A coumarin-chalcone hybrid used as a selective and sensitive colorimetric and turn-on fluorometric sensor for Cd2+ detection

Article abstract of DOI:10.1039/c7nj02569f

A chalcone-based naked-eye colorimetric chemical sensor, (E)-4-hydroxy-3-(3-(4-methoxyphenyl)acryloyl)-2H-chromen-2-one 1a, was developed for selective and sensitive recognition of Cd²⁺ in mixed aqueous-organic media. The chemosensor demonstrates a distinct color change as well as a remarkable variation in the absorption and fluorescence enhancement observed in its emission spectra upon interaction with Cd²⁺. The dual colorimetric and fluorometric responses of the chemosensor 1a towards Cd²⁺ are attributed to the formation of a 1 : 1, 1a-Cd²⁺ complex, which eventually affect its optical properties. The association constants for Cd²⁺ towards receptor 1a obtained from the Benesi-Hildebrand plot and non-linear least square fitting were found to be 9.56 × 10⁵ M^-1 and 1.34 (±0.87) × 10⁶ M^-1, respectively, with a detection limit of 5.84 × 10^-8 M. The fluorescence enhancement of chemosensor 1a upon interaction with Cd²⁺ was attributed to chelation-enhanced fluorescence (CHEF) occurring at pH 7.0.

Full text of DOI:10.1039/c7nj02569f

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January 2016 Pages 1–846
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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Coumarin-chalcone hybrid as selective and sensitive colorimetric
2
+
and turn-on fluorometric sensor for Cd detection
a,b
a
Received 00th January 20xx,
Accepted 00th January 20xx
Shaily* , Ajay Kumar and Naseem Ahmed*
Chalcone based Naked-Eye colorimetric chemical sensor (E)-4-hydroxy-3-(3-(4-methoxyphenyl)acryloyl)-2H-chromen-2-
DOI: 10.1039/x0xx00000x
2
+
one 1a was developed for selective and sensitive recognition of Cd in mixed aqueous-organic media. The chemosensor
www.rsc.org/
demonstrate a distinct color change as well as remarkable variations in absorption and fluorescence enhancement in
2
+
emission spectra upon interaction with Cd . The dual colorimetric and fluorometric responses of the chemosensor 1a
2
+
2+
towards Cd are attributed to the formation of a 1:1 [1a+Cd ] complex, which eventually affects its optical properties.
2
+
The association constant for Cd towards receptor 1a obtained from Benesi–Hildebrand plot and non-linear least squar
5
-1
6
-1
-8
fitting were found to be 9.56 × 10
M and (1.34±0.87) × 10 M respectively with a detection limit 5.84 × 10 M. The
2
+
fluorescence enhancement of chemosensor 1a upon interaction with Cd was attributed to chelation-enhanced
fluorescence (CHEF) occurred at pH 7.0.
source of cadmium is smoking and for non-smokers the main
source is food, but breathing in cadmium-containing dust is
the most harmful route. Since the human body has no
Introduction,
In recent years, the conservation, protection of water
resources and contaminant prevention as well as
anthropogenic activity is a challenging task for researchers and
2
+
machinery to excrete Cd , it accumulates in tissues resulting
in carcinogenic effects or physiological disorders and can cause
serious injury to the human kidney, lung, bone and nervous
1
scientists. Among various inorganic contaminants, the metal
6
system. Moreover, the epidemiological studies carried out on
2
cations play a significant role as components of electrolytes
and may also present inherent risks due to their potential
2
impact on environment and human health. A large range of
+
the populations of general human revealed that Cd increase
the threat of developing prostate, breast and endometrial
7
cancers. According to the USA Act of Comprehensive
metal ions are beneficial to the human health but some heavy
2
metal ions such as Pb , Cd and Hg etc are toxic even in the
+
2+
2+
Environmental Response, Liability and Compensation,
th
2
+
2+
2+ cadmium is ranked 7 position in the merit of the top 275
presence of trace amounts. Considering the Pb , Cd and Hg
ions as hazardous, the European Union’s Restriction on
Hazardous Substances directive banned the use of these ions
8
,9
Hazardous.
According to United State Environmental
Protection Agency (EPA) and WHO (World Health
2
Organization) the maximum permissible limit of Cd in
+
3
in electrical and electronic equipments. Owing to the non-
1
0,11
drinking water is 5 µg/L and 3 µg/L respectively.
In recent
biodegradable nature, these metal ions accumulate in the
4
environment leading to the contaminated food and water.
times, severe health problems and environmental pollution
2
+
caused by Cd make it in great demand for the development
of methods to monitor and detect cadmium levels both in the
environment and biological samples even at very low
Among the various transition metals cadmium is a silver-white
soft metal that is naturally found at low levels in soil, rocks and
small amounts in the earth’s crust. Additionally, cadmium is
1
2-14
3
concentrations.
widely used threshold limit value of 0.05 mg/m for cadmium
Compared with traditional analytical techniques including
voltammetric methods, inductively coupled plasma mass
spectrometry (ICP-MS), ion selective electrodes and atomic
absorption/emission spectrometry, the development of highly
salts and cadmium dust has been suggested in various fields
such as agriculture, industry, alloys, metallurgy, electroplating,
coloring matters and fertilizers as well as in the construction of
5
dry-cell batteries. Inspite of numerous uses and applications,
selective
colorimetric/fluorescent
chemosensors
for
cadmium is highly toxic and possess a severe threat to the
health of human beings and environment. A major exposure
recognition and sensing of environmentally and biologically
significant metal ions has attracted significant attention due to
their good selectivity, high sensitivity, simplicity and rapid
1
5-20
response time.
These traditional analytical techniques
generally suffer from several limitations such as laborious
sample pretreatment processes, expensive instrumentations,
specialized personnel and inadaptability for in site
measurement.
A
plethora of various synthetic sensors
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2
demonstrating fluorescent response toward Cd have been treatment of Cd to 1a solution (Figure 2). Thus, the
+
2+
2
1-31
2+
2+
As Zn and Cd have very similar chemosensor 1a exhibited high selectivity and sensitivity for
reported in literature.
2
chemical properties, many of these synthetic sensors can also Cd over other metal ions.
+
2
respond to Zn . In 2012, Liu et al. developed a highly selective
+
2
+
2+
quinoline based fluorescent sensor for Zn and Cd . Upon
2
interaction with Cd , sensor display a bright “switch-on”
+
2
+
,
status based on the PET mechanism and with Zn
demonstrate a distinct red shift in emission band based on the
2
3
ICT mechanism with small emission enhancements. Hence, it
has been an indispensable task great challenge for analysts to
2
design and develop a Cd selective fluorescence sensor.
+
There are several reports on the detection of cadmium ions
3
3-39
using different probes.
Normally, their sensing mechanism
is based on the fluorescence quenching process (“turn-off”). In Figure 1: (a) Colorometric. (b) Fluorometric changes after the
addition of 10 equivalents of different metal ions to the
solution of 1a (10 μM) in HEPES-buffered solution (20 mM,
CH CN:H O, 3:7, v/v, pH 7.0).
our fluorescence enhancement (“turn-on”) by complexation
with heavy transition metal ions is highly desirable extended
efforts to design and develop new metal ion and anion sensor
3
2
4
0-
with interesting structures feature and advanced functions,
2
+
4
2
To further explore the interaction between 1a and Cd , UV-vis
absorption titration of 1a (10 μM) solution was monitored with
herein we developed a novel discovery coumarin-chalcone
hybrid fluorescent sensor, (E)-4-hydroxy-3-(3-(4-
methoxyphenyl)acryloyl)-2H-chromen-2-one, 1a fluorescence
turn-on” chemosensor for detecting cadmium ions which
2
+
different concentrations of Cd (0–10 equivalents) in HEPES-
buffered solution (20 mM, CH CN:H O, 3:7, v/v, pH 7.0). As
3
2
“
2
shown in Figure 3, upon the gradual addition of Cd (0–10
+
2
+
shows excellent selectivity and sensitivity towards Cd over
many other metal ions.
equivalents) to 1a (10 μM) solution, the absorption band at
3
87 nm decreased slowly and gradually blue shifted with the
generation of a new absorption band appeared at 370 nm.
Thus the absorption spectrum became stable after the
Results and discussion,
2
addition of 10 equivalents of Cd to 1a solution and no
+
The synthesis of 1a is outlined in Scheme 1. The chemical
appreciable changes were observed on further addition of
2+
Cd . These result suggested that a new species was produced
structures of the intermediates and final products were fully
1
13
characterized by H-NMR, C-NMR, FTIR spectroscopies,
HRMS and UV–vis, spectra and all data are provided in the
supporting information. The photophysical properties of 1a
were investigated by absorption and emission studies.
during the titration. The metal complexation with 1a may be
due to its 4-hydroxycoumarin unit, leaving the enolic moiety,
and chalcone moiety providing α,β-unsaturated carbonyl
fraction available for metal complexation via the formation of
one or even two coordination spheres. Thus leads to the
2+
formation of stable 1a-Cd complex. In order to find out the
2
+
Colorimetric and Fluorimetric Responses of 1a to Cd ion
2
binding stoichiometry between 1a and Cd , the continuous
+
The synthesized chemosensor 1a possess a conjugated
β
-
43
variation method (Job’s plot) was used.
2+
The total
hydroxy enone unit, which could coordinate with metal ion,
and a coumarin moiety as a signaling unit. The optical
properties and sensing behavior of chemosensor 1a towards
metal ions was studied through absorption and emission
spectroscopy at room temperature in HEPES-buffered solution
concentration of 1a and Cd was constant (10 μM), with a
continuous variable molar fraction. The Job’s plot of 1a with
2+
Cd showed maxima at a mole fraction of 0.5, revealed that
2+
the complex formed between Cd and 1a follows a 1:1 binding
stoichiometry (Figure S7 in the supporting information). In
2+
addition, the 1:1 complex formation between 1a and Cd was
(20 mM, CH
3
CN:H
2
O, 3:7, v/v, pH 7.0). As shown in Figure 1a,
+
upon addition of 10 equivalents of different metal ion (Na , K ,
+
2
+
Ba , Ca , Mg , Cr , Mn , Fe , Co , Ni , Cu , Zn , Pb ,
2+
2+
3+
2+
3+
2+
2+
2+
2+
2+
further supported by Benesi–Hildebrand plot providing a good
linear relationship between the absorbance versus
+
Ag , Al , Cd , Hg , Hg and Sn ) into the solution of 1a (10
3+
2+
2+
+
2+
2+
concentration of Cd . The association constant of the 1a-Cd
2+
µM), an immediate and obvious change in color was observed
+
from yellow to colorless only with Cd . The results indicated
6
-1
2
complex was then calculated to be 1.79 × 10 M with a linear
relationship by Benesi-Hildebrand plot as evident in inset (b) of
that 1a can act as a highly sensitive “naked-eye” sensor for
44
2+
2
+
Figure 3. The association constant of the 1a with Cd was
also evaluated by non linear least-square fit of the
absorbance vs the concentration of Cd ion and found to be
Cd ion. The absorption spectrum of 1a represents a maxima
centred at 387 nm, which may be attributed to the π−π*
transitions of the coumarin motif. To gain an insight into the
a
2+
5
-1
2
+
(6.93±2.95)
×
a) of Figure 3)
10 M with good non linear relationship (Inset
45, 46
binding feature of 1a toward Cd , the UV−vis spectral changes
upon the addition of different metal ions (10.0 equivalents) to
the solution of 1a were investigated. Fascinatingly, a new
absorption maximum appears at 370 nm while the absorption
band at 387 nm was completely disappeared only on
(
.
2+
The detection limit of chemosensor 1a for Cd analysis was
determined from a plot of normalized absorbance as a
function of the concentration of the added metal ions and
2
| J. Name., 2012, 00, 1-3
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-8
evaluated to be 6.309 × 10 M (Figure S8 in the supporting However, the most significant criterion for a metal ion
4
7, 48
information). The individual UV-vis absorbance response selective chemosensor is the ability to sense a specific metal
of 1a against different metal ions revealed a remarkable ion in the vicinity of other competing metal ions. To further
2
selectivity towards Cd (Figure 2).
+
2+
investigate the selectivity of 1a for Cd , we measured the
2
absorption spectra of 1a in the presence of Cd mixed with
+
various metal ions in HEPES-buffered solution (20 mM,
CH
3
CN:H
2
O, 3:7, v/v, pH 7.0) (Figure 4). The absorbance of
2
Cd –bound 1a is unperturbed in the presence of 10
+
+
+
2+
2+
2+
3+
2+
3+
2+
equivalents of Na , K , Ba , Ca , Mg , Cr , Mn , Fe , Co ,
2
+
2+
2+
2+
+
3+
2+
Ni , Cu , Zn , Pb , Ag , Al , Cd , Hg , Hg and Sn ,
2+
+
2+
2
+
indicating excellent Cd selectivity over these competing
metal ions.
+
To further evaluate the responsive nature of 1a toward Cd ,
2
fluorescence titration was carried out with varying
2
+
concentrations of Cd in HEPES-buffered solution (20 mM,
CH CN:H O, 3:7, v/v, pH 7.0). As shown in Figure 6 the
3
2
chemosensor 1a was almost non fluorescent, when 0–10
2
+
equivalents of Cd was added to the solution of 1a (10 μM), a
gradual increase in fluorescence intensity at 495 nm was
observed. The fluorescence intensity of the chemosensor 1a at
Figure 2: Absorption spectra of 1a (10 μM) in presence of
different metal ions in HEPES-buffered solution (20 mM,
CH CN:H O, 3:7, v/v, pH 7.0).
3 2
2
+
4
95 nm was saturated when 10 equivalent Cd were added.
The absolute fluorescence quantum yield (φ ) of 1a goes from
f
2
+
.10 to 0.88 upon Cd binding. The spectral change indicates
0
2
+
that a co-ordination linkage between 1a and Cd is formed
and the 1a could be a “turn on” fluorescence chemosensor for
2
Cd . As mentioned earlier also, selectivity of chemosensor 1a
+
+
+
2+
2+
2+
toward other different metal ions (Na , K , Ba , Ca , Mg ,
3
+
2+
3+
2+
2+
2+
2+
2+
+
3+
2+
Cr , Mn , Fe , Co , Ni , Cu , Zn , Pb , Ag , Al , Hg , Hg
+
2
+
and Sn ) was also investigated which displayed no changes in
optical properties. Additionally, no significant fluorescence
enhancement was observed upon addition of any other metal
2
+
ion. Individual response of 1a towards Cd against these metal
2
ions represents a remarkable selectivity only for Cd binding
+
2
Figure 5). The Cd –induced selective fluorescent
+
(
enhancement of 1a indicated that these response of the
chemosensor may be attributed to the chelation enhanced
fluorescence (CHEF) due to presence of chelating group such
as C=O and –OH (Scheme 1). In addition, dilute solution of 1a
Figure 3: Absorption spectra of 1a (10 μM) upon titration with
2
+
Cd (0−10 equiv) in HEPES-buffered solution (20 mM,
CH CN:H O, 3:7, v/v, pH 7.0). Inset (a): Non linear fitting of
2+
exhibited light blue fluorescence upon addition of Cd and by
3
2
2
+
irradiation with long UV light (Figure 1b).
absorbance data of 1a with Cd . and Inset (b) A good linear fit
of Benesi-Hildebrand plot confirms the 1:1 binding
stoichiometry.
Cd2+
O
O
OH
O
O
Cd2+
O
O
OMe
O
a
OMe
1
1a-Cd2+
Scheme 1: Proposed sensing mechanism of compound 1a for
Cd .
2
+
Time resolved fluorescence studies of chemosensor 1a in the
2
+
absence and presence of Cd ions have been done using an
excitation wavelength of 387 nm in HEPES-buffered solution
Figure 4: Metal-ion selectivity profiles of 1a (10 μM) in HEPES-
buffered solution (20 mM, CH CN:H O, 3:7, v/v, pH 7.0). Red
3 2
(
3 2
20 mM, CH CN:H O, 3:7, v/v, pH 7.0). As shown in Figure 7b,
bars represent the absorbance of 1a in the presence of 10
equiv. of various metal ions. Yellow bars represent the
the fluorescence lifetime increases from 0.217 ns to 1.97 ns
2
after addition of Cd ions indicating the strong complexation
+
2
+
absorbance of 1a-Cd complex in the presence of 10 equiv. of
2
of 1a with Cd . These considerable changes in lifetimes of 1a
+
the indicated metal ions.
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2
in the presence of Cd proved its credentials as a good sensor Figure 6) than the linear one. Non linear fitting indicated the
+
2
for Cd .
+
2+
1:1 bind stoichiometry ratio of 1a-Cd complex.
(a)
Figure 5: Fluorescence emission spectra of 1a in the presence
of different metal ions such as Na , K , Ba , Ca , Mg , Cr ,
+
+
2+
2+
2+
3+
(
b)
2
+
3+
2+
2+
2+
2+
2+
+
3+
Mn , Fe , Co , Ni , Cu , Zn , Pb , Ag , Al , Cd , Hg , Hg
2+
2+
+
2
+
and Sn in HEPES-buffered solution (20 mM, CH
v/v, pH 7.0). λex= 387 nm, slit width = 3 nm.
3
CN:H
2
O, 3:7,
2
Figure 7: (a) Job’s plot of 1a and Cd showing 1:1
+
2
+
stoichiometry of the complex 1a-Cd . (b) Fluorescence decay
2
+
profile of 1a in the absence and presence of Cd (10 equiv.) in
HEPES-buffered solution (20 mM, CH
λex = 387 nm, slit width = 3 nm.
3 2
CN:H O, 3:7, v/v, pH 7.0).
Figure 6: Fluorescence spectral response of 1a (10 μM) upon
2
+
titration with Cd (0−10 equivalents) in HEPES-buffered
solution (20 mM, CH CN:H O, 3:7, v/v, pH 7.0). Inset (a): Non
linear fitting of fluorescence data of 1a with Cd . and Inset (b)
3
2
2
+
A good linear fit of Benesi-Hildebrand plot confirms the 1:1
binding stoichiometry. λ = 387 nm, slit width = 3 nm.
ex
2
+
Moreover, the binding stoichiometry of 1a-Cd complex was
revealed by Job's plot experiment. The fluorescence intensity
at 495 nm was plotted as a function of the mole fraction of 1a
Figure 8: Metal-ion selectivity profiles of 1a (10 μM) in HEPES-
buffered solution (20 mM, CH CN:H O, 3:7, v/v, pH 7.0). Red
bars represent the fluorescence intensity responses of 1a in
suggesting 1:1 bind stoichiometry ratio of 1a-Cd complex the presence of 10 equivalents of various metal ions. Yellow
under
a constant total concentration. The Job's plot
3
2
approached the maxima when the molar fraction was 0.5,
2
+
2
+
(
Figure 7a). Furthermore, the binding constant was calculated bars represent the fluorescence intensity responses of 1a-Cd
5
-1
to be 9.56 × 10 M according to the Benesi-Hildebrand plot complex in the presence of 10 equivalents of the indicated
metal ions. λex = 387 nm, slit width = 3 nm.
which also supports 1:1 binding stoichiometry of the complex
2
-Cd (Inset (b) of Figure 6). The binding constant was also
+
1
a
4
5, 46
Selectivity of the sensor is very essential as the interference of
other metal ions can affect its sensitivity and selectivity. In
order to check the interference of the other metal ions, the
evaluated by nonlinear least square fit,
better binding constant (1.34±0.87)
which resulted a
-1
6
10
×
M
(Inset (a) of
4
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competitive binding studies of chemosensor 1a were also The chemosensor 1a with Cd
ARTICLE
2
+
displayed excellent
performed. For the competitive binding experiment, equal fluorescence emission at 495 nm at pH 7.0. Thus, these results
2
concentrations of Cd and other metals were taken. Among all demonstrate that the response behavior of 1a-Cd complex is
+
2+
the served metal ions no metal ion interferes were observed pH independent in medium condition (pH 7.0–9.0). From the
2
+
2+
with the selectivity Cd (Figure 8). Hence, chemosensor 1a view of response speed of chemosensor 1a and 1a-Cd , the
2
+
acts as an excellent sensor for Cd even in the presence of pH 7.0 was chosen as optimum experimental condition.
other competition metal ions.
2
+
The limit of detection (LOD) was also determined from the Nature of interaction between chemosensor 1a and Cd ions
fluorescence titration figures based on a reported method. To further support the coordination mode between 1a and
2
+
According to the results of titration experiments, the Cd as proposed above, FTIR and ESI-HRMS spectroscopic
fluorescence data were normalized between the minimum and techniques experiment were performed by KBr pellets and
3
the maximum value leading to the construction of a linear CH CN, respectively. In the chemosensor 1a, carbonyl group
curve. The point at which this linear curve crossed the X-axis (C=O) of the chalcone scaffold and lactone of the coumarin
was considered as the detection limit. The detection limit was ring, and the hydroxyl group of the coumarin moiety show
-8
-1
found to be 5.84 × 10 M (Figure S9 in the supporting characteristic IR peaks at 1608, 1716 and 3440 cm ,
2
information). The limit of detection (LOD) of the synthesized respectively (Figure S5). Unfortunately, upon addition of Cd ,
+
chemosensor 1a was compared with some of the previously the IR peak corresponding to the C=O group of the lactone on
2
+
reported chemosensors for the determination of Cd . It can the coumarin ring did not display a marked shift while the peak
be seen from the compared data in the supporting information corresponding to the C=O group of the chalcone scaffold was
-1
Table 1S, the LOD of proposed sensor is significantly improved shifted to 1575 cm . Furthermore the peak corresponding to –
to the previously reported chemosensors for the OH group of coumarin ring completely disappeared.
2
determination of Cd . We believe that chemosensor 1a Moreover, to further investigate the binding mode of
+
1
imparted sufficient sensitivity for the detection of a trace interaction, the H NMR spectra of chemosensor 1a in absence
2
amount of Cd in environmental samples.
+
2+
and presence of Cd ions were also recorded (Figure S10). In
1
The effect of pH on the emission response of 1a in absence
H NMR spectra of chemosensor 1a, hydroxyl proton peak
2+
2
and presence of Cd were measured and the results are appeared at 18.99 ppm. Upon addition of 10 equiv. Cd ions
+
shown in Figure 9. The fluorescence emission of chemosensor to the solution of chemosensor 1a, the most significant change
1a does not show any significant change over a wide pH range was observed in peak corresponding to hydroxyl proton which
2
+
2+
of 2 to 12. The chemosensor 1a with Cd displayed different completely disappeared due to complexation with Cd ion.
fluorescence properties with emission band at 495 nm in However, the peak corresponding to the methoxy proton
neutral and basic medium. However, the fluorescence displayed slightly downfield shift and the peaks in aromatic
2
+
emission of 1a-Cd complex increases radically in the pH region were also shifted slightly downfield. However, due to
range from 5 to 7 and decreases in basic medium due to the the co-existence of both keto and enol forms together in
formation of metal hydroxide.
equilibrium, the peaks shifting is not very clear. These IR and
1
H NMR data confirmed that the C=O group of the chalcone
scaffold and –OH group of coumarin ring were involved in the
2
+
Cd coordination, whereas the C=O group of the lactone on
the coumarin ring did not participate in the metal-binding
process. Moreover, HRMS (ESI+) m/z for 1a calcd. C H O
1
2+
9 14 5
+
[
M+Na] : 345.0739, found 345.0747 and for 1a+Cd calcd.
2
C H CdO [M+Cd ] : 434.9786, found 434.9763, has
+ +
1
9
13
5
2
suggested about a 1:1 complexation between 1a and Cd (ESI,
+
Figure S6 and S11 ).
Application: Visual colour changes on test papers
To explore the practical appliance of chemosensor 1a, test
strips were prepared by immersing strips into a CH
3
CN solution
-
of 1a (1.0 × 10 molL ) followed by dried in air. The 1a
4
-1
2
containing test strips were utilized to sense Cd ions by
+
2
+
immersing test strips in to the solutions of Cd ions (5.0 × 10
-4
-1
molL ) for 10 sec and then the obvious colour change from
yellow to colourless was observed (Figure 10). Thus, detection
2+
Figure 9: Fluorescence emission behavior of 1a (black line) and
2
+ Cd (red line) at different pH values.
+
1a
of Cd could be easily carried by using these strips at any
moment.
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abbreviations are used to identify the multiplicities of the
reported peaks: br, broad; s, singlet; d, doublet; dd, doublet of
doublet; dt, doublet of triplet; t, triplet; q, quartet; m,
multiplet. High-resolution mass spectrometry (HRMS) was
performed on a Brüker microToF-Q-II electrospray-ionization
(
ESI) mass spectrometer. UV–vis. absorption spectra were
recorded on a Shimadzu UV-2450 spectrophotometer and the
fluorescence spectra were recorded on Fluoromax-4
a
Spectrofluorometer with a 3-cm standard quartz cell. A Varian
Atomic Absorption Spectrophotometer, (Model AA-240), was
Figure 10: Photographs of (a) Colorimetric. (b) Fluorometric
test kit: filter paper coated with 1a (0.1 mM) for detecting Cd
2
used for determination of Cd . The pH was measured by
+
2
+
in HEPES-buffered solution (20 mM, CH
.0).
3
CN: H
2
O, 3:7, v/v, pH means of an MRFS Toshniwal pH meter. Melting points were
recorded on Optimelt automated melting point system.
Quantum yield were obtained using FLS 980 fluorescence
7
Application of the proposed turn-on sensor to real samples
spectrometer (Edinburgh Instruments). IR spectra were
To explore the reliability and analytical applicability of the recorded on an Alpha FTIR spectrometer (Bruker) in the range
−1
chemosensor 1a, it was applied for determination of cadmium 4000–400 cm with KBr pellets. Fluorescence life time spectra
in three real samples lipstick, brown hair coloring material and were obtained by using Horiba Jobin Yvon, Fluorocube
the liquid foundation makeup cream. One gram of tiny pieces fluorescence lifetime system.
of lipsticks were dissolved in 8.0 mL of 65% HNO and 2.0 mL
3
of acetone. After 24 h, it was filtered, separated from the solid UV-vis and Fluorescence measurements
and dried. The dried material was dissolved in absolute Since the chemosensor 1a was not completely soluble in 100%
ethanol and stirred at 1500 rmp for 2 h for complete aqueous media, acetonitrile was used as a co-solvent. A stock
2
dissolution of Cd . After complete removal of solid material by solution of 1a (1 mM) was prepared in acetonitrile and then
+
2
+
centrifugation, the resulting solution was assayed for Cd by sample solution of 1a (10 µM) was prepared in phosphate
the chemosensor 1a and AAS. The same procedure was buffered solution (20 mM, CH CN:H O, 3:7, v/v, pH 7.0), in a
repeated for the brown hair coloring material and the liquid quartz cuvette (1 cm × 1 cm). To the solution was added of 10
3
2
+
+
foundation makeup cream. The accuracy of the method has µL of an aqueous stock solution (10 mM) of metal salt (Na , K ,
2
been verified by the determination of cadmium in all the Ba , Ca , Mg , Cr , Mn , Fe , Co , Ni , Cu , Zn , Pb ,
+
2+
2+
3+
2+
3+
2+
2+
2+
2+
2+
+
3+
2+
2+
+
2+
samples by AAS (Table 1). The results obtained from these two Ag , Al , Cd , Hg , Hg and Sn ). All fluorescence
methods (i.e. spectrofluorometry and AAS) proved that the measurements of 1a were carried out with slit widths of 3 nm.
synthesized chemosensor 1a is highly selective and sensitive
2
+
sensor for the monitoring of Cd in different cosmetic and Synthesis and characterization of (
personal care samples.
methoxyphenyl)acryloyl)-2 -chromen-2-one, 1a
he two step synthesis of our target molecule started with the
Table 1: Determination of Cd in cosmetic, and personal care acetylation of commercially available 4-hydroxycoumarin in
samples by proposed fluorometric and AAS methods.
the presence of POCl using glacial acetic acid as acetylating
E)-4-hydroxy-3-(3-(4-
H
T
2
+
3
2
+
-1
Real sample
Amount of Cd (mol L )
Fluorometric
agent to furnish 3-acetyl-4-hydroxycoumarin, 2a. Then the
final step involved the condensation reaction between 2a with
AAS
-6
-6
4
-methoxybenzaldehyde in the presence of piperidine as a
Lipstick
2.07 × 10
1.96 × 10
promoter in chloroform for 1.5 h to obtain the product 1a
-
6
5
-6
Hair Color
1.12 × 10
7.92 × 10
1.06 × 10
7.20 × 10
(Scheme 2).
-
-5
Makeup Cream
Step 1: Synthesis of 3-acetyl-4-hydroxy-2H-chromen-2-one,
2
a
To a solution of 4-hydroxycoumarin (162.14 mg, 1.0 mmol) in
acetic acid (8.6 ml) was added phosphorus oxychloride (3.0
ml). The mixture was heated at reflux for 30 min. After cooling,
the precipitate was collected and recrystallized from ethanol
to give 3-acetyl-4-hydroxy-2H-chromen-2-one, 2a as white
Experimental
All common reagents and solvents were used of AR grade.
Metal salts used were obtained from HiMedia (Mumbai, India)
and Loba Chemie (Mumbai, India). Spectroscopic-grade
acetonitrile and water were used for electronic spectral and
1
needles (200.09 mg, 89 %). M.P = 135 °C; H-NMR (400 MHz,
1
13
CDCl
.2 Hz, 1H), 8.07 (dd, J = 6.4, 8.0 Hz, 1H); C-NMR (100 MHz,
CDCl , ppm): δ 30.3, 101.5, 115.3, 117.2, 124.6, 125.8, 136.3,
3
, ppm): δ 2.79 (s, 3H), 7.28–7.37 (m, 2H), 7.69 (dt, J = 1.6,
fluorescence studies. H and C nuclear magnetic resonance
NMR) spectra of compounds were recorded in CDCl on a
1
3
7
(
3
3
JEOL ECX-400-II spectrometer and chemical shifts are reported
as part per million (ppm) in δ scale downfield from
tetramethylsilane (TMS; as internal standard). The following
-1
1
2
54.9, 160.2, 178.8, 206.2; IR; νmax (cm ) 3337, 2974, 2877,
570, 1686, 1590, 1514, 1460, 1408, 1344, 1244, 1186, 1124,
6
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OMe
OH
OH
O
O
O
OH
O
O
O
OHC
POCl3,
glacial acetic acid
Chloroform/Piperidine
Reflux
O
O
OMe
2a
1a
4
-Hydroxycoumarin
Scheme 2: Synthetic route of the chemosensor 1a
.
1
072, 799, 741, 637. HRMS (ESI+) m/z for 1a calcd. C11
H O
8 4
low detection limits. The practical ability of chemosensor 1a
was tested for the detection of cadmium ions in different
cosmetic products with complex matrices and the results were
+
M+Na] : 227.0320 found 227.0930.
[
Step
methoxyphenyl)acryloyl)-2
-Acetyl-4-hydroxy-2 -chromen-2-one (204.17 mg, 1.0 mmol)
and the appropriate substituted aromatic aldehyde (136.15
mg, 1.0 mmol) were dissolved in chloroform (1.0 mL). A
catalytic amount of piperidine (0.66 mmol) was added and the
reaction mixture was refluxed for 1.5 h. The chloroform was
distilled out and the residue was washed with methanol and
2:
Synthesis
of
(E)-4-hydroxy-3-(3-(4- obtained satisfactorily.
H
-chromen-2-one, 1a
3
H
Acknowledgements
We thank Ministry of Human Resource and Development
(MHRD), New Delhi, India [grant number MHR01-23-200-428],
for financial supports.
1a was obtained as a yellow solid (239.26 mg, 72 %). M.P = 136
1
C; H-NMR (400 MHz, CDCl
°
3
, ppm): δ 3.85 (s, 3H), 6.93 (d, J = Notes and references
8
.0 Hz, 2H), 7.27–7.33 (m, 2H), 7.64–7.68 (m, 3H), 8.02–8.08
1
Z. Wang, M. A. Palacios and P. Anzenbacher, Anal. Chem. 2008,
0, 7451.
B. A. Fowler, M. Nordberg, L. Friberg and G. Nordberg, G.
1
3
(
m, 2H), 8.31 (d, J = 16.0 Hz, 1H), 18.99 (s, 1H); C-NMR (100
MHz, CDCl , ppm): δ 55.5, 100.5, 114.5, 114.6, 117.0, 119.9,
24.3, 125.8, 127.6, 131.5, 135.8, 147.5, 154.6, 162.6, 181.7;
8
2
3
rd
Handbook on the Toxicology of Metals, 3 ed.; Eds.; Academic
Press: Boston, MA, 2007.
1
-
1
IR; νmax (cm ) 3440, 2946, 2834, 1716, 1608, 1501, 1431, 1321,
259, 1230, 1165, 1102, 1021, 994, 897, 822, 755, 667, 521.
3
The European Parliament and the Council of the European
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1
+
[M+Na] : 345.0739
HRMS (ESI+) m/z for 1a calcd. C19
H
14
O
5
found 345.0747.
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7
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Conclusions
We have successfully developed
a
coumarin–chalcone
2
conjugate fluorescent sensor 1a for the detection of Cd over
+
+
+
2+
2+
2+
other competitive metal ions, e.g. Na , K , Ba , Ca , Mg ,
3
+
2+
3+
2+
2+
Cr , Mn , Fe , Co , Ni , Zn , Pb , Ag , Al , Cu , Hg , Hg
2+
2+
+
3+
2+
2+
+
8
9
2
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2
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+
+
2
+
1
1
0
1
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8.4 nM. The chemosensor behaves as a naked-eye and optical
5
2
sensor for the determination of Cd , with significant color
+
WorldHealthOrganization, Avenue Appia20, 1211 Geneva 27,
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detection by chemosensor 1a was 7.0 in HEPES-buffered
1
1
2
3
,
solution (20 mM, CH
3 2
CN:H O, 3:7, v/v). Thus, the coumarin–
1
chalcone hybrid 1a unambiguously demonstrates the function
M. Mameli, M. C. Aragoni, M. Arca, C. Caltagirone, F. Demartin,
G. Farruggia, G. D. Filippo, F. A. Devillanova, A. Garau, F. Isaia, V.
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of Cd detection in both solid states and solution with very
+
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