Dipodal quinoline-tethered fluorescent probe synthesis and investigation of spectroscopic properties

Article abstract of DOI:10.1016/j.molstruc.2017.05.047

Novel quinoline-tethered fluorescent probe was designed and synthesized as multidentate ligand. Their sensing actions were confirmed by UV–Vis absorbance and emission spectroscopic studies in presence of perchlorate salts of Co²⁺, Li⁺, Fe²⁺, K⁺, Pb²⁺, Cu²⁺, Zn²⁺, Ni²⁺, Hg²⁺, Ag⁺ cations in acetonitrile (1 × 10^?5 M for absorption studies, 1 × 10^?7 M for fluorescence studies). It was found that the dipodal compounds can selectively bind to Cu²⁺ and Ag⁺ metal ions with a significant quenching in their emissions. The capture of Cu²⁺ and Ag⁺ by the probe resulted in deprotonation of the secondary amine conjugated to the quinoline-tethered probe, so that the electron-donation ability of the ‘N’ atom would be greatly enhanced and the probe (2) showed blue-shift in emission and exhibited an on-off fluorescent response. The binding study was explored by using fluorescence spectroscopy with Job plot method.

Full text of DOI:10.1016/j.molstruc.2017.05.047

Accepted Manuscript
Dipodal quinoline-tethered fluorescent probe synthesis and investigation of
spectroscopic properties
Aslıhan Yilmaz Obali, Menzeher Serkan Yilmaz, Halil İsmet Uçan
PII:
S0022-2860(17)30631-2
10.1016/j.molstruc.2017.05.047
MOLSTR 23788
DOI:
Reference:
To appear in: Journal of Molecular Structure
Please cite this article as: Aslıhan Yilmaz Obali, Menzeher Serkan Yilmaz, Halil İsmet Uçan, Dipodal
quinoline-tethered fluorescent probe synthesis and investigation of spectroscopic properties, Journal of
Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.05.047
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HIGHLIGHTS
1. Synthesis of dipodal quinoline-tethered probe is performed originally.
2. Fluorescence properties of dipodal quinoline-tethered probe are investigated.
3. It was found that the dipodal compounds can selectively bind to Cu2+ and Ag+ metal
ions with a significant quenching in their emissions.

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DIPODAL QUINOLINE-TETHERED FLUORESCENT PROBE SYNTHESIS
AND INVESTIGATION OF SPECTROSCOPIC PROPERTIES
Aslıhan YILMAZ OBALI*, Menzeher Serkan YILMAZ, Halil İsmet UÇAN
Department of Chemsitry, Science Faculty, Selcuk University, Turkey
Abstract
Novel quinoline-tethered fluorescent probe was designed and synthesized as multidentate
ligand. Their sensing actions were confirmed by UV–Vis absorbance and emission
spectroscopic studies in presence of perchlorate salts of Co2+, Li+, Fe2+, K+, Pb2+, Cu2+, Zn2+,
Ni2+, Hg2+, Ag+ cations in acetonitrile (1x10-5 M for absorption studies, 1x10-7 M for
fluorescence studies). It was found that the dipodal compounds can selectively bind to Cu2+
and Ag+ metal ions with a significant quenching in their emissions. The capture of Cu2+ and
Ag+ by the probe resulted in deprotonation of the secondary amine conjugated to the
quinoline-tethered probe, so that the electron-donation ability of the ‘N’ atom would be
greatly enhanced and the probe (2) showed blue-shift in emission and exhibited an on-off
fluorescent response. The binding study was explored by using fluorescence spectroscopy
with Job plot method.
Keywords: Dipodal, fluorescence, probe, silver, copper, cation.
1. Introduction
The dipodal fluorescent probes constitute a special class of fluorophores, which consist of
two-armed compounds with each arm bearing a functional group that can coordinate with
the target ion. Among the fluorescent probes that have been developed in recent years,
quinoline-tethered probes have been attracting the interest of scientists due to their
excellent fluorescent properties. Quinoline-tethered probes used in selective recognition
and sensing of cations are of importance in many fields, ranging from environmental
monitoring, industrial purposes to medicine [1-4].
Heavy and transition metal ion (HTM) sensing and detection are significant in the field of
environment and medicine [5-6]. Copper, is the most abundant HTM metal in the body and
in the brain. It plays an important role in many fundamental processes in organisms.
However, it is suspected to cause infant liver damages and after the mercury it is highly toxic
for drinking water. However, the pollution situation caused by copper ion is very severe and
it has been intensively studied as the detection target for many molecular sensors [7-8].
Due to the widespread applications and the broad prospects of silver in the electronic
industry and photographic and imaging industry, much attention has been paid to the
negative impact of silver ions on the environment, especially on organisms [9]. Intake of
excessive silver can lead to accumulation of insoluble precipitates in the skin and eyes. In
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addition, silver ions are known to combine with amine, imidazole and thiol groups in
proteins, resulting in loss of protein function, which creates serious environmental and
health effects [10].
Herein, based on the outstanding spectroscopic properties of 8-aminoquinoline, we
designed and synthesized a novel quinoline-tethered dipodal multidentate ligand as a
fluorescent probe for copper and silver. These ions generally act as fluorescence quenchers.
2. Experimental
2.1. Apparatus
All starting materials and reagents used were purchased from Alfa Aesar, Sigma Aldrich,
Merck and used without further purification. All aqueous solutions were prepared with
deionized water that had been passed through a Millipore milli Q Plus water purification
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system. H-NMR spectra were taken using a Varian 400-MHz Spectrometer. FT-IR spectra
were recorded using a Perkin Elmer Spectrum 100 FT-IR spectrometer. Melting points were
determined by Büchi Melting Point B-540 instrument. Elemental analyses were carried out
using a LECO-CHNS- 932 elementel analyser. UV–vis spectra were recorded on Perkin Elmer
Lambda 25 UV–Vis Spectrometer. The fluorescence measurements were performed using a
Perkin Elmer LS 55 Luminescence Spectrometer.
2.2. Method
2-chloro-N-(quinolin-8-yl)acetamide (1) was synthesized according to the literature method
[11]. Other materials were commercially available and of reagent grade. All of them were
used without purification.
2.3. Synthesis
2-Chloro-N-(quinolin-8yl)acetamide, (1)
To a cooled, stirred solution of 8-aminoquinoline (500 mg, 3.5 mmol) and TEA (2.4 ml, 17.5
mmol) was added a dichloromethane (10 ml) solution of 2-chloroacetyl chloride (1.3 ml, 17.5
mmol) dropwise over 40 min. After 4 h at room temperature, a brown-yellow solidwas
obtained by removing the solvent under reduced pressure. The crude product was purified
by silica gel column chromatography using dichloromethane/ethyl acetate (1:1, v/v) as
eluant to afford 2-chloro-N-(quinolin-8-yl)acetamide. Yield: 90.0%. 1H NMR (300 MHz, CDCl3)
d 10.90 (s, 1H), 8.96e8.81 (m, 1H), 8.79e8.67 (m, 1H), 8.17 (d, 1H), 7.55 (dd, 3.7 Hz, 2H),
7.52e7.42 (m, 1H), 4.45e4.25 (m, 2H).
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2,2’-(1,2-Phenylenebis(azanediyl)bis(N-(quinolin-8-yl)acetamide), (2)
Fluorescent probe (2) was synthesized by refluxing 2-chloro-N-(quinolin-8-yl)acetamide 1 g
(0,0047 mol) and 1,2-phenylenediamine 0,616 g (0,0047 mol) with the addition of 0.06 g
K2CO3 and 0.08 g KI in acetonitrile medium for 24h. The compound was obtained and
recrystallized from acetone with yield %55. M.P.: 120°C, FT-IR (cm-1): N-H (3384), Ar-CH
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(2954), C=O (1620), CH=N (1672), C=C (1523). H-NMR (400 MHz, DMSO) δ: 6.9 (R-CO-NH),
6.0 (R-NH), 7.02-8.66 (Ar-H), 8.6 (CH=N). Elemental analysis: C: 69.09, H: 5.05, N: 17.50.
Fig 1. The synthesis scheme for 2-chloro-N-(quinolin-8-yl)acetamide, (1) and fluorescent
probe 2,2’-(1,2-phenylenebis(azanediyl)bis(N-(quinolin-8-yl)acetamide), (2).
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3. Result and Discussion
3.1. Synthesis and Characterization
A novel pincer-shape fluorescent probe 2,2’-(1,2-phenylenebis(azanediyl)bis(N-(quinolin-8-
yl)acetamide) (2) was synthesized originally. Starting compound, 2-chloro-N-(quinolin-8-
yl)acetamide was synthesized in accordance with the literature method. Fig. 1 shows the
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synthesis scheme. The compounds were characterized by melting point, FT-IR, H-NMR,
elemental analysis and analytical spectroscopy. The FT-IR spectrum of receptor (2) showed
stretching band at 3384 cm-1 due to N-H band, at 1672 cm-1 due to the C=N band and at 1620
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cm-1 due to the C=O band. The H NMR spectra were recorded in d6-DMSO. The spectra of
receptor (2) showed the broad chemical shifts for both N-H groups. The chemical shift for R-
NH group was seen at 6.9 ppm and for R-CO-NH group was seen at 6.0 ppm. The chemical
shift of quinoline CH=N bond is at 8.6 ppm.
3.2. UV-Vis Absorbance and Fluorescence Studies
The cation recognition ability of fluorescent probe 2,2’-(1,2-phenylenebis(azanediyl)bis(N-
(quinolin-8-yl)acetamide) (2) (1.0 eq) was determined by the UV–vis and fluorescence
studies upon addition of various perchlorate salts of Co2+, Li+, Fe2+, K+, Pb2+, Cu2+, Zn2+, Ni2+,
Hg2+, Ag+ cations (0.5 eq) in acetonitrile (1x10-5 M for absorption studies, 1x10-7 M for
fluorescence studies). The binding study was explored by using fluorescence spectroscopy
with Job plot method.
Maximum wavelenghts (λmax) and maximum absorbance values (Amax) and calculated molar
absorptivity values (Ԑ) was given in Table 2, (Ԑ=Amax/l.C (l=1 cm) for the fluorescent probe
and metal perchlorate solutions.
The fluorescent probe (2) exhibits a strong absorption band at λmax: 480 nm (Ԑmax: 120,000
M-1.cm-1). And it has shoulders at 480 nm and 520 nm. When metal perchlorate solutions
were added to the solution of the probe, some spectecular changes were seen. Probe-Pb2+
exhibits absorption band at λmax: 450 nm (Ԑmax: 155,000 M-1.cm-1). And it has shoulders at
450 nm and 520 nm. The other Probe-Mn+ exhibit absorption band same as the probe itself
at λmax: 480 nm with the shoulders at 480 nm and 520 nm. Their absorptivities are
calculated as for Cu2+, Zn2+, Ag+, K+ Ԑmax: 110,000 M-1.cm-1, for Fe2+ Ԑmax: 100,000 M-1.cm-1, for
Ni2+ Ԑmax: 82,000 M-1.cm-1, for Hg2+ Ԑmax: 75,000 M-1.cm-1, for Co2+, Li+, Ԑmax: 60,000 M-1.cm-1.
Additionally, only the maximum wavelenght of Probe-Pb2+ solution is blue shifted to λmax
:
450 nm. The other Probe-Metal solutions and the Probe itself have the maximum
wavelenght of λmax: 480 nm with different absorptivities. (Fig. 2, Table 1, Table 2). And only
the molar absorptivity of Probe-Pb2+ is higher than free probe and other Probe-Metal
solutions.
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Fig. 2. The cation binding absorption profile of the probe (2) upon addiition of perchlorate
salts of Co2+, Li+, Fe2+, K+, Pb2+, Cu2+, Zn2+, Ni2+, Hg2+, Ag+ cations in acetonitrile medium with
the concentration of 1x10-5 M.
Table 1. Table of the maximum wavelenghts for the probe and the probe with metals
.
Sample
(λmax, nm)
(λshoulder, nm)
(λshoulder, nm)
Pb2+
450
480
450
480
520
520
Probe (2)
Co2+, Li+, Fe2+, K+, Cu2+,
Zn2+, Ag+, Ni2+, Hg2+
480
480
520
Table 2. Maximum wavelenghts (λmax) and maximum absorbance values (Amax) and calculated molar
absorptivity values (Ԑ) of the fluorescent probe and metal cations (1x10-5 M) in acetonitrile medium.
Sample
Amax
Ԑ
Amax
Ԑ
(λmax: 450 nm)
(M-1.cm-1)
(λmax: 480 nm)
(M-1.cm-1)
Pb2+
1.55
155.000
Probe (2)
Ag+, K+, Cu2+, Zn2+
Fe2+
1.20
1.10
1.00
0.82
0.75
0.60
120.000
110.000
100.000
82.000
75.000
60.000
Ni2+
Hg2+
Co2+, Li+
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Free probe has an orange color. When metal perchlorate solutions were added to the
solution of the probe, visual color changes were seen. Probe with Li+ and K+ have same color
like the probe, probe with Fe2+, Pb2+, Cu2+, Zn2+, Ni2+, Hg2+ have dark orange color, Ag+ has
light yellow color, and interestingly Co2+ has green color (Fig.3).
Fig. 3. Visual color changes in acetonitrile medium with the probe (2) and probe with
various metals.
Fluorescence studies of the quinoline-tethered fluorescent probe (2) were also performed
with the acetonitrile solutions of the concentration 1x10-7 M. The probe (2) contains no
additional fluorophore, hence upon excitation at λex: 350 nm.
The fluorescence spectrum of the probe (2) exhibits an emission band at λmax: 538 nm. Upon
addition of Li+ and K+ the fluorescence spectra exhibit emission bands at λmax: 538 nm, same
as a free probe. Upon addition of Co2+, Fe2+, Pb2+, Zn2+, Ni2+, Hg2+ metals the fluorescence
spectra exhibit emission bands at λmax: 546 nm and with the addition of Cu2+ and Ag+ the
emission bands were seen at λmax: 520 nm. As seen from fluorescent spectra, probe with
Co2+, Fe2+, Pb2+, Zn2+, Ni2+, Hg2+ metals were red-shifted, seperately, and probe with Cu2+ and
Ag+ were blue-shifted, seperately. These shifts could be attributed to intramolecular charge
transfer (ICT) interaction between the metal cations and the electron rich donor array of
amine groups.
The emission intensities of probes with metals at their maximum wavelenghts were
observed as Probe › K+ › Li+ › Pb2+ › Co2+, Fe2+, Zn2+, Ni2+, Hg2+ › Ag+ › Cu2+. The most quenchers
were Ag+ and Cu2+. The probe itself is more fluorescent than the metal-complexed-probe
molecule. The bands of Ag+ and Cu2+ have lower intensities because of efficient
photoinduced electron transfer (PET) quenching, which comes into play due to complexation
of metals and the probe (Fig.4).
Additionally, changes were recorded in fluorescence spectra of the probe (2) (1x10-7 M)
upon addition of increasing concentration of Probe-Cu2+ and Probe-Ag+, seperately, in
acetonitrile at 520 nm. Upon complexation of the probes with metals, the quenching was
observed (Fig. 5).
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Fig. 4. Changes in fluorescent intensity of the probe (2) upon the addition of various metals
in acetonitrile medium with the concentration of 1x10-7 M (λext: 350 nm).
(a)
(b)
Fig. 5. Changes in fluorescence spectra of the probe-Cu2+ (a) and probe-Ag+ (b) (1x10-7 M)
upon addition of increasing concentrations in acetonitrile at 520 nm.
The stoichiometry of the reaction of probe (2) and probe-metal is 1:2 according to Job’s plot
studies. To determine the stoichiometry of the probe (2) and metal ion binding, solutions of
probe (2) and the Cu2+ and Ag+, seperately, were prepared at ratios of 10 : 0, 9 : 1, 8 : 2, 7 : 3,
6 : 4, 5 : 5, 4 : 6, 3 : 7, 2 : 8, 1 : 9 and 0: 10. The fluorescence spectra were recorded for each
mixture. The plot of [R] versus ([R]+ [Mn+]) was used to determine the stoichiometry of the
complex formed. The result of Job plot identified the 1:2 complexation between probe (2)
and metals, because the probe-cation complex concentration approaches a maximum when
the molar fraction of probe (2) {[R] / ([R]+ [Mn+])} is about 0.30 (Fig. 6). The binding
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stoichiometry is calculated with Job plotting and as expected, detected at a 1:2 ratio of
probe / metal. According to the Jobs plotting studies, the estimated perspective of the
complexes were drawn as in Fig.7.
(a)
(b)
Fig. 6. Job plot of the probe-Cu2+ (a) and probe-Ag+ (b).
Fig. 7. The estimated perspective of the complexes, according to the Job’s plot for the
binding of compounds and the metal cations as 1:2 ratio.
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Conclusion
In conclusion, we have synthesized novel dipodal fluorescent probe, 2,2’-(1,2-
phenylenebis(azanediyl)bis(N-(quinolin-8-yl)acetamide), (2) which response toward Cu2+ and
Ag+ cations. The binding and sensing behaviors of probe (2) toward various cations were
easily monitored by absorption spectral changes. The quenching effect of the probe (2) were
confirmed by fluorescence spectroscopic studies in presence of various perchlorate salts of
Co2+, Li+, Fe2+, K+, Pb2+, Cu2+, Zn2+, Ni2+, Hg2+, Ag+ cations in acetonitrile. Among the metal
cations, Cu2+ and Ag+ cations has quenching effect.
Acknowledgment
We thank the Scientific Research Projects Foundation (BAP) of Selcuk University
(Konya/TURKEY) for financial support of this work.
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