Design, synthesis and evaluation of a new calix[4]arene based molecular receptor for multiple ion selectivity

Article abstract of DOI:10.1007/s10847-014-0432-4

The hydrophobic and conformational motifs of calix[4]arene stereostructure and plausible binding characteristics of heterocyclic 2-oxo-1,2-dihydroquinoline-4-carbohydrazide have been deployed for the design and synthesis of a new molecular receptor, 4 for multi-ion recognition. The target molecule was synthesized through the condensation of 3 with 2-oxo-1,2-dihydroquinoline-4-carbohydrazide (6) in refluxing ethanol. It has been determined that 4 exhibits an exclusive color change from colorless to yellow as well as a 5.5 fold increase in the fluorescence intensity upon interaction with fluoride due to formation of multiple hydrogen bonds. Consequent to fluoride induced deprotonation, 4 displays a dual selectivity for Cu²⁺ and Ni²⁺ ions from amongst plethora of investigated cations.

Full text of DOI:10.1007/s10847-014-0432-4

J Incl Phenom Macrocycl Chem
DOI 10.1007/s10847-014-0432-4
ORIGINAL ARTICLE
Design, synthesis and evaluation of a new calix[4]arene based
molecular receptor for multiple ion selectivity
•
Har Mohindra Chawla Tanu Gupta
Received: 15 January 2014 / Accepted: 26 June 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract The hydrophobic and conformational motifs of
calix[4]arene stereostructure and plausible binding charac-
teristics of heterocyclic 2-oxo-1,2-dihydroquinoline-4-car-
bohydrazide have been deployed for the design and synthesis
of a new molecular receptor, 4 for multi-ion recognition. The
target molecule was synthesized through the condensation of
3 with 2-oxo-1,2-dihydroquinoline-4-carbohydrazide (6) in
refluxing ethanol. It has been determined that 4 exhibits an
exclusive color change from colorless to yellow as well as a
5.5 fold increase in the fluorescence intensity upon interac-
tion with fluoride due to formation of multiple hydrogen
bonds. Consequent to fluoride induced deprotonation, 4
displays a dual selectivity for Cu2? and Ni2? ions from
amongst plethora of investigated cations.
sensors show a multiple ion (or dual) response to both
cations and anions. Most of these receptors lack the
selectivity desired from the molecular probe. It has been
observed that pre-organized molecular receptors capable of
multipoint hydrogen bonding show a very good selectivity
with ionic guests [4–6]. Literature survey indicates that
from amongst anions, development of sensor materials for
fluoride analysis is pivotal as fluoride is essential for pre-
vention of dental caries [7], treatment of osteoporosis [8]
and in the refinement of uranium but its excess in the living
system can usher crippling skeletal fluorosis [9] and kidney
failure. Likewise, from amongst cations, sensor materials
for those ions are of special significance which are highly
toxic but at the same time are essential in smaller quantities
for smooth functioning of the biological systems [10]. Thus
analysis of both cations and anions through a common
molecular probe constitutes extremely important scientific
target [11, 12]. One approach that can help to achieve such
molecular receptors involves the utilization of supramo-
lecular anionic systems that can reorient the receptor sub-
units to generate binding sites for cation selectivity.
Although, fluoride complexes present a high possibility of
spectroscopic metal ion sensing, there are only a limited
number of publications describing the influence of fluoride
ion on luminescence characteristics of receptors towards
metal ions [13].
Keywords Calix[4]arenes ꢀ Quinoline carbohydrazide ꢀ
Multi ion selectivity ꢀ Schiff base ꢀ Sensors
Introduction
The development of new multifunctional sensor systems
with improved sensing properties and recognition mecha-
nisms is an important academic and application challenge
[1–3]. Molecular receptors with differential response
towards multiple analytes are potentially cost effective and
are highly desirable from the viewpoint of practical
applications. However, it has been observed that only a few
Utilizing this strategy, we report herein a new 2-oxo-
1,2-dihydroquinoline-4-carbohydrazide bearing calix[4]ar-
ene Schiff base as a selective molecular receptor for fluo-
ride ion and its deprotonated form for selective sensing of
metal ions. To the best of our knowledge this the first
calixarene based molecular receptor utilizing 2-oxo-1,2-
dihydroquinoline-4-carbohydrazide units. Fluoride inter-
action with 4 exhibits a recognition mechanism based on
the synergism of OHs and NHs, since both OH (phenolic)
H. M. Chawla (&) ꢀ T. Gupta
Department of Chemistry, Indian Institute of Technology Delhi,
Hauz Khas, New Delhi 110016, India
e-mail: hmchawla@gmail.com;
hmchawla@chemistry.iitd.ernet.in;
hmchawla@chemistry.iitd.ac.in
123

J Incl Phenom Macrocycl Chem
and CONH (amide and carbohydrazide) groups facilitate
guest binding. Although many chromogenic/fluorescent
sensors have been designed for F- sensing, they are often
Results and discussion
The synthesis of the target sensor molecule 4 (Scheme 1)
commenced with the synthesis of the calixarene based
aldehyde derivative 3, which was achieved in one step
from 2 with hexamethylenetetramine and trifluoroacetic
acid. The synthesis of sensor 4 was accomplished in good
yield by the condensation of 3 with two equiv of 2-oxo-1,2-
dihydroquinoline-4-carbohydrazide (6) in refluxing etha-
nol. The reference compound 7, on the other hand was
synthesized by condensation of p-hydroxybenzaldehyde
with 6, which in turn was obtained by adopting the pro-
cedures reported in the literature [18] (Scheme 2).
-
inefficient in presence of other anions like H2PO4 and
CH3COO-, hence it is useful to explore newer chromo-
genic sensors for selective recognition of F-. For example,
Chauhan and coworkers have recently reported four new
urea based anion sensors which showed poor discrimina-
tion between different anions [14]. Another report pub-
lished by Li and coworkers has described a new ferrocene
based sensor [15] for F-, which shows cross affinity for
H2PO4-. Additionally, fluorescence enhancement with
anionic guests is a rather challenging task [16, 17] and it is
encouraging that 4 can selectively recognize fluoride
through visible color change and fluorescence turn on
response. The deprotonated form of receptor 4, obtained
following fluoride interaction surprisingly exhibits
increased affinity for Cu2? and Ni2? recognition.
The structures of compounds 4 and 7 were confirmed by
1
recording their spectroscopic and analytical data. The H
NMR spectrum of 4 showed two doublets (4H each) for
methylene bridge protons of calix[4]arene, two singlets
(4H each) corresponding to calixarene aryl ring protons,
two doublets (2H each) and two double doublets (2H each)
corresponding to quinoline aryl ring protons and three
singlets (2H each) corresponding to quinoline and carbo-
hydrazone NH and calixarene OH (Fig. 1). The existence
of compound 4 in cone conformation has been confirmed
1
1
by means of H NMR and 13C NMR spectroscopy. H
NMR spectrum of 4 exhibits distinct doublets for the cal-
ixarene methylene bridge protons at 4.31 ppm (merged
with OCH2 protons) and 3.59 ppm, which are clear indi-
cation of existence of 4 in cone conformation. In addition
to this, 13C NMR spectrum of 4 also showed a signal for
syn Ar2CH2 at 31.46 ppm, thereby confirming the exis-
tence of 4 in cone conformation. Further confirmation of
the structure was done by recording its HRMS which
revealed prominent peaks at m/z 1,135.4810 (Intensity:
2.4 9 104) and 308.1017 (Intensity: 1700) corresponding
to structures 4 and 7 respectively.
Scheme 2 Synthesis of 6. Reagents and conditions: i (CH3CO)2O,
reflux; ii NaOH, H2O, 100 °C; iii SOCl2, MeOH, reflux; iv
NH2NH2.2H2O, EtOH
Scheme 1 Synthesis of 4 and 7. Reagents and conditions: i Ethyl
bromoacetate, K2CO3, CH3CN, reflux; ii HMTA, TFA, reflux; iii
2-Oxo-1,2-dihydroquinoline-4-carbohydrazide, ethanol, reflux
123

J Incl Phenom Macrocycl Chem
t-butyl
ArCH Ar+OCH
2
2
ArCH Ar
2
CH
3
ArH
quin
+ArH
-OCH COO
2
calix
ArH
quin
ArH
calix
NH
ArH
CH
quin
CH
quin
OH
Fig. 1 1H NMR spectrum of 4
UV–Vis spectroscopic studies
The ability of designed receptor 4 to complex with various
anions was studied by spectrophotometric titrations in
DMSO by adding standard solution of corresponding anions
to a solution of the receptor. In the absence of external
analytes, the UV–Vis spectrum of 4 in DMSO could be
characterized by an absorption maxima at 327 nm, and a
shoulder band around 285 nm. The former band could be
attributed to the Ar–CH=N–NH conjugation. The critical
anions of present interest included F-, Cl-, Br-, I-,
HSO4-, H2PO4- and ClO4-. The absorption properties of 4
in the presence of TBA (n-Bu4N)? salts of different anions
were studied in detail. No change was observed in the
absorption spectrum of 4 (30 lM) even upon the addition of
10 molar equivalents of Cl-, Br-, I-, HSO4-, H2PO4- and
Fig. 2 UV–Visible absorption changes of 4 upon addition of 10
equiv of anions
-
ClO4 (Fig. 2). However, with the stepwise addition of
tetrabutylammonium (TBA) fluoride (0–6.5 equiv.) to the
DMSO solution of 4 (30 lM), the original absorption
maximum weakened and an enhancement in the absorption
was noticed in the wavelength range of 355 nm to 450 nm
along with a distinct color change of the solution from
colorless to yellow (Fig. 3). These changes occur presum-
ably due to the charge transfer evoked after the interaction
between the acidic receptor protons and fluoride.
equivalent of TBAF. The reversibility of receptor response
was checked by adding protic solvents (methanol, water) to
the soution of receptor–fluoride complex. Interestingly, the
color of the solution turned back to colorless, thereby
suggesting that the protic solvents destroy the hydrogen
bonding network between the receptor and the fluoride.
A major difficulty encountered in anion sensing
endeavors concerns with the interference of other anions
Figure 4 displays the absorption spectral changes of
receptor 4 (30 lM) upon gradual addition of 0 to 6.5 mol
123

J Incl Phenom Macrocycl Chem
Fig. 3 Color change of a
DMSO solution of 4 upon F-
addition
Fig. 5 Competitive selectivity of 4 for F- in preference of other
anions. Green bar represents the absorbance (at k 373 nm) of 4 in
presence of F- alone and black bar denotes absorbance of F-/X-
coexisting systems. (Color figure online)
The importance of calix[4]arene scaffold for the guest
binding was evaluated by synthesis of an appropriate ref-
erence compound 7 (Scheme 1). 7 showed an absorption
maximum at 317 nm in DMSO. It was observed that no
apparent change was induced in the absorption spectrum of
7 even in the presence of excess TBAF (15equiv.). This
observation affirmed the fact that presence of calix[4]arene
scaffold is essential for guest binding probably because it
provides the rigidity and accurate placement of binding
sites required for interaction with the anionic guest.
Fig. 4 Variation in absorption spectrum of 4 (30 lM) upon titration
with TBAF (0–6.5 equiv)
present in the typical analyte solutions. Therefore, to fur-
ther challenge the reliability of our fluoride detection sys-
tem, we conducted competitive anion titrations, wherein
absorption spectrum of other anions/fluoride ion co-exist-
ing systems was examined. The experiments revealed
(Fig. 5) that highly selective detection of fluoride by 4
could be demonstrated, without much perturbation, even in
the presence of equimolar amounts of other anions. It is
noteworthy that 4 shows a selective color change with
fluoride from colorless to yellow even in the presence of
other anions. In essence, the high selectivity of host for
fluoride could be attributed to several factors, which
include appropriate acidity of the receptor donor groups,
complementarity of shape between host and guest and
multiple hydrogen bonding interactions.
Fluorescence spectroscopic analysis
Anion recognition through fluorescence measurements by 4
was also studied in DMSO. The fluorescence spectrum of 4
exhibited a very weak emission when excited at 325 nm. It
was observed that upon addition of F- (0–6.5 equiv) to
DMSO solution of 4 (50 lM), a new emission band
appeared around 505 nm along with
a significant
enhancement (5.5-fold) in fluorescence intensity at
505 nm. The fluorescence emission intensity of 4 increased
linearly as a function of F- concentration as shown in the
inset of Fig. 7. Amongst various tested anions (F-, Cl-,
Br-, I-, H2PO4-, ClO4 and HSO4-), only F- anion
-
The binding stoichiometry between 4 and fluoride
determined by Job’s method of continuous variation was
1:2 (4:F-) (Fig. 6a).The binding constant for a 1:2 complex
between 4 and fluoride in DMSO was determined from the
increase in absorption intensity at 373 nm by using Bene-
si–Hildebrand equation [19], providing K = 1.2 9 108
M-2 (Fig. 6b). Based upon the UV–Vis measurements, the
detection limit [20] of receptor 4 towards F- was deter-
mined to be 3.1 lM.
induced a sizable enhancement in the fluorescence intensity
of 4, while other anions exhibited a negligible response,
indicating that 4 is a very selective receptor for F-. Fig-
ure 7 describes fluoride induced changes in the fluores-
cence intensity of a DMSO solution of 4 (50 lM).
The association constant for 4.F- complex calculated
from the fluorescence titration measurements by employing
Benesi–Hildebrand equation (1.6 9 108 M-2) (Fig. 8) was
123

J Incl Phenom Macrocycl Chem
Fig. 6 a Job’s plot for determining stoichiometry of receptor 4 with fluoride ions in DMSO. b Benesi–Hildebrand plot of 4 with F- based on
UV–Vis titration data
Fig. 8 Benesi–Hildebrand plot of 4 with F- based on fluorescence
data
Fig. 7 Changes in the emission spectrum of 4 (50 lM) upon addition
respectively. It was observed that after the addition of 0.1
equivalent of fluoride ions to the receptor solution (0.01 M),
the characteristic NH and OH signals became broad to reveal
that the commencement of interaction between 4 and fluoride
ions occurs through H-bonding. The peaks broadened further
as more TBAF was added and finally disappeared com-
pletely upon addition of 0.35 equivalents of F-. These
observations confirmed the assumption that quinoline NH,
carbohydrazide NH and calixarene phenolic OH are
involved in the interaction with fluoride through hydrogen
bonding followed by deprotonation. Moreover, since de-
protonation has been shown to occur at both the upper as well
as lower rim of the calixarene receptor, these observations
substantiate the fact that 4.F- interaction proceeds with a
stoichiometric ratio of 1:2. Figure 10 shows the interaction
mode between 4 and F- proposed on the basis of these
observations, wherein F- first interacts with NH and OH
through H-bond and eventually abstracts them.
of TBAF (0–6.5 equiv.) in DMSO. Inset shows the change in
fluorescence intensity at 505 nm with increasing equivalents of
fluoride
consistent with the value derived from the UV–Vis titration
studies, indicating a strong tendency for the formation of
F- ligand complexation species.
1H NMR spectroscopic studies
The results obtained from the UV–Vis and fluorescence
1
emission spectroscopy were further supported by H NMR
titrations carried out in DMSO-d6 (Fig. 9). 4 exhibited three
singlets in its 1H NMR spectrum corresponding to quinoline
NH protons, carbohydrazide NH protons and calixarene
phenolic protons at
d 12.00, 11.89 and 8.41 ppm
123

J Incl Phenom Macrocycl Chem
Fig. 11 UV–Vis absorption spectrum of 4.F- upon addition of
different metal ions (1.5 equiv) in DMSO
Fig. 9 Partial 1H NMR (300 MHz) spectra of a 4 in DMSO-d6;
b 4 ? 0.1 equiv. F-; c 4 ? 0.2 equiv. F-; d 4 ? 0.35 equiv. F-
are otherwise not detected by 4 alone. The synthesized
receptor also shows different absorption characteristics for
them to allow their distinction from each other. The
detection limit of Cu2? and Ni2? was determined to be
7.9 lM and 23 lM respectively. The selectivity towards
Cu2? and Ni2? could be explained on the basis of the
compatibility of the receptor with these ions in respect of
cavity size, ionic radii, number and nature of binding sites
probably collectively help in the selective complexation.
Conclusion
Fig. 10 Binding model for interaction between 4 and F-
In summary, a novel calix[4]arene based molecular probe
has been synthesized and evaluated as a multiple ion sen-
sor. Fluoride recognition by 4 involves participation from
multitude of hydrogen bond donor groups like phenolic
OH, amide NH and carbohydrazide NH working syner-
gistically. Since 4 shows selective coloration only with
fluoride ion, it can be used as a naked eye sensor for F-.
The deprotonated system obtained after fluoride addition to
4 has been observed to function as an efficient sensor
system for Cu2? and Ni2? ions as well.
Recognition of metal ions through secondary
interactions
Since ligands possessing free electron pairs can coordinate
with metal ions to form metal ion complexes, we also
investigated the behavior of compound 4 in the presence of
perchlorate salts of various metal ions after fluoride addi-
tion. To ensure complete deprotonation of 4, the behavior
of compound 4 towards several alkali (Na?, Cs?, Li?) and
transition metal ions (Mn2?, Co2?, Cu2?, Fe2?, Ni2?
,
Hg2?, Ag?, Cd2?, Zn2, Cr3?) was studied after addition of
fluoride ions (6 equivalents). It was observed that the
system exhibited excellent selectivity towards Ni2? and
Cu2? only (Fig. 11).
Experimental
Materials and methods
Upon addition of Cu2? (Fig. 12a), the maximum cor-
responding to the deprotonated compound at 327 nm got
shifted to 351 nm along with the appearance of a new
absorption peak around 450 nm. While, in the presence of
Ni2? (Fig. 12b), the absorption maximum got shifted to
346 nm. The developed supramolecular system is thus
further deployable for recognition of Cu2? and Ni2? which
All the reagents used in the study were purchased from
Sigma Aldrich or Merck and were chemically pure. The
solvents were dried and distilled prior to use. HPLC grade
solvents were used for UV and fluorescence experiments.
In the titration experiments, all the anions and metal ions
were added in the form of TBA salts and perchlorate salts
123

J Incl Phenom Macrocycl Chem
Fig. 12 Changes in the UV–Vis spectra of 4 in DMSO after addition of F- (6.5 equiv) with increasing amount of a 1.5 equiv of Cu2? and b 1.7
equiv of Ni2?
respectively. H and 13C NMR spectra were recorded in
DMSO-d6 on a 300 MHz Bruker DPX 300 instrument
using tetramethylsilane (TMS) at 0.00 as an internal stan-
dard. Mass spectrum was recorded on a Bruker Compass
Data Analysis 4.0 Mass spectrometer. A Perkin Elmer
Lambda 35 double beam spectrophotometer with variable
bandwidth was used for the acquisition of the UV–Vis
molecular absorbance. Melting points were determined on
an electrothermal melting point apparatus obtained from
M/S Toshniwal and were uncorrected.
1.30 (t, 6H), 1.07(s, 18H); 13C NMR (75 MHz, DMSO-d6,
d in ppm) 14.43, 18.98, 31.46, 34.37, 56.50, 61.36, 72.48,
116.17, 116.68, 121.01, 122.63, 125.36, 126.40, 128.49,
129.22, 131.37, 132.48, 139.72, 145.09, 146.96, 147.53,
150.87, 151.05, 155.55, 161.64, 161.97, 169.36.
1
Analytical data for reference compound 7
Light green solid; Yield: 73 %; Mp: 271 °C; UV (kmax
,
DMSO): 317 nm; HRMS (ESI–MS) m/z:calcd 308.1030,
found 308.1017; IR (KBr pellet, cm-1): 3,350.68,
2,925.0835, 1,579.01, 1,101.72; 1H NMR (300 MHz,
DMSO-d6, d in ppm): 11.98 (s, 1H, NH, D2O exchange-
able),11.95 (s, 1H, NH, D2O exchangeable), 10.03 (s, 1H,
OH, D2O exchangeable), 8.20 (s, 1H), 7.75 (d, 1H), 7.57
(d, 2H), 7.38 (dd, 1H), 7.22 (dd, 1H), 7.15 (d, 1H), 6.83 (d,
2H), 6.67 (s, 1H); 13C NMR (75 MHz, DMSO-d6, d in
ppm) 116.23, 116.64, 119.9, 120.99, 122.66, 125.33, 125.9,
129.59, 131.44, 139.73, 145.07, 149.71, 160.2, 161.61,
162.01.
General procedure for the synthesis of receptor 4
and reference compound 7
5,17-diformyl-11,23-bis(p-tert-butyl)-26,28-bis(ethoxycar-
bonyl methoxy)-25,27-dihydroxy calix[4]arene was
refluxed with 2-oxo-1,2-dihydroquinoline-4-carbohy-
drazide (2 mol equivalent) in dry ethanol for 12 h. The solid
product thus separated out was filtered and recrystallised
from ethanol to yield pure product 4 as a light green solid.
2-Oxo-1,2-dihydroquinoline-4-carbohydrazide(1 equiv)
was refluxed for 8 h with p-hydroxybenzaldehyde in ethanol.
Solid thus obtained was fitered and recrystallised from eth-
anol to afford the reference compound 7 in its pure form.
Acknowledgement Tanu Gupta thanks the CSIR, India for research
fellowship. Financial assistance from DST (FIST grant for HRMS to
Department of Chemistry, IIT Delhi) and MoRD is gratefully
acknowledged.
Analytical data for 4
References
Light green solid; Yield: 75 %; Mp: 288 °C; UV (kmax
,
DMSO): 327 nm; HRMS (ESI–MS) m/z:calcd 1,135.4811,
found 1,135.4810; IR (KBr pellet, cm-1): 3,384.61,
2,956.04, 1,728.40, 1,610.44, 1,196.19; 1H NMR
(300 MHz, DMSO-d6, d in ppm): 12.004 (s, 2H, NH, D2O
exchangeable), 11.891 (s, 2H, NH, D2O exchangeable),
8.418 (s, 2H, OH, D2O exchangeable), 8.352 (s, 2H), 7.786
(d, 2H), 7.578 (m, 6H), 7.39 (d, 2H), 7.22 (dd, 2H), 7.0 (s,
4H), 6.715 (s, 2H), 4.78 (s, 4H), 4.31 (m, 8H), 3.59 (d, 4H),
1. Maity, D., Govindaraju, T.: A differentially selective sensor with
fluorescence turn-on response to Zn2? and dual-mode ratio-
metric response to Al3? in aqueous media. Chem. Commun. 48,
1039–1041 (2012)
´
2. Alfanso, M., Tarraga, A., Molina, P.: Ferrocenyl benzobisimi-
dazoles for recognition of anions and cations. Inorg. Chem. 52,
7487–7496 (2013)
3. Kim, S.K., Lynch, V.M., Young, N.J., Hay, B.P., Lee, C.H., Kim,
J.S., Moyer, B.A., Sessler, J.L.: KF and CsF recognition and
123

J Incl Phenom Macrocycl Chem
extraction by a calix[4]crown-5 strapped calix[4]pyrrole multi-
topic receptor. J. Am. Chem. Soc. 134, 20837–20843 (2012)
4. Reena, V., Suganya, S., Velmathi, S.: Synthesis and anion
binding studies of azo-Schiff bases: selective colorimetric fluo-
ride and acetate ion sensors. J. Fluor. Chem. 153, 89–95 (2013)
5. Sessler, J.L., Gale, P.A., Cho, W.-S.: Anion Receptor Chemistry.
Royal Society of Chemistry, Cambridge (2006)
colorimetric and fluorimetric chemosensors based on bithienyl-
imidazo-anthraquinone chromophores. Org. Lett. 9, 3201–3204
(2007)
14. Garg, B., Bisht, T., Chauhan, S.M.S.: 2,20-Diaminoazo-benzene,
a potential scaffold for the synthesis of bis-ureas and thioureas:
solution phase anion sensing and binding studies. Sens. Actuators
B 168, 318–328 (2012)
6. Cametti, M., Rissanen, K.: Highlights on contemporary recog-
nition and sensing of fluoride anion in solution and in the solid
state. Chem. Soc. Rev. 42, 2016–2038 (2013)
7. Kirk, K.L.: Biochemistry of the Halogen and Inorganic Halides,
p. 58. Plenum press, New York (1991)
8. Kleerekoper, M.: The role of fluoride in the prevention of oste-
oporosis. M. Endocrinol. Metab. Clin. North Am. 27, 441–452
(1998)
15. Li, C., Wang, L., Yu, H., Ma, L., Chen, Z., Wu, Q., Amer, W.A.:
Synthesis of novel colorimetric probe molecules and their
application in anion recognition based on strong hydrogen bond.
J. Organomet. Chem. 726, 32–36 (2013)
16. Ghosh, K., Saha, I.: Triphenylamine-based simple chemosensor
for selective fluorometric detection of fluoride, acetate and
dihydrogenphosphate ions in different solvents. J. Incl. Phenom.
Macrocycl. Chem. 70, 97–107 (2011)
9. Zhang, J.F., Lim, C.S., Bhuniya, S., Cho, B.R., Kim, J.S.: A
highly selective colorimetric and ratiometric two-photon fluo-
rescent probe for fluoride ion detection. Org. Lett. 13, 1190–1193
(2011)
10. Kumar, M., Kumar, R., Bhalla, V.: Thiacalix[4]arene based re-
configurable molecular switches: set-reset memorized sequential
device. Org. Biomol. Chem. 9, 8237–8245 (2011)
17. Qu, Y., Qu, S., Yang, L., Hua, J., Qu, D.: A red-emission dike-
topyrrolopyrrole-based fluoride ion chemosensor with high con-
trast ratio working in a dual mode: solvent-dependent ratiometric
and ‘‘turn on’’ pathways. Sens. Actuators B 173, 225–233 (2012)
18. Cappelli, A., Gallelli, A., Manini, M., Anzini, M., Mennuni, L.,
Makovec, F., Menziani, M.C., Alcaro, S., Ortuso, F., Vomero, S.:
Further studies on the interaction of the 5-Hydroxytryptamine3
(5-HT3) receptor with arylpiperazine ligands. Development of a
new 5-HT3 receptor ligand showing potent acetylcholinesterase
inhibitory properties. J. Med. Chem. 48, 3564–3575 (2005)
19. Shiraishi, Y., Sumiya, S., Kohno, Y., Hirai, T.: A rhodamine
cyclen conjugate as a highly sensitive and selective fluorescent
chemosensor for Hg(II). J. Org. Chem. 73, 8571–8574 (2008)
20. Mashraqui, S.H., Ghorpade, S., Tripathi, S., Britto, S.: A new
indole incorporated chemosensor exhibiting selective colorimet-
ric and fluorescence ratiometric signaling of fluoride. Tetrahedron
Lett. 53, 765–768 (2012)
´
11. Amendola, V., Esteban-Gomez, D., Fabbrizzi, L., Licchelli, M.,
Monzani, E., Sancenon, F.: Metal-enhanced H-bond donor ten-
´
dencies of urea and thiourea toward anions: ditopic receptors for
silver (I) salts. Inorg. Chem. 44, 8690–8698 (2005)
12. Sutariya, P.G., Pandya, A., Lodha, A., Menon, S.K.: Fluorescence
switch on–off–on receptor constructed of quinoline allied
calix[4]arene for selective recognition of Cu2? from blood serum
and F- from industrial waste water. Analyst 138, 2531–2535
(2013)
13. Batista, R.M.F., Oliveira, E., Costa, S.P.G., Lodeiro, C., Raposo,
M.M.M.: Synthesis and ion sensing properties of new
123