Azo dyes functionalized with alkoxysilyl ethers as chemodosimeters for the chromogenic detection of the fluoride anion

Article abstract of DOI:10.1002/asia.201200323

Finding fluoride: An azo dye functionalized with tert-butyldimethylsilyl ether has been synthesized and used as a selective chromogenic fluoride sensor in the acetonitrile/water mixtures. The chromogenic response arises from the fluoride-induced hydrolysi

Full text of DOI:10.1002/asia.201200323

DOI: 10.1002/asia.201200323
Azo Dyes Functionalized with Alkoxysilyl Ethers as Chemodosimeters for
the Chromogenic Detection of the Fluoride Anion
Alessandro Agostini,[a] Michele Milani,[b] Ramꢀn Martꢁnez-MꢂÇez,*[a]
Maurizio Licchelli,*[b] Juan Soto,[a] and Fꢃlix Sancenꢀn[a]
Selective recognition of anions is a very active field in
supramolecular chemistry. In particular, the development of
fluorogenic and chromogenic chemosensors and reagents for
anions has been extensively explored in the last few years,
given the important roles played by anionic species in bio-
logical processes, in deleterious effects such as environmen-
tal pollutants, or as toxic compounds or carcinogenic spe-
cies.[1]
and are unable to display sensing features in water or in
mixed water/organic solvent mixtures, even with a very
small amount of water.[7]
In order to overcome these major drawbacks, the use of
chemodosimeters for the chromo-fluorogenic detection of
fluoride anions has been recently explored. These chemo-
dosimeters employ selective reactions induced by the target
anion coupled with a chromo- or fluorogenic event. In this
area, the well-known fluoride-induced hydrolysis of silyl
ethers has been used to develop probes for the optical rec-
ognition of this anion.[8]
One recent example was published by Akkaya and co-
workers in 2010, who prepared two boron dipyrromethene
(bodipy) derivatives with silyl-protected phenolic moieties.[9]
The emission intensity of both chemodosimeters was
quenched upon fluoride anion addition due to the formation
of phenolate anions. Bodipy derivatives functionalized with
silylacetylenes have also been prepared and used for the flu-
orogenic detection of fluoride.[10] In another recent study,
Bhalla et al. prepared terphenyl derivatives functionalized
with tert-butyldimethylsilyl groups.[11] Upon the addition of
the fluoride anion to the THF solutions of the chemodosim-
eters, a change in color from colorless to violet was observed
Among inorganic anions, fluoride is routinely used for the
prevention of dental caries[2] and for the treatment of osteo-
porosis.[3] However, acute fluoride exposure can cause vari-
ous diseases: nausea, abdominal pain, coma, cardiac arrest
determined by hypocalcemia. Moreover, epidemiological
studies have demonstrated that chronic fluoride exposure
can determine skeletal fluorosis and osteomalacia. Further-
more, there are other studies on the possible carcinogenic
effects of fluoride anion in humans.[4] For all these reasons,
it is not surprising that the development of chromogenic and
fluorogenic chemosensors and reagents for the selective de-
tection of fluoride has increased in recent years. Some of
these probes have been prepared after considering the
“binding site–signaling subunit” approach in which an opti-
cal signaling unit is covalently linked to the binding sites
containing one or several H-bond donor moieties, such as
urea and thiourea moieties.[5] In some of these systems, dual
processes involving coordination and deprotonation have
been reported.[6] However, most of these receptors, which
are based on the coordination and/or basicity properties of
fluoride, have shown certain limitations as practical sensors.
They typically show poor selectivity versus other basic
anions such as cyanide, acetate, and dihydrogen phosphate
À
due to the cleavage of the O Si bond with the concomitant
formation of the corresponding triphenylene derivatives.
Despite following a chemodosimeter approach, the above
fluoride probes only displayed sensing features in organic
solvents. In fact, there are very few examples of optical fluo-
ride probes that are able to detect this anion in water or in
water/organic solvent mixtures. One recent example is the
work of Zhang and co-workers, who prepared a benzothiazo-
lium hemicyanine dye functionalized with a tert-butyldime-
thylsilyl moiety as a specific reaction site for fluoride.[12] The
ethanol/water 3:7 v/v mixtures of this chemodosimeter
showed an emission band at 500 nm, which shifted to
558 nm upon fluoride addition. However, emission changes
were achieved after 50 min. Very recently, Liu and co-work-
ers prepared a diblock copolymer bearing a silylether-pro-
tected nonfluorescent coumarin precursor.[13] Addition of
fluoride anion to phosphate buffer solutions of this polymer
induced the appearance of an intense emission band cen-
tered at 402 nm due to the hydrolysis of the silylether, which
then induced the formation of a coumarin fluorophore.
A colorimetric sensory material for fluoride detection
based on the use of a mesoporous silica solid, MCM-41,
[a] A. Agostini, Prof. R. Martꢀnez-MꢁÇez, Dr. J. Soto, Dr. F. Sancenꢂn
Centro de Reconocimiento Molecular y Desarrollo Tecnolꢂgico
(IDM)
Unidad Mixta Universidad Politꢃcnica de Valencia-Universidad de
Valencia (Spain)
Departamento de Quꢀmica
Universidad Politꢃcnica de Valencia
Camino de Vera s/n, 46022, Valencia (Spain)
CIBER de Bioingenierꢀa, Biomateriales y Nanotecnologꢀa (CIBER-
BNN)
E-mail: rmaez@qim.upv.es
[b] M. Milani, Prof. M. Licchelli
Dipartimento di Chimica, Universitꢄ di Pavia
via Taramelli 12, 27100, Pavia (Italy)
E-mail: mali@unipv.it
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COMMUNICATION
functionalized with different dyes has also been reported.[14]
In this case, the addition of fluoride to the acidic acetoni-
trile/water 7:3 v/v mixtures of the functionalized solid result-
ed in the hydrolysis of the solid support, with a subsequent
dye release and chromogenic response.
Given our interest in the development of chromo-fluoro-
genic chemosensors for anions[15] and the very few examples
described that are able to signal fluoride in the presence of
water, we report herein the synthesis, characterization, and
sensing studies of a new fluoride-selective chemodosimeter
based on a pyridine azo dye functionalized with a tert-butyl-
dimethylsilyl moiety which displays a selective chromogenic
response to fluoride anion in acetonitrile/water mixtures.
The synthesis of chemodosimeter 2 was achieved by
a two-step procedure (see Scheme 1 and the Experimental
Section for details). In a first step, the phenolic pyridine azo
dye (1) was prepared following a well-known diazotation
procedure.[16] In a second step, the phenolic hydroxy group
was protected as tert-butyldimethylsilyl (TBDMS) ether
using TBDMS-Cl and triethylamine. Scheme 1 also shows
the synthesis of trialkoxysilane derivative 3 by a nucleophilic
substitution reaction between 2 and (3-iodopropyl)trime-
thoxysilane. Compound 3 was used to anchor the chemo-
Figure 1. The UV/Vis spectra of the acetonitrile/water 9:1 v/v solutions of
probe 2 (3.0ꢆ10À5 moldmÀ3) at pH 8.0 in the presence of 10 equivalents
of selected anions (added as tetrabutylammonium salts). The dashed line
is the spectrum in the presence of fluoride, the dashed-dotted line is for
CNÀ. The inset shows the e of the 470 nm band in the presence of the se-
lected anions.
solutions of receptor 2 changed
from colorless to orange-red
upon fluoride addition. A simi-
lar but much less pronounced
effect was noted in the presence
of cyanide, whereas acetate,
benzoate, hydrogen sulfate, di-
hydrogen phosphate, chloride,
nitrate, and carbonate anions
induced negligible changes in
Scheme 1. Synthesis of chemodosimeter 2 and trialkoxysilane derivative 3.
the UV/Vis profile of 2.
To further characterize the
1
dosimeter in a silica matrix (see below). The H NMR spec-
chromogenic behavior of probe 2, changes in the band in-
tensity at 470 nm were studied in the presence of increasing
amounts of fluoride. Figure 2 shows a typical titration pro-
file. From this calibration curve, a remarkable detection
limit of 0.04 ppm using conventional UV/Vis equipment was
calculated.
The fluoride-selective chromogenic response arose from
the hydrolysis reaction of the silyl ether moiety induced by
this anion, which resulted in the formation of the corre-
sponding phenolate anion 4 (see Scheme 2). This phenolate
anion has a strong donor negatively charged oxygen atom,
which was responsible for the appearance of the red-shifted
band at 470 nm and the concomitant color modulation ob-
served. The results are in agreement with the assumed case
that the increased donor ability of a donor group in a push–
pull system would induce a bathochromic shift.[17]
The 1H NMR studies were also in agreement with this
proposed response mechanism. Figure 3 shows 1H NMR
peaks due to the aromatic protons of receptor 2 alone and
in the presence of 10 equivalents of the fluoride anion in
trum of 2 showed two singlets at d=0.29 and 1.03 ppm as-
cribed to the methyl moieties linked directly to the Si atom
and to the tert-butyl group, respectively. In the downfield
zone, two pairs of doublets centered at d=7.00 and
7.92 ppm and at d=7.68 and 8.80 ppm were found and at-
tributed to the 1,4-disubstituted benzene and to the pyridine
moieties, respectively.
Acetonitrile/water 9:1 v/v solutions of 2 at pH 8.0 exhibit-
ed an absorption band at 350 nm (e=19000mÀ1 cmÀ1). The
chromogenic behavior of 2 was studied upon the addition of
10 equivalents of selected anions: acetate, benzoate, hydro-
gen sulfate, dihydrogen phosphate, fluoride, chloride, cya-
nide, nitrate, and carbonate (as tetrabutylammonium salts).
The obtained results are shown in Figure 1.
As Figure 1 illustrates, the most remarkable feature was
observed in the presence of fluoride. In this case, the band
at 350 nm underwent a significant hypochromic and a slight
bathochromic shift (of ca. 10 nm), while a new band ap-
peared at approximately 470 nm. Due to these changes, the
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Azo Dyes for Chromogenic Fluoride Anion Detection
To further assess the potential applicability of 2 for the
detection of the fluoride anion in the presence of the water,
UV/Vis measurements were carried out at a given concen-
tration of fluoride (0.01 moldmÀ3) in the presence of differ-
ent amounts of water. When using acetonitrile/water 9:1 v/v
solutions, fluoride-induced silyl ether hydrolysis was rela-
tively fast, whereas the reaction became slower with increas-
ing water content. By way of example, Figure 4 shows the
Figure 2. Calibration curve for fluoride using probe
10À5 moldmÀ3) in acetonitrile/water 9:1 v/v at pH 8.0.
2
(3.0ꢆ
Figure 4. Time-dependent decrease of e at 350 nm upon the addition of
the fluoride anion (final concentration of 0.01 moldmÀ3) to the solutions
of receptor 2 (6ꢆ10À5 moldmÀ3) in a) acetonitrile/water 90:10 v/v, b) ace-
tonitrile/water 75:25 v/v, c) acetonitrile/water 50:50 v/v mixtures.
time-dependent disappearance of the band centered at
350 nm for the acetonitrile mixtures containing 10%, 25%,
and 50% water. It can be seen that the chromogenic re-
sponse is clearly related to the water content in the solvent;
that is, the greater the water content, the lower the silyl
ether hydrolysis. This result was expected and is related to
the larger solvation of the fluoride anion and the concomi-
tant reduction of its nucleophilicity when the amount of
water increases. Figure 4 shows that the reaction was com-
pleted in approximately 15 min when 10% water was used,
whereas a higher percentage of water led to a partial inhibi-
tion of the reaction. For instance, reaction times of approxi-
mately 40 and 60 min were necessary to reach a plateau
when using the 75:25 or the 50:50 v/v acetonitrile/water mix-
tures.
Scheme 2. Mechanism of the chromogenic response of 2 in the presence
of the fluoride anion.
However, it should be noted that although the reaction
became slower as the amount of water increased, the
method using probe 2 allowed sensing of the fluoride, even
though a percentage of 50% water was used. Indeed, to
complete the characterization of the systems using different
amounts of water, the sensing behavior of 2 was studied (via
the changes noted in the 470 nm band) in the presence of in-
creasing amounts of fluoride when using 75:25 or 50:50 v/v
acetonitrile/water mixtures; under these conditions, detec-
tion limits of 0.09 and 0.14 ppm fluoride, respectively, were
calculated.
Figure 3. Aromatic zone of the 1H NMR spectra of probe 2 a) alone and
b) in the presence of 10 equivalents of the fluoride anion in CDCl3. For
the assignation of the aromatic protons of probe 2, see Scheme 2.
CDCl3. As shown, all the aromatic protons in 2 underwent
significant upfield shifts upon fluoride addition. This effect
was in agreement with the formation of the phenolate anion
4 upon the fluoride-induced hydrolysis of the silyl ether
moiety.
As suggested for similar systems, the sensing response
comprises two steps: 1) the nucleophilic attack of the fluo-
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Ramꢂn Martꢀnez-MꢁÇez, Maurizio Licchelli et al.
COMMUNICATION
ride anion at the silyl ether moiety, which would yield an in-
termediate product; 2) the subsequent release of tert-butyl-
dimethylsilyl fluoride with the generation of phenolate 4
(see Scheme 2). Processing the kinetic data shown in
Figure 4 allowed us to obtain the rate constants (k1 and k2)
for these two steps in the presence of different amounts of
water. These data are provided in Table 1. As seen, the rate
60 min were found when 90:10, 75:25, and 50:50 v/v acetoni-
trile/water mixtures were used. Moreover although the reac-
tion became slower as the amount of water increased, the
method using probe 2 allowed fluoride sensing at low con-
centrations, with detection limits of 0.04, 0.09, and 0.14 ppm
in the 90:10, 75:25, and 50:50 v/v acetonitrile/water mix-
tures, respectively. This simple molecule is one of the few
probes capable of displaying selective chromogenic sensing
features for fluoride in mixed aqueous solutions. Further-
more, we designed and prepared TLC silica foils functional-
ized by the reaction with 3, and we used them to detect the
fluoride anion in solution.
Table 1. The rate constants for the reaction of 2 and fluoride using the
acetonitrile/water mixtures containing different water contents.
Water content [%]
k1
k2
10
25
50
2.016
1.086
0.450
47.7ꢆ10À4
17.3ꢆ10À4
9.2ꢆ10À4
Experimental Section
Methods
determining step was the release of tert-butyldimethylsilyl
fluoride. Moreover, the rate constants became lower as the
amount of water increased.
1H and 13C NMR spectra were acquired using a Varian 300 spectrometer
(Sunnyvale, CA, USA). UV/Vis spectroscopy was carried out with
a Lambda 35 UV/Vis Spectrometer (Perkin–Elmer Instruments).
Encouraged by the sensing properties of probe 2, we took
one step further and studied the possible use of 2 to design
dip-sticks for fluoride detection. For this purpose, chemo-
dosimeter 2 was treated with (3-iodopropyl)trimethoxysilane
Reagents
All the reagents and anhydrous acetonitrile were purchased from Sigma–
Aldrich. Analytical grade solvents were acquired from Sharlab (Barcelo-
na, Spain).
to obtain the corresponding pyridinium cation
3 (see
Scheme 1). Compound 3 contains a trialkoxysilane moiety
and was easily anchored onto a silica support. Specifically,
we used silica TLC foils (1ꢆ3 cm) as the inorganic material.
These dip-sticks were used for the semiquantitative chromo-
genic detection of the fluoride anion in the acetonitrile/
water mixtures. In this case, probe 3, which was red,
changed color and became violet in the presence of fluoride.
Photographs of the dip-sticks after their immersion in solu-
tions containing fluoride at concentrations of 1.0ꢆ10À4, 1.0ꢆ
10À3, and 1.0ꢆ10À2 moldmÀ3 were taken. The red, green,
and blue values of each photograph were measured and
Synthesis of (E)-4-(pyridin-4-yldiazenyl)phenol (1)
Azoic dye 1 was obtained through a well-known procedure.[15] 4-amino-
piridine (3 g, 0.0318 mol) was dissolved in 7.5m hydrochloric acid
(25 mL). Then, a mixture containing 10% NaOH (20 mL), phenol (2.5 g,
0.0265 mol), and NaNO2 (2 g, 0.028 mol) was prepared and added drop-
wise at 08C to the 4-aminopyridine solution. The crude product was iso-
lated by filtration and purified by crystallization from acetone/ethanol to
give an orange powder. 1H NMR and 13C NMR spectra agree with those
reported by Cui et al.
Synthesis of (E)-4-(4-(tert-butyldimethylsilyloxy)styryl)pyridine (2)
tert-Butylchlorodimethylsilane (125 mg, 0.833 mmol) was added to trie-
thylamine (0.180 mL, 1.25 mmol) in anhydrous acetonitrile (15 mL). The
appearance of a white precipitate was observed. Then, the mixture was
added to an acetonitrile (50 mL) suspension of 1 (163 mg, 1.22 mmol).
The mixture was stirred overnight in an argon atmosphere. The final
crude product was purified by column chromatography using Al2O3 as
the stationary phase and ethyl acetate/hexane 1:9 v/v as the eluent. The
final dosimeter 2 was isolated as yellow crystals.
1H NMR (300 Mhz, CDCl3): d=0.24 (s, 6H), 0.98 (s, 9H), 6.94 (d, 2H,
J=9 Hz), 7.64 (d, 2H, J=6 Hz), 7.87 (d, 2H, J=9 Hz), 8.74 ppm (d, 2H,
J=6 Hz).
color difference maps were generated (see Figure 5).[18]
A
gradual color change from blue
to light green was observed as
the fluoride concentration in-
creased. Following this simple
procedure, fluoride concentra-
tions of 10À4 moldmÀ3 could be
detected.
In summary, we prepared and
studied a novel azoic-based col-
orimetric chemodosimeter (2)
that can selectively sense fluo-
ride in acetonitrile/water mix-
tures over several other anions
by a visible color change. The
chromogenic response mecha-
nism arises from fluoride hy-
drolysis of a silyl ether moiety
Figure 5. The color difference
maps of fluoride at the speci-
fied
concentrations
(in
moldmÀ3) after the immersion
of the dip-sticks functionalized
with 3 in the acetonitrile/water
9:1 v/v solutions (pH 8.0) con-
taining the anion. For display
purposes, the color range of
the difference maps was ex-
panded from 4 bits to 8 bits
per color (RGB range of 3–16
expanded to 0–225).
13C NMR (300 Mhz, CDCl3): d=À4.05, 18.57, 25.89, 116.44, 120.91,
125.71, 147.48, 151.48, 157.69, 160.27 ppm.
Synthesis of pyridinium salt (3)
Compound 2 (100 mg, 0.32 mmol) and (3-iodopropyl)trimethoxysilane
(0.093 mL, 0.32 mmol) were dissolved in anhydrous acetonitrile (25 mL).
Excess sodium carbonate was added to this solution, and the resulting
suspension was heated at reflux for 72 h in an argon atmosphere. The
crude reaction mixture was filtered to eliminate sodium carbonate, dis-
solved in dichloromethane, filtered again, and evaporated to give com-
pound 3 with no need for further purification.
1H NMR (300 Mhz, CDCl3): d=0.29 (s, 6H), 0.79 (m, 2H), 1.03 (s, 9H),
1.94 (m, 2H) 3.24 (m, 2H), 3.59 (s, 9H), 7.01 (d, 2H, J=9 Hz), 7.72 (d,
2H, J=6 Hz), 7.94 (d, 2H, J=9 Hz), 8.79 ppm (d, 2H, J=6 Hz).
embedded in the chemical structure of the chemodosimeter.
Studies of different acetonitrile/water mixtures showed that
the fluoride signaling reaction slowed down as the amount
of water increased. Typical detection times of 15, 40, and
13C NMR (300 Mhz, CDCl3): d=À4.05, 10.72, 11.21, 18.57, 25.87, 27.54,
50.88, 51.01, 116.79, 120.96, 125.89, 147.50, 150.69, 157.69, 160.27 ppm.
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Azo Dyes for Chromogenic Fluoride Anion Detection
Preparation of the TLC foils functionalized with 3
e) T. W. Hudnall, C. W. Chiu, F. P. Gabbaꢇ, Acc. Chem. Res. 2009, 42,
388–397; f) S. Rochat, K. Severin, Chem. Commun. 2011, 47, 4391–
4393; g) P. Rajamalli, E. Prasad, Org. Lett. 2011, 13, 3714–3717.
[7] a) V. Amendola, D. Estebꢁn-Gꢂmez, L. Fabbrizzi, M. Licchelli, Acc.
Chem. Res. 2006, 39, 343–353; b) M. Boiocchi, L. Del Boca, D.
Estebꢁn-Gꢂmez, L. Fabbrizzi, M. Licchelli, E. Monzani, J. Am.
Chem. Soc. 2004, 126, 16507–16514; c) D. Estebꢁn-Gꢂmez, L. Fab-
brizzi, M. Licchelli, J. Org. Chem. 2005, 70, 5717–5720.
[8] a) S. K. Kim, J. I. Hong, Org. Lett. 2007, 9, 3109–3112; b) T. H. Kim,
T. M. Swager, Angew. Chem. 2003, 115, 4951–4954; Angew. Chem.
Int. Ed. 2003, 42, 4803–4806; c) X. Jiang, M. C. Vieweger, J. C. Bol-
linger, B. Dragnea, D. Lee, Org. Lett. 2007, 9, 3579–3582; d) X.-F.
Yang, Spectrochim. Acta Part A 2007, 67, 321–326; e) X.-F. Yang, S.-
J. Ye, Q. Bai, X.-Q. Wang, J. Fluoresc. 2007, 17, 81–87; f) C. Q. Zhu,
J. L. Chen, H. Zheng, Y. Q. Wu, J. G. Xu, Anal. Chim. Acta 2005,
539, 311–316; g) S. Y. Kim, J. Park, M. Koh, S. B. Park, J. I. Hong,
Chem. Commun. 2009, 4735–4737; h) P. Sokkalingam, C. H. Lee, J.
Org. Chem. 2011, 76, 3820–3828; i) X. Cao, W. Lin, Q. Yu, J. Wang,
Org. Lett. 2011, 13, 6098–6101.
Silica TLC foils (1ꢆ3 cm) were immersed in an acetone solution of che-
modosimeter 3 (3.0ꢆ10À4 moldmÀ3) for 10 min. By this simple procedure,
the alkoxysilane moieties of 3 reacted with the silanols of the surface,
leading to a covalent grafting of the chemodosimeter.
Anion sensing studies
A stock solution of 2 (3.0ꢆ10À4 moldmÀ3) in acetonitrile was obtained
and used to prepare an acetonitrile/water 9:1 v/v solution of 2 (3.0ꢆ
10À5 moldmÀ3), which was used directly for the UV/Vis measurements in
the presence of the selected anions. In a typical assay, the final solution
of 2 (2.5 mL) was placed in a 3 mL glass cuvette and the necessary
amounts of the selected anions (acetonitrile solutions) were added. Final-
ly, the UV/Vis spectrum was measured.
Acknowledgements
[9] A. O. Bozdemir, F. Sozmen, O. Buyucakir, R. Guliyev, Y. Cakmak,
E. U. Akkaya, Org. Lett. 2010, 12, 1400–1403.
[10] L. Fu, F.-L. Jiang, D. Fortin, P. D. Harvey, Y. Liu, Chem. Commun.
2011, 47, 5503–5505.
[11] V. Bhalla, H. Singh, M. Kumar, Org. Lett. 2010, 12, 628–631.
[12] B. Zhu, F. Yuan, R. Li, Y. Li, Q. Wei, Z. Ma, B. Du, X. Zhang,
Chem. Commun. 2011, 47, 7098–7100.
The authors thank the Spanish Government (project MAT2009-14564-
C04), the Generalitat Valenciana (project PROMETEO/2009/016) and
the CIBER-BBN for their support. A.A. also thanks the Generalitat Va-
lenciana for his Santiago Grisolia fellowship.
[13] Y. Jiang, X. Hu, J. Hu, H. Liu, H. Zhong, S. Liu, Macromolecules
2011, 44, 8780–8790.
Keywords: fluorides · hydrolysis · sensors · silyl ether
[14] A. B. Descalzo, D. Jimꢃnez, J. El Haskouri, D. Beltrꢁn, P. Amorꢂs,
M. D. Marcos, R. Martꢀnez-MꢁÇez, J. Soto, Chem. Commun. 2002,
562–563.
[1] a) J. L. Sessler, P. A. Gale, W.-S. Cho, Anion Receptor Chemistry,
Royal Society of Chemistry, Cambridge, 2006; b) A. Bianchi, K.
Bowman, E. Garcia-EspaÇa, Supramolecular Chemistry of Anions,
Wiley-VCH, New York, 1997; c) P. D. Beer, P. A. Gale, Angew.
Chem. 2001, 113, 502–532; Angew. Chem. Int. Ed. 2001, 40, 486–
516.
[2] M. Kleerekoper, Endocrinol. Metab. Clin. North Am. 1998, 27, 441–
452.
[3] R. H. Dreisbuch, Handbook of Poisoning, Lange Medical Publish-
ers, Los Altos, CA, 1980.
[15] See for example: a) F. Sancenꢂn, R. Martꢀnez-MꢁÇez, M. A. Miran-
da, M. J. Seguꢀ, J. Soto, Angew. Chem. 2003, 115, 671–674; Angew.
Chem. Int. Ed. 2003, 42, 647–650; b) M. Comes, G. Rodrꢀguez-
Lꢂpez, M. D. Marcos, R. Martꢀnez-MꢁÇez, F. Sancenꢂn, J. Soto,
L. A. Villaescusa, P. Amorꢂs, D. Beltrꢁn, Angew. Chem. 2005, 117,
2978–2982; Angew. Chem. Int. Ed. 2005, 44, 2918–2922; c) R. Casa-
sffls, E. Aznar, M. D. Marcos, R. Martꢀnez-MꢁÇez, F. Sancenꢂn, J.
Soto, P. Amorꢂs, Angew. Chem. 2006, 118, 6813–6816; Angew.
Chem. Int. Ed. 2006, 45, 6661–6664; d) E. Climent, R. Casasffls,
M. D. Marcos, R. Martꢀnez-MꢁÇez, F. Sancenꢂn, J. Soto, Chem.
Commun. 2008, 6531–6533; e) E. Climent, P. Calero, M. D. Marcos,
R. Martꢀnez-MꢁÇez, F. Sancenꢂn, J. Soto, Chem. Eur. J. 2009, 15,
1816–1820; f) T. balos, S. Royo, R. Martꢀnez-MꢁÇez, F. Sancenꢂn,
J. Soto, A. M. Costero, S. Gil, M. Parra, New J. Chem. 2009, 33,
1641–1645; g) P. Calero, M. Hecht, R. Martꢀnez-MꢁÇez, F. Sance-
nꢂn, J, Soto, J. L. Vivancos, K. Rurack, Chem. Commun. 2011, 47,
10599–10601.
[4] WHO (World Health Organization), Geneva, 2002.
[5] a) P. A. Gale, S. E. Garcia Garrido, J. Garric, Chem. Soc. Rev. 2008,
37, 151–190; b) R. Martꢀnez-MꢁÇez, F. Sancenꢂn, Chem. Rev. 2003,
103, 4419–4476; c) M. E. Moragues, R. Martꢀnez-MꢁÇez, F. Sance-
nꢂn, Chem. Soc. Rev. 2011, 40, 2593–2643; d) J. Yoon, S. K. Kim,
N. J. Singh, K. S. Kim, Chem. Soc. Rev. 2006, 35, 355–360; e) J. W.
Steed, Chem. Soc. Rev. 2009, 38, 506–519; f) C. Caltagirone, P. A.
Gale, Chem. Soc. Rev. 2009, 38, 520–563; g) P. A. Gale, R. Quesada,
Coord. Chem. Rev. 2006, 250, 3219–3244; h) V. Amendola, M. Bo-
nizzoni, D. Estebꢁn-Gꢂmez, L. Fabbrizzi, M. Lichelli, F. Sancenꢂn,
A. Taglietti, Coord. Chem. Rev. 2006, 250, 1451–1470.
[6] See for example: a) J. Y. Lee, E. J. Chao, S. Mukamel, K. C. Nam, J.
Org. Chem. 2004, 69, 943–950; b) C. H. Zhao, E. Sakuda, A. Waka-
miya, S. Yamaguchi, Chem. Eur. J. 2009, 15, 10603–10612; c) Q.-S.
Lu, L. Dong, J. Zhang, J. Li, L. Jiang, Y. Huang, S. Qin, C.-W. Hu,
X.-Q. Yu, Org. Lett. 2009, 11, 669–672; d) T. Mizuno, W. H. Wei,
L. R. Eller, J. L. Sessler, J. Am. Chem. Soc. 2002, 124, 1134–1135;
[16] L. Cui, Y. Zhao, Chem. Mater. 2004, 16, 2076–2082.
[17] a) B. Valeur, I. Leray, Coord. Chem. Rev. 2000, 205, 3–40; b) L. Fab-
brizzi, M. Lichelli, G. Rabaioli, A. Taglietti, Coord. Chem. Rev.
2000, 205, 85–108; c) K. Rurack, Spectrochim. Acta, Part A 2001,
57, 2161–2195.
[18] H. Lin, K. S. Suslick, J. Am. Chem. Soc. 2010, 132, 15519–15521.
Received: April 11, 2012
Published online: && &&, 0000
Chem. Asian J. 2012, 00, 0 – 0
ꢅ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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These are not the final page numbers! ÞÞ

COMMUNICATION
Sensors
Finding fluoride: An azo dye function-
alized with tert-butyldimethylsilyl ether
has been synthesized and used as
a selective chromogenic fluoride
sensor in the acetonitrile/water mix-
tures. The chromogenic response arises
from the fluoride-induced hydrolysis of
the silyl ether moiety, which yields
a highly colored phenolate anion. The
sensor molecule can be grafted to
silica to make dip-sticks for fluoride
sensing.
Alessandro Agostini, Michele Milani,
Ramꢀn Martꢁnez-MꢂÇez,*
Maurizio Licchelli,* Juan Soto,
Fꢃlix Sancenꢀn
&&&& — &&&&
Azo Dyes Functionalized with Alkoxy-
silyl Ethers as Chemodosimeters for
the Chromogenic Detection of the
Fluoride Anion
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www.chemasianj.org
ꢅ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!