A highly selective fluorescent chemosensor for silver(I) in water/ethanol mixture

Article abstract of DOI:10.1016/j.tetlet.2008.11.090

Synthesis, photophysical, and complexation properties of fluorescent chemosensors, L¹ and L², with 'receptor-spacer-fluorophore' motif (L¹: NS₂O₂-cyclic receptor, L²: acyclic analogue recep

Full text of DOI:10.1016/j.tetlet.2008.11.090

Tetrahedron Letters 50 (2009) 671–675
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Tetrahedron Letters
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A highly selective fluorescent chemosensor for silver(I)
in water/ethanol mixture
Chul Soon Park a, Jai Young Lee a, Eun-Ju Kang a, Ji-Eun Lee a,b, Shim Sung Lee a,
*
a Department of Chemistry (BK21) and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, South Korea
b Central Instrument Facility, Gyeongsang National University, Jinju 660-701, South Korea
a r t i c l e i n f o
a b s t r a c t
Synthesis, photophysical, and complexation properties of fluorescent chemosensors, L1 and L2, with
‘receptor-spacer-fluorophore’ motif (L1: NS2O2-cyclic receptor, L2: acyclic analogue receptor) are
described. Maximum chelation-enhanced fluorescence effect (TURN-ON type) was observed in the pres-
ence of Ag+ for both fluoroionophores in a 1:1 (v/v) aqueous ethanol solution: remarkably superior selec-
tivity of L1 (150-fold) with cyclic receptor than that of the L2 (50-fold) with acyclic analogue was found.
According to the fluorescence and NMR titrations, the excellent selectivity of L1 is attributed to its topol-
ogy-based higher affinity in complexation.
Article history:
Received 15 October 2008
Revised 19 November 2008
Accepted 25 November 2008
Available online 28 November 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Chemosensor exhibiting high selectivity toward a target analyte
is in great demand due to its low cost, high throughput capability,
and point-of-care monitoring.1 Thus, many efforts have been
devoted to design and construction of photophysical chemosensors
such as colorimetric and/or fluorescent ones. Owing to their
selective metal ion recognition and sensitive signaling capacity,
macrocycle-receptor-based fluoroionophores make them good
candidates for the chemosensors for the metal ions.2
On the other hand, a range of mono- and multinuclear com-
plexes of thiaoxa- or thiaoxaaza-macrocycles with discrete and
continuous types were reported by us3 and other workers.4 We
are interested in extending these results in the macrocycle-based
approach to develop chemosensors for thiaphilic d10 metal ion spe-
cies such as Ag+ and Hg2+. In particular, Ag+ has received consider-
able attention because of its bioaccumulation and toxicity.5
Furthermore, the mechanism of antimicrobial activities of Ag+
has not been well established because of a lack of suitable detec-
tion and imaging methodologies.6
fluorophore’ motif2c,d has been demonstrated to be an effective
way of developing both anion11 and cation2 chemosensors. In brief,
the Ag+ detection can be tuned by both the choice of receptor and
fluorophore. These two subunits also control the water-solubility
of a sensor molecule. Therefore, the need for developing efficient
fluorescent sensor toward Ag+ that satisfies the TURN-ON type
high selectivity in aqueous media has attractive growing attention.
In this regard, we herein describe the synthesis of an NS2O2-
macrocycle-based fluoroionophore, L1, with the ‘receptor-spacer-
fluorophore’ motif and its photophysical properties as a highly
selective TURN-ON type fluorescence chemosensor for Ag+ in aque-
ous ethanol solution (Scheme 1). At the same time, its acyclic ana-
Recently, several research groups reported NS2-macrocyle-based
donor-acceptor type chemosensors for Ag+ and/or Hg2+ 7
. We also
developed an azo-attached dibenzo-NS2O2 donor-macrocylce as a
chromogenic chemosensor for heavy metal ion in acetonitrile.8
More recently, we employed the same macrocycle to modify the
nanotube as solid matrix for the detection of heavy metal ion.9
The fluoroionophore system showing high selectivity for Ag+ in
aqueous solution associated with fluorescence OFF–ON changes
(TURN-ON type) has important implications for use as chemosen-
sors; however, the number of reported examples of these types is
quite limited.10 The fluoroionophore based on ‘receptor-spacer-
* Corresponding author. Tel.: +82 55 751 6021; fax: +82 55 753 7614.
E-mail address: sslee@gnu.ac.kr (S.S. Lee).
Scheme 1. Synthesis of L1 and L2.
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.11.090

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C. S. Park et al. / Tetrahedron Letters 50 (2009) 671–675
logue L2 as a reference counterpart has also been prepared and in-
cluded for comparison because these two compounds are expected
to have discriminated photophysical properties due to the different
topologies in the receptor units.
Table 1
Spectroscopic and complexation data for L1, L2 and their complexes
Species
kem (nm)
Quantum yielda
logKb
U0
U
U/U0
In the synthesis of the fluoroionophores, N-phenylated macro-
cyclic precursors 2 and 3 were prepared based on reported cou-
pling reactions between ditosylate 1 and corresponding dithiols
(Scheme 1).12,13 The incorporation of 9-methylanthracene moiety
on the spacer unit was achieved by aluminum chloride induced Fri-
edel–Crafts alkylation of with 9-chloromethylanthracene in good
yields.14 The target compounds were purified by silica-gel flash
column chromatography. Their 1H and 13C spectra exhibit charac-
teristic singlets at 4.90 (L1), 4.87 (L2), and 51.85 (L1), 51.58
(L2) ppm, respectively, arising from the each methylene proton be-
tween two aromatic units.
L1
414
414
415
414
0.001
—
0.006
—
—
0.26
—
260
—
10.2
—
[AgÁL1]+
L2
13.7
[AgÁL2]+
0.082
8.9
a
Quantum yields are based on anthracene,
U
= 0.27 in ethanol.15
b
Stability constants for a 1:1 (metal to ligand) complexation with Ag+ were
obtained from the fluorescence titrations shown in Figure 4.16
emission was observed (OFF state) due to the photo-induced elec-
tron transfer (PET) quenching by the lone pair of electrons on the
tertiary N donor atom in each molecule (Table 1).2b However, in
the pH range of 1.0–3.0, the typical anthracene emission was ob-
served. This result makes these compounds very attractive for
use in both physiological and environmental criteria. Lippard17
and Gunnlaugsson18 also reported similar results for Zn2+ and
Cd2+ sensor systems. Based on above results, we employed the
pH 7.2 condition buffered with 20 mM HEPES in EtOH/H2O (1:1
v/v) for the measurements of the photophysical properties
The structure of L1 was also characterized in the solid state by
single-crystal X-ray crystallography (Fig. 1a). Single-crystals of L1
were obtained by slow evaporation from the solution of CH2Cl2/
CH3CN. Since two S donors show exocyclic fashion to the ring cav-
ity, the SÁ Á ÁS distance is as large as 6.286(1) Å. The S1–C–C–N1
[167.5(4)°] and S2–C–C–N1 [À168.6(4)°] are arranged anti-confor-
mation. The pale yellow single crystals of L1 exhibit a broad band
with blue-green emission maxima at 485 nm (kex = 365 nm) arising
from the intermolecular charge transfer (ICT) states between the
N-phenylated macrocylic unit and excited anthracene terminal
group (Fig. 1b).7a,f
To probe the optimum condition for the photophysical proper-
ties of the fluoroionophores prepared, the pH responses were
examined in the 1:1 (v/v) aqueous ethanol solution (Figs. S3 and
S4). In the basic condition (pH 3.5–12), virtually no fluorescent
Figure 2. Fluorescence spectra of (a) L1 and (b) L2 in the presence of metal ions in
EtOH/H2O (1:1, v/v, pH = 7.2, HEPES buffer). Cs+, Ag+, Pb2+, Zn2+, Cd2+,Hg2+, Cu2+ Ni2+
,
Figure 1. (a) Crystal structure and (b) solid state photoluminescence spectrum of
L1.
and Co2+ (10 equiv) and Na+, K+, Ca2+, and Mg2+ (1000 equiv) were added to each
ligand solution (5.0 M).
l

C. S. Park et al. / Tetrahedron Letters 50 (2009) 671–675
673
Figure 3. Normalized fluorescence intensities (I/I0) of L1 and L2 in the presence of
metal ions.
throughout this study. Under this physiological condition, as ex-
pected, L1 and L2 exhibit negligible fluorescence quantum yields
U0 = 0.001 and 0.006 in the absence of Ag+, respectively (Table 1).
To examine the selectivity of L1 and L2 as fluorescent sensors,
responses to diverse metal ions are compared (excitation at
368 nm). It is worth noting that Figure 2 shows the maximum che-
lation enhanced fluorescence (CHEF) effect (ON state) for each fluo-
roionophore upon addition of Ag+. In both cases, the typical pattern
of the anthracene appears very strongly without change in the
emission maxima. This can be explained that the coordination to
such tertiary N donor atom prevents the PET quenching effec-
tively.2b More significantly, upon addition of Ag+ the normalized
fluorescence intensity (I/I0) of L1 (150-fold increase) shows much
higher selectivity compare to L2 (50-fold increase) (Fig. 3). The
group IA, IIA, and d-block transition metal ions, however, show
no or less influences on the fluorescence intensity especially for
L1 which suggests the higher selectivity than that of L2. Further-
more, the competition experiments by a range of the interfering
ions revealed that Ag+-induced fluorescence enhancement for L1
is unaffected in the presence of physiologically (1000 equiv) and
environmentally (10 equiv) relevant metal ions (Fig. S5). As we
understand, the proposed system with cyclic receptor (L1) affords
the largest CHEF reported to date that results from Ag+ complexa-
tion in aqueous media.
Figure 4. Fluorescence titrations of (a) L1 and (b) L2 with AgNO3 in EtOH/H2O (1:1,
v/v, pH 7.2, HEPES buffer).
On the other hand, the fluorescence titrations of L1 and L2 with
AgNO3 in the same solvent media resulted in the intensity gradu-
ally increasing between 0 and 1.0 equiv of Ag+, and then achieves
The magnitude of the Ag+-induced chemical shifts for the pro-
tons varies with their positions. Very notably, the aromatic proton
Ha which is closest to the tertiary N donor shows largest chemical
a plateaus with the quantum yields
U = 0.26 and 0.082, respec-
tively, suggesting a 1:1 complexation (Fig. 4 and Table 1). In addi-
tion, the 1:1 (metal to ligand) stoichiometry for the complexations
was also demonstrated by Job plots (Fig. S6). On the basis of the
nonlinear fitting analysis of the fluorescence titration data, the sta-
bility constants (logK) for the 1:1 complexes of L1 and L2 were
determined to be 10.2 and 8.9 for Ag+, respectively (Table 1). It
should be noted that the preorganized fluoroionophore L1 showed
improved binding (ꢀ20 times) with Ag+ compared to its acyclic
analogue L2 probably due to the additional stabilization of the
macrocyclic effect. The detection limits19 were also estimated from
the titration results (L1; 2.2 Â 10À7 M and L2; 5.8 Â 10À7 M).
Unfortunately, we were not able to obtain the single crystals of
the related Ag+ complexes. Instead, NMR titrations were carried
out in DMSO-d6 to understand further structural characteristics
of the Ag+ complexes in solution (Fig. 5 for L1 and Fig. S7 for L2).
Upon stepwise addition of Ag+, in both cases, every proton in each
ligand shifted, suggesting the stable complexation for the fast
exchanging system. Here again, the NMR titration curves clearly
show an inflection point at mole ratio (Ag+/L) of 1.0, indicating that
the stoichiometry for the formation of the complex is also 1:1 ratio
(metal to ligand).
shift change than others in both cases:
Dd = 0.59 and 0.39 ppm for
L1 and L2, respectively, suggesting the nitrogen-affinity of Ag+ is
important. This change seems to be caused by synergic effect of
the metal-donor and metal–
region, the order of magnitude of the chemical shift variation is
H2
p
interactions.20 For the aliphatic
(D
d: À0.3 ppm), H4 (0.3 ppm) >> H1 (0.1 ppm) > H3,H5
(0.07 ppm): Ag+ causes a much larger shift for the H2 and H4 peaks
than for those of others. Thus, Ag+ appears to be more strongly
coordinated by potential tridentate NS2 donor-set, while the O do-
nors interact with the Ag+ relatively weakly. Similar results were
observed for both L1 and L2 but the L1 shows relatively larger
chemical shift changes than L2, indicating the stronger receptor to-
ward Ag+ in solution. The unexpected Ag+-induced upfield shift for
H2 and H3 appears to be caused by a ring current effect.21 The ob-
served 1:1 stoichiometry for the AgL type complexation is further
confirmed by the ESI-MS of the complex solutions, which corre-
spond to the species [L1ÁAg]+ (m/z 624.9) and [L2ÁAg]+ (m/z
568.8), respectively (Figs. S8 and S9).
In conclusion, two fluoroionophores with ‘receptor-spacer-fluo-
rophore’ motif were synthesized and their photophysical and com-

674
C. S. Park et al. / Tetrahedron Letters 50 (2009) 671–675
Figure 5. (a) 1H NMR spectra of L1 by stepwise addition of AgNO3 and (b) 1H NMR titration curves for L1 with AgNO3 in DMSO-d6.
plexation properties were investigated. The proposed sensor mole-
cule with cyclic receptor unit exhibited excellent turn-on type
fluorescence selectivity toward Ag+ in aqueous ethanol solution.
From the results, it is concluded that the unique selectivity for
Ag+ based on the complexation-induced inhibition of the PET pro-
cess is due to the several cooperative factors, such as transduction
capacity of anthracene fluorophore, the spacer group contribution
and synergic effect of the NS2O2 donors with well-preorganized
coordination environment of the cyclic receptor.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.11.090.
References and notes
1. (a) Czarnik, A. W. Fluorescent Chemosensors for Ion and Molecule Recognition;
American Chemical Society: Washington, DC, 1993; (b) Desvergne, J. P.;
Czarnik, A. W. Chemosensors of Ion and Molecular Recognition; NATO ASI Series;
Kluwer: Dordrecht, The Netherlands, 1997; (c) Valeur, B. Molecular
Fluorescence; Wiley-VCH: New York, 2001.
2. (a) Czarnik, A. W. Acc. Chem. Res. 1994, 27, 302; (b) de Silva, A. P.; Gunaratne, H.
Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T.
E. Chem. Rev. 1997, 97, 1515; (c) de silva, A. P.; Fox, D. B.; Huxley, A. J. M.;
Moody, T. S. Coord. Chem. Rev. 2000, 205, 41; (d) Amendola, V.; Fabbrizzi, L.;
Lincchelli, M.; Mangano, C.; Pallavicini, P.; Parodi, L.; Poggi, A. Coord. Chem. Rev.
1999, 190(192), 649.
3. (a) Seo, J.; Song, M. R.; Lee, J.-E.; Lee, S. Y.; Yoon, I.; Park, K.-M.; Kim, J.; Jung, J.
H.; Park, S. B.; Lee, S. S. Inorg. Chem. 2006, 45, 952; (b) Habata, Y.; Seo, J.; Otawa,
S.; Osaka, F.; Noto, K.; Lee, S. S. Dalton Trans. 2006, 2202; (c) Song, M. R.; Lee, J.-
E.; Lee, S. Y.; Seo, J.; Park, K.-M.; Lee, S. S. Inorg. Chem. Commun. 2006, 9, 75; (d)
Yoon, I.; Seo, J.; Lee, J.-E.; Song, M. R.; Lee, S. Y.; Choi, K. S.; Jung, O.-S.; Park, K.-
M.; Lee, S. S. Dalton Trans. 2005, 2352; (e) Seo, J.; Yoon, I.; Lee, J.-E.; Song, M. R.;
Lee, S. Y.; Park, S. H.; Kim, T. H.; Park, K.-M.; Kim, B. G.; Lee, S. S. Inorg. Chem.
Commun. 2005, 8, 916; (f) Kim, H. J.; Yoon, I.; Lee, S. Y.; Seo, J.; Lee, S. S.
Tetrahedron Lett. 2007, 48, 8464; (g) Kim, H. J.; Yoon, I.; Lee, S. Y.; Choi, K. S.; Lee,
S. S. New J. Chem. 2008, 32, 258.
Acknowledgment
This work was supported by a Korea Science and Engineering
Foundation (R01-2007-000-20245-0).
Supplementary data
Supplementary crystallographic data associated to L1 have been
deposited at the Cambridge Crystallographic Data Centre, CCDC No.
704607. Copies of the data can be obtained free of charge on appli-
cation to CCDC, 12 Union road, Cambridge CB2 1EZ, UK (fax: +44
1223 336 033; e-mail: http://www.deposit@ccdc.cam.ac.uk),
or electronically via http://www.ccdc.cam.ac.uk/data_request/cif.
4. (a) Janzen, D. E.; Mahne, L. F.; VanDerveer, D. G.; Grant, G. J. Inorg. Chem. 2005,
44, 8182; (b) Vetrichelvan, M.; Lai, Y.-H.; Mok, K. F. Eur. J. Inorg. Chem. 2004,
2086; (c) Contu, F.; Dermartin, F.; Devillanova, F. A.; Garau, A.; Isaia, F.; Lippolis,
V.; Salis, A.; Verani, G. J. Chem. Soc., Dalton Trans. 1997, 4401; (d) Watzky, M. A.;

C. S. Park et al. / Tetrahedron Letters 50 (2009) 671–675
675
Waknine, D.; Heeg, M. J.; Endicott, J. F.; Ochrymowyzc, L. A. Inorg. Chem. 1993,
32, 4882; (e) Blake, A. J.; Halcrow, M. A.; Schröder, M. J. Chem. Soc., Dalton Trans.
1992, 2803.
14. Synthesis of L1. 9-Chloromethylanthracene (0.71 g, 3.1 mol), compound 2 (1.0 g,
3.1 mmol), and AlCl3 (0.41 g, 3.1 mmol) were dissolved in dry CHCl3 (50 mL) at
0 °C. The solution was refluxed under stirring overnight. After the reaction was
completed (monitoring by TLC) the solution was cooled and washed with three
80 mL portions of water. The organic portion was dried over Na2SO4. After
evaporation of the solvent, crude product was subjected to column
chromatography (SiO2; 5% ethyl acetate/n-hexane) and yielded pure L1 as
light yellow solid (0.65 g, 41%). Mp 154–155 °C. C31H35NO2S2 (517.8): Anal.
Calcd: C, 71.91; H, 6.81; N, 2.71; S, 12.39. Found: C, 72.02; H, 6.63; N, 2.75; S,
12.08. IR (KBr) 3053, 2920, 2854, 1609, 1515, 1444, 1349, 1281, 1130, 1099,
5. (a) Ratte, H. T. Environ. Toxicol. Chem. 1999, 18, 89; (b) Ganjali, M. R.; Norouzi,
P.; Alizadeh, T.; Adib, M. J. Braz. Chem. Soc. 2006, 17(7), 1217; (c) Zhang, X. B.;
Han, Z. X.; Fang, Z. H.; Shen, G. L.; Yu, R. Q. Anal. Chim. Acta 2006, 562, 210; (d)
Peng, H. Q.; Brooks, B. W.; Chan, R.; Chyan, O.; Point, T. W. L. Chemosphere 2002,
46, 1141; (e) Kazuyuki, M.; Nobuo, H.; Takatoshi, K.; Yuriko, K.; Osamu, H.;
Yashihisa, I.; Kiyoko, S. Clin. Chem. 2001, 47, 763; (f) Wan, A. T.; Conyers, R. A.;
Coombs, C. J.; Masterton, J. P. Clin. Chem. 1991, 37, 1683.
6. (a) Rurack, K.; Kollmannsberger, M.; Resch-Genger, U.; Daub, J. J. Am. Chem. Soc.
2000, 122, 968; (b) Yang, R. H.; Chan, W. H.; Lee, A. W. M.; Xia, P. F.; Zhang, H.
K.; Li, K. A. J. Am. Chem. Soc. 2003, 125, 2884; (c) Coskun, A.; Akkaya, E. U. J. Am.
Chem. Soc. 2005, 127, 10464; (d) Kang, J.; Choi, M.; Kwon, J. Y.; Lee, E. Y.; Yoon, J.
J. Org. Chem. 2002, 67, 4384.
7. (a) Cheung, S.-M.; Chan, W.-H. Tetrahedron 2006, 62, 8379; (b) Ishikawa, J.;
Sakamoto, H.; Nakao, S.; Wada, H. J. Org. Chem. 1999, 64, 1913; (c) Liu, L.;
Zhang, G.; Xiang, J.; Zhang, D.; Zhu, D. Org. Lett. 2008, 10, 4581; (d) Liu, L.;
Zhang, D.; Zhang, G.; Xiang, J.; Zhu, D. Org. Lett. 2008, 10, 2271; (e) Yuan, M.; Li,
Y.; Li, J.; Li, C.; Liu, X.; Lv, J.; Xu, J.; Liu, H.; Wang, S.; Zhu, D. Org. Lett. 2007, 9,
2313; (f) Yang, J.-S.; Lin, Y.-D.; Chang, Y.-H.; Wang, S.-S. J. Org. Chem. 2005, 70,
6066.
734, 661 cmÀ1 1H NMR (300 MHz, CDCl3): d 8.40 (s, 1H), 8.23–8.26 (m, 2H),
.
7.99–8.03 (m, 2H), 7.42–7.46 (m, 4H), 6.96 (d, 2H, J = 8.6 Hz), 6.46 (d, 2H,
J = 8.6 Hz), 4.89 (s, 2H), 3.74 (t, 4H, J = 5.1 Hz), 3.60 (s, 4H), 3.50 (t, 4H,
J = 7.7 Hz), 2.79 (t, 4H, J = 7.7 Hz), 2.69 (t, 4H, J = 5.1 Hz) ppm. 13C NMR
(75 MHz, CDCl3): d 145.1, 132.8, 131.7, 130.5, 129.1, 129.1, 128.4, 126.2,
125.7, 125.0, 124.9, 111.9, 74.3, 29.5, 70.7, 51.9, 32.4, 31.1 ppm. ESI-MS m/z
(MH+) 518.7 (calcd 518.2). Synthesis of L2. The synthetic procedure was almost
the same as for L1 except for the use of compound 3. Column chromatography
(SiO2; 20% dichloromethane/n-hexane) afforded the product as a pale yellow
solid (0.84 g, 49%). Mp 90–91 °C. C29H33NS2 (459.7): Anal. Calcd: C, 75.77; H,
7.24; N, 3.05; S, 13.95. Found: C, 75.85; H, 7.54; N, 3.17; S, 13.72. IR (KBr) 3046,
2960, 2918, 1609, 1515, 1443, 1391, 1344, 1281, 1176, 1140, 724, 687 cmÀ1 1H
.
8. Lee, S. J.; Jung, H. J.; Seo, J.; Yoon, I.; Park, K.-M.; Lindoy, L. F.; Lee, S. S. Org. Lett.
2006, 8, 1641.
9. (a) Lee, S. J.; Lee, J.-E.; Seo, J.; Jeong, I. Y.; Lee, S. S.; Jung, J. H. Adv. Funct. Mater.
2007, 17, 3441; (b) Lee, S. J.; Lee, S. S.; Jeong, I. Y.; Lee, J. Y.; Jung, J. H.
Tetrahedron Lett. 2007, 48, 393; (c) Lee, S. J.; Bae, D. R.; Han, W. S.; Lee, S. S.;
Jung, J. H. Eur. J. Inorg. Chem. 2008, 1559.
NMR (300 MHz, CDCl3): d 8.37 (s, 1H), 8.20–8.24 (m, 2H), 7.97–8.00 (m, 2H),
7.40–7.43 (m, 4H), 6.95 (d, 2H, J = 8.6 Hz), 6.46 (d, 2H, J = 8.6 Hz), 4.89 (s, 2H),
3.38 (t, 4H, J = 7.5 Hz), 2.59 (t, 4H, J = 7.5 Hz), 2.47(q, 4H, J = 7.4 Hz), 1.18 (t, 6H,
J = 7.4 Hz) ppm. 13C-NMR (75 MHz, CDCl3): d 145.1, 132.7, 131.8, 130.5, 129.2,
129.2, 128.9, 126.4, 125.8, 125.06, 124.9, 111.9, 51.6, 32.5, 28.9, 26.3, 15.1 ppm.
ESI-MS m/z (MH+) 460.8 (calcd 460.2).
10. (a) Raker, J.; Glass, T. E. J. Org. Chem. 2001, 66, 6505; (b) Tong, H.; Wang, L. X.;
Jing, X. B.; Wang, F. S. Macromolecules 2002, 35, 7169; (c) Singh, P.; Kumar, S.
Tetrahedron 2006, 62, 6379; (d) Schmittel, M.; Lin, H. W. Inorg. Chem. 2007, 46,
9139; (e) Xu, S.; Li, W.; Chen, K. C. Chin. J. Chem. 2007, 25, 778; (f) Zhu, X.; Fu, S.;
Wong, W.-K.; Wong, W.-Y. Tetrahedron Lett. 2008, 49, 1843.
15. Melhuish, W. H. J. Phys. Chem. 1961, 65, 229.
16.
a
Stability constants were obtained using the computer program
ENZFITTER, available from Elsevier-BIOSOFT, 68 Hills Road, Cambridge
CB2 1LA, United Kingdom.; (b) Connors, K. A. Binding Constants; Wiley:
New York, 1987.
11. (a) Gale, P. A. Acc. Chem. Res. 2006, 39, 465; (b) Yoon, J.; Kim, S. K.; Singh, N. J.;
Kim, K. S. Chem. Soc. Rev. 2006, 35, 355; (c) Gunnlaugsson, T.; Glynn, M.; Tocci,
G. M.; Kruger, P. E.; Pfeffer, F. M. Coord. Chem. Rev. 2006, 250, 3094; (d) Beer, P.
D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486; (e) Schmidtchen, F. P.;
Berger, M. Chem. Rev. 1997, 97, 1609; (f) Ojida, A.; Miyahara, Y.;
Wongkongkatep, J.; Tamaru, S.-I.; Sada, K.; Hamachi, I. Chem. -Asian. J. 2006,
1, 555; (g) Martínez-Máñez, R.; Sancenón, F. Chem. Rev. 2003, 103, 4419; (h)
Gong, W.-T.; Harigae, J.; Seo, J.; Lee, S. S.; Hiratani, K. Tetrahedron Lett. 2008, 49,
2268.
12. (a) Sancenón, F.; Descalzo, A. B.; Martínez-Máñez, R.; Miranda, M. A.; Soto, J.
Angew. Chem., Int. Ed. 2001, 40, 2640; (b) Sancenón, F.; Martínez-Máñez, R.;
Soto, J. Angew. Chem., Int. Ed. 2002, 41, 1416; (c) Descalzo, A. B.; Martínez-
Máñez, R.; Radeglia, R.; Rurack, K.; Soto, J. J. Am. Chem. Soc. 2003, 125, 3418; (d)
Jiménez, D.; Martínez-Máñez, R.; Sancenón, F.; Ros-Lis, J. V.; Soto, J.; Benito, Á.;
García-Breijo, E. Eur. J. Inorg. Chem. 2005, 2393.
17. (a) Nolan, E. M.; Lippard, S. J. Chem. Rev. 2008, 108, 3443; (b) Goldsmith, C. R.;
Lippard, S. J. Inorg. Chem. 2006, 45, 6474; (c) Nolan, E. M.; Jaworski, J.; Racine,
M. E.; Sheng, M.; Lippard, S. J. Inorg. Chem. 2006, 45, 9748; (d) Nolan, E. M.;
Lippard, S. J. J. Am. Chem. Soc. 2003, 125, 14270; (e) Nolan, E. M.; Lippard, S. J. J.
Mater. Chem. 2005, 7, 4943.
18. (a) Gunnlaugsson, T.; Lee, T. C.; Parkesh, R. Org. Lett. 2003, 5, 4065; (b)
Gunnlaugsson, T.; Lee, T. C.; Parkesh, R. Tetrahedron 2004, 60, 11239.
19. (a) Shortreed, M.; Kopelman, R.; Kuhn, M.; Hoyland, B. Anal. Chem. 1996, 68,
1414; (b) Song, K.-C.; Kim, M. H.; Kim, H. J.; Chang, S.-K. Tetrahedron Lett. 2007,
48, 7464.
20. (a) Ungaro, R.; Casnati, A.; Ugozzoli, F.; Pochini, A.; Dozol, J.-F.; Hill, C.;
Rouquette, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 1506; (b) Ikeda, A.; Shinkai,
S. J. Am. Chem. Soc. 1994, 116, 3102; (c) Ma, J. C.; Dougherty, D. A. Chem. Rev.
1997, 97, 1303.
21. Ishikawa, J.; Sakamoto, H.; Nakamura, M.; Doi, K.; Wada, H. J. Chem. Soc., Dalton
Trans. 1999, 191.
13. Ishikawa, J.; Sakamoto, H.; Wada, H. J. Chem. Soc., Perkin Trans. 2 1999, 1273.