Lanthanide luminescence sensing of copper and mercury ions using an iminodiacetate-based Tb(III)-cyclen chemosensor

Article abstract of DOI:10.1016/j.tetlet.2010.07.174

The design, synthesis and photophysical evaluation of 1.Tb.Na, a Tb(III)-cyclen-based sensor, possessing a phenyl iminodiacetate-based receptor, for the selective detection of Cu(II) and Hg(II) ions in water is demonstrated. Sensitisation of the Tb(III) <

Full text of DOI:10.1016/j.tetlet.2010.07.174

Tetrahedron Letters 51 (2010) 5406–5410
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Lanthanide luminescence sensing of copper and mercury ions using
an iminodiacetate-based Tb(III)-cyclen chemosensor
*
Brian K. McMahon, Thorfinnur Gunnlaugsson
School of Chemistry, Centre for Synthesis and Chemical Biology, Trinity College Dublin, Dublin 2, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
The design, synthesis and photophysical evaluation of 1.Tb.Na, a Tb(III)-cyclen-based sensor, possessing a
phenyl iminodiacetate-based receptor, for the selective detection of Cu(II) and Hg(II) ions in water is
demonstrated. Sensitisation of the Tb(III) 5D4 excited state was achieved by excitation of the phenyl
receptor, which in water gave rise to a characteristic time-delayed and line-like Tb(III) emission. The
Tb(III) emission was shown to be pH independent over the physiological pH window. The changes in
the Tb(III) emission were monitored by carrying out metal titrations using various groups I, II and tran-
sition metal ions. Of these, only the titrations of Cu(II) and Hg(II) gave rise to modulations in the Tb(III)
emission; resulting in quenching in the Tb(III) emission by ca. 65% and 40%, respectively.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 10 June 2010
Revised 16 July 2010
Accepted 30 July 2010
Available online 6 August 2010
One of the main research areas within the field of supramolecu-
lar chemistry is the development of sensors for use in competitive
solution.1–4 In particular, the detection and monitoring of biologi-
cally relevant ions in vitro and in vivo has become of critical
importance using luminescent sensors.3,4 Due to shorter-lived
background emission (autofluorescence) and light scattering from
such biological environments, the development of sensors possess-
ing long-lived emission lifetimes has become an active area of
research.5–7 The unique photophysical properties of the lantha-
nides,8–10 such as long wavelength emissions, sharp line-like bands
larly, Hg(II) is toxic in humans and can accumulate in the blood–
brain barrier which can result in severe neurological disorders.19
Hence, the design and development of novel sensors which show
a strong and selective response at low concentration values for
these ions is both an important and a topical area of research.23
Herein, we describe the development of 1.Tb.Na, a Tb(III)-cy-
clen-based chemosensor possessing an iminodiacetate antenna.
The objective is to take advantage of the long-lived and long-wave-
length emission properties of Tb(III) in conjunction with the use of
a structurally simple and combined antenna/receptor moiety that
and relatively long-lived excited state lifetimes [ls for Yb(III) and
Nd(III) to ms for Eu(III) and Tb(III)], makes them very attractive can-
didates for such an application in in vivo sensing as well as for bio-
logical imaging, another topical area of research.5,10–12 Careful
functionalisation of the macrocyclic framework, 1,4,7,10-tetraaza-
cyclododecane (cyclen) has allowed for the formation of many
examples of thermodynamically stable and kinetically inert com-
plexes with LnIII ions, which have been employed in luminescent
sensing of metal ions.12–17 These possess a suitable antennae/recep-
tor unit which can populate the lanthanide excited states via an en-
ergy sensitization process (e.g., the antenna effect); which are
perturbed upon binding to ions, giving rise to changes in both the
lanthanide emission intensities and lifetimes.15,16 The design of
sensors for detecting ions such as Cu(II) and Hg(II) in aqueous solu-
tion at low concentration levels is of current interest in both envi-
ronmental and biomedical monitoring.13,18–20 Bound Cu(II) plays a
vital role in many enzymatic processes, whilst free Cu(II) can dis-
rupt and damage various biological processes, and is the cause of
several conditions such as Wilson and Menkes diseases.21,22 Simi-
N
O
TbIII
O
H
N
N
N
N
N
CO2Na
CO2Na
N
O
O
N
1.Tb.Na
N
could selectively recognize Cu(II) and Hg(II) ions in competitive
media. Whilst many examples of luminescent lanthanide sensors
of group I and II metal ions, as well as several transition metal ions
such as Cu(II) and Zn(II) exist,13–17 the sensing of Hg(II), has, to the
best of our knowledge, not been achieved previously using lantha-
nide luminescence and hence sensor 1.Tb.Na is the first example of
a lanthanide sensor for targeting this ion.
The synthesis of ligand 1 began with the formation of 2, Scheme
1. This involved the initial di-alkylation of aniline with ethyl bro-
moacetate using Na2HPO4 and KI in refluxing CH3CN for 24 h,
which upon purification by flash silica gel column chromatography
* Corresponding author. Tel.: +353 1 896 3459; fax: +353 1 671 2826.
E-mail address: gunnlaut@tcd.ie (T. Gunnlaugsson).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.07.174

B. K. McMahon, T. Gunnlaugsson / Tetrahedron Letters 51 (2010) 5406–5410
5407
(gradient elution of 100 to 90:10 CH2Cl2/CH3OH), resulted in the
isolation of the desired intermediate in 56% yield. Nitration at
the para position was achieved in acetic acid, at 0 °C, using 70% ni-
tric acid. The desired product was obtained in 93% yield after
recrystallisation from EtOH.24 The product was then subjected to
catalytic hydrogenation using 10% Pd/C, in DMF, giving 2 in 90%
cited state, with concomitant characteristic line-like Tb(III) emis-
sion; which would then be expected to be modulated upon
binding of d-metal ions at the iminodiacetate moiety, possibly
involving electron transfer quenching. Indeed, excitation of
1.Tb.Na in H2O at 285 nm (kmax for the antenna) gave rise to Tb-
centred emissions at 490, 545, 586 and 622 nm, respectively,
verifying successful energy transfer from the antennae to the 5D4
excited state, and deactivation to the 7FJ (J = 6, 5, 4, 3) ground state.
The excited state lifetimes were also measured in both H2O and
yield. The formation of the a-chloroamide of 2, was achieved using
chloroacetyl chloride, in the presence of Et3N, at À10 °C in CH2Cl2,
which after washing the organic layer with water, 0.1 M HCl and
brine, gave 3, in 86% yield. With the receptor/antenna unit success-
fully synthesised, the next step involved the introduction to the cy-
clen framework using the mono alkylation procedure recently
published by our group.25 involving refluxing 4 equiv of cyclen
with 1 equiv of 3, in dry CHCl3, in the presence of Et3N for 12 h. Iso-
lation of 4 was achieved in 90% yield after the successful removal
of the unreacted cyclen by extraction using 1 M NaOH. The final
step involved refluxing 4 with 3 equiv of dimethyl acetamide using
K2CO3 and KI in freshly distiled CH3CN for five days. Purification of
the crude mixture by alumina column chromatography (elution
gradient 100 to 80:20 CH2Cl2/CH3OH) was required to give the de-
sired ligand, in 63% yield. The formation of the Tb(III) complex of
ligand 1 was achieved by refluxing overnight with an equivalent
amount of Tb(III) triflate [Tb(CF3SO3)3] in freshly distiled CH3CN,
under an inert atmosphere. Upon completion, the solvent was re-
moved under reduced pressure and the resulting residue re-dis-
solved in MeOH and added slowly into a large volume of dry
diethyl ether, resulting in precipitation of 1.Tb in 80% yield, as a
pale orange solid. The final step involved alkaline hydrolysis of
the diethyl diester moiety of 1.Tb in MeOH/H2O, which gave
1.Tb.Na in 81% yield.26
D2O, upon excitation at 285 nm. This gave
sH2O = 1.469 ms and
sD2O = 1.984 ms, demonstrating the long excited state lifetime,
from which the hydration state q was determined as ꢀ1 indicating
that 1.Tb.Na possesses one metal bound water molecule, and
therefore the Tb(III) ion being overall nine-coordinates within the
complex.
It was clear from the structure of 1.Tb.Na that possible proton-
ation of the aniline moiety as well as potential deprotonation of the
secondary amide (as well as the metal bound water) could perturb
the photophysical properties of the Tb(III) complex.27 In order to
quantify the pH dependence of the Tb(III) emission from 1.Tb.Na,
we carried out a pH titration, the result of which is shown in Figure
1. Here, the Tb(III) emission corresponding to the 5D4?7FJ (J = 6, 5,
4, 3) transition occurring at 490 nm, 545 nm, 586 nm and 622 nm,
respectively, showed some change with respect to the pH environ-
ment, Figure 1. Analysis of the Tb(III) emission for the
DJ = 5 tran-
sition (see inset in Fig. 1) clearly demonstrates that the Tb(III)
emission is ‘switched on’ within the physiological pH range, with
any major modulations in emission intensity only occurring below
pH 5.5, or above pH 11.5. Hence, there exists a large pH window in
which no change in the Tb(III) emission of 1.Tb.Na is observed, and
that this window overlaps with the physiological pH range. Hence,
we would anticipate that any modulation in the emission intensity
observed within this pH range upon titration with various transi-
tion metal ions is solely due to some form of interaction with the
The design of 1.Tb.Na envisaged sensitization of the Tb(III) me-
tal ion via excitation of the covalently attached phenyl chromo-
* *
p–p and n–p
phore, that is, the antenna (possessing both
transitions). This would enable sensititization of the Tb(III) 5D4 ex-
CO2Et CO2Et
N
CO2Et CO2Et
N
N
H
H
H
H
O
O
H
N
H
N
N
N
N
N
O
H
H
Cl
Cl
N
i) Tb(SO3CF3)3
CH3CN
N
N
N
N
N
N
N
N
CO2Et
CO2Et
CO2Et
CO2Et
Cl
Et3N/CH2Cl2
N
N
O
O
O
1.Tb.Na
Et3N/CHCl3
K2CO3/KI
MeCN
ii) NaOH
MeOH/H2O
H
N
HN
3
O
NH2
2
O
4
N
Cl
1
Scheme 1. Synthesis of 1.Tb.Na.
300
250
200
150
100
50
300
200
100
0
1.5
3
4.5
6
7.5
pH
9
10.5 12
0
450
500
550
600
650
Wavelength (nm)
Figure 1. The overall changes in the Tb(III) luminescence of 1.Tb.Na (10 lM) upon excitation of the phenyl antenna (kex = 285 nm) as a function of pH (I = 0.1 M NEt4HClO4
(TEAP)). Inset: The changes at 545 nm versus pH.

5408
B. K. McMahon, T. Gunnlaugsson / Tetrahedron Letters 51 (2010) 5406–5410
complex, and not as a result of a change in the pH of the
solution.8,15
served in the spectra clearly indicate an interaction between the
Cu(II) ions in solution and the iminodiacetate moiety of 1.Tb.Na,
where the absorption band centred at 285 nm was blue-shifted
to 260 nm, with the formation of an isobestic point at ca.
266 nm. The titration profile of the absorbance changes at
285 nm versus the number of equivalents of Cu(II) added is shown
as an inset in Figure 2, and suggests that the most significant inter-
action occurs between 0 and 1 equiv of Cu(II), with minor changes
Having established the pH behaviour of 1.Tb.Na, the next step
was to investigate its ability to recognise various group I, group
II and transition metal ions in solution. Screening a large library
of these in water at pH 7, demonstrated that the Tb(III) emission
was only affected by the presence of Cu(II) and Hg(II), using either
the ClÀ or HClO4 salts of these ions. However, ions such as Co(II)
À
and Ni(II) also gave rise to changes in the Tb(III) emission, but
these were due to the appearance of an absorption band corre-
sponding to these ions, and hence, an inner filter effect, and not
the direct binding of these ions to the receptor of 1.Tb.Na.28 More-
over, it was observed that in the presence of either HEPES or TRIS
buffers alone, both the Cu(II) and Hg(II) ions showed some form of
complexation with the buffers resulting in the formation of a
strong absorption band which overlapped with the absorption of
the antenna in 1.Tb.Na. Given the fact that the Tb(III) emission
can be considered as pH independent within the physiological
pH range, for example, as demonstrated as an inset in Figure 1,
all the titrations discussed herein were carried out in the absence
of any buffer in deionised H2O. Nevertheless, to ensure that there
was no pH effect, the pHs of all the samples were recorded before
and after carrying out these titrations; the pH was not found to
change by more than 0.2 pH units.
occurring between 1 and 2 equiv (0–20 lM). A similar response
was observed on analysis of the singlet excited state of 1.Tb.Na,
where, in the absence of Cu(II), a broad emission band was ob-
served, centred at 350 nm with a slight shoulder at ca. 300 nm.
Upon binding to Cu(II), a moderate emission intensity increase of
ca. 15% was observed (with
a slight hypsochromic shift to
345 nm) being most significant within the addition of 0–2 equiv
of Cu(II), as seen above in the absorption spectra.
We next monitored changes in the Tb(III) emission upon Cu(II)
binding to the receptor which was expected to effect the energy
transfer process from the antenna to the lanthanide, and hence,
the Tb(III) emission. The luminescence spectrum of 1.Tb.Na, upon
titration with Cu(II) is shown in Figure 3, and clearly demonstrates
a gradual decrease in the Tb(III) emission as a function of increased
Cu(II) concentration with ca. 65% quenching being observed at
545 nm, with a similar magnitude of quenching being seen for
the other transitions. The Tb(III) excited state lifetime was also
The changes in the ground-state properties of 1.Tb.Na upon
À
titration with Cu(II) ions (using the HClO4 salt) were first investi-
shortened upon binding to Cu(II), with
sH2O = 1.180 ms. A plot of
gated, the results of which are shown in Figure 2. The changes ob-
the Tb(III) intensity at 545 nm versus Cu(II) equivalents is shown
0.13
0.11
0.09
0.07
0.05
0.2
0.15
0.1
0
1
2
3
4
5
6
7
8
9 10
eq CuII
0.05
0
210
260
310
360
410
Wavelength (nm)
Figure 2. The overall changes in the absorption spectra (uncorrected) of 1.Tb.Na (10
l
M) upon titration with Cu(HClO4)2 in deionised H2O. Inset: Changes observed at 285 nm
as a function of equivalents of Cu(II) added.
350
250
150
50
350
300
250
200
150
100
50
0
1
2
3
4
5
6
7
8
9 10
eq CuII
0
450
500
550
600
650
Wavelength (nm)
Figure 3. Changes in the Tb(III) luminescence spectra of 1.Tb.Na (10 lM) upon titration with Cu(HClO4)2 (being quenched) in deionised H2O (0–100 lM). Inset: Changes
observed at 454 nm as a function of equivalents of Cu(II) added.

B. K. McMahon, T. Gunnlaugsson / Tetrahedron Letters 51 (2010) 5406–5410
5409
as an inset in Figure 3, and demonstrates the ability of 1.Tb.Na to
bind Cu(II), with concomitant changes in the emission properties.
Analysis of the changes in Figure 3 also showed that the sensor
bound the ion in a 1:1 stoichiometry, Figure 4, which demonstrates
that the binding occurs over two log units, with an estimated bind-
ing constant29 of log K = 5.5 ( 0.2). Figure 4, also shows the re-
sponse observed for ions such as Zn(II) and Cd(II) as well as the
group II ions Mg(II) and Ca(II), which did not give rise to any signif-
icant changes in the Tb(III) emission. This also demonstrates the
importance of our receptor design, as structurally related sensors
have been developed by Parker and co-wokers.16 for the selective
sensing of Zn(II); which is not detected by 1.Tb.Na. With the free
Cu(II) concentrations in serum being in the range of 12.5–
the iminodiacetate receptor moiety in solution. These results also
demonstrate that the sensor is more sensitive to Cu(II) over Hg(II)
(cf. Fig. 4). To confirm this, we also carried out a test where first, an
excess amount of Hg(II) was added to a solution of the sensor. This
again, gave rise to quenching in the Tb(III) emission to the same
degree as seen for the Hg(II) titrations. However, subsequent addi-
tion of Cu(II) lead to further quenching in the Tb(III) emission,
clearly demonstrating this selectivity. We also investigated the re-
sponse of 1.Tb.Na toward Cu(II) and Hg(II) in a simulated biological
environment with 150 mM NaCl, 10 mM KCl, 10 mM CaCl2, 10 mM
MgCl2, 10 mM CdCl2 and 10 mM ZnCl2, at pH 7. As expected, no sig-
nificant modulation in the singlet excited state properties of the
Tb(III) metal was observed in the presence of this mimicked biolog-
ical background, but addition of both Cu(II) and Hg(II) to the solu-
tion resulted in quenching of the Tb(III) metal luminescence, to the
same extent as seen in the above titrations.
In summary, we have developed a Tb(III) cyclen-based chemo-
sensor, with the incorporation of an iminodiacetate receptor/an-
tenna unit, for Cu(II) and Hg(II) ions in water at pH 7. Whilst
only minor changes were observed in both the absorption and fluo-
rescence spectra of 1.Tb.Na, upon recognition of these ions, a sub-
stantial quenching was observed in the Tb(III) emission. These
studies showed that the sensor has a high affinity for both of these
ions, where Cu(II) is selectively bound. It was also shown that in
the presence of other biologically relevant ions, the emission
21 l
M,30 it is clear from the titration profile in Figure 4, that
1.Tb.Na can detect Cu(II) within this concentration window. Figure
4 also shows the changes observed in the Tb(III) emission of
1.Tb.Na, upon titration with Hg(II), the overall spectral changes
being shown in Figure 5. A similar response to that seen with Cu(II)
was observed, that is, only the intensity and lifetime were affected,
where upon the addition of 10 equiv (100
ca. 40% luminescence quenching in the Tb(III) emission, with
H2O = 1.302 ms. From these changes, we estimated the Hg(II) bind-
lM) of Hg(II) gave rise to
s
ing affinity of 1.Tb.Na as log K = 4.6 ( 0.2). These studies suggest
that 1.Tb.Na shows both high sensitivity and selectivity for both
Cu(II) and Hg(II) ions; which was achieved through binding at
350
300
Cu(II)
250
Hg(II)
Cd(II)
200
Zn(II)
Ca(II)
150
Mg(II)
100
2.5
3
3.5
4
4.5
5
5.5
6
6.5
p[M(II)]
Figure 4. Plot of the changes in the Tb(III) luminescence of 1.Tb.Na (10
lM) at 545 nm upon titration with M(HClO4)2 or MCl2 (expressed as pM = Àlog [M]) in deionised H2O.
350
300
250
200
150
100
50
0
450
500
550
600
650
Wavelength(nm)
Figure 5. Changes in the Tb(III) luminescence spectra of 1.Tb.Na (10 lM) upon titration with Hg(HClO4)2 (being quenched) in deionised H2O (0–100 lM).

5410
B. K. McMahon, T. Gunnlaugsson / Tetrahedron Letters 51 (2010) 5406–5410
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Acknowledgements
The authors thank TCD, Irish Research Council for Science, Engi-
neering and Technology (IRCSET Postgraduate Award to BKMcM),
and Science Foundation Ireland (SFI RFP 2008 and 2009 research
grants to T.G.), for the financial support.
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23. Nolan, E. M.; Lippard, S. J. Chem. Rev. 2008, 108, 3443; Nolan, E. M.; Lippard, S. J.
J. Am. Chem. Soc. 2007, 129, 5910.
24. Parkesh, R.; Gowin, W.; Lee, T. C.; Gunnlaugsson, T. Org. Biomol. Chem. 2006, 4,
3611.
25. Massue, J.; Plush, S. E.; Bonnet, C. S.; Moore, D. A.; Gunnlaugsson, T. Tetrahedron
Lett. 2007, 48, 805.
26. Ligand 1 was obtained as an orange crystalline solid. (0.5 g, 63% yield). Mp
189–192 °C; HRMS (m/z, ES+) calcd for C36H61N9O8Na m/z = 770.4541 [M+Na].
Found m/z = 770.4549; 1H NMR (400 MHz, CDCl3, dH): 10.40 (s, 1H, N–H), 7.70
(d, 2 H, J = 9 Hz, Ar–H), 6.47 (d, 2 H, J = 9 Hz, Ar-H), 4.17 (q, 4 H, J = 7 Hz,
NCH2CO2CH2CH3) 4.08 (s, 4H, NCH2CO2CH2CH3), 3.30–1.98 (br m, 42H, cyclen-
5. dos Santos, C. M. G.; Harte, A. J.; Quinn, S.; Gunnlaugsson, T. Coord. Chem. Rev.
2008, 252, 2512; Leonard, J. P.; Nolan, C. B.; Stomeo, F.; Gunnlaugsson, T. Top.
Curr. Chem. 2007, 281, 1; Gunnlaugsson, T.; Stomeo, F. Org. Biomol. Chem 2007,
5, 1999; Gunnlaugsson, T.; Leonard, J. P. Chem. Commun. 2005, 3114; Leonard, J.
P.; Gunnlaugsson, T. J. Fluoresc. 2005, 15, 585; Comby, S.; Bünzli, J.-C. G.. In
Handbook of the Chemistry and Physics of Rare Earths; Gschneider, K. A., Bünzli,
J.-C. G., Pecharsky, V. K., Eds.; Elsevier: Amsterdam, 2007; Vol. 37, Murray, B. S.;
New, E. J.; Pal, R.; Parker, D. Org. Biomol. Chem. 2008, 6, 2085; Liellar, F.; Law, G.-
L.; New, E. J.; Parker, D. Org. Biomol. Chem. 2008, 6, 2256; Chauvin, A.-S.; Comby,
S.; Song, B.; Vandevyver, C. D. B.; Thomas, F.; Bünzli, J.-C. G. Chem. Eur. J. 2007,
13, 9515; Gunnlaugsson, T.; Harte, A. J.; Leonard, J. P.; Nieuwenhuyzen, M.
Supramol. Chem. 2003, 15, 505.
6. Cantuel, M.; Lincheneau, C.; Buffeteau, T.; Jonusauskaite, L.; Gunnlaugsson,
T.; Jonusauskas, G.; McClenaghan, N. D. Chem. Commun. 2010, 46, 2486;
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2009, 7, 3074; Plush, S. E.; Gunnlaugsson, T. Dalton Trans. 2008, 3801;
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T. Inorg. Chem. 2006, 45, 9465.
CH2 + 4,7,10-CH2CON(CH3)2 + 1-CH2CONH)1
1.26
(t,
6
H,
J = 7 Hz,
NCH2CO2CH2CH3); 13C NMR (100 MHz, CDCl3, dc): 170.58 (q), 170.52 (q),
170.24 (q), 169.58 (q), 143.48 (CH), 130.65 (CH), 120.72 (CH2), 112.06 (CH2),
60.59 (CH2), 57.44 (CH2), 54.42 (CH2), 53.36 (CH2), 53.03 (CH2), 50.13 (CH2),
35.96 (CH3), 35.71 (CH3), 35.22 (CH3), 35.12 (CH3), 13.80 (CH3); IR m
max (cmÀ1):
2818, 1740, 1646, 1518, 1450, 1400, 1370, 1346, 1297, 1262, 1179, 1102, 1062,
1005, 974, 902, 818, 772, 730, 631.
Complex 1.Tb was obtained as a pale orange solid (0.06 g, 80% yield). Mp
decomposed above 200 °C; calcd for C42H84Cl9F9N9O17S3Tb: C, 29.17; H, 3.85;
N, 7.29. Found C, 29.19; H, 3.85; N, 7.47; HRMS (m/z) calcd for
C
38H61F6N9O14S2Tb m/z = 1204.2937 [M+2(CF3SO3)]. Found m/z = 1204.2952;
1H NMR (400 MHz, CDCl3, dH) 72.47, 61.18, 50.78, 49.44, 46.20, 42.74, 36,48,
35,48, 34.58, 23.40, 19.48, 17.81, 13.79, 7.64, 6.75, 4.25, 3.79, 3.06, 2.76, 2.43,
1.43, 1.34, 0.93. IR mmax (cmÀ1): 3458, 2941, 1735, 1618, 1560, 1520, 1459,
1411, 1246, 1224, 1158, 1081, 1028, 958, 910, 823, 759, 635.
Complex 1.Tb.Na was obtained as a pale yellow solid (0.080 g, 81% yield). Mp
decomposed above 250 °C; HRMS (m/z, ES+) calcd for C34H53N9O14S2F6Tb m/
z = 1148.2311 [MÀCF3SO3À2Na+2H]+. Found m/z = 1148.2357; 1H NMR
(400 MHz, D2O, dH): 85.92, 79.51, 69.02, 67.04, 61.52, 58.42, 54.56, 53.79,
52.79, 49.04, 44.07, 44.38, 22.96, 21.53, 20.53, 16.67, 15.77, 14.20, 11.41, 10.37,
8.35, 7.84, 7.19, 6.72, 6.59, 6.43, 6.34, 3.52, 1.30, 1.17, À0.06, À82.05, À85.69,
À88.45, À97.73, À101.59, À103.47; IR mmax (cmÀ1): 2972, 1603, 1438, 1251,
1229, 1168, 1088, 1035, 945, 906, 878, 864, 765, 687, 638.
7. Sénéchal-David, K.; Pope, S. J. A.; Quinn, S.; Faulkner, S.; Gunnlaugsson, T. Inorg.
Chem. 2006, 45, 10040.
8. McCoy, C. P.; Stomeo, F.; Plush, S. E.; Gunnlaugsson, T. Chem. Mater. 2006, 18,
4336; Gunnlaugsson, T.; McCoy, C. P.; Stomeo, F. Tetrahedron Lett. 2004, 45,
8403.
27. Plush, S. E.; Clear, N. A.; Leonard, J. P.; Fanning, A. M.; Gunnlaugsson, T. Dalton
Trans. 2010, 39, 3644.
28. This was verified by carrying out titrations using these ions in the absence of
the sensor, which on both occasions, gave rise to large absorptions with a kmax
of 400 and 505, which partially overlapped with the emission wavelengths of
Tb(III).
9. Bunzli, J.-C. G.; Piquet, C. Chem. Soc. Rev. 2005, 34, 1048; Nonat, A.; Gateau, C.;
Fries, P. H.; Mazzanti, M. Chem. Eur. J. 2006, 12, 7133.
10. Bünzli, J.-C. G. Chem. Lett. 2009, 38, 104; Song, B.; Vandevyver, D. B.; Deiters, E.;
Chauvin, A.-S.; Hemmila, I.; Bünzli, J.-C. G. Analyst 2008, 133, 1749; Pandya, S.;
Yu, J.; Parker, D. Dalton Trans. 2006, 2757; Yu, J. J.; Parker, D.; Pal, R.; Poole, R.
A.; Cann, M. J. J. Am. Chem. Soc. 2006, 128, 2294.
29. We were unable to fit the changes in the Tb(III) accurately using non-linear
regression analysis.
´
30. Pešák, J.; Opavsky, J. Acta Univ. Palacki. Olomuc. Fac. Med. 2000, 143, 71.