Two highly sensitive and efficient salamo-like copper(II) complex probes for recognition of CN−

Journal Pre-proof Two highly sensitive and efficient salamo-like copper(II) complex probes for recognition of CN−

Zhi-Li Wei, Lan Wang, Ji-Fa Wang, Wen-Ting Guo, Yang Zhang, Wen-Kui Dong PII:

S1386-1425(19)31165-5

DOI:

https://doi.org/10.1016/j.saa.2019.117775

Reference:

SAA 117775

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received date:

26 July 2019

Revised date:

11 October 2019

Accepted date:

5 November 2019

Please cite this article as: Z.-L. Wei, L. Wang, J.-F. Wang, et al., Two highly sensitive and efficient salamo-like copper(II) complex probes for recognition of CN−, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy(2019), https://doi.org/10.1016/ j.saa.2019.117775

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.

© 2019 Published by Elsevier.

Journal Pre-proof

Two highly sensitive and efficient salamo-like copper(II) complex probes for recognition of CN−

Zhi-Li Wei, Lan Wang, Ji-Fa Wang, Wen-Ting Guo, Yang Zhang, Wen-Kui Dong* School of Chemical and Biological Engineering, Lanzhou Jiaotong University,

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Lanzhou, Gansu 730070, China

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Abstract: Two salamo-like copper(II) complex probes, L1-Cu2+ and L2-Cu2+, were

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designed and synthesized for sensitive and efficient identification of CN−. UV spectroscopy, high resolution mass spectrometry, RGB analysis and naked eye

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recognition were performed to explore their recognition mechanisms. High resolution mass spectra indicated that the probes L1-Cu2+ and L2-Cu2+ formed complexes with

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CN−. The two probes could recognize CN− by the naked eye and the color of the solution changed from light yellow to red. In terms of application, the contents of CN−

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in the environmental water samples were tested. In addition, the optimal pH ranges

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for probe detection of CN− were investigated by pH value measurement.

Keywords: Salamo-like probe; Recognition mechanism; cyanide; Naked eye recognition; RGB analysis

1. Introduction Anions are widely found in nature and in organisms, and they are of great value in material science, environmental science, and biochemistry [1]. However, excessive anions can cause environmental pollution or human diseases. For examples, fluoride can prevent dental caries, but excessive intake can cause urolithiasis and acute kidney

*Corresponding author. E-mail addresses: [email protected] (W.-K. Dong).

Journal Pre-proof problems [2]; bisulfite can be used as a preservative, but excess bisulfite can damage the skin and respiratory tract [3]; excess phosphate causes ecosystem problems such as red tides [4]. Among many anions, CN− has attracted the attention of researchers because of its practicability and toxicity. On the one hand, it is a kind of indispensable raw material for many industrial processes such as metallurgy, leather industry and electroplating [5]. On the other hand, cyanide is extremely poisonous and its lethal dosage is 0.5-3.5 mg/kg [6]. Cyanide can be ingested through the lungs, skin, food and drinking water. Very low concentrations of CN− can cause death by inhibiting the

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respiratory and central nervous system of mammalian cells [7]. The World Health Organization (WHO) stipulates that the maximum cyanide concent allowed in

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drinking water is 1.9 μM [8]. Therefore, the effective detection of CN− is of great

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significance [9].

However, a large number of fluorescent probes are not only difficult to

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synthesize, but also use a large proportion of organic solvents in the detection. A large amount of organic solvents will cause new environmental pollution, limiting the

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application of fluorescent probes in real life environments [10]. Therefore, based on

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the excellent properties of salen-like [11] and its analogues salamo-like ligands [12] in the chemical and biological fields [13], two salamo-like bisoxime chemosensors,

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L1-Cu2+ and L2-Cu2+, which have highly selective and sensitive to CN− in EtOH/H2O (1:1 v/v) solution were designed and synthesized according to the complex formation mechanism [10] and nucleophilic addition catalyzed by Cu2+ [14]. Among the many anions, both probes can visually recognize CN− in an aqueous solution, and the color changes from bright yellow to red. Compared with previous work and other probes (Table 1), the two probes synthesized in this work have the advantages of easy synthesis, high sensitivity, and convenient detection and real-time monitoring [15].

Table 1 Examples for detection of CN− by salamo-like probes and other probes.

2. Experimental section

Journal Pre-proof 2.1. Materials and Measurements All the reagents and solvents were analytical grade reagents from Tianjin Chemical Reagent Factory and were used without further purification. Elemental analyses were obtained using a GmbH VarioEL V3.00 automatic elemental analysis instrument. Melting points were obtained by use of a microscopic melting point apparatus made in Beijing Taike Instrument Limited Company and were uncorrected. 1

H NMR spectra were determined by German Bruker AVANCE DRX-400

spectrometer. UV-vis absorption spectra were recorded on the Shimadzu UV-2550

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spectrometer and fluorescence spectra were recorded on the Hitachi F-7000 spectrometers. All pH measurements were made with a pH-10C digital pH meter.

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ESI-MS spectra were measured on the Bruker Daltonics Esquire 6000 mass

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spectrometer.

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2.2. The synthesis method of the probes L1-Cu2+ and L2-Cu2+ 2.2.1. The synthesis method of the ligands H2L1 and HL2

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1,2-Bis(aminooxy)ethane was prepared by the method reported earlier [16].

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Yield: 56.8%. Elemental analysis: Anal. Calc. for C2H8N2O2 (%): C, 26.08; H, 8.76; N, 30.42. Found (%): C, 25.97; H, 8.70; N, 30.49.

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The salamo-like bisoxime ligand H2L1 is synthesized firstly according to similar method reported earlier [17], and the synthetic route is shown in Scheme 1. Yield: 67.3%. m.p.: 189-190 ℃. Elemental analysis: Anal. Calc. for C20H24N2O6 (%): C, 61.84; H, 6.23; N, 7.21. Found (%): C, 61.80; H, 6.30; N, 7.19. 1H NMR (400 MHz, CDCl3): δ 1.47 (t, J = 4 Hz, 6H, -CH3), 4.11 (dd, J = 8, 4 Hz, 4H, -CH2), 4.46 (s, 4H, -CH2), 6.82 (m, 3H, -ArH), 6.88 (m, 3H, -ArH), 8.26 (s, 2H, -CH=N), 9.68 (s, 2H, -OH).

Scheme 1. Synthetic route to the ligand H2L1.

2-[O-(1-ethyloxyamide)]oxime-6-methoxyphenol

and

2,3-dimethoxy-1,4-benzenedialdehyde were synthesized according to the previously

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method

[18].

An

ethanol

solution

of

2-[O-(1-ethyloxyamide)]oxime-6-methoxyphenol was slowly added dropwise to a solution of 2,3-dihydroxy-1,4-benzenedialdehyde in ethanol at 55 °C. After heating and stirring for 12 hours, the solvent was concentrated and the obtained crude product was purified by column chromatography (chloroform/ethyl acetate, 35:1) to obtain the ligand HL2. The synthetic route to HL2 is shown in Scheme 2. 1H NMR spectrum of the ligand HL2 was shown in Figure S1. Yield: 64.7%. m.p.: 105-107 ℃. Elemental analysis: Anal. Calc. for C20H22N2O7 (%): C, 59.70; H, 5.51; N, 6.96. Found (%): C,

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59.60; H, 5.54; N, 6.92. 1H NMR (400 MHz, CDCl3): δ 3.90 (s, 6H, -CH3), 4.01 (s, 3H, -CH3), 4.5 (dd, J = 8, 4 Hz, 4H, -CH2), 6.86 (m, 3H, -ArH), 7.54 (d, J = 8 Hz, 1H,

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-ArH), 7.46 (d, J = 8 Hz, 1H, -ArH), 8.25 (s, 1H, -N=CH), 8.46 (s, 1H, -N=CH), 9.78

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(s, 1H, -CHO), 10.38 (s, 1H, -OH).

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Scheme 2. Synthetic route to the ligand HL2.

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2.2.2. The synthesis method of the probes L1-Cu2+ and L2-Cu2+

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The ligand H2L1 and Cu(NO3)2 were weighed in a molar ratio of 1:1 and dissolved in the ethanol solution. The mixture was stirred at room temperature for 12

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hours to form the probe L1-Cu2+. The probe L2-Cu2+ was synthesized by a similar method mentioned above. Then transfer the ethanol solution of the probes to a volumetric flask for constant volume, respectively. High resolution mass spectra of probes L1-Cu2+ and L2-Cu2+ are displayed in the Figure S2 and Figure S3, respectively.

2.3. Preparation of Stock solution 15 Anion stock solutions including F−, Br−, I−, Cl−, H2PO4−, CN−, CH3COO−, HS−, S2−, NO3−, CO32−, HCO3−, HPO4−, P2O74- and NO2− were prepared in double distilled water at a concentration of 1 × 10-3 M, while the stock solution of the probes L1-Cu2+ and L2-Cu2+ was prepared in ethanol solution at a concentration of 1 × 10-4 M, respectively. The identification of CN− by the two probes in EtOH/H2O (1:1 v/v)

Journal Pre-proof solution was shown in the UV-vis spectra. Therefore, the concentration of the probes’ solution during the experiment was 5 × 10-5 M, and the concentration of various anion solutions was ten times than that of the probe solution.

3. Results and discussion 3.1. Absorption spectra of the probe L1-Cu2+ to various anions In the ultraviolet-visible absorption spectrum, the probe L1-Cu2+ showed two

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absorption bands at 280 and 371 nm, while the probe L2-Cu2+ showed an absorption

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band at 282 nm and a shoulder peak at 375 nm. The absorption of the probe L1-Cu2+ at 371 nm and the shoulder peak of the probe L2-Cu2+ at 375 nm can attributed to the

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ligand-to-metal d-d charge transitions after the ligands are coordinated with the Cu2+

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ions [19]. As shown in Figure 1 and Figure 2, 15 anions (F−, Br−, I−, Cl−, H2PO4−, CN−, CH3COO−, HS−, S2−, NO3−, CO32−, HCO3−, HPO4−, P2O74- and NO2−) were added to

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ethanol solution of the probe to detect their absorption spectra. Only by adding CN−, the probe L1-Cu2+ showed a strong absorption peak at 498 nm, while the probe

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L2-Cu2+ showed at 500 nm, and the intensity enhanced more than 8-fold and 20-fold,

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respectively. The experimental results revealed that both probes can detect CN−

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efficiently and sensitively in aqueous solution.

Figure 1. Absorption spectra of L1-Cu2+ solution (5 × 10-5 M) in the absence and presence of various anions (F−, Br−, I−, Cl−, H2PO4−, CN−, CH3COO−, HS−, S2−, NO3−, CO32−, HCO3−, HPO4−, P2O74- and NO2−).

Figure 2. Absorption spectra of L2-Cu2+ solution (5 × 10-5 M) in the absence and presence of various anions.

In order to explore the specific identification of the two probes for CN−, the competition experiment was performed to detect the function of the two probes in the presence of various anions. As displayed in Figure 3 and Figure 4, measuring the

Journal Pre-proof absorbance values of the probe L1-Cu2+ at 498 nm and the probe L2-Cu2+ at 500 nm in the presence and absence of CN− to make the histogram graphs. In the process of the probe L1-Cu2+ recognizing CN−, even if other anions were present, the absorbance at 498 nm almost unchanged, and the absorbance value did not change obviously, indicating that other anions could not interfere with the recognition of CN−. The probe L2-Cu2+ had the same result as the probe L1-Cu2+, which proved that the probe L2-Cu2+ has good anti-interference performance. In summary, both probes L1-Cu2+ and L2-Cu2+ have high selectivities and sensitivities to CN− in the presence of other

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anions.

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Figure 3. Absorbance values of L1-Cu2+ solution (5 × 10-5 M) at 498 nm in the presence of various anions (F−, Br−, I−, Cl−, H2PO4−, CN−, CH3COO−, HS−, S2−, NO3−,

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CO32−, HCO3−, HPO4−, P2O74- and NO2−). The black bars represent the absorbance

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values of the probe L1-Cu2+ solution on addition of different anions; the red bars represent the absorbance values of the probe L1-Cu2+ solution on addition of different

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anions and CN−.

Figure 4. Absorbance values of L2-Cu2+ solution (5 × 10-5 M) at 498 nm in the

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presence of various anions. The black bars represent the absorbance values of the probe L2-Cu2+ solution on addition of different anions; the red bars represent the absorbance values of the probe L2-Cu2+ solution on addition of different anions and CN−.

During the experiment, it was found that the color of the two probes’ solution changed significantly upon adding CN− gradually. Therefore, the ultraviolet titration experiment was conducted to further study the recognition mechanism for CN−. As revealed in Figure 5 and Figure 6, the color of both probe solutions changed from yellow to red after the gradual addition of CN−. After adding 1 equivalent of CN−, the peak of the probe L1-Cu2+ disappeared at 371 nm, and a new absorption peak emerged at 498 nm. Correspondingly, after 4 equivalent of CN− was added, the

Journal Pre-proof shoulder peak of the probe L2-Cu2+ gradually decreased at 375 nm, and a new peak appeared at 500 nm. Furthermore, the titration data were calculated and linear fitted. The experimental phenomena and data were summarized in Figure 7 and Figure 8. Based on the corrected Benesi-Hildebrand equation, the binding constant [20] of the probe L1-Cu2+ to CN− is 1.74 × 108 M-1, and the binding constant of the probe L2-Cu2+ to CN− is 5.22 × 108 M-1. At the same time, the lower limit of detection (LOD) [21] and the limit of quantity (LOQ) [22] of sensor L1-Cu2+ toward CN− were calculated to be 4.56 × 10−7 M and 1.52 × 10−6 M,

while the values of sensor

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L2-Cu2+ toward CN− were LOD = 2.40 × 10−7 M and LOQ = 8 × 10−7 M, respectively.

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Figure 5. Changes in absorption spectra of the probe L1-Cu2+ solution (5 × 10-5 M) upon the addition of CN− (0-1.0 equiv). Inset: Naked-eyes observable color changes

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of the probe L1-Cu2+ solution before and after addition of CN− (1 equiv.).

Figure 6. Changes in absorption spectra of the probe L2-Cu2+ solution (5 × 10-5 M)

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upon the addition of CN− (0-4.0 equiv.). Inset: Naked-eyes observable color changes

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of the probe L2-Cu2+ solution before and after addition of CN− (4 equiv.).

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Figure 7. (a) Linear fitting of the probe L1-Cu2+ to CN− binding constant; (b) Linear fitting of the probe L2-Cu2+ to CN− binding constant. Figure 8. (a) Benesi-Hildebrand plots of the probe L1-Cu2+ adding different concentrations of CN−; (b) Benesi-Hildebrand plots of the probe L2-Cu2+ adding different concentrations of CN−.

3.2. Effect of pH on the recognition of CN− It is very important that the probe can identify specific ion in different pH environments, so the effect of different pH values on the recognition of CN− by the two probes was investigated. The intensity of the absorption peak of probe L1-Cu2+ at 498 nm and the absorption peak of probe L2-Cu2+ at 500 nm were plotted at different

Journal Pre-proof pH values, respectively, and the experimental data are summarized in Figure 9 and Figure 10. Both probes can recognize CN− in a wide pH range, but the absorption intensity is very weak in a highly acidic and alkali environment, indicating that the probe does not interact with CN− at this time. A suitable pH range for the reaction of probe L1-Cu2+ with CN− is 3-13, while that for probe L2-Cu2+ is 3-11. The experimental results showed that probes L1-Cu2+ and L2-Cu2+ are less affected by pH values and exhibited satisfactory recognition results in the physiological pH range.

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Figure 9. Absorbance spectra at 498 nm of probe L1-Cu2+ (5 × 10-5 M) in the absence

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and presence of CN− at various pH values.

Figure 10. Absorbance spectra at 500 nm of probe L2-Cu2+ (5 × 10-5 M) in the

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absence and presence of CN− at various pH values.

3.4. Detection of CN− in water samples

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In order to evaluate the practicability of the two probes, the concentrations of

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CN− in treated river water, rain water, soil leachate and industrial wastewater were examined. The absorption spectra of the four water samples are shown in Figure 11,

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and the test results are displayed in Table 1 and Table 2. Water samples were measured with three replicates. In addition, the recoveries and Relative Standard Deviation (R.S.D.) [23] values were calculated. The results showed that both probes could be used to detect CN− in environmental samples [24].

Figure 11. (a) Absorption spectra of the probe L1-Cu2+ to CN− in different water samples; (b) Absorption spectra of the probe L2-Cu2+ to CN− in different water samples.

Table 2 Probe L1-Cu2+ detects CN− in different water samples.

Table 3 Probe L2-Cu2+ detects CN− in different water samples.

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3.5. Naked eye observation and RGB analysis After the addition of CN−, the color of the two probes’ solution immediately changed from light yellow to red (Figure 12), while the color of the solution did not change when other anions were added. Both probes can recognize CN− with the naked eye because of the obvious color changes. As can be seen from Figure 13, when adding the same volume of CN−, the color of the solution gradually deepens as the CN− concentration increases. Combined with smartphones’ image processing

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capability, a cost-effective and portable analysis device has been developed. The smartphones’ built-in camera can detect the changes of the RGB color intensity, which

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can achieve quantitatively detection for CN− without the complicated instruments. We

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downloaded the “Colour Assist App” on the Apple iPad Pro 11, and used the rear camera to take pictures about 1 cm away from the sample vial to avoid the effects of

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external light fluctuations. The experimental data were processed according to the method in the literatures [25] and a fitting curve of the R/G values with respect to the

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CN− concentration changes as shown in Figure 14 were plotted by calculation. The

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obtained curve shown a good linear curve between 10 uL and 350 uL, and the linear correlation coefficient R were 0.996 and 0.990, respectively. This method enabled

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real-time monitoring and made it possible to quickly and easily apply probes to actual production and life.

Figure 12. (a) From left to right shows photograph images of probe L1-Cu2+ upon addition of various anions; (b) Photographs of the probe L2-Cu2+ upon addition of various anions.

Figure 13. (a) Detection of different concentrations of CN− by probe L1-Cu2+ (5 × 10-5 M) under natural light; (b) Detection of different concentrations of CN− by probe L2-Cu2+ (5 × 10-5 M) under natural light.

Figure 14. Smartphone-based colorimeter for determining CN− concentrations ((a)

Journal Pre-proof probe L1-Cu2+; (b) probe L2-Cu2+.).

3.6. Recognition mechanism It can be seen from Figure 15 that when the concentration of CN− added is the same and the volume is different, as the moles of CN− increased, the color of the solution gradually deepens and a precipitate formed in the two probes’ solution. Combining the mass spectra and the reference literatures [26], we speculated that the reaction phenomena of identifying CN− were the same, the recognition mechanisms

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were different. In the mass spectrum of L1-Cu2+ (Figure S2), a strong peak appeared at m/z = 450.1166, indicating that a complex with a coordination ratio of 1:1 was

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formed between the ligand H2L1 and Cu2+. Cu2+ coordinates with the N2O2-donor atoms of the ligand (L1)2- unit to form a tetracoordinated copper(II) complex [27]. As

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shown in Figure 16, when CN− was gradually added to the probe solution, a 1:1

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complex was formed between the probe L1-Cu2+ and CN−. A strong peak appeared at m/z = 472.1118 in Figure S3, confirming the mechanism that CN− forms an adduct

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[28] with the probe L1-Cu2+. CN− was coordinated with Cu2+ of the probe L1-Cu2+,

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leading to a formation of a five-coordinated copper(II) complex with one unit of positive charge and the precipitate was formed. Different from the above mentioned

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mechanism, CN− instead of coordinated with probe L2-Cu2+, but break the four coordination bonds (N2O2) of the copper(II) complex, binding with Cu2+ and releasing the ligand HL2. Then, as displayed in Figure 17, Figure S4 and Figure S5, under the catalysis of Cu2+, a nucleophilic addition reaction occurred between the ligand HL2 and CN−, and a strong peak appeared at m/z = 444.0835 that confirmed our viewpoints. Both reactions changed the photophysical properties of the copper(II) complexes and realized the recognition of CN−. But, the experimental results of alternating addition of Cu2+ and CN− indicated that the products of CN− reaction with both probes were more stable, so both of processes of recognizing CN− by the two probes were irreversible.

Journal Pre-proof Figure 15. (a) Detection of different moles of CN− by probe L1-Cu2+ (5 × 10-5 M) under natural light; (b) Detection of different moles of CN− by probe L2-Cu2+ (5 × 10-5 M) under natural light.

Figure 16. Recognition mechanism of CN− by the probe L1-Cu2+.

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Figure 17. Recognition mechanism of CN− by the probe L2-Cu2+.

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4. Conclusions

In summary, we designed and synthesized two salamo-like copper(II) complex

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probes, L1-Cu2+ and L2-Cu2+, which are easy to synthesize and environmentally

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friendly. They have highly selective and sensitive to CN− in aqueous solutions without causing new environmental pollution. The recognition mechanisms of the two

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probes are formation of adduct and nucleophilic addition reaction, respectively, and both of the two probes can specifically recognize CN− without interference from other

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anions. The probes can realize colorimetric recognition to CN− in water, and can be

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detected by RGB analysis by smartphones without complicated instruments. It has the advantages of easy detection and real-time measurement. In addition, the two probes

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have wide ambient adaptability and high application values, and they can be used for the detection of environmental water samples.

Acknowledgements This work was supported by the National Natural Science Foundation of China (21761018) ), Science and Technology Program of Gansu Province (18YF1GA054) and the Program for Excellent Team of Scientific Research in Lanzhou Jiaotong University (201706), three of which are gratefully acknowledged.

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(b) L. Gao, C. Liu, F. Wang, W.K. Dong, Crystals 8 (2018) 77. (c) L. Chen, W.K. Dong, H. Zhang, Y. Zhang, Y.X. Sun, Cryst. Growth Des. 17 (2017) 3636-3648.

(d) Z.L. Ren, J. Hao, P. Hao, X.Y. Dong, Y. Bai, W.K. Dong, Z. Naturforsch. B 73 (2018) 203-210. (e) X.Y. Dong, Q. Zhao, Q.P. Kang, H.R. Mu, H. Zhang, W.K. Dong, Crystals 8 (2018) 230; (f) Y.D. Peng, X.Y. Li, Q.P. Kang, G.X. An, Y. Zhang, W.K. Dong, Crystals 8 (2018) 1079; (g) Y.D. Peng, F. Wang, L. Gao, W.K. Dong, J. Chin. Chem. Soc. 65 (2018) 893-899; (e) F. Wang, L.Z. Liu, L. Gao, W.K. Dong, Spectrochim. Acta A 203 (2018) 56-64; (g) X.Y. Li, Q.P. Kang, L.Z. Liu, Crystals 8 (2018) 43; (h) H. Miyasaka, N. Matsumoto, H. Okawa, N. Re, E. Gallo, C. Floriani, J. Am. Chem. Soc.

Journal Pre-proof 118 (1996) 981-994; (i) S.S. Sun, C.L. Stern, S.T. Nguyen, J.T. Hupp, J. Am. Chem. Soc. 126 (2004) 6314-6326. [14] (a) L. Tang, P. Zhou, K. Zhong, Sens. Actuators B 182 (2013) 439-445. (b) J.H. Lee, A.R. Jeong, I.S. Shin, Org. Lett. 12 (2010) 764-767. (c) Y.H. Kim, J.I. Hong, Chem. Commun. 5 (2002) 512-513. [15] (a) B.J. Wang, W.K. Dong, Y. Zhang, S.F. Akogun, Sens. Actuators B 247 (2017) 254-264; (b) W.K. Dong, X.L. Li, L. Wang, Y. Zhang, Y. Ding, Sens. Actuators B 229 (2016) 370-378; (c) W.K. Dong, S.F. Akogun, Y. Zhang, Y.X. Sun, X.Y. Dong, Sens. Actuators B 238 (2017)

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723-734;

(d) F. Wang, L. Gao, Q. Zhao, Y. Zhang , W.K. Dong, Y.J. Ding, Spectrochim. Acta A 190

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(2018) 111-115;

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(e) S.T. Wang, Y.W. Sie, C.F. Wan, J. Lumin. 173 (2016) 25-29. (f) S. Park, H.J. Kim, Sens. Actuators B 161 (2012) 317-321.

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[16] (a) W.K. Dong, J.C. Ma, L.C. Zhu, Y. Zhang, X.L. Li, Inorg. Chim. Acta. 445 (2016) 140-148;

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(b) J. Hao, X.Y. Li, Y. Zhang, W.K. Dong, Materials 11 (2018) 523.

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(c) W.K. Dong, J.C. Ma, L.C. Zhu, Y. Zhang, New J. Chem. 40 (2016) 6998-7010. [17] S.S. Zheng, W.K. Dong, Y. Zhang, L. Chen, Y.J. Ding, New J. Chem. 41 (2017) 4966.

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[18] Y. Zhang, L.Z. Liu, Y.Q. Pan W.K. Dong, Crystals 8 (2018) 259. [19] (a) Q. Zhao, X.X. An, L.Z. Liu, W.K. Dong, Inorg. Chim. Acta 490 (2019) 6-15. (b) X.Y. Li, Q.P. Kang, C. Liu, Y. Zhang, W.K. Dong, New J. Chem. 43 (2019) 4605-4619; (c) X.X. An, Q. Zhao, H.R. Mu, W.K. Dong, Crystals 9 (2019) 101; (d) Q.P. Kang, X.Y. Li, L. Wang, Y. Zhang, W.K. Dong, Appl. Organomet. Chem. (2019) e5013; [20] (a) Y.J. Dong, X.L. Li, Y. Zhang, W.K. Dong, Supramol. Chem. 29 (2017) 518-527; (b) H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703-2707; [21] J.X. Huang, T.T. Li, R.N. Liu, R. Zhang, Q.Q. Wang, N. Li, Y.Q. Gu, P. Wang, Sens. Actuators B 248 (2017) 257-264 [22] Z. P. Liu, C.L. Zhang, W.J. He, Z.H. Yang, X. Gao, Z.J. Guo, Chem. Commun. 46 (2010) 6138-6140.

Journal Pre-proof [23] L.Z. Liu, L. Wang, M. Yu, Q. Zhao, Y. Zhang, Y.X. Sun, W.K. Dong, Spectrochim. Acta A 222 (2019) 117209. [24] (a) K. Ponnuvel, G. Banuppriya, V. Padmini, Sens. Actuators B 234 (2016) 34-45. (b) X. Sun, Y. Liu, G. Shaw, A. Carrier, S. Dey, J. Zhao, Y. Lei, ACS Appl. Mater. Interfaces 7 (2015) 13189-13197. [25] (a) Y. Upadhyaya, T. Ananda, L.T. Babub, P. Pairab, A.K. SKc, R. Kumara, S.K. Sahoo, J. Photochem. Photobio. A 361 (2018) 34-40. (b) Y. Upadhyay, S. Bothra, R. Kumar, S.K. Sahoo, Chem. Select. 3 (2018) 6892-6896.

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(c) T. Anand, S.K. Sahoo, Phys. Chem. Chem. Phys. 21 (2019) 11839-11845. [26] (a) S. Park, H.J. Kim, Chem. Commun. 46 (2010) 9197-9199.

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(b) K.S. Lee, H.J. Kim, G.H. Kim, Org. Lett. 10 (2008) 49-51.

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(c) D.G. Cho, J.H. Kim, J.L. Sessler, J. Ame. Chem. Soc. 130 (2008) 12163-12167. (d) N. Khairnar, K. Tayade, S. Bothra, S.K. Sahoo, J. Singh, N. Singh, R.Bendre, A. Kuwar,

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RSC Adv. 4 (2014) 41802.

(e) V. Venkatesana, S.K. Ashok Kumara, S.K. Sahoo, J. Name. 00 (2013) 1-3.

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(f) Y.X. Hua, Y.L. Shao, Y.W. Wang, Y. Peng, J. Org. Chem. 82 (2017) 6259-6267.

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[27] (a) A. Shigehisa, T. Takanori, T. Nabeshima, Chem. Lett. (2001) 682-683.

305-315.

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(b) Y.J. Dong, X. Y. Dong, W.K. Dong, Y. Zhang, L.S. Zhang, Polyhedron 123 (2017)

[28] (a) B. Ahlers, K. Cammann, Angew. Chem. 35 (1996) 2141-2143. (b) Y.D. Lin, Y.S. Peng, Tetrahedron 68 (2015) 2523-2526.

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Table 1 Examples for detection of CN− by salamo-like probes and other probes. Naked eye recognition

RGB analysis

Reference

1

MeOH/H2O (1:1 v/v)

Yes

No

[13(e)]

2

DMF/H2O (6:4 v/v)

No

[22]

3

THF/H2O (6:4, v/v)

Yes

Yes

[15(k)]

Yes

No

[15(j)]

DMF

Yes

No

[15(l)]

EtOH/H2O (1:1 v/v)

Yes

Yes

This work

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MeOH/H2O (8:2 v/v)

5

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probe

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solvent

No.

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Table 2 Probe L1-Cu2+ detects CN− in different water samples. Sample River water

CN− found

Recovery

R.S.D.

(µM)

(µM)

(%)

(n = 3) (%)

0.00

0.00

43.06

44.85

0.00

0.00

43.06

66.65

0.00

0.00

43.06

84.5

0.00

0.00

0.00 104.2

1.2 0.0

102.0

2.9

90.45

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43.06

94.2

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Organic wastewater

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Soil extract

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Rainwater

CN− added

0.00 4.9 0.00

94.5

4.6

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Table 3 Probe L2-Cu2+ detects CN− in different water samples. Sample River water

CN− found

Recovery

R.S.D.

(µM)

(µM)

(%)

(n = 3) (%)

0.00

0.00

33.8

51.7

0.00

0.00

33.8

61.83

0.00

0.00

33.8

72.3

0.00

0.00

33.8

74.4

0.0 103.0

2.3 0.00

100.5

1.3

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Organic wastewater

102.9

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Soil extract

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Rainwater

CN− added

98.7

0.00 1.6 0.00 1.7

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Scheme 1. Synthetic route to the ligand H2L1.

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Scheme 2. Synthetic route to the ligand HL2.

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Figure 1. Absorption spectra of L1-Cu2+ solution (5 × 10-5 M) in the absence and

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presence of various anions (F−, Br−, I−, Cl−, H2PO4−, CN−, CH3COO−, HS−, S2−, NO3−,

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CO32−, HCO3−, HPO4−, P2O74- and NO2−).

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Figure 2. Absorption spectra of L2-Cu2+ solution (5 × 10-5 M) in the absence and

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presence of various anions.

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Figure 3. Absorbance values of L1-Cu2+ solution (5 × 10-5 M) at 498 nm in the presence of various anions (F−, Br−, I−, Cl−, H2PO4−, CN−, CH3COO−, HS−, S2−, NO3−, CO32−, HCO3−, HPO4−, P2O74- and NO2−). The black bars represent the absorbance

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values of the probe L1-Cu2+ solution on addition of different anions; the red bars

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anions and CN−.

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represent the absorbance values of the probe L1-Cu2+ solution on addition of different

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Figure 4. Absorbance values of L2-Cu2+ solution (5 × 10-5 M) at 498 nm in the presence of various anions. The black bars represent the absorbance values of the probe L2-Cu2+ solution on addition of different anions; the red bars represent the

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CN−.

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absorbance values of the probe L2-Cu2+ solution on addition of different anions and

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Figure 5. Changes in absorption spectra of the probe L1-Cu2+ solution (5 × 10-5 M)

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upon the addition of CN− (0-1.0 equiv). Inset: Naked-eyes observable color changes

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of the probe L1-Cu2+ solution before and after addition of CN− (1 equiv.).

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Figure 6. Changes in absorption spectra of the probe L2-Cu2+ solution (5×10-5 M)

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upon the additions of CN− (0-4.0 equiv.). Inset: Naked-eyes observable color changes

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of the probe L2-Cu2+ solution before and after addition of CN− (4 equiv.).

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Figure 7. (a) Linear fitting of the probe L1-Cu2+ to CN− binding constant; (b) Linear fitting of the probe L2-Cu2+ to CN− binding constant.

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Figure 8. (a) Benesi-Hildebrand plots of the probe L1-Cu2+ adding different concentrations of CN−; (b) Benesi-Hildebrand plots of the probe L2-Cu2+ adding different concentrations of CN−.

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Figure 9. Absorbance spectra at 498 nm of probe L1-Cu2+ (5 × 10-5 M) in the absence

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and presence of CN− at various pH values.

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Figure 10. Absorbance spectra at 500 nm of probe L2-Cu2+ (5 × 10-5 M) in the

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absence and presence of CN− at various pH values.

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Figure 11. (a) Absorption spectra of the probe L1-Cu2+ (5 × 10-5 M) to CN− in different water samples; (b) Absorption spectra of the probe L2-Cu2+ (5 × 10-5 M) to CN− in different water samples.

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Figure 12. (a) From left to right shows photograph images of probe L1-Cu2+ (5 × 10-5 M) upon addition of various anions; (b) Photographs of the probe L2-Cu2+ (5 × 10-5 M)

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upon addition of various anions.

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Figure 13. (a) Detection of different concentrations of CN− by probe L1-Cu2+ (5 × 10-5 M) under natural light; (b) Detection of different concentrations of CN− by probe

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L2-Cu2+ (5 × 10-5 M) under natural light.

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Figure 14. Smartphone-based colorimeter for determining CN− concentrations ((a) probe L1-Cu2+; (b) probe L2-Cu2+.).

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Figure 15. (a) Detection of different moles of CN− by probe L1-Cu2+ (5 × 10-5 M) under natural light; (b) Detection of different moles of CN− by probe L2-Cu2+ (5 × 10-5 M) under natural light.

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Figure 16. Recognition mechanism of CN− by the probe L1-Cu2+.

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Figure 17. Recognition mechanism of CN− by the probe L2-Cu2+.

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Conflicts of Interest: The authors declare no competing financial interests.

Journal Pre-proof Graphical abstract Two salamo-like copper(II) complex chemical probes, L1-Cu2+ and L2-Cu2+, were designed and synthesized, which can specifically identify CN− in the visible region. Both probes can achieve naked eye recognition for CN− and can be applied to

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the detection of water samples in the environment.

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Highlights:

Two salamo-like copper(II) complex probes, L1-Cu2+ and L2-Cu2+, which can identify CN− by naked eye were designed and synthesized.

Among many anions, both probes can specifically recognize CN− in the visible

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region.

The recognition mechanism is that the probe can form new complex with CN− at a

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ratio of 1:1 and 1:4.

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RGB analysis is tested for real-time monitoring of CN−.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

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Figure 14

Figure 15

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Figure 17