a naked-eye colorimetric receptor for anions based on nitro group featuring with benzimidazole unit

Article abstract of DOI:10.14233/ajchem.2018.21294

A novel receptor based on nitro group featuring with benzimidazole unit (S2) was successfully synthesized and applied to the anion (CN^–, F^–and H2PO4^–) recognition. The S2 changed its colour for light yellow to dark yellow on addition of the anions in DMSO solvent. The LOD and Kass values determined by UV-visible titration was 2.8 × 10^–6 M and 1.2 (± 0.25) × 10⁶ M^–1 for CN^– ion; 1.14 × 10^–6 M and 2.5 (± 0.25) × 10⁶ M^–1 for F^– ion; and 1.23 × 10^–5 M and 6.25 (± 0.177) × 10⁶ M^–1 for H2PO4^– ion, respectively.

Full text of DOI:10.14233/ajchem.2018.21294

Asian Journal of Chemistry; Vol. 30, No. 9 (2018), 1933-1936
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21294
A Naked-Eye Colorimetric Receptor for Anions Based on
Nitro Group Featuring with Benzimidazole Unit
2
R. RAHMAWATI1,2,*, B. PURWONO2,* and S. MATSJEH
1Study Program of Chemistry, Department of Education of Mathematics and Natural Sciences, University of Mataram, Jalan Majapahit 62,
Mataram, Indonesia
2Department of Chemistry, University of Gadjah Mada, Jalan Kaliurang Sekip Utara Bulaksumur 21, Yogyakarta, Indonesia
*Corresponding authors: E-mail: purwono.bambang@ugm.ac.id; tqomari31@gmail.com
Received: 20 February 2018;
Accepted: 24 April 2018;
Published online: 31 July 2018;
AJC-18998
A novel receptor based on nitro group featuring with benzimidazole unit (S2) was successfully synthesized and applied to the anion (CN–, F–
and H2PO4–) recognition. The S2 changed its colour for light yellow to dark yellow on addition of the anions in DMSO solvent. The LOD
and Kass values determined by UV-visible titration was 2.8 × 10–6 M and 1.2 ( 0.25) × 106 M–1 for CN– ion; 1.14 × 10–6 M and 2.5 ( 0.25)
× 106 M–1 for F– ion; and 1.23 × 10–5 M and 6.25 ( 0.177) × 106 M–1 for H2PO4– ion, respectively.
Keywords: Colorimetric, Nitro group, Benzimidazole.
recognition and sensing during the past decades [7]. A nitro
group functionality was introduced into benzimidazole moieties,
which were anticipated to be responsible for colour changes
and also to increase hydrogen bond donor tendency. Incorpora-
ting the nitro group resulted shifting the wavelength absorbance
of sensor, facilitating the occurrence of deprotonation and
resulted strong colour of sensor [5].
In the previous study, we designed a chemosensors com-
pound derived from benzimidazole (S1) [8] which are active
as flourescence receptor and selectively to detect CN– ion.
Sensor S1 are synthesized from vanillin by keeping OH group
as a binding site. In this project, we design a new chemosensor
compound by adding with nitro group at the fifth position on
vanillin ring structure, to produce the 5-nitro vanillin. We made
a new chemosensor (S2) which are derived from benzimidazole
which are bearing by nitro group (Fig. 1).
INTRODUCTION
The development of sensors and receptors capable of
binding and sensing for anions selectively has received a great
attention from chemist due to the key roles played by anions
during the chemical, biological and environmental processes
[1]. The anion can be recognized either by H-bonding or by
the deprotonation of proton in the receptor in organic solvent
[2]. Especially, the colorimetric and ratiometric chemosensors
appear to be particularly attractive due to their simplicity, high
sensitivity and high selectivity. Colorimetric sensing posse-
sses huge advantages in practical application as it can rapidly
provide qualitative information about the analyte without any
expensive instrument [3,4].
Among the chemosensors for the detections of anions,
the colorimetric chemosensor have attracted considerable
attention since they provide immediate qualitative signal,
which allows direct naked-eye detection of anion because of a
specific colour change of solution upon anion complexation
[5]. Binding of anions such as AcO–, F– and H2PO4– results
in a note worthy change in the visible region of spectrum
(approximately 100 nm red shift), which can be detected by
the ‘naked-eye’ [6].
The nitro group was introduced on S2 to affects the change
of LOD value, Kass value and colour mode of the original com-
pound (S1).
EXPERIMENTAL
Melting point was measured using a Electrothermal-9100,
the IR spectra measured using a FTIR Shimadzu Prestige-21,
Mass spectra were taken by gas chromatograph-mass spectro-
–
A large numbers of anion receptors containing NO2
subunits have been designed, synthesized and tested for anion
13
meter (Shimadzu-QP2010S), 1H and C NMR were measured
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1934 Rahmawati et al.
Asian J. Chem.
OCH3
OCH3
RESULTS AND DISCUSSION
N
N
N
N
The S1 compound in DMSO solvent shows a colourless
solution, absorbed at λmax = 295 nm. Addition of anions to the
S1 solution did not any colour change and observation under
366 nm UV lamp shows a fluorescence response only toward
CN– ion (selective). The inclusion of nitro group into S2 indi-
cated a change in properties and response to anions. The S2 in
DMSO solvent is a yellow colour, its means the S2 is a colori-
metric responsive response and observation under 366 nm UV
lamp shows non-fluorescence response. The S2 absorbed at
OH
OH
H
H
NO2
H
S2
S1
Fig. 1. Structures of S1 and S2 compounds
using a JOEL JNM ECA-500 MHz, fluorescent were measured
using a Spectro Fluorophotometer Shimadzu RF-6000.
All the reagents obtained commercially were used without
further purification: DMSO, DCM, water, ethanol. The material
synthesis: vanillin, o-phenylendiamine, boric acid. The anion
were added in the form of sodium cyanide, sodium flouride
and sodium dihydrogen phosphate. All the materials for syn-
thesis is p.a quality Merck.
λ
max = 450 nm (visible region), not selective to certains anions
because S2 responds positively to anions. Addition of anions
to the S2/DMSO solution causes the colour change along with
the increase of anions concentration, from yellow to Amber
colour, shifted absorbance wavelength to λmax = 470 nm. Titra-
tions of anions does not change the colour and λmax caused
only more strong colour and increase the absorbance value.
Compared with S1 sensor that are fluorescent and selective
against CN– ion with LOD 8.8 × 10–6 M and Kass 2.5 ( 0.26)
× 106 M–1, the S2 not only responds as a colorimetric sensor and
is not selective towards CN– ion, but also it can detect F– and
H2PO4– ions. With the inclusion of nitro group, the S2 [LOD
value 2.8 × 10–6 and Kass value 6.25 ( 0.177) × 106 M–1] sensor
becomes more sensitive than the S1.
Naked eye detection of anions: The anion binding study
of receptor S2 (1 × 10–7 M) have been investigated by ‘naked-
eye’ in DMSO solution. Visual inspection of receptor S2
showed a clear colour change from light yellow to dark orange
upon addition of CN–, F– and H2PO4– ions (1 × 10–4 M). On the
other hand, addition of Br– and I– into the solution did not
result in any colour change (Fig. 3).
Method: The method on synthesis of S2 is applied by
Karimi’s method [9]. This synthesis used 5-nitrovanillin as a
carbonyl sources, using hot water (40 °C) to dillute the reactans
and the synthesis was conducted at room temperature. A 5-
nitrovanillin (0.32 g), o-phenylendiamine (0.21 g) and boric
acid (0.1 g), were mixed in 5 mL of hot water. A mixture was
stirred directly at room temperature for 5 min (the progress of
reaction was monitored by TLC).After completion of reaction,
the obtained solid was collected by filtration and purified by
recrystalization from boiled ethanol (Fig. 2). Colour dark
orange powder, 88 % yield, m.p. 207.7-208.5°C; FTIR (KBr,
ν
max, cm–1): 3441.01 O-H from phenol dan N-H, 2931.8 C-H
methyl, 2337.72 C=N imidazole, 1612.49 C=C aromatics
(3093.82 C-H sp2), 1543.05 NO2, 1280.73 cm–1 C-O-C ether;
1H NMR (500 Mhz, CDCl3): 8.307 (s,1H), 8.021 (s, 1H), 7.764
(d, 1H), 7.554 (m, 1H), 7.074 (s, 2H), 5.573 (s, 2H), 3.869 (s,
3H); 13C NMR (500 MHz, CDCl3): 56.778, 110.991, 113.487,
114.572, 116.856, 119.314, 123.115, 127.588, 137.157,
141.986, 150.02, 151.579; MS (EI) : m/z 285 (M+, 75 %), 122
(M+, 100 %).
The 5-nitrovanillin compound was synthesized from
Vanillin by Yadav method [10] with some modifications. A
vanillin (0.07 mol) was dissolved in 55 mL of dichloromethane,
squirted by 12 mL of HNO3, then stirred for 20 min at room
temperature, added 25 mL of ice water then leave it for 2 h,
the solid formed was recrystallized with ethanol. The melting
point of synthesized product was determined and characterized
by FTIR instrument. The synthesized 5-nitrovanillin is light
yellow powder, 64 % yield, m.p 175-177 °C (reference, 176
°C); FTIR (KBr, νmax, cm–1): 1560.77 due to NO2 group.
UV-visible spectroscopy titration: A solution of S2 (1 ×
10–7 M) changed from light yellow to dark yellow upon the
addition of 40 eq. (2 × 10–5 M) of CN– or F– or H2PO4–. The
colouration of the solution was intensified with increasing
anion concentration (Fig. 4).
The ability of S2 to recognize CN–, F– and H2PO4– was
investigated by monitoring UV-visible spectroscopy. Fig. 5
shows the change in UV-visible spectra of S2 during titration
with anions.
In absence of anion, S2 absorbed light at λmax = 455 nm
with absorbance value (A) 0.156.As a concentration of anions
–
(CN–, F– and H2PO4 ) was added, the wavelength shifted to
λ
max 470 nm and absorbance increase. The increasing of anions
concentration does not cause any wavelength shifted but just
caused increasing of the absorbance (A) intensity.
O
HC
O
CH3
OH
H2N
N
N
Boric acid 0.1 g
+
Water 40 °C
stirr, r.t. 5 min
O2N
OCH3
H2N
NO2
H
OH
5-Nitrovanillin (2 mmol)
o-Phenilendiamine (2 mmol)
88 % Dark orange powder (S2)
Fig. 2. Scheme of synthesis the sensor compound (S2)

Vol. 30, No. 9 (2018)
A Naked-Eye Colorimetric Receptor for Anions Based on Nitro Group with Benzimidazole Unit 1935
(c)
(d)
(e)
(f)
(a)
(b)
Fig. 3. Visual colour solution (a) S2, (b) S2+F–, (c) S2+CN–, (d) S2+ H2PO4–, (e) S2+I–, (f) S2+Br–
Figs. 7 and 8 show the probability scheme of interaction
of S2-ions complex.
(a)
(b)
(c)
Determination of LOD and Kass: The colorimetric
detection limit of S2 for anions (CN–, F– and H2PO4–) were
also calculated by using UV-visible data and gave the value of
2.8 × 10–6 M, 1.14 × 10–5 M and 1.23 × 10–5 M, respectively.
On the basis of their stoichiometry ratio, the corresponding
–
binding constant (Kass) of S2 for anions (CN–, F– and H2PO4 )
were calculated based on the UV-visible titration experiments.
For a complex with 1:1 (H:G) stoichiometry ratio, the binding
constant could be determined by non-linear fitting analysis of
the titration curves according to eqn. 1 and for complex 2:1
(H:G) the binding constant could be obtained according to
the eqn. 2 [6].
1/2
CH + CG +1 CH + CG +1

−
− 4CH×CG




K
K
(1)
(2)
A = Ao + (A + Ao )×
Fig. 4. Colour change of S2 upon addition increasing concentration of
2CH
anion : (a) CN–, (b) F– and (c) H2PO4–
(A − Ao ) = [(ε − εo )×CH×K ×CG2 ]−1 +[(ε − εo )CH]−1
The A is intensity of absorbance of host when guest is
added;Ao is intensity of absorbance of host only; ε is extinction
coefficient host-guest; εo is extinction coefficient host only;
CH and CG is concentration of host and guest, respectively;
K is binding constant. The Kass result is 1.2 ( 0.25) × 106 M–
The spectra showed isosbestic point at λ 370 nm (λ 390
nm), λ 375 nm and λ 380 nm for CN–, F–, H2PO4–, respectively,
indicated that S2 reacted with ions form ion complex and the
–
hydrogen-bonding [11]. Meanwhile, for F– and H2PO4 , an
isosbestic point was observed during the titration process.
Suryanti et al. [12] hypothesized that the anion sensing process
first involved hydrogen bonding interaction and than followed
by the protonations upon further addition of ions.
for S2-CN–, 2.5 ( 0.25) × 106 M–1 for S2-F– and 6.25 (
1
0.177) × 106 M–1 for S2-H2PO4–.
Conclusion
In order to determine the stoichiometric ratio between S2
and anion guest, the method of continuous variation (Job’s
plot) [7] was used. The S2-anions (CN–, F– and H2PO4–) complex
concentration approaches a maximum when the mole fraction
of S2 is 0.5, 0.5, 1.0, respectively. This indicated that S2 and
anions form 1:1, 1:1, 2:1 complexes (stoichiometry ratio),
respectively (Fig. 6).
In summary, we have synthesized a ‘naked-eye’ colouri-
metric anion receptor S2 based on nitro group and its shows
–
colorimetric sensitivity for CN–, F– and H2PO4 ions in DMSO
solution. The presence of Nitro group resulted in the change
of nature and character of the original compound (S1 sensor):
the fluorescence changed to colourimetric activity, LOD value
decreased and Kass value increased.
S2
S2
S2
2
1
0
2
2
1
0
S2 + eq. 1
S2 + eq. 2
S2 + eq. 3
S2 + eq. 4
S2 + eq. 5
S2 + eq. 1
S2 + eq. 2
S2 + eq. 3
S2 + eq. 4
S2 + eq. 5
S2 + eq. 1
S2 + eq. 2
S2 + eq. 3
S2 + eq. 4
S2 + eq. 5
S2 + eq. 6
(a)
(b)
(c)
CN– ion
S2 + eq. 6
H2PO4– ion
S2 + eq. 6
F– ion
1
isosbestic
point
isosbestic
point
isosbestic
point
600
300
500
400
600
600
300
500
300
500
400
400
Wavelength (nm)
Wavelength (nm)
Wavelength (nm)
Fig. 5. Change of UV-visible spectral of S2 upon titration of anion (a) CN–, (b) F– and (c) H2PO4–

1936 Rahmawati et al.
Asian J. Chem.
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
(b)
(a)
0.9
0.8
0.7
0.6
0.5
0.4
0
0.5
1.0
1.5
2.0
0
0.5
1.0
1.5
2.0
S2]/[S2] + [CN–]
[
S2]/[S2] + [F–]
[
3.20
3.15
3.10
3.05
3.00
2.95
2.90
2.85
2.80
2.75
y = 3.1001x + 2.8551
R2 = 0.9145
0.7
(c)
(d)
y = 0.5138x + 3.0105
R2 = 0.8927
0.6
0.5
0.4
CN–
F–
y = 1.7057x + 2.8679
R2 = 0.7975
H2PO4–
0.3
0
0.02
0.04
0.06
0.08
0.10
0.12
0
0.5
1.0
1.5
2.0
S2]/[S2] + [H2PO4–]
Increasing of concentration
[
Fig. 6. Job’s plot of S2 ions (a) CN–, (b) F–, (c) H2PO4–. (d) Linear regression curve of ions
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CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
https://doi.org/10.1088/1757-899X/172/1/012038.