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A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives
Accepted Manuscript A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives Reza Azadbakht, Hojat Vaisi, Hossain Mohamadvand, Javad Khanabadi PII: DOI: Reference:
S1386-1425(15)00314-5 http://dx.doi.org/10.1016/j.saa.2015.03.018 SAA 13432
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
26 October 2014 10 February 2015 1 March 2015
Please cite this article as: R. Azadbakht, H. Vaisi, H. Mohamadvand, J. Khanabadi, A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives Reza Azadbakht*, Hojat Vaisi, Hossain Mohamadvand, Javad Khanabadi Department of chemistry, Payame Noor Universtiy, P.O. Box 19395-3697, Iran
Abstract A new naphthalene derivative receptor (L) was synthesized and characterized with common spectroscopic methods. L exhibited a strong fluorescence enhancement in the presence of trace amounts of Pb2+, attributable to photoinduced electron transfer (PET) effect, which also displayed high selectivity over a series of other metal cations (Na+, K+, Cs+, Mg2+, Ba2+, Cr3+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+ ) in acetonitrile/H2O (9:1, v/v) mixture. Keywords: Fluorescence, Chemosensor, Pb2+ ion, Naphthalene.
1. Introduction Heavy metal pollution is a serious environmental problem of global concern. Among these toxic metal ions, Pb2+ is one of the oldest known and most widely studied toxins [1]. Lead widely exists in various forms including elemental, inorganic and organic compounds. Lead compounds are used in construction materials for tank linings, piping, equipment for handling corrosive gases and liquids used in petroleum refining, halogenation, sulfonation, extraction, condensation, metallurgy, and for pigments for paints. It is also used in ceramics, plastics, electronic devices, as a component of lead batteries, and in the production of ammunition, solder, cable covering, and sheet lead. Moreover, lead also remains in trace amount in soil, water and food [2]. In babies and children, exposure to lead in drinking water above the action level can result in delays in physical and mental development, along with *Corresponding author. Tel.: +98 8125221144; fax: +98 8112546840. E-mail address: [email protected] (R. Azadbakht).
1
slight deficits in attention span and learning abilities. In adults, lead can increase blood pressure and cause fertility problems, nerve disorders, muscle and joint pain, irritability, and memory or concentration problems [3-8]. Thus, the concentration of lead in environment should be kept under permanent control. Although some atomic absorption spectroscopy techniques such as ICP-MS and ICP-AES can complete the quantitative analysis of the total amount of Pb2+ ion in the system [9–11], some inherent limitations such as complicated program, high initial cost, costly maintenance and consumables make the usage of these techniques became uneasily accessible. Thus, it is urgent to develop a convenient, sensitive and inexpensive method to detect trace level of Pb2+ ion. In recent years, fluorescence chemosensors have rapidly developed because of their miniature constitution, low cost manufacture, reusability, high selectivity and real-time measurement. Herein, we report the synthesis and properties of a highly turn-on lead fluorescent sensor (L) that binds Pb2+ with high affinity and displays selectivity against other physiological metals in aqueous media. In the presence of Pb2+, L exhibits significant fluorescence enhancements owing to PET (photoinduced electron transfer).
2. Experimental 2.1. Materials and instruments All solvents were of reagent grade quality and purchased commercially. 2-aminophenol was obtained
from
Merck
and
was
used
without
further
purification.
2-[2-(2-
formylnaphthoxy)ethoxy]naphthaldehyde was synthesized according to the literature method [12]. NMR spectra were obtained using a Bruker A V300 MHz spectrometer. Infrared spectra were recorded in KBr pellets using a BIO-RAD FTS-40A spectrophotometer (4000–400 cm1
). Positive ion FAB mass spectra were recorded on a Kratos-MS-50 spectrometer with 3-
nitrobenzyl alcohol as the matrix solvent. Uv–Vis absorption spectra were obtained on a
2
Varian Cary Eclipse 300 spectrophotometer. The fluorescence spectra were recorded on a Varian spectrofluorometer. Both excitation and emission bands were set at 5 nm.
2.2. Synthesis of L A solution of 2-aminoethanol (0.12 g, 2 mmol) in absolute methanol (25 mL) was added dropwise to a hot solution of 2-[2-(2-formylnaphthoxy)ethoxy]naphthaldehyde (0.374, 1 mmol) in absolute methanol (50 mL). The solution was gently refluxed for 6 h. The solution was then allowed to cool to room temperature after which sodium borohydride (1 g, 26 mmol) was added in small portions to the stirred solution over 10 min. Excess water was added to the solution and the pH was adjusted to 12 with potassium hydroxide. The solution was extracted with chloroform (×3). The chloroform extracts were combined and dried over anhydrous sodium sulfate. The dried extracts were then reduced to a small volume on a rotary evaporator. A precipitate was obtained by standing overnight at 0 ºC. Yield (75%). Anal. Calc. for C28H32N2O4: C, 73.02; H, 7.00; N, 6.08. Found: C, 72.98; H, 7.13; N, 6.14 %. IR (KBr,cm-1) 3303 and 1623(NH starching and bending), 3387 (OH); 1HNMR δH (CDCl3, ppm) 2.64 (t, 4H), 3.59 (t, 4H), 4.36 (s, 4H), 4.59 (s, 4H), 7.38 (m, 4H), 7.54 (m, 2H), 7.84 (m, 4H), 8.04 (d, 2H); 13C NMR δC (CDCl3, ppm) 42.82, 50.83, 60.65, 67.78, 113.43, 121.23, 122.87, 123.75, 123.94, 124.10, 127.04, 128.68, 129.17,129.41, 133.39, 154.10. The mass spectrum show peak at m/z = 460 corresponding to L (S. 1).
2. 3. Theoretical calculations
The complex of [PbL]2+ gave fine powders and we were not able to prepare single crystals for structure determination by X-ray spectroscopy. Instead, The geometry of [PbL]2+ was fully optimized at DFT [13,14] levels of theory using the GAUSSIAN 03 program [15]. A starting semiempirical structure was optimized using the HYPERCHEM 5.02 series of programs [16].
3
3. Results and discussion 3.1. Synthesis and characterization of L Synthesis of L can be achieved very easily in 75% yield by schiff base condensation of 2-[2(2-formylnaphthoxy)ethoxy]naphthaldehyde [12] with 2-aminoethanol in methanol, followed by reduction with NaBH4 (S. 2). L was characterized by microanalysis, mass spectrometry, IR, and NMR studies. L was soluble in polar solvents, such as chloroform and methanol and was hydrolytically stable under both basic and acidic conditions. The reduction of the imine groups was indicated in the IR spectrum, by the appearance of weak bands related to N-H in the region of 3303 cm-1, while no bands attributable to C=N were detected. Two absorption bands in the 2919 cm-1 and 2928 are attributed to the asymmetric and symmetric stretching vibration of aliphatic C-H bonds CH2 groups. The stretching vibration of C-H aromatic was absorbed at 3086 cm-1. The 1H NMR spectrum of the L shows a triplet signal at 2.64 ppm, which can be assigned to Hb (4H), a triplet signal at ca. 3.59 ppm attributed to Ha (4H), a singlet signal due to the Hc (4H) resonance at ca. 4.34 ppm, a singlet signal at ca. 4.59 ppm attributed to Hd (4H). In the aromatic region (7.38-8.04 ppm) four signals were found, a multiplet signal at ca. 7.38 ppm attributed to Hh,i (4H), a multiplet signal at ca. 7.54 ppm attributed to Hf (H), a multiplet signal at ca. 7.84 ppm attributed to Hg,j (4H), a doublet signal at ca. 8.04 ppm attributed to He (2H). The 13C NMR spectrum in the region of aliphatic shows four signals at 42.82, 50.83, 60.65, and 67.78 ppm attributed to Cc, Cb, Ca and Cd, respectively. In the region corresponding to the signals of aromatic ring carbons (113.43164.10 ppm), 12 peaks were observed (Figs. S. 2 - 7).
3.2. Theoretical study The structures of [PbL]2+ was optimized by Density Functional Theory (DFT) calculations using B3LYP/6-31G* basis set. The resulting structure for [PbL]2+ was used for further calculations 4
using the effective core potential (ECP) standard basis set LanL2DZ [17-19] for Pb2+ ion and the standard 6-31G* basis set for all other atoms. The resulting structural diagrams are shown in
Fig. 1 and selected calculated bond distances and angles relating to them are shown in Table 1. Lead is bound by the two amine nitrogens, two etheric oxygens and two oxygen atoms from two ethanolate groups in a distorted octahedral arrangement. The spatial distributions and orbital energies of HOMO and LUMO of [PbL]2+ were also determined (S. 8). It was clearly shown that the HOMO distribution of the complex was located essentially over the naphthalen moieties. The energy gap between HOMO and LUMO was computed to be 4.489 eV (S. 8) corresponding to absorption band of aromatic groups in the Uv-Vis spectrum.
S1386-1425(15)00314-5 http://dx.doi.org/10.1016/j.saa.2015.03.018 SAA 13432
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
26 October 2014 10 February 2015 1 March 2015
Please cite this article as: R. Azadbakht, H. Vaisi, H. Mohamadvand, J. Khanabadi, A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A new fluorescent chemosensor for Pb2+ ions based on naphthalene derivatives Reza Azadbakht*, Hojat Vaisi, Hossain Mohamadvand, Javad Khanabadi Department of chemistry, Payame Noor Universtiy, P.O. Box 19395-3697, Iran
Abstract A new naphthalene derivative receptor (L) was synthesized and characterized with common spectroscopic methods. L exhibited a strong fluorescence enhancement in the presence of trace amounts of Pb2+, attributable to photoinduced electron transfer (PET) effect, which also displayed high selectivity over a series of other metal cations (Na+, K+, Cs+, Mg2+, Ba2+, Cr3+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+ ) in acetonitrile/H2O (9:1, v/v) mixture. Keywords: Fluorescence, Chemosensor, Pb2+ ion, Naphthalene.
1. Introduction Heavy metal pollution is a serious environmental problem of global concern. Among these toxic metal ions, Pb2+ is one of the oldest known and most widely studied toxins [1]. Lead widely exists in various forms including elemental, inorganic and organic compounds. Lead compounds are used in construction materials for tank linings, piping, equipment for handling corrosive gases and liquids used in petroleum refining, halogenation, sulfonation, extraction, condensation, metallurgy, and for pigments for paints. It is also used in ceramics, plastics, electronic devices, as a component of lead batteries, and in the production of ammunition, solder, cable covering, and sheet lead. Moreover, lead also remains in trace amount in soil, water and food [2]. In babies and children, exposure to lead in drinking water above the action level can result in delays in physical and mental development, along with *Corresponding author. Tel.: +98 8125221144; fax: +98 8112546840. E-mail address: [email protected] (R. Azadbakht).
1
slight deficits in attention span and learning abilities. In adults, lead can increase blood pressure and cause fertility problems, nerve disorders, muscle and joint pain, irritability, and memory or concentration problems [3-8]. Thus, the concentration of lead in environment should be kept under permanent control. Although some atomic absorption spectroscopy techniques such as ICP-MS and ICP-AES can complete the quantitative analysis of the total amount of Pb2+ ion in the system [9–11], some inherent limitations such as complicated program, high initial cost, costly maintenance and consumables make the usage of these techniques became uneasily accessible. Thus, it is urgent to develop a convenient, sensitive and inexpensive method to detect trace level of Pb2+ ion. In recent years, fluorescence chemosensors have rapidly developed because of their miniature constitution, low cost manufacture, reusability, high selectivity and real-time measurement. Herein, we report the synthesis and properties of a highly turn-on lead fluorescent sensor (L) that binds Pb2+ with high affinity and displays selectivity against other physiological metals in aqueous media. In the presence of Pb2+, L exhibits significant fluorescence enhancements owing to PET (photoinduced electron transfer).
2. Experimental 2.1. Materials and instruments All solvents were of reagent grade quality and purchased commercially. 2-aminophenol was obtained
from
Merck
and
was
used
without
further
purification.
2-[2-(2-
formylnaphthoxy)ethoxy]naphthaldehyde was synthesized according to the literature method [12]. NMR spectra were obtained using a Bruker A V300 MHz spectrometer. Infrared spectra were recorded in KBr pellets using a BIO-RAD FTS-40A spectrophotometer (4000–400 cm1
). Positive ion FAB mass spectra were recorded on a Kratos-MS-50 spectrometer with 3-
nitrobenzyl alcohol as the matrix solvent. Uv–Vis absorption spectra were obtained on a
2
Varian Cary Eclipse 300 spectrophotometer. The fluorescence spectra were recorded on a Varian spectrofluorometer. Both excitation and emission bands were set at 5 nm.
2.2. Synthesis of L A solution of 2-aminoethanol (0.12 g, 2 mmol) in absolute methanol (25 mL) was added dropwise to a hot solution of 2-[2-(2-formylnaphthoxy)ethoxy]naphthaldehyde (0.374, 1 mmol) in absolute methanol (50 mL). The solution was gently refluxed for 6 h. The solution was then allowed to cool to room temperature after which sodium borohydride (1 g, 26 mmol) was added in small portions to the stirred solution over 10 min. Excess water was added to the solution and the pH was adjusted to 12 with potassium hydroxide. The solution was extracted with chloroform (×3). The chloroform extracts were combined and dried over anhydrous sodium sulfate. The dried extracts were then reduced to a small volume on a rotary evaporator. A precipitate was obtained by standing overnight at 0 ºC. Yield (75%). Anal. Calc. for C28H32N2O4: C, 73.02; H, 7.00; N, 6.08. Found: C, 72.98; H, 7.13; N, 6.14 %. IR (KBr,cm-1) 3303 and 1623(NH starching and bending), 3387 (OH); 1HNMR δH (CDCl3, ppm) 2.64 (t, 4H), 3.59 (t, 4H), 4.36 (s, 4H), 4.59 (s, 4H), 7.38 (m, 4H), 7.54 (m, 2H), 7.84 (m, 4H), 8.04 (d, 2H); 13C NMR δC (CDCl3, ppm) 42.82, 50.83, 60.65, 67.78, 113.43, 121.23, 122.87, 123.75, 123.94, 124.10, 127.04, 128.68, 129.17,129.41, 133.39, 154.10. The mass spectrum show peak at m/z = 460 corresponding to L (S. 1).
2. 3. Theoretical calculations
The complex of [PbL]2+ gave fine powders and we were not able to prepare single crystals for structure determination by X-ray spectroscopy. Instead, The geometry of [PbL]2+ was fully optimized at DFT [13,14] levels of theory using the GAUSSIAN 03 program [15]. A starting semiempirical structure was optimized using the HYPERCHEM 5.02 series of programs [16].
3
3. Results and discussion 3.1. Synthesis and characterization of L Synthesis of L can be achieved very easily in 75% yield by schiff base condensation of 2-[2(2-formylnaphthoxy)ethoxy]naphthaldehyde [12] with 2-aminoethanol in methanol, followed by reduction with NaBH4 (S. 2). L was characterized by microanalysis, mass spectrometry, IR, and NMR studies. L was soluble in polar solvents, such as chloroform and methanol and was hydrolytically stable under both basic and acidic conditions. The reduction of the imine groups was indicated in the IR spectrum, by the appearance of weak bands related to N-H in the region of 3303 cm-1, while no bands attributable to C=N were detected. Two absorption bands in the 2919 cm-1 and 2928 are attributed to the asymmetric and symmetric stretching vibration of aliphatic C-H bonds CH2 groups. The stretching vibration of C-H aromatic was absorbed at 3086 cm-1. The 1H NMR spectrum of the L shows a triplet signal at 2.64 ppm, which can be assigned to Hb (4H), a triplet signal at ca. 3.59 ppm attributed to Ha (4H), a singlet signal due to the Hc (4H) resonance at ca. 4.34 ppm, a singlet signal at ca. 4.59 ppm attributed to Hd (4H). In the aromatic region (7.38-8.04 ppm) four signals were found, a multiplet signal at ca. 7.38 ppm attributed to Hh,i (4H), a multiplet signal at ca. 7.54 ppm attributed to Hf (H), a multiplet signal at ca. 7.84 ppm attributed to Hg,j (4H), a doublet signal at ca. 8.04 ppm attributed to He (2H). The 13C NMR spectrum in the region of aliphatic shows four signals at 42.82, 50.83, 60.65, and 67.78 ppm attributed to Cc, Cb, Ca and Cd, respectively. In the region corresponding to the signals of aromatic ring carbons (113.43164.10 ppm), 12 peaks were observed (Figs. S. 2 - 7).
3.2. Theoretical study The structures of [PbL]2+ was optimized by Density Functional Theory (DFT) calculations using B3LYP/6-31G* basis set. The resulting structure for [PbL]2+ was used for further calculations 4
using the effective core potential (ECP) standard basis set LanL2DZ [17-19] for Pb2+ ion and the standard 6-31G* basis set for all other atoms. The resulting structural diagrams are shown in
Fig. 1 and selected calculated bond distances and angles relating to them are shown in Table 1. Lead is bound by the two amine nitrogens, two etheric oxygens and two oxygen atoms from two ethanolate groups in a distorted octahedral arrangement.