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A Schiff base derivative from cinnamaldehyde for colorimetric detection of Ni2+ in water
Sensors and Actuators B 207 (2015) 511–517
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A Schiff base derivative from cinnamaldehyde for colorimetric detection of Ni2+ in water Diecenia Peralta-Domínguez a , Mario Rodríguez a,∗ , Gabriel Ramos-Ortíz a,∗ , José Luis Maldonado a , Marco A. Meneses-Nava a , Oracio Barbosa-García a , Rosa Santillan b , Norberto Farfán c a
Centro de Investigaciones en Óptica, A.P. 1-948, 37000 León, Gto., Mexico Departamento de Química, CINVESTAV del IPN, A.P. 14-740, 07000 Mexico, D.F., Mexico c Facultad de Química, Departamento de Química Orgánica UNAM, Mexico, D.F. 04510, Mexico b
a r t i c l e
i n f o
Article history: Received 31 May 2014 Received in revised form 26 September 2014 Accepted 27 September 2014 Available online 6 October 2014 Keywords: Schiff base Colorimetric sensor Nickel ion detection
a b s t r a c t A novel Schiff base (L1) derivative from cinnamaldehyde with a simple structure was synthesized and evaluated as a sensitive colorimetric Ni2+ sensor in aqueous solution. Addition of nickel dissolved in water into a L1 solution produced a rapid color change from faded yellow to deep orange, corresponding to a large red shift in the absorption peak from 435 to 480 nm. L1 exhibited a detection limit for Ni2+ in water of 1 × 10−7 M measured by absorption spectroscopy, whereas by naked eye the detection limit was of the order of 5 × 10−6 M. Interaction between L1 and other biologically and environmentally relevant metal ions such as Hg2+ , Pb2+ , Co2+ , Cu2+ and Mn2+ , induced minimal spectral changes. These results show that the Schiff base L1 could be an excellent Ni2+ chemosensor with high metal selectivity and with the capability to perform the detection in water over a pH range of 5.5–8. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Recently the development of organic molecules with colorimetric or fluorescent chemosensor properties to detect toxic metal ions has received great attention [1–5]. These sensors find applications in biomedical and environmental sciences. The principal advantages of organic sensors over other recognition methods are the simplicity of their synthesis, high sensitivity and selectivity at low cost. The sensing in water is of paramount importance, so that organic sensors have been developed to detect in this medium metals such as Hg2+ [6], Cu2+ [7], Zn2+ [8], Fe2+ [9], Mn2+ [10], Co2+ [11] and Pb2+ [12]. Other metals, however, have received much less attention. This is the case of Ni2+ for which there is a limited number of chemosensors reported in the literature, and only very few of them perform detection in water [13,14]. Detection of Ni2+ with high sensitivity in environmental media is needed since this metal is a toxic element that can cause lung injury, acute pneumonitis, allergy, carcinogenesis, disorders of the central nervous system and gastrointestinal problems [15,16]. As pollutant, nickel is released
∗ Corresponding authors. E-mail addresses: [email protected] (M. Rodríguez), [email protected] (G. Ramos-Ortíz). http://dx.doi.org/10.1016/j.snb.2014.09.100 0925-4005/© 2014 Elsevier B.V. All rights reserved.
into the environment from a diversity of industrial processes and applications such as electroplating, catalysis, alloy production, nickel–cadmium batteries, super capacitors, etc. [17]. On the other hand, the use of chemosensors for Ni2+ in biomedical sciences is also important since this is an essential element in biophysical process such as respiration, biosynthesis and metabolism. There are various analytical methods for detection of Ni2+ such as atomic absorption spectrometry [18–20], membrane and potentiometric based techniques [21–23]. Although all these techniques offer high selectivity and accurate quantification, they are usually time-consuming, complicated to use and are not easily adaptable for online monitoring. In contrast, organic molecules designed to be used as chemosensors based on either the quenching or enhancement of fluorescence or change in color of solutions through the interaction with Ni2+ imply simpler procedures. For instance, fluorescent chemosensors have been reported using benzothiadiazoyltriazole derivatives [15], calix[4]arenes [17], probes containing thiophene and benzoxazole moieties [24], coumarins [25], porphyrins [26] and common colorants such as fluorescein and rhodamine [27]. Alternatively, organic molecules have been also utilized as colorimetric chemosensors of Ni2+ , although in this case the published reports are rather rare. Recently colorimetric detection of nickel ions has been performed through the use of coumarin derivatives [13,28]. Development of colorimetric Ni2+ sensors with
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Scheme 1. Synthesis of the Schiff base L1.
rapid response is attractive due to their simplicity, real-time analysis and a significantly lower cost in comparison with fluorescent, atomic absorption spectrometry or potentiometric methods, for which specialized equipment is required. In this work it is reported a simple and reliable colorimetric chemosensor (L1) for the detection of Ni2+ in aqueous media. This work was motivated by the fact that most organic molecules reported as Ni2+ chemosensors perform the sensing process in a medium different than water, which limits their application in environmental and life sciences. This new sensor is based on a Schiff base derivative. This type of derivatives belongs to a family of compounds whose properties are exploited in different areas including medicine, catalysis, crystal engineering and materials science [29]. For chemosensor applications, Schiff base derivatives are attractive because their synthesis is easy, present an intense color change after coordination with metals and offer a wide variety of design possibilities. Sensing characteristics of L1 were investigated by using UV–vis absorption spectroscopy in aqueous solutions upon the presence of biologically and environmentally relevant metals, i.e., Ni2+ , Hg2+ , Pb2+ , Mn2+ , Cu2+ and Co2+ . Our results demonstrated that L1 can be employed for sensing Ni2+ in water with a limit of detection of 1 × 10−7 M even under the presence of other ions. This is one of the lowest limits of detection reported for nickel in aqueous media. 2. Experimental 2.1. Materials and instrumentation All solvents involved in the spectroscopic studies and starting materials for the molecular synthesis were purchased from Sigma–Aldrich distributor and were employed without further purification treatment. UV–vis absorption spectra were measured using a spectrophotometer (Lambda 900, Perkin-Elmer). In the case of the synthesis method through ultrasonic bath, an ultrasonic cleaner (8892, Cole Parmer) was employed. NMR experiments were recorded in a jeol Fx 270 spectrometer. Melting point (uncorrected data) of L1 was obtained using Electrothermal 9200 apparatus. Infrared spectrum was measured on a FTIR Varian spectrophotometer with an ATR accessory.
of 80%. M.P: 150–152 ◦ C. Scheme 1 shows the route of synthesis of this novel sensor and its chemical structure. An alternative synthetic method was employed to prepare L1 by using an ultrasonic bath (see Scheme 1). A solution of equimolar quantities of 2-amino-4-chlorophenol and 4-dimetylaminocinnamaldehyde was added to a flask and also 2 mL of methanol. The solution was stirred in the ultrasonic bath for 45 min, the precipitated imine product was then separated by filtration. The brown solid obtained was washed with a mixture of hexane:ethylacetate (9:1) and finally 1 H NMR spectra was compared with the L1 obtained using thermal method. Employing this alternative method the Schiff base L1 was produced with a 78% of yield. Structure of L1 was established in solid state by using Fourier transform infrared (FTIR) analysis and in solution through 1 H and 13 C NMR experiments. IR (KBr) max: 3413 (OH), 1599 (C N) 1566, 1523, 1363, 1323 (C N), 879 cm−1 . 1 H NMR (DMSO-d6 , 500 MHz) ı: 8.31 (1H, d, J = 8.6 Hz, H-7), 7.49 (1H, s, H-6), 7.48 (2H, d, J = 8.6 Hz, H-11), 7.29 (1H, d, J = 15.6 Hz, H-9), 7.27 (1H, d, J = 8.2 Hz, H-4), 6.89 (1H, dd, J = 15.6, 8.6 Hz, H-8), 6.67 (2H, d, J = 8.6 Hz, H-12), 3.01 (6H, s, CH3 ) ppm. 13 C NMR (DMSO, 125 MHz) ı: 166.3 (C-7), 152.0 (C-2), 150.1 (C-13), 148.2 (C-9), 145.7 (C-4), 143.7 (C-1), 130.1 (C10), 123.2 (C-6), 123.1 (C-5), 122.3 (C-10), 120.1 (C-6), 116.5 (C-8), 113.2 (C-3), 112.4 (C-12), 31.2 (CH3 ) ppm. ESI-MS calculated for C17 H17 ClN2 O [M+H]+ 301.1108, found 301.1098 [M+H]+ (ppm error of 0.002). 2.3. Evaluation of sensor properties for L1 Metal sensing experiments based on L1 were performed with metallic ions dissolved in distilled water at pH 7. Sensing properties were evaluated by mixing a DMSO solution of L1 with the water solution containing the ion under test. After mixing these two solutions, the colorimetric performance was detected by naked eye and quantified by using UV–vis absorption spectroscopy. Absorption spectra were obtained in the wavelength interval of 300–700 nm, in steps of 1 nm using a 1-cm-thick quartz cell. Reproducibility (for absorbance value and wavelength shift) was corroborated for each sample. All experiments were performed at room temperature. 3. Results and discussion
2.2. Synthesis of Schiff base compound (L1)
3.1. Synthesis and absorption properties of L1
Compound 4-chloro-2-[(3-(4-(dimethylamino)phenyl)allylidene)amino]phenol (L1) was prepared following a reported methodology for the synthesis of imines derivatives from cinnamaldehyde [30]: L1 was synthesized from the reaction between 2-amino-4-chlorophenol (143 mg, 10 mmol) and 4dimethylaminocinnamaldehyde (175 mg, 10 mmol) in methanol (5 mL) at reflux temperature for 3 h. The solvent excess was distillated by using a Dean-Stark tramp, after that the solution was kept at room temperature and the precipitated product was separated by filtration to obtain 240 mg (8 mmol) of L1 with a yield
The molecular structure of L1 was designed to include a chloroaminophenol moiety as a receptor for specific metal analyte, namely, Ni2+ , and a cinnamaldehyde moiety as chromophoric fragment. The formation of a C N bond links the receptor and chromophoric fragment and allows the elongation of the -electronic conjugation over the main backbone. L1 is an air-stable powder with a brown color and shows good solubility in organic solvents including tetrahydrofuran (THF), dichloromethane (DCM), acetonitrile (ACN), dimethylsulfoxide (DMSO); it also shows solubility in methanol at low concentrations. 1 H and 13 C NMR experiments
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Fig. 1. Normalized absorption spectra of L1 in different solvents at the concentration of 3.3 × 10−4 M. Inset: molar extinction coefficients (the case of methanol is not presented due to the poor solubility of L1 at this concentration).
confirmed the formation of imine (C N) bond (see Supporting information, Fig. S1), with the spectra showing signals at 8.31 and 166.3 ppm corresponding to iminic proton and azomethine carbon, respectively. The configuration of the double bond (C C) was assigned as trans in agreement with the measured coupling constant values J7–8 = 8.6 Hz and J8–9 = 15.6 Hz. In solid state, the formation of compound L1 was validated by IR spectroscopy analysis which showed the stretching band due to C N bond at 1599 cm−1 and the asymmetric stretching of O H bond at 3413 cm−1 (see Fig. S2). Absorption properties of L1 were investigated in solution of different solvents at the concentration of 3.3 × 10−4 M (see Fig. 1). The observed absorption band is assigned to n → * intramolecular charge transition (ICT) from the NMe2 group to the Cl-phenyl ring. In a low polar-aprotic solvent (DCM) the band revealed an energy transition at 463 nm (εDCM = 88.0 × 102 M−1 cm−1 ), while in intermediate and higher polar-aprotic solvents such as THF and ACN, the band was blue shifted 25 and 18 nm to appear at 438 and 445 nm (εTHF = 86.2 × 102 and εACN = 38.5 × 102 M−1 cm−1 ), respectively. When L1 was dissolved in a higher polar medium (DMSO), the band appeared at 435 nm (εDMSO = 69.7 × 102 M−1 cm−1 ). The absorption band dependence on the solvent polarity suggests a solvent–solute interaction that modifies the ICT. On the other hand, in polar protic solvents, i.e., methanol and ethanol, the absorption band appears at 420 nm; this relative high energy is induced by hydrogen bonds interactions between the OH group of L1 with solvent molecules. 3.2. Sensing properties of L1 Before the evaluation of sensing properties of L1 toward transition metal ions dissolved in water, we investigated the stability of this Schiff base in a DMSO/water mixture (1:1 volume relation, at pH 7). Fig. 2 shows that the absorption peak of L1 in this solvent mixture is at 405 nm, corresponding to a blue shifting of 30 nm with respect to DMSO solution (435 nm as shown in Fig. 1). It is well known that imines in aqueous solution undergo hydrolysis, however our results indicate that L1 is stable for at least 30 min in DMSO/water solvent mixture (see Fig. S3). Once the effect of water on the absorption band of L1 was established, we proceeded to study its colorimetric changes when it is in contact with metal ions (Ni2+ , Hg2+ , Pb2+ , Mn2+ , Cu2+ and Co2+ ) dissolved in water. The experimental procedure to test the metal recognition consisted in mixing a DMSO solution of L1 (3.6 × 10−5 M) with an aqueous
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Fig. 2. Absorption spectra of L1 in DMSO/water mixture and L1 in DMSO mixed with aqueous solutions of different metal ions at 1 equiv. Inset: the corresponding photographs for each mixture. In all cases, the mixing of L1 DMSO solution (3.6 × 10−5 M) with an aqueous solution was at 1:1 volume ratio at pH 7.
solution of the metal under test at pH 7. This mixture was prepared at 1:1 volume ratio. Unless other way stated, this procedure for sensing metals in water was used in all the experiments here presented. Our results demonstrated that L1 exhibits selectivity for Ni2+ in water at equimolar (equiv) concentration. This selectivity was clearly observed at naked eye when the sensor L1 showed an intense color change from faded yellow to deep orange (see photograph in the inset of Fig. 2). This change in color took place practically at the moment that L1 solution was in contact with metal solution. L1 displays a less intense color change in presence of Hg2+ indicating a weaker metal–ligand interaction, whereas no significant changes were observed for Co2+ , Pb2+ , Cu2+ , and Mn2+ . Fig. 2 shows that the mixing of L1 with Ni2+ produced a red-shift in the peak of absorption of approximately 75 nm with respect to the ICT band of L1 in DMSO/water. For the mixture of L1 with Hg2+ , the absorption band appears red shifted only 20 nm. These colorimetric changes are promoted by the modification of the ICT process in the main electronic -system due to the metal coordination (N → M2+ ), with a strong binding toward Ni2+ and in less extend to Hg2+ . It must be mentioned, however, that the binding between L1 and Hg2+ was not stable. Binding stability was investigated by monitoring over the time the colorimetric changes observed in L1 after this is mixed with a metal. Fig. 3 presents the absorbance at 480 nm as a function of time for the different L1 + metal mixtures. From this figure it can be observed that the colorimetric property of the complex L1 + Ni2+ is stable in time, while the colorimetric changes from L1 + Hg2+ degraded quickly and disappear completely after few minutes, indicating low stability of the complex. The absorption spectra recorded as a function of time for the interaction of L1 with Ni2+ and Hg2+ are presented in Figs. S4 and S5. Similar sensing results were obtained with the metals under tests dissolved in tap water with ionic strength regulated by Mexican Official Norma (Norma Oficial Mexicana) [31]. These characteristics are important to be remarked, because other sensors carried out the nickel detection directly in organic solvents [15,17,24,28,32–35] and not in water. The potential of L1 as sensor was determined as a function of pH over the range 5.5–8 at the concentration 3.6 × 10−5 M of Ni2+ . The pH was adjusted with CH3 COOH and CH3 COONa. The pH dependence of absorption spectra of L1 and the complex L1 + Ni2+ is shown Fig. 4. As we can see the absorption of the sensor and the
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Fig. 3. Stability in the changes observed in the absorption band at 480 nm of sensor L1 (3.6 ×10−5 M) in the presence of 1 equiv of various metals in DMSO/water solutions (1:1, v/v) at pH 7.
complex is stable in the range of 5.5–8 and could be used for the estimation of Ni2+ in aqueous solution. To further determine the utility of L1 as selective sensor we studied the possible interferences from competing ions. Experiments were carried out by adding simultaneously into a DMSO solution of L1 an aqueous solution of Ni2+ and an aqueous solution of either Pb2+ , Co2+ , Hg2+ , Cu2+ or Mn2+ (at 1 equiv, and pH 7). Fig. 5 shows the absorbance values at 480 nm from these combinations. The intensity of the band due to the L1 + Ni2+ complex was not significantly influenced by the presence of the mentioned ions, including Hg2+ . This feature represents a significant advantage in comparison with other reported sensors, which show less selectivity for Ni2+ and interference in presence of Hg2+ , Cu2+ , Co2+ , Ag2+ , Fe2+ , Pb2+ [15,24,26,27,34–36]. Another experiment was carried out to verify possible interferences in the selectivity showed by L1 toward Ni2+ . DMSO solutions of the chemosensor were mixed with aqueous solutions of metal ions following three different procedures (A, B, and C). In A, the sensor was mixed with all the studied metals except mercury and nickel. In B the sensor was mixed with all the studied metals except nickel. In C the sensor was mixed with all studied metals. Fig. 6 displays the absorption spectra obtained from solutions of A, B and C. In A the absorption spectrum shows very small changes compared to that observed from L1 solution, indicating that Co2+ , Pb2+ ,
Fig. 4. Absorption of L1 and L1 + Ni2+ at 405 nm and 480 nm, respectively, both in DMSO/H2 O (1:1 v/v) solution with different pH ranging from 5.5 to 8. Inset: the corresponding absorption spectra of L1 and L1 + Ni2+ .
Fig. 5. Absorbance at 480 nm of L1 (3.6 × 10−5 M) in the presence of Ni2+ (1 equiv) and competing ions including Co2+ , Pb2+ , Cu2+ , Mn2+ , and Hg2+ (1 equiv) in DMSO/water (1:1, v/v) solution, at pH 7.
Cu2+ , and Mn2+ did not have interaction with the sensor. In B the absorption band showed a small red shifting and a small shoulder about 477 nm, indicating a weak binding interaction of L1 with Hg2+ (which is not stable, as it was previously discussed). In the case of solution containing Ni2+ along with the rest of metals (C procedure), the spectrum shows clearly an absorption peak at 480 nm distinctive of the L1 + Ni2+ complexation. Thus, L1 is able to perform a selective detection of nickel in aqueous solution still in presence of other metals, including mercury. The inset of Fig. 6 presents a photograph for the different metal-sensor mixtures showing that nickel detection can be carried out also by naked eye. 3.3. Stoichiometry and sensitivity of L1 in the nickel detection process The sensitivity of our chemosensor was investigated by the analysis of the absorption spectra during titration of L1 in DMSO with aqueous solution of Ni2+ . Mixtures were stirred constantly during the titration. Fig. 7a displays the changes in the absorption band of L1 promoted by the addition of water with different concentrations of Ni2+ . An increment in Ni2+ concentration leads to a reduction in the absorption intensity at 405 nm and also produces the apparition of a new band at 480 nm due to the formation of L1 + Ni2+ complex. The presence of a sharp isosbestic point at 430 nm implies
Fig. 6. Absorption spectra of L1 in DMSO/H2 O; A: L1 + Pb2+ + Co2 + Cu2+ and Mn2+ ; B: L1 + Pb2+ + Co2 + Cu2+ + Mn2+ and Hg2+ ; C: L1 + Pb2+ + Co2 + Cu2+ + Mn2+ , Hg2+ , and Ni2+ . All metals at 1 equiv with respect to L1 (3.6 × 10−5 M), at pH 7. Inset: photograph of each mixture.
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Table 1 Comparison of L1 with other representative colorimetric and fluorescent chemosensors for Ni2+ . Chemosensor
Method
Detection limit
Medium of detection
Coumarin Glutathione-Ag Nps Benzothiadiazoyl-triazole Pd porphyrin Coumarin Schiff base Dipyrrolyl Quinoxaline Schiff base
Colorimetric Colorimetric Colorimetric/fluorescence Colorimetric/fluorescence Colorimetric Fluorescence Colorimetric Colorimetric
5 × 10−7 7.5 × 10−5
Ethanol Water CH3 CN Water CH3 CN CH3 CN CH3 CN–HEPES Water
1.2 × 10−7
1.47 × 10−6 1 × 10−7
that L1 and L1 + Ni2+ species are in equilibrium during the titration process (no isosbestic point was observed for titration with Hg2+ , see Fig. S6). Moreover, for nickel concentration larger than 1 equiv no significant changes are observed in the absorption spectrum. In order to visualize better the changes on the absorption intensity as a function of the concentration of Ni2+ , we calculated the parameter AN /AM , where AN is the absorption of L1 at different Ni2+ concentrations and AM is the maximum absorption of L1 + Ni2+ at 1:1 equiv, both at 480 nm. With this parameter the stoichiometry formation of L1 + Ni2+ was clearly determined (see Fig. 7b), resulting in a 1:1 (metal:ligand) complex. Detection limit of the chemosensor L1 was calculated from the titration when the concentration of the metal was varied in the range from 0.005 to 0.05 equiv (Fig. 7b). The first distinctive change in the absorption band was clearly determined by spectroscopic method at 0.05 equiv of nickel. This spectroscopic limit of nickel detection corresponds to a concentration of 1 × 10−7 M. This value is around two orders of magnitude lower than the maximum
Binding constant
pH range stability
Metal interference
3–12
Co Cu, Co, Hg Co, Cu
2.34 × 104 2.88 × 107 4.7–7.5 2.9 × 104 11 × 105 1.29 × 105
7.4 5.5–8
Ref. [13] [14] [15] [26] [28] [32] [38] This work
contaminant level goal (MCLG = 1.7 × 10−5 M) established by the American Environmental Protection Agency (EPA) for Ni2+ in drinking water [37]. Jiang also demonstrated a lower detection limit (5 × 10−7 M) that this MCLG through the use of a coumarin based colorimetric sensor [13], however the sensing process free of interference with other metals ions was proved only in solutions of methanol. Likewise, one of the best detection limits (1.2 × 10−7 M) for nickel was reported by Hu et al. [26] with the use of phosphorescent chemosensor based in a Pd-porphyrin derivative, but in this case the sensing process exhibited interference with copper and cobalt, the latter being two metal ions which commonly induce interference with nickel chemosensors. Regarding the use of Schiff bases for sensing nickel, this has been demonstrated using polymeric membranes with potentiometric response and with a detection limit of 3.0 × 10−7 but this sensitivity was observed in non-aqueous media [21]. Finally, we remark that in our studies, color change from L1 + Ni2+ was clearly observed at naked eye at the concentration of 5.4 × 10−6 M. The association constant (Ka ) of L1 with Ni2+ was determined during titration experiments by the following equation [28]: Ka =
A − A0 (Amax − A0 )[Ni2+ ]
where A and A0 represent the absorbance of L1 at 480 nm in the presence and absence of Ni2+ , respectively, Amax is the saturated absorbance of L1 in the presence of excess amount of Ni2+ , while [Ni2+ ] is the concentration of the nickel ion added. The association constant Ka resulted to be 1.29 × 105 M−1 with a good linear relationship (R = 0.98) by a 1:1 binding mode. This association constant for our sensor is comparable with those demonstrated recently for colorimetric sensors based in the use of coumarine Schiff base compounds whose values are in the range 2.3–2.9 × 104 M−1 [13,28], however in the latter examples it is not clear if the sensing process can be performed in water while in our case we have demonstrated that L1 can perform the sensing of nickel dissolved in water. Table 1 presents a summary of the properties of our L1 sensor compared with other representative colorimetric or fluorescent sensors for Ni2+ reported recently in the literature, in terms of detection limit, medium of detection, interference with other metals, pH and binding constant. 4. Conclusions
Fig. 7. (a) Absorption spectra obtained during the titration of L1 with Ni2+ . The equivalence of nickel is denoted. (b) Stoichiometry formation of L1 + Ni2+ complex. Both at pH 7.
A colorimetric chemosensor based on a novel Schiff base 4chloro-2-[(3-(4-(dimethylamino)phenyl)allylidene)amino]phenol (L1) was designed and synthesized. Experimental results indicated that L1 in solution of DMSO has selectivity toward Ni2+ dissolved in water, showing binding-induced color changes from faded yellow to deep orange, and with stable colorimetric response even in the presence of other ion metals. The presence of Hg2+ promotes a moderate and non-stable color change, producing no interference with Ni2+ detection. An important advantage of L1 as chemosensor over other reported sensors is the simplicity of its chemical synthesis and the possibility to detect nickel ions in water. Furthermore,
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this novel colorimetric chemosensor exhibited a spectroscopic detection limit of 1 × 10−7 M and by naked eye this recognition limit is 5.4 × 10−6 M. Acknowledgements Authors acknowledge to CONACyT by Grants 132946 and 183147. Authors thank Martin Olmos and Jenith Mónica Castro for their technical assistance. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2014.09.100. References [1] J.F. Zhang, Y. Zhou, J. Yoon, J.S. Kim, Recent progress in fluorescent and colorimetric chemosensor for detection of precious metal ions (silver, gold and platinum ions), Chem. Soc. Rev. 40 (2011) 3416–3429. [2] H.N. Kim, W.X. Ren, J.S. Kim, J. Yoon, Fluorescent and colorimetric sensors for detection of lead, cadmium and mercury ions, Chem. Soc. Rev. 41 (2012) 3210–3244. ˜ Flourogenic and chromogenic [3] J.M. García, F.C. García, F. Serna, J.L. De La Pena, polymer chemosensor, Polym. Rev. 51 (2011) 341–390. [4] Y. Jeong, J. Yoonet, Recent progress on fluorescent chemosensors for metal ions, Inorg. Chim. Acta 381 (2012) 2–14. [5] M. Formica, V. Fusi, L. Giorgi, M. Micheloni, New fluorescent chemosensors for metal ions in solution, Coord. Chem. Rev. 256 (2012) 170–192. [6] A. Misra, M. Shahid, Chromo and fluorogenic properties of some azo-phenol derivatives and recognition of Hg2+ ion in aqueous medium by enhanced fluorescence, J. Phys. Chem. C 114 (2010) 16726–16739. [7] M. Park, S. Seo, S.J. Lee, J.H. Jung, Functionalized Ni@SiO2 core/shell magnetic nanoparticles as a chemosensor and adsorbent for Cu2+ ion in drinking water and human blood, Analyst 135 (2010) 2802–2805. [8] D. Udhayakumari, S. Saravanamoorthy, M. Ashokb, S. Velmathia, Simple imine linked colorimetric and fluorescent receptor for sensing Zn2+ ions in aqueous medium based on inhibition of ESIPT mechanism, Tetrahedron Lett. 52 (2011) 4631–4635. [9] D. Wei, Y. Suna, J. Yina, G. Weia, Y. Dua, Design and application on Fe3+ probe for “naked-eye” colorimetric detection in fully aqueous system, Sens. Actuators B 160 (2011) 1316–1321. [10] C. Gou, H. Wu, S. Jiang, C. Yi, J. Luo, X. Liu, A Highly selective colorimetric chemosensor for Mn2+ based on bis(N-salicylidene)ethylenediamine in pure aqueous solution, Chem. Lett. 40 (2011) 1082–1084. [11] D. Maity, T. Govindaraju, Highly selective colorimetric chemosensor for Co2+ , Inorg. Chem. 50 (2011) 11282–11284. [12] Y. Lu, X. Li, G. Wang, W. Tang, A highly sensitive and selective optical sensor for Pb2+ by using conjugated polymers and label-free oligonucleotides, Biosens. Bioelectron. 39 (2013) 231–235. [13] J. Jiang, C. Gou, J. Luo, C. Yi, X. Liu, A novel highly selective colorimetric sensor for Ni(II) ion using coumarin derivatives, Inorg. Chem. Commun. 15 (2012) 12–15. [14] H. Li, Z. Cui, C. Han, Glutathione-stabilized silver nanoparticles as colorimetric sensor for Ni2+ ion, Sens. Actuator B 143 (2009) 87–92. [15] S. Maisonneuve, Q. Fang, J. Xie, Benzothiadiazoyl-triazoyl cyclodextrin: a selective fluoroionophore for Ni(II), Tetrahedron 64 (2008) 8716–8720. [16] E. Denkhaus, K. Salnikow, Crit. Rev. Oncol. Hematol. 42 (2002) 35–56. [17] M. Kumar, M. Bhalla, A. Dhir, J.N. Babuet, A Ni2+ selective chemosensor based on partial cone conformation of calix[4]arene, Dalton Trans. 39 (2010) 10116–10121. [18] Z. Sun, P. Liang, Q. Ding, J. Cao, Determination of trace nickel in water samples by cloud point extraction preconcentration coupled with graphite furnace atomic absorption spectrometry, J. Hazard. Mater. B137 (2006) 943–946. [19] M. Ali-Karimi, M. Kafi, Removal, preconcentration and determination of Ni(II) from different environmental samples using modified magnetite nanoparticles prior to flame atomic absorption spectrometry, Arab. J. Chem, in press, http://dx.doi.org/10.1016/j.arabjc.2013.05.018 [20] M.K. Amini, T. Momeni-Isfahani, J.H. Khorasani, M. Pourhossein, Development of an optical chemical sensor based on 2-(5-bromo-2-pyridylazo)-5(diethylamino)phenol in nafion for determination of nickel ion, Talanta 63 (2004) 713–720. [21] V.K. Gupta, A.K. Singh, M.K. Pal, Ni(II) selective sensors based on Schiff bases membranes in poly(vinyl chloride), Anal. Chim. Acta 624 (2008) 223–231. [22] V.T. Kasumov, S. Ozalp-Yaman, E. Tas, Synthesis, spectroscopy and electrochemical behaviors of nickel(II) complexes with tetradentate Schiff bases derived from 3,5-But 2 -salicylaldehyde, Spectrochim. Acta Part A 62 (2005) 716–720. [23] V.K. Gupta, R.N. Goyal, S. Agarwal, P. Kumar, N. Bachheti, Nickel(II)-selective sensor based on dibenzo-18-crown-6 in PVC matrix, Talanta 71 (2007) 795–800.
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Biographies Diecenia Peralta-Dominguez had her M.Sc. in 2009 from Centro de Investigaciones en Optica (CIO), Leon, Mexico. Currently she is pursuing a Ph.D. in CIO. Her research interests are on the design and applications of organic molecules for colorimetric chemosensors. Mario Rodríguez had his Ph.D. from Centro de Investigaciones y de Estudios Avanzados (CINVESTAV) in 2007. Since 2010, he was appointed as an Engineer at Centro de Investigaciones en Óptica (CIO). His current research areas comprise design and synthesis of organic materials with linear and nonlinear optical properties for colorimetric sensor, TPA-biomarkers and organic photovoltaic devices (OPVs). Gabriel Ramos-Ortiz had his B.Sc. degree in physics from the Universidad Nacional Autónoma de México in 1996 and a Ph.D. degree from the University of Arizona, USA, in 2003. In 2004, he became a permanent full time researcher at the Photonics Department of the Optical Research Center (CIO), Leon, Mexico. His researches mostly focus on organic electronics and non-linear optics, including biophotonics, sensors, solar cells, spectroscopy and ultrafast optics. José-Luis Maldonado completed his Ph.D. in physics at UNAM by 1999 and is a Permanent Full Time Researcher at Centro de Investigaciones en Optica (Optical Research Center) now. During 2001–2002, he was a postdoctoral at the Optical Sciences Center, University of Arizona. Current research areas are on Plastic opto-electronics, Linear and nonlinear optical properties of organic and inorganic materials for photonic devices, Solar cells (OPVs) and OLEDs, within the Group of Optical Properties of Materials GPOM of the Photonics Division, CIO. Marco A. Meneses-Nava obtained his Ph.D. from Manchester University, England, in 1994, and then he soon joined the Photonics Group at the National Institute of Astrophysics, Optics and Electronics, at Puebla, Mexico. In 1998, he joined the Group of Optical Properties of Materials at the Optical Research Center in Guanajuato, Mexico. His actual research interests dwell on the fabrication and characterization of doped material with rare earth ions and their applications to photonics, and the use of optical spectroscopy, such as Raman and laser induced breakdown, for the characterization of materials in archeology and industry. Oracio Barbosa-Garcia is the founder (1998) and leader of the research group “Group of Optical Properties of Materials” at the Optical Research Center, Leon, Mexico. He has been involved with energy transfer processes in solids, spectroscopy applied in food and pharmaceutics. Recently, he is working in the field of organic electronics, e.g., photovoltaic solar cells.
D. Peralta-Domínguez et al. / Sensors and Actuators B 207 (2015) 511–517 Rosa Santillan had her M.Sc. and Ph.D. in organic chemistry in 1982 and 1986, respectively, at the Center of Research and Advanced Studies of the National Polytechnic Institute of Mexico. She is currently a professor in the Department of Chemistry in this institution. Her research interests include the synthesis and NMR characterization of steroids appended-molecular rotors in the solid state, X-ray diffraction and multifunctional optical properties of organic molecules.
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Norberto Farfán completed his Ph.D. in organic chemistry in 1986 from CINVESTAVIPN where he was a full professor until 2005 and he is currently a professor in the Department of Chemistry of the National University of México (UNAM). His research interests include the design, synthesis and evaluation of boron compounds with Non-linear Optical properties, the synthesis of macrocyclic boron compounds based on self-assembly, and molecular rotors synthesis and structure determination by NMR and X-ray diffraction.
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A Schiff base derivative from cinnamaldehyde for colorimetric detection of Ni2+ in water Diecenia Peralta-Domínguez a , Mario Rodríguez a,∗ , Gabriel Ramos-Ortíz a,∗ , José Luis Maldonado a , Marco A. Meneses-Nava a , Oracio Barbosa-García a , Rosa Santillan b , Norberto Farfán c a
Centro de Investigaciones en Óptica, A.P. 1-948, 37000 León, Gto., Mexico Departamento de Química, CINVESTAV del IPN, A.P. 14-740, 07000 Mexico, D.F., Mexico c Facultad de Química, Departamento de Química Orgánica UNAM, Mexico, D.F. 04510, Mexico b
a r t i c l e
i n f o
Article history: Received 31 May 2014 Received in revised form 26 September 2014 Accepted 27 September 2014 Available online 6 October 2014 Keywords: Schiff base Colorimetric sensor Nickel ion detection
a b s t r a c t A novel Schiff base (L1) derivative from cinnamaldehyde with a simple structure was synthesized and evaluated as a sensitive colorimetric Ni2+ sensor in aqueous solution. Addition of nickel dissolved in water into a L1 solution produced a rapid color change from faded yellow to deep orange, corresponding to a large red shift in the absorption peak from 435 to 480 nm. L1 exhibited a detection limit for Ni2+ in water of 1 × 10−7 M measured by absorption spectroscopy, whereas by naked eye the detection limit was of the order of 5 × 10−6 M. Interaction between L1 and other biologically and environmentally relevant metal ions such as Hg2+ , Pb2+ , Co2+ , Cu2+ and Mn2+ , induced minimal spectral changes. These results show that the Schiff base L1 could be an excellent Ni2+ chemosensor with high metal selectivity and with the capability to perform the detection in water over a pH range of 5.5–8. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Recently the development of organic molecules with colorimetric or fluorescent chemosensor properties to detect toxic metal ions has received great attention [1–5]. These sensors find applications in biomedical and environmental sciences. The principal advantages of organic sensors over other recognition methods are the simplicity of their synthesis, high sensitivity and selectivity at low cost. The sensing in water is of paramount importance, so that organic sensors have been developed to detect in this medium metals such as Hg2+ [6], Cu2+ [7], Zn2+ [8], Fe2+ [9], Mn2+ [10], Co2+ [11] and Pb2+ [12]. Other metals, however, have received much less attention. This is the case of Ni2+ for which there is a limited number of chemosensors reported in the literature, and only very few of them perform detection in water [13,14]. Detection of Ni2+ with high sensitivity in environmental media is needed since this metal is a toxic element that can cause lung injury, acute pneumonitis, allergy, carcinogenesis, disorders of the central nervous system and gastrointestinal problems [15,16]. As pollutant, nickel is released
∗ Corresponding authors. E-mail addresses: [email protected] (M. Rodríguez), [email protected] (G. Ramos-Ortíz). http://dx.doi.org/10.1016/j.snb.2014.09.100 0925-4005/© 2014 Elsevier B.V. All rights reserved.
into the environment from a diversity of industrial processes and applications such as electroplating, catalysis, alloy production, nickel–cadmium batteries, super capacitors, etc. [17]. On the other hand, the use of chemosensors for Ni2+ in biomedical sciences is also important since this is an essential element in biophysical process such as respiration, biosynthesis and metabolism. There are various analytical methods for detection of Ni2+ such as atomic absorption spectrometry [18–20], membrane and potentiometric based techniques [21–23]. Although all these techniques offer high selectivity and accurate quantification, they are usually time-consuming, complicated to use and are not easily adaptable for online monitoring. In contrast, organic molecules designed to be used as chemosensors based on either the quenching or enhancement of fluorescence or change in color of solutions through the interaction with Ni2+ imply simpler procedures. For instance, fluorescent chemosensors have been reported using benzothiadiazoyltriazole derivatives [15], calix[4]arenes [17], probes containing thiophene and benzoxazole moieties [24], coumarins [25], porphyrins [26] and common colorants such as fluorescein and rhodamine [27]. Alternatively, organic molecules have been also utilized as colorimetric chemosensors of Ni2+ , although in this case the published reports are rather rare. Recently colorimetric detection of nickel ions has been performed through the use of coumarin derivatives [13,28]. Development of colorimetric Ni2+ sensors with
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Scheme 1. Synthesis of the Schiff base L1.
rapid response is attractive due to their simplicity, real-time analysis and a significantly lower cost in comparison with fluorescent, atomic absorption spectrometry or potentiometric methods, for which specialized equipment is required. In this work it is reported a simple and reliable colorimetric chemosensor (L1) for the detection of Ni2+ in aqueous media. This work was motivated by the fact that most organic molecules reported as Ni2+ chemosensors perform the sensing process in a medium different than water, which limits their application in environmental and life sciences. This new sensor is based on a Schiff base derivative. This type of derivatives belongs to a family of compounds whose properties are exploited in different areas including medicine, catalysis, crystal engineering and materials science [29]. For chemosensor applications, Schiff base derivatives are attractive because their synthesis is easy, present an intense color change after coordination with metals and offer a wide variety of design possibilities. Sensing characteristics of L1 were investigated by using UV–vis absorption spectroscopy in aqueous solutions upon the presence of biologically and environmentally relevant metals, i.e., Ni2+ , Hg2+ , Pb2+ , Mn2+ , Cu2+ and Co2+ . Our results demonstrated that L1 can be employed for sensing Ni2+ in water with a limit of detection of 1 × 10−7 M even under the presence of other ions. This is one of the lowest limits of detection reported for nickel in aqueous media. 2. Experimental 2.1. Materials and instrumentation All solvents involved in the spectroscopic studies and starting materials for the molecular synthesis were purchased from Sigma–Aldrich distributor and were employed without further purification treatment. UV–vis absorption spectra were measured using a spectrophotometer (Lambda 900, Perkin-Elmer). In the case of the synthesis method through ultrasonic bath, an ultrasonic cleaner (8892, Cole Parmer) was employed. NMR experiments were recorded in a jeol Fx 270 spectrometer. Melting point (uncorrected data) of L1 was obtained using Electrothermal 9200 apparatus. Infrared spectrum was measured on a FTIR Varian spectrophotometer with an ATR accessory.
of 80%. M.P: 150–152 ◦ C. Scheme 1 shows the route of synthesis of this novel sensor and its chemical structure. An alternative synthetic method was employed to prepare L1 by using an ultrasonic bath (see Scheme 1). A solution of equimolar quantities of 2-amino-4-chlorophenol and 4-dimetylaminocinnamaldehyde was added to a flask and also 2 mL of methanol. The solution was stirred in the ultrasonic bath for 45 min, the precipitated imine product was then separated by filtration. The brown solid obtained was washed with a mixture of hexane:ethylacetate (9:1) and finally 1 H NMR spectra was compared with the L1 obtained using thermal method. Employing this alternative method the Schiff base L1 was produced with a 78% of yield. Structure of L1 was established in solid state by using Fourier transform infrared (FTIR) analysis and in solution through 1 H and 13 C NMR experiments. IR (KBr) max: 3413 (OH), 1599 (C N) 1566, 1523, 1363, 1323 (C N), 879 cm−1 . 1 H NMR (DMSO-d6 , 500 MHz) ı: 8.31 (1H, d, J = 8.6 Hz, H-7), 7.49 (1H, s, H-6), 7.48 (2H, d, J = 8.6 Hz, H-11), 7.29 (1H, d, J = 15.6 Hz, H-9), 7.27 (1H, d, J = 8.2 Hz, H-4), 6.89 (1H, dd, J = 15.6, 8.6 Hz, H-8), 6.67 (2H, d, J = 8.6 Hz, H-12), 3.01 (6H, s, CH3 ) ppm. 13 C NMR (DMSO, 125 MHz) ı: 166.3 (C-7), 152.0 (C-2), 150.1 (C-13), 148.2 (C-9), 145.7 (C-4), 143.7 (C-1), 130.1 (C10), 123.2 (C-6), 123.1 (C-5), 122.3 (C-10), 120.1 (C-6), 116.5 (C-8), 113.2 (C-3), 112.4 (C-12), 31.2 (CH3 ) ppm. ESI-MS calculated for C17 H17 ClN2 O [M+H]+ 301.1108, found 301.1098 [M+H]+ (ppm error of 0.002). 2.3. Evaluation of sensor properties for L1 Metal sensing experiments based on L1 were performed with metallic ions dissolved in distilled water at pH 7. Sensing properties were evaluated by mixing a DMSO solution of L1 with the water solution containing the ion under test. After mixing these two solutions, the colorimetric performance was detected by naked eye and quantified by using UV–vis absorption spectroscopy. Absorption spectra were obtained in the wavelength interval of 300–700 nm, in steps of 1 nm using a 1-cm-thick quartz cell. Reproducibility (for absorbance value and wavelength shift) was corroborated for each sample. All experiments were performed at room temperature. 3. Results and discussion
2.2. Synthesis of Schiff base compound (L1)
3.1. Synthesis and absorption properties of L1
Compound 4-chloro-2-[(3-(4-(dimethylamino)phenyl)allylidene)amino]phenol (L1) was prepared following a reported methodology for the synthesis of imines derivatives from cinnamaldehyde [30]: L1 was synthesized from the reaction between 2-amino-4-chlorophenol (143 mg, 10 mmol) and 4dimethylaminocinnamaldehyde (175 mg, 10 mmol) in methanol (5 mL) at reflux temperature for 3 h. The solvent excess was distillated by using a Dean-Stark tramp, after that the solution was kept at room temperature and the precipitated product was separated by filtration to obtain 240 mg (8 mmol) of L1 with a yield
The molecular structure of L1 was designed to include a chloroaminophenol moiety as a receptor for specific metal analyte, namely, Ni2+ , and a cinnamaldehyde moiety as chromophoric fragment. The formation of a C N bond links the receptor and chromophoric fragment and allows the elongation of the -electronic conjugation over the main backbone. L1 is an air-stable powder with a brown color and shows good solubility in organic solvents including tetrahydrofuran (THF), dichloromethane (DCM), acetonitrile (ACN), dimethylsulfoxide (DMSO); it also shows solubility in methanol at low concentrations. 1 H and 13 C NMR experiments
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Fig. 1. Normalized absorption spectra of L1 in different solvents at the concentration of 3.3 × 10−4 M. Inset: molar extinction coefficients (the case of methanol is not presented due to the poor solubility of L1 at this concentration).
confirmed the formation of imine (C N) bond (see Supporting information, Fig. S1), with the spectra showing signals at 8.31 and 166.3 ppm corresponding to iminic proton and azomethine carbon, respectively. The configuration of the double bond (C C) was assigned as trans in agreement with the measured coupling constant values J7–8 = 8.6 Hz and J8–9 = 15.6 Hz. In solid state, the formation of compound L1 was validated by IR spectroscopy analysis which showed the stretching band due to C N bond at 1599 cm−1 and the asymmetric stretching of O H bond at 3413 cm−1 (see Fig. S2). Absorption properties of L1 were investigated in solution of different solvents at the concentration of 3.3 × 10−4 M (see Fig. 1). The observed absorption band is assigned to n → * intramolecular charge transition (ICT) from the NMe2 group to the Cl-phenyl ring. In a low polar-aprotic solvent (DCM) the band revealed an energy transition at 463 nm (εDCM = 88.0 × 102 M−1 cm−1 ), while in intermediate and higher polar-aprotic solvents such as THF and ACN, the band was blue shifted 25 and 18 nm to appear at 438 and 445 nm (εTHF = 86.2 × 102 and εACN = 38.5 × 102 M−1 cm−1 ), respectively. When L1 was dissolved in a higher polar medium (DMSO), the band appeared at 435 nm (εDMSO = 69.7 × 102 M−1 cm−1 ). The absorption band dependence on the solvent polarity suggests a solvent–solute interaction that modifies the ICT. On the other hand, in polar protic solvents, i.e., methanol and ethanol, the absorption band appears at 420 nm; this relative high energy is induced by hydrogen bonds interactions between the OH group of L1 with solvent molecules. 3.2. Sensing properties of L1 Before the evaluation of sensing properties of L1 toward transition metal ions dissolved in water, we investigated the stability of this Schiff base in a DMSO/water mixture (1:1 volume relation, at pH 7). Fig. 2 shows that the absorption peak of L1 in this solvent mixture is at 405 nm, corresponding to a blue shifting of 30 nm with respect to DMSO solution (435 nm as shown in Fig. 1). It is well known that imines in aqueous solution undergo hydrolysis, however our results indicate that L1 is stable for at least 30 min in DMSO/water solvent mixture (see Fig. S3). Once the effect of water on the absorption band of L1 was established, we proceeded to study its colorimetric changes when it is in contact with metal ions (Ni2+ , Hg2+ , Pb2+ , Mn2+ , Cu2+ and Co2+ ) dissolved in water. The experimental procedure to test the metal recognition consisted in mixing a DMSO solution of L1 (3.6 × 10−5 M) with an aqueous
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Fig. 2. Absorption spectra of L1 in DMSO/water mixture and L1 in DMSO mixed with aqueous solutions of different metal ions at 1 equiv. Inset: the corresponding photographs for each mixture. In all cases, the mixing of L1 DMSO solution (3.6 × 10−5 M) with an aqueous solution was at 1:1 volume ratio at pH 7.
solution of the metal under test at pH 7. This mixture was prepared at 1:1 volume ratio. Unless other way stated, this procedure for sensing metals in water was used in all the experiments here presented. Our results demonstrated that L1 exhibits selectivity for Ni2+ in water at equimolar (equiv) concentration. This selectivity was clearly observed at naked eye when the sensor L1 showed an intense color change from faded yellow to deep orange (see photograph in the inset of Fig. 2). This change in color took place practically at the moment that L1 solution was in contact with metal solution. L1 displays a less intense color change in presence of Hg2+ indicating a weaker metal–ligand interaction, whereas no significant changes were observed for Co2+ , Pb2+ , Cu2+ , and Mn2+ . Fig. 2 shows that the mixing of L1 with Ni2+ produced a red-shift in the peak of absorption of approximately 75 nm with respect to the ICT band of L1 in DMSO/water. For the mixture of L1 with Hg2+ , the absorption band appears red shifted only 20 nm. These colorimetric changes are promoted by the modification of the ICT process in the main electronic -system due to the metal coordination (N → M2+ ), with a strong binding toward Ni2+ and in less extend to Hg2+ . It must be mentioned, however, that the binding between L1 and Hg2+ was not stable. Binding stability was investigated by monitoring over the time the colorimetric changes observed in L1 after this is mixed with a metal. Fig. 3 presents the absorbance at 480 nm as a function of time for the different L1 + metal mixtures. From this figure it can be observed that the colorimetric property of the complex L1 + Ni2+ is stable in time, while the colorimetric changes from L1 + Hg2+ degraded quickly and disappear completely after few minutes, indicating low stability of the complex. The absorption spectra recorded as a function of time for the interaction of L1 with Ni2+ and Hg2+ are presented in Figs. S4 and S5. Similar sensing results were obtained with the metals under tests dissolved in tap water with ionic strength regulated by Mexican Official Norma (Norma Oficial Mexicana) [31]. These characteristics are important to be remarked, because other sensors carried out the nickel detection directly in organic solvents [15,17,24,28,32–35] and not in water. The potential of L1 as sensor was determined as a function of pH over the range 5.5–8 at the concentration 3.6 × 10−5 M of Ni2+ . The pH was adjusted with CH3 COOH and CH3 COONa. The pH dependence of absorption spectra of L1 and the complex L1 + Ni2+ is shown Fig. 4. As we can see the absorption of the sensor and the
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Fig. 3. Stability in the changes observed in the absorption band at 480 nm of sensor L1 (3.6 ×10−5 M) in the presence of 1 equiv of various metals in DMSO/water solutions (1:1, v/v) at pH 7.
complex is stable in the range of 5.5–8 and could be used for the estimation of Ni2+ in aqueous solution. To further determine the utility of L1 as selective sensor we studied the possible interferences from competing ions. Experiments were carried out by adding simultaneously into a DMSO solution of L1 an aqueous solution of Ni2+ and an aqueous solution of either Pb2+ , Co2+ , Hg2+ , Cu2+ or Mn2+ (at 1 equiv, and pH 7). Fig. 5 shows the absorbance values at 480 nm from these combinations. The intensity of the band due to the L1 + Ni2+ complex was not significantly influenced by the presence of the mentioned ions, including Hg2+ . This feature represents a significant advantage in comparison with other reported sensors, which show less selectivity for Ni2+ and interference in presence of Hg2+ , Cu2+ , Co2+ , Ag2+ , Fe2+ , Pb2+ [15,24,26,27,34–36]. Another experiment was carried out to verify possible interferences in the selectivity showed by L1 toward Ni2+ . DMSO solutions of the chemosensor were mixed with aqueous solutions of metal ions following three different procedures (A, B, and C). In A, the sensor was mixed with all the studied metals except mercury and nickel. In B the sensor was mixed with all the studied metals except nickel. In C the sensor was mixed with all studied metals. Fig. 6 displays the absorption spectra obtained from solutions of A, B and C. In A the absorption spectrum shows very small changes compared to that observed from L1 solution, indicating that Co2+ , Pb2+ ,
Fig. 4. Absorption of L1 and L1 + Ni2+ at 405 nm and 480 nm, respectively, both in DMSO/H2 O (1:1 v/v) solution with different pH ranging from 5.5 to 8. Inset: the corresponding absorption spectra of L1 and L1 + Ni2+ .
Fig. 5. Absorbance at 480 nm of L1 (3.6 × 10−5 M) in the presence of Ni2+ (1 equiv) and competing ions including Co2+ , Pb2+ , Cu2+ , Mn2+ , and Hg2+ (1 equiv) in DMSO/water (1:1, v/v) solution, at pH 7.
Cu2+ , and Mn2+ did not have interaction with the sensor. In B the absorption band showed a small red shifting and a small shoulder about 477 nm, indicating a weak binding interaction of L1 with Hg2+ (which is not stable, as it was previously discussed). In the case of solution containing Ni2+ along with the rest of metals (C procedure), the spectrum shows clearly an absorption peak at 480 nm distinctive of the L1 + Ni2+ complexation. Thus, L1 is able to perform a selective detection of nickel in aqueous solution still in presence of other metals, including mercury. The inset of Fig. 6 presents a photograph for the different metal-sensor mixtures showing that nickel detection can be carried out also by naked eye. 3.3. Stoichiometry and sensitivity of L1 in the nickel detection process The sensitivity of our chemosensor was investigated by the analysis of the absorption spectra during titration of L1 in DMSO with aqueous solution of Ni2+ . Mixtures were stirred constantly during the titration. Fig. 7a displays the changes in the absorption band of L1 promoted by the addition of water with different concentrations of Ni2+ . An increment in Ni2+ concentration leads to a reduction in the absorption intensity at 405 nm and also produces the apparition of a new band at 480 nm due to the formation of L1 + Ni2+ complex. The presence of a sharp isosbestic point at 430 nm implies
Fig. 6. Absorption spectra of L1 in DMSO/H2 O; A: L1 + Pb2+ + Co2 + Cu2+ and Mn2+ ; B: L1 + Pb2+ + Co2 + Cu2+ + Mn2+ and Hg2+ ; C: L1 + Pb2+ + Co2 + Cu2+ + Mn2+ , Hg2+ , and Ni2+ . All metals at 1 equiv with respect to L1 (3.6 × 10−5 M), at pH 7. Inset: photograph of each mixture.
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Table 1 Comparison of L1 with other representative colorimetric and fluorescent chemosensors for Ni2+ . Chemosensor
Method
Detection limit
Medium of detection
Coumarin Glutathione-Ag Nps Benzothiadiazoyl-triazole Pd porphyrin Coumarin Schiff base Dipyrrolyl Quinoxaline Schiff base
Colorimetric Colorimetric Colorimetric/fluorescence Colorimetric/fluorescence Colorimetric Fluorescence Colorimetric Colorimetric
5 × 10−7 7.5 × 10−5
Ethanol Water CH3 CN Water CH3 CN CH3 CN CH3 CN–HEPES Water
1.2 × 10−7
1.47 × 10−6 1 × 10−7
that L1 and L1 + Ni2+ species are in equilibrium during the titration process (no isosbestic point was observed for titration with Hg2+ , see Fig. S6). Moreover, for nickel concentration larger than 1 equiv no significant changes are observed in the absorption spectrum. In order to visualize better the changes on the absorption intensity as a function of the concentration of Ni2+ , we calculated the parameter AN /AM , where AN is the absorption of L1 at different Ni2+ concentrations and AM is the maximum absorption of L1 + Ni2+ at 1:1 equiv, both at 480 nm. With this parameter the stoichiometry formation of L1 + Ni2+ was clearly determined (see Fig. 7b), resulting in a 1:1 (metal:ligand) complex. Detection limit of the chemosensor L1 was calculated from the titration when the concentration of the metal was varied in the range from 0.005 to 0.05 equiv (Fig. 7b). The first distinctive change in the absorption band was clearly determined by spectroscopic method at 0.05 equiv of nickel. This spectroscopic limit of nickel detection corresponds to a concentration of 1 × 10−7 M. This value is around two orders of magnitude lower than the maximum
Binding constant
pH range stability
Metal interference
3–12
Co Cu, Co, Hg Co, Cu
2.34 × 104 2.88 × 107 4.7–7.5 2.9 × 104 11 × 105 1.29 × 105
7.4 5.5–8
Ref. [13] [14] [15] [26] [28] [32] [38] This work
contaminant level goal (MCLG = 1.7 × 10−5 M) established by the American Environmental Protection Agency (EPA) for Ni2+ in drinking water [37]. Jiang also demonstrated a lower detection limit (5 × 10−7 M) that this MCLG through the use of a coumarin based colorimetric sensor [13], however the sensing process free of interference with other metals ions was proved only in solutions of methanol. Likewise, one of the best detection limits (1.2 × 10−7 M) for nickel was reported by Hu et al. [26] with the use of phosphorescent chemosensor based in a Pd-porphyrin derivative, but in this case the sensing process exhibited interference with copper and cobalt, the latter being two metal ions which commonly induce interference with nickel chemosensors. Regarding the use of Schiff bases for sensing nickel, this has been demonstrated using polymeric membranes with potentiometric response and with a detection limit of 3.0 × 10−7 but this sensitivity was observed in non-aqueous media [21]. Finally, we remark that in our studies, color change from L1 + Ni2+ was clearly observed at naked eye at the concentration of 5.4 × 10−6 M. The association constant (Ka ) of L1 with Ni2+ was determined during titration experiments by the following equation [28]: Ka =
A − A0 (Amax − A0 )[Ni2+ ]
where A and A0 represent the absorbance of L1 at 480 nm in the presence and absence of Ni2+ , respectively, Amax is the saturated absorbance of L1 in the presence of excess amount of Ni2+ , while [Ni2+ ] is the concentration of the nickel ion added. The association constant Ka resulted to be 1.29 × 105 M−1 with a good linear relationship (R = 0.98) by a 1:1 binding mode. This association constant for our sensor is comparable with those demonstrated recently for colorimetric sensors based in the use of coumarine Schiff base compounds whose values are in the range 2.3–2.9 × 104 M−1 [13,28], however in the latter examples it is not clear if the sensing process can be performed in water while in our case we have demonstrated that L1 can perform the sensing of nickel dissolved in water. Table 1 presents a summary of the properties of our L1 sensor compared with other representative colorimetric or fluorescent sensors for Ni2+ reported recently in the literature, in terms of detection limit, medium of detection, interference with other metals, pH and binding constant. 4. Conclusions
Fig. 7. (a) Absorption spectra obtained during the titration of L1 with Ni2+ . The equivalence of nickel is denoted. (b) Stoichiometry formation of L1 + Ni2+ complex. Both at pH 7.
A colorimetric chemosensor based on a novel Schiff base 4chloro-2-[(3-(4-(dimethylamino)phenyl)allylidene)amino]phenol (L1) was designed and synthesized. Experimental results indicated that L1 in solution of DMSO has selectivity toward Ni2+ dissolved in water, showing binding-induced color changes from faded yellow to deep orange, and with stable colorimetric response even in the presence of other ion metals. The presence of Hg2+ promotes a moderate and non-stable color change, producing no interference with Ni2+ detection. An important advantage of L1 as chemosensor over other reported sensors is the simplicity of its chemical synthesis and the possibility to detect nickel ions in water. Furthermore,
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this novel colorimetric chemosensor exhibited a spectroscopic detection limit of 1 × 10−7 M and by naked eye this recognition limit is 5.4 × 10−6 M. Acknowledgements Authors acknowledge to CONACyT by Grants 132946 and 183147. Authors thank Martin Olmos and Jenith Mónica Castro for their technical assistance. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2014.09.100. References [1] J.F. Zhang, Y. Zhou, J. Yoon, J.S. Kim, Recent progress in fluorescent and colorimetric chemosensor for detection of precious metal ions (silver, gold and platinum ions), Chem. Soc. Rev. 40 (2011) 3416–3429. [2] H.N. Kim, W.X. Ren, J.S. Kim, J. Yoon, Fluorescent and colorimetric sensors for detection of lead, cadmium and mercury ions, Chem. Soc. Rev. 41 (2012) 3210–3244. ˜ Flourogenic and chromogenic [3] J.M. García, F.C. García, F. Serna, J.L. De La Pena, polymer chemosensor, Polym. Rev. 51 (2011) 341–390. [4] Y. Jeong, J. Yoonet, Recent progress on fluorescent chemosensors for metal ions, Inorg. Chim. Acta 381 (2012) 2–14. [5] M. Formica, V. Fusi, L. Giorgi, M. Micheloni, New fluorescent chemosensors for metal ions in solution, Coord. Chem. Rev. 256 (2012) 170–192. [6] A. Misra, M. Shahid, Chromo and fluorogenic properties of some azo-phenol derivatives and recognition of Hg2+ ion in aqueous medium by enhanced fluorescence, J. Phys. Chem. C 114 (2010) 16726–16739. [7] M. Park, S. Seo, S.J. Lee, J.H. Jung, Functionalized Ni@SiO2 core/shell magnetic nanoparticles as a chemosensor and adsorbent for Cu2+ ion in drinking water and human blood, Analyst 135 (2010) 2802–2805. [8] D. Udhayakumari, S. Saravanamoorthy, M. Ashokb, S. Velmathia, Simple imine linked colorimetric and fluorescent receptor for sensing Zn2+ ions in aqueous medium based on inhibition of ESIPT mechanism, Tetrahedron Lett. 52 (2011) 4631–4635. [9] D. Wei, Y. Suna, J. Yina, G. Weia, Y. Dua, Design and application on Fe3+ probe for “naked-eye” colorimetric detection in fully aqueous system, Sens. Actuators B 160 (2011) 1316–1321. [10] C. Gou, H. Wu, S. Jiang, C. Yi, J. Luo, X. Liu, A Highly selective colorimetric chemosensor for Mn2+ based on bis(N-salicylidene)ethylenediamine in pure aqueous solution, Chem. Lett. 40 (2011) 1082–1084. [11] D. Maity, T. Govindaraju, Highly selective colorimetric chemosensor for Co2+ , Inorg. Chem. 50 (2011) 11282–11284. [12] Y. Lu, X. Li, G. Wang, W. Tang, A highly sensitive and selective optical sensor for Pb2+ by using conjugated polymers and label-free oligonucleotides, Biosens. Bioelectron. 39 (2013) 231–235. [13] J. Jiang, C. Gou, J. Luo, C. Yi, X. Liu, A novel highly selective colorimetric sensor for Ni(II) ion using coumarin derivatives, Inorg. Chem. Commun. 15 (2012) 12–15. [14] H. Li, Z. Cui, C. Han, Glutathione-stabilized silver nanoparticles as colorimetric sensor for Ni2+ ion, Sens. Actuator B 143 (2009) 87–92. [15] S. Maisonneuve, Q. Fang, J. Xie, Benzothiadiazoyl-triazoyl cyclodextrin: a selective fluoroionophore for Ni(II), Tetrahedron 64 (2008) 8716–8720. [16] E. Denkhaus, K. Salnikow, Crit. Rev. Oncol. Hematol. 42 (2002) 35–56. [17] M. Kumar, M. Bhalla, A. Dhir, J.N. Babuet, A Ni2+ selective chemosensor based on partial cone conformation of calix[4]arene, Dalton Trans. 39 (2010) 10116–10121. [18] Z. Sun, P. Liang, Q. Ding, J. Cao, Determination of trace nickel in water samples by cloud point extraction preconcentration coupled with graphite furnace atomic absorption spectrometry, J. Hazard. Mater. B137 (2006) 943–946. [19] M. Ali-Karimi, M. Kafi, Removal, preconcentration and determination of Ni(II) from different environmental samples using modified magnetite nanoparticles prior to flame atomic absorption spectrometry, Arab. J. Chem, in press, http://dx.doi.org/10.1016/j.arabjc.2013.05.018 [20] M.K. Amini, T. Momeni-Isfahani, J.H. Khorasani, M. Pourhossein, Development of an optical chemical sensor based on 2-(5-bromo-2-pyridylazo)-5(diethylamino)phenol in nafion for determination of nickel ion, Talanta 63 (2004) 713–720. [21] V.K. Gupta, A.K. Singh, M.K. Pal, Ni(II) selective sensors based on Schiff bases membranes in poly(vinyl chloride), Anal. Chim. Acta 624 (2008) 223–231. [22] V.T. Kasumov, S. Ozalp-Yaman, E. Tas, Synthesis, spectroscopy and electrochemical behaviors of nickel(II) complexes with tetradentate Schiff bases derived from 3,5-But 2 -salicylaldehyde, Spectrochim. Acta Part A 62 (2005) 716–720. [23] V.K. Gupta, R.N. Goyal, S. Agarwal, P. Kumar, N. Bachheti, Nickel(II)-selective sensor based on dibenzo-18-crown-6 in PVC matrix, Talanta 71 (2007) 795–800.
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Biographies Diecenia Peralta-Dominguez had her M.Sc. in 2009 from Centro de Investigaciones en Optica (CIO), Leon, Mexico. Currently she is pursuing a Ph.D. in CIO. Her research interests are on the design and applications of organic molecules for colorimetric chemosensors. Mario Rodríguez had his Ph.D. from Centro de Investigaciones y de Estudios Avanzados (CINVESTAV) in 2007. Since 2010, he was appointed as an Engineer at Centro de Investigaciones en Óptica (CIO). His current research areas comprise design and synthesis of organic materials with linear and nonlinear optical properties for colorimetric sensor, TPA-biomarkers and organic photovoltaic devices (OPVs). Gabriel Ramos-Ortiz had his B.Sc. degree in physics from the Universidad Nacional Autónoma de México in 1996 and a Ph.D. degree from the University of Arizona, USA, in 2003. In 2004, he became a permanent full time researcher at the Photonics Department of the Optical Research Center (CIO), Leon, Mexico. His researches mostly focus on organic electronics and non-linear optics, including biophotonics, sensors, solar cells, spectroscopy and ultrafast optics. José-Luis Maldonado completed his Ph.D. in physics at UNAM by 1999 and is a Permanent Full Time Researcher at Centro de Investigaciones en Optica (Optical Research Center) now. During 2001–2002, he was a postdoctoral at the Optical Sciences Center, University of Arizona. Current research areas are on Plastic opto-electronics, Linear and nonlinear optical properties of organic and inorganic materials for photonic devices, Solar cells (OPVs) and OLEDs, within the Group of Optical Properties of Materials GPOM of the Photonics Division, CIO. Marco A. Meneses-Nava obtained his Ph.D. from Manchester University, England, in 1994, and then he soon joined the Photonics Group at the National Institute of Astrophysics, Optics and Electronics, at Puebla, Mexico. In 1998, he joined the Group of Optical Properties of Materials at the Optical Research Center in Guanajuato, Mexico. His actual research interests dwell on the fabrication and characterization of doped material with rare earth ions and their applications to photonics, and the use of optical spectroscopy, such as Raman and laser induced breakdown, for the characterization of materials in archeology and industry. Oracio Barbosa-Garcia is the founder (1998) and leader of the research group “Group of Optical Properties of Materials” at the Optical Research Center, Leon, Mexico. He has been involved with energy transfer processes in solids, spectroscopy applied in food and pharmaceutics. Recently, he is working in the field of organic electronics, e.g., photovoltaic solar cells.
D. Peralta-Domínguez et al. / Sensors and Actuators B 207 (2015) 511–517 Rosa Santillan had her M.Sc. and Ph.D. in organic chemistry in 1982 and 1986, respectively, at the Center of Research and Advanced Studies of the National Polytechnic Institute of Mexico. She is currently a professor in the Department of Chemistry in this institution. Her research interests include the synthesis and NMR characterization of steroids appended-molecular rotors in the solid state, X-ray diffraction and multifunctional optical properties of organic molecules.
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Norberto Farfán completed his Ph.D. in organic chemistry in 1986 from CINVESTAVIPN where he was a full professor until 2005 and he is currently a professor in the Department of Chemistry of the National University of México (UNAM). His research interests include the design, synthesis and evaluation of boron compounds with Non-linear Optical properties, the synthesis of macrocyclic boron compounds based on self-assembly, and molecular rotors synthesis and structure determination by NMR and X-ray diffraction.