Selective fluorescence sensing of cyanide with an o-(carboxamido)trifluoroacetophenone fused with a cyano-1,2-diphenylethylene fluorophore

Article abstract of DOI:10.1016/j.tetlet.2008.07.065

A novel fluorescence probe has been synthesized, which consists of o-(carboxamido)trifluoroacetophenone moiety as the recognition element and cyano-1,2-diphenylethylene moiety as the signaling unit. Fluorescence titrations of the probe with anions such as F^-, Cl^-, I^-, CN^-, SCN^-, AcO^-, H₂ PO₄^-, HSO₄^-, and ClO₄^- as their Bu₄N⁺ salts in acetonitrile show that CN^- is the most efficient quencher, AcO^- and F^- follow it, and other anions show little changes. In an aqueous medium, MeOH-water (9:1), the probe shows fluorescence quenching only toward cyanide and no changes toward the other anions.

Full text of DOI:10.1016/j.tetlet.2008.07.065

Tetrahedron Letters 49 (2008) 5544–5547
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Selective fluorescence sensing of cyanide with an
o-(carboxamido)trifluoroacetophenone fused with
a cyano-1,2-diphenylethylene fluorophore
*
Hanna Lee, Yun Mi Chung, Kyo Han Ahn
Department of Chemistry, Pohang University of Science and Technology (POSTECH), San 31 Hyoja-dong, Pohang 790-784, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel fluorescence probe has been synthesized, which consists of o-(carboxamido)trifluoroacetophe-
Received 21 June 2008
Revised 9 July 2008
Accepted 10 July 2008
Available online 12 July 2008
none moiety as the recognition element and cyano-1,2-diphenylethylene moiety as the signaling unit.
Fluorescence titrations of the probe with anions such as FÀ, ClÀ, IÀ, CNÀ, SCNÀ, AcOÀ, H2PO4À, HSO4
,
À
and ClO4 as their Bu4N+ salts in acetonitrile show that CNÀ is the most efficient quencher, AcOÀ and
À
F
À follow it, and other anions show little changes. In an aqueous medium, MeOH–water (9:1), the probe
shows fluorescence quenching only toward cyanide and no changes toward the other anions.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Anion sensing
Fluorescence probe
Cyanide sensing
o-(Carboxamido)trifluoroacetophenone
The molecular recognition and sensing of anions have attracted
much research interest with multiple disciplines,1 because anions
play significant roles in biological and chemical processes,2 and
have implications in medicine, catalysis and environment.3 To
mention a few are the acute toxic effects of cyanide ions and the
role of phosphate ions in nucleotides.4 In the development of rec-
ognition and sensing probes for such anions, a paramount chal-
lenge is how to achieve the necessary selectivity and high
sensitivity toward target analytes. To achieve such goals, the
insightful design of recognition motifs and corresponding fluores-
cence sensors has been pursued.
(CDPE) moiety. In this fused form, the binding event occurring at
the trifluoroacetyl group may be directly transduced to the signal-
ing unit, which compares DATFA 2 in which case the trifluoroacetyl
group is not conjugated to the dansyl fluorophore but linked
through the sulfonamide bond. The cyanodiphenylethylene moiety
has been used in various fluorescent materials.9
COCF3
NHSO2
CF3
O
COCF3
Recently, we have introduced a novel anion binding motif based
on trifluoroacetophenone that recognizes anions such as carbon-
ates by forming reversible covalent adducts.5 The new trifluoroace-
tophenone system (CATFA 1) has an o-carboxamido group, which
stabilizes anionic adducts through H-bonding, and thus shows sig-
nificantly enhanced binding affinity toward carboxylates.6 This ap-
CN
NH
R
O
NHCOR
NMe2
CDPE-TFA 3 (R = Et)
CATFA 1
DATFA 2
proach has been also used in the development of
a novel
The desired CDPE-TFA 3 was synthesized starting from 2-nit-
roterephthalic acid (5) as depicted in Scheme 1. A key intermediate
was the mono-protected aldehyde 8, which was prepared by selec-
tive protection of the dialdehyde 7 in 47% isolated yield. Then, the
Knoevenagel condensation of 8 with benzyl cyanide provided the
CDPE derivative 9 in 72% isolated yield. Subsequent steps following
the established reaction conditions6–8 introduced the trifluoro-
acetyl and N-propionyl groups, leading to the desired product 3.
We have also synthesized a reference compound 4, which has no
fluorescence probe, the dansyl analogue DATFA 2,7 which selec-
tively senses highly toxic cyanide ions. In the course of our studies
on anion probes,8 we have designed a new trifluoroacetophenone
derivative (CDPE-TFA 3) in which the binding element trifluoroace-
tyl group is fused with a signaling unit, the cyanodiphenylethylene
* Corresponding author. Tel.: +82 54 2792105; fax: +82 54 2793399.
E-mail address: ahn@postech.ac.kr (K. H. Ahn).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.07.065

H. Lee et al. / Tetrahedron Letters 49 (2008) 5544–5547
5545
COOH
NO2
CO2Me
NO2
CHO
NO2
O
O
O
O
c
d
a
b
NO2
CN
NO2
COOH
CO2Me
CHO
9
6
7
8
5
CHO
CF3
OH
CF3
OH
CHO
e
g
f
CN
10
NO2
CN
NO2
CN
12
NH2
11
CF3
OH
H
N
h
i
3
CN
NH
O
CN
O
4
13
Scheme 1. Synthesis of CDPE-TFA 3. Reagents and conditions: (a) SOCl2, MeOH, 0 °C?reflux, 5 h, 76%; (b) 1.5 M DIBAL in toluene, toluene, À78 °C, 5 min, 84%; (c) 1,3-
propanediol, p-TsOH, benzene, reflux, 2 h, 47%; (d) benzyl cyanide, 1.0 M t-BuOK in THF, t-BuOH/THF, 50 °C, 30 min, 72%; (e) 11-N HCl/THF (1:1), 25 °C, 30 min, 76%; (f) CsF,
TMSCF3, DME, 0 °C?25 °C, 3 h, 88%; (g) SnCl2ÁH2O, EtOAc, 70 °C, 20 min, 76%; (h) EtCOCl, K2CO3, THF, 25 °C, 63%; (i) 1,10-phenanthroline, CuCl, 1,2-diethoxyhydrazine, K2CO3,
THF, 70 °C, 50 min, 70%.
trifluoroacetyl unit. By changing the N-acyl group, we may further
functionalize CDPE-TFA 3.
The fluorescence data collected in Figure 1a compare the rela-
tive intensity at the given guest concentration, showing that CNÀ
is the most efficient quencher among the anions examined, then
AcOÀ and FÀ follow, and other anions show little changes. The
emission response depending on the anions is similar with the ten-
dency observed previously in the case of DATFA 2.7 Formation of
the anionic adduct between 3 and an anion (AÀ) will be dependent
on the anion’s carbonyl carboÀn affinitÀy, which is in the order:
The photophysical properties of CDPE-TFA 3 were evaluated in
CH3CN: Its absorption spectrum displayed two absorption maxima
at kmax = 223 and 331 nm (e
= 14,680 MÀ1 dmÀ1), characteristic
peaks of the CDPE moiety.9 When excited at kex = 331 nm, probe
3 emitted fluorescence at kmax = 476 nm.
We evaluated the sensing ability of 3 toward anions such as FÀ,
ClÀ, IÀ, CNÀ, SCNÀ, AcOÀ, H2PO4À, HSO4À, and ClO4 as their Bu4N+
CNÀ ꢀ AcOÀ > FÀ > H2PO À, Cl , I , CN , SCN , HSO4À, and ClO4
.
À
À
À
À
4
salts. The fluorescence spectra were recorded at kex = 331 nm by
adding increasing amounts of each anion to CDPE-TFA 3, both dis-
solved in acetonitrile at 25 °C. In most cases, we observed little
changes in the fluorescence intensity except for CNÀ, FÀ, and AcOÀ
anions (Fig. 1a).
O
Et
O
Et
N
N
A
H
O
H
O
CN
CN
A
F3C
CF3
Characterization data of selected compounds. Compound 8: mp 96.1–96.3 °C
(CH2Cl2/hexanes = 1/5); Rf = 0.36 (hexanes/EtOAc = 4/1); 1H NMR (300 MHz, CDCl3) d
10.0 (s, 1H), 8.23 (s, 1H), 8.05 (d, J = 8.1 Hz, 1H), 7.99 (d, J = 8.1 Hz, 1H), 6.04 (s, 1H),
4.20 (dd, J = 5.8, 5.2 Hz, 2H), 3.97 (td, J = 9.8, 2.3 Hz, 2H), 2.08–2.21 (m, 1H), 1.44 (d,
J = 13.9 Hz, 1H); 13C NMR (75.5 MHz, CDCl3) d 189.7, 189.6, 148.8, 137.7, 137.0, 132.8,
128.8, 124.7, 96.5, 67.7, 25.5; HRMS (FAB) calcd for C11H11NO5 (M+H+): 238.0715;
found, 238.0721. Compound 9: mp = 136.8–137.5 °C (hexanes/CH2Cl2 = 5/1); Rf = 0.23
(hexanes/EtOAc = 9/1); 1H NMR (300 MHz, CDCl3) d 8.20 (s, 1H), 8.17 (d, J = 8.7 Hz,
1H), 7.97 (d, J = 8.1 Hz, 1H), 7.67 (d, J = 5.8 Hz, 2H), 7.51 (s, 1H), 7.44–7.49 (m, 3H),
6.09 (s, 1H), 4.24 (dd, J = 5.8, 5.2 Hz, 2H), 4.00 (td, J = 9.8, 2.3 Hz, 2H), 2.15–2.23 (m,
1H), 1.46 (d, J = 13.3 Hz, 1H); 13C NMR (75.5 MHz, CDCl3) d 148.6, 138.6, 135.2, 134.0,
133.5, 132.3, 130.1, 129.3, 128.7, 126.3, 124.9, 117.1, 115.2, 96.8, 67.8, 25.7; MS (EI)
An anionic adduct
(adduct I: A = CN)
3
As it was pointed out in the previous works,7,8b the trifluoroace-
tyl group in probe 3 is also intramolecularly hydrogen bonded as
its alkoxide adduct; however, the latter adduct is more stabilized
by its stronger ‘charged’ hydrogen bonding than the case in which
such intramolecular hydrogen bonding is absent. Thus, the fluores-
cence titration results suggest that the anionic adduct is responsi-
ble for the fluorescence quenching. The adduct formation can be
readily characterized by spectroscopic titrations, as already con-
firmed for the CATFA analogues in the previous works. 19F NMR
titrations provided a clear evidence for the adduct formation: As
expected, the CF3 group in the probe 3 appeared as singlet at
4.3 ppm, shifted to À6.4 ppm (singlet) upon addition of 1.0 equiv
of CNÀ (as Bu4N+ salt) in CD3CN. Also, only both the probe 3 and
the adduct peaks appeared with little chemical shifts when 0.5
equiv of the anion was added.
m/z calcd for
mp = 160.7–161.5 °C (hexanes/CH2Cl2 = 5:1); Rf = 0.18 (hexanes/EtOAc = 4/1); 1H
NMR (300 MHz, CDCl3 + DMSO) 8.39 (s, 1H), 8.23 (d, J = 8.1 Hz, 1H), 8.12 (d,
C
19H16N2O4 (M+): 336.1110; found, 336.1112. Compound 11:
d
J = 8.1 Hz, 1H), 7.69 (d, J = 8.1 Hz, 2H), 7.59 (s, 1H), 7.42–7.51 (m, 3H), 6.69 (d,
J = 5.8 Hz, 1H), 6.12 (m, J = 5.8 Hz, 1H); 13C NMR (75.5 MHz, CDCl3 + DMSO) d 148.1,
137.8, 134.8, 132.7, 132.3, 131.3, 130.1, 129.6, 128.7, 125.6, 124.6, 121.8, 116.5, 114.8,
66.1, 65.6, 65.2, 64.8 (q, J = 32.3 Hz, CF3); 19F NMR (282 MHz, CDCl3 + DMSO) d À0.97;
MS (EI) m/z calcd for
C
17H11F3N2O3 (M+): 348.07; found, 348.07. Compound 3:
mp = 116.0–116.7 °C (hexanes/CH2Cl2 = 4:1); Rf = 0.36 (hexanes/EtOAc = 7/3); 1H
NMR (300 MHz, CDCl3) d 11.0 (s, 1H), 9.18 (s, 1H), 8.07 (dd, J = 6.5, 2.2 Hz, 1H), 7.93
(dd, J = 6.9, 1.8 Hz, 1H), 7.71 (m, 2H), 7.57 (s, 1H), 7.45–7.48 (m, 3H), 2.55 (q,
J = 7.6 Hz, 2H), 1.31 (t, J = 7.6 Hz, 3H); 13C NMR (75.5 MHz, CDCl3) d 183.4, 182.9,
182.5, 182.0 (q, J = 34.7 Hz, –COCF3), 173.6, 144.1, 142.3, 139.7, 133.6, 132.63, 132.58,
132.52, 132.47 (q, J = 4.7 Hz (coupled with F), aromatic-C), 130.4, 129.4, 126.5, 122.8,
122.4, 121.5, 118.5, 116.8, 115.5, 114.7 (q, J = 99.3 Hz, –CF3), 117.1, 110.8, 31.9, 9.5;
19F NMR (282 MHz, CDCl3) d 6.82; MS (EI) m/z calcd for C20H15F3N2O2 (M+): 372.1086;
found, 372.1082. Compound 4: mp = 127.9–128.2 °C (hexanes/CH2Cl2 = 4/1); Rf = 0.36
(hexanes/EtOAc = 3/2); 1H NMR (300 MHz, CDCl3) d 8.02 (s, 1H), 7.68–7.58 (m, 4H),
7.53–7.36 (m, 6H), 2.42 (q, 2H), 1.25 (t, 3H); 13C NMR (75.5 MHz, CDCl3) d 172.6,
142.1, 138.8, 134.6, 134.4, 129.8, 129.5, 129.3, 126.2, 125.1, 122.0, 120.2, 118.1, 112.2,
30.9, 9.8; MS (EI) m/z calcd for C18H16N2O (M+): 276.1263; found, 276.1265.
The fluorescence titration of probe 3 with CNÀ (0–30 equiv)
gave an interesting quenching result, as inferred from a plot of
F/F0 versus equivalent of the cyanide ion. The plot can be divided
into two regions in which fluorescence response is different (Fig.
2): A nonlinear change up to 3 equiv of cyanide and a linear change
after that point. In the former region, two different species, 3 and
its cyanide adduct I, seem to be contributing to the fluorescence
intensity observed, resulting in the nonlinear change. In the latter

5546
H. Lee et al. / Tetrahedron Letters 49 (2008) 5544–5547
70k
60k
50k
40k
30k
20k
10k
0
3 and other anions
60k
50k
40k
30k
20k
10k
0
F-
OAc-
CN-
400
450
500
550
600
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
Figure 1. (a) Comparison of the emission spectra obtained when probe 3 (3.0
l
M) was treated with each of the anions (1.0 equiv of ClÀ, IÀ, CNÀ, SCNÀ, H2POÀ4 , HSO4À, ClOÀ4
M) with increasing amount of cyanide (from the top: 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 5.0,
,
CNÀ, FÀ, and AcOÀ as Bu4N+ salts) in CH3CN at 25 °C. (b) Fluorescence titration of 3 (3.0
and 10 equiv) in CH3CN at 25 °C.
l
1.5
1.4
1.3
1.2
1.1
1.0
10
8
6
4
2
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
5
10
15
20
25
30
[CN-], equivalent
[CN-], equivalent
Figure 2. The plot of F0/F versus equivalent of [CNÀ] for the titration of 3 (3.0
6 3.0 equiv; (b) 3.0 equiv 6 [CNÀ].
l
M) with CNÀ (0–30 equiv) in CH3CN at 25 °C, which is divided into two regions: (a) 0 6 [CNÀ]
region, little of free 3 would exist because the association constant
between CNÀ and 3 is large (Kass ꢁ 105 MÀ1),6 and thus quenching
would occur mainly from the interactions between adduct I and
CNÀ. The absorption spectra measured for the titration solutions
with increasing amounts of cyanide (kmax = 332, 325, 318,
315 nm for the solutions containing 1.0, 2.0, 5.0, and 10.0 equiv
of CNÀ, respectively) showed little spectral changes from that of
3, and only gradual hypsochromic shifts and very small changes
in the intensity were observed. Although further experiments such
as luminescence lifetime measurements depending on the concen-
tration of quenchers can provide valuable information on the
quenching mechanism, we tentatively suggest that dynamic
quenching is a dominant process for the latter region because
molecular interactions other than collision are hard to imagine
between the adduct I and cyanide. The Stern–Volmer plot shown
in Figure 2b intercepts not exactly 1.0 but slightly deviated value
from it, which suggests that the dynamic quenching process may
be dominant but not exclusive.10 This fluorescence intensity
behavior depending on the cyanide equivalent also supports the
formation of a 1:1 adduct species I, and, furthermore, the fluores-
cence quenching is mainly due to the adduct formation.
mostly the adduct I). The smaller value of U1:1 compared to U0
supports the observed quenching behavior as shown in Figure 2a.
The quenching probably results from a photo-induced electron
transfer, from the anionic adduct to the CDPE moiety: The
p–
p*
transition from the CDPE fluorophore is likely to be quenched by
the electron transfer from the alkoxide nonbonding orbital.
A critical role of the o-trifluoroacetyl group in the fluorescence
behavior of probe 3 was examined with the reference compound 4.
The fluorescence titration of 4 (3.0 lM) with increasing amounts of
CNÀ (up to 100 equiv) at kex = 310 nm in acetonitrile showed little
changes in the fluorescence spectra, which again demonstrates that
the molecular interaction between anions and the trifluoroacetyl
groupis adeterminingfactorforthefluorescencebehaviorobserved.
As already demonstrated in the previous studies, CNÀ has the stron-
gest carbonyl carbon affinity among the anions examined, whereas
anionssuchas AcOÀ andFÀ haveloweraffinityandother anionshave
very weak affinity.6,7 The formation of adduct I should be dependent
on the anion’s carbonyl carbon affinity, which led to the observed
fluorescence behavior dependent on the anions.
The fact that probe 3 recognizes anions through reversible cova-
lent adducts (RCA), not through H-bonding interactions, the most
widely used paradigm in molecular recognition and sensing,
suggests that we may achieve a selectivity pattern completely
different from the fluorescence probes based on H-bonding
interactions in aqueous media. In other words, the anion selectivity
The quantum yields were determined for the cyanide–3 mix-
tures in which the amounts of cyanide were changed from 0 to
1.0 equiv. A plot of
decrease, from U0 = 0.030 (3 only) to U1:1 = 0.018 (a 1:1 mixture,
U/
U0 versus [CNÀ]/[3] showed a linear

H. Lee et al. / Tetrahedron Letters 49 (2008) 5544–5547
5547
phenone, is fused with a signaling unit, cyano-1,2-diphenylethyl-
ene moiety. The probe recognizes cyanide through the formation
of reversible covalent adduct, and gives selective fluorescence
quenching in acetonitrile. In an aqueous medium, the probe shows
fluorescence quenching only toward cyanide among various anions
examined.
14.0k
12.0k
10.0k
8.0k
6.0k
4.0k
2.0k
0.0
3 and other anions
CN-
Acknowledgments
This work was supported by the Korea Research Foundation
(KRF-2005-070-C00078) and Korea Health Industry Development
Institute (A05-0426-B20616-05N1-00010A).
300
350
400
450
500
550
600
Supplementary data
Wavelength (nm)
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.07.065.
Figure 3. Comparison of the relative fluorescence intensity obtained for the
equimolar mixture between the prÀobe 3 (10
lM) and each of the anions (10 equiv of
FÀ, ClÀ, IÀ, CNÀ, SCNÀ, AcOÀ, H2PO , HSO4À, and ClOÀ4 as Bu4N+ salts) at kex = 314 nm
4
in MeOH–water (9:1).
References and notes
may be modulated in protic solvents that provide competing H-
bonding interactions toward anions. Anions such as FÀ and AcOÀ,
particularly FÀ, have strong H-bonding ability, and thus are favor-
ably sensed over other anions in organic media by H-bond assisted
fluorescence probes. However, such a preference is generally lost in
aqueous media due to the competing H-bond interactions between
the anions and solvents (strong solvation). This fact is also a major
limitation for sensing such anions in aqueous media. The recogni-
tion of anions through the RCA mechanism is in stark contrast to
the H-bond-based recognition mode. We have shown that cyanide
is preferably recognized by the TFA-based ionophores. In addition,
cyanide has poor H-bonding ability compared to FÀ and AcOÀ. Both
properties suggest that CNÀ may be completely discriminated from
the competing FÀ and AcOÀ if we use aqueous solvents. Indeed this
is the case. When probe 3 was titrated with the anions in an aque-
ous medium, MeOH–H2O (9:1),à only CNÀ showed significant fluo-
rescence quenching, and the competing anions FÀ and AcOÀ
showed little changes (Fig. 3).
1. For selected reviews, see: (a) Schmidtchen, F. P.; Berger, M. Chem. Rev. 1997, 97,
1609; (b) Beer, P. D.; Gale, P. A. Angew. Chem. Int. Ed. 2001, 40, 486; (c) Gale, P.
A. Coord. Chem. Rev. 2003, 240, 191; (d) Martínez-Máñez, R.; Sancenón, F. J.
Fluoresc. 2005, 15, 267.
2. Supramolecular Chemistry of Anions; Bianchi, E., Bowman-James, K., García-
Espanã, E., Eds.; Wiley-VCH: New York, 1997.
3. (a) Moss, B. Chem. Ind. 1996, 407; (b) Glidewell, C. Chem. Br. 1990, 26,
137.
4. (a) Knowles, E. L.; Bain, J. T. B. Chem. Ind. 1968, 8, 232; (b) Sidell, F.; Takafuji, E.
T.; Franz, D. R. Medical Aspects of Chemical and Biological Warfare; TMM
Publications: Washington, DC, 1997; p 271; (c) Warburg, O. Hoppe-Seyler’s Z.
Physiol. Chem. 1911, 76, 331; (d) Kellin, D. Proc. R. Soc. London. Ser. B 1929, 104,
206; (e) Hortonand, N. C.; Perona, J. J. Biochemistry 2004, 43, 6841; (f) Petrov, A.
S.; Pack, G. R.; Lamm, G. J. Phys. Chem. B 2004, 108, 6072.
5. (a) Herman, H. B.; Rechnitz, G. A. Science 1974, 184, 1074; (b) Meyerhoff, M. E.;
Pretsch, E.; Welti, D. H.; Simon, W. Anal. Chem. 1987, 59, 144; (c) Lee, H. J.; Yoon,
I. J.; Yoo, C. L.; Pyun, H.-J.; Cha, G. S.; Nam, H. Anal. Chem. 2000, 72, 4694; (d)
Mertz, E.; Zimmerman, S. C. J. Am. Chem. Soc. 2003, 125, 3424; (e) Mertz, E.; Beil,
J. B.; Zimmerman, S. C. Org. Lett. 2003, 5, 3127.
6. Kim, Y. K.; Lee, Y.-H.; Lee, H.-Y.; Kim, M.-K.; Cha, G. S.; Ahn, K. H. Org. Lett. 2003,
5, 4003.
7. Chung, Y. M.; Raman, B.; Kim, D.-S.; Ahn, K. H. Chem. Commun. 2006, 186.
8. (a) Kim, D.-S.; Miyaji, H.; Chang, B.-Y.; Park, S.-M.; Ahn, K. H. Chem. Commun.
2006, 3314; (b) Ryu, D.; Park, E.; Kim, D.-S.; Yan, S.; Lee, J. Y.; Chang, B.-Y.; Ahn,
K. H. J. Am. Chem. Soc. 2008, 130, 2394.
9. (a) An, B.-K.; Lee, D.-S.; Lee, J.-S.; Park, Y.-S.; Song, H.-S.; Park, S. Y. J. Am. Chem.
Soc. 2004, 126, 10232; (b) Detert, H.; Schollmeyer, D.; Sugiono, E. Eur. J. Org.
Chem. 2001, 2927.
10. Connors, K. A. Binding Constants; John Wiley: New York, 1987.
11. For examples of complete selectivity in cyanide sensing, see: (a) Tomasulo, M.;
Raymo, F. M. Org. Lett. 2005, 7, 4633; (b) García, F.; García, J. M.; García-Acosta,
B.; Martínez-Máñez, R.; Sancenón, F.; Soto, J. Chem. Commun. 2005, 2790; (c)
Chung, Y.; Lee, H.; Ahn, K. H. J. Org. Chem. 2006, 71, 9470; (d) Chen, C.-L.; Chen,
Y.-H.; Chen, C.-Y.; Sun, S.-S. Org. Lett. 2006, 8, 5053; (e) Yang, Y.-K.; Tae, J. Org.
Lett. 2006, 8, 5721.
Thus, a complete selectivity toward CNÀ is achieved with the
fluorescence probe 3 in an aqueous medium.11 The result demon-
strates that the recognition through the RCA mechanism is a prom-
ising approach to develop new ionophores or sensors with a
selectivity pattern completely different from the widely used,
H-bonding-based approaches. Recently, the concept of stabiliza-
tion of anionic adducts by intramolecular H-bonding has been
utilized by others for cyanide sensing.12
In summary, we have synthesized a novel fluorescence probe, in
12. Lee, K.-S.; Kim, H.-J.; Kim, G.-H.; Shin, I.; Hong, J.-I. Org. Lett. 2008, 10, 49.
which
a recognition element, o-(carboxamido)trifluoroaceto-
à
For solubility reason, methanol is used as co-solvent.