Positional isomeric chemosensors: Fluorescent and colorimetric cyanide detection based on Si-O cleavage

Article abstract of DOI:10.1039/c7nj01633f

Highly selective and sensitive fluorescent and colorimetric cis/trans isomers 3 were rationally designed and investigated for the fast detection and visualization of cyanide ions (TBACN and NaCN) via CN-promoted Si-O cleavage in aqueous solution and in the solid state. The CN-promoted desilylation induced significant variations of the optical signals of cis- and trans-3, which mainly depend upon the steric arrangement of the Si-O group in relation to the π-extended system.

Full text of DOI:10.1039/c7nj01633f

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Positional isomeric chemosensors: fluorescent
and colorimetric cyanide detection based on Si–O
cleavage†
Cite this:DOI: 10.1039/c7nj01633f
Yayun Chen, Luting Zhao, Hanghai Fu, Caihui Rao, Zheyao Li and
Chuanxiang Liu
*
Received 17th May 2017,
Accepted 4th July 2017
Highly selective and sensitive fluorescent and colorimetric cis/trans isomers 3 were rationally designed
and investigated for the fast detection and visualization of cyanide ions (TBACN and NaCN) via
CN-promoted Si–O cleavage in aqueous solution and in the solid state. The CN-promoted desilylation
induced significant variations of the optical signals of cis- and trans-3, which mainly depend upon the
steric arrangement of the Si–O group in relation to the p-extended system.
DOI: 10.1039/c7nj01633f
rsc.li/njc
The intriguing strategy of cleavage of the Si–O bond for
the sensing of fluoride ions, originally discovered by Kim and
Introduction
The development of cyanide-selective chemosensors is a field Swager in organic solvents, has been popularly developed for
9
that is attracting increasing interest due to the importance of the the design of novel chemodosimeters. Most reported chemo-
1
cyanide ion in biological, industrial, and chemical processes.
dosimeters employ the direct linkage of a Si–O protected
À
The toxic cyanide anion (CN ) interacts strongly with the active fragment to the chromophore/fluorophore (Fig. 1a) or involve
site of cytochrome oxidase, thus causing a decrease in the the insertion of a conjugated system between a Si–O group and
oxidative metabolism. Furthermore, CN ions are widely used a chromophore/fluorophore (Fig. 1b). While significant devel-
in many fields, such as gold mining, electroplating, metallurgy, opments have been made in fluoride-anion sensing, few reports
and the synthesis of fibers and resins. Therefore, there is can be found in the literature regarding the use of desilylation to
a demand to develop efficient methods for the sensitive design chemodosimeters for the detection of cyanide. In
2
À
10
3
1
1
À
and accurate detection of CN ions for various applications. particular, the development of cis/trans isomers for probes based
Compared with conventional analytical methods such as ion- on Si–O cleavage has not yet been extensively investigated.
selective electrodes and ion chromatography, optical methods Herein, we report a simple and efficient protocol for the use of
À
using UV-visible and fluorescence spectroscopy are sensitive, cis/trans isomers for the detection of CN , in which the Si–O
require no expensive equipment, and permit real-time monitoring group and p-conjugated system are connected to the adjacent or
4
of the fluorescence. Therefore, the development of chromogenic reverse sides of the fluorophore (Fig. 1c), in order to provide an
À
and fluorogenic CN -selective chemosensors is of importance
5
in supramolecular chemistry. Recently, a growing number
of optical sensors have also appeared in the literature that
6
a
6b
exploit hydrogen-bonding motifs, oxazines, cationic borane
6
c
6d
6e
derivatives, acridinium salts, b-turn motifs, fluorogenic
ensembles, and reaction-based chemodosimeter approaches
6f,g
6h–k
for the sensing of cyanide. However, few of them displayed
7
differences in binding modes for configurational isomers, thus,
this topic remains extensively underexplored and is deserving
8
of further study.
Department of Chemical and Environmental Engineering, Shanghai Institute of
Technology, 201418 Shanghai, China. E-mail: cxliu@sit.edu.cn
†
Electronic supplementary information (ESI) available: Detailed experimental
Fig. 1 The conventional strategy for (a) anion-induced Si–O cleavage,
and (b) F -triggered cascade reaction; (c) the development of cis/trans
isomers based on Si–O cleavage.
À
procedures, synthesis, spectral and characterization data of the compounds, and
additional spectroscopic data. See DOI: 10.1039/c7nj01633f
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approach to design cis/trans isomers for the development of
configurational chemosensors for anion recognition.
Results and discussion
The synthesis of cis- and trans-3 is shown in Scheme 1. 4-Bromo-
1
,8-naphthalenedicarboxylic anhydride reacted with o-phenylene-
8
diamine to give the isomers cis-1 and trans-1, which were further
condensed with N-hydroxyphthalimide to afford a mixture of
cis-2 and trans-2. The silylation of the isomers 2 with tert-
1
2
butyldiphenylsilyl chloride (TBDPS-Cl) and imidazole in DCM
1
3
yielded the target isomers 3, which were purified by column
chromatography on silica to afford the pure isomers cis-3 and
trans-3. The structures of the two isomers of 3 were confirmed
1
13
by H NMR, C NMR, HRMS, and IR (Fig. S1–S9, ESI†).
Fig. 2 UV-visible spectra of isomers 3 (20 mM) in the presence of different
First, comparative studies were conducted on the selectivity
anions (ca. 42 equiv.) (a) cis-3 in CH
CH CN/H O (4 : 1, v/v), inset: color change (from left to right right: cis-3
O = 4 : 1 v/v) using UV-visible or trans-3 only, CN , NaCN, F , Cl , Br , I , HSO
3 2
CN/H O (9 : 1, v/v) and (b) trans-3 in
of the two isomers of 3 in aqueous environments (cis-3, CH
O = 9 : 1 v/v; trans-3, CH CN/H
spectroscopy (Fig. 2a and b). When tetrabutylammonium cyanide
TBACN) or NaCN (ca. 42 equiv.) was added, a new absorption
peak appeared for each isomer (cis-3 at 520 nm, and trans-3 at
71 nm) in the UV-visible spectra, accompanied by an instanta-
3
CN/
3
2
À
À
À
À
À
À
À
À
À
,
H
2
3
2
4
, H
2
PO
4
, AcO , BF
4
À
À
NO
3
, ClO
4
, NaSCN, Na
2
S); UV-visible titration of isomers 3 (20 mM) with
TBACN (c) cis-3 in CH
3
CN/H
2
O (9 : 1, v/v) and (d) trans-3 in CH
3 2
CN/H O
(
(
4 : 1, v/v), the inset shows the absorbance at (cis-3: 415 nm and 520 nm)
À
and (trans-3: 395 nm and 471 nm) as a function of [CN ].
4
neous color change from light yellow to deep violet (cis-3, Fig. 2a,
inset) or colorless to yellow (trans-3, Fig. 2b, inset). This observed
redshift for the two isomers of 3 indicates different enhanced
p-extended effects upon the liberation of the naphthalenolate
group followed by the CN-promoted Si–O cleavage. Moreover,
À
redshift (105 nm) with increasing concentrations of CN ions,
indicating that the benzene group on the same side as the
binding site Si–O group may provide a larger p-conjugation
effect compared to trans-3 (76 nm). It should be noted that the
2
À
sensing process is very sensitive in CH CN, within only ca. 2.6
(cis-3) or 1.7 equivalents (trans-3) needed to reach the saturation
value (Fig. S12, ESI†). Moreover, competition experiments were
conducted by the addition of CN ions to solutions of cis- or
trans-3 containing equal concentrations of potentially competing
anions (Fig. S13, ESI†), indicating that the two chemosensors
have higher selectivity for CN ions over the other anions tested.
The spectral responses of cis-3 and trans-3 in the absence
and presence of CN at different pH values were also evaluated
Fig. S14, ESI†), which showed CN detection across a moderate
3
except for fluoride and S (Fig. S10, ESI†), other anions such as
À
À
À
À
+
À
À
À
À
À
À
Cl , Br , I , HSO , H PO , AcO , BF , NO3 , ClO4 or SCN
(
4
2
4
4
as their TBA or Na salts, ca. 40 equiv.) did not induce any color
À
change (Fig. 2a and b, inset). This indicates that the probes
show a very typical response based on Si–O cleavage. The
detailed spectral titrations of cis- and trans-3 with TBACN in
CH CN/H O solution are shown in Fig. 2c and d. With the
3 2
addition of increasing concentrations of TBACN (for NaCN, see
À
À
Fig. S11, ESI†), gradual decreases in the absorption peaks at
À
(
415 nm (cis-3) or 395 nm (trans-3) and the simultaneous growth
range of pH values (pH 3–12), indicating that the absorbance of
the probes is relatively insensitive to pH.
In parallel with the absorption binding experiments discussed
above, the changes in the fluorescence emission spectra of the two
of new peaks at 520 nm (cis-3) or 471 nm (trans-3) with clear
isosbestic points at 459 nm (cis-3) or 424 nm (trans-3) were
observed. Interestingly, the spectra of cis-3 exhibited a larger
3 2
isomers of 3 were also monitored in CH CN/H O solvent upon
À
anion sensing. Upon the addition of CN ions to solutions of
cis- or trans-3, significant decreases in the fluorescence intensity at
5
43 nm (cis-3) or 489 nm (trans-3) were observed, and except for
À
2À
À
À
F
and S (Fig. S15, ESI†), none of the other anions (Cl , Br ,
À
4À
À À À À
À
À
I , HSO , H
any significant change in the fluorescence spectra of the probes
Fig. 3a and b). Interference experiments were also performed
2 4 4 3 4
PO , AcO , BF , NO , ClO or SCN ) induced
(
to investigate the fluorescence changes in the two probes in the
presence of the aforementioned anions. Both isomers of 3 were
À
observed to be highly selective for CN ions; there was no
significant change in the fluorescence signals in the presence
of other anions (Fig. S16, ESI†).
Meanwhile, the changes in the fluorescence intensities
À
Scheme 1 Synthetic route of trans-3 and cis-3.
of both isomers of 3 upon titration with CN were further
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Fig. 4 Relative fluorescence intensity at 489 nm for trans-3 in CH
3 2
CN/H O
(
4 : 1 v/v) solution and 543 nm for cis-3 in CH
3
CN/H
2
À
O (9 : 1, v/v) solution
À
in the absence and in the presence of F and CN after 1 min (black),
1
h (green), and 3 h (blue) of reaction.
À
The desilylation pattern between isomer 3 and CN ions was
1
also examined using an H-NMR titration experiment (Fig. S20,
ESI†). When an increasing amount of CN ions was added to
Fig. 3 Fluorescence spectra of isomers 3 (20 mM) in the presence of
À
different anions (a) cis-3 in CH
3 2
CN/H O (9 : 1, v/v) and (b) trans-3 in
3
the solution of trans-3 in CDCl , the signals attributed to
CH CN/H O (4 : 1, v/v), (inset: from left to right: cis-3 or trans-3 only,
3
À
2
À
À
À
À
À
À
À
À
À
À
CN , NaCN, F , Cl , Br , I , HSO
4
, H
2
PO
4
, AcO , BF
4
, NO
3
, ClO ,
4
isomers 3 gradually disappeared with the appearance of a
new set of signals. Upon the addition of ca. 2.0 equivalents of
TBACN, almost all of the original signals completely vanished
and the final spectrum was shifted upfield as a result of the
complete deprotection of the TBDPS group. Further addition of
NaSCN, Na
2
S); emission spectra of isomers 3 upon addition of increasing
À
concentrations of CN (as its TBA salt, 0 to 56.0 equiv.) (c) cis-3 (lex
=
4
59 nm, in CH
CH CN/H O (4 : 1, v/v)), inset: plot of emission intensity (c, cis-3, lem
43 nm) and (d, trans-3, lem = 489 nm) versus TBACN concentration.
3 2
CN/H O (9 : 1, v/v)) and (d) trans-3 (lex = 424 nm, in
3
2
=
5
À
CN did not produce any significant changes in the spectrum.
The upfield shifts were due to the increase in electron density
in the fluorophore through bond propagation due to silyl removal.
The final titration state of trans-3 showed a slightly upfield shift
compared with cis-3 (Fig. S21, ESI†), which indicates that in
the case of trans-3 the benzene moiety on the opposite side as
the oxygen anion may provide greater electron density into the
fluorophore framework compared to cis-3. All these observa-
tions were in good agreement with the absorption and fluores-
cence results noted above.
recorded and are shown in Fig. 3c and d. Upon the addition
of CN (TBACN or NaCN) to the solution of cis-3, the original
À
yellow emission band decreased and a new slight emission band
located at 640 nm eventually appeared in the red region of the
spectrum (Fig. 3c, inset). In the case of trans-3, the emission band
at 489 nm decreased and a moderate new emission band gradually
appeared at 525 nm with a color change from blue to yellow
(Fig. 3d, inset). This fluorescent color change in the two probes
Finally, we examined the suitability of the two isomers of 3
can be directly observed with the naked eye in CH CN solution.
3
14
for visualizing cyanide ions in the solid state. The probes were
For cis-3 (Fig. S17, ESI†), the addition of only 2.3 equivalents of
À
separately adsorbed onto strips of filter paper by immersing the
CN led to the complete disappearance of the fluorescence,
À1
À
3
filter paper into CH CN solutions of each isomer (1.0 mmol L
)
whereas 2.0 equivalents of CN had the same effect on trans-3,
for 5 min and then drying them in air. The test strips were then
immersed for 10 s in aqueous TBACN solutions of varying
concentrations, dried (40 s with a hairdryer in the cold-air-blow
mode at room temperature, followed by 5 min in air), and the
and so the two probes are sufficiently sensitive for cyanide ion
detection using fluorescence spectroscopy. The corresponding
detection limits in the fluorescence mode were determined to be
0.362 mM (cis-3) and 0.339 mM (trans-3) (Fig. S18 and S19, ESI†).
Fig. 4 shows the influence of time on the response of the
two isomers of 3 in aqueous environments in the absence
and presence of TBACN or TBAF. There were almost no time-
dependent effects for cyanide ions in the fluorescence-sensing
process, in that the reduction in emission intensities centered
at 489 nm (trans-3) or 543 nm (cis-3) reached their saturation
values after just one minute as a result of a rapid deprotection
reaction. The probe cis-3 exhibited a comparatively smaller
desilylation in fluorescence in the presence of fluoride: after
1
min, 1 h, and 3 h, ca. 53%, 57%, and 59% of the total amount
of the chemosensor had reacted. For trans-3, almost 90% of the
reaction had occurred after 1 h, which indicated that the high
hydration energy of the fluoride anion in water could inhibit
the deprotection of the TBDPS group.
Fig. 5 The fluorescence changes of the test papers of trans-3 and cis-3
À1
À
(
1.0 mmol L ) with CN ; the test strips were irradiated using a hand-held
UV lamp at 365 nm.
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fluorescence was assessed using a handheld fluorescent lamp. 2-hydroxyisoindoline-1,3-dione (0.58 g, 4.30 mmol), and K
NJC
2
CO
3
Fig. 5 shows the fluorescence intensity and color changes with (1.19 g, 8.59 mmol), and the mixture was stirred 80 1C for 3 h.
À
increasing concentrations of CN ions. The results indicated After the reaction was completed by TLC analysis, the mixture
that the probes can not only be used for in situ/on-site detection was poured into water (50 mL), and filtered, and hydrochloric
of cyanide but also exhibited significant conformational differ- acid was subsequently added dropwise until pH = 2–3. The
ences in the presence of cyanide ions and showed different resulting precipitate was filtered using a Buchner funnel. The
colors for cyanide detection (Fig. S22, ESI†).
residues were dried for 6 h at 80 1C to afford the pure mixtures
of cis-2 and trans-2 (0.70 g, 85.6%). The isomeric mixture
showed a single spot on TLC, and were used directly in the
next step.
Synthesis of trans-3 and cis-3 . To a stirred solution of the
mixture of trans-2 and cis-2 (0.50 g, 1.75 mmol) in DCM (10 mL)
was added tert-butyldiphenylsilyl chloride (TBDPSCl, 0.58 g,
Conclusions
1
3
We have successfully designed and synthesized the trans and cis
isomers of 3 for the rapid and sensitive detection of cyanide
based on a desilylation-triggered chromogenic and fluorogenic
signal. The comparison of the cis and trans isomers for cyanide
sensing via specific Si–O cleavage shows the importance of the
relative position of the benzimidazo/carbonyl group compared
to the Si–O binding site. A simple and inexpensive test strip can
2.11 mmol). The reaction mixture was cooled to 0 1C and
imidazole (0.36 g, 5.29 mmol) was added. After warming to
ambient temperature and stirring for 2 h, the reaction mixture
was diluted with H
HCl and brine, dried over anhydrous Na
2
O and DCM, and then washed with 0.5 M
SO , filtered and
À
2
4
be prepared to determine the CN content of contaminants. The
concentrated under reduced pressure. The crude product was
purified via flash SiO2 chromatography (eluted with PE/EA
strategy involving cis and trans isomers assembled using a
binding site-fluorophore-p-extended system may pave the way
for the development of conformationally controlled sensors, and
efforts are underway in our laboratory to develop a potential CN
detection device for concerned households.
(30 : 1)) to give trans-3 (0.24 g, 26% yield) as a green yellow
solid and cis-3 (0.13 g, 13% yield) as a yellow solid.
À
1
3
trans-3: H-NMR (500 MHz, CDCl ) d 8.91 (d, J = 7.0 Hz, 1H),
8
8
.76 (d, J = 8.5 Hz, 1H), 8.52 (d, J = 7.5 Hz, 1H), 8.63 (d, J =
.0 Hz, 1H), 7.88–7.84 (m, 2H), 7.77 (d, J = 6.5 Hz, 4H), 7.48–7.40
1
3
(
(
m, 8H), 6.70 (d, J = 8.0 Hz, 1H), 1.24 (s, 9H); C-NMR
125 MHz, CDCl ) d: 160.5, 158.6, 149.7, 135.3, 133.5, 132.0,
Experimental section
General
3
1
31.0, 130.6, 128.2, 127.5, 126.7, 126.6, 125.5, 152.1, 119.8,
À1
Unless otherwise noted, solvents and reagents were analytical 115.9, 115.9, 114.7, 26.5, 19.8; IR (KBr, cm ): nmax = 3072,
grade and used without further purification. THF was distilled 1702 (CQO), 1577, 1450, 1387, 1262, 1115, 874, 753, 700, 622, 505;
+
from Na prior to use. UV-visible absorption spectra were obtained HRMS-ESI (m/z): [M + H] (calcd for C34
29 2 2
H N O Si) 525.19983,
on an SHIMADZU UV-1800 spectrophotometer. Fluorescence Found 525.20216.
1
emission spectra were obtained on a Hitach F-4600 Fluorescence
cis-3: H-NMR (500 MHz,CDCl
3
) d: 8.91 (d, J = 8.0 Hz, 1H),
= 3.5 Hz 1H), 8.53 (d, J = 6.0 Hz, 1H), 8.38
NMR spectra were recorded on a Bruker AVANCE III 500 MHz (d, J = 8.5 Hz, 1H), 7.88–7.84 (m, 1H), 7.78 (d, J = 6.5 Hz, 5H),
1 2
spectrophotometer. IR was recorded on a NICOLET 6700 FT-IR. 8.84 (dd, J = 7.5, J
1
13
(
500 MHz for H-NMR) or Bruker AM-400 spectrometer (100 MHz 7.39–7.47 (m, 8H), 6.70 (d, J = 8.0 Hz, 1H), 1.24 (s, 9H); C-NMR
for C-NMR), and chemical shifts were reported in parts per (125 MHz, CDCl ) d 161.1, 155.8, 149.6, 135.4, 132.0, 131.7,
13
3
4
million (ppm, d) downfield from internal standard Me Si (TMS). 131.2, 130.5, 130.1, 128.8, 128.5, 128.2, 126.1, 125.6, 124.7,
À1
Multiplicities of signals are described as follows: s – singlet, 123.1, 119.5, 115.7, 115.0, 26.2, 19.8; IR (KBr, cm ): nmax = 3074,
d – doublet, dd – doublet d, t – triplet, m – multiplet. Coupling 1704 (CQO), 1577, 1428, 1364, 1273, 1113, 1016, 901, 739, 602,
+
constants were reported in hertz (Hz). HRMS was recorded 505; HRMS-ESI (m/z): [M + H] (calcd for C34
H
29
N
2
O
2
Si) 525.19983,
on a solanX 70 FT-MS spectrometer with methanol and water found 525.20205.
(v/v = 1 : 1) as the solvent. Cell imaging was performed using a
Leika TCS SP5 confocal fluorescence microscope. Single-crystal
data were collected on a Bruker APEX2 Smart CCD.
Acknowledgements
8
Synthesis of trans-1 and cis-1 . To an acetic acid solution
We thank the National Natural Science Foundation of China
Grant No. 21202099), the Natural Science Foundation of Shanghai
No. 17ZR1429900) and the Opening Fund of Shanghai Key
(25 mL) of 4-bromo-1,8-naphthalenedicarboxylic anhydride (2.76 g,
(
(
10 mmol) was added o-phenylenediamine (1.10 g, 10 mmol), and
the mixture was refluxed for 3 h. After the reaction was completed
by TLC analysis, the mixture was poured into ice water (50 mL). The
resulting precipitate was filtered and purified by recrystallization
from toluene. The residues were dried for 6 h at 80 1C to afford the
pure mixtures of cis-1 and trans-1 (3.00 g, 85.6%). The isomeric
Laboratory of Chemical Biology for financial support.
Notes and references
1
differences could be assigned by H NMR (Fig. S1, ESI†).
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