Single step synthesis of novel hybrid fluorescence probe for selective recognition of Pr(III) and As(III) from soil samples

Article abstract of DOI:10.1016/j.molstruc.2019.127053

Herein, the synthesis and evaluation of a novel CHEF-PET fluorescence sensor L, based on calix[4]arene comprising two 1-Naphthoicacid groups as binding sites, is described. The selective nature of this fluorescence probe towards Pr³⁺ and As³⁺ has been investigated by emission titration, UV–vis titration, ¹H NMR spectroscopy, FT-IR, PXRD and ESI-MS investigation. The linear concentration range at pH 3.5 of L for Pr³⁺ and As³⁺ is 0–120 nM and 0–145 nM respectively with the detection limit of 1.45 nM for Pr³⁺ and 1.91 nM for As³⁺. Through Benesi-Hildebrand equation, the binding ability was found to be 7.377 × 10⁸ M^?1 for Pr³⁺ and 7.842 × 10⁸ M^?1 for As³⁺. The MOPAC-2016 software package has been used to optimize the L using PM7 and the molecular docking study has been carried out using HEX software.

Full text of DOI:10.1016/j.molstruc.2019.127053

Journal of Molecular Structure 1200 (2020) 127053
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Single step synthesis of novel hybrid fluorescence probe for selective
recognition of Pr(III) and As(III) from soil samples
a
,
*
a
b
Pinkesh G. Sutariya , Heni Soni , Sahaj A. Gandhi
a
Department of Chemistry, Bhavan's Shree I.L.Pandya, Arts-Science and Smt. J.M.Shah Commerce College, Sardar Patel University, V. V. Nagar, 388120,
Gujarat, India
Department of Physics, Bhavan's Shree I.L.Pandya, Arts-Science and Smt. J.M.Shah Commerce College, Sardar Patel University, V. V. Nagar, 388120, Gujarat,
b
India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 May 2019
Received in revised form
Herein, the synthesis and evaluation of a novel CHEF-PET fluorescence sensor L, based on calix[4]arene
comprising two 1-Naphthoicacid groups as binding sites, is described. The selective nature of this
3þ
3þ
fluorescence probe towards Pr and As has been investigated by emission titration, UVevis titration,
26 August 2019
1
H NMR spectroscopy, FT-IR, PXRD and ESI-MS investigation. The linear concentration range at pH 3.5 of
Accepted 8 September 2019
Available online 12 September 2019
L for Pr3 and As is 0e120 nM and 0e145 nM respectively with the detection limit of 1.45 nM for Pr
3þ
þ
3þ
3
þ
and 1.91 nM for As . Through Benesi-Hildebrand equation, the binding ability was found to be
8
ꢁ1
3þ
8
ꢁ1
3þ
7
.377 ꢀ 10 M for Pr and 7.842 ꢀ 10 M for As . The MOPAC-2016 software package has been used
to optimize the L using PM7 and the molecular docking study has been carried out using HEX software.
2019 Elsevier B.V. All rights reserved.
Keywords:
calix[4]arene
CHEF-PET
©
Computational study
1
. Introduction
appropriate techniques to recognize metal ions through tangible
fluorescence signals. The combination of calix [4]arene and fluo-
rescence signalling technique results into edifice simple, selective
and affordable fluorescence probe.
The family of macrocycles has drawn much attention of many
researchers in past few years for developing different effective
molecular sensors. In the 70s, calixarene [1], a new family member
of macrocycles was isolated and characterized by Gutsche [2] et al.
apart from other members such as cyclodextrins, cucurbiturils,
cryptands and crownethers. Though calixarenes have variety of
derivatives like calix [4]arene, calix [6]arene and calix [8]arene;
calix [4]arene has been counted as the most relevant framework for
constructing ion-selective sensors. By functionalizing calix [4]arene
at its upper and lower rim, the power of encapsulating many
different ions is increased and it works as very effective host
molecule [3e11].
In photoinduced electron transfer (PET), the energy of the
HOMO of the free host lies between those of the HOMO and LUMO
of the excited fluorophore and then electron transfer from the
HOMO of the Host to the hole in the HOMO of the fluorophore takes
place. PET process always follow quenching of emission intensity
when guest molecular ions bind to host. Photoinduced charge
transfer (PCT) mechanism has been involved in those fluo-
roionophore which contain electron withdrawing and electron-
donating substituents, this charge transfer may arise over long
distances and be connected with major dipole moment changes,
making the process particularly sensitive to the microenvironment
of the fluoroionophore. Another class of fluoroionophores, where
intramolecular interaction between a pair of different fluorophores
in which one acts as a donor of excited-state energy to the other
(acceptor). As a result that the donor returns to its electronic
ground state and emission may then occur from the acceptor
center. This process is known as fluorescence resonance energy
transfer (FRET). There are also few other mechanism in calix [4]
arene system such as metal-ligand charge transfer (MLCT), proton
transfer, formation of an excimer and chelation-enhanced fluores-
cence (CHEF) for the molecular recognition [12e22].
2
þ
2þ
2þ
3þ
2þ
Metals such as Fe , Cu , Mn and Zn are present in human
body while Pr3 , La and Nd
whereas water contains As
metals subsist in different forms with different quantities every-
where. This has been inspiring for researchers to develop such
molecular sensors which can detect metal ions easily with its well-
defined binding core. Fluorescence signalling is one the most
þ
3þ
exist in different soil samples
3
þ
2þ
and Hg
as impurities. In short,
*
Corresponding author.
E-mail address: pinkeshsutariya@gmail.com (P.G. Sutariya).
https://doi.org/10.1016/j.molstruc.2019.127053
022-2860/© 2019 Elsevier B.V. All rights reserved.
0

2
P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
Among all lanthanoides, Praseodymium (III) ion is one of the
rare chemical which can be found in house equipment such as
television, fluorescent lamps, energy saving lamps and glass. It is
also used in carbon arc lights in the motion picture industry. It is
predominantly used as an alloying agent with magnesium to create
3þ
high-strength metals which are used in aircraft engines. Pr is
very dangerous in working atmosphere and can cause damage to
reproduction and nervous system of animals [23,24]. Arsenic is a
naturally occurring element that is widely spread in the Earth's
crust. It is found in water, air, food, and soil. Scientists, paediatri-
cians and public health advocates are progressively anxious about
the more subtle and long-range health effects of low-level expo-
sures to humans, especially for infants and children exposed to
arsenic in water and some foods, such as rice-based products,
during sensitive windows of development. Most arsenic gets into
the body through absorption of food or water. Arsenic in drinking
water is a problem in many countries around the world, including
Bangladesh, Chile, China, Vietnam, Taiwan, India, and the United
States. Arsenic affects a broad range of organs and systems
including: skin, nervous system, respiratory system, cardiovascular
system, liver, kidney, bladder and prostate [25e27]. Therefore, it is
necessary to develop receptors which can selectively sense such
ions of vital trace elements and biologically important cations by
spectroscopy.
Fig. 1. Schematic design of synthesized scaffold L.
The requisite of various molecular sensors has driven us to
synthesize different fluorescence receptors for selective recogni-
tion and determination of Zn , Cu , Cd , Sr , Fe , F , phos-
2þ
2þ
2þ
2þ
3þ
ꢁ
2.2. Apparatus
phate ions, L-Tryptophan and L-Histidine [28e34]. Though some
reports are available for the selective recognition of Pr and As
3
þ
3þ
Melting points were taken on Opti-Melt (Automated melting
point system). FT-IR spectra were recorded as KBr pellet on Bruker
by calix [4]arene conjugates, to our knowledge, there is no report in
the literature wherein a single system can sense both ions. Further,
the structural characterization of the species of recognition is
rather scarce in the literature. The probe would be useless if it
ꢁ1
TENSOR-27 in the range of 4000e500 cm . Discover Bench Mate
system-240 V (CEM Corporation) microwave synthesizer was used
for synthesis of p-tertbutylcalix [4]arene. GmbH Vario Micro cube
1
3þ
3þ
elemental analyzer was used for elemental analysis. H NMR
would not be used in real samples of Pr and As . By keeping that
in mind, we have also carried out experiments of our fluorescence
probe in soil samples. The demand of multi-ion selective fluores-
cence probe has motivated us to make a convenient, fast respon-
sive, highly selective and sensitive fluorescence sensor; so here we
are proposing a simple, sensitive and selective system, with fast
response time and low detection limit calix [4]arene linked fluo-
rescence probe Synthetic route for 5, 11, 17, 23-tetra t-butyl-26, 28
dimethoxy 25, 27 dicarboxylate naphthalene calix [4]arene (L) re-
ceptor (Fig. 1, Scheme 1) which displays CHEF-PET phenomenon in
spectra was scanned on 400 MHz FT-NMR Bruker Avance-400 in
the range of 0.5e15 ppm using internal standard tetramethylsilane
(TMS) and deuterated DMSO as a solvent. ESI Mass spectra were
taken on a Shimadzu GCMS-QP 2000A. Emission spectrum was
recorded on Horiba Jobin, Fluorolog, and Edinburgh F900. UVeVis
absorption spectra were acquired on a Jasco V-570 UVeVis. Spec-
trometer. Working standard solutions were prepared daily in
deionized water. The crystalline phase of the synthesized samples
were identified by powder X-ray diffractometer (PXRD), non-
destructive fingerprinting technique (PANalytical X-ray diffrac-
3
þ
3þ
selective recognition of Pr and As
.
tometer), recorded with Cu K
at 40 kV and 30 mA.
a
radiation (
l
¼ 1.54060 Å) operating
2
. Experimental
2.1. Chemicals and reagents
2.3. Real sample preparation
0
All the reagents and chemicals like DCC (N, N -dicyclohex-
For the analytical application of proposed fluorescence probe,
ylcarbodiimide), DMAP (4-dimethylaminopyridine) and 1-
Naphthoicacid were used of analytical grade procured from
Sigma Aldrich. Silica gel (Merck, 0.040e0.063 mm) was used for
column chromatography. Metal salts (99e101% purity of SRL) used
for the studies were their perchlorate salts (Caution: Since
perchlorate salts are known to explode under certain conditions,
we have applied this probe for real sample analysis in soil sample
for Pr and As . For soil sample preparation, we collected soil
samples from industrial area of Anand GIDC, Gujarat, India for
3þ
3þ
analysis. The soil samples were first dissolved in concentrate HNO
3
and stirred for 1 h after then we took 10 mL of solution and diluted
up to 100 mL into volumetric flask. From this solution, we took 2 mL
of solution and 2 mL of our synthesized ligand L for fluorometric
analysis by maintaining pH 3.5 with citric acid buffer. This experi-
these are to be handled cautiously!) with formula, M(ClO
Anions used for the studies were their tetra butyl ammonium salts
99e101% purity of SRL) which were prepared in acetonitrile. Stock
4 2 2
) . xH O.
3þ
3þ
(
ment carried out by using in situ generated Pr and As complex
of L with various soil samples. The concentration range during this
experiment was 0e100 nM. This result authorizes the application of
L as fluroionophore having high sensitivity and specificity towards
solutions of cations and anions (0.01 M) are prepared in acetoni-
trile. Further dilutions are completed as per requirement. Spec-
troscopic properties of L was investigated in mixed aqueous organic
medium [citric acid buffer; pH ¼ 3.5)].
3
þ
3þ
Pr and As detection in soil samples.

P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
3
Scheme 1. Synthetic route for 5, 11, 17, 23-tetra t-butyl-26, 28 dimethoxy 25, 27 dicarboxylate naphthalene calix [4]arene (L) receptor.
2
2
.4. Experimental
.4.1. Synthesis of 5, 11, 17, 23-tetra t-butyl-25, 27 dimethoxy calix
between 250 and 380 nm, the peak at 284 nm indicates p- p*
transition of 1-Naphthoicacid system. This compound shows a
strong luminescence peak at 371 nm in acetonitrile with excitation
[
4]arene
A mixture of p-tert-butyl calix [4]arene A (3.5 g. 0.80 mM),
CO (1.9 g, 14.0 mM) and 1-iodomethane (4 mL, 14.0 mM) in dry
at the absorption maxima (lmax) of the 1-Naphthoicacid moiety,
which is at 200e450 nm.
K
2
3
acetone (150 mL) was stirred for 24 h. The actual reaction time was
considered by taking thin layer chromatography (tlc) at regular
interval of time by using mixture of ethylacetate:hexane (8:2). The
solvent was then evaporated under vacuum and the residue taken
2.6. General screening of fluorescence probe L with various ions
Since our fluorescence probe
L possesses binding cores
(Scheme- 1), the ion-selective properties of L with various cations
2
þ
2þ
2þ
2þ
2þ
3þ
þ
3þ
3þ
2þ
3þ
4þ
2þ
2þ
3þ
3þ
2þ
þ
þ
2þ
up with CH
neutrality and dried over anhydrous Na
2
Cl
2
. The organic phase was washed with 0.1 M HCl up to
SO . After complete
(Zn , Cd , Fe , Fe , La , As , Nd , Zr , Ca , Ce , Li , Ag ,
2
þ
þ
2þ
2
4
Ba ,Co , Hg , Na , K , Cu , Ni , Mn , Cr , Pb and Sr )
evaporation of the solvent, the resulting crude product was purified
by column chromatography (silica gel, hexane: ethyl acetate, 9:1);
have been studied by the fluorescence spectroscopy, absorption
spectroscopy, FT-IR and ESI-MS investigation. The binding affinity
of L with cations was investigated by making stock solutions of the
Solubility: Soluble in CHCl
3
, CH
2
Cl
2
, CH
3
CN and insoluble in H
2
O,
ꢁ8
ꢁ6
Yield 2.9 g (81%). Elemental analysis for C46
H
60
O
4
: C, 81.61; H,
compound L (1 ꢀ 10 M) and that of perchlorate salts (1 ꢀ 10 M)
of aforesaid metal ions prepared in freshly purified acetonitrile as
acetonitrile is miscible with water. Then 2.5 mL stock solution of
the compound and 2.5 mL stock solution of each metal salts were
taken in a 5 mL volumetric flask, so that the effective concentration
of the metal is 100 fold than that of the compound L. Further to
determine the connection of the metal ions with the ionophore, the
spectra of the cations added solutions were compared with that of
the original solution. Spectroscopic properties of L was investigated
in mixed aqueous organic medium [citric acid buffer; pH ¼ 3.5)].
ꢁ1
8
3
.93% Found: C, 81.38; H, 8.52%. FT-IR (KBr) ʋ: 3280 cm (Ar-CH),
ꢁ1
1
430 cm (Ar-OH). H NMR:
d
H
(CDCl
3
,500 MHZ), 1.20 (18H, tbutyl,
, t), 3.83 (4H, ArCH Ar,d),
2
Ar, d), 6.42(4H, AreH, s), 6.85(4H, AreH, s), 9.19 (2H,
s) 0.96(18H, t-butyl, s), 4.28 (4H, eOCH
.30(4H, ArCH
OH, s), m. p. 223-228 C. ESI MS (m/z) 677.1 (Mþ1).
3
2
4
O
2.4.2. Synthesis of 5, 11, 17, 23-tetra t-butyl-26, 28 dimethoxy 25, 27
dicarboxylate naphthalene calix [4]arene (L)
A solution of compound 5, 11, 17, 23-tetra t-butyl-25, 27 dime-
thoxy calix [4]arene (0.5 g), DCC (0.25 g), DMAP (0.15 g) and 1-
naphthoicacid (0.27 g) in DCM solvent was stirred for 48 h. The
actual reaction time was considered by taking thin layer chroma-
tography (tlc) at regular interval of time by using mixture of chlo-
roform: methanol (3.5: 1.5). The solvent was then evaporated under
3. Results and discussion
3.1. Emission titration of L
vacuum. Yield: 0.820 g, (90%). Anal calcd for C68
H
72
O
6
: calcd C,
To examine the spectroscopic properties of ligand L, we have
used mixed aqueous organic medium [citric acid buffer; pH ¼ 3.5)].
Naphthalene has been extensively used as fluorophore for the
detection of molecular ions [35]. Herein, we are proposing a calix
[4]arene-based fluoroionophore armed by two naphthoic acid
groups as binding sites. We have noted an on/off/on fluorescent
effect by using our new ligand L having naphthoic acid as two
armed binding sites. In this ligand L, due to the absence of nitrogen
atom, anions cannot bind with ligand L and do not show any
changes in the fluorescence intensity. That's why, here we have
intentionally neglected anions. In the absence of Pr , the fluores-
cence is partially quenched because of photoinduced electron
transfer (PET) effect. However, studies indicate that this CHEF effect
was perceived due to the inhibition of PET mechanism. The fluo-
rescence spectra of the compound was recorded in acetonitrile in
presence of 100-fold excess of various cations and anions which
ꢁ
1
8
2.89; H, 7.37; O, 9.74. Found: C, 82.61; H, 7.18. FT-IR: 1678 cm
1
(
-C]O), H NMR (400 MHz, DMSO):
H, AreH), 7.61 (dd, 8H, AreH), 7.90 (dd, 4H, AreH), 7.92 (dd, 2H,
AreH), 8.04 (dd, 2H, AreH), 8.22 (dd, 2H, AreH), 8.91 (dd, 2H,
d 7.51 (dd, 8H, AreH), 7.60 (dd,
4
AreH), 8.92 (dd, 2H, AreH), 4.70 (d, 8H, ArCH
eCH ), 1.89 (s, 18H, eC(CH ), 1.38 (s, 18H, eC(CH
found 986 (mþ1).
2
Ar), 3.48 (s, 6H,
), ESI MS (m/z):
3
3
)
3
3
)
3
2.5. Photo physical behaviour
3
þ
Absorption spectra of the newly synthesized lower rim
substituted calix [4]arene dimethoxynaphthoicacid (L) was recor-
ded in all the solvents in which it is soluble, however acetonitrile
was selected for further studies since acetonitrile is miscible with
water. This compound shows absorption peak in the region

4
P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
þ
3þ
3þ
were prepared in acetonitrile. We evaluated the interaction of
As3 with L (Fig. 2 A). Therefore it is predicted that Pr and As
ligand with Pr3 and As in the presence of other cations and
þ
3þ
closely interact with L and cause obvious change in fluorescence
intensities with respect to other large number of cations and an-
ions. Hence, for quantitative analysis we have selected these two
anions. The sensing ability of our fluoroionophore was explored by
ꢁ
6
3þ
3þ
ꢁ8
adding 1 ꢀ 10 M solutions of Pr and As into 1 ꢀ 10 M so-
lution to the fluoroionophore (L). From the fluorescence spectra, we
observed that the intensity of L was enhanced because of CHEF
3
þ
3þ
ions (Pr and As ) for further examination.
effect between L and Pr3 whereas As quenched the fluorescence
þ
3þ
3
.3. Sensitivity of L based CHEF-PET probe
intensity of L via PET.
As sensitivity is a vital part for any chemosensor, fluorescence
þ
3þ
3
.2. Selectivity of Pr3 and As with L based CHEF-PET probe
3þ
titration has pursued by gradually varying the concentration of Pr
3þ
(
0e120 nM) and As (0e145 nM) by keeping the concentration of
To obtain insight into the selective nature of our newly syn-
thesized probe L, we have carried out ion-binding study by using
L constant [Fig. 2 (BeC)]. For the mechanism of emission quench-
ing, sternevolmer plots are worthwhile and that is why they are
used to analyze the nature of the quenching process in the
2
þ
2þ
2þ
3þ
3þ
þ
various perchlorate salts of metal ions (Zn , Cd , Fe , Fe , La
,
3þ
3þ
4þ
2þ
3þ
þ
þ
2þ
2þ
2þ
þ
As , Nd , Zr , Ca , Ce , Li , Ag , Ba , Co , Hg , Na , K ,
3þ
chelating complex L-As . As shown in equation (1), the determi-
2
þ
2þ
2þ
3þ
2þ
2þ
Cu , Ni , Mn , Cr , Pb
and Sr ) with ligand L. In this
nation of dynamic or static quenching process can be examined by
plotting relative emission intensities (I /I) against quencher con-
0
centration [Q] in which the slope of the plotted line yields Ksv (the
static quenching constant).
ꢁ
8
experiment, we have kept equal concentration (1 ꢀ 10 M) for L
and numerous above mentioned perchlorate salts in acetonitrile.
From the emission spectra, depicted in Fig. 2, we observed clear
3
þ
3þ
changes upon addition of Pr and As when it is compared to the
spectra of original ligand L. By contrast, no significant changes were
noticed upon addition of other cations into ligand L. Pr and As
induced enhancement and quenching in the fluorescence intensity
I
I
ο
3þ
3þ
¼ 1 þ Ksv½Qꢂ
(1)
of the ligand L by displaying ON-OFF-ON behaviour. The overall
emission changes were dramatic: 2.25 fold for Pr and 0.001 fold
where Io/I and [Q] are the relative emission intensity and quencher
concentration, respectively.
3
þ
ꢁ
8
2þ
3þ
2þ
2þ
2þ
3þ
2þ
3þ
4þ
2þ
3þ
þ
þ
2þ
þ
þ
2þ
,
Fig. 2. (A): Selectivity plot of L (1 ꢀ 10 M) with various cations from top to bottom (Zn , La , Co , Cd , Mn , Fe , Hg , Nd , Zr , Ca , Ce , Li , Ag , Ba , Na , K , Ni
2
þ
2þ
2þ
2þ
Pb , Sr , Fe and Cu ).

P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
5
In our case, typical linear plots for L-As3þ suggest a pure fluo-
rescence static quenching because of a non-fluorescence ground
(L), respectively. The Pr , As and the standard (L) were excited at
the same wavelength. The quantum yield of fluoroionophore L was
obtained using emission spectra of standard fluorophore (naph-
thalene). The reported quantum yield of naphthalene [38] was
3þ
3þ
3
þ
state complex between ligand L and As . The calibration curve
3
þ
shows good linearity with correlation coefficient of 0.9944 for Pr
and 0.9901 for As3 [Fig. 3 (AeB)]. We have also calculated limit of
detection (LOD) as per 3 IUPAC criteria for synthesized probe from
this emission study. The LOD was found to be 1.45 nM for Pr and
þ
approximately 0.23 and that of L with Pr and As ion complex
were found to be 0.47 and 0.0003 respectively. Thus, when Pr
was attached to L, the quantum yield increases whereas for As
3þ
3þ
3
þ
s
3
þ
3þ
;
1
.91 nM for As3
þ
.
quantum yield decreases. Hence L provides a sensitive means to
3
þ
3þ
recognize Pr and As by direct fluorescence measurement.
3
.4. Binding constant of L based CHEF-PET probe for Pr3þ and As3þ
Binding constants for fluoroionophore were calculated by using
emission titration data following the previously reported articles
36,37]. Here, we have displayed representative spectra showing
the changes observed in emission intensities upon the addition of
increasing concentration of ions. According to this method, the
3
.6. UVevisible experiment
[
In addition to confirm the binding event of probe L, UVevisible
investigation was performed in acetonitrile medium. The free
ligand L displayed a strong absorption band at 284 nm. When Pr
and As (as their perchlorate salts in acetonitrile) were added to
the solution of L, the change in absorption band was observed. The
3þ
fluorescence intensity (F) scales with the metal ion concentration
3þ
n
(
(
[M]) through (F
) is obtained by plotting
0
eF)/(F-F
œ
) ¼ ([M]/Kdiss) . The binding constant
K
s
3þ
3þ
selective nature of probe L towards Pr and As was confirmed by
noticing the change in absorption band from 284 nm to 268 nm and
ðF ꢁ FÞ
0
3þ
3þ
Log
¼ Log ½Mꢂ
278 nm upon addition of Pr and As respectively (Fig. 5AeB).
The change in shift indicates bathochromic shift because of cation
binding with ketonic group of the scaffold. To know the detection
ðF ꢁ F
œ
Þ
where F and F are the relative fluorescence intensities without
0
œ
3
þ
3þ
limit of L towards Pr and As , we have also performed UVevis
titration by varying concentration of selective ions
0 nMe100 nM) (Fig. 5CeD). From this investigation, we can assure
addition of guest metal ions and with maximum concentration of
metal ions (when no further change in emission intensity takes
place), respectively. The value of Log [M] at Log[(F
(
0
eF)/(F-F
œ
)] ¼ 0
that when it is matter of sensitivity and low detection limit, fluo-
rescence technique is more reliable than absorption study.
gives the value of log(Kdiss), the reciprocal of which is the binding
constant (K
s
). The observed binding constant from fluorescence
3
þ
3þ
8
ꢁ1
spectra for Pr
and As
are respectively 7.377 ꢀ 10 M
and
8
ꢁ1
7
.842 ꢀ 10 M (Fig. 4A and B).
3.7. ESI-MS investigation
3
.5. Quantum yield of L with Pr3 and As
þ
3þ
For further binding confirmation of Pr3 and As with ligand L,
we have implemented ESI-MS technique. The complex was dis-
solved in CH CN (3 mL) and 10 equivalent amount of the desired
þ
3þ
The quantum yield was calculated by following equation (2)
3
ðF ꢀ Astd ꢀ
h
Þ
cations as perchlorate salt were added into the solutions. The re-
action mixtures were stirred at room temperature for 2 h, the so-
lutions were then filtered off and the filtrates were analysed by ESI
MS instrument. The formation of 1:1 complex was confirmed by
ESI-MS, where the spectrum shows molecular ion peak m/z at
f ¼ fstd
ðFstd ꢀ A ꢀ stdÞ
h
where F and Fstd are the areas under the fluorescence emission
curves of the Pr3 and As ions complexes with L and only stan-
þ
3þ
3þ
3þ
dard L respectively. A and Astd are the areas under relative absor-
984.53 whereas in the presence of Pr and As show peak at
bance of the Pr3 and As ions complexes with L and standard L at
þ
3þ
1125.44, 1059.45 respectively (Fig. 6AeB). These results will give
3
þ
3þ
the excitation wavelength, respectively.
indices of solvent (acetonitrile) used for the Pr , As and standard
h
and
h
std are the refractive
assurance of binding of Pr and As with L ligand via electrostatic
interaction.
3
þ
3þ
Fig. 3. (AeB): (A) Linearity plots of L (1 ꢀ 10ꢁ M) with Pr (0e120 nM) and (B) As (0e145 nM).
8
3þ
3þ

6
P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
Fig. 4. (AeB): Binding constant plots for (A) Pr3 and (B) As with L ligand from emission titration.
þ
3þ
3
.8. FT-IR comparative analysis
eCH aromatic stretching peak and change in eC]O(ketone) peak
3þ
3þ
in presence of Pr and As will give assurance of effective binding
3
þ
3þ
3þ
3þ
The FT-IR spectra of pure ligand L, L þ Pr and L þ As were
recorded by potassium bromide (KBr) disk method and scanned at
the wave number region 4000-500 cm
comparative experiment was also executed in which the binding
of Pr and As with ligand L was evaluated. The broadening of
of Pr and As with L. [Fig. S2 (ESIy)].
ꢁ
1
.
Moreover, FT-IR
3.9. Effect of pH on L CHEF-PET probe and binding mechanism
For making a chemosensor work effectively, it is also necessary
3
þ
3þ
ꢁ
6
3þ
ꢁ6
3þ
Fig. 5. (A): Absorption spectral changes of L (1 ꢀ 10 M) ligand in the presence of Pr .(B): Absorption spectral changes of L (1 ꢀ 10 M) ligand in the presence of As .(C): The plot
ꢁ
6
3þ
demonstrates the absorption spectral changes of L (1 ꢀ 10 M) in the presence of different concentrations of Pr . (0, 10 nM, .100 nM).(D): The plot demonstrates the absorption
spectral changes of L (1 ꢀ 10ꢁ M) in the presence of different concentrations of As . (0, 10 nM, .100 nM).
6
3þ

P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
7
3þ
Fig. 6. (A): ESI mass spectrum showing the isotopic peak pattern of molecular ion peak for 1:1 complex formed between L and Pr .(B): ESI mass spectrum showing the isotopic
3
þ
.
peak pattern of molecular ion peak for 1:1 complex formed between L and As
to check the nature of ligand L in various pH conditions. As shown
with other competing ions showed an obvious fluorescence
enhancement and quenching as aforesaid technique even in the
presence of other cations and anions. From this competitive titra-
tion, we have determined that other cations are unreactive towards
in [Figs. S3eS4 (ESIy)], the fluorescent ligand L displays maximum
enhancement for Pr3 and quenching for As at pH 3.5. This is due
to C]O linkage which makes it acidic in nature. From this inves-
tigation, we can say that our chemosensor will act effectively in
acidic condition. By performing UVevisible experiment, the stoi-
chiometry of the complex formed (1: 1) has been also derived
based on the Job's plot [Figs. S5eS6 (ESIy)]. The reason behind
enhancement and quenching in fluorescence intensity of ligand L is
þ
3þ
3
þ
3þ
the chemosensor L except Pr
and As . Proposed binding
mechanism through hydrogen bonding and electro static interac-
3
þ
3þ
tion with L ligand by Pr and As is shown in Fig. S7 (ESIy).
3.11. Real sample analysis
that Pr3 and As interact with ketonic group of L ligand.
þ
3þ
This CHEF-PET probe is applied for its important applicability to
3
þ
3.10. Interference study
sense Pr in soil samples by using fluorescence titration and also
confirmed the stability of metal-complex. The standard addition
method was applied to evaluate the validity of the proposed sensor.
Table 1 demonstrates analytical results of them. The result gained
3
þ
From our ion-binding study, we have concluded that Pr
enhanced and As3 quenched the fluorescence intensity of ligand L.
However, it is important to check whether the chemosensor re-
þ
3
þ
with excellent recovery of spiked Pr ranged from 94 to 99%,
proving the validity of the developed technique. Furthermore, this
3
þ
3þ
sponds effectively towards Pr and As in the presence of other
metal ions. In order to identify the real potential ability of our probe
L, we have pursued an interference study. As depicted in Fig. 7, the
3þ
fluoroionophore has been applied for As ion detection from soil
samples and its results are shown in Table 2. The concentration of
each sample was measured by the CHEF-PET sensor, using the
3
þ
3þ
fluorescence response of the chelated complex (L-Pr and L-As
)

8
P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
ꢁ
4þ
8
3þ
2þ
3þ
2þ
3þ
2þ
2þ
2þ
2þ
2þ
Fig. 7. Competitive emission spectra of L (1 ꢀ 10 M) with Pr in presence of other cations (a ¼ Ligand þ Pr , b ¼ a þ Zn , c ¼ a þ La , d ¼ a þ Co , e ¼ aþ Cd , f ¼ aþ Mn
,
,
3
þ
2þ
3þ
3þ
þ
þ
2þ
þ
þ
2þ
g ¼ aþ Fe , h ¼ a þ Hg , i ¼ aþ Nd , j ¼ a þ Zr , k ¼ a þ Ca , l ¼ a þ Ce , m ¼ a þ Li , n ¼ a þ Ag ,o ¼ a þ Ba , p ¼ a þ Na , q ¼ a þ K , r ¼ a þ Ni ,s ¼ a þ Pb ,t ¼ a þSr
2
þ
2þ
3þ
u ¼ a þ Fe , v ¼ a þ Cu and w ¼ a þ As ).
Table 1
3
þ
Results of the determination of Pr in industrial water sample.
Sample
Spiked
Pr (nM)
Found by AAS (nM)
Found by proposed sensor (nM)
Recovery (%)
3
þ
Industrial
Water Sample 1
Industrial
Water Sample 2
Industrial
Water Sample 3
Industrial
10
9.75
9.41
96.51 ± 0.5
98.75 ± 0.6
97.75 ± 0.3
99.2 ± 0.7
20
19.34
28.89
39.46
98.80
19.10
28.24
39.18
98.13
30
40
Water Sample 4
Industrial
100
99.32 ± 0.3
Water Sample 5
yElectronic Supplementary Information (ESI) contains materials and methods, synthesis procedure, 1H NMR spectra, FT-IR spectra graph, pH investigation spectra, Job's plot
and computational work.
ꢃ
calibration method. The proposed technique is compared with re-
0.01 and a counting time of 60s per step. Fig. 8 displayed highly
3þ
3þ
ꢃ
ꢃ
ꢃ
ported methods for determination of Pr and As (Table 3). This
comparison undoubtedly endorses that proposed fluorometric
method is superior to others in terms of sensitivity, selectivity and
intense peaks at 2
q
values 7.68 (012), 28.02 (ꢁ102) and 35.57
3
þ
3þ
(121) of ligand L, metal complexes L þ As and L þ Pr respec-
tively. From the overly of PXRD patterns of metal complexes, new
peaks and shifting of peak was observed due to the presence of
3þ
3þ
binding ability to recognize Pr and As [27,39e43].
.12. Powder X-ray diffraction experiment of L-Pr3þ and L-As3þ
The powder diffraction pattern of the ligand L (C68
3
þ
3þ
As and Pr with ligand L. The lattice parameters of the unit cell
and determination of the space group were calculated using match
program (phase identification from powder diffraction), tabulated
3
3
þ
in Table S1. It reveals that ligand L and As complex belong to the
triclinic system with P1 space group and Pr
crystal system with space group P2
H
72
O
6
),
3þ
has monoclinic
3
þ
3þ
3þ
3þ
L þ As (C68
H O
72 6
As ) and L þ Pr (C68
H
72
O
6
Pr ) are presented
1
/c. Analytical indexing of the
ꢃ
in Fig. 8. The experimental 2
q
range 5.00e80.00 with a step size of
Table 2
3þ
Results of the determination of As in industrial water sample.
Spiked As3 (nM)
þ
Found by AAS (nM)
Found by proposed sensor (nM)
Recovery (%)
Sample
Industrial waste water sample 1
Industrial waste water sample 2
Industrial waste water sample 3
Industrial waste water sample 4
Industrial waste water sample 5
10
20
30
40
100
9.82
9.26
94.29 ± 0.4
97.52 ± 0.2
98.81 ± 0.6
98.91 ± 0.5
99.55 ± 0.3
18.98
29.62
38.81
98.87
18.51
29.27
38.39
98.43

P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
9
Table 3
Comparative table of previously reported method with our developed method.
Method
Recognized ion Linear range
Limit of detection
Ref.
3
3
3
þ
þ
þ
þ
þ
þ
ꢁ3
ꢁ2
ꢁ8
ꢁ6
ꢁ2
ꢁ9
ꢁ2
ꢁ9
Ion Selective electrode
Ion Selective electrode
PVC membrane sensor
Colorimetric sensor
Pr
Pr
Pr
1.0 ꢀ 10 to 1.0 ꢀ 10
M
M
M
7.0 ꢀ 10
6.0 ꢀ 10
5.0 ꢀ 10
7.2 ppb
0.62
20 nM
M
M
27
39
40
41
42
43
e
1.0 ꢀ 10 to 1.6 ꢀ 10
ꢁ8
1.0 ꢀ 10 to 1.0 ꢀ 10
3
As
5.0e100 ppb
3
3
ꢁ1
ꢁ1
ꢁ1
Nanoporous gold microelectrode (Anodic stripping voltammetry) As
10e200
m
g L - 2e30
mg L
mg L
Electrochemical detection
Present method
As
0.002e0.8 mM
3þ
0e120 nM for Pr and 0e145 nM for As 1.45 nM for Pr and 1.91 nM for As
3
þ
3þ
3þ
3þ
3þ
Pr and As
Fig. 8. Comparative PXRD investigation of the ligand L, L with As3 and L with Pr
þ
3þ
.
powder patterns for ligand L, L with As3 and L with Pr were
þ
3þ
of different human estrogen protein structures (2Q6J, 2Q98, 2QAB,
2QGT and 4DMA) from the protein data bank and docked with
ligand L. It was evaluated using molecular dynamics, by their
binding affinities, free energy simulations and relative stabilities.
The energy values obtained by docking study was tabulated in
Table S5 revealing the best ligand structure fitting was due to 4DMA
summarized in Tables S2eS4 respectively. The PXRD investigation
will give assurance of cationic (Pr and As ) binding of with
ligand L with 1:1 stoichiometry.
3
þ
3þ
3.13. Computational investigation
(
ꢁ400.05 kcal/mol) compare to other receptors. The molecular
docking pose of 2Q6J, 2Q98, 2QAB, 2QGT and 4DMA with molecule
L as shown in Fig. S9 (ESIy). The docking results will give potential
application of L for protein receptor of human lung cancer cell
The important intended of computational experiment is to
optimize geometry of title molecule L using molecular orbital
package (MOPAC) software [44,45]. This semi-empirical approach
was carried out by creating a Z-matrix of the molecule which was
then converted to its MOPAC input data. Optimization of these data
had provided the specific bond distance, bond angle and dihedral
angle of the most stable molecular geometry. The heat formation
energy was generated ꢁ145.21 kcals/mole using PM7 method.
MOPAC calculations generated visual models of the most stable
molecular geometry in ball and stick configuration as shown in
Fig. S8 (ESIy).
3þ
3þ
4
DMA apart from recognition and determination Pr and As .
4. Conclusion
In summary, we have successfully synthesized and character-
ized a lower rim functionalized calix [4]arene armed with two
naphthoicacid groups which work as fluorogenic units. The probe
displays CHEF-PET phenomena. The sensing properties of our
fluorescence probe is confirmed by fluorescence titration as well as
UVevis titration and competitive study. Proposed fluorescence
probe has lower sensing limit as well as high selectivity towards
3.13.1. Molecular docking study
Molecular docking of the free ligand (L) with different receptors
3
þ
3þ
has done by Hex 8.0 software. Docking is the process of fitting
together of two molecules in 3-dimensional space. It explored ways
in which two molecules, such as drugs and protein receptor fit
together and docked to each other well. The molecule binding to a
receptor, inhibits its function, and thus acts as drug. The collection
1.45 nM for Pr
and 1.91 nM for As . Binding constants with
strongly interacting ions were determined by fluorescence titration
via PET and CHEF mechanism. The possible molecular structure of
3
þ
3þ
the Pr and As complex is proposed on the basis of ESI-Mass, FT-
IR and PXRD. Furthermore, the present system has been applied for

10
P.G. Sutariya et al. / Journal of Molecular Structure 1200 (2020) 127053
different soil samples for selective determination of Pr3þ and As3þ
with 94e99% recovery. The molecular docking results displayed
that the good interaction between title molecule L and protein
receptor of human lung cancer cell 4DMA with energy value
of ꢁ400.05 kcal/mol. This highly sensitive, selective, easy and cost-
effective fluorometric method will provide great interest for
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Acknowledgement
10.1021/ic050702v.
P. G. Sutariya would like to acknowledge Department of Science
and Technology - Science and Engineering Research Board (DST-
SERB) for providing financial assistance under Young Scientist
Scheme (YSS/2015/001258) (New Delhi).
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