Fluorescent Chemosensor for Pb2+ Based on 1,2,4-Triazole

Article abstract of DOI:10.1134/S0022476618050220

A new fluorescent sensor for Pb²⁺ based on functionalized 1,2,4-triazole is synthesized. The crystal structure and molecular conformation is confirmed by single crystal X-ray diffraction. Its binding properties investigated by fluorescence spectroscopy show that it can selectively bind Pb²⁺ with fluorescence quenching.

Full text of DOI:10.1134/S0022476618050220

Journal of Structural Chemistry. Vol. 59, No. 5, pp. 1181-1185, 2018.
Original Russian Text © 2018 D.-H. Zhang, Y.-P. Duan, Y. Liu.
2+
FLUORESCENT CHEMOSENSOR FOR Pb BASED
ON 1,2,4-TRIAZOLE
1
D.-H. Zhang , Y.-P. Duan , and Y. Liu
1
2
2+
A new fluorescent sensor for Pb based on functionalized 1,2,4-triazole is synthesized. The crystal
structure and molecular conformation is confirmed by single crystal X-ray diffraction. Its binding
2+
properties investigated by fluorescence spectroscopy show that it can selectively bind Pb with
fluorescence quenching.
DOI: 10.1134/S0022476618050220
2+
Keywords: synthesis, 2,4-triazole, fluorescence quenching, Pb .
INTRODUCTION
Synthetic nucleoside analogs with modified nucleobase and/or sugar moieties are of considerable importance in the
search for materials endowed with antiviral, anticancer, and antibacterial activities [1]. They can mimic natural nucleosides
and serve as building units or inhibitors that interfere in the nucleic acid synthesis or block nucleoside-dependent biological
processes. Well-known nucleoside drugs include the antiviral drugs ribavirin, acyclovir and zidovudine, and the most
commonly used anticancer nucleoside drugs include gemcitabine and cladribine. We have been engaged in a program to
develop structurally diverse triazole nucleoside analogs. These nucleosides contain triazole as a nucleobase and aromatic
groups appended to it [2, 3] with a view to identifying new structural leads exhibiting biologically interesting activity.
Looking for derivatives of triazoles that contain a new recognition site, we have introduced thioehter and triazole
2+
moieties into the same sensor molecule to strengthen the Pb coordination capacity. We now report the synthesis of such
2+
a compound and its assessment as a selective fluorescent chemosensor for Pb .
EXPERIMENTAL
Instruments and reagents. All reagents obtained from commercial sources were of AR grade. Melting points were
1
determined with an XT4A micromelting point apparatus and were not corrected. The H NMR spectra were recorded on
a Mercury Plus-400 spectrometer with TMS as the internal reference and CDCl as a solvent. IR spectra were recorded on
3
a Perkin-Elmer PE-983 IR spectrometer in KBr pellets. Mass spectra were obtained with a Finnigan Trace MS instrument
using the EI method. Elemental analyses were carried out on a Vario EL III instrument.
1
Hubei Key Laboratory of Pollutant Analysis and Reuse Technology, Hu bei Collaborative Innovation Center for
Rare Metal Chemistry, College of Arts and Science of Hubei Normal University and College of Chemistry and Chemical
2
Engineering, Hubei Normal University, Huangshi, P. R. China; zhangdehua200@163.com. School of Chemistry and
Environmental Science, Shanxi University of Technology, Hanzhong, P. R. China. The text was submitted by the authors in
English. Zhurnal Strukturnoi Khimii, Vol. 59, No. 5, pp. 1221-1225, June-July, 2018. Original article submitted February 17,
2017.
0022-4766/18/5905-1181 © 2018 by Pleiades Publishing, Ltd.
1181

Synthesis and structure determination. Synthesis of 1-[(2-acetoxyethoxy)methyl]-5-(phenylthio)-1H-1,2,4-
4
triazole-3-carboxylate (1) : Methyl 1-((2-acetoxyethoxy)methyl)-5-bromo-1H-1,2,4-triazole-3- carboxylate (32.2 mg,
0.1 mmol), thiophenol (0.12 mmol), and K CO (27.6 mg, 0.2 mmol) were suspended in 2 ml of freshly distilled CH CN
2 3 3
under argon. The vessel was sealed and the reaction was carried out under microwave irradiation at 100 °С for 30 min, and
then cooled to room temperature. The reaction mixture was concentrated under reduced pressure and the crude residue was
purified by flash chromatography on silica gel (petroleum ether/ethyl acetate, 2:1). The purified material was dried in vacuo
1
to afford the corresponding product as colorless oil. Yield 35.2 mg (99%). H NMR (300 MHz, CDCl ): δ 7.51-7.54 (m, 2H,
3
phenyl–H), 7.36-7.38 (m, 3H, phenyl–H), 5.66 (s, 2H, –OCH N–), 4.13 (t, 2H, J = 4.7 Hz, –OCH CH OAc), 3.99 (s, 3H,
2 2 2
13
–OCH ), 3.76 (t, 2H, J = 4.7 Hz, –OCH CH OAc), 2.05 (s, 3H, –C(O)CH ); C NMR (150 MHz, CDCl ): δ 170.9, 159.9,
3
2
2
3
3
+
154.6, 153.5, 132.3, 129.8, 129.2, 78.4, 67.9, 62.8, 53.1, 21.0; Maldi-MS: m/z 352.1 [M+H] ; HRMS: calcd. for
+
C H N O S 352.0962, found 352.0951. Anal. calcd. for C H N O S(351.09): C 51.27, H 4.88, N 11.96, S 9.13. Found: C
15 18
3
5
15 18
3
5
51.12, H 4.77, N 11.87, S 9.25.
5
Synthesis of 1-[(2-hydroxyethoxy)methyl]-5-(phenylthio)-1H-1,2,4-triazole-3-carboxamide (2) : A solution of
NH /MeOH (18 mL) was added to a flask containing compound 1 (90.6 mg, 0.258 mmol), and the mixture was stirred at
3
room temperature for two days. After removal of the solvent, compound 2 (63.9 mg, 84%) was obtained as a white solid.
1
HNMR (300 MHz, DMSO-d ): δ 7.93 (br s, 1H, –C(O)NH ), 7.70 (br s, 1H, –C(O)NH ), 7.39-7.51 (m, 5H, phenyl–H), 5.66
6 2 2
13
(s, 2H, –OCH N–), 4.74 (t, 1H, J = 5.4 Hz, –OH), 3.51-3.55 (m, 2H, –OCH CH OH), 3.44-3.47 (m, 2H, –OCH CH OH);
2 2 2 2 2
C
NMR (75 MHz, DMSO-d ): δ 160.5, 157.7, 151.4, 131.7, 130.9, 130.3, 129.2, 78.7, 71.8, 60.4; Maldi-MS: m/z 295.1
6
+ +
[M+H] ; HRMS: calcd. For C H N O S 295.0859, found 295.0853. Anal. calcd. for C H N O S(294.08): C 48.97, H
12 15
4
3
12 15
4
3
4.79, N 19.04, S 10.89. Found: C 48.78, H 4.68, N 18.97, S 10.76.
X-ray diffraction study of 2. A white crystal of title compound 2 was mounted on a glass fiber in a random
orientation at 298(2) K. The determination of the unit cell and the data collection were performed with MoK radiation
α
(λ = 0.71073 Å) on a Bruker Smart Apex-CCD diffractometer with a ψ–ω scan mode. The structure was solved by direct
methods with the SHELXS-97 program and expanded by the Fourier technique. The non-hydrogen atoms were refined
anisotropically, and the hydrogen atoms were placed at the calculated positions. Crystal data for 2: C H N 0 S, M = 294.33,
12 16
4 3
3
triclinic, space group P2(1)/n, a = 7.347(2) Å, b = 26.952(7) Å, c = 7.708(2) Å, β = 116.505(5)°, V = 1365.7(6) Å , Z = 4,
3
D = 1.431 mg/m , reflections collected 8719, independent reflections 2675 [R = 0.1147], final R indices [I > 2σ(I)]
c
int
R1 = 0.0686, wR2 = 0.1291. R indices (all data): R1 = 0.1183, wR2 = 0.1475.
RESULTS AND DISCUSSION
The synthesis of 2 is shown in Scheme 1. The structure and conformation of compound 2 were elucidated by single
crystal X-ray diffraction (Fig. 1). The three-dimensional molecular packing diagram of 2 is shown in Fig. 2.
Scheme 1. Synthetic route of target compound 2.
Crystals of 2 were obtained by slow evaporation of a solution in an ethyl acetate/petroleum ether (3:1, v/v) mixture.
The crystal structure of 2 reveals that its well-defined geometry is due to the rigidity that the fused rings confer on the
molecule. Selected bond lengths of 2 have been shown (Table 1). The dihedral angle between benzene and other triazole
1182

Fig. 1. Crystal structure of compound 2.
Fig. 2.
Three-dimensional
molecular-packing
diagram of 2.
TABLE 1. Selected Bond Lengths (Å) of 2
C1–S1
C7–S1
C7–N3
1.777(3)
1.747(3)
1.322(4)
C7–N1
C8–N2
C8–N3
1.342(4)
1.316(4)
1.353(4)
C9–N4
C10–N1
N1–N2
1.318(4)
1.461(4)
1.351(3)
rings (N2, N1, C7, N3, C8) is 52.94°. The molecular conformation is stabilized by the N2–H3⋯O3 hydrogen bonding; the
bond length is 2.2969(6) Å. The crystal packing is governed by N4–H4A⋯O3 (the bond length is 1.968(7) Å) and
N4–H4B⋯O2 (the bond length is 2.179(2) Å) interactions, resulting in a three-dimensional network. These values are normal
for the complexation of an aromatic ring by π–π stacking interactions of triazole rings. The distance is 3.347 Å between the
center point.
The binding capacity of 2 towards various metal ions were investigated by fluorescent spectroscopy titration
–5
experiments [6, 7]. Changes in the fluorescence of 1×10 M of 2 in a DMF solution caused by the addition of 15 equiv. of
2+
2+
2+
2+
3+
+
2+
2+
various metal ions (Cu , Cd , Mn , Bi , Fe , Ag , Pb , Sr , Sn , Co , Hg ) were measured once their emission
4+
2+
2+
2+
intensities became constant. The results show that only Pb produced significant quenching of fluorescence emission. The
other metal ions showed a relatively insignificant change (Fig. 3). It can be concluded that the molecule of 2 has a higher
2+
selectivity for the recognition of Pb .
1183

–5
Fig. 3. Fluorescence emission changes of 2 (1⋅10 M)
–5
in DMF in the presence of 12⋅10 various metal ions
(excitation at 400 nm).
2+
The sensitivity of the fluorescence emission response of 2 towards Pb was also examined under the same
2+
conditions with various Pb concentrations (Fig. 4) [8, 9]. The fluorescence intensity decreased continuously upon the
2+ 2+
addition of Pb . When the Pb amount increased to 12 equiv, the fluorescence intensity of 2 was reduced to 52% of the
initial intensity. From a Benesi–Hildebrand plot (Fig. 5) [10, 11] the equation is as follows:
2+
1/F – F = 1/K (F – F )Pb ] + 1/F – F ,
0 a 0 min 0 min
2+
where F stands for the sensor (“host”) fluorescence intensity; F is the fluorescence intensity after adding Pb ; F is the
0
min
2+ 2+
minimum value of the fluorescence intensity; [Pb ] is the molar concentration of Pb ; K is the apparent binding constant.
a
We have calculated the binding constant between them through the above equation. The quenching constants were estimated
4 –1
to be 4.37⋅10 M .
This work was supported by the Hubei Key Laboratory of Pollutant Analysis and Reuse Technology (Grant
No. PA150203), the Hubei provincial Department of Education (Grant No. B2016163), College of Arts and Science of Hubei
Normal University (Grant No. Ky201502) and Local University National College Students Innovation and Entrepreneurship
Training Program (Grant No. 201413256002).
Fig. 4. Fluorescence emission spectra (excitation at
Fig. 5. Benesi-Hildebrand linear analysis plots of 2 at
2+
different Pb concentrations. F on behalf of the host
0
–5
400 nm) of 2 (1⋅10 M) in DMF in the presence of
2+ 2+
different Pb concentrations.The Pb concentration in
of the fluorescence intensity, F on behalf of the
fluorescence intensity after joining to identify
different ion concentrations.
–6 –6
the order from top to bottom: 3.75⋅10 M, 7.5⋅10 M,
–5
1.13⋅10 M, 1.5⋅10 M, 1.87⋅10 M, 2.25⋅10 M,
–6
–6
–5
–5
2.63⋅10 M, 3⋅10 M, 3.38⋅10 M, 3.75⋅10 M,
–5
–5
–5
–5 –5
4.12⋅10 M, 4.54⋅10 M.
1184

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