Novel calix[4]arene based metallo-supramolecular complex for recognition of cyanide ions in aqueous medium

Article abstract of DOI:10.1080/10610278.2016.1222074

A novel bis-naphthalimidocalix[4]arene-Cu(II) supramolecular complex has been observed to provide an efficient recognition system for CN^? ions in aqueous medium. The binding stoichiometry of bis-naphthalimidocalix[4]arene and copper ion has been found to be 1:1 while that for bis-naphthalimidocalix[4]arene-Cu(II) and cyanide ion it has been determined to be 1:2.

Full text of DOI:10.1080/10610278.2016.1222074

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Novel calix[4]arene based metallo-supramolecular
complex for recognition of cyanide ions in
aqueous medium
Mohammad Shahid, Har Mohindra Chawla & Pooja Bhatia
To cite this article: Mohammad Shahid, Har Mohindra Chawla & Pooja Bhatia (2016): Novel
calix[4]arene based metallo-supramolecular complex for recognition of cyanide ions in
aqueous medium, Supramolecular Chemistry, DOI: 10.1080/10610278.2016.1222074
To link to this article: http://dx.doi.org/10.1080/10610278.2016.1222074
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Date: 16 September 2016, At: 21:57

Supramolecular chemiStry, 2016
http://dx.doi.org/10.1080/10610278.2016.1222074
Novel calix[4]arene based metallo-supramolecular complex for recognition of
cyanide ions in aqueous medium
Mohammad Shahid , Har Mohindra Chawla and Pooja Bhatia
Department of chemistry, indian institute of technology Delhi, New Delhi, india
ABSTRACT
ARTICLE HISTORY
received 14 april 2016
accepted 4 august 2016
A novel bis-naphthalimidocalix[4]arene-Cu(II) supramolecular complex has been observed to
provide an efficient recognition system for CN− ions in aqueous medium. The binding stoichiometry
of bis-naphthalimidocalix[4]arene and copper ion has been found to be 1:1 while that for bis-
naphthalimidocalix[4]arene-Cu(II) and cyanide ion it has been determined to be 1:2.
KEYWORDS
calix[4]arene; metallo-
supramolecular complex;
cu2+; cN−; selectivity;
aqueous medium
Introduction
displacement of the metal to produce original molecular
receptor or it may lead to the formation of a new ternary
complex with distinct characteristics that could be mon-
itored by absorption or fluorescence techniques (5–7). In
this communication, we report the synthesis of calix[4]
arene-naphthalimide molecular receptor 4 which forms
a supramolecular complex with copper ions to exhibit an
absorption maxima at 340 nm in aqueous acetonitrile. 4
can selectively recognise both copper and cyanide ions
through a change in UV–vis absorption as well as fluores-
cence measurements.
Calix[4]arene, 1 was acylated with ethyl bromoacetate
in the presence of K2CO3 and KI to yield 2 in 76% by pre-
viously reported procedure (1b). Compound 2 on stirring
with hydrazine hydrate in ethanol at room temperature
gave 3 in 89% yield. Subsequent reaction with 4-bro-
mo-1,8-naphthalic anhydride gave 4 as an off-white solid
in 81% yield (Scheme 1). The characterisation of 2–4 was
done by spectral and analytical data (Figures S1–7).
Previously published methods for recognition of cyanide
involve its nucleophilic attack at the electrophilic carbon
centre (1, 2) of the molecular receptor, hydrogen bond
interaction (1a, 3) or through displacement reactions from
the ligand-metal complexes (1a, 4). Use of metallo-supra-
molecular complexes for recognition of anionic species
has been reported recently (5).
Compared to other anions, the detection and estima-
tion of cyanide ion is more challenging because of its
weaker basicity and existence in several forms under differ-
ent conditions of microenvironment, pH and the solvent.
For example, at pH 9.3–9.5, CN− and HCN are in equilib-
rium (with equal quantity of both ions) and the mixture is
usually referred as free cyanide. At pH 11, over 99% of the
cyanide remains in solution as CN− ions, while at pH 7, over
99% of the cyanide exists as molecular cyanide, HCN (2).
It is envisaged that the metallo-supramolecular
complex on reaction with cyanide may lead to either
CONTACT har mohindra chawla
hmchawla@chemistry.iitd.ac.in
Supplemental data for this article can be accessed here. [http://dx.doi.org/10.1080/10610278.2016.1222074]
© 2016 informa uK limited, trading as taylor & Francis Group

2
M. SHAHId eT Al.
(i)
(iii)
(ii)
O
HO
OH
O
O
OH HO
HO
O
OH
HO
OH
O
O
HO
OH
O
O
HN
NH
O
O
O
N
O
N
O
O
O
O
O
HN
NH2
O
NH
NH2
1
2
3
Br
Br
4
Scheme 1. Synthesis of molecular receptor 4. (i) ethyl bromoacetate/mecN/K2co3/Ki/∆, (ii) hydrazine hydrate/ethanol/stirring at room
temperature, (iii) 4-bromo-1,8-naphthalic anhydride/ethanol/∆.
Figure 1. (a) absorption and (b) emission interaction studies of 4 (10 μm) with different metal ions (20 equiv) in aqueous acetonitrile
(20%, v/v).
The optical behaviour of 4 (10 μM) and its binding
affinity with different metal ions, anions and biomole-
cules (amino acids and dopamine) was evaluated by UV–
vis absorption and fluorescence spectroscopy in aqueous
acetonitrile solution (20%, v/v). 4 displayed a strong
absorption maximum at 340 nm (ε = ~43,990 M−1 cm−1)
and showed a change only when treated with copper ions.
None of the other metal ions affected the spectrum (Na+,
K+, Mg2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Pb2+, Cd2+
and Hg2+; as their nitrate salts; 20 equiv) (Figure 1(a)). A
profound selectivity for Cu2+ ions was observed over other
interferences (Figure S8).
The binding affinity of 4 with Cu2+ ions was examined by
titration experiments. Addition of varying concentration
of Cu2+ ions (0–5 equiv) shifted the band at 340–290 nm
with a significant hyperchromic shift (Figure 2). Though
clear isosbestic point was not observed in the absorption
titrations, saturation point could be observed after 1:1 sto-
ichiometry. Clear isosbestic point could however be deter-
mined during flouremetric titrations with the same ligand
and copper ions (see below). The association constant for
1:1 stoichiometry of copper-ligand complex was found to
be 3.41 × 104 M−1.
Figure 2. uV–vis titrations of 4 with cu2+ ions (0–5 equiv) in
aqueous acetonitrile solution (20%, v/v). inset shows the Benesi–
hildebrand plot.
sensitive optical properties. However, when examined
for interaction with different anions (Br−, Cl−, F−, I−, HSO4−,
H2PO−4, CN− and AcO− as their tetrabutylammonium salts)
as well as different biomolecules (20 equiv, e.g. Cys, lys,
Val, Ala, leu, Ile, Tyr, Trp, His, Pro and dopamine) by UV–vis
absorption spectroscopy, only insignificant changes could
be witnessed (Figure S9).
Since, 4 contains an amide groups, it could be expected
to confer acidity to amide protons to exhibit anion
The ion sensing ability of 4 (λex = 340 nm) was also mon-
itored through fluorescence spectroscopy. The emission

SUPrAMOleCUlAr CHeMISTry
3
Figure 3. Fluorescence titrations of 4 with cu2+ ions (0–5 equiv) in aqueous acetonitrile solution (20%, v/v). inset shows (a) Job’s plot and
(b) Benesi–hildebrand plot.
Figure 4. hrmS spectrumof 4-cu2+ whichshowed themolecularion peak atm/z1373.2591; 1371.2575 (calculated for[c72h70Br2N4o10cu]+
as m/z = 1373.2834; 1371.2844). the 4-cu-cN showed the molecular ion peak at m/z 1425.1130 (calculated for [c72h70Br2N4o10cu-(cN)2]+
as m/z = 1425.2896; 1423.2916.
maximum was observed at 383 nm in aqueous-MeCN
(20%, v/v). No change was observed in the emission spec-
trum except when copper ions were added to a solution
of 4. It was observed that only Cu2+ ions induced a sig-
nificant fluorescence quenching in the emission process
(Figure 1(b)).
addition of Cu2+ ions (0–5 equiv) with a new band appear-
ing at 390 nm (Figure 3). Job’s plot revealed a 1:1 stoichi-
ometry between 4 and Cu2+ ions to lead the association
constant as 4.03 × 104 M−1 (Inset of Figure 3).
The reversibility of interaction of 4 and Cu2+ ions and
possible recovery of spectrum of 4 due to demetallation
of copper ions was checked by adding ethylene diamine
tetraacetic acid (edTA, 50 equiv) to a solution of plausible
emission titrations revealed that fluorescence intensity
of 4 decreased and shifted towards red region on gradual

4
M. SHAHId eT Al.
complex 4-Cu2+. The original spectrum of 4 could be slowly
restored to suggest that mode of complexation of 4 and
copper ions was reversible but it was not immediate metal
displacement as expected (Figure S10) (4c).
The mass spectrum of the complex of 4 with Cu2+
also revealed a 1:1 binding mode when mass peak at
m/z 1373.2591 corresponding to [4+Cu2+] was observed
(Figure 4 and S11). The change in the infrared (Ir) spectrum
of 4 on interaction with Cu2+ ions confirmed the formation
of a metallo-supramolecular complex (the absorptions at
1778, 1694 shifted to 1620 cm−1 with appearance of new
band at 1383 cm−1). No significant change was observed
in the Ir absorption at 3448 cm−1 (Figure S12).
It was revealed that addition of different anions (such as
F−, Cl−, Br−, I−, SCN−, HSO4−, CN−, AcO−, H2PO−4, S2−, as their
sodium salts, 20 equiv) to a solution of 4-Cu2+ complex, did
not give any significant change in the optical properties
except when cyanide ions were added when a new UV–vis
absorption band was observed at 335 nm (Figure S13).
The binding affinity of 4-Cu2+ with CN− ions was esti-
mated by titration experiments. It was determined that
addition of CN− (0–10 equiv), shifted the band at 290 nm
gradually to the red region with a hypochromic shift. The
two isosbestic points were observed at 263 and 349 nm
when metallo-supramolecular complex (1:1) was titrated
with cyanide (Inset of Figure 5(a) and (b)). The association
constant was found to be Kassoc as 7.5 × 108 M−2 when
calculated from the titration data (Figure 5(c)).
The sensing ability of metallo-supramolecular complex,
4-Cu2+ was investigated in the presence of different anions.
Figure 5. uV–vis titrations spectra of 4-cu2+ with cN− (10 equiv) in aqueous acetonitrile (20%, v/v). inset shows (a,b) extended part of
titration spectra and (c) Benesi–hildebrand plot.
Figure 6. emission titrations spectra of 4-cu2+ with cN− (10 equiv) in aqueous acetonitrile (20%, v/v). inset shows (a) Job’s plot and (b)
Benesi–hildebrand plot.

SUPrAMOleCUlAr CHeMISTry
5
The sensing ability of metallo-supramolecular com-
plex, 4-Cu2+ with respect to tested anions was examined
through fluorescence spectroscopy. A significant change
was observed only on interaction with CN− ions (Figure
S14). Subsequent addition of CN− ions led to enhancement
of fluorescence intensity (6) of weak emission bands at
385 and 399 nm. The association constant obtained for
1:2 stoichiometry of 4-Cu2+ complex and cyanide ions was
found to be Kassoc = 7.4 × 108 M−2 (Figure 6).
It was noteworthy to see that the mass spectrum of
4-Cu2+ complex with CN− showed a 1:2 binding mode
between 4-Cu2+ and CN−, revealing that Cu2+ ions in 4-Cu2+
complex binds with two cyanide ions (Figure 4).
The above results support a plausible sensing mech-
anism for fluorescence turn-on response of metallo-
supramolecular complex 4-Cu2+ on addition of CN−. 4-Cu2+
complex appears to show a weak fluorescence emission
due to photo induced electron transfer (PeT) or electronic
energy transfer (eeT) (5) between the naphthalimide unit
and the coordinated Cu2+ ions to initiate quenching of
fluorescence intensity. Further work to understand the
nature and applications of metallo-supramolecular spe-
cies involved is in progress.
reaction was monitored by TlC. The reaction mixture was
evaporated on a rotatory evaporator, washed with cold
water and dried in air to get an off-white solid in 81% yield.
Rf : 0.1 (20% ethyl acetate/hexane); Melting point:
>200 °C; 1H NMr (300 MHz, CdCl3): The structure of
Compound 4 has been confirmed by the appearance of
signals at δ (ppm): 11.54 (s, 2H, NH), 8.25–8.06 (5H), 7.26
(s, 4H, 4 phenyl), 6.94 (s, 4H, phenyl), 4.70 (s, 4H, COCH2),
4.51 (d, 4H, bridging CH2), 3.53 (d, 4H, bridging CH2), 1.36
(t, 6H, CH3), 1.29 (s, 18H, t-Bu), 1.06 (s, 18H, t-Bu); HrMS
obtained at m/z = 1331.3594, 1333.3441 (calculated for for-
mula C72H70Br2N4O10+Na = m/z 1331.3351, 1333.3357);The
FT-Ir (KBr, υ cm−1) spectrum revealed the appearance of
stretching absorption at 3448 cm−1 (OH), 2958 cm−1 (CH2,
asymm strech), 2866, (CH2, sym stretch), 1778 cm−1 (C=O,
acyclic amide), 1694 cm−1 (C=O, cyclic amide) 1233 cm−1
(C–N), and 1045 cm−1 (C–O–C).
Ion binding studies
Stock solutions of 4 (1 × 10−3 M) and anions/metal ions
(1 × 10−1 M) were prepared in aqueous acetonitrile. The
stock solution of 4 was diluted to 10 μM. All the spectro-
scopic studies were performed at 10 μM concentration.
4 μl (20 equiv) of stock solution of each anion/metal ion
was added to 2 ml solution of 4 (10 μM) for interaction
and interference studies. For titration studies, aliquots of
1 μl (0.5 equiv) of CN− (10 mM) were added to 4 (10 μM)
and the changes in the absorption/emission spectra were
measured.
Conclusions
A bis-naphthalimidocalix[4]arene receptor 4 forms a supra-
molecular complex with copper ions which can selectively
recognise cyanide ion through fluorescence enhancement.
Experimental section
Acknowledgement
Materials and methods
Authors are thankful to SerB, department of Science and Tech-
nology, New delhi for financial support vide section No. SB/FT/
CS-010/2013.
All the reagents and solvents were purchased from Merck
and Sigma–Aldrich and were used without any further
purification. Ir spectra were recorded in KBr on Agilent/
Perkin elmer FT-Ir spectrometer. 1H NMr spectra (Chemical
shifts in δ ppm) were recorded on a Bruker 300 FT–NMr
(300 MHz) spectrometer, using TMS as internal standard.
The UV–vis absorption spectra were recorded on Perkin
elmer lambda 35 spectrophotometer using a quartz
curette (path length = 1 cm). Fluorescence spectra were
recorded on a Horiba Fluoromax 4 spectrophotometer.
HrMS were recorded on Bruker MICrOTOF Q II in aque-
ous acetonitrile.
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCiD
Mohammad Shahid
http://orcid.org/0000-0003-0530-2940
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