Quenching effect of some heavy metal ions on the fast peroxyoxalate-chemiluminescence of 1-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane as a novel fluorophore

Article abstract of DOI:10.1016/j.saa.2009.06.025

The fast chemiluminescence (CL) arising from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) with hydrogen peroxide in the presence of 1-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane (L) as a novel fluorophore, and imidazole as catalyst, has been studied in ethyl acetate solution. The relationships between the chemiluminescence intensity and concentrations of TCPO, imidazole, hydrogen peroxide and L are reported. In the presence of imidazole as catalyst, the entire CL signal was completed in less than 3 s. The quenching effect of Cu²⁺, Pb²⁺, Cd²⁺, Hg²⁺ and Ag⁺ ions on the chemiluminescent system was investigated, the resulting Stern-Volmer plots were obtained and the K_Q values were calculated. It was found that the quenching effect of metal ions on the chemiluminescence of L decreases in the order Cu²⁺ > Pb²⁺ > Cd²⁺ > Hg²⁺ > Ag⁺.

Full text of DOI:10.1016/j.saa.2009.06.025

Spectrochimica Acta Part A 74 (2009) 205–209
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Quenching effect of some heavy metal ions on the fast
peroxyoxalate-chemiluminescence of
1
-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane
as a novel fluorophore
a,∗
c
b
b
Mojtaba Shamsipur , Kiomars Zargoosh , Seyed Morteza Hosseini ,
c
Claudia Caltagirone , Vito Lippolis
a
Department of Chemistry, Razi University, Kermanshah, Iran
Department of Chemistry, Tarbiat Modares University, Tehran, Iran
Dipartimento di Chimica Inorganica ed Analitica, Universitá degli Studi di Cagliari, S.S. 554 Bivio per Sestu, 09042 Monserrato (CA), Italy
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The fast chemiluminescence (CL) arising from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO)
with hydrogen peroxide in the presence of 1-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane (L)
as a novel fluorophore, and imidazole as catalyst, has been studied in ethyl acetate solution. The rela-
tionships between the chemiluminescence intensity and concentrations of TCPO, imidazole, hydrogen
peroxide and L are reported. In the presence of imidazole as catalyst, the entire CL signal was completed
Received 15 September 2008
Received in revised form 17 May 2009
Accepted 7 June 2009
Keywords:
Peroxyoxalate-chemiluminescence
H2O2
2+
2+
2+
2+
+
in less than 3 s. The quenching effect of Cu , Pb , Cd , Hg and Ag ions on the chemiluminescent sys-
tem was investigated, the resulting Stern–Volmer plots were obtained and the KQ values were calculated.
It was found that the quenching effect of metal ions on the chemiluminescence of L decreases in the order
1
-(Dansylamidopropyl)-1-aza-4,7,10-
2
+
2+
2+
2+
+
Cu > Pb > Cd > Hg > Ag .
trithiacyclododecane
Quenching effect
Heavy metal ion
© 2009 Elsevier B.V. All rights reserved.
1
. Introduction
phy [15,16]. The coupling of CL detection with separation methods
can significantly increase the sensitivity over absorbance measure-
ments, because CL emission is measured against a dark background.
However, miniaturized separation systems cannot be constructed
using slow CL reactions as detection systems [17], since with
slow chemiluminescence reactions extra flow elements are needed
to observe the reaction in a reasonable time window at maxi-
mum emission intensity, and to overcome the peak broadening.
Thus, only rapid CL reactions are of great importance in this
respect.
Peroxyoxalate-chemiluminescence (PO-CL) is a powerful tech-
nique for the sensitive and some times selective determination
of a large variety of analytes, depending on the roles they play
in the CL reaction as fluorophore [1–4], catalyst [5], quencher
[
6–8] or oxidant [9,10]. In general, PO-CL involves the hydrogen
peroxide oxidation of an aryl oxalate ester in the presence of a flu-
orophore (activator). The reaction has been suggested to follow a
chemicallyinitiated electronexchange luminescence (CIEEL) mech-
anism via the formation of a high energy intermediate(s) such as
In recent years, we have studied the chemiluminescence reac-
1,2-dioxetanedione [11,12]. These metastable intermediates form
tions of peroxyoxalate esters, H O2 and a variety of fluorophores
2
complexes with the fluorophore so that one electron can be donated
to the intermediate [13,14]. This electron is then transferred back to
the fluorophore raising it to an excited state and liberating “light”.
Multiple unique selectivities (based on the role played by each
reagent in the reaction) and high sensitivity of these chemilu-
minescence reactions make PO-CL a valuable detection system
in analytical separation techniques such as liquid chromatogra-
in the presence of suitable basic catalysts such as sodium salicy-
late and imidazole [18–21]. In this paper, we report a study of the
very fast PO-CL reaction of 1-(dansylamidopropyl)-1-aza-4,7,10-
trithiacyclododecane (L), as a novel fluorophore. The relationships
between the chemiluminescence intensity and concentrations of
TCPO, imidazole, hydrogen peroxide and L are reported. An impor-
tant finding is that the entire CL reaction is completed in less than
3
s in the presence of suitable concentration of the imidazole. The
2+
2+
2+
2+
quenching effects Cu , Pb , Cd and Hg ions on the chemilu-
minescent system have also been investigated. It should be noted
that we have recently used L as a very promising fluoroionophore
∗ Corresponding author. Tel.: +98 21 66908032; fax: +98 21 66908030.
E-mail address: mshamsipur@yahoo.com (M. Shamsipur).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.06.025

2
06
M. Shamsipur et al. / Spectrochimica Acta Part A 74 (2009) 205–209
for the preparation of a selective optical sensor for silver ion
22].
[
Fig. 1. Fluorescence (A) and chemiluminescence (B) spectra of L.
lylchloride, hydrogen peroxide and various fluorescent compounds
2. Experimental
[
25], the so-called peroxyoxalate-chemiluminescence (PO-CL) has
2
.1. Reagents and solutions
received an increasing attention [26,21]. In this type of chemilumi-
nescence, the reaction between hydrogen peroxide and an activated
derivative of oxalic acid can produce chemiluminescence in the
presence of a fluorophore [27]. This reaction has successfully been
used as a highly sensitive detection technique in several procedures
developed for low level determinations of a wide variety of analytes
including a range of different fluorophores [4], hydrogen perox-
ide [28], fluorophore labeled amino acids [29] as well as different
quencher species [7,8].
Bis(2,4,6-trichlorophenyl)oxalate (TCPO) was prepared from
the reaction of 2,4,6-trichlorophenol with oxalylchloride in the
presence of triethylamine, as described by Mohan and Turro [23].
Hydrogen peroxide (Merck; Perhydrol Suprapur, 30% in water) was
assayed by potassium permanganate titration [24] and diluted
in ethyl acetate. The fluorophore 1-(dansylamidopropyl)-1-aza-
4
,7,10-trithiacyclododecane (L) was synthesized as described
elsewhere [22]. The stock solutions of reagent grade nitrate salts
of the cations (all from Merck) were prepared in acetonitrile. The
stock solution of L (0.1 mM) was prepared in a calibrated 50-ml
volumetric flask by dissolving an appropriate amount of L in ethyl
acetate and protected from light. Stock solutions of imidazole
Our preliminary experiments revealed that the addition of
excess amount of hydrogen peroxide to an ethyl acetate solu-
−3
−4
tion containing 1.0 × 10 M TCPO, 5.0 × 10 M imidazole and
−4
4
.4 × 10 M L (green-yellow) resulted in the emission of a
very intense blue light. In Fig. 1, the CL spectrum for the
(0.005 M) and the TCPO (0.005 M) were prepared in ethyl acetate
TCPO–H O –imidazole reaction in the presence of L is compared
2
2
shortly before use.
with the fluorescence spectrum of a solution of L in MeCN excited
at 416 nm. A good correspondence exists between the CL and flu-
orescence spectral distributions of the fluorophore, indicating that
the singlet excited state of the fluorescent additive is formed in the
reaction and it is the emitting species [30,31].
2.2. Chemiluminescence measurements
Chemiluminescence measurements were carried out on a
homemade apparatus equipped with a phototube (59 RX Kelman).
The instrument was covered with a black sheet, in order to pre-
vent piping of light to the cell. The voltage applied to the phototube
As expected, the initial concentrations of the reactants involved
were found to affect the intensity of the PO-CL emission [20,32,33].
Thus, in the next steps, the influence of concentrations of L, TCPO,
H O and base catalyst imidazole on the PO-CL system was studied.
◦
was 90 V and the temperature was set at 25.0 ± 0.1 C. The appara-
2
2
tus was connected to a personal computer via a suitable interface
Fig. 2 shows typical response curves (i.e., light intensity versus
–4
(
Zag Chem, Tehran, Iran). Experiments were carried out with mag-
time) for the PO-CL system of fluorophore L (2.5 × 10 M) in the
netic stirring (500 rpm) in a light-tight flat-bottom glass cell of
presence of varying concentrations of TCPO and excess amounts
–
3
1
0 mm diameter. The temperature was adjusted to the desired val-
of H O2 (0.2 M) and imidazole (2.5 × 10 M). In all cases, the peak
2
◦
ues ± 0.1 C using a Thermo Mix Broaun thermostat (Biotechnology
intensity increases rapidly after mixing and reaches a maximum
in few seconds, followed by the decay of light intensity from the
maximum in less than 10 s. As it is seen from Fig. 2 the CL intensity
increases with increasing concentration of TCPO. A nice linear cor-
relation between the chemiluminescence intensity and the TCPO
Int.).
2.3. Fluorescence measurements
2
Steady-state fluorescence spectra were recorded on
a
concentration (R > 0.988) was found. The basis for such linear cor-
PerkinElmer, Ls50 spectrofluorimeter instrument. The excita-
tion and emission monochromators were set at 390 and 495 nm,
respectively. A spectral bandwidth of 3 nm was used. All experi-
ments were carried out using freshly prepared solutions containing
relation has already been discussed in the literature [11,34].
The influence of the concentration of H O2 on the PO-CL of L
2
–4
was studied at constant concentrations of L (2.5 × 10 M), TCPO
–3
–3
(1.5 × 10 M) and imidazole (2.5 × 10 M) and the results are
shown in Fig. 3. As is obvious, the PO-CL intensity strongly increased
with increasing concentration of hydrogen peroxide until a concen-
tration of 0.2 M was reached. However, further addition of hydrogen
peroxide resulted in a gradual decrease in the CL intensity. This
is most probably due to the quenching effect of hydrogen per-
oxide at higher concentrations, which begins to decompose the
reactive intermediate(s), dioxetane species, and hence reduces the
–4
–3
5
.0 × 10 –2.5 × 10 M of L in ethyl acetate, using a 10-mm quartz
cuvette.
3. Results and discussion
Since the first discovery by Chandross of the development
of a strong chemiluminescence from the reaction between oxa-

M. Shamsipur et al. / Spectrochimica Acta Part A 74 (2009) 205–209
207
–
4
Fig. 4. CL intensity as a function of time for reaction of H2O2 (0.2 M), TCPO
Fig. 2. CL intensity as a function of time for reaction of L (2.5 × 10 M), H2O2 (0.2 M)
–
3
–3
–3
(1.5 × 10 M) and imidazole (2.5 × 10 M) in the presence of varying concentration
and imidazole (2.5 × 10 M) in the presence of varying concentration of TCPO in
–4 –4 –4 –4
–4
–3
–3
of L: (1) 1.25 × 10 M, (2) 2.5 × 10 M, (3) 5.0 × 10 M and (4) 7.5 × 10 M.
ethyl acetate solution: (1) 5.0 × 10 M, (2) 1.0 × 10 M, (3) 1.5 × 10 M and (4)
–3
2
.0 × 10 M.
the strong fluorescence of L upon complexation with silver ions
was reported [22]. It is interesting to note that the trend observed
in the fluorescence quenching effect of different metal ions (i.e.,
PO-CL emission [11]. The effect of the concentration of L, at con-
–3
stant amounts of TCPO (1.5 × 10 M), H O2 (0.2 M) and imidazole
2
–
3
+
2+
2+
+
2+
(
2.5 × 10 M), was also studied and the results are shown in Fig. 4.
Ag > Hg > Cu > Tl > Cd ) was found to be in agreement with
the selectivity order deduced from the corresponding complexation
studies in acetonitrile solution. In the present work, for comparison
The PO-CL intensity increased with increasing the concentration of
the fluorophore, consistent with the previous reports [8,11,12].
Finally, in order to investigate the optimal concentration of imi-
2
+
2+
2+
2+
purposes, we studied the quenching effect of Cu , Pb , Cd , Hg
–3
and Ag+ ions on the CL arising from the H O –TCPO–L–imidazole
dazole, the CL response of the H O (0.2 M)–TCPO (1.5 × 10 M)–L
2
2
2
2
–
4
(
2.5 × 10 M) system was measured in the presence of varying con-
reaction system.
centration of the base, and the resulting CL intensity–time plots are
shown in Fig. 5. As is obvious, the PO-CL intensity strongly increased
with increasing concentration of imidazole, the observed intensity
enhancement being indicative of the catalytic effect of the base
Initial studies clearly revealed that the presence of the biva-
lent metal ions considered can quench the PO-CL of L significantly.
As an example, the resulting CL intensity decay curves for the
TCPO–H O –L–imidazole chemiluminescent system in the pres-
2
2
2+
[
20,21,35,36]. Moreover, Fig. 5 shows that the whole CL reaction is
ence of different concentrations of Cu is shown in Fig. 6. The
presence of increasing amounts of Cu2+ resulted in a significant
completed in less than 3 s in the presence of imidazole with concen-
–3
trations above 5.0 × 10 M. Such a fast PO-CL reaction has a good
potential to be used as detecting system in separation techniques
[
17].
As mentioned before, in our previous work, a very efficient and
selective fluorimetric optode membrane for silver ion detection at
low concentration levels based on the considerable quenching of
–4
Fig. 5. CL intensity as a function of time for reaction of L (2.5 × 10 M), TCPO
–
4
–3
Fig. 3. CL intensity as a function H2O2 concentration for reaction of L (2.5 × 10 M),
(1.5 × 10 M) and H2O2 (0.2 M) in the presence of varying concentration of imi-
–3
–3
–3
–3
–3
imidazole (2.5 × 10 M) and TCPO (1.5 × 10 M), in the presence of varying amounts
dazole in ethyl acetate: (1) 1.25 × 10 M, (2) 2.5 × 10 M, (3) 3.75 × 10 M and (4)
–3
of H2O2.
5.0 × 10 M.

2
08
M. Shamsipur et al. / Spectrochimica Acta Part A 74 (2009) 205–209
–
4
+
C O + L → [C O L ]
(3)
(3a)
(4)
2
4
2
C O + Q → non-CL
C2O4 L ] → L ∗ + 2CO2
2
4
–
+
[
L∗ → L + hꢀ
L ∗ + Q → L
L∗ → L + heat
(5)
(5a)
(6)
The asterisk indicates the fluorophore L in its excited state. Based
on this mechanism, the observed quenching effects may be due to
the interaction of the cations with the C O4 intermediate (Eq. (3a))
2
and/or with the excited molecule (Eq. (5a)).
–
4
While in the case of fluorescence studies, on adding metal ions to
a solution of L, a pronounced chelation enhancement of quenching
of the fluorescence (CHEQ effect) is observed [22,41]. In our previ-
ous report, it was observed that the fluorescence quenching effect
of different metal ions on the fluorescence emission of L excited
Fig. 6. CL intensity as a function of time for reaction of L (4.4 × 10 M), TCPO
–3
–3
(
1.0 × 10 M), H2O2 (0.2 M) and imidazole (5.0 × 10 M) in the presence of varying
2+ –6 –4 –4
concentrationofCu :(1)0.00 M, (2)2.5 × 10 M, (3)1.25 × 10 M, (4)6.25 × 10
M
–3
and (5) 1.25 × 10 M.
steady decrease in the CL intensity–time curves in such a way to
maintain the symmetric curve shape created during the rise of the
CL emission in the absence of the metal ion. For the case of other
metal ions, a more or less similar trend was observed.
For such CL systems, in the presence of a quencher, Q, the CL
intensity is reduced from Io to I , the ratio between these quanti-
+
2+
2+
2+
2+
at 416 nm decreased in the order Ag > Hg > Cu > Pb > Cd
,
which is the order of decreasing formation stability constants of the
corresponding 1:1 complexes with L in acetonitrile solution [22].
Our ab initio calculations [22] clearly revealed that, in the case of
free L, the dansylamidopropyl group (as the signaling moiety) is
situated perpendicular to the plane of the ionophore ring (as the
recognition moiety) containing three donating sulfur atoms and a
nitrogen atom, via proper spatial twisting of the carbon atoms of
the propyl group, to result in the lowest conformational energy. In
this conformation, the ligand benefits from maximum fluorescence
intensity. While, in the presence of silver ion, which is coordinated
by the four binding sites of the ligand, the dansylamidopropyl group
is folded over the ligand cavity so that it gets close enough to the
coordinated silver ions for some possible electron transfer process,
responsible for the strong fluorescence quenching of the ligands
system [22].
Q
ties being directly proportional to the quencher concentration, as
expressed by the Stern–Volmer equation [37]:
Io
=
1 + K [Q]
(1)
Q
IQ
where KQ is the Stern–Volmer quenching constant. According to
Eq. (1), a plot of Io/IQ versus [Q] will result in a linear graph with
an intercept of 1 and a slope of K . The higher the K , the stronger
the quenching properties of Q. The resulting plots of Io/IQ versus the
quencher ion concentration for all cations investigated are shown
in Fig. 7. As it is readily seen, the quenching effect of the different
Q
Q
From these results it can be concluded that the quenching order
of cationic species on the fluorescence and chemiluminescence
emissions of the same fluorophore may be completely different
based on the differences in their quenching mechanisms.
2+
2+
metal ions considered decreases in the order Cu (KQ = 7698) > Pb
2
+
2+
(KQ = 1757) > Ag+ (KQ = 344).
(
KQ = 5043) > Cd
(KQ = 2090) > Hg
This order is quite different from the order reported for the quench-
ing effect of the metal ions on the fluorescence emission of L when
+
2+
2+
2+
excited at 416 nm (i.e., Ag > Hg > Cu > Cd ) [22]. Such a discrep-
ancy between the order of quenching effects of metal ions on the CL
and fluorescence behavior of the same fluorophore L is expected to
originate from different mechanistic pathways responsible for the
quenching effects in the two optical systems.
4. Conclusions
The presence of the dansylamidopropyl pendant arm on
-aza-4,7,10-trithiacyclododecane makes 1-(dansylamidopropyl)-
-aza-4,7,10-trithiacyclododecane ligand (L) a very suitable blue
1
1
The most frequently proposed mechanistic pathway that a
quencher Q can follow in the reaction with TCPO, H O2 and a fluo-
fluorescer for use in peroxyoxalate-chemiluminescence proce-
dures. After optimizing the relative concentrations of species
involved, including bis(2,4,6-trichlorophenyl)oxalate, hydrogen
peroxide, and imidazole, as a suitable catalyst, the ligand produced
lightemissions ofstrongintensityfor areaillumination. Meanwhile,
because of the existence of three soft donating sulfurs and a nitro-
gen atom in the macrocyclic unit of the ligand L and its suitable
cavity size, it was found to bind soft cationic species and, con-
sequently, its fluorescence emission was strongly quenched upon
2
rophore L is as follows [8,38–40]:
TCPO + H O → C O (intermediate) + 2, 4, 6-trichlorophenol
2
2
2
4
(2)
metal ion complexation in the order Cu2+ > Pb > Cd > Hg > Ag .
The resulting Stern–Volmer plots were obtained and the KQ values
were also calculated and discussed.
2+
2+
2+
+
Acknowledgements
The support of this work by the Iran National Science Foun-
dation (INSF) is gratefully acknowledged. MIUR is also gratefully
acknowledged for financial support (Project PRIN 2007C8RW53).
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Fig. 7. Stern–Volmer plot of Io/IQ versus concentration of different heavy metal ions.
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