Organochalcogen-supported azacalix[3]arenes as membrane sensor for potentiometric determination of uranyl ions

Article abstract of DOI:10.1080/10426500801900915

An one-pot syntheses of organochalcogen-supported azacalix[3]arenes and their behavior toward metal ions sensing was investigated by spectrochemical (UV-vis,1H NMR and 77Se NMR) methods. The azacalix[3]arenes prepared have shown better potentiometric resp

Full text of DOI:10.1080/10426500801900915

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Phosphorus, Sulfur, and Silicon
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Organochalcogen-Supported
Azacalix[3]arenes as Membrane
Sensor for Potentiometric
Determination of Uranyl Ions
Shabana Khan a , Monika Maheshwari a & Jai Deo
Singh a
a Department of Chemistry , Indian Institute of
Technology Delhi (IITD) , New Delhi, India
Published online: 29 Oct 2008.
To cite this article: Shabana Khan , Monika Maheshwari & Jai Deo Singh (2008)
Organochalcogen-Supported Azacalix[3]arenes as Membrane Sensor for Potentiometric
Determination of Uranyl Ions, Phosphorus, Sulfur, and Silicon and the Related
Elements, 183:4, 961-965, DOI: 10.1080/10426500801900915
To link to this article: http://dx.doi.org/10.1080/10426500801900915
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Phosphorus, Sulfur, and Silicon, 183:961–965, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500801900915
Organochalcogen-Supported Azacalix[3]arenes
as Membrane Sensor for Potentiometric Determination
of Uranyl Ions
Shabana Khan, Monika Maheshwari, and Jai Deo Singh
Department of Chemistry, Indian Institute of Technology Delhi (IITD),
New Delhi, India
An one-pot syntheses of organochalcogen-supported azacalix[3]arenes and their be-
1
havior toward metal ions sensing was investigated by spectrochemical (UV-vis, H
77
NMR and Se NMR) methods. The azacalix[3]arenes prepared have shown better
potentiometric response for uranyl ions compared to alkali (Na+, K+), alkaline-
2+
2+
earth (Mg , Ca , Ba2+), transition and heavy metal (Co2+, Ni2+, Cu2+, Ag+,
Zn2+, Cd2+, Pb2+, Fe3+) ions and thus can act as efficient ion-carriers for the
preparation of PVC membrane based ion-selective electrodes for the determination
of uranyl ions.
Keywords Azacalix[3]arenes; host–guest systems; ion-selective electrode; O, N, Se/Te
donor combinations; potentiometric sensors; uranyl ions
INTRODUCTION
Incorporation of organochalcogen moiety in a conventional host
molecule offers newer possibilities to create novel structural motif
for functional materials and devices and may be greatly rewarding
for imminent application such as chemical sensors in contrast to na-
tive host molecule.1−4 In continuation to our research activities in the
area of organochalcogen chemistry, we recently reported the synthe-
sis of acyclic ligand systems bearing (O, N, Se/Te) donor combinations
and their complexation behavior.5,6 To this end, It was realized that
rationally positioned heavier chalcogen (Se or Te) atoms in a poly-
functional molecular core can significantly decrease the flexibility of
the molecular architecture with respect to their lighter congeners (O
and S) and ensure the possibility that the designed molecular species
would preserve their solid-state structures in solution and thus can
Address correspondence to Jai Deo Singh, Department of Chemistry, Indian In-
stitute of Technology Delhi (IITD), New Delhi 110 016, India. E-mail: jaideo@
chemistry.iitd.ernet.in
961

962
S. Khan et al.
have diverse reactivity patterns than those for its close lighter con-
gener sulfur. To examine the validity of our approach, we now describe
herein the synthesis of cyclic systems bearing (O, N, S/Se/Te) donor com-
binations, i.e., organochalcogen-supported azacalix[3]arenes and their
potential application as efficient ion- carriers for the preparation of
PVC membrane based ion selective electrodes for the determination
of uranyl ions. The organochalcogen supported azacalix[3]arenas were
prepared by the condensation of 2,6-di-hydroxy-4-methylphenol with
organochalogenoalkyl amines. The optimized reaction conditions led to
the isolation of the desired products (1-7) exclusively as viscous mass
in > 60% yields (Scheme 1).
SCHEME 1 Reagents and conditions: E = Se, R = p-FC6H4, 1 (65%); E = Te,
R = p-FC6H4, 2 (63%); E = S, R = p-FC6H4, 3 (67%); E = Se, R = C6H5, 4 (61%);
E = Te, R = C6H5, 5 (67%); E = S, R = C6H5, 6 (64%); E = Se, R = p-ClC6H4, 7
(69%).
1
They were identified by means of H NMR, 13C NMR, 77Se NMR,
UV-vis and FAB-MS spectroscopy and these studies revealed the forma-
tion of organochalcogen supported azacalix[3]arenes, exclusively. The
azacalixarenes in the present study contain -OH group in core and ni-
trogen in the periphery of the cyclic ring followed by chalcogen (Se or
Te) donors in side arms thus could provide attractive binding sites for
guests. An optimized structure for 1 revealed a funnel shaped struc-
ture (Figure 1) and may reveal an appealing complexation-recognition
behavior for guest molecules.
The azacalix[3]arenes in the present investigation showed ex-
emplary selectivity towards UO22+ ions in the presence of various
alkali(Na+, K+), alkaline-earth (Mg2+, Ca2+, Ba2+), transition (Co2+
,
Ni2+, Cu2+, Ag+, Fe3+) and heavy metal (Cd2+, Hg2+ and Pb2+) ions
under nearly neutral conditions. Addition of a solution of UO22+ ion

Organochalcogen-Supported Azacalix[3]arenes
963
FIGURE 1 Energy minimized structure for species 1.
to a solution of 1 gave a visual color change (Colorimetric response;
yellowish-green to red on addition of a methanolic solution of UO22+
ions). as well as significant changes in UV-vis spectra, while other metal
ions including alkali (Na+, K+), alkaline-earth (Mg2+, Ca2+, Ba2+), tran-
sition and heavy metal ions (Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Pb2+
,
1
Fe3+) induced no or much smaller color or spectral changes. H NMR
titrations of 1 with UO22+ were also carried out in order to understand
the nature and extent of possible interactions taking place in solution
state (Figure 2a).
The merging of N-CH2 and Se-CH2 protons in the UO22+ complex
indicates the involvement of N in bonding to UO22+. At the same time,
a single sharp peak at δ 311.13 ppm in the 77Se NMR spectrum of rep-
resentative species 1 was split into a multiplet in the uranyl complex,
which gives an indication of the weaker interactions of selenium in co-
ordination geometry (Figure 2b). The potentiometric sensing ability of
the receptors with ions of alkali, alkaline earth metals and heavy metal
ions have also been monitored. In preliminary experiments, ionophore
1 was used as a potential neutral carrier gave a better response for
uranyl ions compared to the other metal ions studied. The uranyl ion se-
lective electrode based on ionophore 1 exhibited a near-Nernstian slope
of 28.69 mV per decade over a wide linear concentration range of 1.0 ×
10−1 − 5.0 × 10−6 M with an internal reference solution, 1.0 × 10−2
M
[UO2(NO3)2] in methanol. The pH dependence of uranyl ions (UO2)2+
ISE (1) was examined over the pH range 1–13 at a (UO2)2+ ion concen-
tration 1.0 × 10−3 M. The potential was found to remain constant from
pH 1.99 to 5.40. Beyond pH 5.40, the potential was found to decrease
due to the formation of hydroxyl complexes of uranyl ions. At pH < 1.99,
the membrane suffered strong interference from hydrogen ions due to
protonation of the ionophore (Figure 3).

964
S. Khan et al.
1
FIGURE 2 Spectral changes in the (a) H NMR and (b) 77Se NMR spectrum
of the species 1 upon addition of uranyl nitrate solution (CD3OD).
14 8
14 6
14 4
14 2
14 0
13 8
13 6
13 4
13 2
13 0
12 8
0
5
10
15
p H
FIGURE 3 Effect of pH on (UO2)2+-ISE (1) at 1.0 × 10−3 M [UO2(NO3)2]
solution.

Organochalcogen-Supported Azacalix[3]arenes
965
In summary, the syntheses of chalcogen-supported azacalix[3]arenes
are described by coupling 2,6-dihydroxy-4-methylphenols with organo-
chalogenoalkyl amines, which are ideally suited for selectively detecting
UO22+ ions.
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