Test kit for detection of biologically important anions: A salicylidene-hydrazine based Schiff base

Article abstract of DOI:10.1016/j.saa.2012.10.038

Test paper coated with Schiff base [(N,N^/-bis(5-nitro- salicylidene)hydrazine] receptor 1 (host) can selectively detect fluoride and acetate ions (guest) by developing yellow color which can be detected by naked-eye both in aqueous-acetonitrile solution and in solid supported test kit. UV-vis spectral analysis shows that the absorption peaks at 288 and 345 nm of receptor 1 gradually decrease its initial intensity and new red shifted absorption bands at 397 nm and 455 nm gradually appear upon addition of increasing amount of F^- and AcO^- ions over several tested anions such as H₂PO4-, Cl^-, Br^-, I^-, NO3-, NO2-, HSO4-, HSO3-, and ClO4- in aqueous-acetonitrile solvent. The colorimetric test results and UV-vis spectral analysis are in well agreement with ¹H NMR titration results in d₆-DMSO solvent. The receptor 1 forms 1:2 stable complexes with F^- and AcO^- ions. However, similar kind of observation obtained from UV-vis titrations in presence of AcOH corresponds to 1:1 complexation ratio indicating the formation of H-bonding interaction between the receptor and anions (F^- and AcO^- ions). So, the observed 1:2 complexation ratio can only be explained on the basis of deprotonation (～1 eqv.) and H-bonding (～1 eqv.) interactions [1]. The ratiometric analysis of host-guest complexes corroborates well with the proposed theoretical model optimization at Density Functional Theory (DFT) level.

Full text of DOI:10.1016/j.saa.2012.10.038

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 102 (2013) 314–318
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
‘‘Test kit’’ for detection of biologically important anions: A
salicylidene-hydrazine based Schiff base
a
c
a,
Sasanka Dalapati a, Md Akhtarul Alam b, , Sankar Jana , Saswati Karmakar , Nikhil Guchhait
⇑
⇑
a Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India
b Department of Chemistry, Aliah University, DN-41 & 47, Sector-V, Saltlake, Kolkata 700 091, India
c Department of Chemistry, Sree Chaitanya College, Habra, North 24 Parganas, West Bengal, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
‘‘Test kit’’ was prepared for the
detection of biologically important
anions.
"
"
‘‘Test kit’’ can selectively detect Fꢀ
and AcOꢀ ions.
Color change of the ‘‘test kit’’ in
presence of anions were detected by
naked-eye.
"
Predicted complexation behavior
from theoretical structural
optimization corroborates with the
experimental results.
a r t i c l e i n f o
a b s t r a c t
Test paper coated with Schiff base [(N,N/-bis(5-nitro-salicylidene)hydrazine] receptor 1 (host) can selec-
tively detect fluoride and acetate ions (guest) by developing yellow color which can be detected by
naked-eye both in aqueous–acetonitrile solution and in solid supported test kit. UV–vis spectral analysis
shows that the absorption peaks at 288 and 345 nm of receptor 1 gradually decrease its initial intensity
and new red shifted absorption bands at 397 nm and 455 nm gradually appear upon addition of increas-
ing amount of ꢀFꢀ and AcOꢀ ions over several tested anions such as H2POꢀ4 , Clꢀ, Brꢀ, Iꢀ, NOꢀ3 , NO2ꢀ, HSOꢀ4 ,
HSOꢀ3 , and ClO4 in aqueous–acetonitrile solvent. The colorimetric test results and UV–vis spectral anal-
ysis are in well agreement with 1H NMR titration results in d6-DMSO solvent. The receptor 1 forms 1:2
stable complexes with Fꢀ and AcOꢀ ions. However, similar kind of observation obtained from UV–vis
titrations in presence of AcOH corresponds to 1:1 complexation ratio indicating the formation of H-bond-
ing interaction between the receptor and anions (Fꢀ and AcOꢀ ions). So, the observed 1:2 complexation
ratio can only be explained on the basis of deprotonation (ꢁ1 eqv.) and H-bonding (ꢁ1 eqv.) interactions
[1]. The ratiometric analysis of host–guest complexes corroborates well with the proposed theoretical
model optimization at Density Functional Theory (DFT) level.
Article history:
Received 13 August 2012
Received in revised form 15 October 2012
Accepted 23 October 2012
Available online 1 November 2012
Keywords:
Test kit
Schiff base
Colorimetric
Aqueous–acetonitrile
DFT calculation
Anion detection
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
There are a few examples of test kits which are reported in the
current chemical literature for the detection of ions (cation or an-
ion). Importantly, the colorimetric detection of ions by a cheap
method is gaining faster attention in the recent development of
chemosensors design [2–6]. It is found that small quantities of ions
⇑
Corresponding authors. Tel.: +91 33 23508386; fax: +91 33 23519755 (N.
Guchhait).
E-mail addresses: alam_iitg@yahoo.com (M.A. Alam), nguchhait@yahoo.com (N.
Guchhait).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.10.038

S. Dalapati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 102 (2013) 314–318
315
play an important role both in the environmental and biological
NO2
OH
MeOH
25º C
systems [7–12]. However, excess amount of ions may cause of sev-
eral serious diseases as well as immune system disruptions [13–
15]. Because of significant importance, detection of ions with the
help of easily synthesized receptor and minimal instrumental
assistance be always welcomed for the purpose of practical
applications.
+
H2N-NH2
N
NO2
O2N
N
CHO
HO
OH
1
Scheme 1. Synthesis of compound 1.
Recently, Li and co-workers reported and well established a
receptor (as our receptor 1, Scheme 1) without ANO2 signaling unit
capable for selective sensing of Fꢀ ion in DMSO solvent [16]. Due to
the problem of practical applicability of their receptor, here we re-
port nitro substituted Schiff-base receptor 1 by considering three
important factors: (i) the nitro group (ANO2) having electron with-
drawing effect is expected to enhance the acidity of the phenolic
AOH group and as a consequence the hydrogen donor efficiency
of the receptor 1 is also increased, (ii) the stronger acidity of phe-
nolic AOH group may enhance its sensitivity and thus useful in
aqueous environment, (iii) UV–vis and 1H NMR absorption proper-
ties of the chromogenic nitro-phenyl moiety may be altered by
receptor–anions interaction and thus promote the colorimetric
and spectral sensing recognition events [17,18]. The merit of this
designing principle is undoubtedly reflected in our experimental
and theoretical results. Receptor 1 selectively recognizes Fꢀ and
AcOꢀ anions by naked-eye color change, both in aqueous–acetoni-
trile solution as well as in solid supported ‘‘test kit’’. UV–vis and 1H
NMR titration results can precisely explain both the deprotonation
and H-bonding phenomena. Interestingly, UV–vis spectral analysis
reveals that 1 (host) in absence of AcOH form 1:2 complexes with
fluoride and acetate ion (guest), respectively. But, in presence of
AcOH it forms 1:1 H-bonded complex. So, receptor involves both
deprotonation and H-bonding interactions in the absence of acid.
Furthermore, the proposed binding models of the receptor-anions
complexes have been optimized at Density Functional Theory
(DFT) level, which corroborates well with the experimental
findings.
plexes. The binding or association constants (K) have been
determined using Benesi–Hildebrand (B–H) relation [19,20].
The ground state optimization at DFT level has been carried out
in vacuum with B3LYP-hybride functional and 6-311++G(dp) basis
set using Gaussian 03 suit [21].
Synthesis of receptor 1 (N,N/-bis(5-nitro-salicylidene)hydrazine)
For the synthesis of receptor 1 (Scheme 1), a methanolic solu-
tion (10 ml) of 5-nitro-salicylaldehyde (2.00 gm, 11.9 mmol) was
added dropwise to a methanolic solution (5 ml) of hydrazine
monohydrate (0.19 ml, 5.83 mmol) with constant stirring at 0 °C.
The reaction mixture was stirred for 1 h. at room temperature. A
light yellow color solid was precipitated. Filtered off the reaction
mixture and washed with cold methanol. The solid (receptor 1)
was dried under vacuum to obtain the product in the pure form
[22,23]. Yield 82% (1.62 gm, 4.9 mmol). 1H NMR in d6-DMSO,
300 MHz, d (ppm): 7.12 (d, J = 9 Hz, 2H), 8.23 (dd, J = 9 Hz and
2.7 Hz, 2H), 8.66 (d, J = 2.7 Hz, 2H), 9.05 (s, 2H). IR (KBr): 3089
(AOH), 1632 (CH@N), 1574 (C@C), 1234–1486 (ANO2), 969–1099
(NAN) cmꢀ1
.
Result and discussion
Visual color change
Visual color change of receptor 1 (1.0 ꢂ 10ꢀ5 M) has been inves-
tigated in aqueous–acetonitrile solvent. Upon addition of 1–2
equivalents of Fꢀ/AcOꢀ ion in absence of AcOH, the colorless solu-
tion of 1 changes to an intense yellow color, which is detectable by
naked-eye (Fig. S1). This indicates deprotonation/H-bonding inter-
action between the receptor and anions. But, in presence of 10
equivalents AcOH, addition of 1–2 equivalent Fꢀ/AcOꢀ ion the col-
orless solution of 1 changes to light yellow which is also detectable
by naked-eye indicating only H-bonding interaction between the
Experimental
Reagents
All reagents and solvents were used as received from commer-
cial sources without further purification. Tetrabutylammonium
(Bu4Nþ) salts of Fꢀ, AcOꢀ, H2POꢀ, Clꢀ, Brꢀ, Iꢀ, NOꢀ, NOꢀ, HSOꢀ,
4
3
2
4
HSOꢀ3 , and ClO4ꢀ anions and d6-DMSO were purchased from Sig-
ma–Aldrich chemical company. Spectroscopic grade solvents were
used for the spectroscopic measurements.
receptor and anions. In contrast, H2POꢀ ion did not exhibit consid-
4
erable naked-eye color change within the same concentration
range as that of Fꢀ/AcOꢀ ion. However, at higher concentration of
H2POꢀ ion a faint yellow color is observed (Fig. S1) in presence of
4
Apparatus
AcOH indicating H-bonding interaction only. Other ions, such as
Clꢀ, Brꢀ, Iꢀ, NO3ꢀ, NOꢀ2 , HSO4ꢀ, HSO3ꢀ and ClOꢀ4 did not exhibit any
naked-eye detectable color change which means the absence of
such interactions with these ions.
Electronic absorption spectra have been measured by Hitachi
UV–vis (Model U-3501) spectrophotometer. IR spectrum (KBr pel-
let, 4000–400 cmꢀ1) has been recorded on a Parkin Elmer (model
883) infrared spectrophotometer. 1H NMR spectra have been mea-
sured by Bruker, Avance 300 spectrometer using d6-DMSO solvent
with tetramethylsilane (TMS) as internal standards.
UV–vis spectroscopic titration
The anion recognition properties of receptor 1 have also been
investigated by monitoring UV–vis spectral change upon addition
of different anions in aqueous–acetonitrile solvent. Receptor 1
(1.0 ꢂ 10ꢀ5 M) exhibits strong absorption bands at 288 and
345 nm (Fig. 1, blue color1). Upon addition of increasing amount
of Fꢀ ion, the absorbance at 288 and 345 nm gradually decrease
and new red shifted absorption bands at 397 nm and 455 nm
Methods used
Due to poor solubility of 1 in aqueous–acetonitrile media, the
mother solution of the receptor was prepared with solvent mixture
(H2O:CH3CN:DMSO = 4:95:1 v/v). This stock solution has been used
for all experimental consequence (except for 1H NMR titration).
UV–vis titration data were used for the determination of associ-
ation constants (K) and stoichiometries of the host–guest com-
1
For interpretation of color in Fig. 1, the reader is referred to the web version of
this article.

316
S. Dalapati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 102 (2013) 314–318
Fig. 1. UV–vis titration spectra of receptor 1 (1.0 ꢂ 10ꢀ5 M) upon addition of Fꢀ ion
(0–4 equiv.) in aqueous–acetonitrile solvent and Benesi–Hildebrand (B–H) plot for
1:2 complex formed between 1 and Fꢀ ion (inset).
Fig. 3. UV–vis spectral changes of receptor 1 (1.0 ꢂ 10ꢀ5 M) upon addition of AcOꢀ
ion (0–4 equiv.) in aqueous–acetonitrile solvent and (B–H) plot for 1:2 complex
formed between 1 and AcOꢀ ion (inset).
gradually appear (Fig. 1, red/orange color, detection limit 5 lM). A
distinct isosbestic point at 365 nm is observed during the titration
process indicating the existence of equilibrium between the com-
plexed and uncomplexed form of the host (1). The stoichiometry of
host–guest interaction has been determined from UV–vis spectral
titration with the help of Benesi–Hildebrand (B–H) relation. As
shown in Fig. 1 (inset), the B–H plot of 1/[A ꢀ A0] vs. 1/[Fꢀ]2 provides
a straight line indicating 1:2 complexation. In presence of 10 equiv-
alents AcOH, titration with the continuous addition of fluoride anion,
the change in the absorption spectra is almost similar (Fig. 2. detec-
tion limit 12 lM) with that in absence of AcOH, but it involves with
1:1 host–guest interaction (B–H plot of 1/[A ꢀ A0] vs. 1/[Fꢀ] shows
a
straight line, Fig. 2 (inset)) with association constant (K)
3.26 ꢂ 104 Mꢀ1. Similar type of UV–vis spectral changes have been
observed in case of AcOꢀ (Fig. 3) ion and complex is formed with
1:2 ratio (1:OAcꢀ) in absence of AcOH (detection limit 7
l
M) and
M)
with 1:1 ratio in presence of AcOH (Fig. 4, detection limit 15
l
with association constant 8.22 ꢂ 103 Mꢀ1. So, it is noteworthy to
mention here that in absence of AcOH, host–guest interaction in-
volves with deprotonation (1 eqv.) and H-bonding (1 eqv.) phenom-
ena, where as in presence of AcOH it involves with only H-bonding
Fig. 4. UV–vis titration spectra of receptor 1 (1.5 ꢂ 10ꢀ5 M, in presence of 10
equivalents AcOH) upon addition of OAcꢀ ion (0–2 equiv.) in aqueous–acetonitrile
solvent and Benesi–Hildebrand (B–H) plot for 1:1 complex formed between 1 and
OAcꢀ ion (inset).
interaction (1 eqv.). In contrast, H2POꢀ ion exhibits only a tiny spec-
4
tral change even in the presence of 100 times more concentration
Fig. 5. UV–vis spectral changes of receptor 1 (1.0 ꢂ 10ꢀ5 M) upon addition of
H2POꢀ ion (0–400 equiv.) in aqueous–acetonitrile solvent.
4
Fig. 2. UV–vis titration spectra of receptor 1 (1.5 ꢂ 10ꢀ5 M, in presence of 10
equivalents AcOH) upon addition of Fꢀ ion (0–2 equiv.) in aqueous–acetonitrile
solvent and Benesi–Hildebrand (B–H) plot for 1:1 complex formed between 1 and
Fꢀ ion (inset).
(Fig. 5). Presence of AcOH is immaterial in case of H2POꢀ ion, i.e. both
4
(with and without the presence of AcOH) reveal similar results with
the addition of H2POꢀ ion, indicating host–guest H-bonding interac-
4

S. Dalapati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 102 (2013) 314–318
317
ger complexes; Fꢀ > AcOꢀ ꢃ H2POꢀ4 > Clꢀ, Brꢀ, Iꢀ, NOꢀ3 , NO2ꢀ, HSOꢀ4 ,
HSOꢀ3 , ClOꢀ4 [24]. Fluoride anion forms stronger H-bonding com-
plex due its higher basicity.
NMR titration experiments
Furthermore, to investigate the nature of host–guest interaction
in the highest polar organized media, 1H NMR titration experi-
ments were performed in d6-DMSO (partial 1H NMR, Figs. S2–S3).
The receptor 1 exhibits a broad signal (d) at 12.19 ppm corresponds
to the AOH proton in absence of Fꢀ ion. Upon addition of 0.5 equiv.
of Fꢀ ion, peak of the AOH proton disappears and the aromatic pro-
tons Hc and Hd are shifted to upfield from 8.22 to 8.14 and 7.12 to
6.95 ppm, respectively, (Fig. S2) indicating the possibilities of
deprotonation as well as H-bonding interactions. The stronger
host–guest interaction between 1 and Fꢀ ion increases the electron
density in the aromatic ring which is responsible for the upfield
shift of aromatic proton. On further addition of more than two
equivalents of fluoride anion, all the aromatic peaks were shifted
to upfield, which might be due to the complete deprotonation of
phenolic AOH proton. Under similar experimental condition upon
titration of receptor 1 with acetate ion, similar type of chemical
shift was observed indicating invariable host–guest interactions
(Fig. S3). Other competitive anions (Clꢀ, Brꢀ, Iꢀ, NOꢀ3 , NO2ꢀ, HSO4ꢀ,
HSOꢀ3 , and CIOꢀ4 ) hardly induce 1H NMR chemical shift of receptor
1 indicating the absence of such interactions.
Fig. 6. UV–vis spectral changes of receptor 1 (1.0 ꢂ 10ꢀ5 M) upon addition of
different anions (Fꢀ and OAcꢀ = 4 equiv., others anions = 400 equiv.) in aqueous–
acetonitrile solvent.
tion only. Other anions, such as Clꢀ, Brꢀ, Iꢀ, NOꢀ3 , NOꢀ2 , HSOꢀ4 , HSO3ꢀ,
and CIOꢀ4 did not exhibit any notable spectral or color change, indi-
cating the absence of host–guest interactions (Fig. 6).
In general, Schiff-bases have a tendency to undergo phenol-
imine and keto-amine tautomerization equilibrium. In the present
case, keto-amine tautomer of 1 is facilitated by the electron with-
drawing nitro (ANO2) group present at the para position with re-
spect to the phenolic AOH group, as a result the acidity of
phenolic AOH group increases and thereby enhances deprotona-
tion/H-bonding interaction with highly basic fluoride and acetate
ions. The deprotonation/H-bonding interaction increases the elec-
tron density on the phenolic ‘‘O’’ atom (donor) and a charge trans-
fer from electron rich O atom to electron deficient ANO2 group
(acceptor) is facilitated, resulting the appearance of the yellow col-
or [24,25].
Test kit preparation and sensing behaviors of receptor 1
On the basis of host–guest interaction pattern, concluded from
colorimetric, UV–vis and 1H NMR changes; we have shifted our
interest about the potential practical applications of 1 as Fꢀ/AcOꢀ
anion sensor [9]. To explore this possibility, we have prepared a
test paper (Whatman-40) coated with Schiff base (test kit) by
dropping aqueous–acetonitrile solution of 1 (1 ꢂ 10ꢀ4 M) and then
dried it in air. For the detection of anions, solutions of anions
(1 ꢂ 10ꢀ4 M) were dropped onto the test paper (test kit) and then
dried it in air. Interestingly, bright yellow color appears on that
positions where Fꢀ and AcOꢀ ions were actually dropped
The selectivity and sensitivity of receptor 1 toward the anions
can be rationalized on the basis of their basicity as well as their
structural representations. As the basicity of Fꢀ and AcOꢀ ions
are higher with respect to the rest of the anions tested, they are
bound to form stronger complexes with receptor 1 and responsible
for remarkable color changes as well as UV–vis spectral changes.
(Fig. S4). Other anions, such as H2POꢀ and Clꢀ exhibit only a faint
4
yellow color at higher concentration, but Brꢀ, Iꢀ, NO3ꢀ, NO2ꢀ,
HSOꢀ4 , HSO3ꢀ, and ClOꢀ4 ions hardly induce any detectable color
changes. The above experiment describes the potential application
of sensor 1 as a test kit for the detection of fluoride and acetate
ions.
On the other hand, H2POꢀ ion with lower basicity and inability of
4
binding with similar fashion due to its tetrahedral geometry, forms
weaker complex. Therefore, dihydrogenphosphate anion hardly in-
duces color change and UV–vis spectral changes. However, the col-
or discrimination in case of Fꢀ and AcOꢀ ions did not recognize
visually. But, UV–vis spectral changes of 1 in presence of various
anions (Fig. 6) clearly discriminate their interaction behaviors.
The detail spectral analysis (Fig. 6) and association constants of
the host–guest complexation follow the trend as an order of stron-
Simple theoretical modeling and optimization
The most stable conformers of receptor 1 and the nature of
binding interaction with anions have also been predicted with
Fig. 7. Optimized geometry of 1 at DFT level with B3LYP-hybride functional and 6-311++G(dp) basis set.

318
S. Dalapati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 102 (2013) 314–318
Table 1
Some useful theoretical parameters (DFT level with B3LYP functional and 6-311++G(dp) basis set) of receptor 1 and after complexation with anions (Aꢀ is Fꢀ and AcOꢀ anions).
Numbering of atoms is presented in Fig. 7.
Objects
H1ꢄ ꢄ ꢄN1
H1–O1
C@O1
H2ꢄ ꢄ ꢄN2
H2–O2
C@O2
O1ꢄ ꢄ ꢄAꢀ
O2ꢄ ꢄ ꢄAꢀ
1
1.772
2.640
2.765
0.989
1.610
1.628
1.333
1.255
1.254
1.772
2.640
2.765
0.989
1.610
1.628
1.333
1.255
1.254
–
–
1ꢄFꢀ
2.539
2.620
2.539
2.620
1ꢄAcOꢀ
the help of theoretical calculations. The optimized global minimum
of receptor 1 shows that two nitro-salicylidene moieties are situ-
ated in s-trans conformation (Fig. 7) and each phenolic AOH group
is intramolecularly H-bonded with imine nitrogen (distances
H1ꢄ ꢄ ꢄN1 and H2ꢄ ꢄ ꢄN2 are 1.772 Å and 1.772 Å respectively, Table 1).
These kind of structural orientation of the host (1) favors to inter-
act with incoming guest (e.g. fluoride and acetate ion) through
opposite direction and thus form 1:2 host–guest complexes
(Figs. S5–S6). Importantly, optimized structure of 1ꢄFꢀ/1ꢄAcOꢀ
complex shows that both ions are preferably deprotonated the
highly acidic phenolic AOH protons (O1ꢄ ꢄ ꢄFꢀ = O2ꢄ ꢄ ꢄFꢀ = 2.539 Å,
O1ꢄ ꢄ ꢄAcOꢀ = O1ꢄ ꢄ ꢄAcOꢀ = 2.620 Å, Table 1, Figs. 7 and S5–S6). How-
ever, in both complexes (1ꢄFꢀ and 1ꢄAcOꢀ) the O1–H1 and O2–H2
band distances are remarkably higher compared to the bare recep-
tor (1, Table 1). And side by side the keto-bond (C–O1 and C–O2
bonds) distances are decreased (get more double bond character,
Table 1). These bond variations clearly indicate that host–guest
complex formation promotes the receptor 1 to undergo phenol-
imine to keto-amine tautomerization process.
Acknowledgments
This work is supported by grants from DST, India (Project No.
SR/S1/PC/26/2008) and CSIR, India (Project No. 01(2161)07/EMR-
II) to NG and UGC, India (Project No. PSW-194/11-12 (ERO)) to
SK. SD and SJ would like to acknowledge UGC for Fellowship.
MAA thank to the VC of AU for giving him permission to work
at CU.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.10.038.
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In summary, we have demonstrated an easily prepared Schiff
base 1 [N,N/-bis(5-nitro-salicylidene)hydrazine] coated test paper
(test kit) that can selectively detect Fꢀ and AcOꢀ ions without
the help of any spectroscopic instrument by simply developing
naked-eye detectable bright yellow color in aqueous–acetonitrile
medium. The formation of host–guest complex facilitates the
charge transfer process between phenolic oxygen and the electron
withdrawing nitro group, namely: conversion of phenol-imine to
keto-amine tautomer. In the presence of AcOH, 1:1 host–guest
complexation occurs (detection limit belongs to 12–15 lM), indi-
cating H-bonding complex formation. On the other hand, absence
of AcOH, 1:2 host–guest complexation occurs (detection limit be-
longs to 5–7 lM) indicating deprotonation as well as H-bonding
interactions. Bathochromic spectral shift in the UV–vis titration
and chemical shift in 1H NMR titration strongly admit the host–
guest interactions. Furthermore, predicted stoichiometries of
host–guest complexes based on Density Functional Theory (DFT)
level optimization corroborates well with the experimental find-
ings. This easy-to-prepared and cheap test kits would always be
advantageous to detect Fꢀ and AcOꢀ ions in economically poor
and undeveloped regions in the world.
[25] X. Bao, J. Yu, Y. Zhou, Sens. Actuators, B 140 (2009) 467–472.