Highly selective ratiometric fluorescence determination of Ag+ based on a molecular motif with one pyrene and two adenine moieties

Article abstract of DOI:10.1021/ol8006716

(Chemical Equation Presented) A highly selective ratiometric fluorescence sensor for Ag⁺ was developed with a molecular motif containing one pyrene and two adenine moieties.

Full text of DOI:10.1021/ol8006716

ORGANIC
LETTERS
2008
Vol. 10, No. 11
2271-2274
Highly Selective Ratiometric
Fluorescence Determination of Ag+
Based on a Molecular Motif with One
Pyrene and Two Adenine Moieties
Lei Liu,†,‡ Deqing Zhang,*,† Guanxin Zhang,† Junfeng Xiang,† and Daoben Zhu†
Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China, and
Graduate School of Chinese Academy of Sciences, Beijing 100049, China
dqzhang@iccas.ac.cn
Received March 24, 2008
ABSTRACT
A highly selective ratiometric fluorescence sensor for Ag+ was developed with a molecular motif containing one pyrene and two adenine
moieties.
Silver and its compounds are widely used in electrical industry,
photographic and imaging industry, and pharmacy. However,
silver ions inactivate sulfhydryl enzymes and combine with
amine, imidazole, and carboxyl groups of various metabolites.
There are also many reports on silver bioaccumulation and
toxicity.1 Thus, development of sensitive and selective methods
for the determination of trace amounts of silver ions (Ag+) in
various media is of considerable importance for the environment
and human health.
comparison, sensitive and selective optical sensors for Ag+
with simple instrumental implementation and easy-operation
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Various approaches,2 such as atomic absorption spectros-
copy and inductively coupled plasma-mass spectroscopy,
have been described for the trace-quantity (down to ppb
range) determination of Ag+. Potentiometric methods for Ag+
assay based on ion-selective electrodes are also reported with
detection limit reaching 10-8 M range. But, most of these
methods are expensive and time-consuming in practice. In
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† Chinese Academy of Sciences.
‡ Graduate School of Chinese Academy of Sciences.
10.1021/ol8006716 CCC: $40.75
Published on Web 05/02/2008
2008 American Chemical Society

have received a lot of attention.3 To the best of our
knowledge, ratiometric fluorescent sensors for Ag+, espe-
cially with fluorescence enhancement technique, still remain
rare.3f,g Herein, we describe a selective ratiometric fluorescent
sensor for Ag+ based on a molecular motif with one pyrene
and two adenine moieties (compound 1, Scheme 1).
is expected to form; formation of such complex would induce
the pyrene moiety in 1 to be adjacent to each other, and
accordingly result in pyrene excimer emission. The results
show that compound 1 can indeed selectively bind Ag+
inducing the gradual enhancement of the pyrene excimer
emission and the simultaneous decrease of the monomer
emission of the pyrene moiety. Therefore, highly selective
ratiometric fluorescence determination of Ag+ is realized with
compound 1.
The synthesis of 1 started from 1,1,1-tris (hydroxymethyl)
ethane which was converted to trisulfonate 2 by reaction with
benzenesulfonyl chloride. After reaction with 4-nitrophenol
in the presence of K2CO3, compound 2 was transformed into
compound 3. Reduction of 3 and further reaction with maleic
anhydride led to trimaleimide 5. Reaction of trimaleimide 5
with thiol 6 afforded 7 exclusively by controlling the amount
of 6 added to the reaction mixture. In situ reaction of bis-
maleimide 7 with thiol 8 yielded the desired compound 1.8
Figure 1 shows the fluorescence spectrum of compound 1
and those in the presence of different amounts of AgClO4
Scheme 1. Chemical Structure of Compound 1
Our design employs coordination between Ag+ and
nucleobases to induce pyrene excimer emission. Recent
results have revealed that the nucleobases offer a versatile
platform for metal ion coordinations.4 For instance, thymine
can bind Hg2+ specifically, and by making use of this feature
a sensitive and selective “turn on” fluorescent chemosensor
for Hg2+ ion based on a pyrene-thymine dyad has been
described by our group recently.5 9-Substituted adenine offers
three main coordination sites (N1, N3, and N7).6 While most
of the complexes of adenine with metal ions exhibit mono-
and bidentate coordination modes, the 3N (µ-N1, N3, N7)
coordination mode for 9-substituted adenine has been
observed in silver-adenine metallaquartets.7 When com-
pound 1 is allowed to react with Ag+, an extended complex
Figure 1
.
Fluorescence spectra of compound 1 (2.0 × 10-5 M in
THF) in the presence of increasing amounts of AgClO4 (from 0 to
27 µM).
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Soc. 2003, 125, 2884–2885.
in THF. Compound 1 shows typical monomeric emission
bands of pyrene unit around 376 and 395 nm (λex ) 344
nm);9 the emission in the range of 450-600 nm was rather
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(8) Characterization data of compound 1: mp 138 °C dec; 1H NMR (600
MHz, CDCl3, ppm) δ 8.35-8.38 (m, 3H), 8.12-8.18 (m, 4H), 8.00-8.05
(m, 4H), 7.79 (s, 2H), 7.16-7.19 (m, 6H), 6.98 (d, J ) 8.7 Hz, 6H), 5.84
(br, 4H), 5.21 (s, 2H), 4.17-4.20 (m, 4H), 4.08 (s, 6H), 3.78-3.80 (m,
3H), 3.59-3.60 (m, 2H), 3.22-3.27 (m, 3H), 3.09-3.11 (m, 2H), 2.92-2.93
(m, 3H), 2.76-2.80 (m, 3H), 2.60-2.65 (m, 3H), 1.91-1.93 (m, 5H),
1.64-1.67 (m, 12H), 1.40-1.44 (m, 4H), 1.37-1.39 (m, 6H), 1.20-1.25
(m, 6H); 13C NMR (150 MHz, CDCl3) δ 174.73, 174.67, 173.0, 172.8,
158.0, 154.4, 151.9, 149.1, 139.5, 130.9, 130.25, 130.18, 129.8, 128.3,
126.64, 126.57, 126.4, 126.3, 125.9, 124.9, 124.1, 123.9, 123.6, 123.5, 122.5,
118.6, 114.2, 70.4, 69.6, 69.2, 44.8, 42.6, 39.5, 38.1, 38.0, 35.2, 35.0, 30.9,
30.5, 28.8, 28.4, 28.1, 28.0, 27.8, 27.3, 25.2, 24.6, 16.2, 7.6; MALDI-TOF
(M + 2H)+, 1541.7, (M + Na + H)+, 1563.7; HRMS (MALDI-TOF) calcd
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10–13. (a) Other chemical sensors for Hg2+ have been also reported: (a)
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4093–4096. (b) Ono, A.; Togashi, H. Angew. Chem., Int. Ed. 2004, 43,
4300–4302. (c) Tang, Y. L.; He, F.; Yu, M. H.; Feng, F. D.; An, L. L.;
Sun, H.; Wang, S.; Li, Y. L.; Zhu, D. B. Macromol. Rapid Commun. 2006,
27 (6), 389–392. (d) Liu, B.; Tian, H. Chem. Commun. 2005, 3156–3158.
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7 (19), 4217–4220. (f) Guo, X. F.; Qian, X. H.; Jia, L. H. J. Am. Chem.
Soc. 2004, 126, 2272–2273. (g) Nolan, E. M.; Lippard, S. J. J. Am. Chem.
Soc. 2003, 125, 14270–1427.
+
for C84H94N13O10S3 (M + H)+ 1540.6403, found 1540.6388. COSY,
HMBC, HSQC, and TOCSY spectra are provided in the Supporting
(6) (a) Arpalahti, J.; Klika, K. D.; Molander, S. Eur. J. Inorg. Chem.
2000, 1007–1013. (b) De Meester, P.; Goodgame, D. M. L.; Skapski, A. C.;
Warnke, Z. Biochem. Biophys. Acta 1973, 324, 301–303.
Infromation.
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Org. Lett., Vol. 10, No. 11, 2008

weak. However, after addition of AgClO4, the emission bands
at 376 and 395 nm attributed to the monomeric emission of
pyrene unit became gradually weak and simultaneously a
new broad featureless band with λmax ) 478 nm, typical of
pyrene excimer emission, emerged.10 The intensity of this
new emission band increased by increasing the amounts of
AgClO4 added to the solution of 1 as displayed in Figure 1.
The variation of the monomeric emission (reduction of the
intensity) and the excimer emission (enhancement of the
intensity) of pyrene moiety of 1 after addition of AgClO4
led to an isoemission point at 430 nm. Similar fluorescnce
spectral variation was observed for 1 after addition of Ag(I)
Scheme 2. Synthetic Approach for Compound 1
-
-
-
-
salts with different anions (NO3 , PF6 , CF3SO3 , AsF6 ,
-
and BF4 ) (see Figure S8, Supporting Information).
Since an aqueous solution of AgClO4 was used for the
fluorescence measurement, the possibility that the pyrene
excimer emission is due to aggregation of 1 exists. But,
addition of the same volume of water to the THF solution
of 1 did not lead to the pyrene excimer emission; thus, this
control experiment ruled out such possibility. Also, the
competitive experiments with other metal ions, to be
discussed below, support this conclusion.
Figure 2 shows the variation of the fluorescence intensity
ratio (I478/I395) between the emission band at 478 nm and
resulted (I478/I395 ) 0.21[Ag+]-2.51, r ) 0.999, n ) 12) as
shown in Figure 2.
It should be noted that the enhancement of the excimer
emission intensity around 478 nm became rather small while
the monomeric emission band continued to decrease if more
Ag+ ([Ag+] > 2.5 × 10-5 M) was present in the solution of
1; further addition of Ag+ led to the reduction of both
monomeric and excimer emission bands. This can be
attributed to fluorescence quenching by silver ions3c,11 that
bind to coordination sites (N1, N3, N7) in compound 1. It is
expected that more Ag+ would bind adenine moiety if more
Ag+ is present.
In addition, absorption and 1H NMR spectral studies also
clearly indicated the coordination of 1 with Ag+. As shown
in Figure S5 (Supporting Information), the absorption
intensities of 1 in the range of 225-242 and 281-318 nm
increased while those in the range of 249-269 nm decreased
upon on adition of Ag+. Moreover, the absorption bands
around 250 and 340 nm were slightly red-shifted. These
absorption spectral changes indicated the binding of 1 with
Ag+ and formation the coordination complexes, according
to previous report.12 1H NMR spectra of 1 in the presence
Figure 2. Plot of the fluorescence intensity ratio (I478/I395) between
excimer emission band at 478 nm and monomer emission band at
395 nm vs the concentration of AgClO4.
that at 395 nm vs the concentration of AgClO4. Although
the monomeric and excimer emissions started to decrease
and increase, respectively, upon addition of Ag+, the
fluorescence intensity ratio (I478/I395) was small and was
enhanced just slightly when the concentration of Ag+ in the
solution of 1 was below 10 µM; but, it was enhanced
significantly if more Ag+ was added to the solution of 1. A
nearly linear plot of I478/I395 vs the concentration of Ag+
(10) (a) Nishizawa, S.; Kato; Teramae, N. J. Am. Chem. Soc. 1999, 121,
9463–9464. (b) Sahoo, D.; Narayanaswami, V.; Kay, C. M.; Ryan, R. O.
Biochemistry 2000, 39, 6594–6601. (c) Kim, J. S.; Choi, M. G.; Song, K. C.;
No, K. T.; Ahn, S.; Chang, S.-K. Org. Lett. 2007, 9, 1129–1132. (d) Choi,
J. K.; Kim, S. H.; Yoon, J.; Lee, K.-H.; Bartsch, R. A.; Kim, J. S. J. Org.
Chem. 2006, 71, 8011–8015. (e) Yuasa, H.; Miyagawa, N.; Izumi, T.;
Nakatani, M.; Izumi, M.; Hashimoto, H. Org. Lett. 2004, 6, 1489–1492.
(11) Shamsipur, M.; Alizadeh, K.; Hosseini, M.; Caltagirone, C.;
Lippolis, V. Sens, Actuator B-Chem. 2006, 113, 892–899
.
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Org. Lett., Vol. 10, No. 11, 2008
2273

of different amounts of Ag+ were recorded, and the signals
at 7.66 and 7.70 ppm due to protons linked to C-2 and C-8
of adenine units were gradually downfield shifted by increas-
ing the amounts of Ag+ (see Figure S7, Supporting Informa-
tion). This provided further support for the coordination of
1 with Ag+. In fact, a TOF/MS signal at 1648.3 (m/z)
2+
corrsponding to [1·Ag]2 was detected for the sample of 1
with 1.0 equiv of Ag+.
Based on the above studies, the possible stepwise binding
of 1 with Ag+ is illustrated in Scheme 3. Initially, two
Scheme 3
.
Illustration of the Binding Modes of Compound 1
with Ag+
Figure 3. Fluorescence intensity ratio (I478/I395) between the excimer
emission band at 478 nm and the monomeric emission band at 395
nm of compound 1 (1.0 × 10-5 M in THF) in the presence of
various metal ions (1.25 × 10-5 M).
be distinguished from Ag+ by available methods. These
results clearly indicate that compound 1 shows good
selectivity toward Ag+ and that other competitive metal ions,
such as Pb2+, Hg2+, Fe3+, and Cd2+, will induce a rather
low interfering effect on this ratiometric fluorescence assay
for Ag+.
In summary, compound 1 was designed with a view to
developing new fluorescent sensors for Ag+ by making use
of the binding of adenine with Ag+ to induce excimer
emission. Fluorescent spectral results clearly indicate that
compound 1 can be used as ratiometric fluorescent sensor
for Ag+ with good selectivity and sensitivity. Further studies
include the design of new analogues of 1 with good solubility
in water which will enable the practical application of this
type of Ag+ sensor to be implemented.
molecules of 1 are associated through the coordination of
two adenine moieties with one Ag+ and the “dimer” may be
further stabilized by the H-bonding among the adenine
moieties (A in Scheme 3); as a result, the two pyrene moieties
are brought close to induce pyrene excimer emission. When
more Ag+ is present in the solution, coordination of another
Ag+ with another two adenine moieties would occur and
accordingly the “dimer” would be further stabilized (B in
Scheme 3). As mentioned, adenine offers at least three
coordination sites, thus further coordination of 1 with Ag+
can occur as illustrated in Scheme 3C. As a result, the pyrene
moieties would be surrounded by more Ag+, which would
cause the quenching of both monomeric and excimer
emission of pyrene moieties since Ag+ is an effective
fluorescence quencher.
The fluorescence spectrum of 1 was investigated in the
presence of other perchlorate metal ions, including Ba2+,
Ca2+, Cd2+, Co2+, Cs+, Cu2+, Er3+, Fe3+, Fe2+, Gd3+, Hg2+,
K+, Mg2+, Mn2+, Na+, Nd3+, Ni2+, Pb2+, and Zn2+, under
identical conditions. As shown in Figure 3, variation of the
fluorescence intensity ratio (I478/I395) was rather small
(compared to that in the presence of Ag+) after addition of
these metal ions, even for Hg2+ which is usually difficult to
Acknowledgment. The present research was financially
supported by NSFC, Chinese Academy of Sciences, and State
Key Basic Research Program. D.Z. thanks the National
Science Fund for Distinguished Young Scholars.
Supporting Information Available: Synthesis and char-
acterization data; fluorescence and absorption spectra of
compound 1 under different conditions; 1H NMR and TOF/
MS spectra of 1 in the presence of Ag+. This material is
available free of charge via the Internet at http://pubs.acs.org.
OL8006716
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