An azo dye-coupled tripodal chromogenic sensor for cyanide

Article abstract of DOI:10.1016/j.tetlet.2011.10.061

A tripodal receptor bearing phenol as a hydrogen bond donor site and azo dye as the signaling subunit was synthesized. The receptor had a high binding affinity for CN^- as signaled by the change in the color of a solution of sensor 4 upon additi

Full text of DOI:10.1016/j.tetlet.2011.10.061

Tetrahedron Letters 52 (2011) 6919–6922
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An azo dye-coupled tripodal chromogenic sensor for cyanide
Doo Youn Lee a, Narinder Singh b, Apuri Satyender a, 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 tripodal receptor bearing phenol as a hydrogen bond donor site and azo dye as the signaling subunit
was synthesized. The receptor had a high binding affinity for CNÀ as signaled by the change in the color
of a solution of sensor 4 upon addition of CNÀ. Using UV–Vis spectroscopy, the system can be used to
quantify 0–19 Â 10À5 mol LÀ1 of CNÀ, and the sensor was found to successfully function in the presence
of other anions.
Received 2 September 2011
Revised 7 October 2011
Accepted 11 October 2011
Available online 23 October 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Chromogenic
Tripodal receptor
Cyanide
Chemosensor
Azo dye
Some plants have developed protection from herbivores by the
production of cyanide-bound sugars in the form of cyanogenic gly-
cosides.1 Small amounts of cyanide are found in certain plant seeds
such as bitter almonds. While cyanide is produced in nature by cer-
tain bacteria, fungi, algae, and plants, it is a noxious waste product
and pollutant due to anthropogenic usage.2 Cyanide has been used
by the mining industry to dissolve gold and silver ores during
extraction in a procedure called the ‘cyanide process’. In addition,
cyanide is also used in electroplating and in nylon and plastics
industry. Despite its widespread use, cyanide presents a health
threat to animals including humans due to its high toxicity.3 Cya-
nide binds with the iron of the enzyme cytochrome c oxidase,
which is the fourth complex in the electron transport chain found
in the mitochondrial membranes of eukaryotic cells. This binding
leads to retarded transport of electrons from cytochrome c oxidase
to oxygen. As a result, the potential ATP production of the cell de-
creases, making the energy production of the biological system
inefficient for vital organs such as the central nervous system
and the heart.4
methods is the use of time-consuming procedures that involve
the use of sophisticated instrumentation.6 On the other hand, chro-
mogenic (optical) cyanide sensors have been actively studied due to
their operational simplicity, low cost, and rapid implementation.7
Optical cyanide chemosensors (designed principally with cova-
lently linked receptor and signaling subunits) generally make use
of hydrogen bond donor sites from urea and thiourea binding
sites.8 However, the use of phenol hydrogen bond donor sites for
anion recognition has been relatively less studied.9 In this study,
we utilized a hydrogen bond donor site from a phenolic hydroxyl
group as the receptor unit that was covalently attached to an azo
dye. With this design strategy, any binding to the hydroxyl group
of the receptor would be indicated by a color change due to a
change in the ring current of the dye. A second hydrogen bond do-
nor site was provided by an amine moiety in such a way that an
elongated anion such as CNÀ could coordinate simultaneously with
both of the binding sites to generate a bis-chelate ring.
The target compound was synthesized through the series of
reactions detailed in Scheme 1. Compound 1, which was recently
reported by our research group,10 underwent a condensation reac-
tion with salicylaldehyde to yield an imine-linked compound.
Compound 2 was obtained by reduction of the imine linkages with
NaBH4.11 The signaling subunit (azo dye) was attached to the tripo-
dal receptor using diazonium salt 3 under aqueous, alkaline condi-
tions.12 It is important to mention that our attempts to synthesize
receptor 4 through the condensation reaction of compound 1 and
the carboxaldehyde-bearing azo group 5 failed.
Thus, the evaluation of cyanide content is often required for
quality control of water, foodstuffs, and other materials. This need
has encouraged researchers to develop methods for cyanide detec-
tion. Although a number of methods are available for cyanide anal-
ysis including voltammetry, potentiometry, electrochemical
methods, and ion chromatography,5 the major limitation of these
Receptor 4 produced a band at kmax = 375 nm in the absorption
⇑
Corresponding author. Tel: +82 337602261; fax: +82 337602182.
E-mail address: dojang@yonsei.ac.kr (D.O. Jang).
spectrum recorded at a 1.0 Â 10À5 mol LÀ1 concentration of the
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.10.061

6920
D. Y. Lee et al. / Tetrahedron Letters 52 (2011) 6919–6922
OH
N
NH2
N
N
NH
N
OH
N
N
1. Zn(ClO4)2, MeOH, reflux
2. NaBH4, THF, reflux
CHO
N
N
H2N
+
H2N
N
HN
H
N
N
N
HO
HO
N
1
2
OH
N
N
NO2
O2N
aq. NaOH
0 o
N
NH
C
N
N
N
N
N
N
Cl-
N2
O2N
HN
H
N
N
3
HO
HO
N
N
O
HO
N
N
NO2
NO2
5
4
Scheme 1. Synthesis of receptor 4.
receptor in a CH3CN:DMSO:HEPES (93:1:6, v/v/v) solvent system.
To evaluate the binding affinity of receptor 4 for various anions,
solutions which contained a 1.0 Â 10À5 mol LÀ1 concentration of
the linear and ratiometric changes in the absorbance profile of
receptor 4 with respect to the concentration of CNÀ.
To determine the stoichiometric ratio of receptor 4 and CNÀ, the
method of continuous variation (Job’s Plot) was used. Figure 4
shows Job’s plot of the absorbance of receptor 4 versus the mole
fraction of the host [H]/([H]+[G]) for a series of solutions in which
the total concentration of host and guest was constant and the
mole fraction of host was continuously varied.13 The results illus-
trate that the receptor–guest complex concentration approaches
a maximum when the mole fraction of the host is about 0.5, which
indicates that the anion forms a 1:1 complex with the receptor. The
association constant Ka of receptor 4 for CNÀ was calculated on the
basis of a Benesi–Hildebrand plot (for the 1:1 complex) and was
found to be 2.3 Â 103 MÀ1 (Fig. 5).14
receptor 4 together with a particular anion (5.0 Â 10À5 mol LÀ1
)
were prepared. The UV–Vis absorption spectrum of each solution
was compared with the absorption spectrum of receptor 4 (re-
corded in the same solvent system). The results, shown in Figure
1A, clearly show the CNÀ-induced changes in the absorption spec-
trum of receptor 4 at two wavelengths, that is, a decrease in the
absorbance at kmax = 375 nm and an increase in the absorbance
at kmax = 520 nm, along with a clear isosbestic point at 425 nm,
indicative of anion binding. This type of shift was expected for
the anion binding that leads to stabilization of the excited state,
thereby decreasing the energy gap between the ground and excited
states. The significant shift in the absorption band was observed
only with cyanide, which supports the design concept for receptor
4 in which it provides two binding sites placed in such a way that
only a linear anion can take advantage of simultaneous coordina-
tion. The ratiometric change in the UV–Vis absorption spectrum
of receptor 4 with various anions is depicted in Figure 1B, and
the change in the color of the receptor solution upon addition of
particular anions is shown in Figure 2.
1H NMR spectrum of receptor 4 showed signals in the range of
6.16–6.43 responsible for aromatic protons and two broad signals
at 7.91 and 8.29 for –NH and –OH protons. The binding sites of
receptor 4 responsible for the coordination of CNÀ anions were
decided by the successive addition of the tetrabutylammonium salt
of cyanide to the solution of 4 taken in CD3CN:DMSO-d6:D2O
(93:1:6, v/v/v) (Fig. 6). Upon complete addition of 10 equiv of CNÀ
to the solution, the signal at 7.91 ppm was shifted upfield by
To further develop the receptor for sensor applications, the
change in the spectrum upon addition of the analyte must directly
relate to the analyte concentration. To evaluate this point, a titration
was carried out with a fixed concentration of receptor 4 (1.0 Â 10
À5 mol LÀ1) and varying concentrations of tetrabutylammonium
cyanide (0–19 Â 10À5 mol LÀ1). Changes in the spectrum on succes-
sive addition of CNÀ are shown in Figure 3A. The titration results
show that the stepwise binding of CNÀ with receptor 4 (Fig. 3A)
corresponded to the same binding pattern as was exhibited by the
one-time binding of excess CNÀ with 4 (Fig. 1A). Figure 3B shows
D
d = 0.25 ppm and the signal at 8.29 ppm was also shifted upfield
D
by d = 0.05 ppm. These upfield shifts on coordination of the anion
authenticate that in the pure host the magnitude of intramolecular
hydrogen bonding is higher than the one that prevailed in the anion
complex. However, the driving forces for the complex formation ap-
pear to be due to the formation of chelate rings. The further addition
of CNÀ did not cause the shift in any signals. On the other hand,
upon addition of 20 equiv of CNÀ the signals for –OH and –NH did
not disappear while the color of the solution changed to red. This
experiment confirms that CNÀ is actually coordinated in the

D. Y. Lee et al. / Tetrahedron Letters 52 (2011) 6919–6922
6921
Figure 1. (A) Change in the UV–Vis absorption spectrum of receptor 4 (1.0 Â 10À5 mol LÀ1) in the presence of the tetrabutylammonium salts of different anions
(5.0 Â 10À5 mol LÀ1) in CH3CN:DMSO:HEPES (93:1:6, v/v/v, pH 7.1 0.1). (B) Ratiometric absorbance (A520/A375) of receptor 4 upon addition of tetrabutylammonium salts of
different anions in CH3CN:DMSO:HEPES (93:1:6, v/v/v, pH 7.1 0.1).
Host
10 µM
30 µM
50 µM
70 µM
90 µM
110 µM
130 µM
150 µM
170 µM
190 µM
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
A
20 µM
40 µM
60 µM
80 µM
100 µM
120 µM
140 µM
160 µM
180 µM
Figure 2. Change in the color of the receptor
4
solution (1.0 Â 10À5 mol LÀ1
mol LÀ1) upon addition of the tetrabutylammonium salt of a particular anion
(5.0 Â 10À5 mol LÀ1) in CH3CN:DMSO:HEPES (93:1:6, v/v/v, pH 7.1 0.1). Captions
correspond to a solution of (A): receptor 4 only, (B): 4 + fluoride, (C): 4 + chloride,
(D): 4 + bromide, (E): 4 + iodide, (F): 4 + acetate, (G): 4 + hydrogen sulfate, (H):
4 + nitrate, (I): 4 + cyanide, (J): 4 + perchlorate, and (K): 4 + hypophosphite.
310
410
510
610
710
Wavelength (nm)
1.6
1.4
1.2
1
B
pseudocavity of the receptor and the color changed as shown in Fig-
ure 2 is not the consequence of anion-mediated deprotonation. No
splitting in signals was observed during the course of titration, indi-
cating that all the pods are in the same chemical environment that
is a symmetrical complex is formed with the coordination sites of-
fered by all the pods.
To explore the possible interference of other anions on cyanide
complexation with receptor 4, competitive binding experiments
were conducted (Fig. 7). The experiments were performed by mea-
suring the absorbance of a series of solutions containing sensor
receptor 4 (1.0 Â 10À5 mol LÀ1), CNÀ (2–15 equiv of the receptor
concentration), and the competitive anion in the same concentra-
tion as CNÀ at 375 nm. The absorbance at 375 nm was found to
be almost identical to that obtained in the absence of interfering
anions. These results confirmed that none of the other anions
caused any interference in the analysis of CNÀ.
0.8
0.6
0.4
0.2
0
0
50
100
[Cyanide], µM
150
200
Figure 3. (A) Changes in the UV–Vis absorption spectrum of receptor
4
(1.0 Â 10À5 mol LÀ1
) upon increasing concentration of tetrabutylammonium
cyanide in CH3CN:DMSO:HEPES (93:1:6, v/v/v, pH 7.1 0.1). (B) Ratiometric
absorbance (A520/A375) profile of receptor 4 with respect to CNÀ concentration
(0–19 Â 10À5 mol LÀ1).

6922
D. Y. Lee et al. / Tetrahedron Letters 52 (2011) 6919–6922
0.25
0.2
In conclusion, chemosensor 4 was found to provide sensitive
and selective recognition of CNÀ through changes in its absorption
spectrum. This sensor offers the interesting opportunity of being
able to monitor the CNÀ concentration in a medium unaffected
by other anions.
0.15
0.1
Acknowledgments
0.05
0
This work was supported by the India–Korea Joint Program of
Cooperation in Science &Technology (2011-0027710), by an ISIRD
grant from IIT Ropar, and by CBMH.
[H] / ([H]+[G])
References and notes
Figure 4. Job’s plot to determine the stoichiometry of the complex between
receptor 4 and CNÀ.
1. (a) White, W. I. B.; Arias-Garzon, D. I.; McMahon, J. M.; Sayre, R. T. Plant Physiol.
1998, 116, 1219–1225; (b) Poulton, J. E. Plant Physiol. 1990, 94, 401–405.
2. Kulig, K. W. Cyanide Toxicity; U.S. Department of Health and Human Services:
Atlanta, 1991.
12
3. Guidelines for Drinking-Water Quality, 3rd Ed.; World Health Organization:
Geneva, 2008; Vol. 1, Chapter 8.
y = 603.75x + 1.4023
R² = 0.9901
10
8
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Poputnikov, D. M.; Spyer, K. M.; Gourine, V. N. J. Physiol. 2007, 585, 305–316.
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Shan, D.; Mousty, C.; Cosnier, S. Anal. Chem. 2004, 76, 178–183; (c) Rao, V. R.;
Suresh, S. R.; Rao, N. B. S. N.; Rajaram, P. Bull. Electrochem. 1997, 13, 327–329;
(d) Christison, T. T.; Rohrer, J. S. J. Chromatogr. A 2007, 1155, 31–39; (e)
Timofeyenko, Y. G.; Rosentreter, J. J.; Mayo, S. Anal. Chem. 2007, 79, 251–255; (f)
Giuriati, C.; Cavalli, S.; Gorni, A.; Badocco, D.; Pastore, P. J. Chromatogr. A. 2004,
1023, 105–112.
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7. (a) Isaad, J.; Achari, A. E. Analytica Chim. Acta 2011, 694, 120–127; (b) Isaad, J.;
Achari, A. E. Tetrahedron 2011, 67, 5678–5685; (c) Isaad, J.; Achari, A. E.
Tetrahedron 2011, 67, 4939–4947; (d) Isaad, J.; Achari, A. E. Tetrahedron 2011, 67,
4196–4201; (e) Isaad, J.; Perwuelz, A. Tetrahedron Lett. 2010, 51, 5810–5814; (f)
Park, I. S.; Heo, E.-J.; Kim, J.-M. Tetrahedron Lett. 2011, 52, 2454–2457; (g) Xu, Z.;
Pan, J.; Spring, D. R.; Cui, J.; Yoon, J. Tetrahedron 2010, 66, 1678–1683; (h) Chen,
X.; Nam, S.-W.; Kim, G.-H.; Song, N.; Jeong, Y.; Shin, I.; Kim, S. K.; Kim, J.; Park, S.;
Yoon, J. Chem. Commun. 2010, 46, 8953–8955; (i) Poland, K.; Topoglidis, E.;
Durrant, J. R.; Palomares, E. Inorg. Chem. Commun. 2006, 9, 1239–1242.
8. (a) Odagoa, M. O.; Colabelloa, D. M.; Lees, A. J. Tetrahedron 2010, 66, 7465–7471;
(b) Aldrey, A.; Núñez, C.; García, V.; Bastida, R.; Lodeiro, C.; Macías, A. Tetrahedron
2010, 66, 9223–9230; (c) Kumar, V.; Kaushik, M. P.; Srivastava, A. K.; Pratap, A.;
Thiruvenkatam, V.; Guru Row, T. N. Anal. Chim. Acta 2010, 663, 77–84.
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10. Lee, D. Y.; Singh, N.; Kim, M. J.; Jang, D. O. Org. Lett. 2011, 13, 3024–3027.
11. Synthesis of compound 2: A solution of compound 1 (125 mg, 0.21 mmol), 2-
6
4
2
0
0.004
0.006
0.008
0.01
0.012
0.014
0.016
1/[G]
Figure 5. Benesi–Hildebrand plot to determine the stability constant of the
complex between receptor 4 and CNÀ.
hydroxybenzaldehyde (102 mg, 0.83 mmol), and
a catalytic amount of
Zn(ClO4)2 in MeOH (12 mL) was stirred at 65 °C for 12 h. The reaction
progress was monitored by TLC. Upon completion of the reaction, the solvent
was evaporated, and the resulting solid was washed with ether to obtain the
imine. The crude imine was dissolved in MeOH/THF (1:2) (12 mL) and was
treated with NaBH4 (80 mg, 2.1 mmol) at room temperature. The reaction
mixture was heated at 65 °C for 12 h. The solvent was evaporated, water was
poured into the reaction mixture, and the organic material was extracted with
ethyl acetate. The organic layer was dried over anhydrous MgSO4. After
filtration and evaporation, the residue was purified by column
Figure 6. Family of 1H NMR spectrum of receptor 4 upon successive addition of
tetrabutylammonium cyanide in CD3CN:DMSO-d6:D2O (93:1:6, v/v/v).
chromatography on silica gel (hexanes/EtOAc, 3:7) to give
a white solid
(142 mg, 74%); mp 265–267 °C, 1H NMR (DMSO-d6, 400 MHz) d 0.72 (br s, 9H, –
CH3), 2.67 (br s, 6H, –CH2, J = 6.9 Hz), 4.50 (d, 6H, –CH2, J = 5.4 Hz), 5.22 (s, 6H, –
CH2), 6.00 (d, 3H, ArH, J = 5.4 Hz), 6.28 (br, 3H, –NH), 6.79 (d, 3H, ArH,
J = 7.7 Hz), 6.85 (t, 3H, ArH, J = 7.7 Hz), 6.89 (t, 3H, ArH, J = 7.3 Hz), 7.09 (t, 3H,
ArH, J = 7.3 Hz), 7.11 (d, 3H, ArH, J = 7.7 Hz), 7.25 (d, 3H, ArH, J = 7.3 Hz), 7.77
(br s, 3H, ArH), 11.58 (br s, 3H, –OH). 13C NMR (DMSO-d6, 100 MHz) d 14.5,
23.1, 41.8, 42.1, 60.7, 109.2, 114.7, 117.1, 118.9, 119.0, 120.3, 126.6, 128.5,
130.2, 133.6, 140.8, 145.0, 154.8, 155.9. HRMS (FAB) Calcd for C57H58N9O3
([M]+H+): 916.4663. Found: 916.4670.
0.35
0.3
0.25
Cyanide
Cyanide+Fluoride
Cyanide+Chloride
Cyanide+Bromide
Cyanide+Iodide
Cyanide+Acetate
Cyanide+Hydrogen sulfate
Cyanide+Hypophosphite
Cyanide+Perchlorate
Cyanide+Nitrate
0.2
12. Synthesis of compound 4: Compound
2
(100 mg, 0.11 mmol) in sodium
solution of 4-nitrophenyl
hydroxide (1 mol LÀ1
,
2.5 mL) was added to
a
0.15
diazonium salt (81 mg, 0.44 mmol) in water (2 mL) at 0 °C, and the mixture
was stirred for 1 h. The precipitated solid was filtered, washed successively
with cold water and ether, and then dried in vacuo to afford a dark orange solid
(104 mg, 70%); mp 202–204 °C (decomposed), 1H NMR (DMSO-d6, 400 MHz) d
0.74 (br, 9H, –CH3), 2.69 (br, 6H, –CH2), 4.51 (s, 4H, –CH2), 4.65 (s, 2H, –CH2),
5.22 (s, 6H, –CH2), 6.02 (d, 3H, ArH, J = 7.4 Hz), 6.28 (br, 3H, -NH), 6.77 (d, 3H,
ArH, J = 7.4 Hz), 6.88 (t, 3H, ArH, J = 7.4 Hz), 7.01–7.27 (m, 8H, ArH), 7.69–7.93
(m, 9H, ArH), 8.00–8.16 (m, 7H, ArH). 13C NMR (DMSO-d6, 100 MHz) d 14.6,
23.1, 42.0, 109.0, 114.3, 116.8, 118.9, 119.0, 119.4, 120.7, 126.0, 128.6, 130.0,
133.1, 145.3, 154.1, 155.9. Anal. Calcd for C75H66N18O9: C, 66.07; H, 4.88; N,
18.49. Found: C, 66.21; H, 4.68; N, 18.37.
0.1
0.05
0
0
3
6
9
12
15
[CN-] (Equivalents)
Figure 7. Analysis of CNÀ in the presence of other anions in CH3CN:DMSO:HEPES
(93:1:6, v/v/v, pH 7.1 0.1) (the absorbance at kmax = 375 nm was used for
calculations).
13. Job, P. Ann. Chim. 1928, 9, 113–203.
14. Benesi, H.; Hildebrand, H. J. Am. Chem. Soc. 1949, 71, 2703–2707.