New fluorescent sensor for antimony and transition metal cations based on rhodamine amide-arm homotrioxacalix[3]arene

Article abstract of DOI:10.1007/s10847-009-9665-z

A new fluorescent sensor 1 based on the rhodamine amide-armed homotrioxacalix[3]arene was synthesized, and its sensing behavior toward metal ions was investigated by UV-vis and fluorescence spectroscopies. Upon the addition of metal cations (Sb³⁺, Fe³⁺, Ni²⁺), a significant fluorescent enhancement in the range of 500-600 nm and colorimetric change was observed. Springer Science+Business Media B.V. 2009.

Full text of DOI:10.1007/s10847-009-9665-z

J Incl Phenom Macrocycl Chem (2010) 66:125–131
DOI 10.1007/s10847-009-9665-z
ORIGINAL ARTICLE
New fluorescent sensor for antimony and transition metal cations
based on rhodamine amide-arm homotrioxacalix[3]arene
Chong Wu Æ Wen-Juan Zhang Æ Xi Zeng Æ Lan Mu Æ
Sai-Feng Xue Æ Zhu Tao Æ Takehiko Yamato
Received: 6 July 2009 / Accepted: 11 August 2009 / Published online: 25 August 2009
Ó Springer Science+Business Media B.V. 2009
Abstract A new fluorescent sensor 1 based on the rho-
damine amide-armed homotrioxacalix[3]arene was syn-
thesized, and its sensing behavior toward metal ions was
investigated by UV–vis and fluorescence spectroscopies.
quick detection by a simple fluorescent enhancement (turn-
on) or quenching (turn-off) response [5–8]. Fluorescent
chemosensors, which combine two fundamental functional
units: a fluorophore and an ionophore. The part of iono-
phore can selectively bind the substrate, and the part of
fluorophore is attached to the vicinity of the binding site for
signal detection and transduction. The probes not only
provide a means of detection to investigate the process of
molecular recognition, but also can be used as the archi-
tectures for assembling the OFF–ON fluorescent switching.
The rhodamine framework is an ideal mode to act as the
fluorophore of fluorescent chemosensors due to its partic-
ular properties. It is well known that many derivatives of
rhodamine undergo an equilibrium between spirolactam
and ring-opened amide, and the two forms always exhibit
completely different fluorescent properties. Rhodamine-
based OFF/ON-type fluorescent probes have received
increasing interests on different metal ions in recent years
[9–14].
3?
3?
2?
Upon the addition of metal cations (Sb , Fe , Ni ), a
significant fluorescent enhancement in the range of 500–
6
00 nm and colorimetric change was observed.
Keywords Fluorescent sensor Á
Homotrioxacalix[3]arene Á Rhodamine Á
Antimony and transition metal cations
Introduction
The design and synthesis of new chemosensors for heavy
and transition metal (HTM) cations is an important subject
in the field of supramolecular chemistry due to their sig-
nificant importance in chemical, biological, and environ-
mental assays [1–4]. Particular interests in this regard are
fluorescent sensors because they allow nondestructive and
Calixarenes are useful building blocks for the design of
molecular receptors able to bind neutral or charged species.
Their potential applications as sensing agents have
received increasing interest [15–19]. Especially, linkage of
fluorogenic compounds to appropriately functionalized
calixarenes as ion receptors has afforded such efficient
fluorescence chemosensors possessing abilities to selec-
tively sense specific chemical species [20–25].
C. Wu Á W.-J. Zhang Á X. Zeng (&) Á L. Mu
School of Chemistry and Chemical Engineering, Guizhou
University, 550003 Guiyang, Peoples Republic of China
e-mail: zengxi1962@163.com
S.-F. Xue Á Z. Tao
Herein, we report a new fluorescent sensor 1 for heavy
and transition metal cations. We choose rhodamine as a
fluorophore moiety to incorporate to the homotrioxaca-
lix[3]arene skeleton. The homotrioxacalixarene adopts the
cone conformation to form a cavity to encapsulate target
ions. Strong signal output in neutral aqueous environments
of recognition, high sensitivity made 1 to be a potential
powerful candidate as a practical fluorescent sensor for
Key Laboratory of Macrocyclic and Supramolecular Chemistry
of Guizhou Province, Guizhou University, 550025 Guiyang,
Peoples Republic of China
T. Yamato (&)
Department of Applied Chemistry, Faculty of Science and
Engineering, Saga University, Honjo-machi 1, Saga-shi, Saga
840-8502, Japan
e-mail: yamatot@cc.saga-u.ac.jp
123

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26
J Incl Phenom Macrocycl Chem (2010) 66:125–131
3
?
heavy and transition metal cations. This is the first example
of rhodamine-based homotrioxacalix[3]arene fluorescent
chemosensor.
addition of the Sb , a new absorption band centered at
556 nm appears, which induces a color change from
colorless to pink (Fig. 1b). The nonlinear fitting of the
titration curve and the Job’s plot (Fig. 1c) imply that a
3
?
3
:1 stoichiometry is most possible for the binding of Sb
Results and discussion
by 1.
3
?
The complexation of Sb by 1 was also investigated by
As depicted in Scheme 1, sensor 1 was synthesized from 2
and 3 in the presence of excess DCC and HoBt. After the
column chromatography using chloroform/ethyl ace-
tate(1:1) as eluent, 1 was obtained as a white solid in 82%
means of fluorescence titration. As shown in Fig. 2a, upon
3
?
the addition of Sb , a new emission centered at 557 nm
appears, and the intensity increases gradually along with a
remarkable orange fluorescence (Fig. 2b). The linear fitting
3?
of the titration curve assumed a 3:1 stoichiometry of Sb -
1
yield. The finial product 1 was well characterized by H
1
3
NMR, C NMR, ESI–MS, and elemental analysis. The H
1
1 complex (Fig. 2a inset). The Job’s plot (Fig. 2c) reveals a
3
?
NMR spectrum shows three singlets for the tert-butyl
protons at d = 1.04 ppm, ArOCH CO and the aromatic
3:1 binding stoichiometry of Sb -1 complex. Both UV–
vis and fluorescence data lead to a significant OFF–ON
signal.
2
protons at d = 4.11 and 6.93 ppm, and a pair of doublets
for the ArCH OCH Ar protons, suggesting a D -sym-
The selective coordination studies of 1 were then
extended to related heavy, transition, and main group
metal ions by UV–vis spectroscopy. As shown in Fig. 3,
2
2
3h
metrical structure of 1. These indicate that 1 has a cone
conformation [26, 27].
3
?
3?
2?
A acetonitrile aqueous at pH 7 of 1 mM tris-HCl buffer
solution was selected for the spectral investigation. The
addition of Sb , Fe , Ni cations (50 equiv) into the
3
solution of 1, Sb creates a remarkable enhanced (353-
?
3
nitrate salts of Fe , Ag , Ni , Co , Cd , Hg
?
?
2?
2?
2?
2?
3?
;
fold) absorbance. However Fe
displayed a 169-fold
provides 51 folds of emission
enhancement. In contrast, 50 equiv of others cations
3
chlorate salts of Sb , Cu , Fe , Zn and perchlorate
?
2?
2?
2?
2?
enhancement, and Ni
2
?
?
?
salts of Mg , Na , K ions were used to evaluate the
metal ion binding properties of compound 1 in tris-HCl
buffer (pH = 7) acetonitrile aqueous. The fluorescence
spectra were obtained by excitation of the rhodamine
fluorophore at 555 nm. Both the excitation and emission
slits were 5 nm.
2
?
2?
2?
?
2?
2?
2?
2?
?
(Fe , Cu , Co , Ag , Zn , Cd , Hg , Mg , Na ,
?
K ) show almost no increase in absorbance. These imply
?
that 1 can serve as naked-eye detection for Sb , Fe
3
3?
2
?
and Ni
.
The selective fluorimetric response of 1 to all the tested
metal ions was also studied, and a similar result also arises
from the fluorescence spectra (Fig. 4). The respective
Figure 1a shows the UV–vis spectral variation of 1
3
?
upon the gradual addition of Sb . The colorless free 1
solution exhibited almost no absorption peak in the visible
wavelength range ([400 nm), which indicates 1 exists as
a spirocyclic form. Moreover, the spirocyclic form of 1
was also confirmed by the distinctive spirocycle carbon at
3
?
emission enhancements upon addition of 50 equiv of Sb
2?
are 527-fold, 357-fold, 224-fold. Besides
,
3
Fe , Ni
?
2
?
2?
unexpected 57-fold (Cu ) and 40-fold (Fe ) emission
enhancements were arised, almost no emission enhance-
ment could be observed upon addition of 50 equiv of other
1
3
d = 65.64 ppm in the C NMR spectra [28]. Upon the
Scheme 1 Synthesis of
compound 1
1
23

J Incl Phenom Macrocycl Chem (2010) 66:125–131
127
Fig. 1 a UV–vis titration
spectra of 1 (25 lM) upon
3?
.
gradual addition of Sb
b Changes in color. c Job’s plot
3
?
(
[Sb ] ? [1] = 50 lM)
Fig. 2 a Fluorescence titration
spectra of 1 (25 lM) upon
3?
.
gradual addition of Sb
b Changes in color (excitation at
55 nm). c Job’s plot
5
3?
(
[Sb ] ? [1] = 50 lM)
3
?
cations. Therefore, probe 1 can acts as a potential turn-on
The selectivity of 1 for Sb were further tested when
coexist with other cations (Figs. 5, 6). The increases of
absorbance and fluorescence intensity resulting from the
3
?
3?
2?
fluorescent chemosensor for Sb , Fe and Ni . The
3
?
fluorescence quantum yields of 1 with 10 equiv of Sb
,
3
Fe and Ni are determined to be 0.11, 0.10 and 0.09,
?
2?
3?
addition of the Sb were not influenced by the subsequent
3
?
2?
addition of miscellaneous cations except for Fe , Fe ,
respectively, using rhodamine B as a standard (U = 0.89)
2
Cu , these cations enhanced the Sb -induced 1 spectrum
?
3?
[
29].
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1
28
J Incl Phenom Macrocycl Chem (2010) 66:125–131
Fig. 6 Fluorescence response of 1 (5 lM) to various cations and
selectivity of 1 for Sb in the presence of other cations. White bars
represent the addition of the appropriate metal ion (50 equiv). Black
Fig. 3 Absorption spectra of 1 (5 lM) in the absence and presence of
different metal ions (50 equiv)
3?
3?
bars represent the addition of Sb (50 equiv) to the solution
After addition of excess ethylenediamine to a solution
3
?
3?
2?
containing 1 with Sb , Fe , Ni , both pink color and
orange fluorescence immediately disappear. This indicates
a reversible coordination of 1 with metal cations and rules
out the occurrence of an irreversible chemical reaction
[
30–32]. Considering the behaviors of fluorescence and
3
absorption spectra, the turn-on response of 1 to Fe and
?
2
?
Ni
may be explained by the spirocycle open–close
mechanism, as is also the case for rhodamine-based
chemosensors: the free probe 1 is the spirocyclic form,
which is colorless and nonfluorescent, whereas the coor-
dination of the amide carbonyl oxygen to cations leads to
the spirocycle opening, resulting in an appearance of vis-
ible absorption and fluorescence.
Fig. 4 Fluorescence spectra of 1 (5 lM) in the absence and presence
of different metal ions (50 equiv)
Conclusion
we have presented a novel fluorescent sensor 1 based on a
rhodamine amide-armed homotrioxacalix[3]arene, which
showed a strong enhancement of visible color and fluo-
3
?
3?
2?
rescence enhancement upon addition of Sb , Fe , Ni
while showing almost no response to other cations. Com-
pound 1 may therefore be applicable as a homotrioxaca-
lix[3]arene based rhodamine turn-on type fluorescent
chemosensor. The obtained findings also indicate that
various rhodamine-based chemosensors for HTM cations
may easily be made by incorporating various ligand
groups. The works are in progress in our laboratory.
Fig. 5 Absorbance response of 1 (5 lM) to various cations and
selectivity of 1 for Sb in the presence of other cations. White bars
represent the addition of the appropriate metal ion (50 equiv). Black
3?
3?
bars represent the addition of Sb (50 equiv) to the solution
Experimental
response a little. All of these results indicated that the high
3
?
selectivity of 1 for Sb
except in test condition.
over other competing cations
All the melting point determinations were performed on a
Boetius apparatus and are uncorrected. NMR spectra
1
23

J Incl Phenom Macrocycl Chem (2010) 66:125–131
129
(
500 MHz) were recorded on a Varian Nova spectrometer
(20 mL 9 2). The combined organic phase was washed
with SiMe as an internal reference: J-values are given in
4
twice with water and dried over Na SO . The solvent was
2
4
Hz. ESI MS spectra were obtained on a HP LC-MSD
spectrometer without using the LC part. IR spectra were
measured for samples as KBr pellets in a Bruker Vertex 70
FT-IR spectrophotometer. UV spectra were measured by
an Amersham Biosciences Ultrospec 5300 spectropho-
tometer. Elemental analyses were performed by Vario EL
III Elemental Analyzer.
removed in vacuo, after that, the residue was recrystallized
from ethanol and the light yellow cubic crystal 3 was
1
obtained in a 76% yield; m.p. 216–218 °C. H NMR
(CDCl ): d = 1.16 (t, 12H, J = 6.4 Hz, NCH CH ), 2.45
3
2
3
(t, 2H, J = 6.4 Hz, NCH CH NH ), 3.20(t, 2H,
2
2
2
J = 6.0 Hz, NCH CH NH ), 3.33 (q, 8H, J = 6.8 Hz,
2
2
2
NCH CH ), 6.27 (d, 2H, J = 6.4 Hz, Ar–H), 6.37 (s, 2H,
2
3
Ar–H), 6.43 (d, 2H, J = 6.4 Hz, Ar–H), 7.10 (s, 1H, Ar–H),
3
1
Materials
7.45 (t, 2H, J = 5.4 Hz, Ar–H), 7.90 (s, 1H, Ar–H).
NMR (500 MHz, CDCl ): d = 170.20, 153.64, 153.24,
C
3
cone-7,15,23-tri-tert-butyl-25,26,27-tris[(N,N-diethylamino)
methoxy]-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalix[3]
arene and cone-7,15,23-tri-tert-butyl-25,26,27-tris[(hydro-
xycarbonyl)methoxy]- 2,3,10,11,18,19-hexahomo-3,11,19-
trioxacalix[3]arene 2 were prepared according to the
reported procedures [26, 33].
149.16, 132.93, 129.94, 128.18, 123.83, 123.05, 108.78,
104.04, 98.09, 66.63, 44.44, 41.14, 39.93, 12.74. ESI–MS
?
m/z 485.3 (M ? H ) . Anal. calcd for C H N O : C
?
3
0 36 4 2
74.35, H 7.49, N 11.56, O 6.60; found C 73.66, H 7.57, N
11.72, O 7.05.
Synthesis of 1
Preparation of cone-hexahomotrioxacalix[3]arene
triacetic acid (2)
HoBt (270 mg, 2.00 mmol) and 3 (2.70 g, 5.55 mmol)
were added to a solution of 2 (500 mg, 0.667 mmol) in
CH Cl (50 mL). The mixture was then stirred at 0 °C
To a mixture of cone-7,15,23-tri-tert-butyl-25,26,27-tris
2
2
[
(N,N-diethylamino)methoxy]-2,3,10,11,18,19-hexahomo-3,
1,19-trioxacalix[3]arene (1.0 g, 1.14 mmol) in dioxane
35 mL) was added 1 M KOH aqueous solution (40 mL).
while a solution of DCC (1.35 g, 13.55 mmol) in CH Cl
2 2
1
(50 mL) was added dropwise. The solution was stirred for
1 h at 0 °C and for an additional 24 h at room temperature.
After completion, the solvent was removed under reduced
pressure. The residue was purified by column chromatog-
(
After the mixture was refluxed for 3 days, it was condensed
under reduced pressure, then acidified by hydrochloric acid
to pH 1–2. The dispersion was extracted with ethyl acetate
raphy (silica gel, CHCl /ethyl(1:1) acetate) to give 881 mg
3
(
2 9 30 mL). The combined extracts were washed with
water (2 9 20 mL), saturated brine (20 mL), dried
Na SO ) and condensed under reduce pressure. The resi-
of 1 as a colorless solid in 61.5% yield; m.p. 158–161 °C.
1
H NMR (500 MHz, CDCl ):d (ppm) 7.78 (d, 1H,
3
(
J = 6.5 Hz, Ar–H), 7.35 (m, 2H, Ar–H), 7.00 (d, 1H, J =
6.5 Hz, Ar–H), 6.92(s, 2H, Ar–H), 6.45 (d, 2H, J = 8.8 Hz,
Ar–H), 6.35 (d, 2H, J = 2.3 Hz, Ar–H), 6.22,6.24 (d, d,
2
4
due was washed with small amount of diethyl ether to give
the crude 2 as a colorless solid. Recrystallization from
methanol gave 2 (730 mg, 85%) as colorless powder; m.p.
2H, J = 2.7 Hz, Ar–H), 4.65 (d, 2H, J = 13 Hz, ArCH O),
2
1
2
27–229 °C. H NMR (500 MHz, CDCl ):d = 1.17 (s, 27
4.38(d, 2H, J = 13 Hz, ArCH O), 4.05 (s, 2H, ArOCH ),
2
3
2
H, tBu), 4.18 (t, J = 12.4 Hz, 6 H, ArCH O), 4.35 (s, 6 H,
ArOCH ), 4.89 (d, J = 12.4 Hz, 6 H, ArCH O), 6.93 (s, 6
3.24–3.28 (m, 10H, J = 8.5 Hz, NCH CH , CH CH
2 3 2 2
2
NHCO), 3.10 (m, 2H, OCNHCH CH ), 1.05–1.08 (m, 21H,
2 2
13
2
2
1
3
H, Ar–H). C NMR (CDCl /DMSO, 1:1): d = 31.66,
NCH CH , tBu); C NMR (500 MHz, CDCl ): d =
2 3
3
3
3
4.25, 69.58, 70.62, 126.25, 131.15, 145.72, 153.16,
169.02, 168.52, 154.35, 153.25, 152.51, 148.77, 146.40,
130.96, 130.49, 128.72, 126.48, 123.74, 122.90, 108.33,
105.37, 97.92, 73.56, 69.05, 65.24, 44.32, 39.82, 38.84,
34.30, 31.58, 12.74. ESI-Mass m/z (2,172.5) (M ?
?
71.36. ESI–MS m/z 749.4 (M–H ) . Anal. calcd for
?
1
C H O : C 67.18, H 7.25, O 25.57; found C 67.37,
42 54 12
H 7.39, O 25.24.
?
Na ? H) . Anal. calcd for C132H156O N : C 73.72, H
15 12
Synthesis of 3
7.31, N 7.82, O 11.16; found C 73.66, H 7.38, N 7.72,
O 11.24.
To a 100 mL flask, rhodamine B (1 g, 2.1 mmol) was
dissolved in 50 mL ethanol. Ethylenediamine (1 mL,
excess) was added dropwise to the solution and refluxed
overnight (12 h) until the solution loses its red color and
become clear. Then the mixture was cooled and solvent
was removed under reduced pressure. Water (20 mL) was
added to the resultant and extracted with CH Cl
Stoichiometry of metal complexation
To confirm the binding mechanism, IR spectrum of 1
(10 mM) was measured in acetonitrile (Fig. 7). The two
-
amide carbonyl absorption of 1 at 1,685.18 cm drasti-
1
cally shifts to lower frequency upon addition of 10 equiv of
2
2
123

1
30
J Incl Phenom Macrocycl Chem (2010) 66:125–131
Fig. 7 Infrared spectra of 1
25 mM) measured in
acetonitrile with or without 10
(
3
?
3?
2?
,
equiv of Sb , Fe , and Ni
respectively
Scheme 2 The proposed mode
for 1 binding with metal cation
3
?
-1
(1,618.83 cm ), Fe
3?
-1
(1,633.24 cm ), Ni
2?
Sb
4. Rurak, K.: Flipping the light switch ‘ON’—the design of sensor
molecules that show cation-induced fluorescence enhancement
with heavy and transition metal ions. Spectrochim. Acta Part A
Mol. Biomol. Spectrosc. 57, 2161–2195 (2001)
5. Czarnik, A.W.: Fluorescent Chemosensors for Ion and Molecule
Recognition. American Chemical Society, Washington, DC
-
1,632.89 cm ). These indicate that the amide carbonyl O
1
(
of 1 is actually involved in the coordination with metal
cations [34, 35]. Considering the Job’s plot and the above
experimental evidence, coordination of metal cation with 1
forms a 3:1 complex (Scheme 2), where the two binding
sites (two amide carbonyl oxygen) within every arm of 1
form chelate pocket with cations.
(
1993)
6
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Acknowledgments This work was supported by the Foundation of
the Governor of Guizhou Province, China (No. 200617) and the
Talented Person Foundation of Guizhou University (No. 2007039).
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