A colorimetric Schiff base chemosensor for CN- by naked-eye in aqueous solution

Article abstract of DOI:10.1016/j.inoche.2015.02.014

A highly selective colorimetric chemosensor 6,6′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(2,4-dichlorophenol) (1) based on the combination of hydrazine and 3,5-dichloro-2-hydroxybenzaldehyde was designed and synthesized. Receptor 1 showed

Full text of DOI:10.1016/j.inoche.2015.02.014

−
A colorimetric Schiff base chemosensor for CN by naked-eye in aqueous
solution
Hyun Yong Jo, Seul Ah. Lee, Yu Jeong Na, Gyeong Jin Park, Cheal
Kim
PII:
DOI:
Reference:
S1387-7003(15)00066-0
doi: 10.1016/j.inoche.2015.02.014
INOCHE 5886
To appear in:
Inorganic Chemistry Communications
Received date:
Revised date:
Accepted date:
14 January 2015
6 February 2015
12 February 2015
Please cite this article as: Hyun Yong Jo, Seul Ah. Lee, Yu Jeong Na, Gyeong Jin Park,
−
Cheal Kim, A colorimetric Schiff base chemosensor for CN by naked-eye in aqueous
solution, Inorganic Chemistry Communications (2015), doi: 10.1016/j.inoche.2015.02.014
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A colorimetric Schiff base chemosensor for CN by naked-eye in aqueous solution
Hyun Yong Jo, Seul Ah Lee, Yu Jeong Na, Gyeong Jin Park, Cheal Kim*
Department of Fine Chemistry and Department of Interdisciplinary Bio IT Materials,
Seoul National University of Science and Technology, Seoul 139-743, Korea. Fax: +82-
2
-973-9149; Tel: +82-2-970-6693; E-mail:chealkim@seoultech.ac.kr
Abstract
A
highly
selective
colorimetric
chemosensor
6,6'-((1E,1'E)-hydrazine-1,2-
diylidenebis(methanylylidene))bis(2,4-dichlorophenol) (1) based on the combination of
hydrazine and 3,5-dichloro-2-hydroxybenzaldehyde was designed and synthesized. Receptor
1
showed exclusive response toward cyanide by a color change from colorless to yellow in
-
aqueous solution. The binding mode of 1-CN species was determined to be a 1:1
1
stoichiometry through Job plot, H NMR titration, and ESI-mass spectrometry analysis. Also,
the sensor 1 could be recyclable simply through treatment with a proper reagent such as
hydrochloric acid.
Keywords: deprotonation, cyanide, colorimetric, Schiff base, reversible
1

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Development of anion sensors is of great interest in supramolecular chemistry due to their
chemical and biological importance [1]. Among the various anions, cyanide is one of the
most concerned, because it is known as one of the most rapidly acting and powerful
poisons. Its toxicity results from its propensity to bind to the iron in cytochrome c oxidase,
interfering with electron transport and resulting in hypoxia [2-9]. Cyanide could be
absorbed through lungs, gastrointestinal track and skin, leading to vomiting, convulsion,
loss of consciousness, and eventual death [10-13]. Nevertheless, it has been produced in
large quantities and used in various industrial processes, which has led to environmental
contamination as well [14]. Thus, it is absolutely necessary to develop selective and
-
sensitive methods for CN detection in aqueous solution.
-
Several methods to detect CN have been developed using various experimental protocols
and detection techniques, such as chromatography, spectrophotography electrochemical
methods and flow injection analysis technique [15]. However, most of these methods
require sophisticated equipment, tedious sample preparation procedures, and trained
operators. In contrast, colorimetric methods can conveniently and easily monitor target
ions with the naked eye [16-19]. Colorimetric methods have therefore attracted
-
considerable attention in the detection of toxic anions including CN . However, many anion
-
sensors are not capable of distinguishing cyanide effectively from anions such as F and
-
-
AcO , because they possess similar basicity to CN and easily form hydrogen bonds. To
overcome these limitations, we synthesized a new chemosensor capable of exclusively
-
detecting CN by naked-eye.
Herein we report on the synthesis, characterization and sensing properties of a new
colorimetric receptor 1, based on the combination of hydrazine and 3,5-dichloro-2-
hydroxybenzaldehyde. Receptor 1 can detect cyanide by color change from colorless to
yellow via the ‘naked-eye’ in aqueous environment. In particular, it can distinguish
-
-
cyanide effectively from anions such as F and AcO .
The colorimetric chemosensor 1 was synthesized by condensing hydrazine with 3,5-
1
13
dichloro-2-hydroxybenzaldehyde (Scheme 1) and characterized by H NMR, C NMR,
ESI-mass spectrometry, and elemental analysis.
2

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The chromogenic sensing ability of receptor 1 with various anions in a mixture of
CH CN/bis-tris buffer (v/v, 3:7, 10 mM) was monitored by UV-vis absorption spectra (Fig.
3
1
(a)). The best selectivity was observed in the mixture of CH CN/bis-tris buffer (v/v, 3:7)
3
-
among various organic solvent systems. Only the addition of CN induced a distinct
-
-
-
-
-
-
-
-
spectral change while other anions such as F , AcO , Cl , Br , I , H PO , BzO , N and
2
4
3
-
SCN did not induce any spectral changes. Consistent with the change of UV-vis spectrum,
the solution of 1 resulted in an immediate color change from colorless to yellow with
cyanide (Fig. 1(b)), indicating that receptor 1 can serve as a ‘naked-eye’ cyanide indicator
in aqueous solution.
-
To further investigate the chemosensing properties of 1, UV-vis titration of 1 with the CN
-
ion was performed (Fig. 2). On gradual addition of CN to a solution of 1, the absorption
band at 300 nm decreased and a new band at 440 nm emerged and gradually increased to
maxima at 120 equiv with a distinct isosbestic point at 490 nm, indicating the formation of
-
the only one species between 1 and CN . This bathochromic shift led us to propose the
transition of intramolecular charge transfer (ICT) band through the deprotonation of the
-
chemosensor 1 by CN , based on Bhattacharya’s proposal [20,21].
-
The binding mode between 1 and CN was determined through Job plot analysis. The Job
plot exhibited a 1:1 binding interaction (Fig. 3), which was confirmed by ESI-mass
-
spectrometry analysis (Fig. 4). The positive-ion mass spectrum of 1 upon addition of CN
+
+
showed the formation of [1-H + 2TEA] binding mode [m/z: 636.87; calcd: 637.24]. To
-
1
elucidate in more details the binding interaction of receptor 1 with CN , H NMR titration
-
experiments were carried out in DMSO-d (Fig. 5). Upon addition of 1 equiv of the CN to
6
the receptor 1, the proton signals of -OH at 11.81 ppm disappeared completely and the imine
and aromatic protons were shifted to upfield. This result indicates that the cyanide
participates in the deprotonation of the -OH protons. In addition, no new peak was observed
in the range of 5-6 ppm, which shows that the nucleophilic addition of cyanide to the imine
moiety did not occur.
To further confirm whether the color change originated from the transition of ICT through
-
the deprotonation mechanism, the interaction between 1 and OH was also conducted. UV-vis
3

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-
spectral change of 1 upon addition of OH was nearly identical to that of 1 upon addition of
-
-
CN , which supports the deprotonation mechanism of 1 by CN (Fig. S1).
From the Benesi-Hildebrand equation [22], the association constant was found to be 4 x
2
−1
-
1
0 M for the CN recognition of receptor 1 (Fig. S2). This value is within the range of
5
-
those (1.0 ~ 1.0 x 10 ) reported for CN sensing chemosensors [23-27]. The detection limit
-
(
3∂/k) of receptor 1 for the analysis of CN ions was calculated to be 210 μM (Fig. S3) [28].
-
The preferential selectivity of 1 as a colorimetric chemosensor for the detection of CN
was studied in the presence of various competing anions. For competition tests, receptor 1
-
was treated with 120 equiv of CN in the presence of 120 equiv of other anions. No
-
interference was observed for the detection of CN in the presence of other anions, while
H PO did interfere completely (Fig. 6). This result suggests that 1 could be an excellent
2
4
-
sensor for selectively detecting CN in the presence of most of the competing anions.
-
To examine the reversibility of receptor 1 toward CN in a mixture of CH CN/bis-tris
3
buffer (v/v, 3:7, 10 mM) solution, hydrochloride acid (HCl) (120 equiv) was added to the
-
1
-CN solution. As shown in Fig. 7, the solution color changed from yellow to colorless
-
and the absorbance at 440 nm completely disappeared. Upon addition of CN into the
solution again, the color and the absorbance were recovered. The color changes were
-
almost reversible even after several cycles with the sequentially alternative addition of CN
and HCl. These results indicate that receptor 1 could be recyclable simply through
-
treatment with a proper reagent such as HCl, and further confirm that 1 would detect CN
by the deprotonation mechanism.
In summary, we have reported a simple imine-based naked-eye chemo-sensor 1 for the
-
-
detection of CN in aqueous solution. The receptor 1 showed high selectivity toward CN
ions in a 1:1 stoichiometric manner, which induced a fast color change from colorless to
-
yellow. Moreover, the addition of hydrochloric acid (HCl) to the 1-CN solution
regenerated the free 1, indicating that the sensor 1 could be recyclable easily through
treatment with a proper reagent such as hydochloric acid (HCl). Therefore, this type of a
simple, easy-to-synthesize chemo-sensor 1 will contribute to potential use for detecting and
monitoring cyanide in aqueous environment.
4

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Acknowledgements
Basic Science Research Program through the National Research Foundation of Korea
NRF) funded by the Ministry of Education, Science and Technology (2012001725 and
(
2
012008875) are gratefully acknowledged.
Supplementary Information.
Supplementary material associated with this article can be found, in the online version.
References and notes
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Scheme 1. Synthetic procedure of 1.
7

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Scheme 2. Proposed sensing mechanism of 1 for cyanide.
8

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Figure captions
Figure 1. (a) UV-vis spectral changes of 1 (20 µM) upon the addition of various anions
120 equiv) in a mixture of CH CN/bis-tris buffer solution (v/v, 3:7). (b) The color
(
3
changes of 1 (20 µM) upon addition of various anions (120 equiv).
-
Figure 2. UV-vis spectral changes of 1 (20 µM) upon addition of CN (up to 120 equiv).
-
Figure 3. Job plot of receptor 1 and cyanide. The total concentration of CN ions with
-5
receptor 1 was 1.0 x 10 M.
Figure 4. Positive-ion electrospray ionization mass spectrum of 1 (20 µM) upon
-
addition of CN (1 equiv).
1
-
Figure 5. H NMR titration of 1 (10 mM) with CN .
-
Figure 6. (a) Competitive selectivity of 1 (20 μM) towards CN (120 equiv) in the
presence of other anions (120 equiv). (b) The color changes of 1 (20 μM) in the
-
presence of CN (120 equiv) and other anions (120 equiv).
-
Figure 7. (a) UV-vis spectral changes of 1 (20 µM) after the sequential addition of CN
-
and HCl. (b) The color changes of 1 (20 µM) after the sequential addition of CN and
HCl.
9

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(a)
(b)
Fig. 1
1
0

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Fig. 2
1
1

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Fig. 3
1
2

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Fig. 4
1
3

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Fig. 5
1
4

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(a)
(b)
Fig. 6
1
5

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(a)
(b)
Fig. 7
1
6

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Graphical abstract
A highly selective colorimetric chemosensor (1) based on the combination of hydrazine and
,5-dichloro-2-hydroxybenzaldehyde was designed and synthesized. Receptor 1 showed
3
exclusive response toward cyanide by a color change from colorless to yellow in aqueous
-
solution. The binding mode of 1-CN species was determined to be a 1:1 stoichiometry
1
through Job plot, H NMR titration, and ESI-mass spectrometry analysis.
1
7

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Highlights
►
►
A colorimetric Schiff base chemosensor 1 was synthesized.
-
CN resulted in an immediate color change from colorless to yellow.
►
Receptor 1 could be recyclable simply through treatment HCl.
1
8