A simple yet highly selective colorimetric sensor for cyanide anion in an aqueous environment

Article abstract of DOI:10.1039/b808589g

The nucleophilic nature of cyanide is used to create a simple, sensitive, and highly effective sensor, 2-(trifluoroacetylamino)anthraquinone 2 (2-TFAQ), for the easy naked-eye detection of very low concentrations of cyanide in an aqueous environment.

Full text of DOI:10.1039/b808589g

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www.rsc.org/obc | Organic & Biomolecular Chemistry
A simple yet highly selective colorimetric sensor for cyanide anion in an
aqueous environment†
Hao-Tao Niu, Dongdong Su, Xueliang Jiang, Wenzhi Yang, Zhenming Yin, Jiaqi He and Jin-Pei Cheng*
Received 21st May 2008, Accepted 11th July 2008
First published as an Advance Article on the web 18th July 2008
DOI: 10.1039/b808589g
The nucleophilic nature of cyanide is used to create a
simple, sensitive, and highly effective sensor, 2-(trifluoro-
acetylamino)anthraquinone 2 (2-TFAQ), for the easy “naked-
eye” detection of very low concentrations of cyanide in an
aqueous environment.
the so-called “naked eye” detection of cyanide in an aqueous
environment. Our strategy is based on the fact that cyanide is
a well known nucleophile and can attack the carbon atom of a
electron-deficient carbonyl group easily.
Compounds 1-(trifluoroacetylamino)anthraquinone
1
(1-
TFAQ) and 2-(trifluoroacetylamino)anthraquinone 2 (2-TFAQ)
(Fig. 1) were synthesized in a single step according to the liter-
ature method:14 1-aminoanthraquinone/2-aminoanthraquinone
and trifluoroacetic anhydride were stirred in nitrobenzene at room
temperature for one hour. Then the mixture was filtered and puri-
fied via column chromatography (yield >90%). Both compounds
were characterized by 1H NMR, 13C NMR, elemental analysis and
mass spectra. A single crystal of 2 suitable for X-ray diffraction
analysis was obtained by diffusion of water into a DMSO solution
of 2. In the solid state, two intramolecular hydrogen bonds (C1AB–
H1AB · · · O3AB and N2AB–H2AB · · · F1AB hydrogen bonds in
Fig. 2a) are present, and a one-dimensional chain is formed
through intermolecular C–H · · · O hydrogen bonds (Fig. 2a).
Fig. 2b shows the trimer induced by one DMSO molecule through
one N–H · · · O hydrogen bond and two C–H · · · O hydrogen
bonds. Selected hydrogen bond parameters are listed in the ESI
(Table S2)†.
Anions are ubiquitous in both the organic and mineral worlds,
and play important roles in biology, medicine, catalysis, and in the
environment.1 Considerable attention has been paid to the design
and synthesis of abiotic receptors for anionic species in the past
two decades, which makes anion recognition one of the fastest
growing disciplines in the field of supramolecular chemistry.2 In
particular, cyanide is one of the most toxic anions and is harmful
to the environment and human health. The binding of cyanide
to cytochrome oxidase reduces the activity of this enzyme and
inhibits oxygen utilization by cells.3 However, the use of cyanide
can not be avoided completely due to its wide application in the
production of organic chemicals and polymers, such as nitriles,
nylon, and acrylic plastics.4 In addition, it is critical to the gold-
extraction process.5 For these reasons, receptors capable of sensing
or binding cyanide selectively are highly desirable. While a number
of receptors for anions have been designed and synthesized,
relatively few have been developed for cyanide, especially in the
aqueous environment.
Several strategies have been developed to detect cyanide,
including the formation of cyanide complexes with transition
metals,6 boron derivatives7 and CdSe quantum dots,8 nucle-
ophilic addition reactions to carbonyl groups,9 the displacement
approach,10 hydrogen-bonding interactions,11 deprotonation12 and
luminescence lifetime measurement.13 However, many receptors
for cyanide reported to date have several limitations as follows: (i)
poor selectivity, especially in the presence of fluoride or acetate,
(ii) requiring specific conditions, such as high temperature or basic
media, (iii) not instantaneously registering the addition of cyanide,
(iv) requiring the use of instruments such as luminoscopes, or UV
light, (v) running the risk of releasing HCN, (vi) only working
in an organic environment, and (vii) complicated synthesis. With
these considerations in mind, we now report a simple yet effective
colorimetric sensor 2-(trifluoroacetylamino)anthraquinone 2 (2-
TFAQ), which overcomes the above limitations, and can achieve
Fig. 1 Structures of anthraquinone-based receptor 2-TFAQ 2 and
reference compound 1-TFAQ 1.
Addition of cyanide to an organic–aqueous solution
(acetonitrile–water mixture) of 2 (50 lM) causes a color change
from colorless to yellow accompanying a new absorption band at
kmax = 429 nm. To confirm the interaction mechanism between
the cyanide and the receptor, 1H NMR titration experiments
were carried out by addition of Bu4NCN to a acetonitrile-d3
solution of 2 (Fig. 3). All the aromatic protons exhibited an upfield
shift, which is compatible with the proposed switching mechanism
(Scheme 1). The UV-vis spectra changes and the corresponding
color changes of 2 are highly solvent sensitive, especially to the
amount of water present in the medium, probably due to the
strong solvation effect in water. Consequently, a 95 : 5 (v/v)
CH3CN–H2O solvent system was used as the optimized condition
for the titration experiments at room temperature. In the case of the
reference compound 1, addition of cyanide produced no obvious
color changes even in a large excess, which can be ascribed to the
Department of Chemistry, State Key Laboratory of Elemento-Organic
Chemistry, Nankai University, Tianjin, 300071, China. E-mail: chengjp@
nankai.edu.cn
† Electronic supplementary information (ESI) available: Synthesis, ex-
perimental details and characterization for 1 and 2; crystallographic
details, UV-vis titrations, and detection limit calculations. CCDC reference
number 688682. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b808589g
3038 | Org. Biomol. Chem., 2008, 6, 3038–3040
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Fig.
2
a) One-dimensional chain formed through intermolecular
C–H · · · O hydrogen bonds; b) DMSO-induced trimer of receptor 2.
Fig. 4 a) The corresponding color changes and b) absorption spectra
Fig. 3 1H NMR spectra of a solution of 2 in acetonitrile-d3 upon the
addition of Bu4NCN.
when 2-TFAQ 2 (50 lM) was treated with 2.0 equiv of various anions
(vials from the left: 2 only, CN−, F−, AcO−, H2PO4−, Cl−, Br−, I−, HSO4
,
−
NO3−, ClO4−, SCN−, N3−) in CH3CN–H2O (95 : 5, v/v); c) Job plot of
2-TFAQ 2 with CN−.
1 : 1 stoichiometry using nonlinear curve fitting analysis,17 based
on the absorption spectral changes at kmax = 429 nm, yields K =
7.7 × 104 M−1. The response time upon exposure to cyanide
is instantaneous, and the selectivity over F− and AcO− is high
(Fig. 5). This is very important because F− and AcO− are the main
interfering ions in cyanide sensing.
The detection limit of cyanide in aqueous environment was
determined. Fig. S3† shows the plot of A − A0 versus the cyanide
concentration in CH3CN–H2O (95 : 5, v/v) solution. A linear
response was observed in the 10–50 lM range. A detection limit
as low as 0.51 lM was found, which makes sensor 2 a powerful
tool for the detection of cyanide in water.
In summary, we have reported the use of 2-(trifluoro-
acetylamino)anthraquinone as a probe for the sensing of cyanide.
Our method is safe, fast, simple to use and inexpensive. The probe
is easy to synthesize and allows sensitive and highly selective
detection of very low concentrations of cyanide in an aqueous
environment.
Scheme 1 Suggested mechanism for off–on switching in the presence of
CN− anion.
strong intramolecular hydrogen bond between the NH and the
anthraquinone oxygen forming a six-membered ring; hence the
intermediate (cyanohydrin) can not be stabilized by the NH.15
To further investigate the selectivity of the sensor 2, 12 anions
of interest, namely, CN−, F−, AcO−, H2PO4−, Cl−, Br−, I−,
HSO4−, NO3−, ClO4−, SCN−, and N3 were added (as their
−
tetrabutylammonium salts) to a solution of 2 in CH3CN–H2O
(95 : 5, v/v) respectively. It can be seen that only CN− induced
a color change from colorless to yellow (Fig. 4a), and addition
of other anions caused no obvious changes either in color or
in the UV-vis spectra, even in a large excess (Fig. 4b). The
resultant Job plot indicated a 1 : 1 receptor–cyanide binding
stoichiometry (Fig. 4c).16 The binding constants calculated from a
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−
HSO4−, NO3−, ClO4−, SCN−, N3
.
Acknowledgements
This project was supported by the Major State Basic Research
Development Program of China (Grant no. G2007CB808000) and
the Natural Science Foundation of China (NSFC no. 20702038).
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