A novel fluorescent chemosensor for Zn(II) based on 1,2-(2′-oxoquinoline-3′-yl-methylideneimino)ethane

Article abstract of DOI:10.1016/j.inoche.2010.02.014

A new bis Schiff-base ligand (1,2-(2′-oxoquinoline-3′-yl-methylideneimino)ethane, QSB) derived from 2-oxo-quinoline-3-carbaldehyde and ethylene diamine was synthesized and characterized by ¹H-NMR. Spectroscopic investigation revealed that the compound exhibited a high selectivity toward Zn(II) ion over other metal ions in acetonitrile solution. In addition, the crystal structure showed that the coordination form of QSB and Zn(II) was 1:1.

Full text of DOI:10.1016/j.inoche.2010.02.014

Inorganic Chemistry Communications 13 (2010) 606–608
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A novel fluorescent chemosensor for Zn(II) based on
1,2-(2′-oxoquinoline-3′-yl-methylideneimino)ethane
⁎
Zeng-chen Liu, Bao-dui Wang, Zheng-yin Yang , Tian-rong Li, Yong Li
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new bis Schiff-base ligand (1,2-(2′-oxoquinoline-3′-yl-methylideneimino)ethane, QSB) derived from 2-
oxo-quinoline-3-carbaldehyde and ethylene diamine was synthesized and characterized by 1H-NMR.
Spectroscopic investigation revealed that the compound exhibited a high selectivity toward Zn(II) ion over
other metal ions in acetonitrile solution. In addition, the crystal structure showed that the coordination form
of QSB and Zn(II) was 1:1.
Received 22 December 2009
Accepted 23 February 2010
Available online 1 March 2010
Keywords:
© 2010 Elsevier B.V. All rights reserved.
Bis Schiff-base
Fluorescence sensor
Crystal structure
Zn(II) complex
In recent years, there has been an increasing focus on the design
and synthesis of highly selective fluorescent chemosensors for zinc
ion [1–7]. Zinc ion which is the second most abundant transition
metal ion in the human body plays an important role in biological
system such as neuronal signal transmission, regulator of enzymes
and DNA-binding [8–10], in addition, too much zinc is also a harmful
metal pollution to the environment [11]. However, the discrimination
between Zn(II) and many other metal ions is difficult due to the
similar chemical properties [12]. Therefore, the detection of fluores-
cent chemosensors for Zn(II) is very significant for diagnosing disease
and controlling environment pollution [13].
Up to now, many fluorescent chemosensors based on quinoline
derivatives have been reported and some show high fluorescence
selectivity for Zn(II) [14–17], but only a few chemosensors can
distinguish Zn(II) from Cd(II) [18]. Hence, the fluorescence chemo-
sensors for Zn(II) rather than Cd(II) based on quinoline derivates need
to be developed. Owing to simplicity and sensitivity of Schiff-base
type fluorescence sensors, many fluorescent chemosensors based on
Schiff-base have been designed and investigated [19–21]. Herein, we
report a novel bis Schiff-base fluorescent sensor (QSB) derived from
2-oxo-quinoline-3-carbaldehyde and ethylene diamine. As a new
fluorescent sensor for Zn(II), the QSB exhibits a high sensitivity and
selectivity. Simultaneously, the 1:1 coordinative formation between
QSB and Zn(II) is demonstrated by X-ray crystal diffraction.
containing 2-oxo-quinoline-3-carbaldehyde under reflux to obtain
the QSB [24].
The single crystal of Zn–QSB complex was obtained by slow
evaporation in CH3CN to understand the coordinative geometry
between ligand and Zn(II) clearly. A yellow crystal of Zn(II) complex
was measured on a Bruker APEX-II CCD diffractometer with graphite
monochromatic Mokα radiation (λ=0.71073 Å) at 296(2)K [25]. As
shown in Fig. 1, the binding mode of ligand and Zn(II) was 1:1
coordination and the Zn(II) complex exhibited good symmetrical
structure. There were two six atom rings and a five atom ring around
the zinc atom and the coordinative structure was described as a
standard octahedral geometry due to two coordinative H2O molecules
(Zn1O1O2O3O4N2N3). In addition, the unit cell contained two non-
coordinative nitrate radicals and the asymmetric unit cell of the
complex consists of eight crystallographically independent molecules
of the complex.
The influence of different solvent on the fluorescence intensities
was investigated in detail. QSB was dissolved in DMSO to get a 1.0 mM
concentration, then diluted with other solvents. As shown in Fig. 2, the
fluorescence intensity and peak shape in aqueous solution was very
different from that in other anhydrous solution (ethanol, acetone,
acetonitrile, and chloroform), we deduced that this can be a
quenching effect of water molecule and that the fluorescence
intensity in acetonitrile solution was the largest. So all metal ions
were from nitrate salts and were dissolved in acetonitrile at a
concentration of 1.0 mM and the spectroscopic measurements (UV-
Vis and fluorescence) were tested in acetonitrile solution.
As shown in Scheme 1, 2-oxo-quinoline-3-carbaldehyde was
prepared according to the literature [22,23]. An ethanol solution
containing ethylene diamine was added to another ethanol solution
The UV-Vis absorbance titration spectrum of QSB against Zn(II)
showed that the absorbance at 225 nm had a pronounced redshift to
250 nm, simultaneously, the absorption peaks at 300 nm and 350 nm
increased with the addition of Zn(II) and also exhibited appropriate
⁎
Corresponding author. Tel.: +86 931 891 3515; fax: +86 931 891 2582.
E-mail address: yangzy@lzu.edu.cn (Z. Yang).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.02.014

Z. Liu et al. / Inorganic Chemistry Communications 13 (2010) 606–608
607
Scheme 1. Synthesis of ligand (QSB).
redshift (Fig. 3). The changes of UV-Vis absorption spectrum of QSB
with addition of Zn(II) illustrated that a new complex was generated
between QSB and Zn(II).
ion over the other ions. Fig. 5 showed the relative fluorescence
intensity of QSB in the presence of metal ions and without metal ions.
And that the histogram illuminated clearly that the QSB exhibited
high selectivity for Zn(II) in acetonitrile.
Furthermore, the fluorescence titration experiment in acetonitrile
solution was conducted to measure the fluorescence-on behavior in
To investigate the fluorescent selectivity of QSB for various
transition metal ions in detail, the fluorescent titration spectrum
was studied systemically (Fig. 4). The ligand (20 µL, 1 mM) was
titrated with metal ions (40 µL, 1 mM). With addition of 2 equiv. of Zn
(II), the emission intensity at 423 nm increased strongly, however, in
presence of other metal ions such as K(I), Na(I), Mg(II), Cr(III), Cd(II),
Cu(II), Ni(II), Co(II), the fluorescence changed weakly. This phenom-
enon demonstrated that the QSB exhibited a high selectivity for Zn(II)
Fig. 3. UV-Vis titration spectra of QSB (10.0 μM) in the presence of different
concentrations of Zn(II) ion (0, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 μM) in
acetonitrile solution.
Fig. 1. ORTEP view of Zn–QSB complex showing the atom numbering of scheme and
30% thermal ellipsoids probability for the non-hydrogen atoms.
Fig. 4. Fluorescence intensity of QSB (10 μM) in the presence of various metal ions
(20 μM) in acetonitrile solution (excitation 305 nm, emission 423 nm).
Fig. 2. Fluorescence intensity change of QSB with addition of 2 equiv. of Zn(II) in
different solvent (water, ethanol, acetone, acetonitrile, chloroform).

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Z. Liu et al. / Inorganic Chemistry Communications 13 (2010) 606–608
and ethylene diamine is developed. Compared with other metal ions,
the chemosensor QSB exhibits high selectivity and sensitivity for Zn
(II) in acetonitrile solution, moreover, the single crystal between the
ligand and Zn(II) is also obtained, so the coordinative geometry is
demonstrated clearly according to the single crystal analysis. The
remarkable photophysical properties of the chemosensor will be
helpful for the development of fluorescent sensor based on quinoline
derivates.
Acknowledgements
We are grateful for the financial support from the National Science
Foundation of China (20975046) and Gansu NSF (0710RJZA012).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2010.02.014.
Fig. 5. Relative fluorescence intensity at the metal ion to QSB. Excitation wavelength
was 305 nm, emission wavelength was 423 nm. I0 was the fluorescence intensity of QSB
without metal ions, I was the fluorescence intensity of QSB after addition of metal ions.
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Fig. 6. Fluorescence intensity emission spectrum of QSB in presence of different
concentration Zn(II) (0, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, 20.0, 22.5, 25.0, 27.5 and
30.0 μM) in acetonitrile solution.
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added to another ethanol solution (10 mL) containing 2-oxo-quinoline-3-carbalde-
hyde (0.692 g, 4.0 mmol). The mixture was refluxed for 6h with stirring and a white
precipitate separated out. The precipitation was filtrated under decompression and
washed with ethanol. Recrystallization from DMF/H2O (V:V=1:1) gave the ligand,
which was dried under vacuum. Yield, 70%. m.p: 317–319 °C. 1H-NMR (DMSO–d6
300 MHz): δ 11.992 (2H, s, –N1–H), δ 8.562 (2H, s, –CH=N), δ 8. 441 (2H, s, –C4,4′–H),
δ 7.9797–7.838 (2H, m, –C8,8′–H), δ 7.490–7.567 (2H, m, –C7,7′–H), δ 7.279–7.317
(2H, m, –C5,5′–H), δ 7.152–7.224 (2H, m, –C6,6′–H), δ 3.915 (4H, s, –C10,10′–H).
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α(°), 90.00, β(°), 91.009(2), γ(°), 90.00; Reflections collected, 3851/5039; Abs
coeff (mm−1), 0.0998; Final R indices, R1=0.0343, wR2=0.0823.
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the presence of Zn(II). As shown in Fig. 6, the fluorescence intensity of
423 nm increased significantly and reached saturation with the
addition of Zn(II). A plot of relative fluorescence intensity (I/I0)
versus [Zn]/[QSB] explicitly (Fig. 6 inset) illustrated that there was a
more than 20 fold increase when compared to QSB. Simultaneously,
the formation of 1:1 metal complex between Zn(II) and QSB was also
illustrated by the inset [26]. This coordinative mode from fluorescence
titration was corresponding to the structure from X-ray diffraction.
In conclusion, a novel fluorescent chemosensor (QSB) based on a
bis Schiff-base ligand derived from 2-oxo-quinoline-3-carbaldehyde