Calix[4]pyrrole virtuous sensor: a selective and sensitive recognition for Pb(II) ions by spectroscopic and computational study

Article abstract of DOI:10.1080/10610278.2019.1568434

A novel supramolecular sensor derived from calix[4]pyrrole system i.e. calix[4]pyrrole bearing aminoanthraquinone derivative (CAAQ) have been designed and synthesized. The complexation behavior of metal cations [Ag(I), Ba(II), Ca(II), Ni(II), Co(II), Fe(I

Full text of DOI:10.1080/10610278.2019.1568434

Supramolecular Chemistry
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Calix[4]pyrrole virtuous sensor: a selective
and sensitive recognition for Pb(II) ions by
spectroscopic and computational study
Keyur D. Bhatt, Hemangini D. Shah, Krunal M. Modi, Moksha B. Narechania
&
Chirag Patel
To cite this article: Keyur D. Bhatt, Hemangini D. Shah, Krunal M. Modi, Moksha B. Narechania
Chirag Patel (2019): Calix[4]pyrrole virtuous sensor: a selective and sensitive recognition
for Pb(II) ions by spectroscopic and computational study, Supramolecular Chemistry, DOI:
0.1080/10610278.2019.1568434
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SUPRAMOLECULAR CHEMISTRY
https://doi.org/10.1080/10610278.2019.1568434
ARTICLE
Calix[4]pyrrole virtuous sensor: a selective and sensitive recognition for Pb(II)
ions by spectroscopic and computational study
a
b
c
d
d
Keyur D. Bhatt , Hemangini D. Shah , Krunal M. Modi , Moksha B. Narechania and Chirag Patel
a
b
Department of Chemistry, Mehsana Urban Institute of Sciences, Ganpat University, Kherva, India; Department of Chemistry, C. U. Shah
c
University, Wadhwan, Gujarat, India; J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague 8,
Czech Republic; School of Sciences, Gujarat University, Ahmedabad, Gujarat, India
d
ABSTRACT
ARTICLE HISTORY
A novel supramolecular sensor derived from calix[4]pyrrole system i.e. calix[4]pyrrole bearing
aminoanthraquinone derivative (CAAQ) have been designed and synthesized. The complexation
behavior of metal cations [Ag(I), Ba(II), Ca(II), Ni(II), Co(II), Fe(III), Hg(II), Cu(II), Cr(II), Pb(II), Zn(II),
Received 14 October 2018
Accepted 6 January 2019
KEYWORDS
Calix[4]pyrrole;
−
4
−6
(1 × 10 M)] with CAAQ (1 × 10 M) was studied by spectrophotometry and spectrofluorometry.
Metal ion like Pb(II) produces red shift in absorption spectra and quenching in emission spectra
likelihood of strong complexation of Pb(II) ions with CAAQ. Fluorescence cell imaging also
supports the complexation of Pb(II) ions with CAAQ. The binding constants, quantum yield,
stoichiometry of complex, mechanism of quenching by Stern–Volmer equation and Density
functional theory calculation have been determined.
aminoanthraquinone; ion-
binding; fluorescent
quenching; molecular
modeling; DFT calculation
1
. Introduction
specificity/selectivity is generally or mainly determined
on the basis of nature of receptor unit, while sensor
signaling performance i.e. host-guest interaction totally
determined by the fluorogenic unit (8). Fluorescent
techniques are found to be very selective towards spe-
cific ions so they are widely approached as basic tech-
nique for detection of ions. It also imparts ease in
sensing the ions. The signaling of receptor unit results
into either enhancement or quenching in fluorescent
emission (9) due to its selective host-guest interaction
Development of fluorescent sensor which selectively
recognize the analytes from complex and converts to
easily recognizable signal even in very low concentra-
tion have become main technological application in
supramolecular chemistry (1, 2). The development of
such fluorescent sensor via synthesis and designing of
flexible receptors for detection of metal ions have
rapidly increased due to its wide application in vivo or
in vitro in various fields (3). The principle of fluorescent
chemosensors (4–6) for ions typically consist of an ion
recognition unit called as ionophore and a fluorogenic
unit called as fluorophore which covalently binds to the
ionophore through a correct spacer (7). Sensor
(10). The signal detection can be critical depending on
selectivity and sensitivity of targeted species.
As for sensor development of cations and anions,
calix[4]pyrrole (11–13) attracted a great extent of atten-
tion as with appropriate attached groups it behave as
CONTACT Keyur D. Bhatt
drkdbhatt@outlook.com
Department of Chemistry, Mehsana Urban Institute of Sciences, Ganpat University, Kherva
3
84012, India
Supplementary data for this article can be accessed here
©
2019 Informa UK Limited, trading as Taylor & Francis Group

2
K. D. BHATT ET AL.
a good candidate for recognition of moieties. The bind-
ing properties of calix[4]pyrroles can be modulated by
various structural modifications (14) or by the change of
solvent (15). It is also highly selective and specific
towards anions, transition metal, neutral substrate and
their eventual applications as fluorescence sensing (16)
agents have received increasing interest (17, 18).
The high fluorescence quantum yield, good accessi-
bility and biological activity of have gained aminoan-
thraquinone a lot of attraction as a fluorophore,
polymer additives and medicinal agents (19). Further
owing to the tunable properties of aminoanthraqui-
none and calix[4]pyrrole scaffold fixing up them may
lead to development of a new fluorescent sensor (20).
Metal ion like lead is considered as a pollutant and is
highly toxic in biological as well as environmental pro-
cess. Increased level of lead in environment causes
health related problem like anemia, disorder of the
blood, memory loss, kidney damage, muscle paralysis
and mental retardation as it is toxic to the body of adult
and children (21). Long time exposure to lead causes
adverse effects like abdominal pain, weakness in finger,
wrists, or ankles (22). Lead toxicity affects every organ
system. On a molecular level, its toxicity accounts bio-
chemical processes involving its ability to interact,
mimic and inhibit the action of calcium, proteins,
amine, phosphates and carboxyl.
infrared spectra were prepared as KBr pallets; spectra
were recorded on tensor Bruker 27 (Ettlingen, Germany)
−1
and expressed in cm . Elemental analysis (C, H and N)
was performed on vario MICRO-Variant elemental analy-
zer (Mt. Laurel, USA). Electrospray ionization (ESI) mass
spectra (MS) were determined using MicromassQuarter2
(Utah, USA). NMR spectra were recorded on a model DPX
200 MHz and Advance II 400 MHz Bruker FT-NMR instru-
ments (Ettlingen, Germany). UV-Vis and fluorescence
spectra were recorded on a JASCO spectrophotometer
(Easton, US) and JASCO spectrofluorometer FP 8300
(xenon lamp headxe90) (Livingston, US).
2.3. General method to detect cation by
spectrophotometry and spectrofluorimetry
An aliquot (1 mL) of a freshly prepared solution of
−6
CAAQ in DMSO (1 × 10 M) was transferred into
a quartz cell (1 cm width). 1ml from stock solution of
−
6
the nitrate salt of cation (1 × 10 M) was added to the
solution of CAAQ into a quartz cell. The corresponding
UV–vis spectra were recorded at 298 K. Absorption
spectra of resulting solution and that of CAAQ were
compared. Emission spectra of same stock solution of
ligand were used and the metal ions solutions of
desired concentration (1.0–100 equiv.) were prepared
by dilution of stock solution. The emission spectra were
also recorded and compared. Binding constant of com-
plex was also determined using reported literature
procedure.
Pb(II) sensing has been reported using calix[4]arene as
ionophore with various fluorophore such as pyrene (21),
coumarin (17) and aminoanthraquinone (19). Here an
attempt has been made to synthesize aminoanthraquinone
derivative on calix[4]pyrrole with a view to develop a new
fluorescent sensor capable of selective recognition of
a cation. A combination of modified calix[4]pyrrole, chro-
mophoric anthraquinone group and proton donating cap-
ability of amide generates high fluorescence capability
sensor.
2.4. Computational studies
2.4.1. Molecular docking
The Geometry of structure of CAAQ were optimized at
the density functional level (DFT) B3LYP/6-31G* of the-
ory in Gaussian09 (23). The optimized structure were
taken as the starting host and guest conformations for
docking in Hex 8.0 software (24).
2
. Experimental
2
.4.2. Host-guest interactions
2
.1. Chemical and reagents
The optimized structures obtained were taken for the
evaluation of the binding peculiarities of docked host-
guest complex. The binding mechanism have been
interpreted by examining the various interactions
occurred during the event and visualized through
Discovery studio visualizer (25).
All starting materials, reagents, metal nitrate salts, 1-ami-
noanthraquinone and other chemicals were obtained from
Sigma-Aldrich. Silica gel and fluorescence active TLC plates
(F-2009) were purchased from the Merck. All the solvents
employed for synthesis were commercially available and
used as received without further purification.
2
.4.3. Density functional theory (DFT) calculation
Some previous reports B3LYP functional has been suc-
cessfully used for geometry optimization of transition
metal complexes (26–29). The general basis sets were
used for the complex DFT calculation The Becke
2
.2. Instrument
The melting points (uncorrected) were obtained from
a VEEGO Model; VMP-DS, (Mumbai, India). Samples for

SUPRAMOLECULAR CHEMISTRY
3
3
-parameter exchange functional together with the Lee-
Yang-Parr correlation functional (B3LYP) (30, 31) [B3LYP/
-31+G(d,p)/LANL2DZ] were used in calculation of DFT
complex.
The 6-31+G(d,p) were optimized for the C, H, N and
obtained they were treated with Pb(NO ) in serum free
3 2
media for 1 hour, then fluorescent ligand CAAQ was
added and cells were rested for 15 minutes in dark.
Slides were prepared and observed under 40× objective
of fluorescent microscope.
6
O atoms while LANL2DZ relativistic pseudo potential
was used for the lead metal ion (29, 32, 33). The ligand
and metal complexes were demonstrated using
Avogadro version 1.2.0 software (34). Gas phase geo-
metry optimizations were carried out without symmetry
constraint using the Gaussian 09W software (35).
2
.5. Synthesis of CAAQ
2.5.1. Synthesis of 3-(2-(5-methyl-1H-pyrrol-2-yl)
propane-2-yl) phenol (MHCP)
2.5.1.1. Conventional method. Parent 3-methoxy-
substituted calix[4]pyrrole skeleton was synthesized using
general method of acid catalysed condensation reaction of
pyrrole and aromatic ketone.5.36 ml (0.08 mole) Pyrrole was
placed in a 250 ml round bottom flask equipped with
magnetic stirrer and filled with methanol (100 ml).
Methane sulfonic acid (1 ml) was then added to the reaction
flask and stirred for 15 minutes.3-hydroxy acetophenone
(11 gm, 0.08 mole) was dissolved in methanol (50 ml) and
added stepwise to the reaction flask. Reaction mixture was
left to stir for 7 hrs and was monitored by TLC using
petroleum ether: ethyl acetate (9.5:0.5) as the developing
solvent. After completion of reaction, the reaction mixture
was then poured slowly into another 500 ml round bottom
flask equipped with a magnetic stirrer and distilled water
(200 ml) containing triethyl amine to obtain a brown
colored residue (20). It was filtered, collected and dissolved
in diethyl ether (400 ml) to get rid of the black tar. The
solvent was evaporated to obtain deep brown-black resi-
due, which was then recrystallized from methanol to obtain
pure product (58%) (1). Melting point 200 C. Elemental
analysis found: C 77.81, H 5 .99, N 7.56, O 8.64
2
.4.4. Molecular dynamics (MD) simulation
Desmond program version 2.0 (academic version) was
administered for the molecular dynamics (MD) simula-
tion of host-guest complex having minimum binding
obtained via Hex software (32, 33). The system has been
prepared via cubic periodic box containing dimethyl
sulfonyl oxide (DMSO)(10Å × 10Å × 10Å) with
Optimized Potentials for Liquid Simulations (OPLS) in
all-atom force field 2005 (34) followed with addition of
−
counter ions (Na+ and Cl ) for the neutralization pro-
cess. 247 atoms from inclusion complex and 2004
DMSO molecules were provided for the energy minimi-
zation and pre-equilibration in various restrained steps.
10 ns with relaxation time has been chosen for the
molecular dynamics (MD) simulation experiment in
which various parameters have been optimized and
considered as per the standard protocol relaxation
time of 1 ps at constant temperature of 300 K, constant
volume and shape ensemble (NVT) with Nose-Hoover
thermostat, Smooth Particle Mesh Ewald (PME) method
−
9
−1
(
35) (with a 10 tolerance limit), cut-off distance of 9.0
C48H44N4O4 FT-IR(KBr)cm : 3402(pyrrolicNH),3271 and
A (35), and 2084 frames were generated during 10 ns in
the trajectory and captured every 4.8 ps time step for
further analysis.
3109 (b-pyrroleC–H and -OH),1681,1566,1496,1334 and
13
1296. C-NMR (125MHz,d6-DMSO)ppm: 157.61, 151.07,
1
137.44, 115.02, 105.02,66.99,39.59. H NMR (500 MHz,
To decipher the stability an average structure was
selected from the molecular dynamics (MD) simulation
residing to production phase. In addition, root mean
square deviation (RMSD), root mean square fluctuation
DMSO)ppm δ 10.00–9.45 (s, 4H), 9.18 (s, J = 66.5, 25.5 Hz,
4H), 6.85 (dd, J = 24.8, 8.7 Hz, 3H), 6.71 (dd, J = 22.1, 8.3 Hz,
6H), 6.61 (dd, J = 17.1, 8.3 Hz, 7H), 5.96 (dd, 2H), 5.81 (dd, 2H),
5.41 (dd, 2H), 5.31 (dd, 2H), 1.77 (s, 12H). CHCl3 (dd, 7.40),
DMSO (s, 3.37).mass spectrometry m/z % (ESI-MS) 741
[M + 1].
(RMSF), hydrogen bond and radius of gyration (Rg)
evaluation have been performed to investigate the
structural changes and dynamic behaviour of the
complex.
2.5.1.2. Microwave irradiation method. A mixture of
pyrrole 1 (1.0 ml, 0.015 mole) and methane sulfonic acid
(0.1 ml) in methanol (10 ml) were exposed to micro-
wave irradiation for 10 min. A solution of 3-hydroxya-
cetophenone (2.0 gm, 0.015 mole) in methanol (10 ml)
was then added to the reaction mixture and was sub-
jected to microwave irradiation for 10 min with a slight
pause after every 2 minutes. After completion of the
reaction, a deep brown-black reaction mixture was
poured into cold water (50 ml) to obtain brown black
2
.4.5. Cell culture and fluorescence imaging of cells
Lymphocytes were cultured in RPMI1640 medium sup-
plemented with 7% fetal bovine serum (FBS), antibiotics
(100mg Penicillin and 100mg Streptomycin) and 100µl
of PHA to stimulate the cell growth, at 37°C in an
incubator. Cells were proliferated and harvested at
7
0th hour with the help of chilled fixative (1:3 acetic
acid: methanol). Once the pellets of lymphocytes were

4
K. D. BHATT ET AL.
colored precipitates. The residue was filtered off, col-
lected, dried and dissolved in diethyl ether (25 ml × 2)
to obtain brown black colored residue which was then
recrystallized from a methanol mixture to get pure
product (1) for analysis.
IR(KBr)cm −1:1511,1611,3144, 1 H NMR (500 MHz, d6-
DMSO) δ 8.2 (dd, 4H), 7.9–8.2 (dd,12H), 7.4–7.8 (dd, 12H),
3.6 (dd, 4H), 2.6–2.8 (s, 12H), 2.4 (s, 12H) 13C NMR
38.32,39.23 39.44, 39.65,39.86,40.07,115.59,123.67,126.
28,126.37,132.54,133.42, 133.56, 134.44, 134.76, 152.18.
Mass spectroscopy m/z % (ESI-MS)1292.5[M+ Na]
This p-tertbutylcalix[4]pyrrole derivatives has been
modified first time at lower rim with aminoanthraqui-
none derivative linked with acylation of anthraquinone
with macrocycle. The formation of strong H-bonding
and tautomeric equilibrium between carbonyl group
and NH group of amino-anthraquinone provides essen-
tial stability to complex.
2
.5.2. Synthesis of compound 2-chloro-N-(9,
1
0-dioxo-9, 10-dihydroanthracen-1-yl) acetamide
To the solution of 1 aminoanthraquinone (0.6g, 0.9 mmol)
dissolved in CHCl slow addition of 2-chloroacetyl chloride
3
(0.83, 3.7 mmol) was carried out by stirring. These reaction
mixture was further stirred for 2 hour and progress of
reaction mixture was monitored through TLC. After com-
pletion of reaction the reaction mixture was washed with
water and recrystallized fromDCM to obtain 2-chloro-N-(9,
3. Results and discussion
10-dioxo-9, 10-dihydroanthracen-1-yl)acetamide.
The binding property of Pb(II) with ligand CAAQ were
investigated by absorption and emission spectroscopy. All
titration were carried out in DMSO as solvent adding ali-
quots of different cation. In addition to these Computation
Study was also performed to establish a chemistry for the
detection of Pb(II) using CAAQ as a ligand.
2
.5.3. Synthesis of compound CAAQ
The reaction mixture containing MHCP (0.6g, 0.9 mmol),
K CO (0.52g, 3.7mmol), KI(0.56g, 3.7mmol) and 2-chloro-
2
3
N-(9, 10-dioxo-9, 10-dihydroanthracen-1-yl)acetamide
0.83,3.7mmol) in acetone was refluxed for 48 hour and
(
progress of reaction mixture was monitored through TLC.
After completion of reaction temperature was slowly
brought down to room temperature and the solvent
was removed by filtration. The pure compound (2) (52%)
3
.1. Absorbance spectra
The UV–Vis absorption spectrum of the CAAQ was
observed at 260 nm. On addition of Pb(II) ion the absorp-
tion band shifted from 260 to 273 nm forming a broad
red shift (Figure 1) while no change in absorption
(scheme-1) was obtained by chromatography using
ETOH/Hexane as an eluent (1:9). The fraction was sepa-
rated, dried and recrystallized in DMSO to give CAAQ. FT-
Scheme 1. (Colour online) Synthetic scheme of 2-chloro-N-(9, 10-dioxo-9, 10-dihydroanthracen-1-yl)acetamide.
Scheme 2. (Colour online) Synthetic scheme of CAAQ.

SUPRAMOLECULAR CHEMISTRY
5
−
6
−1
Figure 1. (Colour online) Absorption spectra of CAAQ (1 × 10 mol L ) upon addition of 100 equivalent of Pb(II) ions in DMSO
−
6
−1
solvent (1 × 10 mol L ).
spectrum was observed when other metal ions were
added. Broad red shift was observed due to the auxo-
chrome amino group covalently bonded to aromatic
system. The complexation of metal ion with auxochro-
mic amino-anthraquinone chromophore induces broad
red shift in absorption spectra.
Hg(II), Pb(II), Cu(II), Zn(II), Ba(II), Ca(II), Ni(II), Co(II),
Ag(I), Na(I), K(I)as nitrate salt. On addition of Pb(II)
ions to the solution of CAAQ the signal was obtained
at 480 nm showing a significant quenching in the
fluorescence emission compared with other metal
ions (Figure 2). Comparative diagram of different
metal ion intensity is shown in (Figure 3).
A significant quenching in fluorescence titration of
CAAQ with Pb(II) ions was observed due to ICT
mechanism. Carbonyl group of aminoanthraquinone
works as an excellent electron donor, electron rich
3
.2. Emission spectra
The emission spectrum of ligand was carried out in the
presence of various metal ions Fe(III), Cr(III), Bi(III),
−6
−1
−6
−1
Figure 2. (Colour online) The fluorescence spectra of CAAQ (1 × 10 mol L ) upon addition of various metal ions (1 × 10 mol L ) in
DMSO solvent.

6
K. D. BHATT ET AL.
Figure 3. (Colour online) Comparison diagram of CAAQ with metal ions.
oxygen donates electron to electron deficient ring and
undergoes ICT. ICT mechanism continues until metal
ions are not added. On addition of metal ion ICT
decrease as the direct formation of bond between
lead metal ions with carbonyl oxygen of anthraqui-
none ring. Due to decrease in charge density on oxy-
gen atom the charge transfer from oxygen of
anthraquinone group to electron deficient ring stops
thereby decreasing the emission intensity, leading to
quenching (36). Further evidence of ICT mechanism
was studied using density function calculation (20).
3.3. Stern-Volmer analysis
Stern-Volmer analysis was carried out to determine the
mechanism of quenching process. Plotting of relative
emission intensities (I /I) against quencher concentration
0
[M] is carried out in Stern-Volmer analysis. Linear graph
was obtained on placing in Equation (1) showing static
mechanism of quenching (Figure 6) (Figure 7). Here I and
I0 are fluorescence intensities in the presence and
absence of added metal cations. The slope of this line is
K .
sv
−
4
On addition of 10 Pb(II) ions the decrease in emis-
I0
I
¼
1 þ K ½Qꢀ
(1)
sv
−
6
sion intensity was observed while about 10 require
for complete titration thus with decrease in concentra-
tion of ions the increase in emission spectra was
observed. Figure 4 shows %quenching of CAAQ on
addition of different metal ions. Figure 5 shows the
effect of increasing concentration causes decrease in
emission intensity. Thus we appraised that the ligand
act as a turn off fluorescence for Pb(II) ions compared to
other metal ions.
These results obtained are also consistent with the
static quenching. The linear behaviour of complexation
also supported static mechanism of quenching. The
static quenching constants (K ) are given in the
Table 1.
sv
3.4. Binding constant and quantum yield
The notable wavelength shift both in the absorption
and fluorescence spectra in the presence of Pb(II)ions
led us to examine the selective naked-eye detection of
Pb(II)ions. As shown in (Figure 6) only Pb(II) induces
a color change from dark orange to yellow. The addi-
tion of other metal ions does not induce any such
noticeable change.
Binding constant of fluoroionophore (CAAQ) was deter-
mined by following equation (7, 37).
ꢀ
ꢁ
n
F0 ꢁ F
F ꢁ F1
½Mꢀ
¼
(2)
K
diss
According to this procedure, the fluorescence inten-
sity (F) scales with the metal ion concentration ([M]).

SUPRAMOLECULAR CHEMISTRY
7
Figure 4. (Colour online) Bar diagram showing % quenching of ligand (CAAQ) with different metal ions.
−
6
−1)
Figure 5. (Colour online) The fluorescence spectral changes of CAAQ (1 × 10 mol L upon addition of 0–1000 equivalents of
Pb(II) ions in DMSO solvent. Inset: linear regression fit (double- logarithmic plot) of the titration data as a function of concentration
of metal ions.
The binding constant (K ) is obtained by plotting log
The plot of log[(F -F)/(F-F )] versus log [M] for
0 1
s
[
(F -F)/(F-F )] versus log [M], where F and F are the
selected metal ions is shown as insets in Figure 5.
The titration shows very good linear fit of R = 0.98
with above equation. The binding constant obtained
is 1.379 × 10 .
Fluorescence quantum yields (ɸ) was determined via
comparative method (7, 38)
0
1
0
1
relative fluorescence intensities of the complex with-
out addition of guest metal ion and with maximum
concentration of metal ion respectively. On plotting
value of log [M] versus log [(F – F)/(F – F )] gives the
−
8
0
1
value of Kdiss the reciprocal of binding constant (Ks).

8
K. D. BHATT ET AL.
Figure 6. (Colour online) Color response on addition of CAAQ to metal ions.
−
6
Figure 7. (Colour online) Stern-Volmer plots for quenching of ligand (CAAQ) (1 × 10 M) in DMSO solvent by Pb(II) ions.
ðF ꢂ A ꢂ ηÞ
std
Table 1. The highest occupied molecular orbitals (HOMO) and
the lowest unoccupied molecular orbitals (LUMO) of CAAQ and
CAAQ+Pb.
Φ ¼Φstd
(3)
ðF ꢂ A ꢂ η
Þ
std
std
Name
Total Mo’s
Occupied Mo’s
Here Fstd and F are the areas under the florescence
emission curves of the standard CAAQ and metal
Pb(II) ions complexes with CAAQ respectively. Astd and
A are the relative absorbance wavelength of the stan-
dard and sample respectively. ηstd and η are the refrac-
tive indices of solvent (DMSO) used for the standard
and sample. Both standard and sample were excited at
the same relevant wavelength. Reported quantum yield
of amino-anthraquinone is approximately 0.075 while
fluoroionophore (CAAQ) is found to be 0.51 showing
that the number of emitted photons decreases with the
addition of increasing concentration of metal ions i.e.
quenching takes place as shown in Table 1.
CAAQ
CAAQ+Pb
1750
1670
332
336
3.5. Stoichiometry of metal ions complex
The stoichiometry ratio of the metal complex of Pb(II)
ions were determined using jobs method of continuous
variation. The absorbance of ligand A was subtracted
b
from A to get ΔA.
c
ΔA ¼ Ac ꢁ Ab
(4)

SUPRAMOLECULAR CHEMISTRY
9
Figure 8. (Colour online) Job’s plot of CAAQ with Pb(II) in DMSO solvent.
ΔA values were plotted against the mole fraction of
metal ions Pb(II) ions a/a + b (Figure 8). Maximum
values ΔA for Pb(II)ions at a/a + b = 0.80 indicatesthe
ratio of 1:2. The accuracy of these result indicates the
formation of single complex. The measurement was
done at different wavelengths for reliability, which
gave the same values for a/a + b ratio.
(Figure 9). This minimized structure for the docking
experiment with guest compound bound with the
docking energy of −189.7 kJ/mol has been chosen.
3
.6.2. Host-guest interactions
Interactions of host-guest complex are measured after
the docking experiment to correlate the experimental
analysis where 4 metal acceptors and 1 metal donor
bonds is found to bind between host and guest. The
metal acceptor bonds ranges from 1.64 Å to 2.63 Å
while metal donor bond has been obtained with the
value of 2.38 Å (Figure 10).
3
.6. Computational studies
3
.6.1. Molecular docking
Molecular docking has been carried out after the opti-
mization of geometry to anticipate the binding affinity
of host-guest complex. The front and top loaded views
of host provide a structural change according to the
native form of host with some specific energy level
3.6.3. Density functional theory (DFT) calculation
Optimization and Single point energy calculation were
carried out to calculate the strength of the complex in
Figure 9. (Colour online) Geometry optimization views.

1
0
K. D. BHATT ET AL.
Figure 10. (Colour online) Molecular docking view (Energy = −189.7 kJ/mol).
terms of binding energy with minimal errors associated
with basis set superposition.
The binding energy was calculated using following
equation.
structure. The Frontier Molecular Orbital energies were
obtain using B3LYP/6–31 + G(d,p)/LANL2DZ level for opti-
mized molecular structures. The total occupied and unoc-
cupied molecular orbitals of CAAQ and CAAQ+Pb are as in
Table 1. The 3D plot of the frontier orbitals, the highest
occupied molecular orbitals (HOMO) and the lowest unoc-
cupied molecular orbitals (LUMO) of CAAQ and CAAQ+Pb
are shown in Figure11 and Figure 12.
À
Á
ΔEBinding ¼ E
ꢁ ECAAQ þ E
CAAQ PbðIIÞ
PbðIIÞ
¼
ðꢁ4173:59564279Þ ꢁ ðꢁ4166:76233284Þ þ ðꢁ3:39247052Þ
¼
ðꢁ4173:59564279Þ ꢁ ðꢁ4170:15480336Þ
The HOMO and LUMO energy differences of the
Ligand CAAQ and corresponding Ligand-Metal
¼
ꢁ3:44083943Hartrees
¼
ꢁ 2159:159 kcal=mol ð1 Hartrees ¼ 630 kcal=molÞ
(
CAAQ+Pb) complex is determined. The conductor-
DFT studies were carried out to understand ICT mechan-
ism for CAAQ and CAAQ+Pb complex. Molecular orbital
study also provided useful information about electronic
like polarizable continuum model (CPCM) was
employed to investigate the effect of the solvent
(DMSO) on geometries.
Figure 11. (Colour online) HOMO-LUMO orbital of CAAQ with 1AQ and CAAQ_Pb complex. Energy Gap in the units of eV
1eV = 23.060 kcal/mol).
(

SUPRAMOLECULAR CHEMISTRY
11
Figure 12. (Colour online) HOMO-LUMO orbital of CAAQ with 2AQ and CAAQ_Pb complex. Energy Gap in the units of eV
(1eV = 23.060 kcal/mol).
For the receptor CAAQ (Figures 11 and 12) the HOMO
recognition of host-guest complex. For this evaluation
10 ns time level has been selected and specific para-
meters kept as per the Desmond suite. To follow the
protocol explicit quality properties have been obtained
which contains Total energy, Potential energy,
Temperature, Pressure and Volume (Table 2). Figure 13
demonstrates the fluctuations occurred in these para-
meters as well as the stabilization of host-guest com-
plex. Among all of them, Energy −5805 to −5765 kcal/
mol of host-guest complex shows exponential growth
while rest of all possessed fluctuations between some
specific ranges which reveals the stability and confor-
mational changes of host-guest complex. More than 5
Intramolecular H-bonds have been observed (Figure 14)
and root means square deviation (RMSD) (Figure 15) of
complex structure ranges from 5 to 16 Å.
orbital was found to be mainly distributed at the Calix [4]
pyrrole ring systems and half at anthraquinone subunit,
whereas Polarizable Continuum Model showed that the
LUMO was mostly located on both of amino anthraqui-
none molecular system (Figures 11 and 12). Thus it was
observed that the AQ subunit contributed to the LUMO
and the electron flow takes place from CP to AQ in both
states i.e. HOMO and LUMO.
In CAAQ+Pb complex system (Figures 11 and 12) the
HOMO orbital was found to mainly distribute in AQ
group of CAAQ and half of Pb(II) metal ions while
LUMO was mostly located on the Pb(II) metal ions. It
was observed that the Pb(II) metal ions contributed
fewer amounts of HOMO but its contribution towards
LUMO was intense which clearly indicates that the elec-
tron transfer from 1AQ (HOMO) and 2AQ (HOMO+1)
units. Thus red shift in UV, quenching in the fluorescence
spectra and charge transfer hindrance was observed due
to complexation of Pb(II) metal ions (LUMO-1, LUMO-2)
with 1AQ (HOMO) and 2AQ (HOMO+1) respectively.
Table 2. Simulation quality analysis result.
−1
Average
Std. Dev.
11.160
Slope (ps
0.004
)
Total Energy
kcal/mol)
Potential Energy
kcal/mol)
−5785.847
(
−7339.940
25.097
−0.000
(
3
.6.4. Molecular dynamics (MD) simulation
Docked host-guest complex had been preferred for the
anticipation of structural integrity and molecular
Temp.(K)
Pressure (bar)
Volume (Å )
298.464
7.984
24357.345
2.580
183.652
91.968
0.000
0.001
0.002
3

1
2
K. D. BHATT ET AL.
Figure 13. Simulation quality analysis result temperature.
Figure 14. Intra-H bonding graph.
Figure 15. RMSD changes in CAAQ+Pb complex.
3
.7. Fluorescence imaging
when cells were incubated with probe CAAQ while dull
green fluorescence was observed in cells in the presence
of Pb(II) (Figure 16). The result clearly indicates that the
CAAQ+Pb(II) quenches the fluorescence and act as
a effective intracellular Pb(II)ions imaging agent.
The cells which were captured right after exposure of
CAAQ shows full fluorescence while cells which were
kept in dark for 1 hour with CAAQ+Pb(II) shows less
fluorescence. Fluorescent green image was observed

SUPRAMOLECULAR CHEMISTRY
13
Figure 16. (a) Image captured right after exposure of CAAQ; (b) Image captured after 1 hour of incubation in dark.
4
. Conclusion
storage facilities owned by parties and projects contributing
to the National Grid Infrastructure Meta Centrum provided
under the programme “Projects of Large Research,
Development, and Innovations Infrastructures” (CESNET
LM2015042) Czech republic, is greatly appreciated. The
authors also acknowledge Sophisticated Analytical
InstrumentFacility (Panjab University), Gujcost (Gandhinagar)
and INFLIBNET (Ahmedabad) for e-journals.
A novel calix [4]pyrrole bearing amino anthraquinone
CAAQ) sensor has been synthesized as well as character-
(
ized using various spectral methods. The probe exhibited
high selectivity for Pb(II) over other metal ions. The results
presented in this study indicated that CAAQ shows fluores-
cence quenching for recognition of Pb(II) ions. Competitive
studies confirm that CAAQ can sense Pb(II) ions even in the
presence of several other metal ions. The fluorescence turn-
off mechanism can be raised due to prohibition in charge
transfer from oxygen of anthraquinone group to electron
deficient ring on addition of Pb(II) ions. This apprehended
ICT mechanism is also supported by the computational and
DFT studies. The binding stoichiometry was confirmed as
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The financial support of the grant No. 17-18108S (Grant
Agency of the Czech Republic, GAČR) and the institutional
support RVO: 61388955 is highly appreciated.
1
:2 (host/guest) by Job’s plot. The binding constants and
a limit of detection was calculated in the range of 10.0 µM–
00.0 pM. The stability constant for complexation between
1
CAAQ with Pb(II)ions has been confirmed by Valeur’s
method. Furthermore, biological application of CAAQ was
evaluated for the detection of Pb(II)ions in cells. CAAQ was
evinced as a potential cell fluorescence-imaging agent
under microscopy using cells. Fluorescent green image
was observed when cells were incubated with probe
CAAQ alone. However, dull green fluorescence was
observed in cells in the presence of Pb(II) clearly indicating
CAAQ to be an effective intracellular Pb(II)ions imaging
agent.
ORCID
Keyur D. Bhatt
http://orcid.org/0000-0001-9301-576X
References
(1) Abdul Karim, A.; Dou, Q.; Li, Z.; Loh, X.J. Emerging
Supramolecular Therapeutic Carriers Based on Host-
Guest Interactions. Chem. Asian. J. 2016, 11(6), 1300–
1321.
(
2) Desvergne, J.-P.; Czarnik, A.W. Chemosensors of Ion and
Molecule Recognition; Springer: Springer Science &
Business Media, 2012.
Acknowledgments
(
3) Darjee, S.M.; Mishra, D.R.; Bhatt, K.D.; Vyas, D.J.; Modi, K.
M.; Jain, V.K. A New Colorimetric and Fluorescent
Chemosensor Based on Thiacalix [4] Arene for Fluoride
Ions. Tetrahedron Lett. 2014, 55, 7094–7098.
doi:10.1016/j.tetlet.2014.10.149.
The authors gratefully acknowledge the Instruments and soft-
ware facility provided by Gujarat University (Ahmedabad). The
financial support of the grant No. 17-18108S (Grant Agency of
the Czech Republic, GAČR) and the institutional support RVO:
6
1388955 is highly appreciated. The authors give sincere
(4) Goldman, E.R.; Medintz, I.L.; Whitley, J.L.; Hayhurst, A.;
Clapp, A.R.; Uyeda, H.T.; Deschamps, J.R.; Lassman, M.E.;
Mattoussi, H. A Hybrid Quantum Dot− Antibody
Fragment Fluorescence Resonance Energy Transfer-
Based TNT Sensor. J. Am. Chem. Soc. 2005, 127,
6744–6751. doi:10.1142/S1088424602000452.
thanks to Department of Botany, Bioinformatics and Climate
Change Impacts Management, Gujarat University for provid-
ing an opportunity to access the bioinformatics research facil-
ities. The authors give sincere thanks to Department of
zoology for fluorescence imaging. Access to computing and

1
4
K. D. BHATT ET AL.
(
(
5) Jung, H.S.; Kwon, P.S.; Lee, J.W.; Kim, J.I.; Hong, C.S.;
Kim, J.W.; Yan, S.; Lee, J.Y.; Lee, J.H.; Joo, T. Coumarin-
Derived Cu2+-Selective Fluorescence Sensor: Synthesis,
Mechanisms, and Applications in Living Cells. J. Am.
Chem. Soc. 2009, 131, 2008–2012. doi:10.1021/
ja808611d.
6) Zhang, M.; Yu, M.; Li, F.; Zhu, M.; Li, M.; Gao, Y.; Li, L.; Liu, Z.;
Zhang, J.; Zhang, D. A Highly Selective Fluorescence
Turn-On Sensor for Cysteine/Homocysteine and Its
Application in Bioimaging. J. Am. Chem. Soc. 2007, 129,
(18) Nielsen, K.A.; Cho, W.-S.; Jeppesen, J.O.; Lynch, V.M.;
Becher, J.; Sessler, J.L. Tetra-TTF Calix [4] Pyrrole:
A Rationally Designed Receptor for Electron-Deficient
Neutral Guests. J. Am. Chem. Soc. 2004, 126,
16296–16297. doi:10.1021/ja044664a.
(19) Stoikov,
I.;
Sitdikov,
R.;
Mostovaya,
O.
Aminoanthraquinone Derivatives Based on P-Tert-
Butylthiacalix [4] Arene. Synthesis and Fluorescence
Properties. Russ. J Org. Chem. 2014, 50, 581–588.
doi:10.1134/S107042801404023X.
10322–10323. doi:10.1021/ja073140i.
(20) Bhatt, K.D.; Shah, H.D.; Panchal, M. A Switch-Off
(
(
(
7) Bhatt, K.D.; Gupte, H.S.; Makwana, B.A.; Vyas, D.J.; Maity, D.;
Jain, V.K. Calix Receptor Edifice; Scrupulous Turn off
Fluorescent Sensor for Fe (III), Co (II) and Cu (II). J. Fluoresc.
Fluorescence Probe Towards Pb (II) and Cu (II) Ions Based
on A Calix [4] Pyrrole Bearing Amino-Quinoline Group.
Luminescence 2017, 32, 1398–1404. doi:10.1002/bio.3336.
(21) Kumar, M.; Babu, J.N.; Bhalla, V.; Kumar, R. Ratiometric/
‘On–Off’sensing of Pb 2+ Ion Using Pyrene-Appended
Calix [4] Arenes. Sens. Actuators. B Chem. 2010, 144,
183–191. doi:10.1016/j.snb.2009.10.050.
(22) Bergeson, L.L. The Proposed Lead NAAQS: Is
Consideration of Cost in the Clean Air Act’s Future?
Environ. Qual. Manage. 2008, 18, 79–84. doi:10.1002/
tqem.v18:1.
2012, 22, 1493–1500. doi:10.1007/s10895-012-1086-5.
8) Wu, J.; Liu, W.; Ge, J.; Zhang, H.; Wang, P. New Sensing
Mechanisms for Design of Fluorescent Chemosensors
Emerging in Recent Years. Chem. Soc. Rev. 2011, 40,
3483–3495. doi:10.1039/c0cs00224k.
9) Bhatt, K.D.; Makwana, B.A.; Vyas, D.J.; Mishra, D.R.;
Jain, V.K. Selective Recognition by Novel Calix System:
ICT Based Chemosensor for Metal Ions. J. Lumin. 2014,
1
46, 450–457. doi:10.1016/j.jlumin.2013.10.004.
(23) Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.;
Cheeseman, J.; Scalmani, G.; Barone, V.; Mennucci, B.;
Petersson, G. Gaussian 09, Revision A. 02; Gaussian Inc:
Wallingford, CT, 2009; See also: URL: http://www.gaus
sian.com
(24) Mehta, V.; Athar, M.; Jha, P.; Kongor, A.; Panchal, M.;
Jain, V. A Turn-Off Fluorescence Sensor for Insensitive
Munition Using Anthraquinone-Appended Oxacalix [4]
Arene and Its Computational Studies. N. J. Chem. 2017.
doi:10.1039/C7NJ01111C.
(
(
10) Misra, A.; Shahid, M.; Srivastava, P. Optoelectronic
Behavior of Bischromophoric Dyads Exhibiting Zn 2+/F
−
Ions Induced “Turn-On/Off” Fluorescence. Sens.
Actuators. B Chem. 2012, 169, 327–340. doi:10.1016/j.
snb.2012.05.006.
11) Bhatt, K.D.; Vyas, D.J.; Makwana, B.A.; Darjee, S.M.;
Jain, V.K. Highly Stable Water Dispersible Calix [4]
Pyrrole Octa-Hydrazide Protected Gold Nanoparticles
as Colorimetric and Fluorometric Chemosensors for
Selective Signaling of Co (II) Ions. Spectrochim. Acta.
(25) Visualizer, D.S. Release 3.5; Accelrys Inc: San Diego, CA,
2012.
A
Mol. Biomol. Spectrosc. 2014, 121, 94–100.
doi:10.1016/j.saa.2013.10.076.
(26) Georgieva, I.; Trendafilova, N. Bonding Analyses, Formation
Energies, and Vibrational Properties of M− R2dtc
Complexes (M= Ag (I), Ni (II), Cu (II), or Zn (II)). J. Phys.
Chem. A 2007, 111, 13075–13087. doi:10.1021/jp075008a.
(27) Chen, L.; Liu, T.; Ma, C.A. Metal Complexation and
Biodegradation of EDTA and S, S-EDDS: A Density
Functional Theory Study. J. Phys. Chem. A 2009, 114,
443–454. doi:10.1021/jp904296m.
(28) Vura-Weis, J.; Fujisawa, K.; Gorelsky, S.I.; Hodgson, K.O.;
Sarangi, R.; Basumallick, L.; Hedman, B.; Solomon, E.I.
Spectroscopic and DFT Investigation of [M {HB (3, 5-I Pr 2
Pz) 3}(SC 6 F 5)](M= Mn, Fe, Co, Ni, Cu, and Zn) Model
Complexes: Periodic Trends in Metal¿ Thiolate Bonding.
Inorg. Chem. 2005, 44, 4947–4960. doi:10.1021/ic050371m.
(29) Niu, Y.; Feng, S.; Ding, Y.; Qu, R.; Wang, D.; Han, J.
(
12) Bhatt, K.D.; Vyas, D.J.; Makwana, B.A.; Darjee, S.M.;
Jain, V.K.; Shah, H. Turn-On Fluorescence Probe for
Selective Detection of Hg (II) by Calixpyrrole
Hydrazide Reduced Silver Nanoparticle: Application to
Real Water Sample. Chinese. Chem. Lett. 2016, 27,
731–737. doi:10.1016/j.cclet.2016.01.012.
(
(
13) Makwana, B.A.; Vyas, D.J.; Bhatt, K.D.; Jain, V.K.; Agrawal, Y.K.
Highly Stable Antibacterial Silver Nanoparticles as Selective
Fluorescent Sensor for Fe 3+ Ions. Spectrochim. Acta. A Mol.
Biomol. Spectrosc. 2015, 134, 73–80. doi:10.1016/j.
saa.2014.05.044.
14) Sessler, J.L.; Anzenbacher, P.; Miyaji, H.; Jursíková, K.;
Bleasdale, E.R.; Gale, P.A. Modified Calix [4] Pyrroles. Ind.
Eng. Chem. Res. 2000, 39, 3471–3478. doi:10.1021/
ie000102y.
Theoretical
Investigation
on
Sulfur-Containing
(
(
(
15) Anzenbacher, P.; Nishiyabu, R.; Palacios, M.A.
Chelating Resin-Divalent Metal Complexes. Int.
J. Quantum. Chem. 2010, 110, 1982–1993.
N-Confused Calix [4] Pyrroles. Coord. Chem. Rev. 2006,
2
50, 2929–2938. doi:10.1016/j.ccr.2006.09.001.
(30) Becke,
A.D.
Density-Functional
Exchange-Energy
16) Akyildiz, I.F.; Su, W.; Sankarasubramaniam, Y.; Cayirci, E.
Approximation with Correct Asymptotic Behavior. Phys.
Rev. A 1988, 38, 3098. doi:10.1103/PhysRevA.38.3098.
(31) Lee, C.; Yang, W.; Parr, R.G. Development of the
Wireless Sensor Networks: A Survey. Com. Net. 2002, 38,
393–422. doi:10.1016/S1389-1286(01)00302-4.
17) Miyaji, H.; Kim, H.-K.; Sim, E.-K.; Lee, C.-K.; Cho, W.-S.;
Sessler, J.L.; Lee, C.-H. Coumarin-Strapped Calix [4]
Pyrrole: A Fluorogenic Anion Receptor Modulated by
Cation and Anion Binding. J. Am. Chem. Soc. 2005, 127,
Colle-Salvetti
Correlation-Energy
Formula
into
a Functional of the Electron Density. Phys. Rev. B
1988, 37, 785. doi:10.1103/PhysRevB.37.785.
(32) Belcastro, M.; Marino, T.; Russo, N.; Toscano, M. Interaction
of Cysteine with Cu2+ and Group IIb (Zn2+, Cd2+, Hg2+)
12510–12512. doi:10.1021/ja053612y.

SUPRAMOLECULAR CHEMISTRY
15
Metal Cations: A Theoretical Study. J. Mass. spectrom. 2005,
0, 300–306. doi:10.1002/jms.755.
Petersson, G. Gaussian 09, Rev. A. 02; Gaussian Inc:
Wallingford, CT, 2009.
4
(
33) Marino, T.; Toscano, M.; Russo, N.; Grand, A. Structural
and Characterization of the Complexes Obtained by the
Interaction between Bare and Hydrated First-Row
Transition-Metal Ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+,
Zn2+) and Glycine. J. Phys. Chem. B 2006, 110,
(36) Dhir, A.; Bhalla, V.; Kumar, M. Ratiometric Sensing of
Hg2+ Based on the Calix [4] Arene of Partial Cone
Conformation Possessing a Dansyl Moiety. Org. Lett.
2008, 10, 4891–4894. doi:10.1021/ol801984y.
(37) Patra, S.; Paul, P. Synthesis, Characterization,
24666–24673. doi:10.1021/jp0645972.
Electrochemistry
and
Ion-Binding
Studies
of
(
34) Hanwell, M.D.; Curtis, D.E.;
Lonie,
D.C.;
Ruthenium (II) Bipyridine Receptor Molecules
Containing Calix [4] Arene-Azacrown as Ionophore.
Dalton Trans. 2009, 8683–8695. doi:10.1039/b905695e.
(38) Maree, M.D.; Nyokong, T.; Suhling, K.; Phillips, D. Effects of
Axial Ligands on the Photophysical Properties of Silicon
Octaphenoxyphthalocyanine. J. Porphyr. Phthalocyanines
2002, 6, 373–376. doi:10.1142/S1088424602000452.
Vandermeersch, T.; Zurek, E.; Hutchison, G.R.
Avogadro: An Advanced Semantic Chemical Editor,
Visualization, and Analysis Platform. J. Cheminform.
2
012, 4, 17. doi:10.1186/1758-2946-4-17.
(35) Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.;
Cheeseman, J.; Scalmani, G.; Barone, V.; Mennucci, B.;