Dipodal colorimetric sensor for Ag+ and its resultant complex for iodide sensing using a cation displacement approach in water

Article abstract of DOI:10.1016/j.tetlet.2017.01.098

We synthetized a sulfonamide-based dipodal receptor capable of recognizing Ag⁺ selectively in water in the presence of other possible competing cations through color change. The resultant Ag-complex showed suitability as a chemosensor for the sensing of I^? ions in water in the presence of other anions through a cation displacement process. The detection limits of the receptor for Ag⁺ and of the resultant complex for I^? were identified as 2.43 and 5.31?μM, respectively.

Full text of DOI:10.1016/j.tetlet.2017.01.098

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+
Dipodal colorimetric sensor for Ag and its resultant complex for iodide sensing
using a cation displacement approach in water
Hanna Goh, Tae Kyu Nam, Amanpreet Singh, Narinder Singh, Doo Ok Jang
PII:
S0040-4039(17)30142-9
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.01.098
TETL 48601
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
31 August 2016
23 January 2017
27 January 2017
Please cite this article as: Goh, H., Nam, T.K., Singh, A., Singh, N., Jang, D.O., Dipodal colorimetric sensor for Ag
+
and its resultant complex for iodide sensing using a cation displacement approach in water, Tetrahedron Letters
(2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.01.098
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Graphical Abstract
Dipodal colorimetric sensor for Ag+ and its resultant complex for
iodide sensing using a cation displacement approach in water
Hanna Goh, Tae Kyu Nam, Amanpreet Singh, Narinder Singh,* and
Doo Ok Jang*

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1
Tetrahedron Letters
Dipodal colorimetric sensor for Ag+ and its resultant complex for iodide sensing using
a cation displacement approach in water
Hanna Goh,a Tae Kyu Nam,a Amanpreet Singh,b Narinder Singh,b,* and Doo Ok Janga,*
aDepartment of Chemistry, Yonsei University, Wonju 26493, Korea
bDepartment of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India
nsingh@iitrpr.ac.in; dojang@yonsei.ac.kr
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We synthetized a sulfonamide-based dipodal receptor capable of recognizing Ag+
selectively in water in the presence of other possible competing cations through color
change. The resultant Ag-complex showed suitability as a chemosensor for the sensing of I-
ions in water in the presence of other anions through a cation displacement process. The
detection limits of the receptor for Ag+ and of the resultant complex for I- were identified
as 2.43 and 5.31 µM, respectively.
Available online
Keywords:
sensor
2009 Elsevier Ltd. All rights reserved.
colorimetric
Ag+
iodide
cation displacement assay
recognition
1. Introduction
Therefore, the monitoring of iodide concentrations is used to
diagnose many diseases. Due to the strong affinity of silver for
The visual detection of analysts, particularly in water, has been
receiving substantial attention in supramolecular chemistry.1–5
Colorimetric sensors present several advantages over other
analytical techniques – including electrochemical sensors,6–8
atomic absorption spectroscopy, inductively-coupled plasma
spectroscopy, and gas chromatography. In terms of
manufacturing costs and time consumption.9-11 Generally,
colorimetric sensors are built from highly conjugated organic
receptors such as rhodamine11,12 and salen.13–15 These receptors
are used in organic solvents, as they are mostly insoluble in
water. Other approaches involve the use of metal complexes,
inorganic-organic hybrid polymers, or nanoparticles-based
sensors.16,17 However, these classes of receptors present major
issues in their stability and non-uniform size distribution.18
Therefore, simple and cheap colorimetric receptors with high
sensitivity are highly needed. Although many sensors highly
sensitive to metal ions and anions have been developed,19–22
multifunctional and reverse sensors are rare.23,24 Dual sensing can
be achieved with a cation displacement assay,25-40 which is a
promising method for the detection of anionic species in water.
Generally, anion receptors consist of hydrogen bonding sites.
However, competitive binding by polar solvents can happen.41,42
This problem can be resolved by introducing ionic interactions
provided by metal ions.
iodide, high-sensitivity anion sensors can be constructed using a
cation displacement approach.25-40 In this approach, a primary
receptor is used as a sensor for an analyte that is readily
eliminated by the second analyte, causing a release of the primary
receptor.
In this context, we designed and synthesized a sulfonamide-
based dipodal receptor for the sensing of Ag+. The resultant
complex was used as a colorimetric sensor for the probing of I- in
water. We expected the receptor to be capable to encapsulate a
cation selectively thanks to its multiple binding sites, and its Ag-
complex to recognize I- based on the high affinity of silver with
iodide. In addition, considering the high polarity of the
sulfonamide group, the receptor was expected to be soluble in
water.
2. Results and discussion
Receptor 1 was prepared as per Scheme 1. The condensation
of p-toluenesulfonylhydrazide with isophthaloyl dichloride in
o
CH2Cl2 at 0 C afforded receptor 1 in a 98% yield. For control
experiments, a second receptor (2) was similarly prepared from
the reaction of p-toluenesulfonylhydrazide with benzoyl chloride
instead of isophthaloyl dichloride.
Among all transition metal ions, silver is one of the most
important cations used in the electronic and photographic
industries.43,44 Its consumption has increased significantly over
the last two decades. Therefore, to limit its harmful effects –
particularly on plants, the silver concentrations in the
environment and in industrial waste should be monitored. Iodide
has attracted considerable attention for its important role in the
biological system.16,45,46 It plays a key role in the thyroid gland
function and in normal human growth.47 A deficit or excess of
iodide in the thyroid can cause serious health problems.
Photophysical studies of receptor 1 were performed in water
(10 mM HEPES, pH 7.5). The absorbance spectrum of receptor 1
(10 M) showed absorbance maxima at 226 nm. Further binding
studies of receptor 1 were conducted with various metal ions
(Cu2+, Fe3+, Zn2+, Ni2+, Mg2+, Ag+, Co2+, Cd2+, Ca2+, Ba2+, Na+,
and K+), as per Figure 1. None of these showed significant
changes in absorbance, except for Ag+ ions, which showed a new
absorbance band at 426 nm. This new absorbance band was
attributed to
a
metal-to-ligand charge-transfer (MLCT)
mechanism, which confirmed that a complex was formed. As

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seen in Figure 2, the bar diagram at 426 nm showed a high
selectivity of receptor 1 for Ag+ over other metal ions, with a
350-fold increase in intensity. This was accompanied by a color
change in the solution, from colorless to yellow (Figure 3). The
emission spectrum of receptor 1 was also recorded in the
presence of various cations (excitation at max = 226 nm) (Figure
S1). It remained almost the same with most of the metal ions,
although the emission profile was changed with a cut-off around
450 nm for Ag+ ions. To analyze the binding pattern of receptor
1, binding experiments with mono-podal receptor 2 were
performed using absorbance spectroscopy. The absorbance
spectrum of receptor 2 was recorded in the presence of different
metal ions (Figure S2). Although Ag+ ions showed some
enhancement of the absorbance intensity at 426 nm, it was
significantly lower than with receptor 1. Along with Ag+ ions,
Fe3+ ions also showed a small enhancement in the absorbance
intensity. This revealed that the sensitivity and selectivity of the
receptors depend on their cavity size and number of pods.
Figure 3. Photographic images of receptor 1 (10 µM) in water (10 mM
HEPES, pH 7.5) in the presence of metal ions (5 equiv) (From 0 to 12:
receptor 1, Cu2+, Fe3+, Zn2+, Ni2+, Mg2+, Ag+, Co2+, Cd2+, Ca2+, Ba2+, Na+, and
K+).
Titration experiments were performed to understand the
photophysical behavior of receptor 1 for the recognition of Ag+
ions (Figure 4). Upon the stepwise addition of Ag+ ions to a 10
M solution of receptor 1 in water (10 mM HEPES, pH 7.5), the
intensity at 426 nm increased gradually. From the titration data,
the binding constant of receptor 1 to Ag+ ions was calculated as
3.23 (±0.2) x 103 M-1 with the Benesi-Hildebrand plot (Figure
S3).48
O
O
O
O
NH
O
HN
O
HN
S
NH
Cl
Cl
O
S O
CH2Cl2, 0 oC, 2 h, 98%
H2N
O
NH
S
O
1
O
O
S
Cl
O
HN
NH
O
Figure 4. Absorbance changes in receptor 1 (10 µM) upon addition of
Ag+ ions (0-2.7 equiv) in water (10 mM HEPES, pH 7.5).
CH2Cl2, 0 oC, 2 h, 80%
2
Scheme 1. Synthesis of receptors 1 and 2
To evaluate the stoichiometry of complex formation, a Job’s
plot was constructed (Figure S4).49 The x-axis of the Job's plot—
the mole fraction—is the ratio of Ag+ concentration to the total
concentration of Ag+ and receptor 1, whereas the y-axis—labeled
[HG]—is the concentration of the complex 1-Ag calculated from
spectroscopic techniques. The Job’s plot indicated that receptor 1
and Ag+ formed a 1:1 complex. The formation of the complex 1-
Ag was also confirmed with a comparison of the IR spectrum of
receptor 1 (Figure S5) with that of the complex (Figure S6). The
IR absorption frequency of the S=O asymmetric stretch moved
from 1340 to 1366 cm-1. The frequency of the S=O symmetric
stretch also changed from 1166 to 1193 cm-1. These changes in
the IR spectrum imply that the Ag+ ion coordinates with the
oxygen atoms of sulfonyl groups. The IR spectrum of the
complex 1-Ag had a strong band at 3427 cm-1, which implied the
presence of H2O. Furthermore, a FAB HRMS was used to verify
the stoichiometry of the complex and the presence of H2O in it
(Figure S7). It showed m/z = 663.1517, which corresponded to (1
+ Ag + 3H2O) (calcd: 663.0349). The detection limit of receptor
1 for the estimation of Ag+ was determined as 2.43 µM (Figure
S8).50
Figure 1. UV-vis absorbance of receptor 1 (10 µM) upon addition of
particular metal (5 equiv) in water (10 mM HEPES, pH 7.5).
To examine the effects of other metal ions on the detection of
Ag+ ions, competing binding tests were performed. The
absorbance spectra of receptor 1 were recorded in the presence of
different concentrations of Ag+ ions with other possible
competing metal ions at a ratio of 1:1. As per Figure 5, there was
no obvious perturbation in the UV-vis intensity of receptor 1
irrespective of the presence or absence of other metal ions in low
concentrations, although a small perturbation was observed after
15 equivalents of metal ions. These results confirmed that
receptor 1 can estimate Ag+ ions without interference in the
presence of other metal ions.
Figure 2. UV-vis absorbance of receptor 1 (10 µM) upon addition of
particular metal (5 equiv) in water (10 mM HEPES, pH 7.5) at 426 nm.