A new isoindoline–based highly selective “turn-on” fluorescent chemodosimeter for detection of mercury ion

Article abstract of DOI:10.1016/j.saa.2017.02.003

A new isoindoline–based highly efficient turn-on fluorescent chemodosimeter S with a thioamide functionality as a binding site for selective detection of Hg^2?+ ion has been developed. The chemodosimeter S showed an extreme selectivity for detection of Hg^2?+ ion among various two and three-valent metal ions in acetonitrile/water (70/30, v/v). It was found that, in the presence of Hg^2?+ ion the non-fluorescent chemodosimeter S was efficiently and rapidly desulfurized to the corresponding highly fluorescent amide 1. A good linear relationship was shown between the fluorescence intensity and the concentration of Hg^2?+ within the range of 0–1?μM, with a detection limit of 2.03?×?10^??8?M.

Full text of DOI:10.1016/j.saa.2017.02.003

Accepted Manuscript
A new isoindoline–based highly selective “turn-on” fluorescent
chemodosimeter for detection of mercury ion
Hassan Zali-Boeini, Mohammad Zareh Jonaghani, Negar Fadaei,
Hadi Amiri Rudbari
PII:
DOI:
Reference:
S1386-1425(17)30091-4
doi: 10.1016/j.saa.2017.02.003
SAA 14925
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
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31 January 2017
2 February 2017
Please cite this article as: Hassan Zali-Boeini, Mohammad Zareh Jonaghani, Negar Fadaei,
Hadi Amiri Rudbari , A new isoindoline–based highly selective “turn-on” fluorescent
chemodosimeter for detection of mercury ion. The address for the corresponding author
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ACCEPTED MANUSCRIPT
A New Isoindoline–based Highly Selective “Turn-On” Fluorescent
Chemodosimeter for Detection of Mercury Ion
Hassan Zali-Boeini*, Mohammad Zareh Jonaghani, Negar Fadaei, Hadi Amiri Rudbari
Department of Chemistry, University of Isfahan, 81746-73441, Isfahan, Iran
Fax: +98-313-6689732
E-mail: h.zali@chem.ui.ac.ir
Abstract
A new isoindoline–based highly efficient turn-on Fluorescent chemodosimeter S with a
thioamide functionality as a binding site for selective detection of Hg2+ ion has been developed.
The chemodosimeter S showed an extreme selectivity for detection of Hg2+ ion among various
two and three-valent metal ions in acetonitrile/water (70/30, v/v). It was found that, in the
presence of Hg2+ ion the non-fluorescent chemodosimeter S was efficiently and rapidly
desulfurized to the corresponding highly fluorescent amide 1. A good linear relationship was
shown between the fluorescence intensity and the concentration of Hg2+ within the range of 0–1
μ
M, with a detection limit of 2.03×10-8 M.
Keywords
Fluorescent
Chemodosimeter
Mercury Ion
Thioamide
1. Introduction
Recently, Fluorescent chemosensors and chemodosimeters have been attracted substantial
attentions for detection of toxic heavy metal ions due to their simplicity, instantaneous response
and high detection limit [1-2], when compared with other detection methods such as atomic
absorption spectrometry [3-4], potentiometric ion-selective electrode [5], and inductively
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coupled plasma mass spectrometry [6-9] and so on. Mercury is one of the most toxic and
widespread global pollutants [10-11] among heavy metal ions. Due to presence of sulfur
containing amino acids such as cysteine and N-acetyl cysteine in enzymes and proteins and high
affinity of Hg2+ ion for sulfur atom, even very low concentrations of mercury ion, can causes
serious health problems such as destroying endocrine systems, central nervous system and vision
loss [12-15]. Hence, there have been significant efforts for selective and efficient detection of
Hg2+ ion which is an important issue in environmental and food chemistry. Although some
fluorescent chemosensors based on rhodamine [16-17], benzothiazole derivatives [18-19],
fluorescein [20-21] and other fluorophores [22-32] have been synthesized and used for detection
of mercury ion, nonetheless most of these sensors have some shortcomings such as weak
fluorescence intensity, cross-sensitivities with other metal ions, fluorescence quenching upon
Hg2+ addition, low selectivity and sensitivity, and difficult syntheses [33-38]. Therefore
developing a new sensor with high selectivity and sensitivity for Hg2+ is still a valuable
challenge. Chemodosimeter sensors, especially ‘turn-on’ fluorescence probes owing to their high
sensitivity and selectivity have become interesting field in fluorescence sensing methods when
compared with classical fluorescent chemosensors [39-45]. To date several fluorescent
chemodosimeters have been developed for detection of Hg2+ ions based on the robust thiophilic
character of Hg2+ ion and their mechanisms including: desulfurization reactions by hydrolysis
[46-49], cyclization [50], and elimination reactions [51]. However, several significant limitations
such as moderate sensitivity and selectivity, long reaction times, and operating at elevated
temperatures still exist [52-54]. Intrigued to find a solution to these problems, we were interested
in exploring a new chemodosimeter sensor for detection of Hg2+ ions in low temperatures, with a
short response time, with high selectivity and sensitivity, and strong fluorescence emissions. In
continuation of our studies on developing novel efficient sensors [55], herein, we report a new
turn-on fluorescent chemodosimeter for detection of mercury ion based on desulfurization
reaction of (Z)-3-(quinolin-2-ylmethylene)isoindoline-1-thione S.
2. Experimental
2.1 Materials and methods
1
All reagents and solvents were obtained commercially and used without further purification. H
NMR and 13C NMR spectra were recorded on a Bruker-Avance400MHz spectrophotometer
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using DMSO-d6and residual solvent as an internal standard. Infrared spectra (IR) spectra were
recorded on a Jasco, FT/IR-6300 spectrometer. Absorption spectra were determined on a
Shimadzu UV-160. Fluorescence spectra were recorded with a Shimadzu RF-5000
Spectrofluorometer.
2.2 Preparation of (Z)-3-((quinolin-2-yl)methylene)isoindolin-1-one (1)
In a two-neck round bottom flask equipped with magnetic stirrer and a condenser, phthalimide
(10 mmol, 1.47 g), quinaldine (5 mmol, 0.72 g), dry ZnCl2 (21 mmol, 2.86 g) and N,N-
dimethylaniline (15.0 ml) were charged and heated under nitrogen ventilation at 150 °C for 24 h.
After completion (TLC), the reaction mixture was poured in HCl (10%, 600 mL) and stirred at
°
95°C for 1 h. After cooling to 50 C, the reaction mixture was filtered and washed with water
(2×50 mL). The product was dried under vacuum to obtain (Z)-3-((quinolin-
1
2yl)methylene)isoindolin-1-one as a fine yellow powder in good yield (1.1 g, 81%); H NMR
(400 MHz, DMSO-d6) δ: 7.07 (s , 1 H), 7.66-7.74 (m, 2H), 7.80-7.92 (m, 4H), 8.05 (d, , J= 7.4
Hz, 1H), 8.15 (d, , J= 7.4 Hz, 1H), 8.33 (d, , J= 8.4 Hz, 1H), 11.49 (s, 1H); 13C NMR (100 MHz,
DMSO-d6) δ: 101.2, 121.1, 123.1, 123.2, 126.1, 126.7, 127.2, 127.9, 128.5, 130.5, 130.7, 132.8,
137.6, 138.1, 139.3, 145.8, 154.9, 168.1; IR (KBr); 3289(NH), 1702(C=O), 1651, 1591, 1296,
1200, 846, 757.
2.3 Preparation of (Z)-3-((quinolin-2-yl)methylene)isoindoline-1-thione(S)
In a round bottom flask, Compound 2 (2 mmol, 0.54 g) and 2,4-bis(4-methoxyphenyl)-1,3,2,4-
dithiadiphosphetane-2,4-dithione (Lawesson’s Reagent) (2 mmol, 0.81 g) were dissolved in
diethylene glycol diethyl ether and the reaction mixture was heated for 2h at 80°C. After cooling,
the reaction mixture was poured over crushed ice. Then, the crude precipitated product was
filtered and subjected to flash chromatography using alumina as the stationary phase and
petroleum ether/ethyl acetate (2:1) as eluent to afford compound S as an orange solid (0.35 g,
1
61% yield); H NMR (400 MHz, DMSO-d6) δ: 7.21 (s, 1 H), 7.65-7.76 (m, 3H), 7.81-7.87 (m,
2H), 7.95-8.01 (m, 2H), 8.14 (t, J= 6.8 Hz, 1H), 8.47 (d, J= 8.4 Hz, 1H), 13.01 (s, 1H); 13C NMR
(100 MHz, DMSO-d6) δ: 104.4, 120.7, 123.8, 123.9, 126.4, 127.0, 128.0, 128.3, 128.6, 130.5,
130.6, 131.5, 132.5, 135.4, 137.4, 155.2, 170.3; IR (KBr); 3219(NH), 1173(C=S), 1642, 1589,
1476, 1403, 1340, 1294, 737.
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3. Results and discussion
At the beginning of our study, (Z)-3-((quinolin-2-yl)methylene)isoindolin-1-one1 was
synthesized from reaction of phthalimide and quinaldine in the presence of ZnCl2 at rather
elevated temperature. Then, the corresponding thioamide chemodosimeter S was prepared by the
thionation reaction of compound 1 with Lawesson’s reagent in diethylene glycol diethyl ether as
1
solvent (yield 61%, Scheme 1). The structure of compounds 1 and S were established by H
NMR and 13C NMR spectroscopy. Moreover, the structure of compound 1 was further confirmed
by X-ray analysis (Figure 1, CCDC1502691).
Scheme 1.Synthetic route to compounds 1 and S.
Figure 1. ORTEP representation of compound 1. Displacement ellipsoids are drawn at the 30% probability level
and H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are shown as dashed lines.
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3.1 Absorption and Fluorescence spectral responses
Absorption and Fluorescence spectral responses of S toward various metal cations were
investigated in aqueous solution of acetonitrile (CH3CN-H2O 70/30, v/v). Hence, UV absorption
spectra of S was taken alone and in the presence of various metal cations (Figure 2A). As shown
in figure 2, absorption spectrum of free chemodosimeter S displayed a maximum placed at 426
nm with shoulders at 407 nm and 449 nm. When a solution containing 2.5 equiv. of Zn2+, Sn2+,
Cr3+, Al3+, Cd2+, Mn2+, Cu2+, Ba2+, Co2+, Ca2+, Ni2+, Pb2+ or Ag+ metal ions were added, the
absorption spectra of S did not change, whereas in the presence of Hg2+ ion intensity of the
absorption maxima exhibited a little increase with a notable blue shift (Δλ= 25 nm). When
chemodosimeter S (10 μM) was excited at 426 nm, a very weak emission at 529 nm (quantum
yield, Φ= 0.007) in aqueous CH3CN solution at room temperature was observed. Upon the
addition of Hg2+ (10 μM), a remarkable enhancement in the fluorescence intensity (quantum
yield, Φ = 0.56, Fig. 2B and) was detected. To examine the selectivity of S toward mercury ion,
fluorescence emission spectra of S in the presence of 50 equiv. of various metal ions in aqueous
solution of acetonitrile (CH3CN-H2O 70/30, v/v) were recorded. As shown in figure 2B the bare
chemodosimeter S (0.1 μM) displays no fluorescence emission (fluorescence off-state) whereas,
in the presence of Hg2+ ion intensively fluoresces at 529 nm. The signaling mechanism is more
likely based on desulfurative oxidation of thioamide functionality of chemodosimeter S with
mercury ion to corresponding amide 1 which shows strong green fluorescence emission
(fluorescence on-state). None of all other metal ions including monovalent, divalent, and
trivalent cations show measurable effect on S.
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Figure 2. (A) UV-vis absorption spectra of the chemodosimeter
CH3CN/H2O (70:30). [Mn+] = 50 μM; (B) Fluorescence spectra of
metal ions in CH3CN/H2O (70:30, v/v) at room temperature [Mn+] = 5 μM.
S
(20 μM) with various metal ions in
S
(0.1 μM) in the presence of various
Scheme 2. The proposed signaling mechanism of chemodosimeter S with Hg2+.
The proposed mechanism for the operation of chemodosimeter S is shown in scheme 2. In order
to approve the operation mechanism of chemodosimeter S, Infrared and 1H NMR spectrum of S
was recorded before and after addition of mercury ion. As shown in the figure 3A upon the
addition of Hg2+ ion appearance of a new peak in IR spectrum corresponding to the carbonyl
group at 1702 cm-1 was evident for the formation of amide 1. This explicitly confirms the
proposed desulfurative mechanism for conversion of thioamide functionality of chemodosimeter
S to the analogous amide 1. In the 1HNMR spectrum of compound S, there is a singlet signal at
13.1 ppm (1H) which belongs to NH group of thioamide functionality. During addition of
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mercury ion, this characteristic signal was shifted drastically to upfield region (11.8 ppm, ∆δ=
1.3 ppm) which further approves the proposed operation mechanism of chemodosimeter S
(Figure 3).
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Figure 3. (A) FT IR spectra of the S and S + Hg2+; (B) 1H NMR spectra of 1, S, and S + 1.0 equiv. of HgCl2 in
DMSO-d6 at room temperature.
Figure 4A shows the fluorescence behavior of the chemodosimeter S upon addition of diverse
metal ions. It was distinctly observed that, after addition of Hg2+ ion, the nonfluorescent solution
of S was immediately turned to a bright green fluorescent solution under UV light. Figure 4B
shows the fluorescence emission of compound 1 and a mixture of compound 1 and Hg2+ ion.
This clearly indicates that the intense green emission is only related to compound 1 which is not
affected by probable complexation between 1 and Hg2+ ion.
Figure 4. (A) Fluorescence changes upon addition of various metal cations to S in CH3CN/water
under UV light (365nm); (B) Fluorescence emission of compound 1 alone and in the presence of Hg2+.
The fluorescence and absorbance titration experiments of the chemodosimeter S with Hg2+ ion
were performed in CH3CN/H2O mixture (70/30, v/v) (Figure 5A, and 5B). In the absorption
spectra, intensity of the band centered at 426 nm decreased and shifted to 401 nm during the
addition of Hg2+ ion. A good linear detection range was observed in the emission spectra at 529
nm upon addition of 0.2–1 μM of Hg2+ (Figure 5C). The detection limit of the chemodosimeter S
for Hg2+ ion was estimated to be 2.03×10-8 M. Figure 5D obviously demonstrate extreme
selectivity of S toward Hg2+ ion over other metal ions.
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Figure 5. (A) Fluorescence spectra of S (0.1 μM) in the presence of 0.2-5 μM of Hg2+; (B) UV-vis absorption spectra
of the chemodosimeter S (20 μM) with various concentrations of Hg2+ ion ([Hg2+]= 0-50 μM); (C) Plot of
fluorescence intensities of S at 529 nm against 0.2-1.2 μM concentrations of Hg2+; (D) Emission intensity of S (0.1
μM) in the presence of Hg2+ and other metal ions (5 μM) in CH3CN/H2O (70/30, v/v) at room temperature
Since response time is an important factor in chemodosimeter sensors, the time dependence for
the interaction of S with Hg2+ ion was studied and the results are shown in Figure 6A. The
fluorescence intensity at 529 nm was increased rapidly upon addition of 5 μM Hg2+‏ion to 0.1
μM S and then remained constant after 1 min. The stoichiometric ratio between the S and Hg2+
was determined by Job’s plots. As shown in figure 6B, a 1:1 stoichiometry for the interaction of
S with Hg2+ ion was observed.
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Figure 6. (A) Time dependence of fluorescence emission of S (0.1 μM) to addition of Hg2+ ion 5 μM); (B) Job’s plot
diagram of chemodosimeter sensor S for Hg2+ (the total concentration of S and Hg2+ was 2 μM)
Conclusion
In summary, (Z)-3-((quinolin-2-yl)methylene)isoindoline-1-thione S as a new compound was
synthesized in two simple steps from readily available starting materials. The compound S was
shown to be as an efficient, fast, and highly selective chemodosimetersensor for detection of
Hg2+ ion among various mono, di, and tri-valent metal ions. It was found that, the presented
chemodosimeter worked based on irreversible desulfurization reaction of thioamide functionality
of S to amide functional group in the presence of mercury ion. The selectivity of S for detection
of Hg2+ ion was attributed to high affinity of Hg2+ toward sulfur atom of thioamide moiety in the
chemodosimeter S. Fortunately, the vivid green fluorescent response of S to Hg2+ can be even
sensed and persuaded by the naked eye. This property make this simple molecule as a promising
chemodosimeter sensor for the facile visualization of trace amounts of Hg2+ ion which is an
important issue in environmental chemistry.
Acknowledgements
We are grateful to the University of Isfahan research council for financial support of this work.
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A New Isoindoline–based Highly Selective “Turn-On” Fluorescent Chemodosimeter for Detection of
Mercury Ion
Hassan Zali-Boeini*, Mohammad Zareh Jonaghani, Negar Fadaei, Hadi Amiri Rudbari
Graphical abstract
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Highlights
- A new isoindoline–based highly efficient turn-on Fluorescent chemodosimeter for selective
detection of Hg2+ ion has been developed.
- A desulfurative reaction is proposed for the operational mechanism of chemodosimeter.
- Sensing protocol and the mechanism of the chemodosimeter is supported by 1H NMR, IR,
and Fluorescence studies.
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