Coumarin-Cu(II) ensemble-based cyanide sensing chemodosimeter

Article abstract of DOI:10.1021/ol2018856

An "ensemble"-based chemodosimeter 1-Cu(II) for cyanide detection is reported. 1-Cu(II) can recognize a cyanide ion over other anionic species to show a marked fluorescence enhancement under aqueous conditions. "Off-on" fluorescence change of 1-Cu(II) is proceeded by addition of cyanide, which induces decomplexation of the Cu(II) ion from nonfluorescent 1 followed by hydrolytic cleavage of the resulted Schiff base to give a strongly fluorescent coumarinaldehyde (2). The selective detection of cyanide with 1-Cu(II) for biological application was also performed in HepG2 cells.

Full text of DOI:10.1021/ol2018856

ORGANIC
LETTERS
2
011
Vol. 13, No. 19
056–5059
Coumarin-Cu(II) Ensemble-Based Cyanide
Sensing Chemodosimeter
5
†
Hyo Sung Jung, Ji Hye Han, Zee Hwan Kim, Chulhun Kang,* and
‡
†,§
,‡
,†
Jong Seung Kim*
Department of Chemistry, Korea University, Seoul, 136-704, Korea, The School of
EastꢀWest Medical Science, Kyung Hee University, Yongin, 446-701, Korea, and
Research Institute for Natural Sciences, Korea University, Seoul, 136-701, Korea
kangch@khu.ac.kr; jongskim@korea.ac.kr
Received July 13, 2011
ABSTRACT
An “ensemble”-based chemodosimeter 1ꢀCu(II) for cyanide detection is reported. 1ꢀCu(II) can recognize a cyanide ion over other anionic
species to show a marked fluorescence enhancement under aqueous conditions. “Offꢀon” fluorescence change of 1ꢀCu(II) is proceeded by
addition of cyanide, which induces decomplexation of the Cu(II) ion from nonfluorescent 1 followed by hydrolytic cleavage of the resulted Schiff
base to give a strongly fluorescent coumarinaldehyde (2). The selective detection of cyanide with 1ꢀCu(II) for biological application was also
performed in HepG2 cells.
4
Cyanide isextremely toxic tomammals withevena small
amount of this species, leading to vomiting, loss of con-
imaging studies. Much effort has been drawn to develop
the chemosensors for various biological substances such as
cations, anions, sugars, and proteins. In particular, the
fluorescent sensors have been mainly focused on cation
targeting and on their corresponding bioimaging studies in
1
sciousness, and eventually to death. Nevertheless, it has
been produced in large quantities and used in various
industrial processes, which has led to environmental con-
2
tamination as well. Therefore, its concentration in drink-
5
living cells. However, bioimaging studies of fluorescent
chemosensors toward anions have been rarely reported,
probably because of low solubility in aqueous media, low
ing water is limited to less than 2 μM according to the
World Health Organization. In this regard, the sensitive
3
6
detection method of cyanide such as fluorescence sensing
probes has attracted considerable attention in recent years.
Fluorescence sensing of specific anions via suitable
chemosensors is a valuable technique with high sensitivity,
rapid response, and easyperformance, offering application
methods not only for in vitro assays but also for in vivo
selectivity, and low sensitivity.
(
4) (a) Geddes, C. D.; Lakowicz, J. R. Topics in Fluorescence Spectro-
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Chem. Rev. 2007, 107, 3780. (c) de Silva, A. P.; Gunaratne, H. Q. N.;
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J.; Kim, J. S. Chem. Soc. Rev. 2011, 40, 3416. (d) Domaille, D. W.; Que,
E. L.; Chang, C. J. Nat. Chem. Biol. 2008, 4, 168. (e) Que, E. L.;
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†
Department of Chemistry, Korea University.
The School of EastꢀWest Medical Science, Kyung Hee University.
‡
§
Research Institute for Natural Sciences, Korea University.
1) Baskin, S. I.; Brewer, T. G. In Medical Aspects of Chemical and
(
Biological Warfare; Sidell, F., Takafuji, E. T., Franz, D. R., Eds.; TMM
Publications: Washington, DC, 1997; Chapter 10, pp 271ꢀ286.
(2) Young, C.; Tidwell, L.; Anderson, C. Cyanide: Social, Industrial,
and Economic Aspects; Minerals, Metals, and Materials Society: Warren-
dale, 2001.
(
3) Guidelines for Drinking-Water Quality; World Health Organization:
(6) (a) O’Neil, E. J.; Smith, B. D. Coord. Chem. Rev. 2006, 250, 3068.
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nez-M ꢀa n~ ez, R.; Sancen oꢀ n, F. Chem. Rev. 2003, 103, 4419.
Geneva, 1996.
1
0.1021/ol2018856 r 2011 American Chemical Society
Published on Web 08/29/2011

The detection principles of the most reported chemo-
7
sensors for cyanide are based on nucleophilic addition,
an emission via subsequent hydrolysis of its Schiff base by
ꢀ
water. It is well-known that CN ion has strong binding
ability to Cu(II) ion because of its strong back-bonding
8
hydrogen-bonding interactions, cyanide complexes/ad-
9
10
nꢀ
dition, or coordination of copper ion with cyanide.
However, there are still limitations regarding the sensitiv-
ity, selectivity, and compatibility within an aqueous or
biological environment. Another consideration would be
contribution to the metal ion to form a stable [Cu(CN) ]
x
1
complex. On the basis of this ensemble system, it would
2
be plausible to suggest that 1ꢀCu(II) is hydrolyzed by
ꢀ
CN ion with aid of water to give fluorescence enhance-
ment as indicated in Scheme 2.
ꢀ
cation effect in sensing system for the CN detection,
whereas tetrabutylammonium (TBA) has been usually
We found that 1ꢀCu(II) is initially nonfluorescent (Φ =
f
7ꢀ10
ꢀ
used as a countercation in many reports.
Since potas-
0.02). Addition of CN ion to 1ꢀCu(II) induces a 57 nm
sium cyanide (KCN) is the toxic species defined by the U.S.
Environmental Protection Agency (EPA) standard, detec-
hypsochromic shift of the absorption maximum from 521
to 464 nm and a perceived color change from orange-red to
green (Figure 1a). In addition, the fluorescence intensity at
þ
ꢀ
tion of KCN rather than that of (n-Bu) N CN would be
4
more meaningful in aspect of a practical application of the
ꢀ
λem = 514 is concomitantly enhanced (Φ = 0.65) as a
f
CN detection.
In light of these considerable drawbacks in the CN
function of time as indicated in Figure 1b. A newly formed
emission band by the addition of cyanide ion to a solution
of 1ꢀCu(II) is found to be the same as that of 2 (Table S1,
Supporting Information). Therefore, it is reasonable that
ꢀ
sensing reported so far, we have prepared an ensemble-
based nonfluorescent 1ꢀCu(II) able to selectively and
ꢀ
ꢀ
sensitively detect the CN (particularly KCN) ion in the
CN in a solution of 1ꢀCu(II) causes a formation of stable
manner of “turn-on” fluorogenic sensing as well as naked-
eye detection for the KCN. Taking advantage of this
offꢀon fluorescence sensing system, it has been applied
Cu(CN)x to release free 1 followed by in turn easily
hydrolyzed to provide 2 which is strongly fluorescent.
ꢀ
to intracellular CN detection in HepG2 cells in this study
as well.
Probe 1ꢀCu(II) was prepared by modification of our
1
1
previously reported synthetic procedures (Scheme 1). As
in our earlier studies, we found that 1 is easily hydrolyzed
to produce 2 strongly fluorescent in aqueous media. The
crystal structure of 1ꢀCu(II) (Figure S1, Supporting
Information) confirms that the o-OH group in 1 serves as
an additional binding site for the Cu(II) ion binding to
provide a stable complex which gives a reduced fluores-
cence presumably due to MLCT-based heavy metal ion
effect.
Scheme 1. Compounds 1, 1ꢀCu(II), and 2
1
1
On the basis of our previous report, it is clear that
removal of Cu(II) from the 1ꢀCu(II) complex will induce
(
7) (a) Kim, Y.-H.; Hong, J.-I. Chem. Commun. 2002, 512. (b)
Anzenbacher, P., Jr.; Tyson, D. S.; Jursikova, K.; Castellano, F. N. J.
Am. Chem. Soc. 2002, 124, 6232. (c) Chow, C.-F.; Lam, M. H. W.;
Wong, W.-Y. Inorg. Chem. 2004, 43, 8387.
Figure 1. Time-dependent (a) UVꢀvis and (b) fluorescence
spectra of 1ꢀCu(II) (5.0 μM) in aqueous solution (10 mM
PBS buffer, pH 7.4, 1.0% DMSO) upon addition of cyanide
(16 equiv). Excitation at 479 nm (slit = 1.5/1.5). Inset: plot of (a)
A464/A521 vs time and (b) emission intensity at 514 nm vs time.
(
8) (a) Sun, S.-S.; Lees, A. J. Chem. Commun. 2000, 1687. (b) Miyaji,
H.; Sessler, J. L. Angew. Chem., Int. Ed. 2001, 40, 154.
9) (a) Tomasulo, M.; Sortino, S.; White, A. J. P.; Raymo, F. M. J.
Org. Chem. 2006, 71, 744. (b) Ren, J.; Zhu, W.; Tian, H. Talanta 2008,
5, 760. (c) Kwon, S. K.; Kou, S.; Kim, H. N.; Chen, X.; Hwang, H.;
(
7
Nam, S.-W.; Kim, S. H.; Swamy, K. M. K.; Park, S.; Yoon, J.
Tetrahedron Lett. 2008, 49, 4102.
To investigate compatibility of the ensemble-based anion
detection ability of 1ꢀCu(II) with the biological environment,
(
10) Ganesh, V.; Sanz, M. P. C.; Mareque-Rivas, J. C. Chem.
Commun. 2007, 5010.
11) Jung, H. S.; Han, J. H.; Habata, Y.; Kang, C.; Kim, J. S. Chem.
(
(12) Kurmia, K.; Giles, D. E.; May, P. M.; Singh, P.; Hefter, G. T.
Talanta 1996, 43, 2045.
Commun. 2011, 47, 5142.
Org. Lett., Vol. 13, No. 19, 2011
5057

ꢀ
the absorption and emission spectra of 1ꢀCu(II) in an
aqueous solution (10 mM PBS buffer, pH 7.4, 1.0%
DMSO) were examined with respect to various anions
commonly found in biological media. Indeed, as shown in
Figure 2(a), 1ꢀCu(II) revealed remarkable enhancement
easily transforms into 2 by the addition of CN ion in
aqueous media.
Figure S4 (Supporting Information) demonstrates that
ꢀ
chemodosimetric reaction of 1-Cu(II) with CN is linear
ꢀ
8
ꢀ
and sensitive enough to detect the 10 M CN ion in
aqueous solution. In pH variable test, this florescence
“offꢀon” system is working properly in the pH range from
6 to 10 in aqueous solution (Figure S5, Supporting Infor-
mation). Therefore, it should be noteworthy that probe
1ꢀCu(II) in our study is a desirable fluorescence probe in
that it is simple, reliable, selective, and biocompatible
ꢀ
of emission intensity only in the presence of CN , whereas
no noticeable changes were observed with other anions
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(
HCO , SCN , OH , CO , HPO4 , PO4 , adenosine
F , Cl , Br , I , AcO , H PO , HSO , NO , ClO ,
3ꢀ
2
2ꢀ
4
4
3
4
ꢀ
ꢀ
2ꢀ
3
3
monophosphate (AMP), adenosine diphosphate (ADP),
and adenosine triphosphate (ATP)). Competitive experi-
ments shown in Figure 2 also confirm that 1ꢀCu(II) shows
ꢀ
reaction-based CN sensor.
Figure S6 (Supporting Information) illustrates fluores-
ꢀ
a selective response to the CN even in the presence of
other anions.
cence spectral changes during the reaction of 1ꢀCu(II)
ꢀ
with varied [CN ]. In their emission spectra, a significant
enhancement of fluorescence intensity at 514 nm was
observed upon excitation at 479 nm. Interestingly, the
fluorescence intensity within the first 2 min shows a linear
ꢀ
response to the [CN ] whereas the fluorescence change
within 15 min is sigmoidal. This apparent discrepancy
between two different kinetic behaviors in 2 min and in
15 min may be related with the reaction mechanism as
shown in Scheme 2. Time courses of the fluorescence
intensity for the reaction of 1-Cu(II) with various amount
ꢀ
of CN are shown in Figure 3. The progress curve with 80
ꢀ
μM of CN clearly demonstrates biphasic responses com-
posed of a fastphase within 3 min and a slow phase starting
around 5 min. This biphasic time course is found in the
ꢀ
samples at almost all range of CN concentrations. It
would be interesting to remind that the fast phase linearly
ꢀ
responds to the CN concentration, which may be im-
ꢀ
portant in quantification of CN .
Figure 2. (a) UVꢀvis and (b) fluorescence spectra of 1ꢀCu(II)
(
DMSO) upon addition of various anions (16 equiv). Excitation
5.0 μM) in aqueous solution (10 mM PBS buffer, pH 7.4, 1.0%
at 479 nm after 20 min (slit = 1.5/1.5).
Figure 3. Time course of the fluorescence response of 1ꢀCu(II)
(
5.0 μM) in aqueous solution (10 mM PBS buffer, pH 7.4, 1.0%
DMSO) upon addition of various concentrations of cyanide
(0ꢀ16 equiv). The excitation and emission wavelength were 479
and 514 nm, respectively.
An ESI-MS spectrometric analysis of 1ꢀCu(II) treated
ꢀ
with CN in aqueous solution revealed signals for the
formation of the expected 2 (m/z 270.2, [2 þ H] ) (Figure
þ
1
S2, Supporting Information). H NMR spectroscopy of
the reaction product also showed the same splitting pat-
terns anticipated from the structure 2 (Figure S3, Support-
The kinetic analysis implicates that both phases depend
ꢀ
ꢀ
on CN concentration and the CN plays important roles
in decomplexation of Cu(II) from 1ꢀCu(II) as well as in
hydrolysis of probe 1ꢀCu(II) to give the free 2. (Figure S7,
Supporting Information). This conclusion is further sup-
ported by the facts that fluorescence emission from
ing Information). In addition, the fluorescence quantum
ꢀ
yield (Φ = 0.65) of a mixture of 1ꢀCu(II) and CN is
f
similar to that of 2 (Φ = 0.66) (Table S1, Supporting
f
Information). These results again support that 1ꢀCu(II)
5
058
Org. Lett., Vol. 13, No. 19, 2011

Scheme 2. Schematic Illustration of Turn-on Fluorescence
Sensing Mechanism of 1ꢀCu(II) for Cyanide
Figure 4. Confocal microscopic images of HepG2 cells in the
presence of 1ꢀCu(II) (1.0 μM). The fluorescence images were
acquired after 1 min of treatment of KCN (125, 250, and 500 μM)
on HepG2 cells. Bottom panels show an overlay of the image
with a confocal phase contrast image.
ꢀ
separately prepared 2 is unchanged in the presence of CN
(Figure S8, Supporting Information) and that hydrolysis
of 1 is accelerated with cyanide (Figure S9, Supporting
Information). The latter reaction is presumed as an exam-
1
ple of base-catalyzed Schiff base hydrolysis. Also, an
3
In summary, we demonstrated that an “ensemble”-based
chemodosimeter 1ꢀCu(II) can selectively probe the cya-
nide ion in aqueous media with respect to a marked fluo-
rescence enhancement over other anionic species under
aqueouscondition. The “offꢀon” fluorescencemechanism
of 1ꢀCu(II) with cyanide ion is suggested as a decom-
plexation of Cu(II) from nonfluorescent 1 followed by
hydrolytic cleavage of the Schiff base to give a strongly
fluorescent coumarinaldehyde 2. Both reactions are con-
tributed by the cyanide ion. The selective cyanide detection
with 1ꢀCu(II) for the biological application was also
performed in HepG2 cells to show the “offꢀon” fluores-
cence cellular image as well.
ESI-MS spectrometric analysis of 1ꢀCu(II) treated with
ꢀ
CN in aqueous solution from a fast phase within 3 min
revealed signals corresponding to the formations of the
þ
þ
þ
expected 1 (m/z 361.2, [1 þ H] ), 2 (m/z 292.2, [2 þ Na] ),
and 1 ꢀ Cu(II) (m/z 500.1, [1 þ Cu þ DMSO ꢀ H] )
(
Figure S10, Supporting Information). This results is also
indicative of biphasic responses composed of 1ꢀCu(II) for
ꢀ
CN ion.
To demonstrate that 1ꢀCu(II) is able to detect the CN
ꢀ
ion in cells, the cells preloaded with 1ꢀCu(II) complex were
treated with various amounts of KCN (Figure 4). Time-
dependent and [CN ]-dependent increases of fluorescence
ꢀ
intensity were observed inside of the cells, as shown in the
inset, after the KCN treatment (Figure S11, Supporting
Information, and Figure 4, respectively). Fluorescence was
only slightly observable on the cells after 40 min of
incubation prior to the KCN treatment (Figure S7, Sup-
portingInformation), and any significant changeofthe cell
morphology or floating appearance of the cells was not
observed. The fluorescence intensities in Figures 4 and S6
Acknowledgment. This work was supported by the CRI
program (No. 2011-0000420) from National Research
Foundation of Korea. Z.H.K. also acknowledges the
Priority Research Centers Program through the National
Research Foundation of Korea (NRF) funded by the
Ministry of Education, Science and Technology (NRF-
20100020209).
(
Supporting Information) are apparently caused by che-
ꢀ
modosimetric reaction of 1ꢀCu(II) complex with CN ion
in the cells to give a strongly fluorescent coumarinaldehyde 2.
Supporting Information Available. Text and figures
giving details of the X-ray crystal structure, additional
1
spectral data, H NMR spectra, and confocal microscopic
images. This material is available free of charge via the
Internet at http://pubs.acs.org.
(
13) (a) Kayser, R. H.; Pollack, R. M. J. Am. Chem. Soc. 1977, 99,
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1
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04, 730.
Org. Lett., Vol. 13, No. 19, 2011
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