An Imidazole based probe for relay recognition of Cu2+ and OH- ions leading to and logic gate

Article abstract of DOI:10.1007/s12039-015-0880-4

2-(2-methoxyphenyl)-4,5-diphenyl-1H-imidazole 1, an imidazole-based compound, was found to sense Cu²⁺ ions via fluorescence and absorption spectroscopy over a number of other metal ions. During Cu²⁺ sensing, the chemosensor 1 followed a "switch-off" mechanism. Job's plot supported 1:1 stoichiometry of 1-Cu²⁺ complex. The 1-Cu²⁺ complex formed in situ underwent different absorption changes with OH^- ions. These differential absorption changes observed with the addition of Cu²⁺ and OH^- ions were used to mimic AND logic gate using A_274nm as output. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-015-0880-4

J. Chem. Sci. Vol. 127, No. 7, July 2015, pp. 1253–1259. ꢀc Indian Academy of Sciences.
DOI 10.1007/s12039-015-0880-4
2
+
−
An Imidazole based probe for relay recognition of Cu and OH ions
leading to AND logic gate
∗
NAVNEET KAUR and PRIYA ALREJA
Department of Chemistry, Panjab University, Chandigarh, 160 014, India
e-mail: neet_chem@yahoo.co.in; neet_chem@pu.ac.in
MS received 9 February 2015; revised 30 March 2015; accepted 2 April 2015
Abstract. 2-(2-methoxyphenyl)-4,5-diphenyl-1H-imidazole 1, an imidazole-based compound, was found to
sense Cu2 ions via fluorescence and absorption spectroscopy over a number of other metal ions. During Cu
+
2+
sensing, the chemosensor 1 followed a “switch-off” mechanism. Job’s plot supported 1:1 stoichiometry of 1-
2
+
2+
−
Cu complex. The 1-Cu complex formed in situ underwent different absorption changes with OH ions.
2
+
−
These differential absorption changes observed with the addition of Cu and OH ions were used to mimic
AND logic gate using A274nm as output.
Keywords. Imidazole; Chemosensor; Cu2 sensing; quenching; logic gate
+
1
. Introduction
copper can cause gastrointestinal disturbance and also
12
liver or kidney damage upon long term exposure.
2
+
Imidazoles are common scaffolds in highly significant
bio molecules, including biotin, histidine, histamine
and many alkaloids, which have been shown to exhibit
antimicrobial, anticryptococcal, cytotoxic and other
biological activities. Biological activity of imidazole
derivatives is the main motive for their wide use
in medicine, agriculture and pharmaceutical industry.
Moreover, they also have a great potential in the area
of optical and chemical sensors, fuel cell membranes,
luminescent materials, ion-conducting electrolytes
Therefore, detection of Cu is of great importance for
elucidating its complex physiological and pathologi-
cal roles. A number of recent literature reports show
quenching of fluorescence intensity with addition of
1
2
+
13
Cu ions in non-aqueous medium.
Also, the ability of chemosensors to produce differ-
ent optical signals lead to the construction of photonic
driven systems and network that functions as molecu-
2
3
4
7
8
1
4
14
lar logic gates, molecular keypad lock devices, lab-
6
14b,16
17
on-molecule type devices,
and ion-pair receptors.
and photovoltaic materials for solar cell applications.
These systems use physical or chemical inputs to gen-
erate outputs based on a set of logical operators and
mimic the function of logic gates by applying the laws
of Boolean algebra.
The presence of a donor pyridine like nitrogen atom
within the imidazole ring makes it a good metal ion
sensor. In this sense, the binding properties of the imi-
dazole core may be modulated by linear or angular
annulations to aza-heterocycles leading to expanded
Herein, we report an imidazole possessing chemo-
sensor (1) which can function as a molecular AND
9
2+
imidazole derivatives bearing several binding sites.
type binary logic gate with two inputs viz. Cu and
−
Moreover, the appreciable changes observed in the
fluorescence upon metal binding makes imidazole
derivatives more attractive as chelators. Therefore, imi-
dazole derivatives have been used to construct highly
sensitive fluorescent chemosensors for sensing and
imaging of metal ions as well as making organic light
OH ions. The output is the increased absorbance in the
presence of both the inputs. The literature survey for
1
8
efficient synthesis of 1 reveals several methods with
19
and without catalyst. Imidazole derivatives similar
to 1 possess antinociceptive, anti-inflammatory and
analgesic activity and have been recently reported to
20
19b
10
2+
exhibit α-glucosidase inhibition to treat diabetes.21
emitting diodes. Amongst different metal ions, Cu
ions play significant roles in various biological pro-
cesses such as hemopoiesis, metabolism, growth, and
11
immune system. However exposure to high level of
2. Experimental
The chemosensor 1 was synthesized according to
scheme 1.
∗
For correspondence
1253

1254
Navneet Kaur and Priya Alreja
H CO
3
O
O
HN
N
CHO
CH COONH4
3
OCH3
CH COOH
+
3
1
Scheme 1. Synthesis of chemosensor 1.
Benzil (1 g, 4.75 mmol) and ammonium acetate
10.56 g, 137 mmol) were dissolved in 10 mL of
0.35
.3
0.25
.2
0.15
.1
(
0
hot glacial acetic acid. While the mixture was stirred,
a solution 2–methoxy benzaldehyde (0.646 g, 4.75
mmol) in 10 mL of glacial acetic acid was added drop
0
◦
wise to the mixture. The mixture was heated at 90 C
for 3 h and was then poured in 200 mL of water.
The solution was neutralized with ammonia to pH
0
7
and the contents were filtered to yield crude pre-
cipitates which were washed with large portions of
0.05
0
22
water. Recrystallization of crude product from mix-
ture of methanol and chloroform resulted in formation
of pure chemosensor 1 (figure S1–S4). Pale white solid,
L
Na
K
Mg Al Mn Fe Co Ni Cu Zn Cd Hg
n+
Metal ions (M )
◦
−1
8
3
(
(
-
0% Yield, M.p: 190–194 C; IR peaks (KBr, cm ):
1
063 (υ ), 2978 (υAromatic C-H), 1584(υ ); H NMR Figure 1. UV-vis. absorption responses of 1 (10 μM) to
N−H
C=N
various metal ions (1000 μM) in CH3CN. Bars represent the
intensity of absorption at 315 nm.
CDCl , 400 MHz, ppm) δ: 3.96 (s, 3H, - OCH ), 6.95
3
3
d, J = 8.28 Hz, 1H, Ar-H), 7.04(t, 1H, Ar-H), 7.30
7.18 (m, 7H, Ar-H ), 7.51 (s, 4H, Ar-H), 8.43 (dd,
JA = 7.76 Hz, J
= 1.68 Hz, 1H, Ar-H), 10.52
B
2+
equiv. of Cu ions (figure 1). Therefore, chemosen-
13
(
s, 1H, NH); C NMR (CDCl , 75 MHz, ppm) δ:
3
2+
sor 1 showed selective detection of Cu ions in the
presence of other metal ions such as alkali, alkaline
earth and transition metal ions. This Cu selectivity
could be attributed to the highest Lewis acid charac-
ter of Cu amongst dipositive cations in parallel with
Irving-Williams series of stability of dipositive metal
55.92, 111.21, 118.06, 121.73, 127.27, 127.82, 128.61,
1
28.71, 129.60, 144.03, 155.75. LC-MS: m/z = 327
2
+
+
(
M +1).
2
+
3
. Results and Discussion
22
ion complexes.
The selectivity of 1 was also investigated by measur-
ing the fluorescence emission spectra against different
3.1 Spectral Characteristics of 1 towards metal ions
The metal binding ability of chemosensor 1 was ini- metal ions in CH CN. Figure 2 shows clearly that very
3
tially evaluated by UV-vis spectral analysis using dif- little change in fluorescence intensity resulted by the
2+
ferent metal perchlorates. In the absence of metal ions, addition of different metal ions except in case of Cu .
the maximum absorption of 1 in CH CN was at about This data explicitly showed the selectivity of 1 towards
3
+
2+
2+
3
15 nm. On addition of Cu2 (10 equiv.) to the solu- Cu ions. The quenching caused by Cu transition
tion of chemosensor 1 (10 μM), decrease in absorbance metal ion can be attributed to its paramagnetic nature by
at 315 nm was observed. The addition of other metal which it can easily participate in energy transfer or elec-
ions did not show any significant change in absorp- tron transfer processes with organic fluorophores via
tion spectra even with large excess of metal ions viz. non-radiative deactivation channel and thus, resulting in
+
+
2+
2+
3+
2+
2+
2+
2+
2+
24
Na , K , Mg , Al , Mn , Fe , Co , Ni , Cu , quenching effect.
2
+
Cd and Hg . However, addition of 100 equiv. of
To determine the quantitative sensitivity range for
2+
2+
Zn results in 40% decrease in absorbance as com- binding of 1 with Cu , spectrophotometric titration
pared to 67% decrease in absorbance observed with 10 experiments were performed in the presence of Cu2
+

Imidazole based chemosensor
1255
5
4
3
2
1
00
00
00
00
00
0
500
0
500
400
µM
3
00
400
200
2+
Cu
1
00
0
3
2
1
00
00
00
0
0
2
4
2
+
Cu conc. (in µM)
3
µM
3
30
380
430
480
L
Na K Mg Al Mn Fe Co Ni Cu Zn Cd Hg
n+
Wavelength(nm)
Metal ions (M )
Figure 4. Fluorescence response of chemosensor 1 (0.5
μM) on addition of Cu ions in CH3CN; λex 315 nm. Inset:
Figure 2. Fluorescence responses of 1 (0.5 μM) to var-
ious metal ions (50 μM) in CH3CN. Bars represent the
fluorescence intensity at 382 nm.
2+
Change in the fluorescence intensity of 1 as a function of
2+
Cu ion concentration.
The limit of detection (LOD) and limit of quantifica-
tion (LOQ) are calculated from UV-vis titrations. Lin-
ear regression graph of titrations was used to calculate
standard deviation and slope of linear response.
ions. The UV-vis titration data suggested that the inten-
sity of the absorbance at λ 315 nm decreased gradu-
max
ally with the increase in concentration of Cu2 to solu-
+
tion of chemosensor 1 (10 μM) in CH CN, upto 30
3
−
1
LOD = 3σ s
μM and then a plateau was achieved (figure 3). The
chemosensor 1 (0.5 μM) showed emission maximum at
−
1
LOQ = 10σ s
3
82 nm in CH CN when excited at 315 nm.
3
where σ = standard deviation of response and s = slope
Figure 4 shows the gradual change in fluorescence
of the calibration curve. The detection limit and limit
intensity of 1 upon progressive addition of Cu2 in var-
+
2
+
of quantification for Cu ions has been reasonably
2
+
ious concentration ranges. Addition of 3 equiv. of Cu
26
estimated to be 1.24 μM and 4.12 μM.
showed quenching close to 100% with negligible spec-
tral shift. This data probably suggested photoinduced
electron transfer (PET). PET sensors usually exhibit
little or no spectral shift with increase or decrease in
emission intensity.25
3.2 Calculation of binding constant
2+
Figure 5 supports the 1:1 stoichiometry of 1-Cu
complex.
The binding constant of the chemosensor 1 with
Cu2 was 1.77 x 10 M as calculated using Benesi-
+
5
−1
0
.3
.25
.2
.15
.1
.05
27
0
µM
Hildebrand equation.
0
.3
2
+
1
1
1
0
Cu
=
+
0.2
A − A
Amax − A
[Amax − A ] K [C]
o
o
o
1
000µM
0
0.1
0
Here, A , A, and A is the absorbance of free 1, mea-
o
max
2
+
sured with Cu and measured with excess amount of
Cu at 315 nm, respectively and K is the association
constant and [C] is the concentration of Cu ion added.
Plotting of 1/(A-A ) versus 1/[Cu ] showed a linear
0
2
+
0
20 40 60 80
2
+
2
+
0
Cu conc. (in
µ
M)
2
+
0
relationship (figure 6), which also indicated that 1 is
0
2
+
associated with Cu in a 1:1 stoichiometry. Although
Job’s plot clearly indicated 1:1 stoichiometry of the
complex, it was observed in the UV-vis titration that
0
2
35
285
335
385
435
485
2
+
Wavelength (nm)
nearly three times [Cu ] was required to achieve the
plateau. This might be due to the reversibility of the
Figure 3. Family of UV-vis spectra taken in the course of
the titration of 1 (10 μM in CH3CN) with Cu ions. Inset:
Change in the absorbance of 1 as a function of Cu ion
concentration.
2
+
2+
reaction. Addition of large excess of Cu concentration
made the complex equilibrium to be shifted towards
2
+
28
complex formation.

1256
Navneet Kaur and Priya Alreja
0
.1
0.3
0
.25
.2
.15
.1
.05
0
0
0
0
.08
.06
.04
.02
0
0
0
0
0
0
0
0.2
0.4
0.6
0.8
1
Anions (An-)
X
Figure 5. Job’s plot for the determination of the stoichiom- Figure 8. UV-vis. absorption responses of 1 (10 μM) to
2
+
etry of 1.Cu in CH3CN.
various anions (1000 μM) in CH CN. Bars represent the
3
intensity of absorption at 315 nm.
-
-
-
-
-
-
-
-
-
-
6.2
6.4
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
1
0.5
0.4
5
K=1.77*10
1
/A-Ao
1500µM
0.3
-
OH
0
0
.2
.1
0
0
µM
0000
20000
30000
40000
/C
50000
60000
70000
1
2
25
275
325
375
425
475
Figure 6. Plot of 1/(A-A0) versus 1/[Cu2 ] showing a
linear relationship.
+
Wavelength (nm)
Figure 9. UV-vis. absorption responses of 1-Cu2 (10
μM) on addition of OH ions in CH3CN.
+
−
0.2
315 nm
where the other cations were used in higher concentra-
tion (figure 7). From the bar diagram, one could eas-
ily understand that the effects on absorbance of 1 upon
the addition of higher concentrations of various cations
were almost negligible. These results showed excellent
0
0
.15
0.1
2
+
selectivity for Cu over a wide range of cations.
.05
0
3.3 Spectral Characteristics of 1 towards anions
Lig Na
K
Mg Al Mn Fe Co Ni Zn Cd Hg
n+
As the chemosensor 1 possesses imidazole NH that can
bind with anions, so the binding ability of 1 towards
Metal ions (M
)
Figure 7. UV-vis absorption response of 1 (10 μM) con- different anions was also monitored. Figure 8 shows
2
+
taining 50 μM Cu (Lig.) to the selected metal ions (1000
μM).
the absorption changes of chemosensor 1 (10 μM)
−
−
towards 1000 μM of various anions viz. CN , F ,
−
−
−
−
−
2−
−
−
Cl , Br , I , AcO , H PO , SO , HSO and OH .
2
4
4
4
2+
To establish the selectivity of 1 toward Cu over This bar diagram points towards negligible interaction
+
+
2+
3+
a range of various metal ions (Na , K , Mg , Al , of chemosensor 1 with various anions.
2
+
2+
2+
2+
2+
2+
2+
2+
2+
Mn , Fe , Co , Ni , Cu , Zn , Cd and Hg ),
However, 1+Cu complex is expected to act as a
we carried out the competitive recognition studies chemosensing ensemble for anion recognition especially

Imidazole based chemosensor
1257
−
2+
for more basic OH ion. For this, the probe 1 +Cu
conditions. The conventional computer, based on
2
+
was prepared in situ by addition of 5 equiv. of Cu to 1 silicon-circuitry, uses electrical signal as input and out-
solution (10 μM). The addition of OH ions (0–1500 put. Following laws of Boolean algebra, the tailor-made
μM) to the solution of in situ generated 1+Cu com- chemosensors can be viewed as computational devices
plex results in a new hypsochromically shifted absorp- that use physical or chemical inputs to generate outputs
tion in the region 270–290 nm (figure 9). The intensity based on a set of logical operators.
−
2+
of this new band gradually increased with increasing
concentratioon of OH ion.
The first example of a molecular logic gate is
described by de Silva in 1993 that mimicked an AND
function. The AND gate is the principal logic gate
and gives logical multiplication output. Here, the UV-
vis absorbance behaviour of chemosensor 1 in the pres-
−
28
3.4 Sensing mechanism
2
+
−
ence of Cu and OH can satisfactorily mimic an AND
The possible binding model of chemosensor 1 is shown
2
+
−
logic gate function with Cu and OH as inputs and
A274 nm as output. Free 1 showed low absorbance at
λmax 274 nm, corresponding to a “0” state. Upon the
individual presence of Cu or OH , the absorbance
at 274 nm was still low (“0” state). However, the
simultaneous presence of Cu and OH could give
high absorbance at 274 nm, corresponding to “1” state.
The absorption changes at 274 nm in the presence
in scheme 2. The Cu2 ions are expected to bind
+
through imidazole nitrogen and methoxy oxygen to
2
+
2+
make 1-Cu complex. Binding of Cu with imida-
2
+
−
zole N makes imidazole NH more acidic, increasing its
−
binding ability towards more basic OH ion.
2+
−
3.5 Logic gate
2
+
−
of Cu and OH ions and the corresponding truth
Logic gate devices are used to perform basic logic oper- table with logic circuit for AND function are given in
ations whose output (high or low) depends on input figure 10.
H CO
3
H CO
3
H CO
3
Cu2+
-HO H
Cu2+
Cu2+
H
OH-
N
N
N
1
N
HN
N
1-Cu2+
- OH-
-Cu2+
1
Scheme 2. The possible binding model of chemosensor 1.
0
.35
.3
.25
.2
.15
.1
.05
0
In
Cu
1
In
(OH )
2
Out
(A274 nm)
0
2
+
-
(
)
0
0
1
0
1
0
0
1
1
0
0
0
1
0
0
0
0
2
+
In (Cu
)
0
1
0
1
1
-
In (OH )
0
0
1
1
2
Cu2+
OH-
A274 nm
Figure 10. A274 nm responses of 1 (10 μM) in CH3CN in the presence of
2
+
−
2+
−
2+
Cu , OH and Cu + OH . 1 mimic an AND logic gate function with Cu
−
and OH as inputs and A274 nm as output.

1
258
Navneet Kaur and Priya Alreja
and Wen Y S 2004 Chem. Mater. 16 2480; (c) Chen C
4
. Conclusions
H and Shi J 1998 Coord. Chem. Rev. 171 161
0. (a) Uauy R, Olivares M and Gonzalez M 1998 Am. J.
Clin. Nutr. 67 952S; (c) Mu L, Shi W, Chang J C and
Lee S 2008 Nano Lett. 8 104
1
In conclusion, an imidazole based chemosensor 1 has
been established as the molecular AND logic gate for
relay recognition of Cu2 and OH ions. The Cu
+
−
2+
1
1. (a) Jung H S, Kwon P S, Lee J W, Kim J I, Hung C S,
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2009 J. Am. Chem. Soc. 131 2008; (b) Georgopoulos P
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sensing by 1 followed “switch-off” mechanism. The
sensing selectivity and sensitivity of this chemosensor
toward Cu ions were established by both UV-vis and
fluorescence spectroscopy.
2+
2001 J. Toxicol. Environ. Health B 4 341
1
2. (a) Huang L, Zhang J, Yu X, Ma Y, Huang T, Shen
X, Qiu H and He X 2015 Spectrochim. Acta A: Mol.
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Supplementary Information
Supplementary Information is available at www.ias.ac.
in/chemsci.
1
3. (a) Alfonso M, Espinosa A, Tarraga A and Molina P
2
014 Chem. Open 3 242; (b) Magri D C, Brown G J,
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DST-SERB under grant number SR/FT/CS-36/2011.
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