New colorimetric chemosensor based on rhodamine hydrazide to detect Cu2+ ions by naked eye

Article abstract of DOI:10.1007/s11164-014-1588-7

A rhodamine-based chemosensor for naked-eye detection of Cu²⁺ has been designed and synthesized, which exhibited excellent selectivity and high sensitivity for Cu²⁺ in CH₃CN and CH₃CN/H₂O mixed soluti

Full text of DOI:10.1007/s11164-014-1588-7

Res Chem Intermed
DOI 10.1007/s11164-014-1588-7
New colorimetric chemosensor based on rhodamine
hydrazide to detect Cu ions by naked eye
2
+
Datong Zhang
•
Yuntong Ma Ruibing An
•
Received: 26 December 2013 / Accepted: 5 March 2014
Ó Springer Science+Business Media Dordrecht 2014
2
?
Abstract A rhodamine-based chemosensor for naked-eye detection of Cu has
been designed and synthesized, which exhibited excellent selectivity and high
2
sensitivity for Cu in CH CN and CH CN/H O mixed solutions. When Cu was
?
2?
3
3
2
added to the solution of sensor 1, a dramatic color change from colorless to bluish
2?
?
2?
?
2?
2?
violet was observed, while the cations K , Ca , Na , Hg , Zn , Co , Ni
2?
,
Fe , Al , Pb , Ag , and Cd did not interfere with the recognition process for
3
?
3?
2?
?
2?
2
?
Cu . The pH effect investigations indicated that it can be applied to analysis of
samples over a wide pH range.
2
?
Keywords Colorimetric sensor Á Cu Á Naked-eye detection Á Rhodamine
Introduction
As transition metal cations play an important role in living systems and have an
extremely toxic impact on the environment, the development of specific chemo-
sensor for the detection of metal cations has received considerable attention [1–7].
Among transition elements, copper is one of the important elements in humans and
plays a critical role as a catalytic cofactor for a variety of metalloenzymes [8–12].
Electronic supplementary material The online version of this article (doi:10.1007/s11164-014-1588-
7) contains supplementary material, which is available to authorized users.
D. Zhang Á Y. Ma Á R. An
School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology,
Jinan 250353, Shandong, People’s Republic of China
D. Zhang (&)
Shandong Provincial Key Laboratory of Fine Chemicals, Jinan 250353, Shandong,
People’s Republic of China
e-mail: dtzhang@qlu.edu.cn
123

D. Zhang et al.
However, excess copper can cause a variety of intoxications. For example, the
increasing concentration of copper cations in the body causes imbalance in cellular
processes resulting in pathogenesis, such as Wilson’s disease [8, 13, 14],
amyotrophic lateral sclerosis [15], Menkes syndrome [16, 17], Alzheimer’s disease
[
18], and Parkinson’s disease [19]. Since copper has many excellent properties, such
as chemical stability, high electrical conductivity, germicidal efficacy, and the
ability to form alloys with other metal ions [20], it is widely used in industrial,
pharmaceutical, and agricultural fields. At the same time, due to its ionic form of
2
?
Cu , its widespread use is accompanied by a serious threat to the environment and
2
?
people’s health [21]. Therefore, rapid and selective detection of Cu
physiological samples is of toxicological and environmental concern [22–26].
in
2
Since Cu is a fluorescence quencher for its paramagnetic nature, most of the
?
2
?
fluorescence chemosensors for Cu exhibit ‘‘turn-off’’ fluorescence responses,
which, however, limit their applications [27–29]. Alternatively, colorimentric
chemosensors based on absorption changes are desirable, and can be broadly used
owing to the low cost and lack of equipment required, and there is a perceptible
color change, even at very low analyte concentrations [30]. Consequently, it is
important to synthesize selective colorimetric probes for naked-eye detection of
2
?
Cu [31–35].
The rhodamine framework is an ideal template to use in constructing chelation-
enhanced fluorescence OFF–ON fluorescent chemosensors for mental ions due to its
particular structural properties [36]. As is well known, rhodamine derivatives exist
in a spirocyclic form which is nonfluorescent and colorless. The addition of specific
cations leads to ring-opening of the spirolactam via coordination or irreversible
chemical reaction [37–40], resulting in the appearance of a color or fluorescence.
The unique color change and absorption behavior accompanied with ring-opening
and metal coordination also make them available as colorimentric chemosensors
[
molecular sensors, here we report a rhodamine-based spirolactam derivative 1 as a
41]. Based on the understanding of the sensing mechanism of rhodamine-based
2
?
chemosensor for Cu by ultraviolet–visible light. The rhodamine sensor 1 is
colorless in organic media indicating that the spirolactam form of 1 predominates.
2
?
The significant change in visible absorption spectra of 1 after the addition of Cu
makes 1 a selective visual chemosensor for rapid and selective detection of Cu
Also, it is stable under a broad range of pH conditions.
2
?
.
Experimental
Chemicals
Rhodamine B was purchased from Aladdin (Shang Hai) and used without further
purification. In the spectrophotometric studies, all the metal salts were of analytical
?
2?
?
2?
grade and bought from Aladdin (Shang Hai). K , Ca , Na , Cu , Zn , Hg
2?
2?
,
2
?
2?
3?
3?
2?
?
2?
Co , Ni , Fe , Al , Pb , Ag , and Cd were used as their nitrates in the
titrations analysis. The solvents used were of analytical grade and purchased from
Sinopharm.
1
23

2
Rhodamine hydrazide to detect Cu ions by naked eyes
?
Cl-
+ Cl-
N
+
N
O
N
N
O
POCl3
COOH
COCl
H
N
O
N
N
NH2
N
O
2
N
O
N
N
O
N
N
N
H
N
O
O
1
Scheme 1 Synthesis of 1
Instruments
1
13
H NMR and C NMR were measured on a Bruker AVANCE II 400 spectrometers
with CDCl as solvent and TMS as an internal standard. Melting points were
3
determined by a WRS-1B digital melting-point apparatus and were uncorrected.
The IR spectrum was measured on a Bruker Vector FT-IR spectrophotometer as
KBr pellets. The high resolution mass spectra were obtained with an Agilent-6510-
Q-TOF spectrometer. UV–visible spectra were obtained using a T6 New century
spectrometer with a quartz cuvette. The absorption spectra were recorded between
8
00 and 200 nm. Fluorescence spectra measurements were performed on a Hitachi
F-4500 spectrofluorimeter equipped with a xenon lamp as the excitation source. The
pH titrations were performed with the Equip-Tronics Digital pH meter, model
EQ 610.
Procedure for synthesis of 1 (Scheme 1).
Synthesis of 2
Hydrazine hydrate (80 %, 1.1 ml, 22.8 mmol) and 2-chloro-4, 6-dimethoxy-1, 3,
5-triazine (1 g, 5.7 mmol) in CH CN (20 ml) were stirred for 0.5 h at room
3
temperature. The product was collected by filtration and washed twice with 10 ml of
cold CH CN. The residue was dried at 40 °C in vacuo to give 2 (900 mg) as a pale
3
123

D. Zhang et al.
pink powder solid, which was unstable and used for the next step without further
purification.
Synthesis of 1
To a solution of rhodamine B (1.0 g, 2.3 mmol) in dry 1,2-dichloroethane (12 ml)
was added phosphorus oxychloride (0.6 ml) dropwise over 5 min. The solution was
stirred for 3 h at 80 °C under reflux conditions. After cooling, the mixture was
evaporated in vacuo to give rhodamine B acid chloride as dark oil, which was used
for the next step without further purification.
A solution of the crude acid chloride, 2 (400 mg, 2.3 mol), triethylamine (2 ml)
and dry CH Cl (20 ml) was stirred for 3 h under reflux conditions. After cooling,
the mixture was washed with water (30 ml 9 2), the organic layer was dried over
2
2
Na SO . After removal of the solvent in vacuo the residue was purified on silica gel
4
2
with petroleum ether/ethyl acetate (1:1) to afford 1 as a pink powder solid. Yield:
1
5
J = 7.2 Hz, 1H), 7.50–7.58 (m, 2H), 7.19 (d, J = 7.2 Hz, 1H), 6.66 (s, 1H), 6.51 (s,
6 %; m.p. 244.3–245.7 °C. H NMR (400 MHz, CDCl ) d (ppm): 8.01 (d,
3
1
H), 6.31 (d, J = 2.0 Hz, 2H), 6.28 (d, J = 2.0 Hz, 2H), 3.85 (s, 6H), 3.35 (q,
1
-
J = 7.2 Hz, 8H), 1.17 (t, J = 7.2 Hz, 12H). IR (KBr, m/cm ) 3,221, 2,968, 1,715,
1
3
1
,614, 1,577, 1,554, 1,516, 1,475, 1,464, 1,373, 1,346, 1,222, 1,118, 1,016.
C
NMR (75 MHz, CDCl ) d (ppm): 169.01, 164.83, 153.38, 150.69, 148.28, 132.79,
3
1
1
5
28.83, 127.88, 123.79, 123.02, 107.36, 103.99, 97.54, 65.65, 54.22, 45.60, 44.04,
?
2.02. HRMS (ESI) calcd. for [M ? H] C H N O : 596.29853, found:
96.29901.
3
3 37 7 4
Results and discussion
Synthesis
As illustrated in Scheme 1, compound 1 was conveniently obtained in good yield
from the reaction of compound 2 with rhodamine B acid chloride, and characterized
by spectroscopic methods with satisfactory spectral data.
Spectroscopic study
?
The recognition ability was primarily investigated by adding various cations (K ,
2
?
?
2?
2?
2?
2?
2?
3?
3?
2?
?
2?
Ca , Na , Cu , Hg , Zn , Co , Ni , Fe , Al , Pb , Ag , Cd ) to the
2
CH CN solution of 1. When 3 equivalent of Cu was added to the solution of 1
?
3
(
10 lM), the sensor responded with dramatic color change from colorless to bluish
violet, which could be attributed to the coordination between Cu and the opening
2?
spirolactam ring of 1 (Fig. 1a). In the corresponding UV–Vis spectra (Fig. 1b), both
2
Cu and Hg had a strong absorption band at 564 and 558 nm, respectively.
?
2?
2
However the absorption of Cu exhibited red shift more obviously, especially at
?
3
00 nm. Although Fe , Al , and Zn cations showed a moderate or slight
?
3?
2?
6
absorption at 564 nm but none of them created UV absorption at 600 nm,
1
23

2
Rhodamine hydrazide to detect Cu ions by naked eyes
?
Fig. 1 a Color change observed upon the addition of various cations (3.eq) to the solution of sensor 1
2
?
2?
3?
3?
2?
?
2?
?
2?
2?
(
10 lM) in CH CN. Left to right free 1, Zn , Hg , Fe , Al , Cu , K , Ca , Na , Co , Ni ,
3
2? ?
2?
Pb , Ag , and Cd . (For interpretation of the reference to color in this figure legend, the reader is
3
referred to the web version of this article.) b Absorption change of sensor 1 (10 lM) in CH CN upon the
addition of 3 equiv. of different nitrates salts. (Color figure online)
suggesting that 600 nm could be used as the detection wavelength. To establish
sensor 1’s utility in practice, the response of the sensor toward metal cations was
investigated in CH CN/H O (9:1/v:v). As shown in Fig. 2, the UV–vis spectrum of
3
2
2
?
Cu
attenuated more obviously. These results suggested that 1 could serve as a potential
exhibited no significant change, but the absorption of the other cations
2
?
naked-eye chemosensor selective for Cu
To further quantitatively investigate the absorption features of the chemosensor,
.
2
?
a solution of increasing concentration of Cu (0.1 to 5 eq) was added to the 10 lM
2
solution of 1 in CH CN. With the increasing concentration of Cu , the linear
?
3
responses of the absorption at 564 and 600 nm were observed in Fig. 3a, indicating
that 1 can be used for the practical quantitative detection. When the solution was
2
?
changed to the mixture of CH CN/H O (9:1/v:v), the titration of Cu ion with
3
2
different concentrations (10 lM, 30 lM, 50 lM) of 1 were successively investi-
gated. As shown in Fig. 3b, with the increasing concentration of sensor 1, the linear
responses of the absorption became better and an excellent liner dependence of
absorbance was obtained in the 50 lM solution of 1. These results suggested that
the chemosensor could be applied to the aqueous system. The detection limit within
2
?
visual color changes in 10 lM solution of 1 is allowable to 4 lM level of Cu ions
Fig. 4).
As sensor 1 showed specific selectivity for Cu , a series of experiments were
(
2
?
2
?
carried out to investigate the Cu recognition capability and mechanism of 1. The
123

D. Zhang et al.
Fig. 2 UV–Vis absorption spectra of 1 in the presence of 3 equiv. of various cations in CH
9:1/v:v) at room temperature
3 2
CN/H O
(
change of the fluorescence spectrum of 1 in the presence of various metal ions was
investigated in CH CN. Sensor 1 itself created a non-fluorescence intensity near
3
3
80 nm. When Fe or Al were introduced to the solution of 1, a significant
?
3?
5
enhancement of fluorescence with an emission maximum at 580 nm was created,
which indicated that the spirolactam ring was opened. However, the addition of
2
Cu caused almost no fluorescence (Fig. S1). Furthermore, fluorescence produced
?
3
?
by the addition of Al disappeared and meanwhile a strong absorption band
2
appeared at 564 nm after the addition of Cu to the solution of 1:Al (Fig. S2).
?
3?
2
?
The well-known paramagnetic effect of the d9 Cu system could be responsible for
the fluorescence quenching. The strong absorption and the colorimetric response
2
?
could be ascribed to the formation of a complex between Cu and ring-opening
2?
intermediate. The stoichiometry of 1-Cu
was determined by the method of
continuous variations (Job’s plot) (Fig. 5). The plot of absorption showed that the
absorption value arrived at its maximum at a molar fraction of ca.0.66, which
2
demonstrated the formation of a 1:2 complex between the sensor 1 and Cu . The
?
2
?
ESI-mass spectra of 1-Cu
m/z = 846.16829 (calculate value 846.1333) corresponding to [1 ? 2Cu
also showed a 1:2 stoichiometry. The peak at
2
?
?
NO3 ? H] was clearly observed when Cu was added to 1 (Fig. S3). The
-
2?
2?
2
binding constant of sensor 1 with Cu
2
?
was calculated by using a Benesi–
4
-1
Hildebrand plot and found to be 3.7 9 10 M (Fig. S4).
Selectivity is an important parameter with which to evaluate the performance of a
chemosensor. To further exploit the scope of sensor 1 as an ion-selective sensor for
2
Cu , competitive experiments were carried out in the presence of 3.0 equiv. of
?
2
Cu and 3.0 equiv. of various metal ions in CH CN/H O (9:1/v:v). The addition of
?
3
2
2
?
Cu ion still resulted in large absorption changes at 600 nm even in the presence of
miscellaneous competitive cations (Fig. 6). The color of all the solutions turned into
2
bluish violet (Fig. 7). This indicates that the selectivity of 1 for Cu over other
?
1
23

2
Rhodamine hydrazide to detect Cu ions by naked eyes
?
2
?
Fig. 3 a Change in the absorbance of 1(10 lM, in CH
3
CN) at 600 and 564 nm as a function of Cu
CN/H O (9:1/
added. b Change in the absorbance of different concentrations (10, 30, 50 lM) of 1 in CH
3
2
2
?
v:v) upon titration with increasing concentration of Cu (1–30 lM)
2?
Fig. 4 Color change observed upon titration with increasing concentration of Cu to the solution of
sensor 1 (10 lM) in CH CN/H O (9:1/v:v). Left to right 1, 2 , 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, and 16 lM.
Color figure online)
3
2
(
123

D. Zhang et al.
2
?
2?
3
Fig. 5 Job’s plot of 1 and Cu in CH CN, indicating the 1:2 stoichiometry of the 1-Cu complex. The
2
?
total concentration of 1 and Cu is 10 lM
3 2
Fig. 6 UV–Vis spectra profiles of compound 1 (10 lM) in CH CN/H O (9:1/v:v) with various of metal
ions. Red bars represent the absorption of compound 1 with the addition of the analytes (30 lM): 1 free, 2
Zn , 3 Al , 4 Hg , 5 Ca , 6 Co , 7 Fe , 8 Cd , 9 K 10 Na , 11 Ni , 12 Pb , 13 Ag . Green
2
?
3?
2?
2?
2?
3?
2?
?
?
2?
2?
?
2
?
bars represent the absorption of compound 1 in the presence of the metal ions and Cu (30 lM). (Color
figure online)
competitive cations in the aqueous systems is remarkably high and 1 would have
practical applications in industrial and environmental fields.
For practical applicability, the changes of the absorption spectra should be
applied over a wide pH range, which may occur in the analysis of samples from
2
?
mildly acidic to basic environments. Therefore, the pH dependence study on 1-Cu
was monitored in CH CN/H O (9:1/v:v) solutions ranging of 1.0 to 14.0. As
illustrated in Fig. 8, almost no substantial change in the absorption band of 1 at
3
2
1
23

2
Rhodamine hydrazide to detect Cu ions by naked eyes
?
2
Fig. 7 Color change observed before and after the addition of Cu (3 equiv.) to the solution of sensor 1
?
2
?
2?
(
10 lM) CH CN/H O (9:1/v:v) in the presence of miscellaneous cations. Left to right free 1, Zn , Hg ,
3 2
3? 3? ? 2? ? 2? 2? 2? ? 2?
Fe , Al , K , Ca , Na , Co , Ni , Pb , Ag , and Cd . (Color figure online)
2
?
3 2
Fig. 8 Absorption intensity (600 nm) of free 1 (10 lM) and 1 ? 3 equiv of Cu in CH CN/H O (9:1/
v:v) with different pH conditions
6
00 nm was observed in the pH range from 1.0 to 14.0. However, the absorbance
2
?
intensity at 600 nm was significantly enhanced upon the addition of Cu ions
between pH 4.0 and 9.0. Thus, the uniform activity over such a wide range of pH
values makes this molecule suitable for the analysis of environmental samples or for
the use in unbuffered media.
Conclusion
In summary, a convenient and highly selective chemosensor 1 based on rhodamine
B was synthesized and its chemosensing properties were investigated. The selective
123

D. Zhang et al.
2
?
recognition of Cu gave rise to a major color change from colorless to bluish
violet, which was clearly visible to the naked eye even at the low concentration of
4
lM. Since the absorption spectrum of 1 remains unperturbed in the pH range
4.0–9.0), it can be used for rapid monitoring of aqueous Cu without resorting to
2?
(
buffered media.
Acknowledgment This study was supported by the self-innovation project for universities and institutes
of Jinan City (No. 201202035).
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