Exploration of selective recognition of iodide with dipodal sensor: 2,2′-[ethane-1,2-diylbis(iminoethane-1,1-diyl)]diphenol

Article abstract of DOI:10.1039/c3dt52690a

A dipodal fluorescent receptor, 2,2′-[ethane-1,2-diylbis(iminoethane- 1,1-diyl)]diphenol (2), with amine and hydroxyl moieties as binding sites has been synthesised and characterized with spectroscopic methods and single crystal X-ray techniques. The reco

Full text of DOI:10.1039/c3dt52690a

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Exploration of selective recognition of iodide with
dipodal sensor: 2,2’-[ethane-1,2-diylbis-
Cite this: Dalton Trans., 2014, 43,
3584
(
iminoethane-1,1-diyl)]diphenol†
a,b
c
d
b
a
Kundan Tayade,d Judith Gallucci, Hemant Sharma, Sanjay Attarde, Rahul Patil,
a
Narinder Singh* and Anil Kuwar*
A dipodal fluorescent receptor, 2,2’-[ethane-1,2-diylbis(iminoethane-1,1-diyl)]diphenol (2), with amine
and hydroxyl moieties as binding sites has been synthesised and characterized with spectroscopic
methods and single crystal X-ray techniques. The recognition of the anions with receptor 2 was studied
Received 27th September 2013,
Accepted 20th November 2013
DOI: 10.1039/c3dt52690a
1
using UV-Vis and fluorescence spectroscopy. The H-NMR spectroscopic and DFT studies revealed the
www.rsc.org/dalton
distinct recognition of I− ions over the other surveyed anions.
hydrogen-bonding and metal-coordination, have been
Introduction
18–20
reported.
Iodide has a large ionic radius, low charge density
The advance of innovative molecular arrays for the fluoro- and low hydrogen bonding ability, it is challenging to develop
1
–3
4–6
metric detection of anions,
moieties
cations
or neutral specific probes for this entity based on hydrogen bonding.
In the current article, we report a convenient and efficient
7
–10
has gained foremost importance due to their
application in the material sciences, biology and environ- route for the preparation of the noncyclic receptor 2 and fur-
mental management. At the present time, active effort towards thermore explore its new application as an anion sensor. For
the development of molecular complexation systems that con- iodide sensing, the synthesized noncyclic receptor 2 provides
1
1
currently bind anions and is cost-effective is still needed.
two amine and two hydroxyl groups as an array of converging
Normally, amide, urea, amine and hydroxyl groups act as recognition sites. To date, there is no report of a synthesis of
1
2
binding sites for anions.
receptor 2 by the reduction of 2,2′-{ethane-1,2-diylbis[nitrile
Iodide plays a basic role in many important physiological (1E)eth-1-yl-1-ylidene]}diphenol (2) which was herein used for
−
functions, including neurological activity and thyroid the molecular recognition of the I ion. The interesting feature
13–15
function.
Due to its significance in physiological processes, of this work is that there is a Turn-ON fluorescence response
a method for the rapid, sensitive and selective detection of upon interaction with the iodide anion. In the literature, most
iodide in food, pharmaceutical products, and biological samples sensors reported showed fluorescence quenching upon binding
16
1a,21–24
such as urine is of great significance. In addition, elemental with iodide.
However, the Turn-ON signal is always pre-
iodine is commonly involved in chemical synthesis, including ferable over Turn-OFF because it can detect low concentrations
17
pharmaceuticals and dyes. Literature reports revealed that fluo- relative to a dark background. This increases the sensitivity and
25,26
rescent sensing systems measuring the stability of iodide are of authenticity of the receptor towards the analyte.
Another
considerable significance owing to their high simplicity and sen- advantage is the ease of preparation and low detection limit,
sitivity. Nevertheless, relatively few examples of fluorescent already existing sensors have complex structures and multistep
sensors for iodide, based on two recognition strategies including syntheses, e.g. gold nanoclusters, CdSe nanoparticles, use of
PVC membranes, complexes of transition metal ions, etc., as
shown in Table S1.† However, the present work involves a
simple condensation reaction followed by reduction. These
points increase the scope of receptor 2 as a highly selective and
a
School of Chemical Sciences, North Maharashtra University, Jalgaon 425 001,
India. E-mail: kuwaras@gmail.com
b
School of Environmental and Earth Sciences, North Maharashtra University,
sensitive chemosensor for iodide anion.
Jalgaon 425 001 (MS), India
c
Department of Chemistry and Biochemistry, Ohio State University, Columbus, OH
4
3210, USA
d
Department of Chemistry, Indian Institute of Technology, Ropar, Rupanagar,
Results and discussion
Punjab, India. E-mail: nsingh@iitrpr.ac.in
†
Electronic supplementary information (ESI) available. CCDC 952233. For ESI
2
,2′-{Ethane-1,2-diylbis[nitrile(1E)eth-1-yl-1-ylidene]}diphenol
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3dt52690a
(compound 1) was synthesized by refluxing an alcohol solution
3584 | Dalton Trans., 2014, 43, 3584–3588
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of 2-hydroxyacetophenone and ethane-1,2-diamine (2 : 1 molar the methyl group, the hydrogen atoms were added at calcu-
ratio) for one hour. The reaction mixture was cooled and lated positions using a riding model with U(H) = 1.5*Ueq
bright yellow coloured crystals of compound 1 precipitated. (bonded carbon atom). The torsion angle, which defines the
The crystals were filtered off and recrystallized from ethanol to orientation of this methyl group about the C–C bond, was
give bright yellow crystals. Compound 1 was obtained with a refined. The rest of the hydrogen atoms were included in the
2
7
good yield. A further receptor 2 was obtained from com- model at calculated positions using a riding model with
pound 1 by reduction with NaBH
4
in a good yield (Scheme 1).
U(H) = 1.2*Ueq (bonded atom).
The synthesized receptor 2 was characterized by melting
The recognition properties of receptor 2 towards various
1
13
point, IR, H-NMR, C-NMR, mass spectroscopy and X-ray anions were evaluated with different spectroscopic techniques
1
13
crystallographic methods (Fig. S1–S4†). IR, H-NMR, C-NMR, such as UV-Vis, fluorescence and NMR spectroscopy. Firstly,
mass spectroscopy and X-ray crystallographic methods pro- the ability of receptor 2 to bind with anions in CH CN was
3
vided confirmation of the structure of receptor 2. The assigned examined using UV-Vis absorption spectroscopy. For the anion
structure of receptor 2 was further supported with X-ray binding assay, tetrabutylammonium (TBA) salts of various
−
−
−
−
−
−
−
−
crystallography and an ORTEP diagram, as shown in Fig. 1, anions (F , Cl , Br , I , HSO , CN , NO , CH COO and
and the crystallographic details for receptor 2 are listed in
4
3
3
−
2 4
H PO ) were used in the experiment. The introduction of
Table S2.† The CIF file for receptor 2 was deposited in the various anions did not cause a significant change in the
2
8
−
Cambridge Structure Database with CCDC no 952233.
absorption profile of 2 except in the case of I (Fig. 2). The
Examination of the diffraction pattern from a Nonius addition of I− into the solution of receptor 2 (0.1 mM) pro-
Kappa CCD diffractometer indicated a tetragonal crystal duced a dramatic change in the absorption profile (Fig. 2). The
system. The molecule contains a crystallographic two-fold receptor 2 showed a ratiometric estimation of I− having three
E
rotation axis. The N–H and O–H hydrogen atoms were located isosbestic points (I ) at 218, 230 and 260 nm as shown in
on electron density maps and refined isotropically. The –OH Fig. 3. To verify this recognition and find out its mechanism of
group is involved in an intermolecular hydrogen bond with a action, a titration was carried out between receptor 2 (0.1 mM)
−
nitrogen atom and the N–H group is involved in an intramole- and the I anion (Fig. 3). Receptor 2 exhibited a broad absorp-
−
cular hydrogen bond with the oxygen atom. (Table S3†). For tion band centred at 276 nm. The continuous addition of I to
the solution of receptor 2 (0.1 mM) resulted in a new band at
245 nm and a simultaneous decrease in intensity at 276 nm
(
Fig. 3). This new absorption band may arise due to an n–π*
type transition, which could be attributed to hydrogen
−
bonding of the I ion with receptor 2.
The well-defined isosbestic points at 218, 230 and 260 nm
were observed, indicating the formation of a new species upon
−
treatment of receptor 2 with the I ion and it also shows that
−
29
the 2·I complex is an equilibria system. The crystal structure
and DFT optimized structure of 2 reveal that the receptor has a
well-defined cavity enriched with an array of hydrogen
bonding N–H and O–H groups (Fig. 1 and 7a). Therefore, the
driving force behind binding is H-bonding, which is also
Scheme 1 Synthesis route of receptor 2.
Fig. 1 ORTEP diagram of receptor 2 drawn with 50% probability displa-
cement ellipsoids. The molecule contains a crystallographic two fold
rotation axis.
Fig. 2 The anion binding absorption profile of receptor 2 (0.1 mM)
upon addition of tetrabutylammonium salts of various anions (0.5 equiv.
of each).
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Fig. 5 Fluorescence response (ΔF = F − F
0
) of receptor 2 (0.1 mM)
upon addition of 0.5 equiv. of tetrabutylammonium iodide ion and
equiv. of other tetrabutylammonium anion salts in CH CN.
Fig. 3 Changes in absorption spectra of 2 (0.1 mM) upon addition of
−
3
3
various amounts of
equivalents).
I
3
anion (1 mM) in CH CN solution (0–3
The sensing properties of receptor 2 towards I− ion were
further investigated with a titration using fluorescence spec-
troscopy and the results are shown in Fig. S5.† Upon progress-
supported by the DFT optimized structure of 2·I− (Fig. 7b).
Nevertheless, the weaker binding of the iodide ion among
halides on the basis of its basicity is well known. There are
−
−
−
−
ive addition of I (0 to 3 equiv.) to the solution of receptor 2, a
many examples where Cl , Br and I ions bind principally
because of the complementary size of the pseudocavity formed
gradual enhancement in the fluorescence emission maximum
at 340 nm can be observed along with a blue shift of 4 nm.
The enhancement and blue shift could be attributed to intra-
3
0
within the receptor. From the above investigation, we find
that the flexible cavity size in receptor 2, which is confirmed by
the single crystal X-ray structure and DFT calculations, was
−
molecular charge transfer (ICT) interaction between the I ion,
−
having a low charge density, and the electron rich donor array
of amine and hydroxyl groups.
more compatible with the I ion than with other anions.
Next we studied the fluorescence properties of receptor 2
In order to investigate the sensing of I− in a real environ-
ment competitive titrations were performed. The competition
upon the addition of various tetrabutylammonium salts of the
−
−
−
−
−
−
−
−
−
F , Cl , Br , I , HSO , CN , NO , CH COO and H PO
4
4
3
3
2
−
experiments were conducted in the presence of 0.5 equiv. of I
ions in CH CN solution. Fig. 4 and 5 show the emission
3
mixed with an excess of different anions (3 equiv.). It was
observed that receptor 2 selectively recognized I− even in the
presence of other competing anions with moderately low inter-
ference from the other ions (Fig. S6†). These results indicate
that receptor 2 shows a good sensitivity and selectivity towards
spectra of receptor 2 upon addition of various anions. The
−
addition of I caused an enhancement along with a blue shift
in the emission profile of receptor 2 (Fig. 4 and 5). However,
other anions remain almost silent upon excitation at 260 nm.
−
the I ion versus other competitive anions. The binding con-
4
−1
stant was calculated to be 8.6 ± 0.01 × 10 M (Benesi–Hildeb-
rand, Scatchard and Connor’s fitting methodology, Fig. S7–
3
1
−
S9†). The binding stoichiometry between receptor 2 and I
ion was measured with the continuous variation method (Job’s
3
2
plot). The total concentration of host and guest was kept con-
stant while mole fractions were varied. A graph was plotted
between [HG] and [H]/([H] + [G]) which has a maximum at 0.5
−
which corresponds to a 1 : 1 stoichiometry of 2·I (Fig. S10†).
The LC-MS mass spectrum of complex 2·I− ion shows a
peak at m/z 437.40 [(C18
H
25
N
2
O
2
I)·1/2H
2
O], corresponding to
−
[
2·I ] fragment pattern also supports the formation of a 1 : 1
3
3
complex (Fig. S11†). Thus, receptor 2 can be used for the
−
−
selective recognition of I , and it can detect I up to a low con-
centration of 1.38 µM. Besides selectivity and sensitivity,
response time is the third most important parameter for ON-
site detection of an analyte. An ideal receptor should have
high selectivity, sensitivity, low detection limit and a short
response time. Fig. S12† represents the response time of recep-
tor 2 towards the iodide anion. It is observed that the fluo-
rescence intensity becomes stable after 50 s upon addition of
Fig. 4 Changes in fluorescent intensity of receptor 2 (0.1 mM) upon the
−
−
−
−
−
4
addition of various tetrabutylammonium salts of F , Cl , Br , I , HSO ,
−
−
−
−
3 3 2 4 3
CN , NO , CH COO and H PO in CH CN (λex = 276 nm).
3586 | Dalton Trans., 2014, 43, 3584–3588
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complex. The optimization energy is also calculated for each
structure and is listed in Table S4.†
In conclusion, we have synthesized an easy-to-make dipodal
fluorescent anion receptor 2 based upon amine and hydroxyl
moieties which is confirmed by a single crystal X-ray tech-
nique, and investigated its anion binding using UV-visible and
fluorescence spectroscopy. Receptor 2 exhibited ratiometric
estimation of iodide using absorption spectroscopy and an
−
enhancement in fluorescence intensity upon addition of the I
anion. The stoichiometry of the 2·I− complex (1 : 1) was con-
firmed by a Job’s plot and mass spectroscopy. The binding
constant, detection limit, short response time and interference
studies advocate the selectivity and sensitivity of receptor 2
1
Fig. 6 Partial H-NMR spectrum of (A) only receptor 2 and (B) presence
−
towards I .
−
of 1 equivalents of [nBu
4
N]I ion in receptor 2.
Experimental
equiv. of iodide into a solution of receptor 2. Further, to
3
−
1
strengthen the mechanism of binding of I , H-NMR spectra
of receptor 2 were recorded in the presence and absence of
iodide. It is observed that the signals of the –NH and –OH
protons at δ 11.38 and δ 1.67–1.75 vanish upon addition of
All commercial grade chemicals and solvents were procured
1
13
and used without further purification. H and C NMR
spectra were recorded on a Varian NMR mercury system 300
spectrometer operating at 300 and 75 MHz, respectively, in
1
equivalent of I− as shown in (Fig. 6). These results clearly
CDCl
were recorded in CH
3
and DMSO-d
6
. The fluorescence and UV-visible spectra
CN on a fluoromax-4 spectrofluorometer
show that the –NH and –OH protons of receptor 2 form hydro-
gen bonds with iodide.
3
and a Shimadzu UV-24500 in the range of 200–600 nm,
respectively, at room temperature using a 1 cm path length
cell. X-ray crystallographic data was measured on a Nonius
Kappa CCD diffractometer at 150 K using an Oxford Cryo-
systems Cryostream Cooler. The data collection strategy was
set up to measure an octant of reciprocal space with a redun-
dancy factor of 4.6, which means that 90% of these reflections
were measured at least 4.6 times. Phi and omega scans with a
frame width of 0.5° were used. Data integration was done with
Denzo and scaling and merging of the data was done with Sca-
We also tried to grow a single crystal of the I− complex of
receptor 2. Unfortunately, we did not get crystals which are
suitable for a diffraction study. Therefore, to understand the
electronic environment and changes in structure of receptor 2
−
upon complexation with I , DFT calculations were performed
3
4
using the B3LYP/LANL2DZ basis set. The optimized structure
of receptor 2 has more or less a similar geometry to the struc-
ture obtained from crystallography (Fig. 7a). The two pods of
receptor 2 have –OH groups in opposite directions. Three elec-
tronegative atoms (O22, N26 and N25) arrange in a particular
way for the encapsulation of the analyte as shown in Fig. 7a.
This sensor has a selectivity for the iodide anion; therefore
35
lepack. The structure was solved with the direct methods pro-
36
cedure in SHELXS-97. Full-matrix least-squares refinements
2
37
based on F were performed in SHELXL-2013, as incorpor-
optimization is performed with the iodide complex of receptor
38
ated in the WinGX package. Neutral atom scattering factors
were used and include terms for anomalous dispersion.
−
2
. The optimized structure of 2·I showed that two benzene
39
rings are very far from each other due to the large size of
iodide (Fig. 7b). Table S4† illustrates some of the structural Synthesis of receptor 2
parameters for comparison of receptor 2 with the 2·I−
Compound 1 was synthesized by refluxing one mole of ethane-
1,2-diamine (0.60 g, 10 mmol) with two moles of 2-hydroxy
acetophenone (2.72 g, 20 mmol) in ethanol (50 mL) with stir-
ring for 1 h. Compound 1 was obtained and appears as a
yellow crystalline powder in a 70% yield, mp > 250 °C. Further,
receptor 2 was obtained from compound 1 by reduction under
4 3
NaBH in CH OH in a good yield. The X-ray quality crystal of
receptor 2 was obtained by a slow evaporation of a chloroform
solution. Yield 81%, mp ≥ 250 °C. IR (KBr, cm− ): ν = 3291,
1
2
9
1
841, 2556, 1900, 1815, 1591, 1450, 1352, 1242, 1197, 1032,
68, 932, 873, 760 cm−
1
;
1
3
H-NMR (300 MHz, CDCl ): δ =
.42–1.46 (d, 6H, 2-CH ), 1.67–1.75 (bs, 2H, 2-OH), 2.72–2.80
3
Fig. 7 The DFT optimized structure of (A) receptor 2 and (B) the 2·I−
complex calculated at the B3LYP/LANL2DZ level. The red, blue, gray,
purple and dark pink spheres refer to O, N, C, I− atoms, respectively.
(t, 4H, 2-CH
Ar-H), 11.38 (s, 2H, NH). C NMR (75 MHz, CDCl
of DMSO): δ = 21.1, 46.8, 58.9, 116.5, 119.0, 126.4, 127.9, 128.2,
2
–), 3.80–3.89 (q, 2H, 2vCH–), 6.74–7.17 (m, 8H,
1
3
3
= few drops
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+
1
56.9. LC-MS (M + H ) calcd for C18
25 2 2
H N O = 301.19, found 14 K. Wygladacz and E. Bakker, Analyst, 2007, 132, 268.
for C H N O = 301.07. CHN analysis; calcd C, 71.97; H, 15 E. C. V. Butler, Trends Anal. Chem., 1996, 15, 45.
1
8
25 2 2
8
.05; N, 9.33; found C, 71.82; H, 8.19; N, 9.37.
16 S. Jayaraman, L. Teiltler, B. Skalski and A. S. Verkman,
Am. J. Physiol. Cell Physiol., 1999, 277, C1008.
Anion recognition studies
1
7 B. S. Hetzel, The conquest of iodine deficiency: a special
challenge to Australia from Asia, Proc. Nutr. Soc. Austr,
1991, 16, 69.
The anion recognition studies were performed at room temp-
erature, and the solution was shaken before recording absorp-
tion and emission spectra to ensure uniformity. The anion 18 B. Ma, F. Zeng, F. Zheng and S. Wu, Chem.–Eur. J., 2011,
binding ability of receptor 2 in a CH CN media was studied by
17, 14844.
tetrabutyl- 19 Z. He, H. Li and Z. Li, J. Org. Chem., 2010, 75, 4636.
ammonium salt (1 mM) to a standard solution of receptor 2 20 L. Xu, Y. Xu, W. Zhu, Z. Xu, M. Chen and X. Qian, New
0.1 mM, 2 mL) in CH CN and by keeping the solvent ratio
J. Chem., 2012, 36, 1435.
constant throughout the experiment. The binding study was 21 H. Wang, L. Xue and H. Jiang, Org. Lett., 2011, 13, 3844.
3
adding fixed amounts (0.5 equivalent) of
a
(
3
explored by using fluorescence spectroscopy.
22 Z. B. Shang, Y. Wang and W. J. Jin, Talanta, 2009, 78,
64.
23 R.-H. Yang, K.-M. Wang, D. Xiao and X.-H. Yang, Analyst,
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38, 2085.
3
Stoichiometry determination
2
Consecutively, to determine the stoichiometry of the receptor
−
−
2
·I ion binding, solutions of receptor 2 and the I ion were
1
prepared at ratios of 3.0 : 0.0, 2.7 : 0.3, 2.4 : 0.6, 2.1 : 0.9,
2
2
2
2
5 L.-R. Lin, W. Fang, Y. Yu, R.-B. Huang and L.-S. Zheng,
Spectrochim. Acta, Part A, 2007, 67, 1403.
6 L. J. Fan and W. E. Jones, J. Am. Chem. Soc., 2006, 128,
1
0
.8 : 1.2, 1.5 : 1.5, 1.2 : 1.8, 0.9 : 2.1, 0.6 : 2.4, 0.3 : 2.7 and
.0 : 3.0. These solutions were allowed to stand for 1 h with fre-
quent shaking in between. The fluorescence spectra were
recorded for each mixture. The plot of [HG] versus X was used
to determine the stoichiometry of the complex formed. The
fluorescence intensity of the emission peak maximum at
6784.
i
7 R. M. Ramadan, M. S. A. Hamza and S. A. Ali, J. Coord.
Chem., 1998, 43, 31–39.
8 These data can be obtained free of charge from The Cam-
bridge Crystallographic Data centre via www.ccdc.cam.ac.
uk/data_request/cif.
3
41 nm was used for the stoichiometry calculations. The
concentration of [HG] was calculated by the equation of
HG] = (ΔF/F ) [H] and X = Mole Fraction = [H] /[H] + [G]
[
0
i
v
v
v
.
2
3
9 K. Ghosh and T. Sen, Tetrahedron Lett., 2008, 49, 7204.
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3588 | Dalton Trans., 2014, 43, 3584–3588
This journal is © The Royal Society of Chemistry 2014