A new colorimetric and fluorescent chemosensor based on thiazolyl-hydrazone for sensitive detection of copper ions

Article abstract of DOI:10.1007/s13738-019-01802-3

Abstract: A Cu²⁺-specific chemosensor probe thiazolyl-hydrazone (BL) has been designed and prepared, which provide tridentate chelate NNO coordination mode for Cu²⁺ with binding stoichiometry of 1:1. The BL solution exhibits a rapid color change from colorless to yellow along with a new intense absorption band at 414?nm upon binding to Cu²⁺ cation, whereas other metal cations do not induce such a change. The analytical detection limit is 0.75?μM, and the naked eye detection limit is as low as 20?μM. Additionally, the emission signal of BL could be quenched by Cu²⁺ and Fe³⁺ with a detection limit of 7.2?μM and 4.3?μM, respectively. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-019-01802-3

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01802-3
ORIGINAL PAPER
A new colorimetric and fuorescent chemosensor based
on thiazolyl‑hydrazone for sensitive detection of copper ions
Zhaodong Jia1 · Jingna Wei1 · Yaping Ren1 · Ning Zhang1 · Xin‑Qi Hao1 · Xinju Zhu1 · Yan Xu1
Received: 11 April 2019 / Accepted: 20 October 2019
© Iranian Chemical Society 2019
Abstract
A Cu2+-specifc chemosensor probe thiazolyl-hydrazone (BL) has been designed and prepared, which provide tridentate
chelate NNO coordination mode for Cu2+ with binding stoichiometry of 1:1. The BL solution exhibits a rapid color change
from colorless to yellow along with a new intense absorption band at 414 nm upon binding to Cu2+ cation, whereas other
metal cations do not induce such a change. The analytical detection limit is 0.75 μM, and the naked eye detection limit is as
low as 20 μM. Additionally, the emission signal of BL could be quenched by Cu2+ and Fe3+ with a detection limit of 7.2 μM
and 4.3 μM, respectively.
Graphic abstract
Keywords Colorimetric probe · Copper(II) ions · Thiazolyl-hydrazone derivative
Introduction
Copper plays an important role in many physiological activi-
ties, and its concentration above or below the normal levels
will cause an adverse efect on the organism [1–3]. There-
Electronic supplementary material The online version of this
fore, the design and synthesis of probes to detect copper
ions is an important research topic [4–8]. It is well known
that copper ions can be detected using several instrumental
techniques, such as atomic absorption spectroscopy, phys-
icochemical techniques, and electrochemistry. However,
these methods rely on expensive instruments and need
tedious sample preparation and operation scheme [9–11].
Recently, colorimetric methods for ion detections have
article (https://doi.org/10.1007/s13738-019-01802-3) contains
supplementary material, which is available to authorized users.
* Xinju Zhu
zhuxinju@zzu.edu.cn
* Yan Xu
xuyan@zzu.edu.cn
1
College of Chemistry and Molecular Engineering,
Zhengzhou University, Zhengzhou 450001, China
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
received great attention due to their low cost and operational
simplicity [12, 13]. To date, some Schif base derivatives
have shown highly sensitive detection of copper(II) ion with
either a color change/absorption spectra change or fuores-
cent spectra change, due to their well-known coordinative
capability [14–18]. From complexation point of view, phe-
nol hydrazone derivatives could give similar geometric and
cavity control compared with Schif base. However, to the
best of our knowledge, only a few chemosensors comprising
phenol hydrazone units have been demonstrated to exhibit
selective and sensitive for the detection of Cu2+ [19–21]. In
this paper, we designed and synthesized phenol hydrazone
derivative BL functionalized with thiazole, which provided a
good possibility for chelation with transition metal ions [22,
23]. Specially, BL exhibits an exclusive sensing property
toward the Cu2+ in the UV–Vis experiments as well as with
a visual color change.
DMSO-d6) δ 168.5, 146.4, 140.7, 131.0, 127.1, 120.5, 120.0,
116.6, 104.8. Anal. Calcd for C20H16N6O2S2: C, 55.15; H,
3.33; N, 19.37; S, 14.81. Found: C, 55.03; H, 3.69; N, 19.25;
S, 14.69. IR (KBr, cm−1): 3289, 3060, 1620, 1600, 1566,
1493, 1476, 1456, 1407, 1344, 1312, 1288, 1254, 1222,
1055, 756.
Results and discussion
Compounds L1 and L2 are synthesized according to the
reported synthetic procedure, respectively [24, 25]. The
compound BL is then obtained by the reaction of 1,4-dibro-
mobutanedione and 2-hydroxybenzaldehyde in 82% yield
(Scheme 1). The chemical structure of BL is confrmed
1
by various characterizations (MS, H, 13C NMR, EA, and
FT-IR).
The absorption spectrum of BL (50 μM) in DMSO
exhibits a strong band with the maximum absorbance peak
at about 358 nm due to intramolecular π–π* electronic tran-
sition, resulting in nearly colorless solution [26]. Upon an
increase in the concentration of Cu2+ (0.2–2.2 equiv), the
absorption intensity at 358 nm gradually decreased with a
slightly hypsochromic shift. Notably, a new absorption peak
at 414 nm is observed with a shoulder at 448 nm (Fig. 1a).
The intensities of the absorption (414 nm) are linearly
related to the copper ion concentration (Fig. 1b), suggesting
that the detection limit of BL for Cu2+ is 0.75 μM, which is
lower than those previously reported chemosensors based on
phenol hydrazone derivatives [27, 28]. Moreover, as shown
in Fig. 1c, the colorless solution of BL becomes yellow upon
addition of Cu2+ and it is easy to detect by the naked eye at
0.4 equivalents (20 μM).
Experimental section
General
Unless otherwise indicated, all of the starting materials and
regents were commercially available and utilized without
further purifcation. Melting points were determined on
an Electrothermal Programmable Melting Point Appara-
tus (XT4B). Infrared (IR) spectra were measured using a
PerkinElmer with KBr pellets. 1H NMR and 13C NMR spec-
tra were recorded on a Bruker Avance-600 spectrometer.
Chemical shifts were expressed in ppm and coupling con-
stants (J) in Hz. Mass spectrometric data were obtained by
positive electron spray ionization (ESI–MS) technique on a
Bruker Esquire 3000. Elemental analysis (EA) was carried
out in a Flash EA 1112 elemental analyzer. Absorption and
fuorescence spectra at room temperature were determined
on TU-1901 spectrophotometer and Hitachi F-4600 fuores-
cence spectrometer, respectively. The solutions of metal ions
in deionized water were prepared from their chloride salts.
Obviously, the above observations result from the com-
plexation between BL and Cu2+. Meanwhile, when the
Cu2+ concentration is higher than 2.0 equiv, the absorp-
tion spectrum shows little changes, suggesting that the
complexation between Cu2+ and BL reaches equilibrium.
To understand the structure of the BL–Cu2+ complexes,
Typical procedure for the synthesis of BL
H
N
NH2
CHO
OH
S
C2H5OH
N
+
Thiazolyl-hydrazone (BL): 2-(2-hydroxybenzylidene)
hydrazine-1-carbothioamide L1 (780 mg, 4.0 mmol) and
1,4-dibromobutanedione L2 (492 mg, 2.0 mol) were dis-
solved in 50 ml absolute ethanol. The reaction mixture
was refuxed 4 h. After cooling to room temperature, the
precipitate was fltered and recrystallized with DMF and
ethanol to get brown compound BL. Yield: 924 mg (53%);
calc. for C20H16N6O2S2 [M+H]+: 436.08; found: 436.3. 1H
NMR (600 MHz, DMSO-d6) δ 12.20 (s, 2H), 10.15 (s, 2H),
8.34 (s, 2H), 7.64 (dd, J=11.4, 10.3 Hz, 2H), 7.29-7.18 (m,
2H), 7.01 (s, 2H), 6.96–6.84 (m, 4H).13C NMR (150 MHz,
reflux
S
H2N
NH2NH2
OH
L1
C2H5OH
80 o 4h
C,
O
O
Br2 CHCl
,
3
CH2Br
CH3
BrH2C
H3C
O
O
L2
H
N
OH
N
S
N
N
S
N
N
H
HO
BL
Scheme 1 Synthetic route to compound BL
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Journal of the Iranian Chemical Society
Fig. 1 a Absorption spectra of BL recorded in DMSO (5.0×10−5 M)
after the addition of 0.2 to 2.2 equiv. Cu2+. b Plot for calculation of
the detection limit of BL (50 μM) with Cu2+ in DMSO. c Visual color
changes upon addition of 0.1 to 1.0 equiv. Cu2+ in the receptor solu-
tion
Fig. 2 a Job plot of the Cu2+–BL complex in DMSO. The total con-
centration of BL and Cu2+ was 50.0 μM. The monitored wave length
1
was 482 nm. b Benesi–Hildebrand plot of BL with Cu2+. c H NMR
the composition of BL–Cu2+ complex is studied by the
Job’s plots using the changes in absorption intensity at
414 nm as a function of mole fraction of BL (Fig. 2a). The
maximum intensity is reached when the molar fraction of
BL is 0.5, which indicated the complex formed by BL and
Cu2+ is 1:1. The binding constant of BL–Cu2+ complex is
calculated by utilizing Benesi–Hildebrand (B-H) equation
[29]. From the B-H plot (Fig. 2b), a well linear relation-
ship is obtained from the measured absorption intensity [1/
(A − A0)] as a function of 1/[Cu2+] at 414 nm. The binding
changes of BL in the presence of Cu2+ ions (0–1.0 eq) recorded in
DMSO d6 at 298 K
constant value of BL–Cu2+ complex is then obtained from
the slope and intercept (K = 4.481 × 103 M−1, R2 = 0.9966)
[30]. Furthermore, the proton signal (Ha) at 12.15 ppm
almost completely disappears upon the addition of Cu2+
(1.0 equiv), which not only indicates the formation of
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Journal of the Iranian Chemical Society
complexes with 1:1 stoichiometry but also indicates Cu2+
binds to deprotonated phenol group (Fig. 2c).
Selectivity is an important characteristic for an ion-
selective chemosensor. The absorption spectral changes
of BL in the presence of some common ions (10 equiv)
including Zn2+, Ni2+, Cd2+, Co2+, Pb2+, Al3+, Cr3+, Fe3+,
Ag+, Na+, and K+ are investigated. As shown in Fig. 3a,
b, the absorption spectra and the color of solution have
no signifcant change except of Cu2+ ions. Encouraged
Fig. 4 a Emission spectra change of BL (in DMSO) upon addition of
diferent metal cations (10 equiv). b Curve of fuorescence intensity
at 482 nm of BL (50 μM) versus increasing concentrations of Cu2+. c
A plot of fuorescence intensity versus concentrations of Fe3+ for BL.
Excitation wavelength was 358 nm
Fig. 3 a Absorbance spectra change of the sensor BL (50 μM) upon
the addition of various metal ions in DMSO. b Color change of BL
in the presence of diferent metal cations. c The absorbance of BL
toward Cu2+ ions and relevant metal ions in DMSO. The green bars
in each group represent the absorbance of BL in the presence of vari-
ous metal ions (10 equiv). The red bars in each group represent the
change in absorbance that occurs upon subsequent addition of Cu2+
ions (10 equiv)
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Journal of the Iranian Chemical Society
Acknowledgements Financial support from the National Natural Sci-
ence Foundation of China (Grant Nos. 21672192 and 21803059), the
China Postdoctoral Science Foundation (Grant Nos. 2016M602254 and
2016M600582), the Program for Science & Technology Innovation
Talents in Universities of Henan Province (Grant No. 17HASTIT004),
the Aid Project for the Leading Young Teachers in Henan Provincial
Institutions (Grant No. 2015GGJS-157), and the Natural Science
Foundation of Henan Province (Grant No. 182300410255) is grate-
fully appreciated.
from the high selectivity, the sensing capabilities are next
investigated under competition environment. The subse-
quent addition of 2.0 equiv. Cu2+ to the mixed solution of
BL and other metal ion (10 equiv) results in an absorp-
tion spectral change (red bar) similar with that of BL and
Cu2+ (green bar) (Fig. 3c). These results indicate that the
detection of Cu2+ based on BL is hardly interfered by the
coexistent common metal ions, and thus BL could be used
as a potential chemosensor for Cu2+ with a high selectivity.
As BL could exhibit intense fuorescence with peak at
around 482 nm, cations-induced changes in the emission
intensity of BL are also carried out. Upon the addition of
Cu2+ and Fe3+ (3 equiv), the BL solution shows a signif-
cant fuorescence quenching (Fig. 4a), which is probably
due to the deactivation of emission from excited state of
BL caused by the paramagnetic nature of Cu2+ and Fe3+
ions [31]. However, under similar experimental conditions,
the other common cations (such as K+, Na+, Cd2+, Ag+,
Co2+, Ni2+, Zn2+, Pb2+, Al3+, Fe3+, and Cr3+) show either
little increase or neglect change in the emission intensity.
Additionally, the static and dynamic model for BL fuo-
rescence quenching is studied by addition of small ali-
quots of Cu2+/Fe3+ (Fig. S1). The uniform quenching of
fuorescence intensity shows good linearity in the range
0–200 μM with a lower detection limit of 7.2 μM for Cu2+
and 4.3 μM for Fe3+, suggesting that BL is a potential
fuorescent sensor for copper ions and ferric irons (Fig. 4b,
c). Additionally, as shown in Fig. S2, the subsequent addi-
tion of Cu2+/Fe3+ (3 equiv) to the solution of BL and other
common cations (10 equiv) elicits a protuberant fuores-
cence quenching (blue bar), suggesting that the common
metal cations do not show signifcant interference on the
Cu2+/Fe3+ assay.
Supplementary material Containing fuorescence titration and selec-
tivity of BL with Cu2+ and Fe3+ in DMSO.
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In conclusion, a new colorimetric and fuorescent sensor
BL, bearing a thiazolyl-hydrazone unit as a metal binding
pocket, has been successfully prepared. The key fnding with
the BL is that a new absorption peak at ca. 414 nm appears
upon titration with Cu2+ ions followed by a solution color
change from colorless to yellow, which is not afected by the
other common metal ions. The selectively detection limits
are 0.75 μM by UV–Vis spectrometer and 20 μM by the
naked eye, respectively, suggesting that BL can be useful in
the detection of trace quantities of Cu2+ ions. Additionally,
this new chemosensor further displays turn-of fuorescence
responses toward Cu2+ and Fe3+ ions with detection limits
of 7.2 μM and 4.3 μM, respectively. Therefore, this study
provides a sensitive and selective sensor for the detection
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