A facile naphthalene-based fluorescent 'turn-on' chemodosimeter for palladium ions in aqueous solution

Article abstract of DOI:10.1016/j.tetlet.2016.02.012

A novel and simple depropargylation-triggered spontaneous cyclization reaction based fluorescent turn-on chemodosimeter for the detection of Pd²⁺ has been reasonably designed and developed. Based on the specific reactivity of palladium ion-promoted hydrolysis reaction, the probe exhibited a high selectivity and sensitivity for Pd²⁺ with a low detection limit (53 nM, 5.7 μg/L) under physiological conditions in neutral PBS (only containing 1% organic cosolvent) without any additional reagents.

Full text of DOI:10.1016/j.tetlet.2016.02.012

Accepted Manuscript
A Facile Naphthalene-Based Fluorescent “Turn-On” Chemodosimeter for Pal-
ladium Ions in Aqueous Solution
Yu Chen, Bo Chen, Daijun Luo, Yiyu Cai, Yaning Wei, Yifeng Han
PII:
S0040-4039(16)30122-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.02.012
TETL 47285
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
25 November 2015
29 January 2016
3 February 2016
Please cite this article as: Chen, Y., Chen, B., Luo, D., Cai, Y., Wei, Y., Han, Y., A Facile Naphthalene-Based
Fluorescent “Turn-On” Chemodosimeter for Palladium Ions in Aqueous Solution, Tetrahedron Letters (2016), doi:
http://dx.doi.org/10.1016/j.tetlet.2016.02.012
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A Facile Naphthalene-Based Fluorescent
Turn-On” Chemodosimeter for Palladium
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Ions in Aqueous Solution
Yu Chen, Bo Chen, Daijun Luo, Yiyu Cai, Yaning Wei, and Yifeng Han*

1
Tetrahedron Letters
A Facile Naphthalene-Based Fluorescent “Turn-On” Chemodosimeter for Palladium
Ions in Aqueous Solution
Yu Chen, Bo Chen, Daijun Luo, Yiyu Cai, Yaning Wei, and Yifeng Han*
Department of Chemistry, The Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Zhejiang Sci-Tech University, Hangzhou, 310018,
China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel and simple depropargylation-triggered spontaneous cyclization reaction based
2+
fluorescent turn-on chemodosimeter for the detection of Pd has been reasonably designed and
developed. Based on the specific reactivity of palladium ion-promoted hydrolysis reaction, the
2+
probe exhibited a high selectivity and sensitivity for Pd with a low detection limit (53 nM, 5.7
μg/L) under physiological conditions in neutral PBS (only containing 1% organic cosolvent)
without any additional reagents.
Available online
Keywords:
2
009 Elsevier Ltd. All rights reserved.
Fluorescent probe
Chemodosimeter
Palladium ion
Reaction-based
Depropargylation-triggered
1. Introduction
O
O
O
OH
O
N
O
Palladium, which is widely distributed in the environment duo
CN
CN
Cl
Cl
N
to its use in alloys, fuel cells, chemical catalysts and especially in
automobile catalytic converters, is one of the most ubiquitous and
OH
HO
1
Y. Pang, 2012
poisonous heavy metals. Palladium ions are not biodegradable,
O
NH
K. H. Ahn, 2010
and hence can be concentrated through the food chain, which
may cause serious health problems. Excess palladium
accumulation may result in the degradation of cell mitochondria
O
W. Liu, 2011
O
O
2
and DNA, and also enzyme inhibition. Thus, the governmental
S
S
N
O
O
regulation on the proposed maximum dietary intake of palladium
O
O
O
O
3
3
3
is less than 1.5-15 μg per person per day. Therefore, the
N
N
H
H2N
development of convenient and effective methods for palladium
analysis is crucial both to the monitoring of environmental
pollution and to the diagnosis of clinical disorders.
N
O
N
I
I
N
F
N
B
N
N
B
F
F
F
X. Peng, 2014
Y. Kim, 2014
K. Singh, 2014
Conventional techniques used for quantification of palladium
species, such as atomic absorption spectroscopy, inductively
coupled plasma atomic emission spectroscopy, and solid-phase
microextraction high-performance liquid chromatography, often
need the complicated sample preparation and the expensive and
sophisticated instrumentation, and are therefore not suitable for
Figure 1. Structures of some reported palladium probes.
However, many of them still have limitations such as
interference from other coexisting metal ions, only work in
organic solvents and/or water-organic cosolvents, need additional
reagents, and laborious synthesis processes expensive chemicals.
4
real-time and in situ analysis. Thus, current research has been
focused on fluorescent probe techniques because of their ease of
application in solution as well as their high sensitivity and
2+
Furthermore, among the few available Pd chemodosimeters
reported, most employ the pH-sensitive fluorescein or rhodamine
as the fluorophore and their pH-dependence may pose detection
errors to the results. It is therefore strongly desirable to develop
novel and simple yet specific fluorescent chemodosimeters for
5
selectivity for trace analytes.
Recently, considerable efforts have been made to develop
2
+
2+
fluorescent probe for Pd
based on Pd
catalyzed
catalyzed
2+
2+
the detection of Pd .
depropargylation and deallylation reaction, Pd
oxidative cyclization reaction, Pd catalyzed ring-opening
catalyzed C-I cleavage reaction, a6nd the
coordination of Pd to heteroatom-based ligands (Fig. 1).
2+
Our research group is actively engaged in the development of
novel specific fluorescent probes for heavy metal ions. Herein,
we report a novel yet simple depropargylation-triggered
2+
reaction, Pd
7
2+

2
Tetrahedron
CN
CN
CN
CN
NH
spontaneous
cyclization
- N
O
O
O
SPd2
strongly-fluorescent
almost non-fluorescent
deprotection
PdCl2, H2O
CN
CN
CN Pd+
CN Pd+
keto-enol tautomerism
O
OH
O
O
Scheme 1. The “deprotection-cyclization” strategy for the design of
SPd2.
spontaneous cyclization based fluorescent chemodosimeter
2
+
(
SPd2) that shows high selectivity and sensitivity for Pd . It
2+
should be mentioned that SPd2 could be used to detect Pd
o
under physiological condition (at 37 C in PBS, pH 7.4, only
containing 1% organic cosolvent) without any additional
reagents.
It is well known that the terminal propargyl ether can be
specifically cleaved by palladium-catalyzed hydrolysis reaction
6d, 6m
to generate the corresponding free hydroxyl group.
We
envisioned that the fluorescent intensity of the SPd2 might
greatly reduce due to the effect of intramolecular rotation. On the
other hand, the deprotection of the propargyl ether group of SPd2
2+
by Pd -promoted hydrolysis reaction would releases the hydroxy
intermediate, which wills spontaneous cyclize to form a highly
fluorescent chemodosimeter (Scheme 1).
2
. Results and discussions
Figure 2. (a) UV-vis absorption spectra of SPd2 (20.0 μM) in the
2+
As shown in Scheme 2, SPd2 can be readily prepared in two
absence and presence of Pd (20.0 μM), and compound 4. (b)
Fluorescence spectra of SPd2 (10.0 μM) in the absence and presence of
convenient steps under facile conditions with high yield starting
with commercially available 2-hydroxy-1-naphthaldehyde. The
product (SPd2) was well characterized by H, C NMR, and HR-
2+
Pd (100.0 μM). Inset: Fluorescence changes excited by UV lamp (365
1
13
2+
nm) in the absence and presence of Pd . All spectra were acquired 1 h
2+
MS (ESI†).
after Pd addition at 37 °C in PBS buffer solutions (10 mM, pH 7.4,
containing 1.0% EtOH). λex = 395 nm.
We firstly assessed the UV-vis spectroscopic properties of
SPd2 in PBS buffer solution (10 mM, pH 7.4, containing 1.0%
EtOH) (Fig. 2a). SPd2 (20.0 μM) displayed a moderate UV-vis
2+
absorption around 390 nm. Upon the addition of Pd (20.0 μM),
the maximum absorption peak seems, underwent a blue-shift to
3
25 nm. But the absorption spectra of compound 4 were clearly
2+
shown that the absorption band at 325 nm belongs to the Pd
CHO
CHO
OH
(a)
O
(b)
1
2
CN
CN
NH
CN
O
(c)
O
3
(SPd2)
4
Figure 3. Fluorescence spectra of SPd2 (10.0 μM) in PBS buffer
solution (10 mM, pH 7.4, containing 1.0% EtOH) in the presence of
2
+
Scheme 2. Synthesis of SPd2: (a) 3-bromopropyne/K
2
CO
3
, acetone,
different concentrations of Pd (0-250.0 μM) (λex = 395 nm). Inset:
2+
reflux, 4 h, 77%; (b) malononitrile, piperidine, EtOH, rt, 4 h, 98%; (c)
PdCl , EtOH, rt, 4 h, 88%.
Fluorescence intensity (at 457 nm) changes of SPd2 as a function of Pd
2
concentration.

3
2+
(
(
Fig. 2a, and S1, ESI). On the other hand, in the presence of Pd
100.0 μM), SPd2 (10.0 μM) showed a dramatic increase in cyan
fluorescence emission at 457 nm (in PBS buffer solution, 10 mM,
pH 7.4, containing 1.0% EtOH) (Fig. 2b).
2+
The speculative mechanism of the Pd induced fluorescence
response is shown in Scheme 1. Efforts were then made to
explore the nature of the palladium ion induced response. To this
2+
end, a comparison of fluorescent spectra between the SPd2-Pd
system and compound 4 was made to confirm the generation of 4
2
+
1
13
after treatment with Pd (Fig. S2, ESI†). The H- and C- NMR
2+
spectra of the isolated product of the SPd2-Pd solution were
also measured to support the depropargylation-triggered
spontaneous cyclization of SPd2 (see ESI†).
Next, the emission spectra of SPd2 and its fluorescent titration
2+
with Pd were recorded in PBS buffer solution (10 mM, pH 7.4,
containing 1.0% EtOH) (Fig. 3). As expected, SPd2 alone is
almost non-fluorescent (λex = 395 nm, Φ = 0.08%, Table S1,
ESI†) duo to the effect of intramolecular rotation (Scheme 1).
Figure 5. Fluorescence responses of SPd2 to various metal ions
3+
2+
2+
+
2+
2+
3+
2+
2+
2+
2+
(including Al , Ca , Co , Cs , Cu , Fe , Fe , Hg , Mg , Ni , Pb ,
2+
2+
However, with progressive addition of Pd , the emission band at
and Pd ). Black bars represent the addition of 10.0 equiv. of the
457 nm rapidly increased (Fig. 3), which was attributed to the
appropriate metal ion to a 10.0 μM solution of SPd2 (in PBS buffer
cleavage of propargyl ether group by palladium ion-promoted
hydrolysis followed by spontaneous cyclization reaction to form
solution, 10 mM, pH 7.4, containing 1.0% EtOH). Red bars represent the
2+
addition of 10.0 equiv. of Pd to the solutions containing SPd2 (10.0
μM) and the appropriated metals (100.0 μM) (λex = 395 nm).
the highly fluorescent cyclic compound
4 (Scheme 1).
Furthermore, the fluorescence titration curve revealed that the
fluorescence intensity at 457 nm increased linearly with
2+
increasing concentration of Pd (Fig. S3, ESI†) and further
smoothly increased until a maximum was reached up to 100.0
2+
μM Pd (λex = 395 nm, Φ = 0.103, Table S1, ESI†). Owing to the
specific reactivity of palladium ion-promoted hydrolysis reaction,
2+
SPd2 displayed a high sensitivity toward Pd .
Subsequently, the time-dependence of fluorescence was also
2+
evaluated in the presence of Pd in PBS buffer solution (10 mM,
pH 7.4, containing 1.0% EtOH) (Fig. 4 and Fig. S4, ESI†). The
result shows that the fluorescence of the tested solutions
remarkably increased to the maximum value within 100 minutes.
Accordingly, the observed rate constant (kobs) for the formation of
-2
-1
compound 4 has been calculated to be 2.7  10 min (Fig. S5,
8
ESI†).
Further, the fluorescence titration of SPd2 with various metal
ions was then conducted to examine the selectivity (Fig. 5, and
S6, ESI†). Much to our delight, the turn-on response of SPd2 is
Figure 6. Effect of the pH on the fluorescence emission of SPd2 (10.0
μM) alone and SPd2 (10.0 μM) reacted with Pd (10.0 equiv.).
2+
2
+
highly specific for Pd and no obvious change of fluorescent
3+
2+
2+
+
2+
2+
3+
2+
2+
2+
2+
emission was observed when it is treated with Al , Ca , Co ,
Cs , Cu , Fe , Fe , Hg , Mg , Ni , and Pb . It should be
2+
mentioned that SPd2 still responded to Pd sensitively even in
the presence of other relevant competing ions (Fig. 5, and S7,
ESI†). Therefore, these results suggest that SPd2 displays high
2
+
selectivity toward Pd in neutral aqueous solution.
2+
Moreover, the Pd -sensing ability of SPd2 at a wide range of
pH values was investigated. As depicted in Fig. 6, SPd2 alone
was inert to pH in the range of 6.0-9.3. On the other hand, it
2+
readily reacted with Pd within the biologically relevant pH rang
6.0-8.5). These results indicate that SPd2 could be used in
(
neutral natural systems, or a mildly acidic or basic environment.
For practical purposes, the detection limit of SPd2 for the
2+
analysis of Pd
was also an important parameter. The
fluorescence titration curve revealed that the fluorescence
intensity of SPd2 at 457 nm increased linearly with the amount
2
+
2
of Pd in the range of 0-20.0 μM (R = 0.994) (Fig. S8, ESI†).
2+
Thus, the detection limit of SPd2 for Pd was calculated to be
.3  10 M (Pd content = 5.7 μg/L), which indicated that
SPd2 could be a sensitive fluorescent chemodosimeter for
-8
2+
9
Figure 4. Time-dependent fluorescence intensity (at 457 nm) changes of
5
2+
SPd2 (10.0 μM) upon addition of Pd (10.0 equiv.) in PBS buffer
solution (10 mM, pH 7.4, containing 1.0% EtOH) (λex = 395 nm).
2+
quantitative detection of Pd .

4
Tetrahedron
3. Conclusions
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In conclusion, we have successfully developed a novel and
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1
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solubility, and excellent selectivity and sensitivity response
towards Pd , with a low detection limit (53 nM, 5.7 μg/L). We
anticipate that the experimental results of this study will inspire
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chemical and biological applications.
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Acknowledgments
This work was supported by the National Natural Science
Foundation of China (20902082), the Project Grants 521 Talents
Cultivation of Zhejiang Sci-Tech University, and the Program for
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Supplementary Material
Supplementary data (additional spectroscopic of SPd2)
associated with this article - copies of H and C NMR Spectra
can be found, in the online version, at http://dx.doi.org.
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