Nanomolar detection of AgI Ions in aqueous medium by using naphthalimide-based imine-linked fluorescent organic nanoparticles - Application in environmental samples

Article abstract of DOI:10.1002/ejic.201402473

The synthesis of fluorescent organic nanoparticles (FONPs) with an imine-linked 1,8-naphthalimide-based dipodal chemosensor for Ag^I is described. The FONPs were prepared by using a re-precipitation method, and they were successfully applied for

Full text of DOI:10.1002/ejic.201402473

FULL PAPER
DOI:10.1002/ejic.201402473
Nanomolar Detection of AgI Ions in Aqueous Medium by
Using Naphthalimide-Based Imine-Linked Fluorescent
Organic Nanoparticles – Application in Environmental
Samples
Hemant Sharma,[a] Vimal K. Bhardwaj,[a] and Narinder Singh*[a]
Keywords: Analytical methods / Sensors / Fluorescence / Nanomolar detection / Silver / Environmental chemistry
The synthesis of fluorescent organic nanoparticles (FONPs)
with an imine-linked 1,8-naphthalimide-based dipodal
chemosensor for AgI is described. The FONPs were prepared
by using a re-precipitation method, and they were success-
ous media. More specifically, the chemosensor was utilized
for the selective and ratiometric sensing of AgI in a concen-
tration range 15–65 n
M with a 15.5 nM detection limit. The
work was extended to monitor the AgI concentration in sam-
fully applied for the nanomolar detection of AgI ions in aque- ples of environmental importance.
that can detect AgI in organic solvents and aqueous solu-
Introduction
tions selectively;[13–18] contrary to this, only few reports are
available about ratiometric fluorescent sensors for the AgI
ion.[19]
Over the past 20 years, a wide range of industrial uses
for silver have been, and continue to be, introduced.[1] From
organic catalysis to non-corroding electrical switches, silver
is extensively used in every industry.[2–4] The main applica-
tions are coins and medals, jewelry, electronics, and in the
imaging industry.[5,6] The large-scale use of silver leads to
its slow discharge into the environment.[7,8] The alarming
impact of silver ions, especially, on flora and fauna has re-
ceived much attention.[8] Silver can inactivate sulfhydryl en-
zymes and accumulate in the body, where it causes the
irreversible darkening of the skin and mucous mem-
branes.[9,10] A number of analytical methods are available in
the literature for the estimation of silver ion concentration;
however, they suffer from being costly, time-consuming,
and tedious protocols.[11,12] The development of fluorescent
chemosensors with high sensitivity, high selectivity, a low
detection limit, and a broad detection range has been re-
ceiving considerable attention because of their vital role in
biological, medical, and environmental analysis.[13] How-
ever, the detection of silver in aqueous medium remains
challenging because of the low solubility of chemosensors
in aqueous medium. Silver does not have an intrinsic spec-
troscopic or magnetic signal (silent ion), and it is therefore
very difficult to differentiate from other chemically closely
related ions. In this regard, considerable efforts have been
made to synthesize AgI-selective fluorescent chemosensors
To the best of our knowledge, there are no reports about
fluorescent organic nanoparticles (FONPs) used for the ra-
tiometric estimation of AgI in aqueous medium, although
many other metal ions have been investigated. Here,
FONPs were prepared by using naphthalimide-based imine-
linked dipodal chemosensors for the nanomolar detection
of AgI in water. Organic nanoparticles (ONPs) offer many
advantages, like their solubility in aqueous systems, which
helps to avoid toxic organic solvents, real-time detection, a
broad detection range, and a low detection limit.[16,20–27]
There are several methods to prepare ONPs, such as emul-
sion, drying, and re-precipitation. The re-precipitation
method has been employed for the synthesis of imine-linked
dipodal ONPs. The role of imine linkages for the binding
of AgI in receptor pseudocavity has already been estab-
lished.[28] In the design of the present investigation, the sp2
nitrogen binding sites from imine linkages are provided in
such a way that the receptor should offer five-membered
chelate ring.
Results and Discussion
Synthesis of the Chemosensors
Chemosensor 1 was synthesized through a series of steps,
as illustrated in Scheme 1. The compounds 2 and 4 were
synthesized by using literature methods.[29,30] The dipodal
aldehydes 3a and 3b were synthesized by the nucleophilic
reaction of dibromide 2 with 2-hydroxybenzaldehyde and 3-
hydroxybenzaldehyde, respectively, under basic conditions.
[a] Department of Chemistry, Indian Institute of Technology
Ropar (IIT Ropar),
Rupnagar, Panjab 140001, India
E-mail: nsingh@iitrpr.ac.in
http://www.iitrpr.ac.in/chemistry/nsingh
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402473.
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A purification by column chromatography on silica gel proposed sensor activity for ions, compounds 5 and 6 were
yielded the pure products 3a and 3b in 78 and 75% yield, synthesized in 67 and 66% yield, respectively, by using a
respectively.
literature method (Scheme 2).[22,30,31]
Preparation of ONPs and Recognition Studies
The re-precipitation method was employed for the prepa-
ration of ONPs. The receptor 1 (2 mg) was dissolved in
10 mL of THF, and the solution was filtered through a po-
rous membrane (pore size of 0.3 μm). This solution was
rapidly injected into 990 mL of highly purified water with
sonication for 15 min at room temperature. The solution
was kept for 5 h to check the stability of the system. The
UV/Vis spectra of receptors 1a and 1b were recorded in
pure THF, and they exhibit a broad band in the visible re-
gion (453 nm and 443 nm, respectively), as shown in Fig-
ure 1 (A). In aqueous media, a significant bathochromic
shift was observed in both cases. The receptors 1a and 1b
have absorbance maxima at 460 nm and 453 nm, respec-
tively, in aqueous media (Figure 1, A). Further, emission
spectra of 1a and 1b were recorded in pure THF and water
(Figure 1, B). In the case of 1a, an enhancement in the
emission intensity and a slight redshift were observed (Fig-
ure 1, B). A similar response was seen for 1b, however, with
more a prominent enhancement and a redshift in the peak
(Figure 1, B). This dramatic change in the photophysical
properties of 1a and 1b can be explained on the basis of the
formation of organic nanoparticles (ONPs). On formation
of ONPs, the rigidity increases in the molecule, which leads
to a prevention of non-radiative decay and enhances the
fluorescence intensity with a redshift.[32] To explore the ef-
fect of water content on the formation of ONPs, emission
spectra of 1a and 1b were recorded in different media with
a varying water fraction between 0 and 99% (Figure 1, C
Scheme 1. Synthesis of imine-linked 1,8-naphthalimide-based dipo-
dal chemosensors. Reagents and conditions: (I) (HCHO)n, HBr in
acetic acid, reflux for 15 h; (II) K2CO3, CH3CN, TBAHSO4, 2-
hydroxy benzaldehyde or 3-hydroxy benzaldehyde, reflux for 15 h;
(III) NH2–NH2, ethanol, stir for 5 h; (IV) CHCl3/CH3OH (1:1),
reflux for 12 h.
A condensation reaction between dialdehydes 3a and 3b
and amine 4 yielded the imine-linked chemosensors 1a and
1b, respectively, in 64 and 66% yield, respectively. These
new compounds were fully characterized with spectroscopic
1
methods, which includes H NMR spectroscopy, where a
singlet signal at 8.65 and 8.74 ppm is observed for 1a and
1b, respectively, which is assigned to the imine linkages
(–CH=N), as shown in Figures S1–S4. To support the
Figure 1. (A) Absorbance spectra of compounds 1a (10 μm) and 1b
(10 μm) in THF and of ONPs of 1a (2.3 μm) and 1b (2.3 μm) in
water. (B) Emission spectra of compounds 1a (10 μm) and 1b
(10 μm) in THF and of ONPs of 1a (2.3 μm) and 1b (2.3 μm) in
water. (C) Change in the emission profile of 1a upon varying the
water fraction. (D) Change in emission profile of 1b upon varying
the water fraction.
Scheme 2. Synthesis of controls 5 and 6. Reagents and conditions:
(I) n-propylamine, reflux overnight; (II) n-propylamine, CH3CN,
reflux for 12 h.
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and D). During the course of ONP development, the size formation of excimers. The excimers contribute towards the
and distribution of ONPs were determined with the exter- ACQ effect. Therefore, an optimized concentration (2.3 μm)
nal-probe feature of dynamic light scattering (DLS). The was used in further studies. It gives appropriate absorption
external-probe feature of DLS allows to continuously and and emission profiles along with uniformly distributed
rapidly monitor the size of ONPs. The external probe ONPs in the range 98–102 nm (Figure 2, Figures S5D and
equipped with a laser diode was dipped in the solutions. It S5E). The shape and size of ONPs of 1a and 1b were also
is worth noting that in media 80% or more water the forma- characterized through TEM images, as shown in Figure 2
tion of ONPs could be achieved, as shown in Figure S5.
(F and G). The TEM analysis showed that discrete ONPs
Beyond 80% water content, emission intensity as well as of 1a and 1b have a size of 20 and 25 nm, respectively (Fig-
uniformity in the distribution of size were increased (see ure 2, F and G). The difference in the sizes determined by
Figure 1, C and D and Supporting Information, Figure S5). TEM and DLS measurements is due to the fact that DLS
Suitably uniform and nano-sized ONPs of 1a and 1b were measures the hydrodynamic size of nanoparticles, whereas
obtained at 99% water content (Figures S5D and S5E). TEM records the size of discrete particles. Moreover, the
Moreover, the concentration for the formation of ONPs time of sonication also controls the size and quality of
was optimized. The absorption and emission spectra of ONPs. A sonication less than 10 min produced large and
ONPs 1a and 1b were recorded at different concentrations, unstable ONPs, which start to agglomerate with time.
for example, 1.0, 2.3, 4.5, 7.0, and 10.0 μm (Figure 2). The
The interaction of different metal ions with ONPs of 1a
concentration of receptor and the size of ONPs have a lin- and 1b was examined. It was observed that none of the
ear relationship. The size of ONPs increased with the con- metal ions disturbed the absorbance profiles of 1a and 1b
centration of 1a and 1b (Figure 2, E). The large ONPs have (Figures S6A and B). These results indicate a non-selective
broad and prominent absorption bands (Figure 2, A and behavior of ONP of 1a and 1b in absorption spectroscopy.
B). However, the emission intensity of ONPs increased with Further, the emission profiles of ONP1a and ONP-1b were
the concentration of receptor only up to a certain limit recorded with various metal ions. The emission profile of
(Figure 2, C and D). Beyond 7.0 μm, quenching was ob- ONP-1b showed a significant change with AgI ions, as
served. The possible reason behind the quenching is “aggre- shown in Figure 3 (A). The addition of AgI ions produced a
gation-caused quenching” (ACQ).[33,34] The aromatic rings ratiometric change in the emission profile of ONP-1b. Two
of naphthalimide undergo π–π stacking, which results in the
Figure 2. (A) Effect on the absorption spectra of ONPs of 1a upon
changing the concentration of 1a. (B) Effect on the absorption
spectra of ONPs of 1b upon changing the concentration of 1b. (C)
Effect on the emission spectra of ONPs of 1a upon changing the
concentration of 1a. (D) Effect on the emission spectra of ONPs
of 1b upon changing the concentration of 1b. (E) Variation in size
of ONPs of 1a and 1b as a function of the concentration of com-
pounds 1a and 1b in water. (F) TEM images of ONPs of 1a (20 nm)
and (G) TEM images of ONPs of 1b (25 nm).
Figure 3. (A) Changes in the fluorescence spectra of ONP-1b
(2.3 μm) in the presence of different metal nitrate salts (100 nm) in
aqueous media. (B) Changes in the fluorescence spectra of ONP-
1b (0.2 μm) upon successive addition of AgI ions (0–70 nm); inset
shows the linear relationship between ratiometric intensity (I627/522
)
and concentration of AgI ion.
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isosbestic points were observed at 496 and 587 nm (Fig-
ure 3, A). To study this in more detail, a of ONP-1b was
titrated with small aliquots of AgI ions. Upon addition of
AgI ions, the emission intensity of ONP-1b was quenched
at 522 nm and enhanced at 627 nm, which is consistent with
the clear isoemissive points shown in Figure 3 (B). To find
the linear range of detection, the ratiometric fluorescence
intensity (I627 522) was plotted against the concentration of
/
AgI ions. A linear relationship was observed in the concen-
tration range 15–65 nm (inset of Figure 3, B). The minimum
detection limit was calculated to be 15.5 nm. It was hypoth-
esized that the shape and size of the ONPs is influenced
after interacting with AgI ions. Therefore, SEM images of
ONP-1b before and after treatment with AgI were recorded.
ONPs of 1b are spherical in shape, as shown in Figure S7A.
However, a robust change in the morphology of ONPs-1b
was seen after interacting with AgI ion, and big clumps
were observed (Figures S7A and B). This means that the
AgI ions interact on the surface of the ONPs and initialize
the aggregation of particles. The increase in particle size
was also confirmed by DLS studies. The size of the ONPs
was increased with a broad distribution in size and a maxi-
mum at about 190 nm (Figure S7B).
Figure 4. (A) Effect of acidic medium on the emission intensity of
ONP-1b upon changing the pH of the solution (7.5–2.3). (B) Effect
of basic medium on emission intensity of ONP-1b upon changing
the pH of the solution from (7.5–12.3). (C) Changes in emission
intensity of ONP-1b upon changing the ionic strength of the solu-
tion (0–100 μm, TBAClO4). (D) Plot of fluorescence intensity of
ONP-1b and AgI at different concentrations as a function of time
(sec).
The binding constant and stoichiometry were calculated
by using the Lehrer–Chipman Equation (1) for a (Ag+n·1)
complex.[35,36]
to the ONP-1b solutions, and fluorescence spectra were re-
corded, as shown in Figure S10A. The fluorescence inten-
sity at 522 nm was plotted against the pH of the solution
ln[(F – F0)/(Fϱ – F)] = nln[Ag+] + nln(Kasscn
)
(1)
The symbol n corresponds to the number of AgI ions (Figure S10A). It was noticed that the change was almost
attached to each molecule of 1b, Kasscn is the binding con- similar in all cases, which means that the pH of the solution
stant, F0 is the fluorescence intensity of receptor 1b only, F does not interfere with the recognition of AgI ions. Ad-
is the fluorescence intensity of 1b at a particular concentra- ditionally, the effects of the ionic strength on the emission
tion of AgI ions, and Fϱ is the fluorescence intensity of 1b profile of ONP-1b were examined by using various concen-
at maximum concentration. The slope of the plot of trations (0–100 μm) of tetrabutylammonium perchlorate
ln[(F – F0)/(Fϱ – F)] against ln[Ag+] gave the stoichiometry, (TBAClO4), as shown in Figure 4 (C). The results show that
and it is about 2.0, which corresponds to a 1:2 ratio between even 100 μm of TBAClO4 do not affect the emission profile
host and guest (Figure S8). The intercept of the plot gave of the ONP-1b. Similar to pH studies, the detection of AgI
the binding constant of 1b·Ag+, and it is about was executed in solutions of varying ionic strength (0–
4.5(Ϯ0.4)ϫ105 m–2. To further confirm the stoichiometry 100 μm). Figure S10B shows that the response of ONP-1b
between ONP-1b and AgI ions, a Job plot was drawn be- towards AgI ions remains same in solutions of different
tween compound 1 and AgI in pure THF. The concentra- ionic strength. Moreover, response time is one of the key
tion of the host–guest complex [HG] was plotted against factors for real-time sensing of AgI ions. To calculate the
{[G]/([H] + [G])}, where [G] is the concentration of the response time of ONP-1b for AgI, a set of solutions were
guest AgI and [H] is the concentration of the host ONP-1b, prepared with different concentrations of AgI ions, and the
and the plot has maximum at 0.7, which corresponds to a ratiometric fluorescence intensity (I627/522) was measured as
1:2 stoichiometry between host and guest molecule (Fig- a function of time, as shown in Figure 4 (D). The response
ure S9). Furthermore, the effect of pH on the emission pro- time of ONP-1b for AgI does not depend on the concentra-
file of ONP-1b was evaluated. To perform this experiment, tion of the AgI ions; in each case, 84 s is sufficient to reach
emission spectra of ONP-1b were recorded in aqueous me- the equilibrium. Figure 4 (D) illustrates that once the equi-
dia with varying pH (by using HCl and tetrabutylammo- librium was reached, no change in the ratiometric intensity
nium hydroxide). It is noteworthy that ONP-1b is quite re- at (I627/522) was observed, which indicates the stability of
sistant to show any change in the emission profile upon the system. Moreover, selectivity is another deciding factor
varying the pH of the solution (Figure 4, A and B).
for good sensing; the emission intensity at 522 nm of ONP-
This wide operational pH range (2.3–12.3) increased the 1b was measured in the presence and absence of equimolar
scope of ONP-1b as a sensor for AgI ions. To evaluate the amounts of other competing cations. It was noticed that
effect of pH on the recognition of AgI ions, a set of solu- ONP-1b recognized AgI ions selectively even in the presence
tions of ONP-1b were prepared, which had different pH in of other competing cations (Figure 5). To illustrate the
the range 2–12. A solution of AgI ions (70 nm) was added mechanism and the role of the moieties for the binding of
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AgI ions, different derivatives of naphthalimide and dipodal corded in the presence and absence of AgI ions. The cyclic
aldehyde were prepared. The metal binding test of ortho- voltammogram of ONP-1b exhibits an oxidation wave at
substituted 1a was performed. Likewise, ONPs of 1a were 0.040 V and a reduction wave at 0.486 V (Figure S13). The
prepared by the re-precipitation method. Figure S11 indi- addition of a AgI solution (100 nm) led to a shift of the
cates that ONP-1a shows a ratiometric response with AgI oxidation wave to higher potential; however, the reduction
ions; however, the response is less prominent compared to potential remained almost the same and showed an increase
ONP-1b. However, it also has a similar response with CdII, in the intensity of the wave, as shown in Figure S13. To
HgII, CoII, and other transition metal ions. These results check the nature of the binding interactions, tetrabutylam-
point out the non-selective behavior of ONP-1a towards monium chloride (TBACl) was added to the above solution.
cations. Further, to check the role of naphthalimide in After stirring for 5 min, the voltammogram was recorded.
metal binding, compound 5 was synthesized and sub- It was observed that ONP-1b regains its redox profile upon
sequently used for ONP preparation. The metal-binding addition of TBACl, because the Cl– anions extract the AgI
test results depict that ONP-5 has a non-selective profile in ions from the binding sites (Figure S13). This means that
emission spectroscopy (Figure S12A). Similarly, compound the binding of AgI ions to ONP-1b occurs reversibly
6 was synthesized to evaluate the role of the dipodal alde- through non-covalent interactions. Interestingly, ortho-sub-
hyde. ONP-6 also exhibits a non-selective response to metal stituted ONP-1a also has a non-selective response. To ex-
ions (Figure S12B).
plain this phenomenon, DFT calculations were carried out
with a Becke three-parameterized Lee–Yang–Parr (B3LYP)
exchange functional with a 6-31G and LANL2DZ basis
sets for the receptors and their silver complexes, respec-
tively.[37–41] On careful examination of the optimized geo-
metries of 1a and 1b, we found that 1b has a more symmet-
rical geometry, in which two pods are arranged in opposite
direction (Figure 6, A and B). However, 1a has a very com-
pact shape, and most of the electronegative atoms are in-
volved in H-bonding interactions.
Figure 5. Estimation of AgI in the presence of other metal ions
[NaI, KI, MgII, CaII, SrII, BaII, CrIII, MnII, FeIII, CoII, NiII, CuII,
ZnII, CdII, HgII, PbII, and AlIII] in water.
These results inferred that the binding of AgI occurred
only when the Schiff base was formed from 3 and 4. There-
fore, the binding site for AgI ions consists of the
(–CH=N–) imine linkage along with the naphthalimide
moiety, which provide the platform for this binding site, as
shown in Scheme 3. The red hemisphere represents the
binding site for AgI, and the other part provides the proper
orientation of these binding sites (Scheme 3).
Figure 6. Energy-minimized optimized structures of the receptors
1a and 1b, and of the complex 1b·AgI , calculated by using B3LYP/
6-31G and B3LYP/LANL2DZ functional/basis set combinations,
respectively. The red, blue, gray, dark green, and sea green spheres
correspond to O, N, C, Cl, and AgI atoms, respectively.
Scheme 3. Mechanism of AgI binding.
Therefore, 1b is more liable for binding as compared to
To understand the effect of AgI ions on the redox behav- 1a, which is also confirmed by optimization energies, dipole
ior of ONP-1b, cyclic voltammograms of ONP-1b were re- moments, and ΔEHOMO–LUMO (Table 1). These parameters
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indicate the different configurations of 1a and 1b. Further, was also monitored through inductively coupled plasma
the AgI complex of 1b was optimized by using the B3LYP mass spectrometry (ICP-MS). The samples were collected
functional with a LANL2DZ basis set (Figure 6, C).
on different days of the week, and results suggest that the
content of silver varied from 17 to 35 nm (Table 2). These
results are also in good agreement with the data obtained
from ICP-MS, as shown in Table 2.
Table 1. A comparison of optimized parameters of receptors 1a
and 1b and of complex 1b·AgI, calculated by using B3LYP/6-31G
and B3LYP/LANL2DZ functional/basis set combinations, respec-
tively.
Table 2. Comparison of results obtained from AgI analyses with
ONP-1b and ICP-MS.
Energy
[a.u.]
ΔEHOMO–LUMO
Dipole moment
[Debye]
Sample code ONP-1b [nm](average)[a] ICP-MS [nm] (average)[a]
[a.u.]
1a
–3477.751
–3477.755
–2878.875
0.12742
0.12737
0.12109
4.689
5.188
10.783
E1
E2
E3
E4
E5
E6
E7
19Ϯ0.2
21Ϯ0.1
35Ϯ0.4
20Ϯ0.6
32Ϯ0.3
17Ϯ0.5
22Ϯ0.2
20.2Ϯ0.5
21.4Ϯ0.4
34.9Ϯ0.1
21.1Ϯ0.2
32.3Ϯ0.6
18.1Ϯ0.2
22.4Ϯ0.4
1b
1b·AgI
The optimization parameters (energy and dipole mo-
ment) also point to a higher stability of 1b·AgI (Table 1).
To understand the molecular interactions upon binding, the [a] Average of three different readings.
orbital maps of the HOMOs and LUMOs of 1b and 1b·AgI
were generated from the optimized geometries. The picto-
rial representations s show that HOMO and HOMO–1 are
main contributors in the binding of AgI ions (Figure 7).
Conclusions
Figure 7 also shows that the dz2 orbital of the AgI is in-
The ortho (1a) and meta (1b) derivatives of imine-linked
naphthalimide-based dipodal FONPs were synthesized.
The FONP (of 1a and 1b) were treated with various metal
ions; only ONP-1b was found to be a selective sensor for
AgI ions. The broad range of operational pH (2.3–12.3),
low detection limit (15.5 nm), short response time (84 s),
and broad range of detection (15–65 nm) make it a valuable
sensor for AgI detection. Further, control samples 5 and 6
were also prepared and evaluated their metal-binding prop-
erties. The results show that the imine-linkage is responsible
for the binding site for AgI ions. Furthermore, DFT calcu-
lations were performed to elucidate the mechanism of bind-
ing.
volved in the binding. The decrease of energy in the
HOMO–LUMO gap also authenticate the binding phe-
nomena.
Experimental Section
General Information: All chemicals were purchased from Sigma–
Aldrich and used without any further purification. The NMR stud-
ies were carried out with a Avance-II (Bruker) instrument and a
JEOL 300 NMR spectrometer by using TMS as an internal stan-
dard and CDCl3 as the solvent (400 and 300 MHz for 1H NMR
and 100 and 75 MHz for 13C NMR). The UV/Vis absorption mea-
surements were performed with a Specord 250 Plus Analytikjena
spectrometer. A Perkin–Elmer L55 fluorescence spectrophotometer
was employed for fluorescence measurements and equipped with a
quartz cuvettes of 1 cm path length and a xenon lamp as the exci-
tation source. TEM images were recorded with a Hitachi (H-7500)
instrument operating at 80 kV. A 400-mesh carbon-coated copper
grid was used for sample preparation. The size distribution of
nanoparticles was determined with a Metrohm Microtrac Ultra
Nanotrac particle-size analyzer (dynamic light scattering). The pH
measurements were made with a Toshcon lab pH meter. The elec-
trochemical measurements were recorded with a Potentiostat–Gal-
vanostat BASI EPSILON instrument by using a Pt disk as the
working electrode, an Ag/AgCl electrode as the reference (3 m KCl),
and a Pt wire as the counter electrode. An Agilent 7700 Series ICP
Figure 7. Representation of HOMO, HOMO–1, LUMO, and
LUMO+1 of 1b (left) and 1b·AgI (right), calculated by using
B3LYP/6-31G and B3LYP/LANL2DZ, respectively.
In jewelry industry, silver is extensively used for various
purposes. With increasing demand of silver ornaments, the
chance of contamination of natural resources like water is
increasing. We randomly selected the effluent from Sarafa
Bazaar in Ludhiana, India, one of the twenty most polluted
cities in the world. The samples were centrifuged and fil-
tered before analysis. The silver content of these samples mass spectrometer was used for the determination of silver content
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in water samples. The ICP-MS instrument was equipped with a
ASX-500 series ICP-MS auto-sampler.
Acknowledgment
V. K. B. is thankful to the Department of Science and Technology
(DST) for the DST-INSPIRE Faculty fellowship and research
grant (IFA-11CH-09).
Compound 1a: Compound 4 was prepared according to a literature
method.[30] The compounds 3a (500 mg, 1 mmol) and 4 (635 mg,
2 mmol) were dissolved in CHCl3/CH3OH (1:1) and heated at re-
flux for 12 h, yield 64%, m.p. Ն 250 °C. 1H NMR (300 MHz,
CDCl3): δ = 2.20 (s, 6 H, –CH3), 2.29 (s, 3 H, –CH3), 4.99 (s, 4
H, –CH2), 6.71 (s, 1 H, –Ar), 6.98–7.03 (m, 4 H, –Ar), 7.40 (t, J =
7.2 Hz, 2 H, –Ar), 7.57–7.69 (m, 4 H, –Ar), 8.20 (d, J = 7.8 Hz, 4
H, –Ar), 8.35–8.40 (m, 4 H, –Ar), 8.65 (s, 2 H, –CH=N) ppm. 13C
NMR (75 MHz, CDCl3): δ = 15.59, 19.96, 66.15, 96.31, 113.04,
121.62, 122.0, 122.23, 123.50, 127.31, 127.77, 128.37, 128.46,
129.19, 130.33, 130.76, 131.18, 132.12, 133.75, 138.63, 138.76,
139.18, 159.21, 159.71, 159.95, 166.43 ppm. C49H34Cl2N4O6
(845.74): calcd. C 69.59, H 4.05, N 6.62; found C 69.52, H 4.12, N
6.68.
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Compound 1b: Compounds 3b (500 mg, 1 mmol) and 4 (635 mg,
2 mmol) were dissolved in CHCl3/CH3OH (1:1) and heated at re-
flux for 12 h, yield 66%, m.p. Ն 250 °C. 1H NMR (400 MHz,
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Eur. J. Inorg. Chem. 2014, 5424–5431
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: May 28, 2014
Published Online: September 29, 2014
Eur. J. Inorg. Chem. 2014, 5424–5431
5431
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim