PAPER
www.rsc.org/analyst | Analyst
Highly effective chemosensor for mercury ions based on bispyrenyl derivative†
Manoj Kumar,* Abhimanew Dhir, Vandana Bhalla, Richa Sharma, Rajiv Kumar Puri
and Rakesh Kumar Mahajan
Received 21st October 2009, Accepted 7th April 2010
First published as an Advance Article on the web 5th May 2010
DOI: 10.1039/b922072k
A new bispyrenyl azadiene derivative has been synthesized and examined for its cation recognition
abilities toward different cations. The ligand shows strong affinity for Hg2+ ions over other cations such
as Cu2+, Pb2+, Zn2+, Ni2+, Cd2+, Ag+, K+, Na+ and Li+. An ‘‘Off-On’’ type of fluorescent behaviour was
observed with simultaneous presence of Cu2+ and Hg2+ ions. An ion selective electrode (ISE) is also
formed which showed excellent selectivity to Hg2+ over all the other cations tested. The lower limit of
detection is 7.08 106 M.
Introduction
Selective signalling of metal ions and anions has potential
analytical applications in many fields like chemistry, medicine,
biology and environment.1–5 A variety of compounds selective
towards alkali and alkaline earth metal ions4,5 have been well
developed but the development of practical chemosensors for the
heavy and transition metal ions is still a challenge. Among the
heavy metal ions mercury is one of the most significant cations.
The toxic effects6 of mercury ions in the environment have been
well documented and its contamination is wide spread which
arises from a variety of natural and anthropogenic sources7
including oceanic and volcanic emission,8 gold mining,9 solid
waste incineration and combustion of fossil fuels. The exposure
to mercury even at very low concentrations, leads to digestive,
kidney and especially neurological diseases.10–12 The Environmental Protection Agency (EPA) standard for the maximum
allowable level of inorganic Hg(II) in drinking water is 2 ppb.13
Keeping in view the roles played by mercury in day to day life, the
development of techniques for mercury hazard assessment and
mercury pollution management are in great demand. Fluorescence signalling is one of the first choices due to its high detection
sensitivity and simplicity which translates molecular recognition
into tangible fluorescence signals.14 Thus, designing fluorescent
sensors for mercury15–20 has drawn worldwide attention.
Recently, the molecular designs showing an inverted fluorescence response upon changes in the chemical surroundings have
been a topic of considerable interest. Responding to an external
stimulus to achieve the conversion between two different states
with ‘‘on’’ and ‘‘off’’ functions make use of such molecules for the
construction of molecular switches and molecular electronic
devices. These molecular devices and their direction of movements have been accomplished using different external
stimuli.21,22 In most cases the fluorescence has been ‘‘switched
off’’ by a change in external stimuli. In contrast molecular devices
showing ‘‘on’’ state against the external stimulus are unique and
attractive prospects for new type of molecular switching
Department of Chemistry Guru Nanak Dev University, UGC- centre for
advanced studies, Amritsar, India 143005
† Electronic supplementary information (ESI) available: Further
experimental results. See DOI: 10.1039/b922072k
1600 | Analyst, 2010, 135, 1600–1605
materials.23–25 Our research involves the design and synthesis of
receptors which are selective for soft metal ions26–31 and
anions32,33 and evaluation of their logic behaviours34–37 for
application as molecular switches and logic gates. We recently
reported on-off switchable (Cu2+/K+) binuclear chemosensor
based on thiacalix[4]arene armed with pyrene moieties.38 Now,
we have synthesized new bispyrene based receptor functionalized
with imine units which undergoes fluorescence enhancement on
addition of only Hg2+ ions. While this work was in progress
Shiraishi et al.20 reported a ‘‘turn on’’ fluorescent sensor for Hg2+
ions, however a pyrene based sensor reported in this manuscript
has better sensing ability. An ion selective electrode (ISE) for
Hg2+ is also formed which shows excellent selectivity with a lower
limit of detection of 7.08 106 M, which adds to the real world
application of the receptor.
Results and discussion
Condensation of 1,2-diaminoethane with 2.2 mol equiv. of 1pyrene carboxaldehyde in ethanol gave compound 3 in 45% yield
(Scheme 1). The structure of compound 3 was characterized by
its spectroscopic and analytical data. The IR spectrum showed
a stretching band at 1615 cm1 due to the C¼N and there is no
band due to the free amino and aldehyde groups which indicate
that the condensation has taken place. The 1H NMR spectrum of
3 showed singlet at d 9.32 ppm due to imino protons (2H), singlet
at d 4.35 ppm due to methylene protons and multiplet from
d 7.76–8.68 ppm for 18H protons of pyrene (see figure S7 of
supporting information†). The FAB-mass spectrum showed
a parent ion peak at m/z 485 (M + 1)+ (see figure S8 of supporting
Scheme 1
This journal is ª The Royal Society of Chemistry 2010
information†). These spectroscopic data corroborate the structure 3 for this compound.
Binding studies
The binding behaviour of compound 3 was studied towards
different cations (Cu2+, Hg2+, Pb2+, Zn2+, Ni2+, Cd2+, Ag+, K+,
Na+, Li+) by UV-Vis and fluorescence spectroscopy. All the
titration experiments were carried out in dry THF by adding
aliquots of different metal ions. The UV-Vis absorption spectrum of 3 (10 mM) is characterized by the presence of typical
pyrene absorption bands at l 361 nm and l 389 nm (Fig. 1). The
addition of increasing amount of Hg2+ ions from (1–100 mM)
resulted in a decrease in absorption at 361 nm and an increase in
absorption at 389 nm, and formation of a broad red shifted band
at 447 nm. The formation of the new band at 447 nm is due to the
interaction of Hg2+ ions with the imino nitrogen leading to the
ICT (intramolecular charge transfer) phenomenon from pyrenyl
group to the imine linkage.
In the fluorescence spectrum, receptor 3 (5 mM), showed
a weak monomer and very weak excimer emission39,40 at 398 nm
and 480 nm respectively when excited at 343 nm (Fig. 2). Upon
addition of small amounts of Hg2+ (0–10 mM) to the solution of
compound 3, increase in the monomer and excimer emission was
observed. The increase in excimer emission stops after addition
of 4 mM of Hg2+ ions whereas monomer emission continues to
increase up to 10 mM of Hg2+ ions (Fig. 2 and inset of Fig. 2). The
reason for the increase of monomer band at 398 nm is attributed
to the suppression of photoinduced electron transfer (PET) from
imino nitrogen atoms to the photoexcited pyrene moiety. Upon
Hg2+ binding, the redox potential of the nitrogen atoms is raised
so that the relevant HOMO becomes lower in energy than that of
the pyrene, consequently, PET is not possible any more and
fluorescence quenching is suppressed. On further addition of
Hg2+ ions from 12 mM to 20 mM the monomer emission decreases
with a blue shift of 10 nm while a new red shifted excimer band
appears at 505 nm which indicates that stacking of pyrene has
taken place in the presence of Hg2+ ions (12 mM to 20 mM)
(Fig. 3).
Under the same conditions as used above for Hg2+, we also
tested the fluorescence response of 3 to the other metal ions such
as (Cu2+, Pb2+, Zn2+, Ni2+, Cd2+, Ag+, K+, Na+, Li+) and as shown
in Fig. 4, no significant fluorescence changes of 3 occurred in the
presence of (0 to 10 mM) of these metal ions except Cu2+ where
quenching of fluorescence was observed using 10 mM of Cu2+
2+
Fig. 1 UV-Vis Spectra of 3 (10 mM) and 3 + 100 mM of Hg ions in THF.
This journal is ª The Royal Society of Chemistry 2010
Fig. 2 Fluorescence emission spectra of 3 (5 mM) in the presence of Hg2+
ions (0–10 mM) in THF. Excitation wavelength was 343 nm. Inset curve
shows the changes in the fluorescence emission at 398 nm on respective
additions of Hg2+ ions.
ions. This remarkable fluorescence quenching induced by Cu2+ is
ascribed to reverse PET41 from pyrene units to the nitrogen atom
of which the electron density is diminished by metal ion
complexation (see figure S2 of supporting information†).
Fitting the changes in the fluorescence spectra of compound 3
with mercury ions using nonlinear regression analysis program
SPECFIT42 gave a good fit and demonstrates that 2 : 1 stoichiometry (host : guest) is the most stable species in the solution
with a binding constant log b2,1 ¼ 10.53 (Ka ¼ 3.38 10 10 M1)
(see figure S10 and S11 of supporting information†). The method
of continuous variation (Job’s Plot)43 was also used to prove the
2 : 1 stoichiometry (host : guest) (see figure S1 of supporting
information†). Binding constant of 3 with Cu2+ ions was found to
be 5.07 (Ka ¼ 1.95 105 M1) using nonlinear regression analysis
program SPECFIT42 which gave a good fit for 2 : 1 stoichiometry (host : guest).
To test the practical applicability of compound 3 as a Hg2+
selective fluorescence sensor competitive experiments were
carried out in the presence of Hg2+ at 10 mM mixed with Cu2+,
Pb2+, Zn2+, Ni+, Cd2+, Ag+, Li+, Na+, K+ at 10 mM, no significant
variation in the intensity was found by comparison with and
without the other metal ions besides Hg2+ (see figure S3 of supporting information†). This means that compound 3 has a high
selectivity for Hg2+ ions.
The detection limit44 of 3 as a fluorescent sensor for the analysis of Hg2+ was determined from a plot of fluorescence intensity
Fig. 3 Fluorescence emission spectra of 3 (5 mM) in the presence of Hg2+
ions (12–20 mM) in THF. Excitation wavelength was 343 nm.
Analyst, 2010, 135, 1600–1605 | 1601
Fig. 4 Fluorescence Intensity changes [(I0 I)/I0 100]% of 3 (5 mM) at
wavelength 398 nm upon addition of 10 mM of various metal perchlorates.
Fig. 6 Fluorescence emission spectra of 3 (5 mM) in the presence of
10 mM of Cu2+ ions in THF and further addition of 15 mM of Hg2+ ions to
the solution. Excitation wavelength was 343 nm.
as a function of the concentration of the added metal ions. It was
found that 3 has a detection limit of 4.5 106 mol L1 for Hg2+
which is sufficiently low for the detection of submillimolar
concentration range of Hg2+ ions found in many chemical
systems. A noticable colour change with mercury ions was also
observed by mixing the receptor 3 (5 mM) with various cations
(50 mM). The colourless solution of receptor 3 in THF became
bright sea green when mercury ions were added (Fig. 5).
To elucidate the binding mode of receptor 3 with mercury ions,
the 1H NMR spectrum of its complex with mercury perchlorate
was also recorded. The imino protons of the receptor undergo
a significant downfield shift of d1.45 ppm which indicates that the
lone pair of electrons on nitrogen atoms are involved in binding
with the mercury ions (see figure S9 of supporting information†).
Recently there has been a lot of interest in the design of photoactive molecules which undergo inverted fluorescence response
upon change in their chemical surroundings. To utilise our
system as molecular switch, we investigated its switching
behaviour in simultaneous presence of Cu2+ and Hg2+ ions. We
observed an interesting ‘‘Off-On’’ type of fluorescent behaviour
of receptor 3. Addition of Cu2+ ions (10 mM) quenched the
fluorescence emission of 3 which was restored on adding Hg2+
ions (15 mM) to the 3-Cu2+ complex (Fig. 6) whereas no change
was observed on addition of Cu2+ ions to 3$Hg2+ complex. This
may be ascribed to the negative allosteric effect between45 Hg2+
and Cu2+ ions in which Hg2+ ions decomplex 3$Cu2+ complex.
However Cu2+ ions were unable to decomplex Hg2+ ions from
3$Hg2+ complex. This may be attributed to the strong affinity of
Hg2+ ions towards receptor 3 as is evident from binding constant
data of complexes of both the ions.
Fig. 5 Photograph of emission changes of 3 (5 mM) in THF upon
addition of metal perchlorates (20 mM); (A) only 3 and in the presence of
(B) Cu2+, (C) Pb2+, (D) Ag+, (E) Hg2+, (F) Cd2+, (G) Ni2+, (H) Zn2+.
1602 | Analyst, 2010, 135, 1600–1605
ISE studies
Based on the results of these binding studies (UV-Vis, fluorescence and NMR) we envisaged that it should be possible to
construct mercury ion selective PVC membrane based on
compound 3. Thus, a sensor membrane for 3 was prepared and
assembled as reported earlier from our laboratory.46 The
potentiometric cell used was Ag/AgCl (3.0 M KCl) 1.0 103 M
Hg(NO3)2/PVC membrane/Test solution/(3.0 M KCl)Ag/AgCl.
The composition of this membrane is listed in Table 1.
The optimized PVC membrane of the cation receptor generated a stable potential when placed in contact with mercury
nitrate solution (for optimization results see Table S1 and text on
page 12 and 13 of Supporting Information†). The electrode
demonstrates a linear response for Hg2+ ions in the concentration
range from 1.0 101 to 1.0 105 mol dm3 (Fig. 7). The slope
of the plot was approximately 30.67 1 mV per decade mV of
concentration which indicates the Nernstian nature of the electrode. The response time of the membrane was measured at
different concentrations of analyte and was found to be less than
10 s and no change was observed up to 5 min (See figure S12 of
supporting information†). The reproducible and stable potentials with the standard deviation of 1 mV at various concentrations of Hg(NO3)2 solutions were recorded. Under the same
conditions as used above for Hg2+, we also fabricated and tested
the emf responses of the membranes of the other metal ions such
as Na+, K+, Ca2+, Cu2+, Co2+, Mg2+, Cd2+, Pb2+, Zn2+, NH4+, Fe3+,
Ni2+, Ag+. No significant emf responses of membranes was
observed in the presence of (1 101 to 106 M) of these metal
ions (see figure S4 of supporting information†).
The pH dependence of PVC membrane sensor based on 3 was
examined at 1.0 103 M Hg(NO3)2 concentration (See figure S5
of supporting information†). The potential was found to remain
constant in the pH range 1.0–4.90, which was considered as
a functional pH range of the sensor. The most important feature
of an ion selective electrode is its response towards primary ion in
the presence of various other cations. This is measured in terms
of the potentiometric selectivity coefficients (log KPotHg , B)
which was evaluated by fixed interference method (FIM). In this
2+
This journal is ª The Royal Society of Chemistry 2010
Table 1 Composition and potential response characteristics of Hg2+ ion-selective electrodea,b
PVC/mg
DOS/mg
NaTPB/mg
Ionophore/mg
Linear Range/M
Detection Limit/M
Slope (mV/decade)
100.6
201.6
1.4
5.7
1.0 101–1.0 105
7.08 106
30.67 1
a
NaTPB: Sodium tetraphenylborate.
b
DOS: Dioctyl sebacate as plasticizer.
(Table 2) which have been reported to be major interfering ions
in many of the reports.
The practical significance of the ion selective electrode was
tested by using it as an indicator electrode during the potentiometric titration of Hg2+ with a standard solution of sodium
iodide. A 20 ml solution of 1.0 102 M mercury nitrate was
titrated against 1.0 102 M sodium iodide solution. The sharp
rise in the potential indicates the end point (See figure S6 of
supporting information†).
Conclusion
Fig. 7 Potentiometric response curve of ISE based on 3 toward Hg2+
ions.
method, the concentration of the primary ion, Hg2+ ion, is varied
whereas the concentration of the secondary ion is kept constant
in test solution which is 1.0 102 M in the present case. The
potentiometric selectivity data of ion selective electrode for
various secondary ions is given in Table 2. It is evident from the
selectivity coefficient values that the sensor exhibits a high preference for Hg2+ ions in comparison to alkali, alkaline earth and
heavy transition metal ions. Different univalent, divalent and
trivalent metal ions except Ag+ ion exhibited selectivity coefficients (log KPotHg , B) within a range of 0.85 to 4.09 and have
not been found to be interfering in the normal functioning of the
proposed Hg2+ ion selective electrode. Although the selectivity
coefficient value for the Ag+ ion is higher than the values for
other secondary metal ions (log KPotHg , Ag ¼ 0.2), it has been
found that Ag+ ion does not interfere in the normal functioning
of the proposed Hg2+ ion selective electrode. There are some ion
selective electrodes for Hg2+ reported in literature47–52 (See Table
S2 of supporting information†) but from the comparative study
of proposed mercury(II) ion selective electrode and those which
are already reported in literature, the proposed electrode based
on 3 as an ionophore has been found to be better in terms of its
wide concentration range (1 101 to 1 105), lower detection
limit (7.08 106) and improved selectivity with respect to the
various secondary ions, especially the silver(I), Fe3+ and Cd2+
2+
2+
+
In conclusion, we synthesized a novel receptor which shows
pronounced selectivity for Hg2+ ions. An ‘‘Off–On’’ type of
fluorescence behavior was observed by adding Cu2+ and Hg2+
respectively. The simple molecular design presented here may
contribute to the development of more useful fluorescent signalling material using Hg2+ inputs and more sophisticated
molecular level devices with multiple functions. Hg2+ selective
membrane sensor is also prepared which works well in the pH
range of 1.0 to 4.90 with response time of less than 10 s. The
selectivity coefficient values obtained by proposed electrode
showed its better sensitivity and selectivity for Hg2+ ions in
comparison to various secondary ions.
Experimental
General
All reagents were purchased from Aldrich and were used without
further purification. All the Fluorescence spectra were recorded
on SHIMADZU RF 5301 PC spectrofluorometer. 1H and 13C
NMR spectra were recorded on JEOL-FT NMR-AL300 MHz
spectrophotometer using CDCl3 and CD3CN as solvent and
TMS as internal standards. Data are reported as follows:
chemical shifts in ppm (d), multiplicity (s ¼ singlet, d ¼ doublet,
m ¼ multiplet), coupling constants (Hz), integration, and interpretation. Solutions of receptor 3 and all metal perchlorates were
prepared in THF AR grade. The curve fitting was performed
with SPECFIT\32 software. The plasticizer bis(2-ethylhexyl)sebacate (DOS) and high molecular weight poly(vinylchloride) (PVC) were used as received from Fluka. Anion
excluder, sodium tetraphenyl borate (NaTPB) was obtained
from Aldrich. Hg(NO3)2 and other metal ion nitrates received
Table 2 Selectivity coefficient values of Hg2+-selective electrode 3
Secondary ions
Na+
Ca2+
K+
Cu2+
Co2+
Mg2+
Cd2+
Pb2+
Zn2+
NH4+
Fe3+
Ni2+
Ag+
Log KPotHg
0.85
3.15
0.95
2.8
3.05
2.85
3.05
3.10
3.20
1.45
4.09
3.40
0.2
,B
2+
This journal is ª The Royal Society of Chemistry 2010
Analyst, 2010, 135, 1600–1605 | 1603
from Merck and were used without any further purification.
Doubly distilled deionised water was used throughout.
support under FIST programme, UGC for SAP programme and
Guru Nanak Dev University for providing research facilities.
Synthesis of compound 3
References
1-Pyrenecarboxyaldehyde (2) (100 mg, 0.434 mmol) was added
dropwise to a stirred solution of 1,2- diaminoethane (1)
(13.10 mg, 0.217 mmol) in ethanol (10.0 ml). The reaction
mixture was refluxed for one hour at 85 C. During this hour
a cream colour solid precipitated out. This solid was filtered,
washed with ethanol and recrystalized from chloroform: methanol (1 : 1) to give pure compound 3 in 45% yield (80 mg);
melting point 225 C; IR (KBr) nmax ¼ 1615 cm1; 1H NMR
(CDCl3, 300 MHz), d 4.35 (4H, s, CH2), d 7.76–8.68 (18H, m,
pyrene), d 9.32 (2H, s, HC ¼ N); FAB-MS: m/z 485 (M + 1)+.
Anal. Calcd for C36H24N2: C, 89.23; H, 4.99; N, 5.78; Found: C,
89.03; H, 4.47; N, 5.13.
1 B. Valeur and I. Leray, Coord. Chem. Rev., 2000, 205, 3.
2 P. A. Gale, Coord. Chem. Rev., 2000, 199, 181.
3 J. P. Desvergne and A. W. Czarnik, ed., Chemosensors of ions and
molecular recognitions, NATO ASI Series; Kluwer Academic
Dordrecht, The Netherlands, 1997.
4 A. P. de Silva, H. Q. N. Gunaratne, T. Gunnalaugsson, A. J. Huxley,
C. P. McCoy and J. T. Rademacher, Chem. Rev., 1997, 97, 1515.
5 L. Fabbrizi and A. Poggi, Chem. Soc. Rev., 1995, 24, 197.
6 W. Kaim and B. Schwederski, Bioinrganic Chemistry: Inorganic
Elements in the chemistry of life, an Introduction and Guide; WileyInterscience: New York, 1991.
7 J. M. Benoit, W. F. Fitzgerald and A. W. Damman, Environ. Res.,
1998, 78, 118.
8 A. Renzoni, F. Zino and E. Franchi, Environ. Res., 1998, 77, 68.
9 O. Malm, Environ. Res., 1998, 77, 73.
10 P. Grandjean, P. Weihe, R. F. White and F. Debes, Environ. Res.,
1998, 77, 165.
11 T. Takeuchi, N. Morikawa, H. Matsumoto and Y. Shiraishi, Acta
Neuropathol., 1962, 2, 40.
12 M. Harada, Crit. Rev. Toxicol., 1995, 25, 1.
13 Mercury Update: Impact on Fish Advisories. EPA Fact Sheet EPA823-F-01-011; EPA, Office of Water: Washington, DC, 2001.
14 A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson,
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice,
Chem. Rev., 1997, 97, 1515.
15 A. Caballero, R. Martinez, V. Loveras, I. Ratera, J. Vidal-Gancedo,
K. Wurst, A. Tarraga, P. Molina and J. Veiana, J. Am. Chem. Soc.,
2005, 127, 15666.
16 J. Wang and X. Qian, Chem. Commun., 2006, 109.
17 H. Zheng, Z. H. Qian, L. Xu, F. Yuan, L. D. Lan and J. G. Xu, Org.
Lett., 2006, 8, 859.
18 Y. Zhao, and Z Zhong, J. Am. Chem. Soc., 2006, 128, 9988.
19 R. Martinez, A. Espinosa, A. Tarraga and P. Molina, Org. Lett.,
2005, 7, 5869.
20 Y. Shiraishi, H. Maehara, K. Ishizumi and T. Hirai, Org. Lett., 2007,
9, 3125.
21 E. Yashima, K. Maeda and Y. Okamoto, Nature, 1999, 399, 449.
22 A. M. Brouwer, C. Frochot, F. G. Gatti, D. A. Leigh, L. Mottier,
F. Paolucci, S. Rofia and G. W. Wurpel, Science, 2001, 291, 2124.
23 J. M. Lehn, Science, 2002, 295, 2400.
24 H Miyake, K. Yoshida, H. Sugimoto and H. Tsukube, J. Am. Chem.
Soc., 2004, 126, 6524.
25 C. Piguet, G. Bernardinelli and G. Hopfgartner, Chem. Rev., 1997, 97,
2005.
26 R. Kumar, V. Bhalla and M. Kumar, Tetrahedron, 2008, 64, 8095.
27 V. Bhalla, R. Kumar, M. Kumar and A. Dhir, Tetrahedron, 2007, 63,
11153.
28 R. K. Mahajan, V. Sharma nee Bhalla, H. Singh, N. Sharma and
I. Kaur, Tetrahedron Lett., 2001, 42, 5315.
29 M. Kumar, V. Sharma nee Bhalla and J. N. Babu, Tetrahedron, 2003,
59, 3267.
30 V. Bhalla, M. Kumar, H. Katagiri, T. Hattori and S. Miyano,
Tetrahedron Lett., 2005, 46, 121.
31 V. Bhalla, J. N. Babu, M. Kumar, T. Hattori and S. Miyano,
Tetrahedron Lett., 2007, 48, 1581.
32 J. N. Babu, V. Bhalla, M. Kumar and H. Singh, Lett. Org. Chem.,
2006, 3, 787.
33 J. N. Babu, V. Bhalla, M. Kumar, R. K. Mahajan and R. K. Puri,
Tetrahedron Lett., 2008, 49, 2772.
34 M. Kumar, A. Dhir and V. Bhalla, Org. Lett., 2009, 11, 2567.
35 M. Kumar, A. Dhir and V. Bhalla, Tetrahedron, 2009, 65, 7510.
36 A. Dhir, V. Bhalla and M. Kumar, Org. Lett., 2008, 10(21), 4891.
37 A. Dhir, V. Bhalla and M. Kumar, Tetrahedron Lett., 2008, 49, 4227.
38 M. Kumar, A. Dhir and V. Bhalla, Eur. J. Org. Chem., 2009, 4534.
39 J. B. Birks, Photophysics of Aromatic molecules; Wiley Inter-Science;
London, 1970.
40 F. M. Winnik, Chem. Rev., 1993, 93, 587.
41 S. K. Kim, S. H. Lee, J. Y. Lee, J. Y. Lee, R. A. Bartsch and J. S. Kim,
J. Am. Chem. Soc., 2004, 126, 16499.
UV-Vis titrations
UV-Vis titrations were performed on 1 105 M solution of
ligand 3 in THF. Typical aliquots of freshly prepared metal
perchlorates (Hg2+,Cu2+, Pb2+, Zn2+, Ni+, Cd2+, Ag+, Li+, Na+,
K+) standard solutions (1 101 M to 1 103 M solutions in
THF) were added and the UV-Vis spectra of samples were
recorded.
Fluorescence titrations
Fluorescence titrations were performed on 5 106 M solution
of ligand 3 in THF. Typical aliquots of freshly prepared metal
perchlorates (Hg2+,Cu2+, Pb2+, Zn2+, Ni+, Cd2+, Ag+, Li+, Na+,
K+) standard solutions (1 101 M to 1 104 M solutions in
THF) were added and the fluorescence spectra of samples were
recorded.
Preparation of PVC membrane based potentiometric sensors
The membrane was prepared by dissolving PVC, plasticizer,
additive and ionophore in about 5.0 mL of tetrahydrofuran
(THF). The mixture was shaken vigorously and the clear solution
was poured in petridish (50 mm in diameter). The solvent was
allowed to evaporate at room temperature. The resulting
membrane of 0.4 mm thickness was cut to the size, attached to
the PVC tube with the help of PVC glue and conditioned with
metal ion solution for 2–3 days till it gave reproducible and stable
potential. All the measurements of the electrode potentials were
made with an EQUIPTRONICS model EQ-602 potentiometer.
The pH measurements were made using an Elico LI-MODEL120 pH meter. Silver/silver chloride electrodes with 3.0 M KCl as
salt bridge were used as internal and external reference electrode.
Acknowledgements
We are thankful to CSIR (New Delhi) for financial support
[project no. 01(1934)/04/EMR-II]. VB is thankful to DST (New
Delhi) for financial support (Ref. No. SR/FT/CS/10-2006). AD is
thankful to CSIR (New Delhi) for Senior research fellowship.
We are also thankful to the Central Drug Research Institute
(CDRI), Lucknow, for FAB mass spectra, DST (New Delhi) for
1604 | Analyst, 2010, 135, 1600–1605
This journal is ª The Royal Society of Chemistry 2010
42 H. Gampp, M. Maeder, C. J. Meyer and A. D. Zubberbulher,
Talanta, 1985, 32, 95.
43 P. Job, Ann. Chim, 1928, 9, 1320.
44 G. L. Long and J. D. Winefordner, Anal. Chem., 1983, 55, 712A.
45 L. Kovbasyuk and R. Kramer, Chem. Rev., 2004, 104, 3161.
46 R. K. Mahajan, M. Kumar, V. Bhalla and I. Kaur, Analyst, 2001, 126, 505.
47 R. K. Mahajan, R. K. Puri, A. Marwaha, I. Kaur and M. P. Mahajan,
J. Hazard. Mater., 2009, 167, 237.
This journal is ª The Royal Society of Chemistry 2010
48 A. K. Jain, V. K. Gupta and L. P. Singh, Bull. Electrochem., 1996, 12,
418.
49 W. Szczepaniak and J. Oleksy, Anal. Chim. Acta, 1986, 189, 237.
50 Z. Brzozka and M. Pietraszkiewicz, Electroanalysis, 1991, 3,
855.
51 J. Lu, X. Tong and X. He, J. Electroanal. Chem., 2003, 540, 111.
52 M. Mazloum, M. K. Amini and I. M. Baltork, Sens. Actuators, B,
2000, 63, 80.
Analyst, 2010, 135, 1600–1605 | 1605