Bifunctional Calix[4]arene Sensor for Pb(II) and Cr2O 7 2- Ions

Article abstract of DOI:10.1007/s10895-013-1200-3

A readily available chromionophore 5,11,17,23-tetra-tert-butyl-25,27- bis(hydrazidecarbonylmethoxy)-26,28-dihydroxycalix[4]arene (HCC4) was employed as a chromogenic sensing probe selective for Pb(II) and Cr₂O ₇ ^2- ions among a series of various ions such as Li(I), Na(I), K(I), Rb(I), Ba(II), Sr(II), Al(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and Zn(II) as well as Cr₂O₇ ^2-, CH₃CO₂ ^-, Br^-, Cl^-, F^-, I^-, ClO₄ ^- and NO₃ ^- that have been examined by UV-visible and fluorescence spectroscopic techniques. The HCC4 in DCM-MeCN system forms 2:1 (ligand-metal) complex with Pb(II). It also shows 2:1 stoichiometry with Cr₂O ₇ ^2-. The complexation phenomenon has been confirmed by FTIR spectroscopy that favors the selective nature of HCC4 with Pb(II) and Cr₂O₇ ^2-. Thermal gravimetric analysis (TGA) also supports its utility in drastic conditions.

Full text of DOI:10.1007/s10895-013-1200-3

J Fluoresc (2013) 23:575–590
DOI 10.1007/s10895-013-1200-3
ORIGINAL PAPER
Bifunctional Calix[4]arene Sensor for Pb(II)
2−
and Cr2O7 Ions
Mansoor Ahmed Qazi & Ümmühan Ocak & Miraç Ocak &
Shahabuddin Memon & Imam Bakhsh Solangi
Received: 14 November 2012 /Accepted: 24 February 2013 /Published online: 6 March 2013
#
Springer Science+Business Media New York 2013
Abstract A readily available chromionophore 5,11,17,23-
tetra-tert-butyl-25,27-bis(hydrazidecarbonylmethoxy)-
26,28-dihydroxycalix[4]arene (HCC4) was employed as a
comprehensively in recent years and as such there is now a
superfluous of literature regarding the design, synthesis and
study of chromoionophores for metal ion binding [1]. Al-
though the beginnings of anion recognition can be traced to
the same period as that of their cation counterparts, the last
20 years have seen remarkable advances in the construction of
supramolecular hosts for such guests [2–4].
Toxic heavy metals like Cd(II), Hg(II) and Pb(II) etc. in
high concentration can have a severe impact on the aqueous
environment, animals, and humans. Among them, detection
and sensation of Pb(II) ion from environmental or biomed-
ical applications has gain intense attraction because this
lethal metal is widely dispersed in the environment, and on
exposure, it can lead to a number of adverse health effects
like anemia, kidney damage, a disorder of the blood, mem-
ory loss, muscle paralysis and mental retardation due to
Pb(II) poisoning [5].
2−
chromogenic sensing probe selective for Pb(II) and Cr2O7
ions among a series of various ions such as Li(I), Na(I), K(I),
Rb(I), Ba(II), Sr(II), Al(III), Cd(II), Co(II), Cu(II), Hg(II),
Ni(II), Pb(II) and Zn(II) as well as Cr2O72−, CH3CO2 , Br−,
−
Cl−, F−, I−, ClO4− and NO3− that have been examined by UV-
visible and fluorescence spectroscopic techniques. The HCC4
in DCM-MeCN system forms 2:1 (ligand-metal) complex
2−
with Pb(II). It also shows 2:1 stoichiometry with Cr2O7
.
The complexation phenomenon has been confirmed by FTIR
spectroscopy that favors the selective nature of HCC4 with
Pb(II) and Cr2O72−. Thermal gravimetric analysis (TGA) also
supports its utility in drastic conditions.
.
.
Keywords Chromoionophore Complexometric titration
.
.
Anions Non-covalent chemistry Fluorescence
On the other hand, a great deal of devotion has recently
been focused on the selective sensing of anions by means of
synthetic receptors due to anionic biological and environ-
mental significance [6]. Cations are usually discriminated
on the basis of charge and size whereas, anions of interest,
for example; oxoanions are often multiatomic structures
with a delocalization of the negative charge over a rather
complex molecular geometry. This complexity and varied
physical properties of anions such as larger size, being
spherical; linear, planar, tetrahedral or octahedral geometry,
they have to be taken into account for the design of molec-
ular systems to selectively recognize an anion via the intro-
duction of specific binding sites [7].
Introduction
Design and development of macromolecular hosts for cation
and anion guests is the exciting topic of coordination chemis-
try because of their extreme importance in biological process-
es involving molecular recognition of cationic and anionic
species. The field of supramolecular chemistry has advanced
:
:
M. A. Qazi S. Memon (*) I. B. Solangi
National Center of Excellence in Analytical Chemistry,
University of Sindh, 76080 Jamshoro, Pakistan
e-mail: shahabuddinmemon@yahoo.com
Oxoanions like dichromate are considered to be very
noxious, carcinogenic to human beings [8–11]. Wastewater
generated by industries contains chromium and its deriva-
tives either in hexavalent Cr(VI) or trivalent Cr(III) form
and it is a renowned fact that the hexavalent form of
:
Ü. Ocak M. Ocak
Department of Chemistry, Faculty of Arts and Sciences,
Karadeniz Technical University, 61080 Trabzon, Turkey

576
J Fluoresc (2013) 23:575–590
chromium is very dangerous for human health [12].
measurement was carried out through Thermo Nicollet AVA-
TAR 5700 using KBr pellets in a wide spectral range, i.e.
4,000–400 cm−1. Whereas CHNS instrument model Flash EA
1112 elemental analyzer was used for elemental analyses.
UV-visible spectral studies of chromoionophore HCC4
(Scheme 1) as well as its complexation investigations with
metals and anions were carried on a Perkin Elmer Lambda-
35, double beam spectrophotometer using standard 1.00 cm
quartz cells. Fluorescence spectral studies were performed
with a Photon Technologies International Quanta Master
Spectrofluorimeter (model QM-4/2006). All the Reagents
and solvents purchased from Merck, Aldrich and Fluka were
of analytical grade and used without further purification.
Analytical TLC was performed on pre-coated silica gel
plates (SiO2, Merck PF254).
2−
2−
Hexavalent chromium compounds CrO4 or Cr2O7 are
known as human carcinogens, being both mutagenic and
genotoxic [13, 14] In general, anion binding by neutral
receptors is achieved by usage of hydrogen bond formed
by amide [15, 16], urea [17–19], thiourea [20, 21] and
hydroxyl groups [22, 23] or amino moiety [24, 25].
Calixarenes, cyclic oligomers of phenolic units linked
by methylene bridges through the ortho positions are a
fascinating class of macrocycles. Chemical modification of
the upper or lower rim has made this class of synthetic
ionophores effective complexing and sensing agents for
the detection of anionic and cationic guest molecules [26,
27]. The importance of favorable amine, amide, or imide
hydrogen bonding interactions for anion binding has re-
cently been exploited in the design of calix[4]arene anion
receptors, because of their stable aromatic core structure
against oxidation and suitability for extraction due to
exclusive characteristics of hydrogen bonding, π–π inter-
actions, electrostatic interactions, and dipole-dipole mo-
ments [28, 29]. Although such host molecules are still
relatively rare. In recent years, some calix[4]arene-based
receptors have been reported possessing effective anion
binding ability. This feature can be useful for multiple
applications such as laboratory, clinical, environmental
and industrial process analyses [30, 31]. Although several
works regarding the synthesis and complexation of metal
cations and toxic anions with calix[4]arene derivatives
have been reported [32–34]. However, according to the
best of our knowledge there is no other published study
on chromogenic/fluorescent sensing of Cr2O72−. Therefore,
this work aims to expand the study and provide a new
path way for the design and development of bifunctional
ligand that could bind both metal and dichromate anions,
which can be detected by means of UV-visible and fluo-
rescent methods. Thus, in connection with our efforts for
the development of different sensing derivatives [35–39],
herein we report the binding and sensing behavior of a
calix[4]arene derivative, i.e. HCC4 toward a series of
selected alkali, alkaline earth and transition metal ions
such as Li(I), Na(I), K(I), Rb(I), Ba(II), Sr(II), Al(III),
Fe(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and
Synthesis
Synthesis of HCC4
The required starting material p-tert-butylcalix[4]arene (2),
Diester derivative of calix[4]arene (3) and HCC4 (4) were
prepared by earlier published procedures [40, 41].
Synthesis of Metal Complexes with HCC4
For TGA and FT-IR experiments, saturated DCM solution
of receptor HCC4 was prepared in round bottomed flask, an
2−
stoichiometric amount of Pb(II) or Cr2O7 salts was
dissolved in MeCN separately. Mixed up both the contents
and stirred at room temperature for 24 h. Filtered the satu-
rated solution and residue was washed with DCM. Finally,
poured the combined filtrate and washing on a Petri dish,
evaporated the entire solvent and vacuum dried the resultant
crystals.
Analytical Procedure
Solvent Extraction
Pedersen’s procedure was applied for liquid–liquid extraction
experiments [42]. 10 ml mixture of an aqueous metal picrate
solution (2.5×10−5M) and HCC4 in DCM (1×10−3M) in 1:1
ratio were vigorously agitated in a Stoppard glass tube with a
mechanical shaker for 2 min then magnetically stirred in a
shaker at 25 °C for 1 h, and finally left standing for an
additional 30 min. The picrate ion concentration before and
after extraction in the aqueous phase was spectrophotometri-
cally determined as previously published procedure [43].
Alkali metal picrates were prepared as described elsewhere
[44] by gradual addition of a 2.5×10−5M aqueous picric acid
solution to a 0.14 M aqueous solution of metal hydroxide,
until neutralization which was checked by pH control with a
−
−
Zn(II) as well as anions like Cr2O72−, CH3CO2 , ClO4 ,
NO3 , Br−, Cl−, F−, I− using UV-visible, fluorescence and
−
FT-IR spectroscopic techniques.
Experimental Section
General Experimental Information
Melting points were determined on a Gallenkamp (UK) appa-
ratus in a sealed capillary tube. FT-IR spectroscopic

J Fluoresc (2013) 23:575–590
577
(b)
(a)
(c)
Scheme 1 Synthetic methodology for synthesis of hydrazide calix[4]arene derivative. Reagents and conditions. (a) HCHO/NaOH (b) K2CO3-
BrCH2CO2Me/Acetone (dry) (c) N2H4.H2O/CHCl3-MeOH
2−
glass electrode. Finally, they were rapidly washed with etha-
nol and ether before being dried in vacuum for 24 h. Transition
metal picrates were prepared by stepwise addition of a 1×10−2
M of metal nitrate solution to a 2.5×10−5M aqueous picric
acid solution and shaken at 25 °C for 1 h.
was applied for HCC4-Cr2O7 stoichiometry, however;
absorbance was measured at 272 nm.
Fluorescence Emission Measurement of HCC4
and Its Complexes
Stoichiometric Determination of Complexes
Emission intensities of HCC4 (1.25×10−5M) excited at
300 nm were measured in DCM-MeCN at room tempera-
ture. Titration experiment was performed by placing 50 μl
of HCC4 into a cuvette, adding appropriate aliquot (2
equvi.) of each metal and anion stock, followed by dilution
with DCM-MeCN up to 4 ml. Same equivalents (2 equvi.)
were taken for the interference study of foreign ions into the
solution of HCC4 with metal and anion complexes. For all
measurements, excitation was 300 nm; excitation and emis-
sion slits widths were both 5 nm each.
Method of continuous variation, i.e. Job’s method [45] was
applied for the determination of stoichiometry of HCC4
with cations and anions for their complexation in DCM-
MeCN as binary solutions. For Pb(II), the equimolar solu-
tions (1.25×10−5M) of both components, i.e. ligand and
metal were mixed under the condition that sum of the
ligand-metal concentration remains constant. The absor-
bance was measured at 230 nm. Moreover, same procedure

578
J Fluoresc (2013) 23:575–590
Result and Discussion
230 nm and possess only weak shoulder at 280 nm.
Hypsochromic shifting with well-defined bands of HCC4
in less polar solvents like 1,4-dioxane, DCM, CF may be
ascribed to the presence of four intermediate nature bearing
nitrogen atoms. That’s why it gives blue shifting (i.e.
negative solvatochromism) in less polar solvents. How-
ever, in DMF and DMSO, presence of a distinctive tran-
sition in these solvents series may be justified only by the
overlapping of π→π* and n→π* bands which are very
close in energy.
The p-tert-butylcalix[4]arene (2), Diester derivative of ca-
lix[4]arene (3) and HCC4 (4) were prepared by previously
published procedures [40, 41]. The synthetic pathway is illus-
trated in Scheme 1. The characterization of the compounds for
the confirmation of their structure and purity was made by
various techniques such as, melting point, TLC, IR, and
elemental analysis.
Attempts have been made to observe the solvatochromic
behavior of HCC4 in MEOH, ACO and MeCN even at low
concentration; but due to partial solubility, aggregation and
too much noise in the spectra, all of them have been discarded.
Solvatochromic Effect
Solvatochromic properties of a compound in various solvent
systems are generally as a result of differential solvation in
ground/first excited state of molecule. Thus, with increasing
solvents polarities, better stabilization by the solvation of
the molecule in the first excited state compare to the ground
state will lead to positive solvatochromism (red shift) and
vice versa is true for negative solvatochromism.
Analytical Perspectives of HCC4 as Chromogenic Sensor
By keeping view of our previous investigations [35–39], Hy-
drazine derived calix[4]arene amide derivative have been cho-
sen for synthesis and complexation study. Presence of amide
functionality provides selectivity to this bi-functional receptor
for simultaneous detection of cations as well as anions. Thus,
with ease of two step synthetic route, possessing soft nature
(borderline) of nitrogen donor atom along with macrocyclic
effect, all these features makes these derivatives might be a
promising candidate for stronger complex formation and se-
lective sensing with soft/borderline amino/thiophilic metal cat-
ions such as Cu(II), Hg(II) and Pb(II) etc. we have carried out
various titration experiments go investigate the selective com-
plexation affinity with cations and anions and therefore several
analytical parameter have been examined in this regard. Cat-
ionic and anionic properties of HCC4 were investigated and
confirmed by UV-visible, fluorescence, TGA, FT-IR
spectroscopies.
In pursuit of all these factor, HCC4 was dissolved in
various solvent like acetone (ACO), chloroform (CF), 1,4-
dioxane, dichloromethane (DCM), dimethylformamide
(DMF) and dimethylsulfoxide (DMSO) with optimized
fixed concentration of 1.25×10−5M. UV-visible spectral
data of compound HCC4 in different solvents are shown
in Fig. 1a and b. After comprehensive analysis of a number
of annotations, we can precise the following main remarks:
for each solvent used, In case of DCM and CF the absorp-
tion spectra of receptor HCC4 obtained is characterized by
the presence two absorption bands, with λmax at 230–240
and 282 nm respectively. The effect of solvents polarity on
the absorption spectrum was revealed by a blue shift for the
first band (230 nm) for 1, 4-dioxane, DCM, CF is more
remarkable as compare to DMF and DMSO. These results
indicate that the spectrum of HCC4 in these media is
characterized by two electronic transitions, of π→π* and
n→π* transitions arising from solvent polarity. DMF and
DMSO shows devoidness of previously mentioned band at
With careful analysis of solvatochromic spectral features
of HCC4 as mentioned above, DCM-MeCN was selected as
binary solvent system for complexation studies on the basis
of solubility of metal perchlorate and tetrabutylammonium
2.5
(a)
(b)
0.2
DCM
DMSO
2
1,4-dioxane
0.15
0.1
0.05
0
DMF
1.5
1
CF
DCM-MeCN
MeCN-H2O
0.5
0
200
230
260
290
320
350
260
280
300
320
340
Wavelength (nm)
Wavelength (nm)
Fig. 1 Absorption spectral behavior of HCC4 in different solvents (1.25×10−5M)

J Fluoresc (2013) 23:575–590
579
salts, less toxicity effects, no aggregation, maximum num-
ber of bands with in standard absorption limits and well-
defined spectral properties in aforementioned binary sol-
vents. However, we also investigate the complexation prop-
erties of HCC4 in other binary solvents such as methanol,
THF, 1,4-dioxane, isopropanol alone or with DCM at dif-
ferent concentrations but significant complexation proper-
ties was observed with DCM-MeCN.
HCC4 (Fig. 2a, b), only pronounced response has been
found for Pb(II). The band intensity at 230 nm was surpris-
ingly increased from 1.0 to 1.6 followed by disappearance
of shoulder at 382 nm in case of Pb(II) ions (Fig. 2c).
The electronic spectra of these complexes observed at
230 and 282 nm could be assigned to π-electrons of car-
bonyl group and nitrogen/oxygen-metal charge transfer ab-
sorption upon complexation with metal [46]. However,
similar titration experiment carried out for other metal ions
even border line metal ions such as Cu(II), Ni(II), Co(II),
Hg(II) and Zn(II), causes only a minimal enhancement in
the absorption intensities which implies the selective re-
sponse of HCC4 towards Pb(II). This remarkable complex-
ation affinity towards Pb(II) ion proved that besides the soft
nature of ligand or metal ion, thermodynamic stability, ionic
radii, cavity size as well as geometry of ligand and metal ion
are also important aspects for specificity which confers the
affinity of ligand toward a metal ion.
Complexation Affinity of HCC4
UV-Visible Study
For complexation study, all of the titration experiments were
performed in DCM-MeCN by adding aliquots (2 eq) of
different guests (cation and anion). The UV-visible absorp-
tion spectrum of the HCC4 exhibits strong absorption band
at 230 nm and comparatively weak absorption at 282 nm.
These two absorption may be assigned to π→π* and n→π*
transitions respectively (Fig. 2). On addition of tested metal
ions representative of Li(I), Na(I), K(I), Rb(I), Ba(II), Sr(II),
Al(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II), Zn(II)
ions were added (2equiv.) to the solution (1.25×10−5M) of
Furthermore, we have also examined the anion binding
studies of HCC4 with different anions like of F−, Cl−, Br−,
I−, CH3CO2−, NO3−, ClO4 and Cr2O7
as their
−
2−
tetrabutylammonium salt under same conditions (Fig. 3).
The characteristic UV-visible absorption changes have been
1.2
1.2
(b)
1
(a)
1
HCC4, Li(I), Na(I),K (I), Rb(I), Ba(II),
0.8
0.6
0.4
0.2
0
Sr(II), Al(III),
0.8
HCC4, Cd(II), Co(II), Cu(II),
Hg(II), Ni(II), Zn(II)
0.6
0.4
0.2
0
215
235
255
275
295
315
215
235
255
275
295
315
Wavelength (nm)
Wavelength (nm)
0.1
0.08
0.06
0.04
0.02
0
1.6
(c)
HCC4
Pb(II)
HCC4
Pb(II)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
260
270
280
290
300
310
Wavelength (nm)
215
235
255
275
295
315
Wavelength (nm)
Fig. 2 Absorption spectra of HCC4 (1.25×10−5M) and its complexes with various (a) Alkali and alkaline earth metal ions (2equvi.) (b) Transition
metal ions (2equvi.) (c) With Pb(II)ion

580
J Fluoresc (2013) 23:575–590
1.25
The absorption change (A0-A) and ratiometric behavior
(A/A0) of 4 in the presence of guest ion (cation or anion)
also supports the pronounced Pb(II) and Cr2O72− selectivity
of HCC4. From the bargraph representative of absorption
change (A0-A), Only Pb(II) and Cr2O72− shows remarkable
changes from HCC4 among rest of ions (Fig. 4a–d).
Pb(II) quantitative binding characteristics of HCC4
was determined by gradual increment of these metal ion
concentrations into the solution of HCC4. Investigation
of UV-visible spectral variation shows linear relationship
between absorption intensity to Pb(II) ion concentration
(Fig. 5a).
By plotting the changes in HCC4 in the absorbance
intensity at 230 nm as a function of Pb(II) concentrations,
Hoerl curve was obtained as shown in inset of Fig. 5a. From
the inset, the inflection point was determined as 2.0 for
([Pb(II)]/[HCC4]) which explores 1:2 (ligand: metal) stoi-
chiometry of complex.
1
0.75
0.5
-
HCC4, CH3COO-, ClO4 ,
Br-, Cl-, I-, F-
2-
HCC4+Cr2O7
0.25
0
220
250
280
310
340
370
400
430
Wavelength (nm)
Fig. 3 Absorption spectra of HCC4 (1.25×10−5M) and its complexes
with different anions (2equvi.)
recorded upon the addition of tetrabutylammonium salts to a
solution of HCC4 (1.25×10−5M). Among the anions tested,
HCC4 selectively bind Cr2O72− anion. The absorption spec-
2−
trum shows that upon addition of Cr2O7 ion, not only
Association constant for Pb(II) was also calculated from
Benesi-Hildebrand equations for UV-visible spectroscopic
titration [47, 48].
strong absorption in the region 250–300 nm takes place
but also a formation of new band in the visible region at
380–430 nm is the informative sign of complex formation.
HCC4-Cr2O72− selective complexation can be explained by
the hydrogen bonded interaction between Cr2O7 and hy-
drazide protons (–NH) of HCC4.
For 1:2 (host: guest) stoichiometry:
ꢀ
ꢁꢀ
ꢁ
2 þ 1
2−
A0
"
1
0
¼
A ꢀ A0
"0 ꢀ "
KB½Guestꢁ
(a)
(b)
0.1
0
(b)
1.6
1.4
1.2
1
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
0.8
0.6
0.4
0.2
0
Metal ions
Metal ions
(c)
(d)
1.4
1.2
1
0.05
-0.05
-0.15
-0.25
-0.35
-0.45
0.8
0.6
0.4
0.2
0
Anions
Anions
Fig. 4 UV-visible ratiometric behavior (A/A0) and absorption change (A0-A) of HCC4 (L) with various ions (a,b) cations (c,d) anions

J Fluoresc (2013) 23:575–590
581
2.5
2
4
3.5
3
(a)
(b)
y = 5E-07x + 0.257
2
1.5
1
R² = 0.99
1.5
1
0.5
0
2.5
2
0
2
4
6
8
10
12
1.5
1
[Pb(II)]
0.5
0
0.5
0
220
240
260
280
300
0
2000000 4000000 6000000 8000000
1/[Pb(II)]
Wavelength (nm)
Fig. 5 (a) Influence of the addition of increasing amounts (0.2→10 eq.) of Pb(II) on the absorption spectra of HCC4 (1.25×10−5M) in DCM-
MeCN (b) A graph of A0/A-A0 versus 1/[Pb(II)] for the determination of association constant
2−
Where A0 and A represents the absorbance of HCC4
measured before and after the addition of cations, respective-
ly; ε0 and ε are the corresponding molar extinction coeffi-
cients of HCC4 in the absence and presence of the cations,
respectively. [Guest] is the concentration of the titrants and
KB represents the association constant of host-guest
complexation.
Same spectral behavior was obtained for Cr2O7 ions as
absorption profile of absorbance intensity versus Cr2O72− ion
concentration shows linearity (Fig. 6a). The log K value was
found to 6.27 (R2=0.99) for HCC4-Cr2O72− (Fig. 6b) with the
inflection point 2.0 ([Cr2O72−]/[HCC4]) which reveals the 1:2
2−
(ligand:anion) stoichiometry of HCC4-Cr2O7 complex
(Table 1).
By plotting the ratio of A0/(A-A0) plotted versus 1/[Pb(II)]
as in Fig. 5(b), the value of log K was 5.71 (R2=0.99) for
HCC4-Pb(II) complex.
The stoichiometry of these complexes was evaluated by the
method of continuous variation (Job’s plot). Figure 7a repre-
sents the typical Job’s plots of HCC4-Pb(II) complexation at
Fig. 6 (a) Influence of the
(a)
addition of increasing amounts
12
(0.2→10 eq.) of Cr2O72− on the
1.2
10
1O eq
absorption spectra of HCC4
8
6
4
2
(1.25×10−5M) in DCM-MeCN
1
(b) A graph of A0/A-A0 versus
1/[Cr2O72−] for the
0.8
determination of association
constant
0
0.6
0.4
0.2
0
0.2 eq
0
5
10
15
2-
[Cr2O7
]
220
260
300
340
380
420
460
500
Wavelength (nm)
(b)
3
2.5
2
y = 3E-07x - 0.5587
R² = 0.99
1.5
1
0.5
0
1000000
3000000
5000000
7000000
2-
9000000
11000000
I/[Cr2O7
]

582
J Fluoresc (2013) 23:575–590
Table 1 Association constants
of different ions
Stability constants
Cations
Li(I)
Na(I)
n/a
K(I)
n/a
Rb(I)
n/a
Ba(II)
n/a
Sr(II)
n/a
Al(III)
n/a
Cd(II)
n/a
n/a
Co(II)
n/a
Cu(II)
n/a
Hg(II)
n/a
Ni(II)
n/a
Pb(II)
5.71
Zn(II)
n/a
Anions
Br−
n/a
Cl−
n/a
F−
I−
ClO4
Cr2O7
6.27
NO3
−
−
2−
−
CH3CO2
n/aNot available because
of minor spectral changes
n/a
n/a
n/a
n/a
n/a
230 nm, a plot of absorbance versus mole fraction shows that
the value goes through a maximum at a molar fraction of 0.67
indicating a 1:2 stoichiometry in the complex which indicated
that two Pb(II) ions were interacting with receptor HCC4.
Job’s plot experiment regarding stoichiometric determi-
causes appearance of new band in the visible region. This
anion complex also found to be stable even after 3 days
(Fig. 8c).
Foreign ion Effect
2−
nation between HCC4 and Cr2O7 at 272 nm shows 1:2
ratio, i.e. two dichromate ions coordinate (Cr2O72−) with
HCC4 (Fig. 7b).
The effect of foreign ion is an important parameter in com-
plexation study since its tell us about strong or weaker com-
plexation nature of ligand towards particular ions. The
interference effect of some alkali (Li (I), Na(I), K(I)), Rb(I))
alkaline-earth (Ba(II), Sr(II)) and transiton metal ions as well
Stability determination of chromogenic sensor as well as
its complexes with respect to time is the zealous area of
study; since it provide important information that our com-
pound which is selective to particular ion make stable com-
plex with the passage of time in a specific solvent.
In order to examine the stability of chromogenic sensor
−
−
as anions CH3CO2 , F−, Cl−, Br−, I−, ClO4 , and NO3− during
sensing of Pb(II) and Cr2O72− respectively, was investigated.
The competitive experiments were carried out at fixed con-
centration of these ions at 1.25×10−5molL−1 and then record-
ing the change of the absorption intensity before and after
adding the interferent (2 equiv. each) into the Pb(II) and
2−
as well its complexes with Pb(II) and Cr2O7 the absorp-
tion spectra of HCC4 as well as its complexes in DCM-
MeCN were instantly acquired (Fig. 8a–c) after continuous
UV irradiation with the passage of 0, 50, 100, 150, 200, 250,
300, 350, 400 and 450 min [49].
On addition of Pb(ClO4)2 3H2O, HCC4 responds very
fastly with significant enhancement in absorption intensity
of a band at 230 nm followed by disappearance of another
band 280 nm occurs very fast within 1 min: which remains
constant for more than a week (Fig. 8b).
2−
Cr2O7 solutions. The UV-visible spectra show that no any
other ions except Hg(II) caused significant variation in the
absorption spectra of HCC4-Pb(II) complex (Fig. 9a). These
results reveal that HCC4 showed high affinity towards Pb(II).
Moreover, the results obtained from the study regarding
interfering effect of afformentioned anions also confirms the
2−
Cr2O7 selective nature of HCC4 sensor as except slight
inference from I−, no other ion causes signifcant variations
However, treatment with tetrabutylammoniumdichromate
[{(CH3CH2CH2CH2)4N}2 Cr2O7] shows distinctive behavior
2−
in the UV-visible spectra of HCC4-Cr2O7 (Fig. 9b).
1.5
(a)
(b)
0.3
1.2
0.9
0.6
0.3
0
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
2-
[HCC4]/[HCC4]+[Cr2O7
]
[HCC4]/[HCC4]+[Pb(II)]
Fig. 7 Job’s plot determination of complexes of HCC4 (1.25×10−5M) (a) Pb(II) (b) Cr2O7
2−

J Fluoresc (2013) 23:575–590
583
1.8
1.5
1.2
0.9
0.6
0.3
0
(a)
(b)
1
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
HCC4
0.8
HCC4 -Pb(II) complex
(0-450 min)
(0-450 min)
0.6
0.4
0.2
0
0
100 200 300 400 500
Time (min)
0
100 200 300 400 500
Time (min)
215
235
255
275
295
315
335
215
235
255
275
295
315
335
Wavelength (nm)
Wavelength (nm)
0.6
(c)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
HCC4-Cr2O72-complex
(0-450 min)
0.4
0.2
0
100 200 300 400 500
Time (min)
0
250
300
350
400
450
Wavelength(nm)
Fig. 8 Time-dependent absorption spectra of (a) HCC4 (b) HCC4-Pb(II) complex (c) HCC4-Cr2O7 at 1.25×10−5M in DCM-MeCN upon
2−
irradiation of UV light; (inset) graphs showed stability of HCC4 and its complexes with respect to time
Same trend can been seen from absorption change (A0-A)
and ratiometric behaviors (A/A0) of metal and anion com-
plexes of HCC4 (Fig. 10 a–d).
aqueous to organic medium (Fig. 11a), i.e. DCM. The
extraction efficiency (%E) of HCC4 toward all aforemen-
tioned metal picrates is given in Fig. 12a and Table 2. As
seen from Table 2, extraction ranges of HCC4 towards all
the metal cations between 10 % and 96.4 % using DCM as
organic solvent. Among the metal cations, it has been ob-
served that HCC4 shows greater extraction ability toward
Pb(II) as compared to parent compound 1, i.e. 94 %. How-
ever, the %E value for Hg(II) ion was found to be 47 %
which may be ascribed to the borderline nature of Hg(II) as
well as HCC4 which possess borderline nitrogen donor
atom binding functionality therefore, it may coordinate with
Liquid–Liquid Extraction Study
In order to further verify the Pb(II) selective complexation
of HCC4, liquid–liquid extraction procedure was applied to
evaluate the cation binding affinity of HCC4 in transferring
different metals, such as, alkali (Li(I), Na(I), K(I)), Rb(I)),
alkaline earth (Ba(II), Sr(II)) and transition metals (Al(III),
Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and Zn(II)) from
1.2
2
(a)
(b)
-
I interference
1
0.8
0.6
0.4
0.2
0
1.5
Hg (II) interference
1
0.5
0
215 230 245 260 275 290 305 320 335 350
220
260
300
340
380
420
Wavelength (nm)
Wavelength (nm)
Fig. 9 Absorption response of HCC4 (1.25×10−5M) in DCM-MeCN upon addition of various metal ions into the solution of (a) HCC4-Pb(II)
2−
complex (b) HCC4-Cr2O7 complex

584
J Fluoresc (2013) 23:575–590
(a)
(b)
0.6
0.4
0.2
0
1.8
1.6
1.4
1.2
1
-0.2
-0.4
-0.6
-0.8
0.8
0.6
0.4
0.2
0
Interferring ions
Interferring ions
(c)
(d)
8
7
6
5
4
3
2
1
0
0
-0.1
-0.2
-0.3
-0.4
-0.5
Interfering Ions
Interfering Ions
Fig. 10 Ratiometric and absorption response of HCC4 towards interfering ions in the presence of (a,b) Pb(II) (c,d) Cr2O7
2−
borderline cations, Fe(II), Co(II), Ni(II). The trend of ex-
traction ability of HCC4 toward the metal ions was found in
the order: Pb(II)>Hg(II)>K(I)>Cu(II)>Ni(II)>Zn(II)>
Cd(II)>Co(II)>Na(I)>Al(III)>Ba(II)>Rb(I)>Sr(II)>Li(I).
These enhanced extraction ability of HCC4 for Pb(II) may
be due to the arrangement of its amide binding functional-
ities according to the geometries of these metal ions, as well
as the compatibility between the ionic radii and cavity size
of HCC4. These features enhance the utility of HCC4 in
various fields such as environmental chemistry, membrane
technology, and ion selective electrodes technology and
phase-transfer reactions.
All these above mentioned discussion discloses that ap-
propriate cationic size, presence of donor nitrogen atoms in
the binding sites of HCC4 in a periphery, their effectiveness
and aggregation, and their collective/cooperative behavior
100
(a)
90
0.1
80
70
60
50
40
30
20
10
0
(b)
-0.1
y = 0.1477x
-0.3
-0.5
-0.7
-0.9
-6
-5
-4
-3
-2
-1
Log[L]
Metal Ions
Fig. 11 (a) % Extraction efficiency of HCC4 towards various metal
picrates. Aqueous phase, [metal picrate]=2.5×10−5M; organic phase,
DCM, [HCC4]=1×10−3M at 25 °C for 1 h. (b) Log D versus log [L]
for the extraction of Pb(II) picrate by HCC4 from an aqueous phase to
organic phase, i.e. DCM at 25 °C

J Fluoresc (2013) 23:575–590
585
Fig. 12 Emission spectra of
HCC4 (1.25×10−5M) upon
addition of various (a) metal
ions (b) anions (2equiv.) in
DCM-MeCN; (Inset.) spectra
with selected wavelength
showed major changes in the
fluorescent spectra HCC4
towards various ions
(a)
3600000
2700000
1800000
900000
0
300000
200000
100000
0
HCC4 + Pb(II)
HCC4+Pb(II)
HCC4
HCC4
HCC4+other metal ions
590
610
630
650
670
Wavelength(nm)
250
400
550
700
Wavelength (nm)
4000000
3500000
3000000
2500000
2000000
1500000
1000000
500000
0
(b)
5.00E+05
4.00E+05
3.00E+05
2--
HCC4+Cr2O7
-
-
HCC4, CH3CO2 , ClO4 ,
2.00E+05
1.00E+05
0.00E+00
-
-
- - -
NO3 , Br ,Cl ,F , I
297
317
337
357
377
397
2-
HCC4+ Cr2O7
Wavelength (nm)
250
300
350
400
450
500
550
600
650
700
Wavelength (nm)
along with the size of aromatic ring play an important role in
complexation phenomenon.
D, as given in Eq. 3, and taking log of both sides, we
obtain Eq. 4.
nþ
Â
Ã
n
Maq þ Picꢀaq þ x½LꢁðorgÞ Ð MðpicÞnðLÞx
ð1Þ
Log-log Plot Analysis
org
Extraction equilibrium constant is expressed as Eq. (2)
For the characterization extraction ability, the dependence
of the distribution coefficient D of the selective metal ion
between the two phases upon the calixarene concentration
was examined [51]. If the general extraction equilibrium is
assumed to be Eq. 1 with Mn+ metal ion, ‘L’ neutral ligand
and the over lined species referring to species in the or-
ganic phase, the overall extraction equilibrium constant is
given by Eq. 2. When introduce the distribution coefficient
Â
Ã
MðpicÞnðLÞx
Kex
¼
ð2Þ
n
x
½Mnþꢁ½Picꢀꢁ ½Lꢁ
and the distribution ratio D would be defined by the Eq. (3).
Â
Ã
MðpicꢀÞnðLÞx
½ðMnþÞꢁ
D ¼
ð3Þ
Table 2 Comparative (%) Ex-
traction results of metal ions by
Extracted metal picrates (%)
compound 2 and HCC4
Ligand
2a
Li(I)
18.9
Na(I)
8.5
K(I)
3.3
Rb(I)
–
Ba(II)
–
Sr(II)
–
Al(III)
Cd(II)
9.4
34
–
HCC4
12
31
43
16
19
14.8
Zn(II)
–
20
Co(II)
Cu(II)
Hg(II)
Ni(II)
Pb(II)
<1
2a
7.9
32
9.9
40
15.5
47
6.3
38
HCC4
94
36
aRef. [50]

586
J Fluoresc (2013) 23:575–590
One obtains Eq. (IV), by introducing it into equation (II)
and taking log of both sides
(2 eq) of Pb(II) ion into the solution of HCC4 (1.25×10−5
M), the emission intensity at band 306 nm was remarkably
increased up to 6 fold along with formation of new band at
609 nm (inset Fig. 12a), However, rest of metal ions such as
Li(I), Na(I), K(I), Rb(I), Ba (II), Sr(II) Al(III), Cd(II), Co(II),
Cu(II), Hg(II), Ni(II), and Zn(II) under same aforemen-
tioned condition did not cause significant influence on the
emission spectra of HCC4. These pronounced result
obtained after Pb(II) addition among series of various cat-
ions confirms the HCC4 as Pb(II) selective potential probe.
Furthermore, HCC4 as a highly Cr2O72− selective On-Off
fluorescent sensor was confirmed by its fluorescence
quenching nature in band intensity at 306 nm among series
n
Log D ¼ LogðKexðPicꢀꢁ Þ þ ꢂ log½Lꢁ
ð4Þ
With these possibilities, a plot of the log D vs. log [L]
should be linear and its slope should be equal to the number
of ligand molecules per cation in the extraction species [47].
Figure 11b shows a plot of Log D versus Log [L] for the
extraction of Pb(II) by HCC4. A linear relationship between
Log D and -Log [L] with the slope of lines of Pb(II) roughly
equal to 0.147, suggesting that HCC4 forms 2:1(M:L) com-
plex with Pb(II).
−
−
of other tested anions like CH3CO2 , F−, Cl−, Br−, I−, ClO4 ,
−
and NO3 (Fig. 12b). Fluorescence quenching ratio [(I−I0)
Fluorescence Study
/I0×100] and emission changes (I/I0) also reflects the strong
2−
complexation of HCC4 towards Pb(II) and Cr2O7 ions
(Fig. 13a–d).
To investigate the fluorescence behavior of HCC4 towards
Pb(II) and Cr2O72−, titration experiment was performed
under same condition as in UV-visible spectroscopy. In the
fluorescence spectrum (Fig. 12), HCC4 exhibited a typical
strong emission band at 288 nm along with two weak
emissions 306, 580 nm. Upon addition of small amount
The competition experiments were also conducted for
HCC4 to observe the significant changes in the fluorescence
emission of HCC4, with or without addition of Pb(II) and
2−
Cr2O7 ions in the presence of other co-existing ions.
(a)
(b)
600
500
400
300
200
100
0
7
6
5
4
3
2
1
0
-100
Metal Ions
Metal ions
(c)
(d)
80000
30000
1.2
1
-20000
-70000
0.8
0.6
0.4
0.2
0
-120000
-170000
-220000
-270000
-320000
Anions
Anions
Fig. 13 Fluorescence quenching ratio (I−I0)/I0×100 and ratiometric response (I/I0) of HCC4 (L) towards various (a,b) cations (c,d) anions

J Fluoresc (2013) 23:575–590
587
4000000
On the other hand, addition of foreign anions into the
solution of HCC4 in the presence of Cr2O72− ions gave more
or less similar response except I− which causes slight inter-
ference. Relative fluorescence intensity (I/I0) and fluores-
(a)
3500000
3000000
Hg Interference
2500000
2000000
1500000
1000000
500000
0
2−
cence quenching ratio [(I−I0)/I0×100] of Pb(II) and Cr2O7
complexes also shows that except some interference they
were not significantly affected by presence of 2 equiv. of
other ions (Fig. 15a–d).
All the results obtained from UV-visible and fluorescence
study shows that receptor HCC4 possess ideal geometry with
maximum number of both soft/hard binding sites to accommo-
date Pb(II) ion. Moreover, binding possibility at narrow rim of
calix[4]arene can be discarded by the presence of strong intra-
molecular hydrogen bonding between phenolic hydrogens.
For a molecule to be effective as an anion host, it is
necessary that its structural features are compatible with
those of the guest anion. The dichromate (Cr2O72−) ions
are oxo/dianions with oxide functionalities at their periph-
ery; consequently, these functionalities are potential sites for
hydrogen bonding to the Cr2O72−. Therefore, receptor
HCC4 that is fixed in a cone conformation carrying hydra-
zide binding groups at both rims is seems to be ideal in
250
350
450
550
650
750
850
Wavelength (nm)
Fig. 14 Fluorescence response of HCC4 (1.25×10−5M) in DCM-
MeCN upon addition of various metal ions into the solution of (a)
HCC4-Pb(II) complex
When 2 equiv. of interfering ions was added into the solu-
tion of HCC4 in the presence of 2 equiv of Pb(II) ion, except
Hg(II), the fluorescence spectra with other ions displayed a
similar pattern at near 306 and 609 nm as compare to Pb(II)
ion only (Fig. 14). However, addition of Hg(II) causes
breaking of 4-Pb(II) complex and results in restoration of
ligand fluorescence spectral properties.
2−
terms of Cr2O7 binding.
(a)
(b)
10
900
9
8
7
6
5
4
3
2
1
0
800
700
600
500
400
300
200
100
0
Interferring Ions
Interferring Ions
(c)
(d)
1.05
8
7
6
5
4
3
2
1
0
0.9
0.75
0.6
0.45
0.3
0.15
0
Interfering Ions
Interfering Ions
Fig. 15 Fluorescence quenching ratio (I−I0)/I0×100 and relative fluorescence intensity (I/I0) of HCC4 towards interfering ions in the presence of
2−
(a,b) Pb(II) (c,d) Cr2O7

588
J Fluoresc (2013) 23:575–590
Fig. 16 Proposed interactions between receptor HCC4 and metal/anion
Thus, with reference to Jobs’ plot and molar ratio stoi-
chiometric analysis, therefore, the proposed mechanism for
metal–ligand as well as anion–ligand interaction is shown in
Fig. 16.
Thermal behavior
The thermo gravimetric analysis (TGA) provides us an
informative sign for thermal stability, amount confirmation
(a)
(b)
274 0
50.64 uV
C
89 0
97.8%
C
60
50
40
30
20
10
0
110
100
90
233 0
92.2%
C
HCC4
HCC4+Pb(II)
258 0
90.8%
C
HCC4
HCC4+Pb(II)
385 0
69.8%
398 0
67.9%
C
80
364 0
22.25 uV
C
144 0
C
C
70
79.5%
251 0
C
554 0
46.3%
C
60
21.56 uV
50
373 0
47.7%
C
411 0
C
40
45.6%
30
-10
-20
694 0
25.0%
C
20
100 200 300 400 500 600 700 800 900
100 200 300 400 500 600 700 800 900
Temp. (0C)
Temp. (0C)
337 o
25.10 uV
C
(c)
(d)
217 0
27.72 uV
C
351 o
24.52 uV
C
110
100
90
130 0
97.6%
C
475 o
18.07 uV
C
237 0
91.9%
C
30
20
10
HCC4
HCC4 + Cr2O7
130 0
C
162 0
330 0
80.8%
C
2-
C
HCC4
HCC4 + Cr2O7
96 %
95.5%
248 o
C
256 0
C
2-
381 0
70.5%
396 0
68.2%
C
21.51 uV
90.9%
80
321 o
20.70 uV
C
301 o
2054uV
C
C
70
372 0
63.5%
385 0
60.8%
C
0.0
364 o
22.25 uV
C
60
C
565 0
45.8%
C
50
-10
-20
40
563 0
39.2%
C
30
100
200
300
400
500 600
700
800
100
200
300
400
500
600
700
800
900
Temp. (0C)
Temp. (0C)
Fig. 17 The TG/DTA curves of HCC4 and its complexes with (a,b) Pb(II), (c,d) Cr2O72− in N2 atmosphere

J Fluoresc (2013) 23:575–590
589
83
80
70
60
50
40
30
(b)
78
1769
1675
3456
(II)
(l)
(a)
73
68
63
58
1762
1669
3376
1111
629
1365
900
3445
3450
1693
1900
1388
1400
3400
2900
2400
2950
2450
1950
1450
950
450
Wavenumber (cm-ı)
Wavenumber (cm-ı)
Fig. 18 (I) Comparative FT-IR spectral data for [(a) HCC4 and (b) Pb(II) complex] (II) Cr2O72−-complex
and purity of the compounds. Therefore, thermal stability of
the HCC4 as well as and its complexes with Pb(II) and
Cr2O7 were evaluated by thermal analysis (TG//DTA). It
Raman spectroscopic studies on complexation phenomena.
It offers various powerful methods to obtain deeper insight
into the chemical structural changes of macrocycles caused
by complex formation. The potential applicability of HCC4
as Pb(II) selective sensor was further confirmed by FT-IR
spectroscopic analysis and are presented in Fig. 18(I).
FT-IR spectrum of HCC4 showed distinguish bands
(KBr/cm−1) at 3,376 [υ(O••••H)], 1,762 and 1,693 for
υ(C=O), 1,365 for υ(C–N), l511 and 1,484 for aromatic
υ(C=C) and 1,200 for υ(C–O) respectively. After complexa-
tion, the spectrum of HCC4 shows distinctive variations in
terms of shifting, disappearance and appearance of new bands.
From the Fig. 18(I), it has been observed that the region at
3,500–3,000 cm−1 shows significant differences as the band at
3,482 cm−1 for υ(O••••H) was blue shifted to 3,456 cm−1
clearly gives the indication for changing in the geometry of
molecule as a result of introduction of Pb(II) into ligand cavity.
Noticeable changes appeared at region 2,000–1,500 cm−1,
where two sharps peeks υ(C=O) at 1,762 and 1,693 cm−1
was completely disappeared after complexation with both
metal ions. Furthermore, Pb(II) complex shows remarkable
red shifting of peak from 1,365 to 1,388 cm−1(υ(C–N)) due
to metal-nitrogen stretching vibration which gives clear indi-
cation for involvement of nitrogen donors with Pb(II) ion.
On contrary, FT-IR complexation analysis of HCC4 with
2−
was found that HCC4 undergo a three-step thermal degra-
dation (Fig. 17a–d). The first step (89–233 °C) is due to the
loss of moisture, whereas the second step (258–385 °C)
could be attributed to the loss of the corresponding amide
functionalities of HCC4, while the third one (398–554 °C) is
due to the cleavage of the calixarene backbone. TG curve of
HCC4-Pb(II) complex, shows two step thermal degradation
process and relatively appears to be less stable as compare to
its parent molecule as it reduced to 48 % (52.3 % mass loss,
1.25 mg) in the first step up to 373 °C and finally reduced to
25 % (mass loss 75 %, 2.068 mg) at 653 °C at second step
respectively whereas parent molecule was found to be stable
up to this stage, i.e. 554 °C and reduced to only 46 % (54 %
mass loss, 2.64 mg). The DTA result of the HCC4 showed the
weight loss exothermic weight loss two exothermic peaks at
248, 301, 321 and 364 °C which becomes replaced by only
one sharp hypsochromic shifted weight loss exothermic peak
at temperature of 274 °C after complexation with Pb(II).
Thermal behavior of anionic complex of HCC4, i.e.,
2−
HCC4-Cr2O7 was also determined. TG curves of afore-
mentioned complex shows two step thermal degradation
process at 162–372 °C and 385–563 °C with finally reduced
to 39 % (61 % total mass loss, 3.61 mg). DTA curves of
2−
Cr2O7 also shows different spectral characteristics
2−
HCC4-Cr2O7 complex shows weight loss exothermic
(Fig. 18(II)), where two sharps peaks at 1,762 and
1,693 cm−1 ascribed for υ(C=O) remains present after com-
plexation followed by disappearance of peak at 1,365 cm−1
(υ(C–N)). At 629 cm−1 new sharp also appears which may
weight loss four exothermic peaks at 217, 337, 351, and
475 °C. Although thermal gravimetric analysis of all com-
plexes shows relatively more thermal sensitivity with re-
spect to their parent HCC4 nevertheless, this technique
confirms formation of this complexes [39].
be attributed to the involvement of protons of amines bind-
2−
ing sites with both Cr2O7
.
FT-IR Study
Conclusions
Infrared spectroscopy is considered to be the most informa-
tive method for the characterization of host–guest interac-
tions and numerous authors reported FT-IR and FT-IR
In summary, we show here the selective chromogenic and
fluoregenic characteristics of hydrazide derived calix[4]

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arene sensing derivative. HCC4 was appeared to be bifunc-
tional potential chemosensor for Pb(II) ion. Selectivity study
shows the slightly interference from foreign ions on HCC4-
Pb(II) complex as the presence of soft binding sites seems to
be ideal in terms of size, arrangement and accommodation
of Pb(II) ions. On the other hand, we also have explored
highly selective dichromate (Cr2O72−) ion selective
chromogenic/fluorescent sensor first time with minor for-
eign ion effect as presence of protons of hydrazide moieties
with in calix[4]arene frame work confers its high specificity
towards Cr2O72−. All of complexation process was further
verified by TGA and FT-IR and spectral analysis.
Mainly, the design approach and extraordinary
photophysical properties of the sensor HCC4 would help to
extend the development of fluorescent sensors for other toxic
metal ions and anions.
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Acknowledgements We thank the National Centre of Excellence in
Analytical Chemistry, University of Sindh, Jamshoro/Pakistan and
Scientific and Technological Research Council of Turkey (TUBITAK,
B.02.1.TBT.0.06.01-216.01/895-6391) for the financial support of
this work.
31. Qureshi I, Memon S, Yilmaz M (2009) J Hazard Mater 164:675
32. Memon S, Yilmaz A, Roundhill DM, Yilmaz M (2004) J
Macromol Sci A 41:433
33. Tabakci M, Memon S, Yilmaz M, Roundhill DM (2003) J Incl
Phenom Macrocycl Chem 45:265
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