Dipodal fluorescent chemosensor for Cu2+ and resultant complex as a chemosensor for iodide

Article abstract of DOI:10.1016/j.tetlet.2012.05.067

A dipodal receptor was synthesized by condensation of isophthalaldehyde and p-toluenesulfonylhydrazide. The receptor was found to be selective for Cu ²⁺ recognition in CH₃CN. The resultant Cu²⁺ receptor complex selectively

Full text of DOI:10.1016/j.tetlet.2012.05.067

Tetrahedron Letters 53 (2012) 3900–3902
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Tetrahedron Letters
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Dipodal fluorescent chemosensor for Cu2+ and resultant complex as a
chemosensor for iodide
Hanna Goh a, Min Joung Kim a, Preeti Saluja b, Narinder Singh b, Doo Ok Jang a,
⇑
a Department of Chemistry, Yonsei University, Wonju 220-710, Republic of Korea
b Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A dipodal receptor was synthesized by condensation of isophthalaldehyde and p-toluenesulfonylhydraz-
ide. The receptor was found to be selective for Cu2+ recognition in CH3CN. The resultant Cu2+ receptor
complex selectively recognized iodide through cation displacement assay in a CH3CN/H2O (8:2, v/v) sol-
vent system.
Received 10 April 2012
Revised 9 May 2012
Accepted 14 May 2012
Available online 26 May 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Cu(II)
Iodide
Chemosensor
Fluorescent
Recognition
The emergence of molecular devices for biologically important
cations and anions has led to a parallel need to develop multifunc-
tional sensors.1 During the last few decades, various analytical
methods have been reported for the investigation of cations and
anions.2 Among these methods, fluorescent probes have become
widely used due to their high sensitivity.3 Various classes of fluo-
rophores, such as quantum dots, fluorescent proteins, organic dyes,
and metal complexes, have been successfully employed for analyt-
ical studies.4 Nevertheless, there is room to develop new fluores-
cent probes that can act as multifunctional probes.5
receptor was also synthesized with the same type of binding sites as
that of the dipodal receptor (Scheme 1).8
The UV–vis absorption spectrum was recorded with a 10 lM
concentration of receptor 1 in CH3CN. It displayed a band at
kmax = 271 nm (Fig. S1). Receptor 1 excited at kmax = 271 nm and
exhibited weak emission at kmax = 385 nm. The metal recognition
properties of receptor 1 were inspected by changes in its fluores-
cence intensity in the presence of various metal ions (Fig. 1). Upon
addition of 4 equiv of Cu2+ ions to a CH3CN solution of receptor 1
(10 lM), the fluorescence intensity enhanced and blue-shifted.
A few recent reports have focused on the concept of cation
displacement assay in sensor systems. This idea relies on the
assumption that an organic receptor acts as a sensor for a cation
and that the resulting metal complex acts as sensor for an anion.6
In this strategy, an organic receptor is fabricated with binding sites
for cation recognition. Cation recognition modulates the fluores-
cence signal of the pure organic receptor. Upon addition of an an-
ion to the complex, interactions between the metal complex and
the anion displace the metal ion from the coordination sphere of
the organic receptor. Thus, the original fluorescence signal of the
receptor is restored. This strategy has the advantage that synthet-
ically simple receptors can be tuned as efficient fluorescent probes.
To develop simple receptor systems, we synthesized a dipodal
receptor by the condensation of isophthalaldehyde and p-toluene-
sulfonylhydrazide.7 To establish a dipodal framework, a monopodal
However, under the same conditions, no obvious changes were ob-
served for other tested metal ions. The metal binding ability of
receptor 2 was similarly investigated, and receptor 2 was found to
have a non-selective binding profile (Fig. S2). This result explains
the judicial choice of binding sites in the design of receptor 1.
Fluorescent titration was performed to gain insight into the rec-
ognition properties of receptor 1 as a Cu2+ sensor (Fig. 2A). Upon
addition of Cu2+ to receptor 1, the emission band at 313 nm gradu-
ally increased. Cu2+-induced changes in the fluorescence signal of
receptor 1 are consequences of a modulated CT band9 and molecular
rigidity due to complex formation.10 Free receptor 1 has a highly
flexible structure that may undergo non-radiative decay. Metal
complexation results in the structure’s rigidity. This rigidity negates
the non-radiative decay, resulting in increased fluorescence inten-
sity. Conversely, close binding of a metal ion to the fluorophore
can modulate the energy gap and cause a shift in the emission kmax
.
Titration of receptor 1 with Cu2+ ions confirmed the modulation of
⇑
Corresponding author.
E-mail address: dojang@yonsei.ac.kr (D.O. Jang).
charge transfer transitions due to the close binding of Cu2+ to the
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.05.067

H. Goh et al. / Tetrahedron Letters 53 (2012) 3900–3902
3901
NH2
HN
H
H
H
H
H
S
N
O
N
O
N
O
O
O
HN
S
PhCHO, Zn(ClO4)2
MeOH, rt, 2 h
HN
S
NH
S
O
O
O
O
O
Zn(ClO4)2, MeOH, rt, 2 h
2
1
Scheme 1. Synthesis of receptors.
A
A
B
B
Figure 1. (A) Changes in fluorescence intensity of receptor 1 (10
of a particular metal nitrate (40
Fluorescence ratio ((IÀI0)/I0) of receptor 1 (10
of a particular metal nitrate (40 M) in CH3CN.
l
M) upon addition
l
M) in CH3CN (excitation at kmax = 271 nm); (B)
l
M) at kmax = 313 nm upon addition
l
Figure 2. (A) Fluorescence spectra changes of receptor 1 (10
Cu2+ (0–40
absorbance of receptor 1 (10
l
M) upon addition of
l
M) in CH3CN (excitation at kmax = 271 nm); (B) Changes in UV–vis
fluorophore of receptor 1. Titration progress was monitored by
UV–vis spectroscopy (Fig. 2B). With a continuously increasing con-
centration of Cu2+ ions, absorption at 271 nm gradually decreased
along with the emergence of a new band at 325 nm. On the basis
of non-linear fitting analysis of titration, the association constant
for receptor 1 and Cu2+ was calculated to be 1.55 Â 105 MÀ1
(Fig. S3). 11 On the basis of Job’s plot, the stoichiometry of the com-
l
M) upon addition of Cu2+ (0–78
l
M) in CH3CN.
plex formed between receptor 1 and Cu2+ was found to be 1:1
12
(Fig. S4).
Furthermore, the same stoichiometry was confirmed
by a mass spectrum (Fig. S5) showing m/zÀ= 298.2, which corre-
sponds to [M+H]2+, where M is 1ÁCu2+ + NO3
.
A 1:1 solution of receptor 1 (10 l lM) in a
M) and Cu2+ ions (10
CH3CN/H2O (8:2, v/v) solvent system was prepared to investigate
the utility of 1ÁCu2+ as an anion sensor. The water fraction of solvent
was deliberately taken to investigate anion content in aqueous
medium. Anion recognition under aqueous medium is difficult be-
cause the anion has to compete with solvent for anion recognition
sites. However, cation displacement assay has the advantage of en-
abling anion recognition even under semi-aqueous medium. The
Figure 3. Changes in fluorescence intensity of receptor 1ÁCu2+ (10
lM) upon
addition of tetrabutylammonium anion salt (50 lM) in a CH3CN/H2O (8:2, v/v)
fluorescence spectrum of 1ÁCu2+ (10
lM) upon addition of 50 lM
solvent system (excitation at kmax = 271 nm).
concentration anion is shown in Figure 3. Careful analysis of Figure
3 shows that the presence of some anions influences the magnitude
of the fluorescence intensity of 1ÁCu2+. However, upon addition of
Next, a series of competitive titrations were attempted to deter-
mine the limit at which iodide could be measured in the presence
of other competing anions. Figure S6 shows that iodide could be
50 lM iodide, approximately 95% of the fluorescence intensity that
originated from 1ÁCu2+ was quenched.5,13

3902
H. Goh et al. / Tetrahedron Letters 53 (2012) 3900–3902
Cu2+
H
H
H
H
N
O
N
O
N
O
N
O
HN
S
NH
S
Cu2+
HN
S
NH
S
O
O
O
O
I-
Cu2+
I-
I-
Scheme 2. Proposed mechanism for the recognition behavior of receptor 1ÁCu2+ for iodide.
Table 1
References and notes
(A) Truth table for fluorescence emission of receptor 1 with Cu2+ and iodide as
chemical inputs; (B) combined logic gate represents A and B as inputs and Q as output
1. (a) Andréasson, J.; Pischel, U.; Straight, S. D.; Moore, T. A.; Moore, A. L.; Gust, D.
J. Am. Chem. Soc. 2011, 133, 11641–11648; (b) Bozdemir, O. A.; Guliyev, R.;
Buyukcakir, O.; Selcuk, S.; Kolemen, S.; Gulseren, G.; Nalbantoglu, T.; Boyaci, H.;
Akkaya, E. U. J. Am. Chem. Soc. 2010, 132, 8029–8036; (c) Konry, T.; Walt, D. R. J.
Am. Chem. Soc. 2009, 131, 13232–13333; (d) Kaur, N.; Singh, N.; Cairns, D.;
Callan, J. F. Org. Lett. 2009, 11, 2229–2232.
A
Input A (Cu2+
)
Input B (IÀ)
Output Q (Flu@313)
0
0
1
1
0
1
0
1
0
0
1
0
2. (a) Pandey, R.; Kumar, P.; Singh, A. K.; Shahid, M.; Li, P.-Z.; Singh, S. K.; Xu, Q.;
Misra, A.; Pandey, D. S. Inorg. Chem. 2011, 50, 3189–3197; (b) Halámek, J.; Tam,
T. K.; Chinnapareddy, S.; Bocharova, V.; Katz, E. J. Phys. Chem. Lett. 2010, 1, 973–
977; (c) Moyer, B. A.; Delmau, L. H.; Fowler, C. J.; Ruas, A.; Bostick, D. A.; Sessler,
J. L.; Katayev, E.; Pantos, G. D.; Llinares, J. M.; Hossain, M. A.; Kang, S. O.;
Bowman-James, K. Adv. Inorg. Chem. 2007, 59, 175–204; (d) Pramanik, A.;
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Lee, K. S.; Yu, H.; Hossain, M. A. Org. Biomol. Chem. 2011, 9, 4444–4447.
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2009, 253, 893–962; (c) Valeur, B.; Leray, I. Coord. Chem. Rev. 2000, 205, 3–40.
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(b) Ruiter, G. D.; van der Boom, M. E. Acc. Chem. Res. 2011, 44, 563–573; (c) Soe,
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4900–4902; (e) van Dongen, E. M. W. M.; Evers, T. H.; Dekkers, L. M.; Meijer, E.
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R.; Cui, J.; Yoon, J. Tetrahedron 2010, 66, 1678–1683.
B
A
B
Q
Q = A AND NOT B
measured accurately by receptor 1ÁCu2+ in the presence of equal
amounts of any another tested anion. This may be due to the high-
er binding affinity of iodide with receptor 1ÁCu2+. The detection
limit was calculated to be 1.9 l
M.14 The proposed mechanism
underlying the recognition behavior of receptor 1ÁCu2+ for iodide
is shown in Scheme 2.
From the logic gate viewpoint, Cu2+ (input A) and iodide (input
B) satisfy the Boolean algebra of a gate, as shown in Table 1.15 The
logic gate output is defined as fluorescence intensity at 313 nm. If
present alone, receptor 1 does not exhibit any fluorescence emis-
sion at 313 nm. However, if present with Cu2+, emission is shown
at 313 nm. Receptor 1 in the presence of iodide or Cu2+ and iodide
exhibits no fluorescence emission. The fluorescence emission at
313 nm (output Q) shows combined logic gate with Cu2+ (input
A) and iodide (input B).
7. Synthesis of compound 1: A solution of isophthalaldehyde (179 mg, 1.34 mmol)
and a catalytic amount of Zn(ClO4)2 in MeOH (10 mL) were stirred for 30 min at
room temperature.
A solution of p-toluenesulfonylhydrazide (500 mg,
2.68 mmol) in MeOH (10 mL) was slowly added to the solution above. The
reaction mixture was stirred for 2 h at room temperature. After evaporation of
the solvent, the residue was recrystallized in acetone/CH2Cl2 (1:3, v/v),
resulting in a solid with 93% yield (586 mg). Mp 119–120 °C; IR (KBr) 3200,
1054 cmÀ1 1H NMR (400 MHz, DMSO-d6): d 2.35 (s, 6H, –CH3), 7.40 (m, 5H,
;
Ar), 7.55 (m, 2H, Ar), 7.76 (m, 5H, Ar), 7.92 (s, 2H, –N@C–H), 11.53 (s, 2H, –NH);
13C NMR (100 MHz, DMSO-d6): d 20.9, 124.5, 127.1, 128.2, 129.2, 129.6, 134.2,
136.1, 143.4, 146.2. Anal Calcd for C22H22N4O4S2: C, 56.15; H, 4.71; N, 11.91.
Found C, 56.31; H, 4.78; N, 12.22.
In conclusion, a receptor with imine linkages was synthesized.
The receptor’s recognition properties toward various metal ions dis-
closed that its pseudocavity is compatible for recognizing Cu2+ ions.
The resultant complex 1ÁCu2+ selectively recognized iodide through
cation displacement assay in a CH3CN/H2O (8:2, v/v) solvent system.
8. McMahon, R. J.; Abelt, C. J.; Chapman, O. L.; Johnson, J. W.; Kreil, C. L.; LeRoux, J.
P.; Mooring, A. M.; West, P. R. J. Am. Chem. Soc. 1987, 109, 2456–2469.
9. Martínez-Máñez, R.; Sancenón, F. Chem. Rev. 2003, 103, 4419–4476.
10. Haugland, R. P. Handbook of Fluorescent Probes and Research Products, 8th Ed.;
Eugene: Molecular Probes, 2001.
11. Valeur, B. Molecular Fluorescence. Principles and Applications; Weinheim: Wiley,
2002. pp 337–348.
12. Job, P. Ann. Chim. 1928, 9, 113–203.
Acknowledgments
13. For some examples for sensing iodide ions: (a) James, D.; Rao, T. P. Electrochim.
Acta 2012, 66, 340–346; (b) Wang, H.; Xue, L.; Jiang, H. Org. Lett. 2011, 13,
3844–3847; (c) Li, H.; Han, C.; Zhang, L. J. Mater. Chem. 2008, 18, 4543–4548;
(d) Singh, N.; Jang, D. O. Org. Lett. 2007, 9, 1991–1994; (e) Ho, H. A.; Leclerc, M.
J. Am. Chem. Soc. 2003, 125, 4412–4413.
This work was supported by the India-Korea Joint Program of
Cooperation in Science & Technology (2011-0027710) and the CSIR
project. PS would like to thank UGC India for his research fellowship.
14. Shortreed, M.; Kopelman, R.; Kuhn, M.; Hoyland, B. Anal. Chem. 1996, 68, 1414–
1418.
Supplementary data
15. (a) Strack, G.; Ornatska, M.; Pita, M.; Katz, E. J. Am. Chem. Soc. 2008, 130, 4234–
4235; (b) Margulies, D.; Felder, C. E.; Melman, G.; Shanzer, A. J. Am. Chem. Soc.
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Willner, I. Org. Biomol. Chem. 2006, 4, 989–991; (d) Kou, S.; Lee, H. N.; Noort, D.
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Supplementary data spectroscopic data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.tetlet.2012.05.067.