A colorimetric probe based on diketopyrrolopyrrole and tert-butyl cyanoacetate for cyanide detection

Article abstract of DOI:10.1039/c5nj01214g

A new colorimetric probe 1 comprising a diketopyrrolopyrrole-based Michael receptor, which recognized cyanide anions with high selectivity, was designed and synthesized. Addition of CN^- aqueous solution to 1 in THF resulted in a rapid color cha

Full text of DOI:10.1039/c5nj01214g

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A colorimetric probe based on
diketopyrrolopyrrole and tert-butyl cyanoacetate
for cyanide detection†
Cite this:DOI: 10.1039/c5nj01214g
Lingyun Wang,* Linhui Zhu and Derong Cao
A new colorimetric probe 1 comprising a diketopyrrolopyrrole-based Michael receptor, which recognized
cyanide anions with high selectivity, was designed and synthesized. Addition of CNꢀ aqueous solution to 1
in THF resulted in a rapid color change from pink to light yellow together with a large blue shift from 530
to 487 nm, while other anions did not induce any significant color change. Furthermore, Michael addition
of cyanide to 1 elicited 94% fluorescence quenching at 640 nm accompanied by appearance of a weak
new emission at 560 nm, which constituted the fluorescence signature for cyanide detection. The
detection limits were determined to be 0.75 mM using the fluorescence spectral changes, which were
far lower than the WHO guideline of 1.9 mM. Moreover, 1-based test strips could successfully detect
CNꢀ in water solutions.
Received (in Montpellier, France)
14th May 2015,
Accepted 6th July 2015
DOI: 10.1039/c5nj01214g
www.rsc.org/njc
to produce a color change, a shortcoming that restricted
its utility.5k Likewise, the oxazine-based indicators required specific
1. Introduction
Cyanide is well known as one of the most toxic species and is biphasic conditions,5q,r while the acridinium salts required an
extremely harmful to mammals. Any accidental release of elevated reaction temperature.5s There is an ever-present need
cyanide to the environment causes serious problems.1 There- to develop new reaction-based CNꢀ sensors, as these can help
fore, the maximum permissive level of cyanide in drinking overcome lingering obstacles in their detection, such as selec-
water is set at 1.9 mM by the World Health Organization tivity, sensitivity, response times, sensor stability, reaction
(WHO). Nevertheless, cyanide salts are still widely used as conditions, etc.
industrial materials in gold mining, electroplating, plastics
On the other hand, diketopyrrolopyrrole (DPP) and its
production and other fields. Therefore, it is highly desirable to derivatives represent a class of brilliant red dyes and exhibit
develop sensitive, selective and quick detection methods for toxic large extinction coefficients, high fluorescence quantum and
cyanide anions.
exceptionally high stability upon exposure to light, weather,
Traditionally, hydrogen bonding or supramolecular inter- and heat, which makes them good candidates for chemo-
actions have been used in the detection of low concentrations sensors.6 Deng et al. used DPP as a fluorophore and a malono-
of cyanide in solution.2,3 These approaches, however, usually nitrile moiety as the reactive site for thiol, which simultaneously
result in poor selectivity over other common anions.4 The displayed the colorimetric and ratiometric signal transduction.6f
burgeoning field of reaction-based indicators has made progress Hua’s group reported a colorimetric and ratiometric fluores-
in this area because of the unique reactivity of CNꢀ toward a cent chemosensor for fluoride ions based on DPP due to
variety of organic functional groups including CQO, CQN, deprotonation of the amide moiety by fluoride ions.6g To date,
CQC, and so on.5 The irreversible formation of chemical bonds only limited DPP-derived probes for reaction-based cyanide
can provide chemodosimetric information and develop ratio- detection have been reported. Jang et al. reported a DPP-
metric fluorescent probes. Unfortunately, none of these is ideal. based colorimetric and fluorescent probe for cyanide detection,
For instance, the cationic borane receptor was very promising in which cyanide attacked the carbonyl carbon atom of the
in that reaction with cyanide took place in water, but failed DPP ring.7 In this regard, we have recently reported a DPP–
indandione conjugate for cyanide detection, which exhibited
high sensitivity and selectivity to cyanide through the exciplex
School of Chemistry and Chemical Engineering, State Key Laboratory of
process.8 However, an improvement in the DPP–indandione
Luminescent Materials and Devices, South China University of Technology,
conjugate system is required because of the emission band
Guangzhou, 510640, China. E-mail: lingyun@scut.edu.cn; Fax: +86 20 87110245;
located at 572 nm, which largely hinders their application in
Tel: +86 20 87110245
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nj01214g in vivo imaging.
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Scheme 1 Synthesis of probe 1.
Considering our objectives, we designed probe 1 (Scheme 1) pyrrole-1,4-dione (compound 5) was synthesized according
keeping in mind the following. (1) The signal reporting of the to our published literature.9
probe derives from the more reactive vinyl moiety activated by
The recognition between 1 and different anions was investi-
electron withdrawing cyano and ester groups, which could gated by UV-Vis and fluorescence spectroscopy in a THF solution
selectively react and enhance the sensitivity of the nucleophilic at room temperature. The stock solution of 1 and anions was
addition reaction between the vinyl group and CNꢀ. (2) Electron- used at a concentration of 10.0 mM. After 1 and anions with
deficient DPP is selected as a chromophore considering its desired concentrations were mixed, they were measured by
many advantageous features including its enhanced vinyl moiety UV-Vis and fluorescence spectroscopy.
reactivity with CNꢀ and strong red fluorescence as well as its
2.2. Synthesis of compound 1
distinct rigid ring structure. (3) The DPP–tert-butyl cyanoacetate
conjugate (1) will have a longer emission band at 640 nm.
Herein, we report 1 as a doubly activated Michael addition type
probe for the colorimetric fluorescence detection of cyanide. The
probe displays high selectivity and sensitivity for CNꢀ over other
anions with a fast response.
A mixture of 5 (56.8 mg, 0.10 mmol), tert-butyl cyanoacetate
(56.4 mg, 0.40 mmol), ammonium acetate (48 mg, 0.63 mmol),
and acetic acid (1 mL) in toluene (20 mL) was refluxed under an
argon atmosphere for 5 h. After cooling to room temperature, the
reaction was quenched by water and the mixture was extracted
using CH2Cl2. The organic layer was dried over anhydrous Na2SO4
and the solvent was removed by rotary evaporation. The crude
product was further purified by column chromatography to give
1 as a dark red solid in 85% yield. m.p.160–161 1C.
2. Experimental
2.1. Chemicals and instruments
1H-NMR (THF-d8, 400 MHz, d), 8.15 (s, 2H), 8.08 (d, 2H), 7.99
(d, 2H), 3.75(t, 4H), 1.62–0.75 (m, 48H). 13C-NMR (THF-d8,
100 MHz, d), 161.20, 160.24, 151.32, 146.36, 133.61, 131.61, 130.46,
128.94, 114.55, 110.26, 105.70, 82.69, 41.00, 28.77, 28.55, 26.14,
22.12, 13.04. HRMS (ESI, m/z), [M + H]+ calcd for (C50H62N4NaO6),
837.4562, found, 837.4571.
Nuclear magnetic resonance spectra were recorded on Bruker
Avance III 400 MHz and chemical shifts are expressed in ppm
using TMS as an internal standard. The UV-Vis absorption
spectra were recorded using a Helios Alpha UV-Vis scanning
spectrophotometer. Fluorescence spectra were obtained using a
Hitachi F-4500 FL spectrophotometer with a quartz cuvette
(path length = 1 cm). KHSO4, NaF, NaCl, KBr, KI, Na2CO3,
NaHCO3, Na2SO3, NaHSO3, Na2SO4, Na2S, CH3COONa, Na3PO4,
KNO3, Na2HPO4 and NaH2PO4 were purchased from Guangzhou
Chemical Reagent Company.
3. Results and discussions
3.1. Synthesis and structural characterization
N-Methyl-2-pyrrolidone (NMP) was dried using CaH2 and Compared with the general Michael acceptors, the doubly acti-
distilled under a nitrogen atmosphere. Other solvents were vated acceptors, in which two electron-withdrawing groups are
obtained from commercially available resources without further attached to the CQC group,10,11 are more reactive,12–15 and allow
purification. 2,5-Dioctyl-3,6-bis(40-formylphenyl)pyrrolo[3,4-c] the Michael addition reaction to occur under mild conditions.
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Clearly, to improve the sensitivity, it is necessary to enhance the
reactivity of the probe to cyanide. We reasoned that this could
be accomplished by increasing the electrophilicity of the b-carbon.
With this in mind, we decided to introduce electron withdrawing
cyano and ester groups, as well as the electron-deficient DPP
moiety to obtain probe 1. Thus, it is anticipated that probe 1
should be highly reactive to CNꢀ.
2,5-Dioctyl-3,6-bis(40-formylphenyl)pyrrolo[3,4-c] pyrrole-1,4-
dione (compound 5) was prepared from p-cyanobenzaldehyde
as a starting material, in four steps following Scheme 1. Probe 1
was obtained by a straightforward aldol-type condensation
reaction of compound 5 with tert-butyl cyanoacetate in 85%
yield as a dark red solid. The 1H NMR spectrum of probe 1
showed the distinctive signals corresponding to the resonance
of vinyl proton at 8.15 ppm. The 1H, 13C NMR and HRMS
spectra of 1 are shown in Fig. S1–S3 (ESI†).
Fig. 2 UV-Vis spectral changes of 1 in THF (10 mM) with increasing
concentrations of the cyanide anion aqueous solution.
3.2. Spectral characteristics of 1 with CNꢀ
The photophysical properties of 1 were studied in THF. 1 showed
two major absorption peaks at 355 and 530 nm. To exploit
its sensing behavior, we first examined the time dependent
changes in the absorption spectra of 1 (10 mM) upon reaction
with CNꢀ (3 equiv.) at room temperature. Generally, reaction-
based chemosensors suffer from a long response time. In our
case, the response of 1 to CNꢀ was found to be very fast. The
addition of CNꢀ aqueous solution elicited not only a significant
absorption increase at around 487 nm but also dramatic absorp-
tion decreases at around 355 and 530 nm (Fig. 1). After 8 minutes,
the UV-Vis spectra of 1 were unchangeable, indicating that a
nucleophilic addition reaction between the vinyl group and
CNꢀ was completed. It is well known that the nucleophilicity of
anions is greatly decreased in water due to hydrogen bond for-
mation between the anions and water molecules. For instance,
Guo’s group reported that the reaction of the anthracene-
indanedione Michael receptor and cyanide could be completed
within 2 minutes at an elevated temperature of 50 1C in 9/1
CH3CN–water, and 10 equiv. of cyanide was required to reach
the spectral saturation.16 Herein, in the presence of 3 equiv. of
cyanide, the nucleophilic CNꢀ addition to 1 occurred very rapidly
(within 8 minutes), indicating high reactivity as the unique feature
of 1, which was impressive as many reported cyanide probes
require high equivalents of cyanide and long reaction time to
reach a maximal spectral signal.17–27
To get insight into the binding of CNꢀ with 1, the absorption
spectra of 1 in THF upon titration with CNꢀ aqueous solution
were recorded. As shown in Fig. 2, the absorption peaks of 1 at
355 and 530 nm gradually decreased following the formation of
a new band centered at 487 nm. Meanwhile, two isosbestic
points at 416 and 472 nm were observed, which implied that new
species with less conjugation were formed. Notably, the ratios of
A497/A530 and A497/A355 increased over 2.15 and 20.43-fold in the
presence of 20 equiv. CNꢀ, respectively.
Fig. 1 Time-dependent absorption intensities of probe 1 (10 mM) in THF at
355 (’ in black), 530 (K in red) and 487 nm (m in blue) in the presence of
CNꢀ (3 equiv.) at room temperature.
Fig. 3 Fluorescence spectral changes of 1 (10 mM) in THF with increasing
concentrations of CNꢀ in THF.
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Fig. 4 (a) UV-Vis absorption spectra and (b) color changes of 1 in THF (10 mM) upon addition of 10 equiv. of each anion aqueous solution.
The CNꢀ sensing property was further examined through and biothiols was also investigated. A dramatic change in the
fluorescent titration studies in detail. As shown in Fig. 3, 1 absorption spectrum induced by CNꢀ was observed, while
showed a major emission peak at 640 nm. Upon addition almost no changes could be found in the presence of other
2ꢀ
of CNꢀ aqueous solution to 1, the PL intensity at 640 nm anions (Fꢀ, Clꢀ, Brꢀ, Iꢀ, CO32ꢀ, HCO3ꢀ, SO32ꢀ, HSO3ꢀ, SO4
,
decreased gradually and a new emission peak at 560 nm S2ꢀ, SCNꢀ, CH3COOꢀ, NO3ꢀ, PO43ꢀ, HPO4 and H2PO4ꢀ) and
appeared. A plateau with the addition of 80 equiv. of CNꢀ with biothiols (cysteine (Cys), homocysteine (Hcy) and glutathione
94% fluorescence quenching at 640 nm was obtained. The inset (GSH)) (Fig. 4a). More importantly, the color change from
of Fig. 3 shows the emission color photographs of L in the pink to light yellow can be clearly observed by the naked
presence of CNꢀ upon excitation at 365 nm, where strong red eye in the presence of CNꢀ, while other anions and biothiols
2ꢀ
emission was absent.
did not induce any significant color change, which suggested
that naked-eye selective detection of CNꢀ became possible
(Fig. 4b).
3.3. Selectivity of 1 with CNꢀ
For the purpose of evaluating the selectivity of 1 to cyanide, the
Meanwhile, only CNꢀ rendered a remarkable ‘‘Turn-Off’’
absorption spectral change of 1 upon addition of other anions fluorescence response, whereas all other anions revealed a
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Fig. 5 (a) Fluorescence and (b) emission color changes of 1 in THF (10 mM) upon addition of 10 equiv. of each anion aqueous solution.
negligible change in the fluorescence spectra of L (Fig. 5a). in Fig. 6. As can be seen, these competitive species did not
In the presence of 80 equivalents of CNꢀ, an emission peak at lead to any significant interference. In the presence of these
640 nm with 94% fluorescence quenching was observed. Fig. 5b anions and biothiols, the CNꢀ still produced similar optical
shows the photographs of L in the presence of different anions spectral changes. These results showed that the selectivity of
and biothiols upon excitation at 365 nm using a portable sensor 1 toward CNꢀ was not affected by the presence of other
UV lamp. The disappearance of the intense red color of the competitive species.
solution upon interaction of L with CNꢀ was observed. How-
ever, other anions and biothiols did not induce any significant fluorescence titration data according to a reported method.28
emission color change. Under optimal conditions, calibration graphs for the determi-
The detection limit of 1 for CNꢀ was calculated based on the
Another important feature of 1 is its high selectivity toward nation of CNꢀ were constructed. The decreased fluorescence
the CNꢀ in the presence of other competitive anions. Changes intensity of the system showed a good linear relationship with
in fluorescence spectra of 1 (10 mM) caused by CNꢀ (80 equiv.) the concentration of CNꢀ in the range of 1–9 mM (R2 = 0.998), as
and miscellaneous competing species (80 equiv.) are shown shown in Fig. 7. The detection limit for CNꢀ was determined to
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Fig. 6 Selectivity of 1. The black bars represent fluorescence intensity
at 640 nm of 1 (10 mM) in THF in the presence of other competitive
species (800 mM). The red bars represent the fluorescence intensity
upon subsequent addition of 800 mM of CNꢀ to the above solution.
Fig. 8 Partial 1H NMR spectrum of 1-CNꢀ in CD3COCD3.
From 1 to 20, control, Fꢀ, Clꢀ, Brꢀ, Iꢀ, CO32ꢀ, HCO3ꢀ, SO32ꢀ, HSO3
,
ꢀ
SO42ꢀ, S2ꢀ, SCNꢀ, CH3COOꢀ, NO3ꢀ, PO43ꢀ, HPO42ꢀ, H2PO4ꢀ, Cys, GSH
and Hcy.
observations clearly indicated that the cyanide anion was added
to the vinyl group, and the anionic species was formed. The
possible reactive mechanism between 1 and CNꢀ ions is shown
in Scheme 2.
3.4. Practical application
Active material-based test strips represent a group of conveni-
ent probing substrates for practical utilization. A 1-based test
strip was thus fabricated by immersing a filter paper into a
THF solution of 1 (1.0 ꢁ 10ꢀ3 M) and drying in air, which
was energy- and cost-effective. The corresponding probing
experiments were carried out subsequently. The results
indicated that this protocol really proved to be effective. The
obvious color change from pink to yellow was observed by
immersing this test strip into aqueous solutions of CNꢀ,
exhibiting colorimetric changes differentiable to the naked
eyes (Fig. 9a). As shown in Fig. 9b, when the 1-exposed test
strip was immersed into aqueous solutions of CNꢀ (0.01 M),
strong red fluorescence disappeared and could be easily dis-
tinguished. Since the color change was rapidly and clearly
detected, the test strips could conveniently detect CNꢀ in water
solutions.
Fig. 7 The linear relationship for the concentration of CNꢀ in the range of
1–10 mM.
be 0.75 mM based on S/N = 3, which was far lower than the WHO
guideline of 1.9 mM cyanide.
To gain further insight into the nature of 1–cyanide inter-
actions, the 1H, 13C NMR and MALDI-TOF-MS spectra were
4. Conclusions
monitored (Fig. S4–S6, ESI†). As shown in Fig. 8 for the partial A colorimetric fluorescent CNꢀ probe (1) was designed with
1H NMR spectrum of [1-CN]ꢀ, it was obvious that the resonance diketopyrrolopyrrole (DPP) as the fluorophore, which shows
signal corresponding to the vinyl proton at 8.16 ppm disappeared absorption at 355 and 530 nm as well as a red emission at
completely, whereas a new signal appeared at 5.25 ppm corres- 640 nm with large Stokes shift (110 nm). In the presence of
ponding to the a-proton (Ha ). Meanwhile, the benzyl protons CNꢀ, the absorption peak shows 43 nm blue-shift and 94%
0
displayed an upfield shift compared to 1 due to the breaking fluorescence quenching at 640 nm. Correspondingly, the color
of the conjugation. The 13C NMR spectrum of [1–CN]ꢀ also of the probe solution changed from pink to light yellow, and
confirmed the reaction between 1 and CNꢀ (Fig. S5, ESI†). the fluorescence was quenched upon interaction with CNꢀ.
Fig. S6 (ESI†) shows a MALDI-TOF-MS spectrum which reveals Test strips for detection of CNꢀ in practical applications are
the cyanide adduct (found for [1-CN]ꢀ, 867.899). All these successfully realized.
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Scheme 2 Schematic illustration of a nucleophilic addition reaction of CNꢀ with the CQC bond of 1.
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Acknowledgements
The support from the National Natural Science Foundation of
China (No. 21274045), the Pearl River in Guangzhou city of
Nova of Science and Technology Special Funded Projects (No.
2012J2200009), the Fundamental Research Funds for the Cen-
tral Universities (2015ZZ037), the Natural Science Foundation
of Guangdong Province (10351064101000000) and National
Basic Research Program of China (2012CB720801) is gratefully
acknowledged.
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