A new Tb3+-selective fluorescent sensor based on 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide

Article abstract of DOI:10.1016/j.saa.2009.07.014

A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission

Full text of DOI:10.1016/j.saa.2009.07.014

Spectrochimica Acta Part A 74 (2009) 575–578
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
3+
A new Tb -selective fluorescent sensor based on 2-(5-
(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide
a,b,∗
a
c
a,b
M.R. Ganjali
, B. Veismohammadi , M. Hosseini , P. Norouzi
a
Center of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran, Tehran, Iran
Endocrinology & Metabolism Research Center, Medical Sciences/University of Tehran, Tehran, Iran
Department of Chemistry, Islamic Azad University, Savadkooh Branch & Young Researcher Club, Savadkooh, Iran
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 December 2008
Accepted 7 July 2009
A
novel
fluorescent
chemosensor
2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-
phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm
and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quench-
ing upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to
the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective
Keywords:
Fluorescence
Quenching
Tb(III)
−7
detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 × 10
−5
−7
to 1.0 × 10 M and the detection limit is 1.4 × 10 M. The association constant of the 1:1 complex
+
3
6
−1
M , and the fluorescent probe exhibits high
formation for L–Tb was calculated to be 6.01 × 10
Sensor
selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for
Tb(III) ions over a large number of interfering cations.
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
donating atoms of the recognition moiety play the most important
role in selectivity behavior and binding efficiency of the sensor [10].
Terbium oxide is used in green phosphors in fluorescent lamps
and color TV tubes. Sodium terbium borate is used in solid state
devices. The brilliant fluorescence allows terbium to be used as a
probe in biochemistry, where it somewhat resembles calcium in its
behavior. Terbium “green” phosphors (which fluorescence a bril-
liant lemon-yellow) are combined with divalent Europium blue
phosphors and trivalent europium red phosphors to provide the
“trichromatic” lighting technology, which is by far the largest con-
sumer of the world’s terbium supply. Trichromatic lighting provides
much higher light output for a given amount of electrical energy
than incandescent lighting [11]. They have long fluorescence life-
time and their excited states have strong fluorescence emission,
thus europium(III) and terbium(III) have extensive applications in
biological medicine, especially in the fluorescence imagery cancer
radiation treatment [12], fluorescence mark [13], and fluorescence
analysis [14].
Difficultiesinthequantityofdeterminationoflanthanidesresult
from the great chemical similarity of their ions [1,2]. Available
instrumental methods for this purpose including, flame photome-
try, atomic absorption spectrometry, electron microscope analysis
and neutron activation analysis often suffer from such parameters
as high cost, need for large size samples and inability for continuous
monitoring.
In the past two decades, an increasing interest has been focused
on the development of fluorescent sensors, which offer distinct
advantages in terms of sensitivity, selectivity, response time and
remote sensing [3–9]. The key point in development of such fluo-
rescence sensors is the design of a fluorescence sensing element,
which usually consists of a fluorophore (signaling moiety) linked
to an ionophore (recognition moiety), called as a fluoroionophore.
Here, the recognition process by the ionophore part is converted to
a change in the fluorophore’s fluorescence signal, brought about by
the perturbation of such photoinduced processes as energy trans-
fer, charge transfer, electron transfer, formation or disappearance of
excimers and exciplexes. Obviously, the topology, size and nature of
On the other hand, dansyl groups are one of the most attrac-
tive fluorophores [15–17] due to its strong fluorescence, relatively
long emission wavelength and easy derivation. Commonly a typi-
cal fluorescent cation sensor consists of a fluorophore and a binding
unit.
In this paper, a novel and simple fluorescent cation receptor was
obtained by incorporating phenylhydrazinecarbothioamide moi-
eties (binding sites) into dansyle group (fluorophore). As expected,
the receptor L, Scheme 1, (5 × 10 M) exhibited a quenching in the
∗
Corresponding author at: Center of Excellence in Electrochemistry, Faculty of
Chemistry, University of Tehran, Tehran, Iran. Tel.: +98 21 61112788;
fax: +98 21 66495291.
−
6
E-mail address: ganjali@khayam.ut.ac.ir (M.R. Ganjali).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.07.014

5
76
M.R. Ganjali et al. / Spectrochimica Acta Part A 74 (2009) 575–578
Scheme 1. Chemical structure of compound L.
fluorescent emission intensity upon addition of cations tested in
MeCN when excited at ꢀex = 360 nm.
2
. Experimental
Fig. 1. Changes in the UV–vis spectra of L (5 × 10−5 M) upon addition of Tb+3
−
3
(
1 × 10 M) in MeCN solution.
2.1. Reagents
at 360 nm. As illustrated in Fig. 2, compound L showed a typical
emission band of the dansyl group around 530 nm, which was con-
siderably quenched in the presence of Tb3+. This phenomenon may
occur by electron transfer from the exited dansyl moiety to the
All Chemicals were of the reagent-grade from Fluka and Merck
chemical companies.
The fluorogenic reagent
L was prepared as follows: A
mixture of phenyliosthiocyanate (2 mmol, 0.27 gr) and 5-
dimethylamino)-1-naphthalene sulfonohydrazide) (2 mmol,
.53 gr) in dichloromethane (35 ml) was stirred at ambient tem-
perature for 5 h. The precipitate was filtered and washed with
dichloromethane (5 ml) [18]. The solid was recrystallized from 1:1
acetone–ethanol and the product was obtained as yellow crystals.
3+
proximate terbium ions [19]. When the concentration of Tb ions
(
0
−
6
was increased up to 2.6 × 10 M, more than 80% quenching of the
initial fluorescence of L was observed (Fig. 2). The shape and posi-
tion of the fluorescence excitation and emission bands does not
change in the presence of terbium ions compared to those of the
free ligand. Both the excitation and emission intensities sharply
H NMR (100 MHZ, CDCl ):
3
3+
decreased as a function of Tb . It is noteworthy that because of
2
.99 (6H, S, NMe ), 7.35 (1H, t, J = 7.5 Hz, CH), 7.38 (1H, d,
2
very short fluorescence lifetimes and low concentration conditions
used, the effect of the concentration quencher should be negligible.
J = 6.5 Hz, CH), 7.43 (1H, dd, J = 8.9 Hz, J = 6.0 Hz) CH, 7.64 (1H,
dd, J = 8.5 Hz, J = 6.3 Hz CH), 7.70–7.75 (4H, M, 4CH), 8.22 (1H, d,
J = 6.3 Hz, CH), 8.30 (1H, d, J = 8.5 Hz, CH), 8.35 (1H, d, J = 8.9 Hz, CH),
8
.9 (1H, br, NH), 10.05 (1H, S, NH) 45.20 (NMe ), 112.25, 114.39,
2
1
1
1
19.65, 126.69 (4CH), 126.95, 127.43 (2CH), 128.33, 129.05 (2CH),
29.61 (Cl, 130.15, 133.64 (2CH), 133.17 (C), 135 (CH) 153.72 (C),
90.39 C = S.
2.2. Apparatus
All fluorescence measurements were carried out on
a
PerkinElmer LS50 luminescence spectrometer.
. Result and discussion
The cation binding properties were investigated by UV–vis
3
absorption and fluorescence spectroscopy. The titration experi-
ments were carried out in CH CN solution by adding aliquots of
3
Tb(III). As shown in Fig. 1, this ligand possessed three intensive
absorption bands centred at 240 (ε = 18680) and 330 (ε = 10640)
which can be contributed to n→␲* and ␲→␲* transition. Notably,
the titration of L against Tb3 led to a pronounced and red-shifted
shoulder in the UV spectra (ꢁꢀmax = 40 nm shift) with two well
defined isosbestic point at 266 nm and 314 nm (Fig. 1).
+
All of the fluorescence titration experimental was performed in
MeCN solution and maximum excitation wavelength was selected
+3
in MeCN solution, [L] = 5 × 10−6 M,
Fig. 2. Fluorescence titration of L with Tb
[Tb ] = 5 × 10 M, ꢀex = 360 nm.
+
3
−4

M.R. Ganjali et al. / Spectrochimica Acta Part A 74 (2009) 575–578
577
Fig. 3. Stern–Volmer plot of titration of L with Tb3+
.
−
6
Fig. 5. Quench ratio (Io − I)/Io of fluorescence intensity of L (5 × 10 M) upon the
addition of two equiv metal ions in MeCN solution.
From the fluorescence titration experiments, the association
3+
constant (Ka) of the 1:1 complex formation for L–Tb was cal-
6
−1
culated to be (6.22 ± 0.02)10 M by the Stern–Volmer equation
20]. Furthermore, the detection limit of L as a fluorescent sen-
As shown is Fig. 4, the case of free ligand, the benzo ring and the
dibenzo dansyl groups in the ligand are located in a more or less
planar situation whilst in the case of the complex, the structure is
somewhat folded to result in the lowest conformational energy. In
the optimized complex structure, compound L is a tri dentate ligand
and establishes coordination bonds with the lanthanide ion over its
two sulfurs and one nitrogen donating groups.
[
3+
sor for the analysis of Tb was also determined from the plot
of the fluorescence intensity as a function of the concentration
of added metal ions (Fig. 3). It was found that L has a detection
−7
3+
limit of 1.4 × 10 M for Tb ions [21], which is quite low for the
detection of the Tb3+ ions found in many chemical and biological
systems.
Under the same conditions as above, we also tested the fluo-
Toobtainmoreinformationabouttheconformationalchangesof
Luponcomplexationtothelanthanideion, themolecularstructures
of the uncomplexed compound L and its complex with the lan-
thanide ion were build using the molecular mechanics calculations.
It is worth mentioning that, in many cases, large molecular systems
can be modeled successfully by molecular mechanics, whilst avoid-
ing quantum mechanical calculations entirely [22]. The calculations
3+
rescent response of L to other metal ions besides Tb . As shown
in Fig. 5, though the fluorescence of L at 520 nm was strongly
3+
quenched by Tb , no significant spectral changes of L occurred in
3+
3+
3+
3+
3+
3+
3+
the presence of two equiv Nd , Sm , Yb , Er , La , Ce , Lu
,
Eu , Gd , Ho , Tm , Pr3+, Dy3+, Cu2+, Hg2+, Pb2+, Ag , Cs and
respectively, in MeCN solution. Furthermore, the Ka values of
:1 complexes L–M for other metal ions were calculated from the
3+
3+
3+
3+
+
+
+
K
n+
1
+
carried out in this study were based on the use of MM Molecular
fluorescence titration experiments, and summarized in Table 1. The
Mechanics force field, with a Polak-Ribiere algorithm having a con-
3+
selectivity towards Tb with respect to other metal ions (expressed
−1
vergence limit 0.01 kcal mol , performed on a Pentium IV personal
computer with Hyperchem version 7.0 [23]. The structure of the free
ligand was optimized using the 6-31G* basis set at the restricted
Hartree-Fock (RHF) level of theory. The optimized structure of the
ligandwasthenusedtofindouttheinitialstructureofitslanthanide
complex. Finally, the structure of the resulting 1:1 complex was
optimized at the semiempirical PM3 [24] level of theory employ-
ing the restricted Hartree-Fock (RHF). The optimized structures are
shown in Fig. 4.
as the ratio of the stability constants) was found to be around 55-
fold or more. These results implied that L showed high selectivity
3+
towards Tb over other metal ions tested in a neutral aqueous
solution.
To test the practical applicability of L as a Tb3+-selective fluores-
cence chemosensor, competition experiments were carried. Thus,
−6
−1
3+
−5
−1
−1
L (5 × 10 mol L ) was treated with Tb (5 × 10 mol L ) in the
−4
presence of background metal ions (5 × 10 mol L ), respectively,
which resulted in diverse fluorescence behaviors. As shown in Fig. 6,
except for La3+, Er , and Ho ions, other background metal ions
had little or no obvious interference with the detection of Tb3+
ions. These results suggested that compound L could be used as
a potential Tb3+-selective fluorescent chemosensor.
3+
3+
Table 1
n+
The formation constants of L–M complexes.
Cation
log Kf
3
+
Tm
Ce
2.15 ± 0.15
2.15 ± 0.11
<2.0
2.25 ± 0.11
3.46 ± 0.17
3.86 ± 0.17
6.22 ± 0.17
2.78 ± 0.17
3.88 ± 0.17
<2.0
3
+
3
+
Nd
Sm
3
+
3
+
La
Er
3
+
3
+
Tb
+
Dy3
3
+
Ho
Eu
Yb
3
+
3
+
2.45 ± 0.15
3
+
Lu
<2.0
Fig. 4. Optimized structures of free L (A) and its 1:1 complex with Tb3+ ion.

5
78
M.R. Ganjali et al. / Spectrochimica Acta Part A 74 (2009) 575–578
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[
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−
7
1
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