, such as Cys and Met via naked-eye. The binding properties of Cu2þ-2$1 with GSH were further studied by UVevis titration experiment (Fig. 8). Upon addition of GSH to a solution of Cu2þ-2$1, the absorption band at 427 nm significantly decreased, and a new absorption band at 360 nm gradually reached a maximum at 2 equiv of GSH. Three isosbestic points were observed at 314 nm, 396 nm and 489 nm, demonstrating that the only one product was generated from the interaction of Cu2þ-2$1 with GSH. The binding stoichiometry of GSH and Cu2þ-2$1 was revealed by Job plot analysis, which indicated a 1:1 stoichiometric ratio (Fig. S8).62 In addition, the 1:1 stoichiometry between Cu2þ-2$1 complex and GSH was demonstrated by ESI-mass spectrometry analysis (Fig. S9). The positive-ion mass spectrum showed that a peak at m/z ¼ 298.10 was assigned to [1þHþ]þ (calcd, 298.12), generated from the demetallation of Cu2þ-2$1 complex by GSH. Based on the UVevis titration, Job plot and ESI-mass spectrometry analysis, we proposed the sensing mechanism of GSH by Cu2þ-2$1 complex (Scheme 3). From the UVevis titration of Cu2þ-2$1 complex with GSH, the association constant (K) was determined as 2.5 103 M1 by using BenesieHildebrand equation (Fig. S10).74 The detection limit for GSH was founded to be 2.98 mM on the basis of 3s/k (Fig. S11),66 and the value is the lowest one among the colorimetric chemosensors for the sequential detection of GSH, to the best of our knowledge. To examine the practical applicability of Cu2þ-2$1 complex for
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(a)
Absorbance
0.4 1
0.3 2+
1+Cu +GSH 2+
0.2
1+Cu
2+
1+Cu +Other amino acid
0.1
0.0 300
400
500
600
Wavelength (nm) (b)
Fig. 7. (a) Absorption spectral changes of Cu2þ-2$1 complex (30 mM) upon the addition of 2 equiv of various amino acids and peptide in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0). (b) The color changes of Cu2þ-2$1 complex (30 mM) upon the addition of 2 equiv of various amino acids and peptide.g
Scheme 3. Proposed sensing mechanism of GSH by Cu2þ-2$1 complex.h
0.6 Absorbance at 427 nm
0.12
Absorbance
0.5 0.4
314 nm
0.10
0.08
0.06
0.04
0.3
0.0
396 nm
0.5
1.0
2+
1.5
2.0
2.5
[GSH]/([1+Cu ]+[GSH])
0.2 0.1
489 nm
0.0 300
400
500
GSH, the competition experiments were performed with 19 various amino acids and peptide such as Cys, Gly, Ile, Ala, Met, Val, Ser, Thr, Phe, Asp, Gln, Asn, Leu, Arg, Pro, Lys, His, Trp and Glu (Fig. 9). When Cu2þ-2$1 complex was treated with 2 equiv of GSH in the presence of the same concentration of other amino acids and peptide, there was no interference for naked-eye detection of GSH by Cu2þ-2$1. These results indicated that Cu2þ-2$1 could be an excellent chromogenic sensor with high selectivity for GSH in the presence of various amino acids, particularly sulfur-containing substances such as Cys and Met. In order to verify the pH dependence of Cu2þ-2$1 toward GSH, we conducted the pH effect test in a series of solutions with pH values ranging from 2 to 12 (Fig. S12). The absorbance intensity of the complex with GSH showed an obvious pH dependence between pH 6 and 7.
600
Wavelength (nm) Fig. 8. Absorption spectral changes of Cu2þ-2$1 complex (30 mM) after addition of increasing amounts of GSH in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0) at room temperature. Inset: absorption at 427 nm versus the number of equiv of GSH added.
g We retook the picture of Fig. 7b, and replaced it with a new one. Although the picture does not look clear, it is clear enough through “naked-eye”. h We proposed the practical structure of Cu-GSH in Scheme 3, based on the structures reported in Refs.72,73
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
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Fig. 9. The color changes of competitive selectivity of Cu2þ-2$1 (30 mM) toward GSH (2 equiv) in the presence of other amino acids and peptide (2 equiv).
4. Conclusion We have designed and synthesized a new selective and sensitive chemosensor 1 for the sequential detection of Cu2þ and GSH via naked-eye. Sensor 1 showed an excellent sensitivity and selectivity toward Cu2þ by the obvious color change from colorless to pale yellow in aqueous solution. In addition, the detection limit (0.14 mM) for Cu2þ is much lower than the guideline (31.5 mM) of WHO in drinking water. 1 could also be used to quantify Cu2þ with satisfactory recoveries and R.S.D. values in water samples. Moreover, Cu2þ-2$1 complex can be used as a colorimetric sensor for GSH with no interference in the presence of other amino acids, and the detection limit for the analysis of GSH was found to be 2.98 mМ, which is the lowest one among the colorimetric chemosensors for the sequential detection of GSH. Therefore, these results indicate that senor 1 may contribute to the development of a novel type of chemosensor for the sequential recognition of Cu2þ and GSH using a colorimetric method in aqueous solution. Acknowledgements Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2015R1A2A2A09001301) are gratefully acknowledged. This subject is also supported by Korea Ministry of Environment (MOE) as “The Chemical Accident Prevention Technology Development Project”. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.tet.2017.06.051. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
Valeur B. Coord Chem Rev. 2000;205:3e40. Aragay G, Pons J, Merkoçi A. Chem Rev. 2011;111:3433e3458. Zhang JF, Zhou Y, Yoon J, Kim JS. Chem Soc Rev. 2011;40:3416e3429. Kaur K, Saini R, Kumar A, et al. Coord Chem Rev. 2012;256:1992e2028. Maity D, Manna AK, Karthigeyan D, Kundu TK, Pati SK, Govindaraju T. Chem - A Eur J. 2011;17:11152e11161. Goswami S, Das S, Aich K, Sarkar D, Mondal TK. Tetrahedron Lett. 2013;54: 6892e6896. Kim MS, Jo TG, Ahn HM, Kim C. J Fluoresc. 2016;27:357e367. Wang W, Fu A, You J, Gao G, Lan J, Chen L. Tetrahedron. 2010;66:3695e3701. Mahapatra AK, Hazra G, Das NK, Goswami S. Sens Actuators B Chem. 2011;156: 456e462. Park GJ, You GR, Choi YW, Kim C. Sens Actuators, B Chem. 2016;229:257e271. Maity D, Govindaraju T. Chemistry. 2011;17:1410e1414. Ryu KY, Lee JJ, Kim JA, Park DY, Kim C. RSC Adv. 2016;6:16586e16597. Jang YK, Nam UC, Kwon HL, Hwang IH, Kim C. Dye Pigment. 2013;99:6e13. Sheng R, Wang P, Liu W, Wu X, Wu S. Sens Actuators B Chem. 2008;128: 507e511. Jung HS, Kwon PS, Lee JW, et al. J Am Chem Soc. 2009;131:2008e2012. Tang L, Zhou P, Zhang Q, Huang Z, Zhao J, Cai M. Inorg Chem Commun. 2013;36: 100e104.
17. Peralta-Domínguez D, Rodriguez M, Ramos-Ortiz G, et al. Sens Actuators, B Chem. 2016;225:221e227. 18. Li G, Tao F, Liu Q, et al. New J Chem. 2016;40:4513e4518. 19. Li Y, Zhang X, Zhu B, Xue J, Zhu Z, Tan W. Analyst. 2011;136:1124e1128. 20. Yu M-M, Li Z-X, Wei L-H, Wei D-H, Tang M-S. Org Lett. 2008;10:5115e5118. 21. Rurack K. Spectrochim Acta Part A Mol Biomol Spectrosc. 2001;57:2161e2195. 22. Tang L, Cai M, Huang Z, et al. Sens Actuators B Chem. 2013;185:188e194. 23. Jo TG, Na YJ, Lee JJ, Lee MM, Lee SY, Kim C. New J Chem. 2015;39:2580e2587. 24. Gordon B, Callan P, Vickers C. WHO Chron. 2008;38:564. 25. Narayanaswamy N, Govindaraju T. Sens Actuators B Chem. 2012;161:304e310. 26. Park GJ, Hwang IH, Song EJ, Kim H, Kim C. Tetrahedron. 2014;70:2822e2828. 27. Na YJ, Choi YW, Yun JY, Park KM, Chang PS, Kim C. Spectrochim Acta - Part A Mol Biomol Spectrosc. 2015;136:1649e1657. 28. Jo TG, Na YJ, Lee JJ, Lee MM, Lee SY, Kim C. Sens Actuators, B Chem. 2015;211: 498e506. 29. You GR, Park GJ, Lee JJ, Kim C. Dalton Trans. 2015;44:9120e9129. 30. Noh JY, Park GJ, Na YJ, Jo HY, Lee SA, Kim C. Dalton Trans. 2014;43:5652e5656. 31. Lee JH, Lim CS, Tian YS, Han JH, Cho BR. J Am Chem Soc. 2010;132:1216e1217. 32. Yin J, Kwon Y, Kim D, et al. J Am Chem Soc. 2014;136:5351e5358. 33. Yin C, Huo F, Zhang J, et al. Chem Soc Rev. 2013;42:6032e6059. 34. Hyman LM, Franz KJ. Coord Chem Rev. 2012;256:2333e2356. 35. Chen X, Zhou Y, Peng X, Yoon J. Chem Soc Rev. 2010;39:2120e2135. 36. Xu C, Li H, Yin B. Biosens Bioelectron. 2015;72:275e281. 37. Wang F, Zhou L, Zhao C, et al. Chem Sci. 2015;6:2584e2589. 38. Dalton TP, Shertzer HG, Puga A. Annu Rev Pharmacol Toxicol. 1999;39:67e101. 39. Akerboom TPM, Bilzen M, Sies H. J Biol Chem. 1982;257:4248e4252. 40. Hwang C, Sinskey A, Lodish H. Science. 1992;257:1496e1502. 41. Chen W, Luo H, Liu X, Foley JW, Song X. Anal Chem. 2016;88:3638e3646. 42. Gao YG, Zhang Y, Shi Y Di, Hao HJ, Gong B, Lu ZL. Bioorg Med Chem. 2016;24: 1550e1559. 43. Liu T, Huo F, Li J, Chao J, Zhang Y, Yin C. Sens Actuators, B Chem. 2016;232: 619e624. 44. Hu Y, Heo CH, Kim G, et al. Anal Chem. 2015;87:3308e3313. 45. Jia H, Yang M, Meng Q, et al. Sensors. 2016;16:79. 46. He G, Li J, Wang Z, et al. Tetrahedron. 2017;73:272e277. 47. Lee SA, Lee JJ, Shin JW, Min KS, Kim C. Dye Pigment. 2015;116:131e138. 48. Choi YW, Lee JJ, You GR, Kim C. RSC Adv. 2015;5:38308e38315. 49. Yang S-J, Tian XZ, Shin I. Org Lett. 2009;11:3438e3441. 50. Kim YS, Park GJ, Lee SA, Kim C. RSC Adv. 2015;5:31179e31188. 51. Becke AD. J Chem Phys. 1993;98:5648. 52. Lee C, Yang W, Parr RG. Phys Rev B. 1988;37:785e789. 53. Frisch, C. G. and J. A. P. M. J.; Trucks, G. W., et al., Gaussian, Inc., Wallingford CT, 2004. 54. Hariharan PC, Pople JA. Theor Chim Acta. 1973;28:213e222. 55. Francl MM, Pietro WJ, Hehre WJ, et al. J Chem Phys. 1982;77:3654e3665. 56. Hay PJ, Wadt WR. J Chem Phys. 1985;82:270. 57. Wadt WR, Hay PJ. J Chem Phys. 1985;82:284e298. 58. Wadt WR, Hay PJ. J Chem Phys. 1985;82:299e310. 59. Barone V, Cossi M. J Phys Chem A. 1998;102:1995e2001. 60. Cossi M, Barone V. J Chem Phys. 2001;115:4708. 61. O'Boyle NM, Tenderholt AL, Langner KM. J Comput Chem. 2008;29:839e845. 62. Job P. Ann Chim. 1928;9:113e203. 63. Grynkiewicz G, Poenie M, Tsien RY. J Biol Chem. 1985;260:3440e3450. 64. Xiang Y, Tong A, Jin P, Ju Y. Org Lett. 2006;8:2863e2866. 65. Wu S-P, Du K-J, Sung Y-M. Dalton Trans. 2010;39:4363e4368. 66. Tsui Y-K, Devaraj S, Yen Y-P. Sens Actuators B Chem. 2012;161:510e519. 67. Shang X, Ren K, Li J, Li, et al. Inorg Chim Acta. 2017;456:199e206. 68. Shabbir M, Akhter Z, Ahmad I, et al. Polyhedron. 2017;124:117e124. 69. Li Q, Guo Y, Shao S. Sens Actuators B Chem. 2012;171e172:872e877. 70. Peng R, Lin L, Wu X, Liu X, Feng X. J Org Chem. 2013;78:11602e11605. 71. Meng Q, Jia H, Succar P, et al. Biosens Bioelectron. 2015;74:461e468. 72. Kumar DN, Singh BK, Garg BS, Singh PK. Spectrochim Acta Part A Mol Biomol Spectrosc. 2003;59:1487e1496. 73. Green KN, Brothers SM, Lee B, Darensbourg MY, Rockcliffe DA. Inorg Chem. 2009;48:2780e2792. 74. Benesi HA, Hildebrand JH. J Am Chem Soc. 1949;71:2703e2707.
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A new indazole-based colorimetric chemosensor for sequential detection of Cu2þ and GSH in aqueous solution Min Seon Kim a, Jae Min Jung a, Ji Hye Kang a, Hye Mi Ahn a, Pan-Gi Kim b, Cheal Kim a, * a
Department of Fine Chemistry and Department of Interdisciplinary Bio IT Materials, Seoul National University of Science and Technology, Seoul 139-743, South Korea b School of Ecology & Environmental Systems, Kyungpook National University, Sangju 37224, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 April 2017 Received in revised form 20 June 2017 Accepted 26 June 2017 Available online 29 June 2017
A new selective and sensitive colorimetric chemosensor 1 was developed for the sequential detection of Cu2þ and glutathione (GSH) in aqueous solution. The sensor 1 detected Cu2þ ion by an obvious color change from colorless to pale yellow. Importantly, 1 could be used to detect and quantify Cu2þ ion in water samples, and the detection limit (0.14 mM) of 1 for Cu2þ was much lower than the guideline (31.5 mM) of WHO in drinking water. Also, Cu2þ-2$1 complex can be used as a colorimetric sensor for GSH via naked-eye. The detection limit for GSH was founded to be 2.98 mM. Moreover, the sensing ability of 1 for Cu2þ was supported by theoretical calculations. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Colorimetric Copper Glutathione Sequential detection Theoretical calculations
1. Introduction The development of selective and sensitive chemosensors is an important assignment for detecting transition metal ions, which play important roles in chemical, biological, and environmental processes.1e7 Among them, copper is one of the most vital metal ions in biological system, because it acts as an essential cofactor correlated with activities of various enzymes, including superoxide dismutase, cytochrome c oxidase, and tyrosinase.8e12 Thus, a steady intake of copper is indispensable for our good health.13 However, an excessive accumulation of copper can cause fatal diseases such as Alzheimer's, Parkinson's, Wilson's and prion diseases.14e18 Moreover, copper is a significant environmental pollutant because of its widespread use in industry and agriculture.19e23 The World Health Organization (WHO) has set the maximum acceptable limit of copper in drinking water at 2 ppm (31.5 mM).24,25 For these reasons, chemosensors with high sensitivity, selectivity and low detection limit capable of rapidly detecting Cu2þ are needed to be urgently developed.26e30 Biological thiols, such as glutathione (GSH) and cysteine (Cys), play important roles in the regulation of various physiological and
* Corresponding author. E-mail address: [email protected] (C. Kim). http://dx.doi.org/10.1016/j.tet.2017.06.051 0040-4020/© 2017 Elsevier Ltd. All rights reserved.
pathological processes, including biological redox homeostasis, biocatalysis, metal binding and post translational modifications.31e35 In particular, GSH is the most abundant cellular thiol with concentration range from 1 to 10 mmol/L,36,37 which plays essential roles in many cellular functions such as antioxidant defense, maintenance of intracellular redox activity and gene regulation.38e40 However, an abnormal level of GSH concentration can induce various diseases including psoriasis, liver damage, cancer, Alzheimer's disease and AIDS.41e43 Accordingly, the development of sensitive and selective sensors for the detection of GSH has become an important subject of current chemical research. Recently, the development of sensors for the sequential detection of diverse cations and amino acids has received a lot of attentions.44e48 Among the different types of chemosensors, the colorimetric sensors based on the sequential color change of metal ions and amino acids have many advantages due to the rapid and convenient detection, and low cost of analysis.49,50 Therefore, we have been interested in the colorimetric sequential recognition of metal ions and amino acids. Herein, we report a new colorimetric chemosensor 1 for the sequential detection Cu2þ and GSH, which was synthesized by the combination of 3-amino-4-methoxy-1H-indazole and 3methoxysalicylaldehyde. The sensor 1 could detect Cu2þ by color change from colorless to pale yellow. In addition, the resulting
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
Cu2þ-2$1 complex could selectively recognize GSH in the presence of other amino acids via naked-eye. 2. Experimental 2.1. Materials and equipment All solvents and reagents (analytical and spectroscopic grade) were obtained commercially and used as received. 1H and 13C NMR spectra were recorded on a Varian 400 MHz and 100 MHz spectrometer and chemical shifts (d) were recorded in ppm. Electro spray ionization mass spectra (ESI-MS) were collected on a Thermo Finnigan (San Jose, CA, USA) LCQ™ Advantage MAX quadrupole ion trap instrument by infusing samples directly into the source using a manual method. Spray voltage was set at 4.2 kV, and the capillary temperature was at 80 C. Absorption spectra were recorded at room temperature using a Perkin Elmer model Lambda 2S UVeVis spectrometer. Elemental analysis for carbon, nitrogen, and hydrogen was carried out by using a MICRO CUBE elemental analyzer (Germany) in Laboratory Center of Seoul National University of Science and Technology, Korea. 2.2. Synthesis of 1 3-Amino-4-methoxy-1H-indazole (0.08 g, 0.5 mmol) was dissolved in 5 mL of methanol and 3-methoxysalicylaldehyde (0.09 g, 0.6 mmol) was added into the solution. The reaction solution was stirred for 12 h at room temperature. The orange powder was filtered and washed with iced methanol and ether. The yield: 0.11 g (73%); 1H NMR (400 MHz DMSO-d6, ppm): d 13.76 (s, 1H), 13.08 (s, 1H), 9.33 (s, 1H), 7.31 (t, J ¼ 8.0 MHz, 1H), 7.28 (d, J ¼ 8.0 MHz, 1H), 7.14 (d, J ¼ 8.0 MHz, 1H), 7.07 (d, J ¼ 8.0 MHz, 1H), 6.91 (t, J ¼ 8.0 MHz, 1H), 6.62 (d, J ¼ 8.0 MHz, 1H), 3.93 (s, 3H), 3.84 (s, 3H); 13 C NMR (100 MHz DMSO-d6, ppm): 162.09, 154.22, 151.36, 148.42, 147.37, 143.76, 128.78, 124.57, 119.68, 118.92, 115.84, 108.78, 103.64, 101.04, 56.18, 55.91. ESI-MS m/z [1þH]þ: calcd, 298.12; found, 298.10. Anal. Calc. for C16H15N3O3: C, 64.64; H, 5.09; N, 14.13. Found: C, 64.79; H, 5.00; N, 13.85%. 2.3. UVevis titration For Cu2þ, 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of this solution (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make a final concentration of 30 mM. Cu(NO3)2 (0.01 mmol) was dissolved in DMSO (1 mL) and 0.45e4.5 mL of the Cu2þ ion solution (10 mM) were transferred to the solution of 1 (30 mM) prepared above. After mixing them for a few seconds, UVevis spectra were taken at room temperature. For GSH, 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of this solution (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make a final concentration of 30 mM. 3.6 mL of Cu2þ solution (10 mM) was transferred to each sensor solution (30 mM) to give 0.4 equiv. Then, GSH (0.01 mmol) was dissolved in bis-tris (10 mM, 1 mL) and 2.25e20.25 mL of this GSH solutions (10 mM) were transferred to Cu2þ-2$1 solution (30 mM) to give 2 equiv. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.4. Job plot measurements For Cu2þ, a stock solution of sensor 1 (10 mM) was prepared in 1 mL of DMSO. Cu2þ solution (10 mM) was prepared by dissolving its nitrate salt in DMSO (1 mL). 13.5, 12.0, 10.5, 9, 7.5, 6, 4.5, 3 and 1.5 mL of the 1 solution were taken and transferred to vials. Each vial
4751
was diluted with bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make a total volume of 2.985 mL. Then, 1.5, 3, 4.5, 6, 7.5, 9, 10.5, 12 and 13.5 mL of the Cu2þ solution were added to each diluted 1 solution. Each vial had a total volume of 3 mL. After shaking the vials for a minute, UVevis spectra were taken at room temperature. For GSH, a stock solution of sensor 1 (10 mM) was prepared in 1 mL of DMSO. Cu2þ solution (5 mM) was prepared by dissolving its nitrate salt in DMSO (1 mL). The two solutions were mixed to make Cu2þ-2$1 complex. 36, 32, 28, 24, 20, 16, 12, 8 and 4 mL of the Cu2þ2$1 complex solution were taken and transferred to vials. Each vial was diluted with 2.96 mL of bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0). GSH solution (7.5 mM) was dissolved in 10 mM bistris buffer (1 mL). 4, 8, 12, 16, 20, 24, 28, 32 and 36 mL of the GSH solution were added to each diluted Cu2þ-2$1 solution. Each vial had a total volume of 3 mL. After reacting the vials for a few seconds, UVevis spectra were taken at room temperature. 2.5. Competition experiments For Cu2þ ion, sensor 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of the sensor 1 (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make the final concentration of 30 mM. MNO3 (M ¼ Na, K, 0.02 mmol), M(NO3)2 (M ¼ Mn, Ni, Co, Zn, Hg, Ag, Fe, Cd, Mg, Ca, Pb, 0.02 mmol), or M(NO3)3 (M ¼ Al, Ga, In, Fe, Cr, 0.02 mmol) was separately dissolved in 1 mL DMSO. 1.8 mL of each metal-ion solution (20 mM) was taken and added into 3 mL of each sensor 1 solution (30 mM) prepared above to make 0.4 equiv. Then, 3.6 mL of Cu(NO3)2 solution (10 mM) was added into the mixed solution of each metal ion and sensor 1 to make 0.4 equiv. After mixing them for a few seconds, UVevis spectra were taken at room temperature. For GSH, sensor 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL) and 18 mL of this solution (5 mM) was diluted with 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 7.0) to make the final concentration of 30 mM. Cu(NO3)2$2.5H2O (0.01 mmol) was dissolved in DMSO (1 mL). 3.6 mL of this Cu2þ solution (10 mM) was transferred to the 1 solution (30 mM) to make copper complex. Then, various amino acids and peptide such as Ala, Arg, Asn, Asp, Cys, Gln, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Val and glutathione (GSH) (0.02 mmol) were separately dissolved in bis-tris buffer (10 mM, 1 mL). 9 mL of each amino acid and peptide solution (20 mM) was taken and added into each copper complex solution prepared above to make 2 equiv. Then, 9 mL of the GSH solution (20 mM) was added into the mixed solution of each amino acid or peptide and copper complex to make 2 equiv. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.6. pH effect test For Cu2þ, a series of buffers with pH values ranging from 2 to 12 was prepared by mixing sodium hydroxide solution and hydrochloric acid in bis-tris buffer. After the solution with a desired pH was achieved, sensor 1 (1.49 mg, 0.005 mmol) was dissolved in DMSO (1 mL), and then 18 mL of the sensor 1 (5 mM) was diluted to 2.982 mL bis-tris buffer/DMSO (7:3; v/v, 10 mM bis-tris, pH 2e12) to make the final concentration of 30 mM. Cu(NO3)2 (0.01 mmol) was dissolved in DMSO (1 mL). 3.6 mL of the Cu2þ solution (10 mM) was transferred to each sensor solution (30 mM) prepared above. After reacting them for a few seconds, fluorescence spectra were taken at room temperature. For GSH, a series of solutions with pH values ranging from 2 to 12 was prepared by mixing sodium hydroxide solution and hydrochloric acid in bis-tris buffer. After the solution with a desired pH was achieved, 18 mL of the 1 solution (30 mM) and 3.6 mL of the
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M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
Scheme 1. Synthesis of 1.
Cu(NO3) 2 solution (10 mM) were added to 2.9784 mL bis-tris buffer/DMSO (7/3, v/v, pH 2e12). Then, 9 mL of the GSH solution (20 mM) was transferred to the Cu2þ-2$1 complex solution prepared above. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.7. Determination of Cu2þ in real samples UVevis spectral measurements of water samples containing Cu2þ were carried out by adding 18 mL solution of the sensor 1 (5 mM) and 0.21 mL of 100 mM bis-tris buffer stock solution to a 1.872 mL sample solution. 0.90 mL of DMSO was taken and added into the sample solution. The sample solution had a total volume of 3 mL. After mixing them for a few seconds, UVevis spectra were taken at room temperature. 2.8. Theoretical calculations All DFT/TDDFT calculations based on the hybrid exchange correlation functional B3LYP51,52 were carried out using Gaussian 03 program.53 The 6-31G** basis set54,55 was used for the main group elements, whereas the Lanl2DZ effective core potential (ECP)56e58 was employed for copper. In vibrational frequency calculations, there was no imaginary frequency for the optimized geometries of 1 and Cu2þ-2$1, suggesting that these geometries represented local minima. For all calculations, the solvent effect of water was considered by using the Cossi and Barone's CPCM (conductor-like polarizable continuum model).59,60 To investigate the electronic properties of singlet excited states, time-dependent DFT (TDDFT) was performed in the ground state geometries of 1 and Cu2þ-2$1. The 25 singlet-singlet excitations were calculated and analyzed. The GaussSum 2.161 was used to calculate the contributions of molecular orbitals in electronic transitions. 3. Results and discussion The sensor 1 was obtained by the combination of 3-amino-4methoxy-1H-indazole and 3-methoxysalicylaldehyde with 73% yield in methanol (Scheme 1), and characterized by 1H NMR and 13C NMR, ESI-mass spectrometry and elemental analyses. 3.1. Colorimetric and spectral responses of 1 toward Cu2þ The colorimetric sensing ability of 1 was primarily examined with the nitrate salts of various metal ions (Agþ, Al3þ, Ca2þ, Cd2þ, Co2þ, Cr3þ, Cu2þ, Fe2þ, Fe3þ, Ga3þ, Hg2þ, In3þ, Kþ, Mg2þ, Mn2þ, Naþ, Ni2þ, Pb2þ, and Zn2þ) in bis-tris buffer/DMSO (7:3; v/v, 10 mM, pH 7.0). Upon the addition of 0.4 equiv of each metal ion, other metal ions showed no significant change on the color and absorption peak, while only copper complex did both a distinct spectral change (Fig. 1a) and a color change from colorless to pale yellow (Fig. 1b).
c We obtained the copper complex under the sensing condition, and found that its formation yield was 89%.
The formation yield of the copper complex was 89%.c These results indicated that sensor 1 can serve as a “naked-eye” chemosensor for Cu2þ in aqueous solution. To study the binding property of 1 with Cu2þ, UVevis titration experiment was performed (Fig. 2). Upon addition of Cu2þ to a solution of 1, the absorption band at 360 nm significantly decreased, and a new absorption band at 427 nm steadily increased. Two isosbestic points were observed at 407 nm and 470 nm, indicating that the only one product was generated from the interaction of 1 with Cu2þ. The Job plot analysis indicated a 2:1 complexation stoichiometry between 1 and Cu2þ (Fig. S1),62 which was further supported by ESI-mass spectrometry analysis (Fig. 3). The positive-ion mass spectrum showed that the peak at m/z ¼ 656.10 was assigned to [2$1 - Hþ þ Cu2þ]þ (calcd, 656.14). On the basis of the UVevis titration of 1 with Cu2þ, the association constant (K) was calculated to be 5.0 109 M2 by using Li's equation (Fig. S2),63 which was within the range of those (103-1012) reported for Cu2þ chemosensors.64,65 To check interference of other metal ions on Cu2þ-2$1 complexation, the competition experiments were conducted in the presence of Cu2þ (0.4 equiv) mixed with the same concentration of interfering cations such as Agþ, Al3þ, Ca2þ, Cd2þ, Co2þ, Cr3þ, Fe2þ, Fe3þ, Ga3þ, Hg2þ, In3þ, Kþ, Mg2þ, Mn2þ, Naþ, Ni2þ, Pb2þ, and Zn2þ. As shown in Fig. 4, the competing metal ions did not interfere with naked-eye detection of Cu2þ by 1. Thus, 1 could be used as a selective colorimetric sensor for Cu2þ in the presence of competing metal ions. For practical application, the pH dependence of Cu2þ-2$1 complex was investigated in the pH range of 2e12 (Fig. S3). The absorbance intensity of the complex exhibited a strong pH dependence between pH 7 and pH 10, which attests that Cu2þ could be clearly detected by naked-eye or UVevis absorption measurements. We constructed a calibration curve for quantitative determination of Cu2þ by 1 (Fig. 5). Sensor 1 indicated a good linear relationship between the absorbance of 1 and Cu2þ concentration (0.0e2.7 mM) with a correlation coefficient of R2 ¼ 0.9951 (n ¼ 3), which signifies that 1 could be appropriate for quantitative detection of Cu2þ. The detection limit for Cu2þ was calculated as 0.14 mM on the basis of 3s/k,66 which is much lower than guideline (31.5 mM) by the World Health Organization (WHO) in drinking water.24 To examine the practical applicability of 1 with Cu2þ, 1 was applied for the determination of Cu2þ in both tap and drinking water samples. As shown in Table 1, satisfactory recoveries and RSD values were obtained for the water samples. These results suggested that sensor 1 could be practical for the measurement of Cu2þ in chemical and environmental applications. 3.2. Theoretical calculations of 1 with Cu2þ In order to demonstrate the colorimetric sensing mechanism of 1 toward Cu2þ, we conducted density functional theory (DFT) calculations with the B3LYP/6-31G (d, p) method basis set using the Gaussian 03 program. The calculated energy-minimized structures
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
(a)
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0.4 1, 1 + Other metals
Absorbancce
0.3
0.2 1 + Cu
2+
0.1
0.0 300
400
500
600
Wavelength (nm) (b)
Absorbance
0.4
0.3 407 nm
Absorbance at 427 nm
Fig. 1. (a) Absorption spectral changes of 1 (30 mM) in the presence of 0.4 equiv of different metal ions in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0). (b) The color changes of 1 (30 mM) upon addition of various metal ions (0.4 equiv).d
0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.0
0.1
0.2
0.3
0.4
0.5
2+
[Cu ]/[1]
0.2
0.1
470 nm
0.0 300
400
500
600
Wavelength (nm) Fig. 2. Absorption spectral changes of 1 (30 mM) in the presence of different concentrations of Cu2þ (from 0 to 0.5 equiv) at room temperature. Inset: Plot of the absorbance at 427 nm as a function of Cu2þ concentration.
of 1 and Cu2þ-2$1 species are shown in Fig. 6. The energyminimized structure of 1 showed a nearly flat structure with the dihedral angle of 1 N, 2C, 3 N and 4C ¼ 179.846 and the bond length of 3 N and 4C ¼ 1.2705 Å (Fig. 6a). Because ESI-mass spectroscopy and Job plot analyses showed that 1 reacted with Cu2þ in the 2:1 stoichiometric ratio, all theoretical calculations of the copper complex were performed with the 2:1 stoichiometry. Cu2þ2$1 complex exhibited a tetrahedral structure with the dihedral
d
We retook the picture of Fig. 1b, and replaced it with a new one. Although the picture does not look clear, it is clear enough through “naked-eye”.
Fig. 3. Positive-ion electrospray ionization mass spectrum of 1 (0.1 mM) upon addition of Cu(NO3)2 (0.5 equiv).
angle of 1 N, 2C, 3 N, 4C ¼ 140.842 , and Cu2þ was coordinated to 3 N, 30 N, 7O and 70 O. The length of Cu-3N (or 30 N) bond was longer than that of Cu-7O (or 70 O), and these results are well consistent with the crystal structures previously reported for a similar type of copper complexes.67,68 e Then, the copper complex had sp2 hybridized imine groups (bond length ¼ 1.3178 Å (3 N, 4C)) (Fig. 6b). The transition energies and oscillator strengths of 1 and Cu2þ-2$1 complex obtained from TD-SCF calculation and GEN basis set were selected (Figs. S4e6). For 1, the main molecular orbital (MO)
e We tried to get crystals, but it was not successful. Therefore, we made a comparison between the calculated data of the proposed Cu2þ-2$1 complex and some similar crystal structures reported in Refs.67,68
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Absorbance at 427 nm
(a) 0.4 1
0.3
2+
1+Cu 2+ 1+Cu +Other metals
0.2
0.1
0.0 300
400
500
600
Wavelength (nm) (b)
Fig. 4. (a) Competitive selectivity of 1 (30 mM) toward Cu2þ (0.4 equiv) in the presence of other metal ions (0.4 equiv) in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0). (b) The color changes of 1 (30 mM) upon addition of Cu2þ (0.4 equiv) in the absence and presence of 0.4 equiv of various metal ions in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0).
contribution of the 1st lowest excited state was determined for HOMO / LUMO transition (351.91 nm, Fig. S4). In case of Cu2þ-2$1 complex, the main molecular orbital (MO) contributions of the 16th lowest excited state were determined for HOMO / LUMO þ 2 (b), HOMO / LUMO þ 1 (a) and HOMO - 1/ LUMO (a) transitions (418.40, Fig. S5). The calculated HOMO / LUMO þ2 (b) excitation indicated p / p* transition. MO diagrams and excitation energies of 1 and Cu2þ-2$1 are shown in Fig. S6. On the basis of Job plot, ESImass spectroscopy analysis and theoretical calculations, the binding mode of Cu2þ-2$1 complex was proposed in Scheme 2. 3.3. Colorimetric and spectral responses of Cu2þ-2·1 complex toward GSH
Fig. 5. Absorbance (at 427 nm) of 1 as a function of Cu(II) concentration ([1] ¼ 30 mmol/L and [Cu(II)] ¼ 0.3e2.7 mmol/L). Conditions: all samples were conducted in bis-tris buffer/DMSO (7:3; v/v).
Since it has been known that the thiol-containing amino acid and peptide strongly bind to Cu2þ ions D,69e71 we also investigated the selectivity of Cu2þ-2$1 complex toward 20 different amino acids and peptide, Cys, Gly, Ile, Ala, Met, Val, Ser, Thr, Phe, Asp, Gln, Asn, Leu, Arg, Pro, Lys, His, Trp, Glu, and glutathione (GSH) in bistris buffer/DMSO (7:3, v/v). Upon the addition of 2 equiv of each amino acid and peptide to Cu2þ-2$1, only GSH exhibited both an obvious color change from pale yellow to colorless and a spectral
Table 1 Determination of Cu(II) in water samples.a Sample
Cu(II) added (mmol/L)
Cu(II) found (mmol/L)
Recovery (%)
R.S.D (n ¼ 3) (%)
Tap water
0.00 2.70 0.00 2.70
0.00 2.86 0.00 2.82
e 105.9 e 104.4
e 0.67 e 0.12
Drinking water a
Conditions: [1] ¼ 30 mmol/L in 10 Mm bis-tris buffer/DMSO solution (v/v, 7/3, pH 7.0).
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
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Fig. 6. The energy-minimized structures of (a) 1 and (b) Cu2þ-2$1 complex.
Scheme 2. Proposed binding mode of Cu2þ-2$1 complex.
change (Fig. 7). The final UVevis spectrum was almost similar to the original absorption spectrum of 1 (Fig. S7), which indicates that 1 might be recovered from the Cu2þ-2$1 complex by the chelation of GSH with copper (Scheme 3).72,73 These results suggested that somewhat soft Cu2þ ion might like irreversibly to bind to the soft sulfur atom of GSH.f Importantly, this is the second example for the colorimetric detection of GSH by using copper complex as a sensor. Therefore, these results indicated that Cu2þ-2$1 complex could be a selective chemosensor for detecting GSH over other sulfur-
f We tried to get crystals of Cu-GSH, but it was not successful. Therefore, we proposed the practical structure of Cu-GSH in Scheme 3, based on the structures reported in Refs.72,73 In addition, we found that the reaction in Scheme 3 was irreversible, based on our reversible test.
containing amino acids, such as Cys and Met via naked-eye. The binding properties of Cu2þ-2$1 with GSH were further studied by UVevis titration experiment (Fig. 8). Upon addition of GSH to a solution of Cu2þ-2$1, the absorption band at 427 nm significantly decreased, and a new absorption band at 360 nm gradually reached a maximum at 2 equiv of GSH. Three isosbestic points were observed at 314 nm, 396 nm and 489 nm, demonstrating that the only one product was generated from the interaction of Cu2þ-2$1 with GSH. The binding stoichiometry of GSH and Cu2þ-2$1 was revealed by Job plot analysis, which indicated a 1:1 stoichiometric ratio (Fig. S8).62 In addition, the 1:1 stoichiometry between Cu2þ-2$1 complex and GSH was demonstrated by ESI-mass spectrometry analysis (Fig. S9). The positive-ion mass spectrum showed that a peak at m/z ¼ 298.10 was assigned to [1þHþ]þ (calcd, 298.12), generated from the demetallation of Cu2þ-2$1 complex by GSH. Based on the UVevis titration, Job plot and ESI-mass spectrometry analysis, we proposed the sensing mechanism of GSH by Cu2þ-2$1 complex (Scheme 3). From the UVevis titration of Cu2þ-2$1 complex with GSH, the association constant (K) was determined as 2.5 103 M1 by using BenesieHildebrand equation (Fig. S10).74 The detection limit for GSH was founded to be 2.98 mM on the basis of 3s/k (Fig. S11),66 and the value is the lowest one among the colorimetric chemosensors for the sequential detection of GSH, to the best of our knowledge. To examine the practical applicability of Cu2þ-2$1 complex for
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(a)
Absorbance
0.4 1
0.3 2+
1+Cu +GSH 2+
0.2
1+Cu
2+
1+Cu +Other amino acid
0.1
0.0 300
400
500
600
Wavelength (nm) (b)
Fig. 7. (a) Absorption spectral changes of Cu2þ-2$1 complex (30 mM) upon the addition of 2 equiv of various amino acids and peptide in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0). (b) The color changes of Cu2þ-2$1 complex (30 mM) upon the addition of 2 equiv of various amino acids and peptide.g
Scheme 3. Proposed sensing mechanism of GSH by Cu2þ-2$1 complex.h
0.6 Absorbance at 427 nm
0.12
Absorbance
0.5 0.4
314 nm
0.10
0.08
0.06
0.04
0.3
0.0
396 nm
0.5
1.0
2+
1.5
2.0
2.5
[GSH]/([1+Cu ]+[GSH])
0.2 0.1
489 nm
0.0 300
400
500
GSH, the competition experiments were performed with 19 various amino acids and peptide such as Cys, Gly, Ile, Ala, Met, Val, Ser, Thr, Phe, Asp, Gln, Asn, Leu, Arg, Pro, Lys, His, Trp and Glu (Fig. 9). When Cu2þ-2$1 complex was treated with 2 equiv of GSH in the presence of the same concentration of other amino acids and peptide, there was no interference for naked-eye detection of GSH by Cu2þ-2$1. These results indicated that Cu2þ-2$1 could be an excellent chromogenic sensor with high selectivity for GSH in the presence of various amino acids, particularly sulfur-containing substances such as Cys and Met. In order to verify the pH dependence of Cu2þ-2$1 toward GSH, we conducted the pH effect test in a series of solutions with pH values ranging from 2 to 12 (Fig. S12). The absorbance intensity of the complex with GSH showed an obvious pH dependence between pH 6 and 7.
600
Wavelength (nm) Fig. 8. Absorption spectral changes of Cu2þ-2$1 complex (30 mM) after addition of increasing amounts of GSH in bis-tris buffer/DMSO (7/3, 10 mM bis-tris, pH ¼ 7.0) at room temperature. Inset: absorption at 427 nm versus the number of equiv of GSH added.
g We retook the picture of Fig. 7b, and replaced it with a new one. Although the picture does not look clear, it is clear enough through “naked-eye”. h We proposed the practical structure of Cu-GSH in Scheme 3, based on the structures reported in Refs.72,73
M.S. Kim et al. / Tetrahedron 73 (2017) 4750e4757
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Fig. 9. The color changes of competitive selectivity of Cu2þ-2$1 (30 mM) toward GSH (2 equiv) in the presence of other amino acids and peptide (2 equiv).
4. Conclusion We have designed and synthesized a new selective and sensitive chemosensor 1 for the sequential detection of Cu2þ and GSH via naked-eye. Sensor 1 showed an excellent sensitivity and selectivity toward Cu2þ by the obvious color change from colorless to pale yellow in aqueous solution. In addition, the detection limit (0.14 mM) for Cu2þ is much lower than the guideline (31.5 mM) of WHO in drinking water. 1 could also be used to quantify Cu2þ with satisfactory recoveries and R.S.D. values in water samples. Moreover, Cu2þ-2$1 complex can be used as a colorimetric sensor for GSH with no interference in the presence of other amino acids, and the detection limit for the analysis of GSH was found to be 2.98 mМ, which is the lowest one among the colorimetric chemosensors for the sequential detection of GSH. Therefore, these results indicate that senor 1 may contribute to the development of a novel type of chemosensor for the sequential recognition of Cu2þ and GSH using a colorimetric method in aqueous solution. Acknowledgements Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2015R1A2A2A09001301) are gratefully acknowledged. This subject is also supported by Korea Ministry of Environment (MOE) as “The Chemical Accident Prevention Technology Development Project”. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.tet.2017.06.051. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
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