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Reaction-based colorimetric signaling of Cu2 þ ions by oxidative coupling of phenols with 4aminoantipyrine Hong Yeong Kim, Hyo Jin Lee, Suk-Kyu Chang
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Received date: 27 July 2014 Revised date: 26 September 2014 Accepted date: 29 September 2014 Cite this article as: Hong Yeong Kim, Hyo Jin Lee, Suk-Kyu Chang, Reactionbased colorimetric signaling of Cu2 þ ions by oxidative coupling of phenols with 4-aminoantipyrine, Talanta, http://dx.doi.org/10.1016/j.talanta.2014.09.048 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Reaction-based colorimetric signaling of Cu2+ ions by oxidative coupling of phenols with 4-aminoantipyrine
Hong Yeong Kim, Hyo Jin Lee, Suk-Kyu Chang* Department of Chemistry, Chung-Ang University, Seoul 156-756, Republic of Korea
*Corresponding author. Tel.: +82 2 820 5199; Fax: +82 2 825 4736. E-mail address: [email protected] (S.-K. Chang)
Abstract: A new Cu2+-selective chromogenic probe system based on the oxidative coupling of phenols with 4-aminoantipyrine was developed. Cu2+ ions promoted facile coupling of phenols with 4-aminoantipyrine to yield quinoneimine dyes. Signaling with a number of phenols having no para-substituent, such as o-cresol and m-cresol, as well as pchlorophenol having para substituent that could be expelled during the oxidation process was possible. The signaling of Cu2+ ions was not interfered by the presence of representative metal ions except for Al3+ ions. The possible interference from Al3+ ions was successfully removed by using fluoride ions as a masking agent. The phenol−4aminoantipyrine probe system showed chromogenic Cu2+ signaling by prominent color change from colorless to pink with a detection limit of 8.5 × 10−7 M. The signaling of Cu2+ ions in practical samples using tap water and simulated semiconductor wastewater was also tested.
Keywords: Cu2+ signaling, Colorimetry, Oxidative coupling, 4-Aminoantipyrine,
1
Phenol, Quinoneimine dye.
1. Introduction Copper ions are the third most biologically important transition metal ions after iron and zinc [1,2]. It is a key constituent of the copper proteins involved in oxygen transport, oxygenation, electron transport, and antioxidative functions [3]. Copper has also been known as an important environmental pollutant [4]. The copper concentration in the environment varies widely with an average concentration of 0.01 mg/L in surface water and up to 100 mg/L in semiconductor wastewater [5]. Owing to the extensive use of copper in modern industrial applications, sensitive and selective chemosensors for Cu2+ ions have attracted much attention in environmental monitoring [6,7]. Recently, chemodosimeters or chemical probes using a reaction-based signaling approach have received much research interest [8]. The advantages of this strategy are cumulative, and specific chemical reactions between the probe molecule and analytes allow high sensitivity and excellent selectivity in signaling [9]. In particular, development of selective reaction-based probes for Cu2+ ions has been successfully realized. A number of probes have been devised based on the spirolactam ringopening process of rhodamine derivatives [10,11]. In addition, Cu2+-induced hydrolysis processes have become another important strategy for the design of Cu2+selective probes. A classical example reported by Czarnik’s group is the spirolactam ring-opening of rhodamine-hydrazide followed by hydrolysis [12]. Other probes are generally based on activated esters, Schiff-bases, and hydrazone function containing dyes [13-16]. Cu2+-mediated oxidation and oxidative cyclization processes have also
2
been successfully used for the development of selective and sensitive probes for Cu2+ ions [6,17,18]. 4-Aminoantipyrine (AAP) has been used as a useful chromogenic reagent for the determination of various phenols in aqueous solution [19]. The determination is based on the oxidative coupling of phenols with AAP by oxidants such as H2O2, persulfate, and K3Fe(CN)6 to yield highly colored diagnostic quinoneimine dyes [20,21]. On the other hand, coupling reaction of phenols with 4-aminoantipyrine is a well-established process for the determination of oxidants, such as hydrogen peroxide, in industrial analytes [22,23]. The same reaction can also be used for the determination of glucose in blood by using phenol, AAP, and glucose oxidase [24]. Interestingly, Cu2+ ions have been reported to act as an oxidant in the coupling of catechol with 4-aminoantipyrine [25]. However, no studies have been carried out on the construction of Cu2+-selective probes employing this useful reaction. In this paper, we report a new colorimetric signaling system for Cu2+ ions based on a metal ion-induced coupling of phenols with 4-aminoantipyrine. Upon treatment with Cu2+ ions, coupling of phenols with 4-aminoantipyrine smoothly proceeded to form a new quinoid dye with a prominent color change from colorless to pink.
2. Experimental Section 2.1 General. 4-Aminoantipyrine, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), and ammonium persulfate were purchased from Sigma-Aldrich Co. Boric acid was obtained from Wako Co. Phenol, 4-nitrophenol, 2,4,6-trimethylphenol, m-cresol, o-
3
cresol, and p-chlorophenol were obtained from commercial sources. For the spectroscopic studies, perchlorate salts of Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, and Pb2+ were obtained from SigmaAldrich Co. Chromium(III) nitrate nonahydrate was purchased from Sigma-Aldrich Co. Sodium fluoride and ethylenediaminetetraacetic acid (EDTA) were purchased from Fluka. UV–vis measurements were performed using spectroscopy grade acetonitrile purchased from J.T. Baker. All chemicals and solvents were used without further purification. 1H NMR (600 MHz) and 13C NMR (150 MHz) spectra were acquired on a Varian VNS spectrometer and referenced to the residual solvent signal. UV–vis spectra were acquired using a Jasco V-550 spectrophotometer and Scinco S-3100 equipped with a Peltier temperature controller. Column chromatography was performed using silica gel (240 mesh). Electron-impact (EI) mass spectra (LRMS) were recorded on a Micromass Autospec spectrometer. Compound 1 was prepared following the reported procedure [26].
2.2 Purification of Cu2+ signaling compound. Phenol (0.48 g, 5.1 mmol) and copper (II) perchlorate hexahydrate (1.26 g, 3.4 mmol) were dissolved in 100 mL of HEPESbuffered 90% aqueous acetonitrile solution. 4-Aminoantipyrine (70 mg, 0.34 mmol) dissolved in 10 mL of distilled water was added dropwise to the solution. The reaction mixture was stirred at room temperature for 1 h, and 100 mL of dichloromethane was poured in order to extract the Cu2+-signaling product. After separation of the dichloromethane layer, the organic solution was concentrated under reduced pressure. The residue was purified by simply passing through a silica gel plug using
4
dichloromethane/methanol (9:1, v/v) to obtain 52 mg (52% yield) of the Cu2+-signaling compound as a dark orange powder. 1H NMR (600 MHz, CDCl3) δ 8.50 (dd, J = 10.3, 2.7 Hz, 1H), 7.53-7.34 (m, 5H), 7.24 (dd, J = 9.9, 2.7 Hz, 1H), 6.54 (dd, J = 9.9, 2.3 Hz, 1H), 6.44 (dd, J = 10.3, 2.3 Hz, 1H), 3.36 (s, 3H), 2.50 (s, 3H);
13
C NMR (150 MHz,
CDCl3) δ 188.01, 156.88, 153.43, 150.37, 143.72, 133.93, 133.24, 130.40, 129.58, 129.09, 128.52, 126.13, 119.92, 35.18, 10.78; MS (EI): m/z calcd for M+ (C17H17N3O2) : 295.13, found 295.16.
2.3 Measurement of signaling behaviors. UV–vis signaling behaviors of the probe system towards Cu2+ ions and other metal ions were measured in a mixture of CH3CN and HEPES-buffered solution (pH 7.5) (1:9, v/v). The stock solutions of phenol and 4-aminoantipyrine were prepared in acetonitrile, and metal ions and buffer solutions were made in distilled water. Sample solutions for measurement were prepared by successively adding the stock solutions of metal ions (37.5 μL, 10 mM), HEPES buffer (30 μL, 1 M), phenol (225 μL, 5 mM), and 4-aminoantipyrine (75 μL, 1 mM) in each vial. The solution was diluted with CH3CN and HEPESbuffer solution to make a final volume (3.0 mL) with a composition of 1:9, v/v. Final concentrations of metal ions, phenol, 4-aminoantipyrine, and HEPES buffer were 1.25 × 10−4 M, 3.75 × 10−4 M, 2.5 × 10−5 M, and 10 mM, respectively.
2.4 pH effects on the signaling towards Cu2+. The effects of pH on the signaling towards Cu2+ were elucidated by measuring the responses in a pH range between 4.0 and 10.0 that adjusted with buffer solutions. The buffer solutions used were acetate buffer for 4.0 to 5.8, HEPES buffer for 7.0 to 8.0, and borate buffer for 9.0 to 10.0. 5
Final concentrations of Cu2+, phenol, 4-aminoantipyrine, and each buffer solution were 1.25 × 10−4 M, 3.75 × 10−4 M, 2.5 × 10−5 M, and 10 mM, respectively, under the same measurement conditions.
2.5 Preparation of simulated semiconductor wastewater. Referring to the two relevant literatures on wastewater compositions [27,28], the following metal concentrations were used for the preparation of the simulated semiconductor wastewater: [Al3+] = 8.64 × 10–5 M, [Fe3+] = 5.37 × 10–5 M, [Pb2+] = 7.24 × 10–6 M, [Mn2+] = 1.82 × 10–6 M, [Zn2+] = 1.07 × 10–5 M, and [Ni2+] = 1.36 × 10–5 M.
2.6 Determination of the detection limit for Cu2+ ions. Following IUPAC recommendations, the detection limit for the Cu2+ ions was determined using the equation 3×sbl/m, where sbl denotes the standard deviation of the blank signal (the number of measurements = 20) and m represents the slope of the calibration curve [29].
3. Results and Discussion A novel colorimetric signaling system for Cu2+ ions based on a metal ion-induced coupling of phenols with 4-aminoantipyrine was developed. The signaling behavior of
the
probe
system
toward
metal
ions
was
investigated
by
UV-vis
spectrophotometry. A mixture (15:1 molar ratio) of phenol and 4-aminoantipyrine (PhOH-AAP) showed no significant absorptions above 400 nm in 90% aqueous acetonitrile solution buffered at pH 7.5 (HEPES buffer). The molar ratio was chosen
6
on the basis of the observation that Cu2+ signaling increased proportionally as the phenol concentration increased up to 15:1 molar ratio of phenol and AAP and then became constant (Fig. S1, Supplementary data). Upon treatment of this PhOH-AAP system with various metal ions, a pronounced change was observed exclusively with Cu2+ ions (Fig. 1 and Fig. S2, Supplementary data). In the presence of Cu2+ ions, a new strong absorption at 501 nm developed and the solution color of the PhOHAAP system prominently changed from colorless to pink. No significant responses were observed from the other metal ions. On the other hand, meaningful fluorescence properties of PhOH-AAP were not observed for the signaling of any surveyed metal ions.
The prominent colorimetric signaling of Cu2+ ions by the PhOH-AAP system is due to the transformation depicted in Scheme 1. Phenol and AAP were oxidatively coupled to form a highly colored quinoneimine dye 1 promoted by Cu2+ ions. The formation of the aminoantipyrine-coupled product of phenols such as 1 by a practical persulfate oxidant was already known [26]. The proposed signaling process was confirmed by 1H and
13
C NMR spectroscopy. For this, the 1H NMR spectrum of the
Cu2+-signaling PhOH-AAP system was measured after purification of the reaction mixture. The resulting spectrum was identical to that obtained for compound 1 prepared independently using persulfate as an oxidant (Fig. 2 and Fig. S3, Supplementary data). In particular, the resonance peaks for the para-H (6.87 ppm) of
7
phenol disappeared and the remaining four protons of the quinoid subunit appeared as two pairs of doublets (8.50 and 6.44 ppm for H-6 and H-5, 6.54 and 7.24 ppm for H-3 and H-2). One of the resonance peaks (H-6), assigned by means of a 2D 1H−13C HSQC spectrum (Fig. S4, Supplementary data), experienced a large shift to the lower field from 7.20 to 8.50 ppm due to a large anisotropic effect of nearby antipyryl group [26].
13
C NMR and UV–vis spectral evidences also confirmed the formation of
1 under the signaling conditions (Fig. S5 and Fig. S6, Supplementary data). Furthermore, treatment of the Cu2+-signaling PhOH-AAP system with chelating EDTA did not affect the UV–vis spectrum of the resulting solution, indicating the irreversible nature of the suggested reaction-based signaling process (Fig. S7, Supplementary data).
The Cu2+-selective signaling was not affected by the presence of common alkali, alkaline earth, and transition metal ions except for Al3+, Cr3+, and Fe2+, as background. The signaling ratio AMetal+Cu(II)/ACu(II) observed at 501 nm varied across a narrow range, from 0.99 for Li+ ions to 1.02 for Fe3+ ions (Fig. 3). On the other hand, considerable interference was observed with Al3+ ions with a AAl(III)+Cu(II)/ACu(II) ratio of 0.70. However, the interference from Al3+ ions was successfully removed by using fluoride ions as a masking agent [30]; in the presence of 40 equiv of fluoride ions, the interference from Al3+ ions disappeared completely (Fig. S8, Supplementary data). In the presence of Fe2+ or Cr3+, the Cu2+-signaling of the probe system
8
decreased to 53% by Fe2+, or totally suppressed by Cr3+. These interferences are due to the fact that undesirable interaction of Cu2+ ions with redox-active Fe2+ and Cr3+ ions [31,32]. The reaction of Cu2+ ions with Fe2+ or Cr3+ ions resulted in the decreases in Cu2+ level in the analytes, and leads to a significant reduced signal for Cu2+-triggered oxidative condensation between phenol and AAP. This observation implies that the present system could work as a practically applicable Cu2+-selective probe in commonly encountered environmental systems except for the analytes rich in redox-active metal ions of Fe2+ or Cr3+.
To check the quantitative analytical behavior of the PhOH-AAP system for Cu2+ signaling, a UV–vis titration was carried out in 90% aqueous acetonitrile (buffered at pH 7.5 using HEPES). As the concentration of Cu2+ ions increased, the absorption profile of the PhOH-AAP system changed progressively to that of 1 while showing a steadily increasing new band at 501 nm (Fig. 4). From the titration data, the detection limit in the determination of Cu2+ ions by the PhOH-AAP system was estimated to be 8.5 × 10−7 M in 90% aqueous acetonitrile solution (Fig. S9, Supplementary data) [29].
The effects of pH on the signaling were assessed by measuring the responses of the PhOH-AAP system as a function of the pH of the medium. As shown in Figure S10 9
(Supplementary data), the Cu2+ signaling was most pronounced between pH 7 and 8. Signaling speed was fast and the response was completed within 10 min after mixing the analyte solutions (Fig. S11, Supplementary data). Additionally, the PhOH-AAP mixture was stable under the ambient temperature and open laboratory atmosphere for more than 1 day. The Cu2+-selective signaling was possible for a number of phenols, such as o-cresol and m-cresol as well as p-chlorophenol (Fig. 5 and Fig. S12, Supplementary data). In the case of p-chlorophenol, the para-chloro substituent is known to be expelled during the oxidative process to form a quinoid dye [26]. Furthermore, practical applicability of the Cu2+-selective signaling by the PhOHAAP system was confirmed in tap water and simulated semiconductor wastewater (Fig. S13 and S14, Supplementary data). In particular, the interference from Al3+ in simulated semiconductor wastewater was successfully removed by using fluoride ions as a masking agent (Fig. S15, Supplementary data). The Cu2+ signaling by PhOH-AAP system in simulated semiconductor wastewater was possible up to 1.0 × 10−4 M.
4. Conclusion In summary, a new chromogenic probe system for the selective signaling of Cu2+ ions was developed based on the Cu2+-induced oxidative coupling of phenols and 4aminoantipyrine. The mixture of phenol and 4-aminoantipyrine exhibited pronounced Cu2+-selective chromogenic signaling with a color change from colorless to pink.
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Interference from Al3+ ions was successfully eliminated by using fluoride ions as a masking agent. The detection limit for the determination of Cu2+ ions was 8.5 × 10−7 M in 90% aqueous acetonitrile solution. The reported sensing approach would be useful as a convenient and practical colorimetric signaling system for Cu2+ ions in chemical and environmental applications, such as preliminary monitoring of Cu2+ levels in tap water and semiconductor wastewater.
Acknowledgements This research was supported by a fund from the Korea Research Foundation of the Korean Government (NRF-2013R1A1A2008574).
Appendix. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:**.****.
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Figure Captions
Scheme 1. Colorimetric signaling of Cu2+ ions by phenol and 4-aminoantipyrine pair (PhOH-AAP).
Fig. 1. Changes in UV–vis spectra of the PhOH-AAP system in the presence of various metal ions. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Mn+] = 1.25 × 10−4 M, [Pb2+] = 2.5 × 10−5 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). Spectral data for Cr3+ and Fe2+ were obtained against a reagent blank.
14
Fig. 2. Partial 1H NMR spectra of (a) PhOH and AAP (1:1 molar ratio) and (b) purified product after Cu2+ signaling of the PhOH-AAP system. Each compound was dissolved at 3.0 × 10−2 M in CDCl3.
Fig. 3. Competitive signaling of Cu2+ ions by the PhOH-AAP system in the presence of other metal ions as background. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M, [Mn+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). To prevent precipitation, [Pb2+] = 2.50 × 10−5 M.
Fig. 4. Changes in absorption spectrum of the PhOH-AAP system as a function of Cu2+ concentration. Inset: absorbance change at 501 nm as a function of Cu2+ ion concentration. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 0−2.5 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v).
Fig. 5. Photograph of mixtures of various phenols and AAP in the absence or presence of Cu2+. [AAP] = 2.5 × 10−5 M, [phenol] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). (a) 4-Nitrophenol, (b) 2,4,6-trimethylphenol, (c) m-cresol, (d) o-cresol, and (e) p-chlorophenol.
15
Highlights:
• Cu2+-selective probe based on oxidative coupling of phenols with 4-aminoantipyrine was devised. • “Naked-eye” detection of Cu2+ was possible via color change from colorless to pink. • Applicability in tap water and semiconductor wastewater was also investigated. • Detection limit of the probe system for Cu2+ in aqueous acetonitrile was 8.5 × 10–7 M.
16
*Graphical Abstract (for review)
Graphical Abstract
Scheme-1
Scheme 1. Colorimetric signaling of Cu2+ ions by phenol and 4-aminoantipyrine pair (PhOH-AAP).
Figure-1
Fig. 1. Changes in UV–vis spectra of the PhOH-AAP system in the presence of various metal ions. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Mn+] = 1.25 × 10−4 M, [Pb2+] = 2.5 × 10−5 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). Spectral data for Cr3+ and Fe2+ were obtained against a reagent blank.
1
Figure-2
Fig. 2. Partial 1H NMR spectra of (a) PhOH and AAP (1:1 molar ratio) and (b) purified product after Cu2+ signaling of the PhOH-AAP system. Each compound was dissolved at 3.0 × 10−2 M in CDCl3.
1
Figure-3
Fig. 3. Competitive signaling of Cu2+ ions by the PhOH-AAP system in the presence of other metal ions as background. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M, [Mn+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). To prevent precipitation, [Pb2+] = 2.50 × 10−5 M.
1
Figure-4
Fig. 4. Changes in absorption spectrum of the PhOH-AAP system as a function of Cu2+ concentration. Inset: absorbance change at 501 nm as a function of Cu2+ ion concentration. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 0−2.5 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v).
1
Figure-5
Fig. 5. Photograph of mixtures of various phenols and AAP in the absence or presence of Cu2+. [AAP] = 2.5 × 10−5 M, [phenol] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). (a) 4Nitrophenol, (b) 2,4,6-trimethylphenol, (c) m-cresol, (d) o-cresol, and (e) p-chlorophenol.
1
Scheme-1-in-Black-and-White
Scheme 1. Colorimetric signaling of Cu2+ ions by phenol and 4-aminoantipyrine pair (PhOH-AAP).
Figure-1-in-Black-and-White
Fig. 1. Changes in UV–vis spectra of the PhOH-AAP system in the presence of various metal ions. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Mn+] = 1.25 × 10−4 M, [Pb2+] = 2.5 × 10−5 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). Spectral data for Cr3+ and Fe2+ were obtained against a reagent blank.
1
Figure-2-in-Black-and-White
Fig. 2. Partial 1H NMR spectra of (a) PhOH and AAP (1:1 molar ratio) and (b) purified product after Cu2+ signaling of the PhOH-AAP system. Each compound was dissolved at 3.0 × 10−2 M in CDCl3.
1
Figure-5-in-Black-and-White
Fig. 5. Photograph of mixtures of various phenols and AAP in the presence or absence of Cu2+. [AAP] = 2.5 × 10−5 M, [phenol] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). (a) 4Nitrophenol, (b) 2,4,6-trimethylphenol, (c) m-cresol, (d) o-cresol, and (e) p-chlorophenol.
1
Reaction-based colorimetric signaling of Cu2 þ ions by oxidative coupling of phenols with 4aminoantipyrine Hong Yeong Kim, Hyo Jin Lee, Suk-Kyu Chang
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PII: DOI: Reference:
S0039-9140(14)00826-1 http://dx.doi.org/10.1016/j.talanta.2014.09.048 TAL15137
To appear in:
Talanta
Received date: 27 July 2014 Revised date: 26 September 2014 Accepted date: 29 September 2014 Cite this article as: Hong Yeong Kim, Hyo Jin Lee, Suk-Kyu Chang, Reactionbased colorimetric signaling of Cu2 þ ions by oxidative coupling of phenols with 4-aminoantipyrine, Talanta, http://dx.doi.org/10.1016/j.talanta.2014.09.048 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Reaction-based colorimetric signaling of Cu2+ ions by oxidative coupling of phenols with 4-aminoantipyrine
Hong Yeong Kim, Hyo Jin Lee, Suk-Kyu Chang* Department of Chemistry, Chung-Ang University, Seoul 156-756, Republic of Korea
*Corresponding author. Tel.: +82 2 820 5199; Fax: +82 2 825 4736. E-mail address: [email protected] (S.-K. Chang)
Abstract: A new Cu2+-selective chromogenic probe system based on the oxidative coupling of phenols with 4-aminoantipyrine was developed. Cu2+ ions promoted facile coupling of phenols with 4-aminoantipyrine to yield quinoneimine dyes. Signaling with a number of phenols having no para-substituent, such as o-cresol and m-cresol, as well as pchlorophenol having para substituent that could be expelled during the oxidation process was possible. The signaling of Cu2+ ions was not interfered by the presence of representative metal ions except for Al3+ ions. The possible interference from Al3+ ions was successfully removed by using fluoride ions as a masking agent. The phenol−4aminoantipyrine probe system showed chromogenic Cu2+ signaling by prominent color change from colorless to pink with a detection limit of 8.5 × 10−7 M. The signaling of Cu2+ ions in practical samples using tap water and simulated semiconductor wastewater was also tested.
Keywords: Cu2+ signaling, Colorimetry, Oxidative coupling, 4-Aminoantipyrine,
1
Phenol, Quinoneimine dye.
1. Introduction Copper ions are the third most biologically important transition metal ions after iron and zinc [1,2]. It is a key constituent of the copper proteins involved in oxygen transport, oxygenation, electron transport, and antioxidative functions [3]. Copper has also been known as an important environmental pollutant [4]. The copper concentration in the environment varies widely with an average concentration of 0.01 mg/L in surface water and up to 100 mg/L in semiconductor wastewater [5]. Owing to the extensive use of copper in modern industrial applications, sensitive and selective chemosensors for Cu2+ ions have attracted much attention in environmental monitoring [6,7]. Recently, chemodosimeters or chemical probes using a reaction-based signaling approach have received much research interest [8]. The advantages of this strategy are cumulative, and specific chemical reactions between the probe molecule and analytes allow high sensitivity and excellent selectivity in signaling [9]. In particular, development of selective reaction-based probes for Cu2+ ions has been successfully realized. A number of probes have been devised based on the spirolactam ringopening process of rhodamine derivatives [10,11]. In addition, Cu2+-induced hydrolysis processes have become another important strategy for the design of Cu2+selective probes. A classical example reported by Czarnik’s group is the spirolactam ring-opening of rhodamine-hydrazide followed by hydrolysis [12]. Other probes are generally based on activated esters, Schiff-bases, and hydrazone function containing dyes [13-16]. Cu2+-mediated oxidation and oxidative cyclization processes have also
2
been successfully used for the development of selective and sensitive probes for Cu2+ ions [6,17,18]. 4-Aminoantipyrine (AAP) has been used as a useful chromogenic reagent for the determination of various phenols in aqueous solution [19]. The determination is based on the oxidative coupling of phenols with AAP by oxidants such as H2O2, persulfate, and K3Fe(CN)6 to yield highly colored diagnostic quinoneimine dyes [20,21]. On the other hand, coupling reaction of phenols with 4-aminoantipyrine is a well-established process for the determination of oxidants, such as hydrogen peroxide, in industrial analytes [22,23]. The same reaction can also be used for the determination of glucose in blood by using phenol, AAP, and glucose oxidase [24]. Interestingly, Cu2+ ions have been reported to act as an oxidant in the coupling of catechol with 4-aminoantipyrine [25]. However, no studies have been carried out on the construction of Cu2+-selective probes employing this useful reaction. In this paper, we report a new colorimetric signaling system for Cu2+ ions based on a metal ion-induced coupling of phenols with 4-aminoantipyrine. Upon treatment with Cu2+ ions, coupling of phenols with 4-aminoantipyrine smoothly proceeded to form a new quinoid dye with a prominent color change from colorless to pink.
2. Experimental Section 2.1 General. 4-Aminoantipyrine, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), and ammonium persulfate were purchased from Sigma-Aldrich Co. Boric acid was obtained from Wako Co. Phenol, 4-nitrophenol, 2,4,6-trimethylphenol, m-cresol, o-
3
cresol, and p-chlorophenol were obtained from commercial sources. For the spectroscopic studies, perchlorate salts of Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, and Pb2+ were obtained from SigmaAldrich Co. Chromium(III) nitrate nonahydrate was purchased from Sigma-Aldrich Co. Sodium fluoride and ethylenediaminetetraacetic acid (EDTA) were purchased from Fluka. UV–vis measurements were performed using spectroscopy grade acetonitrile purchased from J.T. Baker. All chemicals and solvents were used without further purification. 1H NMR (600 MHz) and 13C NMR (150 MHz) spectra were acquired on a Varian VNS spectrometer and referenced to the residual solvent signal. UV–vis spectra were acquired using a Jasco V-550 spectrophotometer and Scinco S-3100 equipped with a Peltier temperature controller. Column chromatography was performed using silica gel (240 mesh). Electron-impact (EI) mass spectra (LRMS) were recorded on a Micromass Autospec spectrometer. Compound 1 was prepared following the reported procedure [26].
2.2 Purification of Cu2+ signaling compound. Phenol (0.48 g, 5.1 mmol) and copper (II) perchlorate hexahydrate (1.26 g, 3.4 mmol) were dissolved in 100 mL of HEPESbuffered 90% aqueous acetonitrile solution. 4-Aminoantipyrine (70 mg, 0.34 mmol) dissolved in 10 mL of distilled water was added dropwise to the solution. The reaction mixture was stirred at room temperature for 1 h, and 100 mL of dichloromethane was poured in order to extract the Cu2+-signaling product. After separation of the dichloromethane layer, the organic solution was concentrated under reduced pressure. The residue was purified by simply passing through a silica gel plug using
4
dichloromethane/methanol (9:1, v/v) to obtain 52 mg (52% yield) of the Cu2+-signaling compound as a dark orange powder. 1H NMR (600 MHz, CDCl3) δ 8.50 (dd, J = 10.3, 2.7 Hz, 1H), 7.53-7.34 (m, 5H), 7.24 (dd, J = 9.9, 2.7 Hz, 1H), 6.54 (dd, J = 9.9, 2.3 Hz, 1H), 6.44 (dd, J = 10.3, 2.3 Hz, 1H), 3.36 (s, 3H), 2.50 (s, 3H);
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C NMR (150 MHz,
CDCl3) δ 188.01, 156.88, 153.43, 150.37, 143.72, 133.93, 133.24, 130.40, 129.58, 129.09, 128.52, 126.13, 119.92, 35.18, 10.78; MS (EI): m/z calcd for M+ (C17H17N3O2) : 295.13, found 295.16.
2.3 Measurement of signaling behaviors. UV–vis signaling behaviors of the probe system towards Cu2+ ions and other metal ions were measured in a mixture of CH3CN and HEPES-buffered solution (pH 7.5) (1:9, v/v). The stock solutions of phenol and 4-aminoantipyrine were prepared in acetonitrile, and metal ions and buffer solutions were made in distilled water. Sample solutions for measurement were prepared by successively adding the stock solutions of metal ions (37.5 μL, 10 mM), HEPES buffer (30 μL, 1 M), phenol (225 μL, 5 mM), and 4-aminoantipyrine (75 μL, 1 mM) in each vial. The solution was diluted with CH3CN and HEPESbuffer solution to make a final volume (3.0 mL) with a composition of 1:9, v/v. Final concentrations of metal ions, phenol, 4-aminoantipyrine, and HEPES buffer were 1.25 × 10−4 M, 3.75 × 10−4 M, 2.5 × 10−5 M, and 10 mM, respectively.
2.4 pH effects on the signaling towards Cu2+. The effects of pH on the signaling towards Cu2+ were elucidated by measuring the responses in a pH range between 4.0 and 10.0 that adjusted with buffer solutions. The buffer solutions used were acetate buffer for 4.0 to 5.8, HEPES buffer for 7.0 to 8.0, and borate buffer for 9.0 to 10.0. 5
Final concentrations of Cu2+, phenol, 4-aminoantipyrine, and each buffer solution were 1.25 × 10−4 M, 3.75 × 10−4 M, 2.5 × 10−5 M, and 10 mM, respectively, under the same measurement conditions.
2.5 Preparation of simulated semiconductor wastewater. Referring to the two relevant literatures on wastewater compositions [27,28], the following metal concentrations were used for the preparation of the simulated semiconductor wastewater: [Al3+] = 8.64 × 10–5 M, [Fe3+] = 5.37 × 10–5 M, [Pb2+] = 7.24 × 10–6 M, [Mn2+] = 1.82 × 10–6 M, [Zn2+] = 1.07 × 10–5 M, and [Ni2+] = 1.36 × 10–5 M.
2.6 Determination of the detection limit for Cu2+ ions. Following IUPAC recommendations, the detection limit for the Cu2+ ions was determined using the equation 3×sbl/m, where sbl denotes the standard deviation of the blank signal (the number of measurements = 20) and m represents the slope of the calibration curve [29].
3. Results and Discussion A novel colorimetric signaling system for Cu2+ ions based on a metal ion-induced coupling of phenols with 4-aminoantipyrine was developed. The signaling behavior of
the
probe
system
toward
metal
ions
was
investigated
by
UV-vis
spectrophotometry. A mixture (15:1 molar ratio) of phenol and 4-aminoantipyrine (PhOH-AAP) showed no significant absorptions above 400 nm in 90% aqueous acetonitrile solution buffered at pH 7.5 (HEPES buffer). The molar ratio was chosen
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on the basis of the observation that Cu2+ signaling increased proportionally as the phenol concentration increased up to 15:1 molar ratio of phenol and AAP and then became constant (Fig. S1, Supplementary data). Upon treatment of this PhOH-AAP system with various metal ions, a pronounced change was observed exclusively with Cu2+ ions (Fig. 1 and Fig. S2, Supplementary data). In the presence of Cu2+ ions, a new strong absorption at 501 nm developed and the solution color of the PhOHAAP system prominently changed from colorless to pink. No significant responses were observed from the other metal ions. On the other hand, meaningful fluorescence properties of PhOH-AAP were not observed for the signaling of any surveyed metal ions.
The prominent colorimetric signaling of Cu2+ ions by the PhOH-AAP system is due to the transformation depicted in Scheme 1. Phenol and AAP were oxidatively coupled to form a highly colored quinoneimine dye 1 promoted by Cu2+ ions. The formation of the aminoantipyrine-coupled product of phenols such as 1 by a practical persulfate oxidant was already known [26]. The proposed signaling process was confirmed by 1H and
13
C NMR spectroscopy. For this, the 1H NMR spectrum of the
Cu2+-signaling PhOH-AAP system was measured after purification of the reaction mixture. The resulting spectrum was identical to that obtained for compound 1 prepared independently using persulfate as an oxidant (Fig. 2 and Fig. S3, Supplementary data). In particular, the resonance peaks for the para-H (6.87 ppm) of
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phenol disappeared and the remaining four protons of the quinoid subunit appeared as two pairs of doublets (8.50 and 6.44 ppm for H-6 and H-5, 6.54 and 7.24 ppm for H-3 and H-2). One of the resonance peaks (H-6), assigned by means of a 2D 1H−13C HSQC spectrum (Fig. S4, Supplementary data), experienced a large shift to the lower field from 7.20 to 8.50 ppm due to a large anisotropic effect of nearby antipyryl group [26].
13
C NMR and UV–vis spectral evidences also confirmed the formation of
1 under the signaling conditions (Fig. S5 and Fig. S6, Supplementary data). Furthermore, treatment of the Cu2+-signaling PhOH-AAP system with chelating EDTA did not affect the UV–vis spectrum of the resulting solution, indicating the irreversible nature of the suggested reaction-based signaling process (Fig. S7, Supplementary data).
The Cu2+-selective signaling was not affected by the presence of common alkali, alkaline earth, and transition metal ions except for Al3+, Cr3+, and Fe2+, as background. The signaling ratio AMetal+Cu(II)/ACu(II) observed at 501 nm varied across a narrow range, from 0.99 for Li+ ions to 1.02 for Fe3+ ions (Fig. 3). On the other hand, considerable interference was observed with Al3+ ions with a AAl(III)+Cu(II)/ACu(II) ratio of 0.70. However, the interference from Al3+ ions was successfully removed by using fluoride ions as a masking agent [30]; in the presence of 40 equiv of fluoride ions, the interference from Al3+ ions disappeared completely (Fig. S8, Supplementary data). In the presence of Fe2+ or Cr3+, the Cu2+-signaling of the probe system
8
decreased to 53% by Fe2+, or totally suppressed by Cr3+. These interferences are due to the fact that undesirable interaction of Cu2+ ions with redox-active Fe2+ and Cr3+ ions [31,32]. The reaction of Cu2+ ions with Fe2+ or Cr3+ ions resulted in the decreases in Cu2+ level in the analytes, and leads to a significant reduced signal for Cu2+-triggered oxidative condensation between phenol and AAP. This observation implies that the present system could work as a practically applicable Cu2+-selective probe in commonly encountered environmental systems except for the analytes rich in redox-active metal ions of Fe2+ or Cr3+.
To check the quantitative analytical behavior of the PhOH-AAP system for Cu2+ signaling, a UV–vis titration was carried out in 90% aqueous acetonitrile (buffered at pH 7.5 using HEPES). As the concentration of Cu2+ ions increased, the absorption profile of the PhOH-AAP system changed progressively to that of 1 while showing a steadily increasing new band at 501 nm (Fig. 4). From the titration data, the detection limit in the determination of Cu2+ ions by the PhOH-AAP system was estimated to be 8.5 × 10−7 M in 90% aqueous acetonitrile solution (Fig. S9, Supplementary data) [29].
The effects of pH on the signaling were assessed by measuring the responses of the PhOH-AAP system as a function of the pH of the medium. As shown in Figure S10 9
(Supplementary data), the Cu2+ signaling was most pronounced between pH 7 and 8. Signaling speed was fast and the response was completed within 10 min after mixing the analyte solutions (Fig. S11, Supplementary data). Additionally, the PhOH-AAP mixture was stable under the ambient temperature and open laboratory atmosphere for more than 1 day. The Cu2+-selective signaling was possible for a number of phenols, such as o-cresol and m-cresol as well as p-chlorophenol (Fig. 5 and Fig. S12, Supplementary data). In the case of p-chlorophenol, the para-chloro substituent is known to be expelled during the oxidative process to form a quinoid dye [26]. Furthermore, practical applicability of the Cu2+-selective signaling by the PhOHAAP system was confirmed in tap water and simulated semiconductor wastewater (Fig. S13 and S14, Supplementary data). In particular, the interference from Al3+ in simulated semiconductor wastewater was successfully removed by using fluoride ions as a masking agent (Fig. S15, Supplementary data). The Cu2+ signaling by PhOH-AAP system in simulated semiconductor wastewater was possible up to 1.0 × 10−4 M.
4. Conclusion In summary, a new chromogenic probe system for the selective signaling of Cu2+ ions was developed based on the Cu2+-induced oxidative coupling of phenols and 4aminoantipyrine. The mixture of phenol and 4-aminoantipyrine exhibited pronounced Cu2+-selective chromogenic signaling with a color change from colorless to pink.
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Interference from Al3+ ions was successfully eliminated by using fluoride ions as a masking agent. The detection limit for the determination of Cu2+ ions was 8.5 × 10−7 M in 90% aqueous acetonitrile solution. The reported sensing approach would be useful as a convenient and practical colorimetric signaling system for Cu2+ ions in chemical and environmental applications, such as preliminary monitoring of Cu2+ levels in tap water and semiconductor wastewater.
Acknowledgements This research was supported by a fund from the Korea Research Foundation of the Korean Government (NRF-2013R1A1A2008574).
Appendix. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:**.****.
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Figure Captions
Scheme 1. Colorimetric signaling of Cu2+ ions by phenol and 4-aminoantipyrine pair (PhOH-AAP).
Fig. 1. Changes in UV–vis spectra of the PhOH-AAP system in the presence of various metal ions. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Mn+] = 1.25 × 10−4 M, [Pb2+] = 2.5 × 10−5 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). Spectral data for Cr3+ and Fe2+ were obtained against a reagent blank.
14
Fig. 2. Partial 1H NMR spectra of (a) PhOH and AAP (1:1 molar ratio) and (b) purified product after Cu2+ signaling of the PhOH-AAP system. Each compound was dissolved at 3.0 × 10−2 M in CDCl3.
Fig. 3. Competitive signaling of Cu2+ ions by the PhOH-AAP system in the presence of other metal ions as background. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M, [Mn+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). To prevent precipitation, [Pb2+] = 2.50 × 10−5 M.
Fig. 4. Changes in absorption spectrum of the PhOH-AAP system as a function of Cu2+ concentration. Inset: absorbance change at 501 nm as a function of Cu2+ ion concentration. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 0−2.5 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v).
Fig. 5. Photograph of mixtures of various phenols and AAP in the absence or presence of Cu2+. [AAP] = 2.5 × 10−5 M, [phenol] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). (a) 4-Nitrophenol, (b) 2,4,6-trimethylphenol, (c) m-cresol, (d) o-cresol, and (e) p-chlorophenol.
15
Highlights:
• Cu2+-selective probe based on oxidative coupling of phenols with 4-aminoantipyrine was devised. • “Naked-eye” detection of Cu2+ was possible via color change from colorless to pink. • Applicability in tap water and semiconductor wastewater was also investigated. • Detection limit of the probe system for Cu2+ in aqueous acetonitrile was 8.5 × 10–7 M.
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*Graphical Abstract (for review)
Graphical Abstract
Scheme-1
Scheme 1. Colorimetric signaling of Cu2+ ions by phenol and 4-aminoantipyrine pair (PhOH-AAP).
Figure-1
Fig. 1. Changes in UV–vis spectra of the PhOH-AAP system in the presence of various metal ions. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Mn+] = 1.25 × 10−4 M, [Pb2+] = 2.5 × 10−5 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). Spectral data for Cr3+ and Fe2+ were obtained against a reagent blank.
1
Figure-2
Fig. 2. Partial 1H NMR spectra of (a) PhOH and AAP (1:1 molar ratio) and (b) purified product after Cu2+ signaling of the PhOH-AAP system. Each compound was dissolved at 3.0 × 10−2 M in CDCl3.
1
Figure-3
Fig. 3. Competitive signaling of Cu2+ ions by the PhOH-AAP system in the presence of other metal ions as background. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M, [Mn+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). To prevent precipitation, [Pb2+] = 2.50 × 10−5 M.
1
Figure-4
Fig. 4. Changes in absorption spectrum of the PhOH-AAP system as a function of Cu2+ concentration. Inset: absorbance change at 501 nm as a function of Cu2+ ion concentration. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Cu2+] = 0−2.5 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v).
1
Figure-5
Fig. 5. Photograph of mixtures of various phenols and AAP in the absence or presence of Cu2+. [AAP] = 2.5 × 10−5 M, [phenol] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). (a) 4Nitrophenol, (b) 2,4,6-trimethylphenol, (c) m-cresol, (d) o-cresol, and (e) p-chlorophenol.
1
Scheme-1-in-Black-and-White
Scheme 1. Colorimetric signaling of Cu2+ ions by phenol and 4-aminoantipyrine pair (PhOH-AAP).
Figure-1-in-Black-and-White
Fig. 1. Changes in UV–vis spectra of the PhOH-AAP system in the presence of various metal ions. [AAP] = 2.5 × 10−5 M, [PhOH] = 3.75 × 10−4 M, [Mn+] = 1.25 × 10−4 M, [Pb2+] = 2.5 × 10−5 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). Spectral data for Cr3+ and Fe2+ were obtained against a reagent blank.
1
Figure-2-in-Black-and-White
Fig. 2. Partial 1H NMR spectra of (a) PhOH and AAP (1:1 molar ratio) and (b) purified product after Cu2+ signaling of the PhOH-AAP system. Each compound was dissolved at 3.0 × 10−2 M in CDCl3.
1
Figure-5-in-Black-and-White
Fig. 5. Photograph of mixtures of various phenols and AAP in the presence or absence of Cu2+. [AAP] = 2.5 × 10−5 M, [phenol] = 3.75 × 10−4 M, [Cu2+] = 1.25 × 10−4 M in a mixture of CH3CN and HEPES buffer solution (pH 7.5, 10 mM), (1:9, v/v). (a) 4Nitrophenol, (b) 2,4,6-trimethylphenol, (c) m-cresol, (d) o-cresol, and (e) p-chlorophenol.
1
