Calix[4]arene based highly efficient fluorescent sensor for Au3+ and I-

Article abstract of DOI:10.1007/s10895-015-1642-x

This approach disclose the selective fluorogenic ion sensing ability of 5,11,17,23-tetratertbutyl-25,27-bis((2hydroxynaphthylimino)1,2-ethylenediaminecarbonylmethoxy)-26,28 dihydroxycalix[4]arene (C4NSB). Binding property of receptor probed by using selected various cations and anions with conferring of results that demonstrates 'turn-off' fluorescence response and significantly high chromogenic selectivity toward Au³⁺ and I^-. Furthermore, selective nature of receptor was investigated in the presence of different co-existing competing ions. The limit of detection (LOD) for Au³⁺ and I^- was determined as 1.5∈×∈10^-5 and 4.5∈×∈10^-6 M respectively. Receptor C4NSB form (1:1) stoichiometric complex with both ions and their binding constants were calculated as 8.0∈×∈10² for Au³⁺ and 15.6∈×∈10² M^-1 for I^-. Complexes were also characterized through FT-IR spectroscopy.

Full text of DOI:10.1007/s10895-015-1642-x

J Fluoresc
DOI 10.1007/s10895-015-1642-x
ORIGINAL ARTICLE
Calix[4]arene Based Highly Efficient Fluorescent Sensor for Au3+
and I−
Shahabuddin Memon1 & Ashfaque Ali Bhatti1 & Asif Ali Bhatti1 & Ümmühan Ocak2
&
Miraç Ocak2
Received: 28 March 2015 /Accepted: 6 August 2015
#
Springer Science+Business Media New York 2015
Abstract This approach disclose the selective fluorogenic
ion sensing ability of 5,11,17,23-tetratertbutyl-25,27-
b i s ( ( 2 h y d r o x y n a p h t h y l i m i n o ) 1 , 2 -
e t h y l e n e d i a m i n e c a r b o n y l m e t h o x y ) - 2 6 , 2 8
dihydroxycalix[4]arene (C4NSB). Binding property of recep-
tor probed by using selected various cations and anions with
conferring of results that demonstrates ‘turn-off’ fluorescence
response and significantly high chromogenic selectivity to-
ward Au3+ and I−. Furthermore, selective nature of receptor
was investigated in the presence of different co-existing com-
peting ions. The limit of detection (LOD) for Au3+ and I− was
determined as 1.5×10−5 and 4.5×10−6 M respectively. Recep-
tor C4NSB form (1:1) stoichiometric complex with both ions
and their binding constants were calculated as 8.0×102 for
Au3+ and 15.6×102 M−1 for I−. Complexes were also charac-
terized through FT-IR spectroscopy.
has remained in keen interest because they controls important
functions in living systems and have an extremely toxic im-
pact on the environment [1–5]. Gold ions are known as inhib-
itors of macrophages and polymorphonuclear leucocytes [6]
and to suppress inflammation in rheumatic joints [7]. Au3+ has
highly toxic effects to DNA and the nervous system [8] and
subsequently damages DNA via catalytic cleavage [9].
On the other hand I− is biologically important anion and is
significant micronutrient which plays a key role in many phys-
iological activities such as brain development, metabolism,
neurological functions and thyroid gland activity [10]. It is
essential element for life and biosynthesize thyroid hormones
which is necessary for metabolism and mental growth [11].
However, its deficiency leads severe delays in neurological
development, cretinism and endemic goiter while an exces-
sive ingestion can also cause hyperthyroidism [12]. Accord-
ingly, selective sensing of these ions would be very useful for
the development of cellular imaging probes and other pur-
poses in various biological and environmental fields. Molec-
ular recognition is a crucial process in biological systems,
such as enzymes, antibodies or genes and is fundamental to
supramolecular chemistry [13–15]. The development of pow-
erful and highly selective chemosensors for the detection of
ions have continuously been charming zone of supramolecu-
lar chemistry [16–18]. Among them fluorescent
chemosensors are very important due to instantaneous, remote
and constant analytical measurements, allowing increased
sensitivity and selectivity against competing analytes, reduced
instrumental drift and miniaturization capabilities which are
reliable and low cost [19]. It is one of the most promptly
emerging fields in biology and medicine, which opens the
door for molecular probes in vitro and in vivo monitoring of
biologically relevant analytes [20]. This method of detection
requires fluoroionophores, which are composed of an ion rec-
ognition unit, known as ionophore, and a fluorogenic unit as a
.
.
.
.
Keywords Calix[4]arene Fluorescent LOD Complex
FT-IR spectroscopy
Introduction
Selective and sensitive determination of biologically and en-
vironmentally relevant cations and anions by chemosensors
* Shahabuddin Memon
shahabuddinmemon@yahoo.com
1
National Center of Excellence in Analytical Chemistry, University of
Sindh, Jamshoro 76080, Pakistan
2
Department of Chemistry, Faculty of Sciences, Karadeniz Technical
University, Trabzon 61080, Turkey

J Fluoresc
probe, the photophysical property of which perturbs during
the recognition process producing changes in luminescent
emission [21]. Recently there has been momentous advance-
ment in exploitation of supramolecules for the development of
novel fluorescent sensors. Calix[4]arene has been widely
employed as the basic molecular scaffold for the development
of many fluorescent chemosensors. Their macrocyclic core
being accessible in a variety of sizes, easily pre-organised into
a number of flexible three dimensional topographies and read-
ily selectively functionalized for the introduction of
iopnopores make them perfect structural platforms for molec-
ular design to generate fluorescent receptors [22]. These
metacyclophanes are versatile ionophores, which provide a
platform for attachment of convergent binding groups to de-
velop complexing host molecules primarily for cations, anions
and small molecules [23–29].
internal standard at room temperature. Thermo Nicollet AV-
ATAR 5700 FT-IR spectrometer was used for recording
IR spectra within a spectral range from 4000 to
400 cm−1. Analytical TLC was performed on pre-coated
silica gel plates (SiO2, Merck PF254). Absorption spectral
investigation of C4NSB and its complexes were per-
formed on a Perkin Elmer Lambda-35 double beam spec-
trophotometer using standard 1.00 cm quartz cells where-
as emission spectra were recorded on a Photon Technol-
ogies International Quanta Master Spectrofluorimeter
(model QM-4/2006).
Synthesis of 5,11,17,23-tetratertbutyl-25,
27-bis((2hydroxynaphthylimino)
1,2-ethylenediaminecarbonylmethoxy)-26,28
dihydroxycalix[4]arene (C4NSB)
Moreover, presence of ligating groups determines
their selective nature for efficient recognition of cations
and anions. The introduction of signaling functioinality
such as ether, amide, Urea, Thiourea, Schiff bases and
also pyrene, anthracene, naphthalene and densyl as
fluorophores that selectively recognize both metals and
anions [30–36]. Significant research has devoted for the
development of selective fluorescent chemosensors of
Au3+ and I− [37–45]. But calix[4]arene based fluores-
cent chemosensors are rare. Keeping in view the above
approaches and in continuation of our efforts for the
exploration of calix[4]arenes as selective and efficient
sensors [46–51]. Herein we report the newly synthesized
2-hydroxynaphthaldehyde functionalized calix[4]arene
Schiff base (C4NSB) as florescent sensor Au3+ and I−.
Synthesis of compounds 1, 2 and 3 is depicted in Scheme 1
was carried out by following reported procedures [52–54] and
finally receptor C4NSB was synthesized by treating (0.087 g,
0.50 mmol) solution of 2-hydroxynaphthaldehyde in absolute
ethanol and was added drop wise into a stirring solution of
calix[4]arene (3) (0.30 g, 0.252 mmol) in ethanol (30 ml). The
reaction contents were allowed to stirring for overnight at
room temperature followed by continuous refluxing for
78 h. The reaction was monitored by TLC and FT-IR. The
precipitate was filtered off and filtrate was concentrated at
reduced pressure to yellow solid powder. The solid masses
were washed with ethanol and the residue obtained was fur-
ther recrystallized from THF to furnish compound C4NSB.
Yield (0.150 g, 0.121 mmol, 67 %); m.p. 395 °C, FT-IR
(KBr):3360 cm−1 (OH), 1635 (CO-NH), 1615 (C=N), 1483,
1426, 1364, 1315, 1246, 1200 and 1190 cm−1 (C-O), and (C-
N); 1HNMR (400 MHz, DMSO, TMS, ppm): δH: 1.02 (18 H,
s, t-Bu), 1.26 (18 H, s, t-Bu), 3.65 (4H, d, J=13.2 Hz, ArCH2-
Ar), 3.90 (4 H, m, NHCH2CH2NHCOThio), 4.20 (4H, m,
NHCH2CH2NHCOThio), 4.40 (4H, s, OCH2CO), 4.49 (4H,
d, J=13.2 Hz, ArCH2Ar), 5.5 (2H, s, Ar-OH), 7.08 (4H, s,
ArH), 7.12 (4H, s, ArH), 7.20 (2H, s, Ar-OH), 7.21 (2H, t, Ar
naphth), 7.26 (2H, d, Ar naphth), 7.30 (2 H, t, Ar naphth),
7.59 (2 H, t, Ar naphth),7.63 (2 H, m, Ar naphth), 7.86 (2 H,
d, Ar naphth), 8.11 (2H, s, N=CH), 8.29 (4H, s, NH), 30.3,
31.6, 32.8, 39.9, 40.6, 48.1, 55.9, 112.4, 119.2, 122.6, 124.6,
126.5, 128.0, 129.2, 129.7, 132.1, 138.8, 148.3, 158.4, 160.6,
164.1, ESI-MS (m/z): 1187.6 [(M+1)+], Anal. Calc. for
C70H80N4O6; C, 70.82; H, 6.74; N, 4.72; Found: C, 70.38;
H, 6.71; N, 4.69 %.
Experimental
Chemicals
All reagents and solvents of standard analytical grade
were purchased from Alfa Aesar (Germany), Merck
(Darmstadt, Germany) and were used without further
purification. Standard salt solutions of metals were pur-
chased from Sigma and Aldrich. All aqueous solutions
were prepared with deionized water that was passed
through a milli pore milli Q Plus water purification
system.
Instrumentation
Melting points were determined on a Gallenkamp (UK) appa-
ratus in a sealed capillary tube. Elemental analyses (CHNS)
were performed using Flash EA 1112 elemental analyzer.
NMR spectra were recorded with an Agilent 400 MHz spec-
trometer in DMSO using tetramethylsilane (TMS) as an
Synthesis of Complexes with C4NSB
Solid state complexes of C4NSB with Au3+ and I− were syn-
thesized in the same molar ratio determined by job’s plot.
Saturated solutions of C4NSB in ethanol were prepared in

J Fluoresc
Scheme 1 Synthesis of C4NSB
(I) HCHO/NaOH (II)
BrCH2COOCH3/K2CO3 (III)
NH2C2H4NH2 (IV) 2-
(II)
(I)
hydroxynaphthaldehyde
HO
OH
OH
HO
HO
HO
OH
O
O
O
O
H3CO
OCH3
(III)
HO
OH
O
O
O
O
NH
HN
(IV)
N
N
HO
O
OH
O
O
CH
HC
O
OH
HO
NH
HN
H2N
NH2
round bottom flasks separately. Stoichiometric amount of
Au3+ and I− were added into each respective reaction flask.
The mixture was stirred at room temperature for 24 h. Solution
was filtered off and volume was abridged to small at reduced
pressure. The mixture was poured on petri dish to dry at room
temperature. The resultant crystals were dried in vacuum oven
and used for characterization.
Results and Discussion
UV-visible Study
Selective nature of receptor for particular ion makes it a robust
chemosensor. In this regard the absorptive and fluorescent
behavior of receptor was examined upon addition of various
metal ions. To examine the chromogenic behavior and selec-
tivity of C4NSB titration experiments were carried out in Et-
OH+H2O system for selected series of mono, di and tri valent
cations such as Li+, Na+, K+, Rb+, Cs+, Ag+, Ba2+, Ca2+,
Mn2+, Mg2+, Sr2+, Ni2+, Cd2+, Co2+, Cu2+, Hg2+, Pb2+,
Zn2+, Pd2+, Fe2+, Fe3+, Cr3+, As3+, Sb3+, Au3+, Tl3+, V3+
and W3+. Preliminary examinations reveal that free ligand
C4NSB exhibit three less intensive characteristics bands at
318, 375, 420 nm. These absorption bands ascribe to the
π-π* and n- π* transitions respectively due to the excitation
of lone pair and aromatic π electrons (Fig. 1). There was
minimal variations occurring and only a slight enhancement
in the absorption intensity of C4NSB was observed upon ad-
dition of different metal ions except W3+ which also brought
about very minimal change in it’s behavior. Contrary to this, a
prominent change was observed in the absorption behavior of
C4NSB by the addition of Au3+. The band at 420 nm
completely disappeared and the bands at 318, 375 nm merged
together to a single sharp higher absorption intensity band at
325 nm. Consequently the band at 318 nm red shifted to
325 nm (Fig. 1). These spectral changes of C4NSB-Au3+
UV-visible and Fluorescence Procedure
Sensing ability and selectivity of C4NSB toward different
metals and anions were monitored by using UV-visible and
fluorometer. Stock solution of ligand (2.6×10−3 M) was pre-
pared in 25 mL of ethanol and followed by dilution to (2.6×
10−5 M) into 100 ml. emission response of receptor C4NSB
was estimated through titration experiments in a binary sol-
vent system of Et-OH+H2O (1:1 v/v). In 10 ml test tubes, 2 ml
of ligand (2.6×10−5 M) and 2 ml of metal salts (2.6×10−4 M)
were mixed together. Final concentration of both receptor and
metals in 4 ml of mixture was calculated as (1.3×10−5 and
1.3×10−4 M) respectively. Four milliliters of mixture contain-
ing 10 M equivalents of each metal and absorbance was mea-
sured using a 1 cm absorption cell. Emission intensities of
C4NSB were measured at excitation wavelength 330 nm for
metals and anions at room temperature. Interference study of
co-existing ions was carried out by using 10 equivalents (1.3×
10−4 M) of all ions mixed into C4NSB complexes solution as
described above.

J Fluoresc
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
complex from 290 to 400 nm could be assigned due to the
involvement of π-electrons of (C=N) imine aromatic rings
and lone pair of electrons present on oxygen/nitrogen with
Au3+ and O/N to metal charge transfer took place when
Au3+ contacts with 2-hydroxynaphthalimide moiety of
C4NSB [55].
Characteristics binding ability of C4NSB for different an-
−
−
2−
ions like of F−, Cl−, Br−, I−, CO32−, HCO3 , CH3CO2 , SO4
,
HSO4 , CN−, SCN−, NO3 , ClO4 , Cr2O72− and S2O72− also
investigated under same conditions (Fig. 2). The distinctive
UV-visible absorption changes were recorded upon the addi-
tion of anions into C4NSB (1.3×10−5 M). Different anions
produce slight variations in spectral properties of receptor.
However, a dramatic change was observed in spectral re-
sponse of C4NSB on addition of I− which caused emergence
of two new bands at 296 and 366 nm in the visible region.
While hyper chromic effect along with blue shift was ob-
served in the bands at 318, 375 and 420 nm. These bands
shifted ≈23 and 9 nm to shorter wavelength region respective-
ly. This mode of interaction of C4SB-I− complex can be ex-
plained by the hydrogen bonded interaction between hydroxyl
protons (−OH) of C4NSB and I−. This response suggests very
strong and selective affinity of C4NSB toward Au3+ and I−.
Correspondence of functional groups along with thermody-
namic stability, ionic radii, cavity size as well as geometry of
ligand and ions are also important aspects for specificity which
confers the affinity of receptor toward a both Au3+ and I−.
−
−
−
240
290
340
390
440
Wavelength
Fig. 2 Absorption spectra of C4NSB (2.6×10−5 M) and C4NSB with
different anions (10 eq.) in Et-OH+H2O (1:1 v/v)
The emission intensity remarkable quenched up to 59 fold
(Fig. 3). This distinctive result obtained after Au3+ addition
among series of various cations confirms the C4NSB as Au3+
selective potential probe. The decrease in fluorescence inten-
sity during complexation is attributed to deactivation of ICT
process occurring between the 2-hydroxy naphthalene moiety
and the imine functional group site. Upon contact of Au3+
within C4NSB cavity O and N drift their electrons to Au3+
and thus diminish ICT process by reducing the delocalization
into naphthalene ring.
Similarly more investigations were also carried out to eval-
uate fluorogenic selectivity of C4NSB toward I−. Fluores-
cence ability of receptor for aforementioned anions were scru-
tinized and resultantly no any prominent changes in the fluo-
rescent spectra of receptor were noticed on titration with dif-
ferent anions except I− that caused quenching in fluorescence
response. Discriminating response of C4NSB for I− was
reflected by prominent fluorescent changes in the behavior
of receptor as the strong emission band at 360 nm was effec-
tively quenched upon addition of (10 eq.) of I−, i.e. consider-
able reduction in the emission intensity up to 95 fold followed
which was ascribed to C4NSB–I− complex (Fig. 4).
Fluorescence Study
Fluorescence sensing ability of C4NSB toward aforemen-
tioned different biological crucial and noxious metals was
investigated under similar conditions at excitation wavelength
of 330 nm as shown in (Fig. 3). Fluorescence response of
receptor C4NSB did not produce any significant distinctions
upon interaction with different metals. However receptor
demonstrated prominent change in fluorescence intensity on
interaction with Au3+ that causes quenching in its response.
Since receptor C4NSB contains 2-hydroxy naphthalene
and phenyl fluorophore rings along with imine functional
2000000
1600000
1200000
800000
400000
0
0.5
0.4
0.3
0.2
0.1
0
340
390
440
490
240
290
340
390
440
Wavelength
Wavelength
Fig. 1 Absorption spectra of C4NSB (1.3×10−5 M) with different metals
(10 eq.) in Et-OH+H2O (1:1 v/v)
Fig. 3 Fluorescence spectra of C4NSB (1.3×10−5 M) and with different
metals (10 eq.) in Et-OH+H2O (1:1 v/v)

J Fluoresc
group having N and O electron donating atoms that exhibit
strong fluorescence intensity at 360 nm. The higher intensive
response is due to the fact of Au3+ that is a heavy metal ion or
the C=N isomerization and ICT effect in C4NSB may be
inhibited upon coordination of receptor with Au3+. Fluores-
cence quenching of receptor may be recognized due to the
enhancement of spin-orbit coupling on interaction with Au3+
ion [56, 57]. The heteroatoms (N, O) share their electrons
toward Au3+ and decrease the electronic density into
naphthaldehyde rings and thus weaken the ICT mechanism
over C=N imine group. This quenching effect demonstrates
effective on–off fluorescent behavior. While in the case of I−
large fluorescence quenching was observed that is
distinguishing feature of C4NSB for the fluorometric
sensing of I− among rest of the anions. The hydroxyl
protons engaged in hydrogen bonding with I−. Such
interaction increases the electron density on hydroxyl
oxygen atom and increase electronic charge within
fluorophore rings. Consequently enhanced fluorescence
intensity of C4NSB is drastically quenched on interac-
tion with I−.
Further investigation about quantitative analytical mea-
surement of C4NSB was executed as a function of emission
profiles on increasing ions concentration. There were spectral
variations noticed by the gradual increment of Au3+ and I−
concentration Increasing concentration of metal ion up to 10
equivalents to receptor (1.3×10−4 M) caused gradual
quenching in fluorescence intensity of C4NSB at 360 nm
for Au3+ (Fig. 5). Similarly in the case of I− fluorescence
emission intensity of receptor also quenched with respect to
increasing molar concentration that caused stable decrease in
emission intensity (Fig. 6). This quenching effect of
complexes is due to the strong interaction of C4NSB
with Au3+ as well as I− and subsequently decrease
ICT on coordination. Thus C4NSB demonstrates clear
‘turn-off’ fluorescence response and significantly high
chromogenic selectivity toward Au3+ and I−. Detection
limit and limit of quantification was calculated from the
1500000
1000000
500000
0
y = -81520x + 1E+06
²
R = 0.987
0
2
4
6
8
10
[Au3+]
Fig. 5 Calibration Plot of quenching behavior of C4NSB (1.3×10−5 M)
versus increasing amounts (0→ 10 eq.) of Au3+ in Et-OH+H2O (1:1 v/v)
fluorescence intensity as a function of concentration
added and was found as 1.5×10−5, 5.2×10−5 for Au3+
and 1.3×10−6, 4.5×10−6 for I− respectively. This suffi-
ciently low detection limit of these ions is helpful for
determination in many chemical systems. The associa-
tion constant Ka of C4NSB for Au3+ and I− was calcu-
lated on the basis of the Benesi–Hilderbrand plot [58].
It was found to be 8.0×102 for Au3+ and 15.6×102 M−1
for I−. The stoichiometric ratio of the complexes was
determined by Job’s plot [59] at 360 nm and it was
found to be 1:1 for both C4NSB-Au3+ and I− com-
plexes (Fig. 7a and b). Hence, all of these results con-
firmed that C4NSB has remarkably high selectivity and
sensitivity towards Au3+ and I− ions.
Efficient and selective sensing property of C4NSB was
further explored by examining the effect of co-existing ions.
Competitive experiments were carried out with 10 equivalents
of other different metal and anions mixed with complexes
solution of same concentration. The fluorescence responses
of C4NSB–Au3+ and I− complexes remained same in compar-
ison to other metal ions and did not cause any disturbances in
their fluorescence response. Interference study of com-
plexes was further visualized by using ratiometric fluo-
rescence behavior (I/IO) as shown in (Fig. 8). Selective
3000000
2500000
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1500000
1000000
500000
0
1500000
1000000
500000
0
y = -64780x + 1E+06
²
R = 0.984
340
390
440
490
0
2
4
6
8
10
Wavelength
[I-]
Fig. 4 Fluorescence spectra of C4NSB (1.3×10−5 M) and with different
anions (10 eq.) in Et-OH+H2O (1:1 v/v)
Fig. 6 Calibration Plot of quenching behavior of C4NSB (1.3×10−5 M)
versus increasing amounts (0→ 10 eq.) of I− in Et-OH+H2O (1:1 v/v)

J Fluoresc
a
1.00E+00
8.00E-01
6.00E-01
4.00E-01
2.00E-01
0.00E+00
3
2.5
2
1.5
1
0.5
0
Interfering Anions
Fig. 9 Fluorescence intensities change ratio [I/Io] of C4NSB-I− (1.3×
10−5 M) at 330 nm upon addition of different metal ions (10.0 eq.) in Et-
OH+H2O (1:1, v/v)
0
0.2
0.4
0.6
0.8
1
Mole Fractions
b
3
2.5
2
Volmer plots are a useful method of presenting data
on emission quenching. Plotting relative emission in-
tensities (Io/I) against quencher concentration (metals)
yields a linear Sterne Volmer plot for a static
quenching process. These results are consistent with
static quenching. The static quenching constants
(Ksv) were found as 8.3×102, 1.3×102 for Au3+ and
I− (Fig. 9).
1.5
1
0.5
0
0
0.2
0.4
0.6
0.8
1
Mole Fractions
Fig. 7 a Job’s Plot of C4NSB-Au3+ complex b C4NSB-I−
Proposed Interaction
Since the receptor C4NSB containing O and N present
in hydroxyl, amide and imine functionality as soft
binding site that donate their electron pair to soft acid,
i.e. Au3+ and hydroxyl protons share hydrogen bond-
ing with I−. These interactions help to accommodate
guest ions into receptor’s cavity. Furthermore, thermo-
dynamic stability, ionic radii, cavity size as well as
geometry of receptor are central features for selective
affinity of C4NSB for both ions. On this basis pro-
posed binding mode of C4NSB for Au3+ and I− is
shown in (Fig. 10).
nature of C4NSB toward Au3+ and I− was remained
almost same by the involvement of other co-existing
ions and these findings confirmed the remarkable selec-
tive nature of C4NSB for Au3+ and I−.
Sterne Volmer Analysis
The quenching nature of the complexes was further
probed by using SterneVolmer plots [46]. Sterne
0.99
0.97
0.95
0.93
0.91
Interfering cations
Fig. 8 Fluorescence intensity change ratio [I/Io] of C4NSB-Au3+ (1.3×10−5 M) at 330 nm upon addition of different metal ions (10.0 eq.) in Et-OH+
H2O (1:1, v/v)

J Fluoresc
HO
OH
O
O
HO
OH
O
O
HO
OH
O
O
O
O
O
O
O
O
NH
HN
NH
NH
HN
HN
N
N
N
N
N
N
CH
HC
CH
CH
HC
HC
OH
OH
HO
OH
HO
HO
Fig. 10 Proposed structure of complexes
FT-IR Study
to metal-nitrogen/oxygen stretching and bending vibra-
tions give clear indication for involvement of nitrogen
oxygen and π electrons with Au3+. While on complex-
ation I− some evidences also suggest strong host -
guest interaction (Fig. 11b). Similarly after complexa-
tion there was a broad band observed from 3740 to
3300 cm−1 because of hydroxyl protons make hydrogen
FT-IR helps to deeply understand the interaction modes
between different functional groups. Selectivity of
C4NSB toward toxic Au3+ and I− was characterized
by using FT-IR spectroscopy. Receptor C4NSB shows
various characteristic stretching and bending bands as
shown in (Fig. 11a). The bands indicate the existence
of various functional groups in calix[4]arene moiety
such as 3360 cm−1 for O-H, 1635, 1552 and
1615 cm−1 are stretching bands for carbonyl (amide)
and C=N (imine) functionalities respectively. 1483, and
1426 cm−1 implies to C-O-H and 1364 cm−1 C-N, 1315,
1304 and 1246 cm−1 represents C-N, C-O, 1200,
1190 cm−1 C-N, 1127, 1050 and 873, 865, 830,
775 cm−1 for C-O-C of calix[4]arene rings.
bonding with I− Moreover, the band position at 3360
.
shifted to 3462 cm−1. Carbonyl band at 1635 cm−1
changed its position to 1615 cm−1 besides this intensity
of bands at 1504, 1200 increased along with blue
shifted to 1483 and bands at 1246, 1127 become less
intensive. Furthermore new bands appeared at 1525,
1395, 948, 818 and 783 cm−1 as result of strong inter-
action with I− (Fig. 11c). These spectral changes strong-
ly support the formation C4NSB- I− complex. The se-
lective sensing response of C4NSB for Au3+ and I− is
significantly demonstrated by disappearance and ap-
pearance of new bands of specific functional groups
occurred as a result of guests’ introduction into recep-
tor’s cavity.
After complexation with Au3+ carbonyl bands at
1635, 1552 cm−1 is slightly blue shifted to 1657,
1570 cm−1 respectively. Beside this, the band at
1364 cm−1 decrease in intensity along with red shifted
to 1352 cm−1. These changes are informative sign due
120
Fig. 11 FT-IR spectra of a)
C4NSB b) C4NSB-Au3+ c)
C4NSB-I−
100
a
1635
80
3360
b
60
c
1352
1657, 1570
40
20
1615
3462
1483
1200
0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber cm-1

J Fluoresc
13. Steed JW, Atwood JL (2000) Supramolecular chemistry. John
Wiley and Sons, Chichester
Conclusion
14. Schneider HJ, Yatsimirsky A (2000) Principles and methods in
supramolecular chemistry. John Wiley and Sons, Chichester
15. Wang R, Bu J, Liu J, Liao S (2008) Calix[4]arene based selective
fluorescent chemosensor for organic acid recognition. Front Chem
Chin 3:348–352
16. Czarnik AW (1992) Fluorescent chemosensors for ion and mole-
cule recognition; ACS Symposium Series 538. American Chemical
Society, Washington, DC
17. De Silva AP, Gunnlaugsson T, McCoy CP (1997) Photoionic
supermolecules: mobilizing the charge and light bridges. J Chem
Educ 74:53–58
18. Bodenant B, Weil T, Businelli-Pourcel M, Fages F, Barbe B, Pianet
I, Laguerre M (1999) Synthesis and solution structure analysis of a
bispyrenyl bishydroxamate calix[4]arene-based receptor, a fluores-
cent chemosensor for Cu2+ and Ni2+ metal ions. J Org Chem 64:
7034–7039
A fluorescence and chromogenic sensing ability of newly
synthesized receptor, i.e. C4NSB was explored for efficient,
rapid and selective sensing of Au3+ and I− Receptor exhibited
.
a high affinity and selectivity for Au3+ and I− relative to most
of the other competent co-existing ions by remarkable change
in spectral response. Moreover complexes of C4NSB with
Au3+ and I− were characterized by using FT-IR spectroscopy.
Since the geometry and ideal binding sites containing N, O
and C=N in C4NSB possessing conformity in size, nature,
and lodging helps to accommodate both ions. We expect that
present strategy and photo physical properties of this fluores-
cent chemosensor will help to extend applications for both
Au3+ and I−.
19. Park SM, Kim MH, Choe JI, No KT, Chang SK (2007) Cyclams
bearing diametrically disubstituted pyrenes as Cu2+ and Hg2+ selec-
tive fluoroionophores. J Org Chem 72:3550–3553
Acknowledgments We thank the National Center of Excellence in An-
alytical 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.
20. Bonacchi S, Genovese D, Juris R, Montalti M, Prodi L, Rampazzo
E, Sgarzi M, Zaccheroni N (2011) Luminescent chemosensors
based on silica nanoparticles. Top Curr Chem 300:93–138
21. Subrata P, Ravi G, Lo R, Suresh E, Bishwajit G, Parimal P (2012)
Cation-induced fluorescent excimer emission in calix[4]arene-
chemosensors bearing quinoline as a fluorogenic unit: experimen-
tal, molecular modeling and crystallographic studies. New J Chem
36:988–1002
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