Organic-Inorganic Hybrid Cerium-Encapsulated Selenotungstate including Three Building Blocks and Its Electrochemical Detection of Dopamine and Paracetamol

Article abstract of DOI:10.1021/acs.inorgchem.0c02318

A novel organic-inorganic hybrid cerium-encapsulated selenotungstate comprising three polyoxotungstate building units Na16H6{[Ce3W4O10(H2O)9(CH3COO)3]2(Se2W7O30)(B-α-SeW9O33)4}·(C5H8NBO3)·119H2O (1) was synthesized by the portfolio approach of an in situ self-assembly reaction and step-by-step synthesis. The hybrid polyoxoanion of 1 is constructed from an acetate-coordinated heterometallic {[(Ce3W4O10)(H2O)9(CH3COO)3]2(Se2W7O30)}10+ core encompassing four trilacunary [B-α-SeW9O33]8- subunits. Interestingly, the heterometallic core contains a remarkable [Se2W7O30]10- building block in which seven WVI atoms form a W7 plane and two SeIV atoms are situated on two opposite faces of the W7 plane. In addition, the electrochemical performances of the 1?CFMCN composite (CFMCN: carboxyl-functionalized multiwalled carbon nanotube) were investigated. The 1?CFMCN/GCE (GCE: glass carbon electrode) sensor demonstrates a promising potential in electrochemically sensing dopamine (DPA) or paracetamol (PCM) or even simultaneously detecting DPA and PCM with low limits of 0.053 μM for DPA and 2.03 μM for PCM over a wide linear range at high sensitivity.

Full text of DOI:10.1021/acs.inorgchem.0c02318

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Article
Organic−Inorganic Hybrid Cerium-Encapsulated Selenotungstate
Including Three Building Blocks and Its Electrochemical Detection of
Dopamine and Paracetamol
Jun Jiang, Lulu Liu, Guoping Liu, Dan Wang, Yan Zhang, Lijuan Chen,* and Junwei Zhao*
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sı Supporting Information
ABSTRACT: A novel organic−inorganic hybrid cerium-encapsulated selenotungstate
comprising three polyoxotungstate building units Na H {[Ce W O (H O) -
1
6
6
3
4
10
2
9
(
CH COO) ] (Se W O )(B-α-SeW O ) }·(C H NBO )·119H O (1) was synthe-
3 3 2 2 7 30 9 33 4 5 8 3 2
sized by the portfolio approach of an in situ self-assembly reaction and step-by-step
synthesis. The hybrid polyoxoanion of 1 is constructed from an acetate-coordinated
1
0+
heterometallic {[(Ce W O )(H O) (CH COO) ] (Se W O )} core encompassing
3
4
10
2
9
3
3 2
2
7
30
8
−
four trilacunary [B-α-SeW O ] subunits. Interestingly, the heterometallic core
contains a remarkable [Se W O ] building block in which seven W atoms form a
W plane and two Se atoms are situated on two opposite faces of the W plane. In
9
33
10−
VI
2
7
30
IV
7
7
addition, the electrochemical performances of the 1@CFMCN composite (CFMCN:
carboxyl-functionalized multiwalled carbon nanotube) were investigated. The 1@CFMCN/GCE (GCE: glass carbon electrode)
sensor demonstrates a promising potential in electrochemically sensing dopamine (DPA) or paracetamol (PCM) or even
simultaneously detecting DPA and PCM with low limits of 0.053 μM for DPA and 2.03 μM for PCM over a wide linear range at
high sensitivity.
INTRODUCTION
Selenotungstates (SeTs), as an important subset of POMs,
have been rapidly developed in the past decade. The Se
■
IV
Polyoxometalates (POMs) are extraordinary kinds of metal−
oxygen anionic clusters composed of high-oxidation-state early
transition metals (typically Mo , W , V , Nb , and Ta ) with
not only glamorous structures but also application prospects in
catalysis, optics, magnetism, materials science, and so on.
heteroatom contains a pair of lone electrons, so the pyramidal
2−
SeO3 group can serve as a template for constructing POM-
VI
VI
V
V
V
based open-framework SeTs and further concatenating with
different sorts of metals to form diverse structures. Earlier
1
−5
studies (before 2016) were focused on the “pure” SeTs and
The key to building POMs is the type of heteroatom, which
determines the structures of polyoxoanions and exhibits some
20−30
TM-substituted SeTs.
In the last decade, Ln-containing
POMs have drawn incremental attention on account of the
6
−8
31,32
particular traits. To date, most available POMs are based on
excellent luminescence properties of Ln cations.
Com-
IV
IV
conventional tetrahedral heteroatoms such as Si , P , and
pared with TM ions, Ln ions have abundant coordination
modes and intense oxophilicity, making it easy for them to
IV 9−11
Ge .
However, with the deepening and expanding study
on POMs, the pyramidal heteroatoms containing lone-pair
capture lacunary POM fragments to expand structural
III
III
III
IV
IV
33−37
electrons (e.g., As , Sb , Bi , Se , and Te ) have aroused
diversity.
In the last 5 years, research has been focused
1
2−14
38−46
increasing concern.
In contrast to the tetrahedral
on Ln-substituted SeTs (LnSSeTs).
The first LnSSeTs are
heteroatoms, the most distinct advantage of heteroatoms
containing lone-pair electrons is that the steric effect caused by
lone-pair electrons could prevent the formation of saturated
Keggin POMs, and it is also means that lacunary POM
fragments could be directly generated without presynthesized
the octameric nanoclusters reported by Su’s group, which
could be self-assembled to hollow spheres in dilute solution,
and the electrochemical and magnetic properties of these
38
LnSSeTs were investigated. We have devoted ourselves to
synthesizing LnSeSTs and achieved some prominent re-
42−46
1
5
sults.
Typically, trimeric and hexameric LnSSeTs have
precursors. The vacant POM fragments could self-assemble
into high-nuclearity clusters or coordinate with other
transition-metal (TM) or lanthanide (Ln) ions to derive
Received: August 4, 2020
1
6
various POMs. In addition, a growing amount of research has
2
−
III
III
III
IV
confirmed that pyramidal XO3 (X = As , Sb , Bi , Se ,
IV
Te , etc.) could be used as a linker to bridge POM fragments
and/or other metal centers, thus manufacturing a variety of
1
7−19
structures.
©
XXXX American Chemical Society
https://dx.doi.org/10.1021/acs.inorgchem.0c02318
A
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been isolated in the presence of different organocations. Their
catalytic performances were also investigated, and the results
showed that they can triumphantly catalyze the oxidation of
the linear range of 4−100 μM for DPA and 8−600 μM for
PCM.
44
RESULTS AND DISCUSSION
aromatic sulfides by H O . Last year, we published the penta-
2
2
■
Ln-cluster including Dawson-type SeTs, which were also used
Synthesis. Almost all the reported LnSSeTs were
synthesized by the one-step self-assembly method in water.
To obtain the innovative LnSSeTs including two or more
kinds of SeT building blocks, the new synthesis strategy should
be applied. Therefore, 1 was synthesized via the portfolio
approach of an in situ self-assembly reaction in mixed solvent
and step-by-step synthesis based on simple raw materials
to produce surfactant-functionalized nanosized materials, and
46
their fluorescence properties were systematically explored.
Through reviewing the related literature on LnSSeTs, we
can summarize the following features. Almost all of the
reported LnSSeTs were prepared by the one-step self-assembly
method, and in this flexible reaction environment, the template
2−
effect of SeO3 can prompt simple tungstates to directly
aggregate into SeT building blocks and then combine with Ln
cations to form fascinating and multifarious LnSSeTs. These
structures have the commonality that they all consist of one
kind of SeT building blocks and some isopolyoxotungstate
fragments. However, it is rare to find LnSSeTs including two
or more kinds of SeT building blocks. On one hand, under a
background of developing organic−inorganic hybrid materials,
organic-ligand-functionalized POMs are gradually flourishing.
Nearly all of the LnSSeTs are purely inorganic, while organic-
ligand-functionalized LnSSeTs are extremely rare. Thus, this
background provides a good chance to discover novel
organic−inorganic hybrid LnSSeTs containing multiple and
neoteric SeT building blocks. Obviously, the conventional one-
step self-assembly method in aqueous solution could not meet
the above demands, so the mixed solvent method comes into
sight. Acetic acid (HAc), as an organic solvent, can be miscible
with water and can improve the solubility of organic ligands in
the reaction system, which boosts the possibility of
coordination between organic ligands and POM segments.
Moreover, HAc could adjust the pH value of the whole
reaction system as an appropriate acidity regulator. More
importantly, HAc has a carboxyl group and has a great
coordination ability with various metals. On the other hand,
the portfolio approach of the in situ self-assembly reaction in
mixed solvent and step-by-step synthesis is introduced into the
reaction system. In the HAc−NaAc buffer solution, tungstate
reacts with selenite to in situ generate SeT building blocks.
The glacial acetic acid is used to dissolve Ln salts and organic
components. Finally, two solutions are mixed to prepare our
desired organic−inorganic hybrid LnSSeTs under heating. On
the basis of these thoughts, we obtained an organic−inorganic
Na WO ·2H O, Na SeO , Ce(NO ) ·6H O, and 3-pyridinyl-
2 4 2 2 3 3 3 2
boronic acid (Figure 1). First, some documents prove that
Figure 1. Schematic synthesis route for 1.
various SeT building blocks could be straightforwardly formed
in the pH range of 3.0−5.0, so in the synthesis process, the 0.2
M NaAc−HAc buffer solution provided an acidic context (pH
4
.5) for Na WO ·2H O and Na SeO , which would facilitate
2 4 2 2 3
to the in situ formation of SeT building blocks. Second, HAc
not only works as the acidity regulator of the whole reaction
process, but also functions as the solvent for 3-pyridinylboronic
acid. 3-Pyridinylboronic acid should be first dissolved in glacial
acetic acid together with Ce(NO ) ·6H O, followed by being
3
3
2
poured into the A reaction system. If 3-pyridinylboronic acid
was directly added to the A reaction system, then the reaction
solution became turbid and could become clear again.
III
hybrid Ce -encapsulated SeT Na H {[Ce W O (H O) -
16
6
3
4
10
2
9
(
1
CH COO) ] (Se W O )(B-α-SeW O ) }·(C H NBO )·
3 3 2 2 7 30 9 33 4 5 8 3
19H O (1). Noticeably, the fascinating [Se W O ]
2 2 7 30
Similarly, if Ce(NO ) ·6H O was directly added to the A
1
0−
3 3
2
solution, then the solution rapidly became turbid because of
VI
building block is sparsely encountered, in which seven W
3+
the hydrolyzation of Ce cations. Hence, Ce(NO ) ·6H O
3
3
2
atoms form a dumbbell-shaped W7 plane. Evidently, the
was dissolved in glacial acetic acid, which also increased the
chance of coordination between Ce cations and acetate.
structure of 1 comprises three kinds of POM building blocks,
3+
1
3+
10−
namely, [Ce W O ] , [Se W O ] , and [B-α-
3
4
10
2
7
30
Third, the A and B solutions were mingled, and in this step,
8−
SeW O ] , which to some degree indicates that the portfolio
3+
9
33
Ce cations bridged the in-situ-generated SeT building blocks
III
approach of the in situ self-assembly reaction in mixed solvent
and step-by-step synthesis has a great potential in constructing
complicated and multicomponent poly(POM) aggregates
containing two or more types of POM building blocks. In
addition, 1 was loaded on CFMCN to produce the 1@
CFMCN composite, which can be utilized as a 1@CFMCN/
GCE electrochemical sensor (ECS) to detect dopamine
to build organic−inorganic hybrid Ce -encapsulated SeT 1.
Additionally, 3-pyridinylboronic acids work as fillers in the
space packing of polyoxoanions (POAs) of 1 to reduce steric
hindrance. The final pH of the reaction was also very critical in
the production of 1. Experimental results showed that 3.90 was
the best pH for crystal growth when a few drops of HAc were
replenished in the mixed reaction system. In addition, when
3
+
(
DPA) and paracetamol (PCM). The results illustrate that
other Ln cations were used to replace Ce cations, no similar
species have been formed to date, which may be related to the
this ECS exhibits outstanding detection performance toward
DPA, PCM, and both of them simultaneously with low limits
of detection of 0.053 μM for DPA and 2.03 μM for PCM in
3
+
certain particularity of Ce cations in this reaction system, and
38,47,48
this phenomenon has also appeared in the literature.
B
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8
−
Figure 2. (a) POA of 1. (b) Combination of the {Ce Se W } heterometal cluster and four trilacunary [B-α-SeW O ] segments in 1. (c) View of
6
2
15
9
33
8
−
4−
the [B-α-SeW O ] segment. (d) View of the hypothetical plenary Keggin-type [SeW O ] POA. (e) Connection mode between two {Ce W }
9
33
12 40
3
4
subunits and a {Se W } subunit in the {Ce Se W } heterometal cluster. (f) View of the {Ce W } subunit. (g) View of the {Se W } subunit. (h)
2
7
6
2
15
3
4
2
7
Connection mode in the {Ce W } subunit. (i) Connection mode between two Se ions and the W7 plane in the {Se W } subunit. (j) View of the
3
4
2
7
{
Ce Se W } heterometal cluster. (k) View of the POA skeleton for 1 viewed along the a axis. W, bright green; C, black; N, blue; O, red; Ce,
6 2 15
turquoise; Se, lavender; {WO }, red and yellow.
6
8
−
Structural Discussion. The pure phase of 1 has been
identified by powder X-ray diffraction (Figure S1). It
one [B-α-SeW O ] segment by two O atoms [Ce−O:
9
33
2.461(13)−2.617(10) Å] as well as three water molecules
[Ce−O: 2.504(11)−2.621(12) Å] (Figure S3a−c). Surpris-
ingly, in the specific {Se W } building block, the central W
̅
crystallizes in monoclinic space group P1 (Table S1). The
molecular unit of 1 is composed of 1 tetrameric
2
7
{
[(Ce W O )(H O) (CH COO) ] (Se W O )(B-α-
atom and two triangular triads formed by three edge-sharing
3
4
10
2
9
3
3
2
2
7
30
2
2−
SeW O ) }
POA (Figure 2a), 1 C H NBO zwitterion
{WO } octahedra are aligned in the dumbbell-shaped motif
9
33 4
5
8
3
6
+
(Figure S2), 16 Na cations, and 119 lattice water molecules. It
and the seven W atoms are approximately situated in the same
plane (W plane) (Figure 2i). Opposite faces of the W plane
should be pointed out that the POA of 1 is composed of a Ce−
7
7
IV
W−Se heterometal cluster {[(Ce W O )(H O) -
are capped by two Se atoms in the asymmetical motif (Figure
2i), and the distance between the Se atom and the W plane
3
4
10
2
9
1
0+
IV
(
CH COO) ] (Se W O )} ({Ce Se W }) surrounded by
3
3 2
2
7
30
6
2
15
7
8−
four trilacunary [B-α-SeW O ] segments (Figure 2b). The
trilacunary [B-α-SeW O ] segment (Figure 2c) can be seen
is 3.011 Å. Therefore, two {Ce W } subunits are located on
9
33
3
4
8
−
3+
the two faces of the central {Se W } unit by linking Ce ions
9
33
2 7
as the remainder of the hypothetical plenary Keggin-type
and the {Se W } group to form the heterometal {Ce Se W }
2 7 6 2 15
4−
[
{
(
(
1
SeW O ] (Figure 2d) by removal of an edge-sharing
cluster core (Figure 2j). In this direction, there are five planes:
1
2
40
3
+
W O } triad. The special {Ce Se W } heterometal cluster
one W plane is in the center, two planes arranged by six Ce
3
13
6
2
15
7
F i g u r e 2 e ) c o n s i s t s o f
2
[ ( C e W O ) -
cations are in the mezzanine, and two planes defined by eight
W atoms are on the surface (Figure 2k). These planes are
substantially parallel, and the heterometal {Ce Se W } cluster
3
4
1 0
10+
H O) (CH COO) ] ({Ce W }) subunits (Figure 2f) and
2
9
3
3
3
4
1
0−
[Se W O ] ({Se W }) subunit (Figure 2g) through 10
2
7
30
2
7
6
2
15
3+
3+
oxygen atoms. In the {Ce W } subunit, Ce2 and Ce3 ions
core is centered on the W7 plane to make up a misaligned
sandwich formation. Overall, the POA of 1 is fabricated from
three kinds of building blocks, namely, four trilacunary Kiggin-
3
4
connect two {W O } fragments and the Ce1 ion chelated by
2
11
one acetate group is suspended on one {W O } cluster
2
11
8−
through linking W1 and W3 together (Figure 2h). Also, two W
type [B-α-SeW O ] fragments, two acetate-coordinated
9 33
centers in each {W O } cluster are bridged by one acetate
heterometallic {Ce W } units, and an extraordinary {Se W }
2
11
3
4
2
7
3+
group. Three crystallographically independent Ce cations
segment.
In POM chemistry, {X W } (n = 0, 1, 2) building blocks are
3
+
3+
3+
(
Ce1 , Ce2 , and Ce3 ) in {Ce W } all employ severely
3 4
n
7
contorted monocapped square antiprism geometry (Figure
uncommon compared with saturated Keggin {XW },
monovacant {XW }, divacant {XW }, and trivacant {XW }
11 10 9
12
3
+
S3a−c). The Ce1 cation binds to the {Se W } unit by two O
2
7
atoms (O64, O53) and to one {W O } group by two O atoms
segments. For example, the pentavacant Keggin [B-α-
2
11
1
0−
(
O26, O59) [Ce−O: 2.436(11)−2.628(10) Å], together with
TeW O ]
segment in [Ln (OH)(B-α-TeW O )-
7
28
2 7 28
1
4−
one acetate group [Ce−O: 2.548(13)−2.559(13) Å] and three
Sn (CH ) (W O )]
is derived from the classical trivacant
fragments by eliding an edge-sharing
2
3 4
5
18
2
3
+
8−
water molecules [Ce−O: 2.509(14)−2.556(11) Å]. Ce2 and
[B-α-TeW O ]
9 33
3
+
49
10−
III
Ce3 cations link two {W O } clusters by four O atoms and
{W O } subunit (Figure 3a). The [XW O ] (X = As ,
2 10 7 28
2
11
C
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Figure 3. (a) Pentavacant Keggin [B-α-TeW O ] segment in [Ln (OH)(B-α-TeW O )Sn (CH ) (W O )] . (b) [XW O ] (X = AsIII,
1
0−
14−
10−
7
28
2
7
28
6−
2
3
4
5
18
2
7
28
III
6−
III
III
P ) segment in [HXW O Ru(dmso) ] (X = As , P ). (c) Paratungstate [W O ] segment in {Cu(cyclam)} (W O ). (d) V-shaped
7
28
3
7
24
3
7
24
10−
16−
24−
(
W O ) unit in [Co (H O) (OH) P W O ] . (e) Planar {W } unit in [H W Se O148] . (f) {Se W } building block in 1.
7 26 7 2 2 2 2 25 94 7 2 43 3 2 7
III
6−
P ) segment in [HXW O Ru(dmso) ] is different from [B-
of inspiration to expore and fabricate novel carboxylated
POMs by selecting appropriate organic carboxylic acid ligands.
In addition, it is fascinating that C H NBO zwitterions exist
7
28
3
1
0−
α-TeW O ] , which is considered to be a fusion of a
W O } triad and an edge-sharing half-round {W O } quad
7
28
{
3 13 4 18
5
8
3
through a corner-sharing motif together with a {XO } linker
around the POAs of 1, which are formed by 3-pyridinylboronic
3
5
0
6−
53
(
Figure 3b). The V-shaped heptatungstate [W O ]
segment in {Cu(cyclam)} (W O ) can be seen as a central
acid combining a hydroxy group from aqueous solution.
7
24
+
Besides, Na as a counter cation for charge balance and lattice
3
7
24
{
WO } octahedron connecting a cricoid hexamer around it by
water molecules are necessary and could interact with POAs of
1 to generate the 3D supramolecular structure. If each POA of
1 is simplified as a parallelogram using Se2, Se3, Se2A, and
Se3A (Figure S5a), then spatial packing architectures for POAs
of 1 could be more easily understood. Packing structures for
POAs of 1 along the a, b, and c axes all manifest the −AAA−
arrangement (Figure S5b−d), and their corresponding
simplified packing architectures are shown in Figure S5e−g.
If C H NBO zwitterions are added to the 3D packing
6
51
the edge-sharing mode (Figure 3c). In addition, there were
two {W } building blocks similar to that observed in 1. One is
7
1
0 −
t h e V - s h a p e d [ W O
]
s e g m e n t i n
that can be looked on as a
derivative of a hexavacant α-Keggin {W O } unit capped by a
7
2 6
6−
1
[Co (H O) (OH) P W O ]
7 2 2 2 2 25 94
6
22
{
WO } group in the central cavity between two {W O } triads
6
3
1
3
by an edge-sharing mode (Figure 3d, Figure S4a) in which the
hexavacant α-Keggin {W O } unit can be seen as a product of
6
22
5
8
3
the trivacant B-α-Keggin {W O } fragment by elimating one
structure of 1, then it is clear that C H NBO zwitterions exist
in intervals between the POAs of 1 (Figure S6).
9
33
5 8 3
5
2
10−
{
W O } triad. In the V-shaped [W O ]
segment, the
3
13
7
26
two {W O } triads are respectively seated at two planes with a
Electrochemical Properties. Electrochemical sensing
investigations on small biomolecules and drug molecules
have brought about heightened concern owing to the quick
response, low toxicity, broad linearity, and high sensitivity and
3
13
dihedral angle of 79.52° (Figure S4a). The other is the planar
24−
{
W } unit in [H W Se O148] that is composed of a central
7 2 43 3
pentagonal {WO } subunit and two vertex-sharing {W O }
7
3
21
5
4,55
groups linked together in the edge-sharing style (Figure 3e,
selectivity.
Among them, electrode materials play a
2
2
Figure S4b). In this planar {W } unit, the angle of two
considerable role in signal enhancement. Carbon nanomateri-
als can be considered to be a class of excellent electrode
materials due to their high electrical conductivity and stability,
7
terminal W atoms and the central W atom is 142.41° (Figure
S4b). In this article, seven W atoms in the special {Se W }
2
7
5
6,57
building block form one dumbbell-shaped plane, and the
terminal and central W atoms were located in a straight line
nanosize, and biocompatibility,
but in practice, the
shortcomings of carbon nanomaterials should not be ignored,
such as easy agglomeration and a weak response to target
(
Figure 3e, Figure S4b). So this dumbbell-shaped W plane is
7
58
significantly different from other {W } building blocks.
objects. In fact, POMs can donate and accept electrons
without structural variation, and this reversible charge-transfer
ability enables them to serve as candidates for electron
7
It is noticeable that in this work acetate groups as organic
constituents modify the POA structure of 1. Among them,
3
+
59
acetate groups can be coordinated with not only the Ce1
cation, but also two W centers in each {W O } unit because of
exchange reactions. Many POMs could not be used directly
as electrode materials for detection in aqueous solution due to
their solubility. Therefore, the effective way to produce
electrode materials is to load POMs on the carbon nanoma-
terials. On one hand, the responses of POM-loaded carbon-
nanomaterial-modified electrodes to the testing samples can be
significantly improved. On the other hand, POM-loaded
carbon nanomaterials could be dispersed in aqueous solution
2
11
39,40
the appropriate location and steric hindrance.
Above all,
two acetate groups as linkers combine two adjoining W atoms.
Such a phenomenon in which an acetate group directly bridges
two W centers is unusual in POM chemistry, which provides a
great likelihood of constructing carboxyl bridging polyoxo-
tungstates and gives us extreme enlightenment and a high level
D
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to get a homogeneous, stable suspension. Thus, along with
these ideas, we utilize the as-synthesized 1-loaded CFMCN as
the electrode material for fabricating 1@CFMCN/GCE ECS.
The SEM image of 1@CFMCN and energy-dispersive
spectroscopy (EDS) patterns of CFMCN and 1@CFMCN
have been obtained. The appearance of W and Ce elements in
the 1@CFMCN material confirms that 1 has been loaded onto
CFMCN (Figure S7).
ECS was prepared to test electrical signals in 50 mL of 0.1 M
NaH PO −Na HPO solution with/without DPA (c = 500
2
4
2
4
μM) and/or PCM (c = 500 μM). A pair of redox peaks at E
1
/2
= 0.391 V ascribed to DPA in the presence of DPA (Figure
S8a) and a pair of redox peaks at E1/2 = 0.585 V ascribed to
PCM in the presence of PCM (Figure S8b) are visible. In the
NaH PO −Na HPO solution containing both DPA and
2
4
2
4
PCM, two redox peak signals could be explicitly seen and
completely distinguished (Figure 4b, Figure S8c), which
indicates that the 1@CFMCN/GCE ECS could be used to
simultaneously detect DPA and PCM. In order to validate the
high activity of the 1@CFMCN material in the detection of
DPA and PCM, the differential pulse voltammetry (DPV)
method was also utilized to evaluate CFMCN/GCE and 1@
CFMCN/GCE to compare their signal response strengths for
detecting DPA or/and PCM. The DPV peak currents of
individual DPA or PCM increase in turn in the order of bare
GCE, CFMCN/GCE, and 1@CFMCN/GCE (Figure S9a,b).
In NaH PO −Na HPO buffer solution with DPA (c = 500
As is known, DPA, as the most plentiful form of
catecholamine neurotransmitters in the human brain, is vital
60,61
for regulating and controlling the central nervous system.
The abnormal synthesis, parasecretion, and dysfunction of
DPA are associated with Parkinson’s disease, depression,
62,63
Huntingdon’s disease, and drug dependence.
PCM, also
known as acetaminophen, is a common analgesic and febrifuge
drug that could be used in place of aspirin when patients are
allergic to and intolerant of aspirin. However, a PCM overdose
would influence the sympathetic nervous system and cause life-
threatening liver damage. Therefore, the detection of DPA and
PCM is crucial to the diagnosis and treatment of related
diseases. Meanwhile, in in vivo studies, the long-term ingestion
of PCM probably affects the level of DPA, so the simultaneous
detection of DPA and PCM is conducive to understanding the
clinical significance and determining the pharmaceutical
2
4
2
4
μM) and PCM (c = 500 μM), this phenomenon still exists,
which testifies to the good electrochemical activity of 1@
CFMCN/GCE (Figure 4c, Figure S9c). Also, the separation of
peak potentials between DPA and PCM (ΔE) for CFMCN/
GCE ECS (0.190 V) and 1@CFMCN/GCE ECS (0.181 V) is
much larger than that for the bare GCE (0.169 V),
demonstrating that 1@CFMCN/GCE ECS is a promising
candidate for the electrochemical detection of DPA and PCM
(Figure 4c).
6
4,65
dosage.
@CFMCN/GCE ECS for DPA and PCM detection were
In this article, the electrochemical responses of
1
systematically investigated. In this process, DPA and PCM
could be easily electro-oxidized into their corresponding oxides
as follows (Scheme 1) so that they can be detected
According to the literature, the utility of an electrode
materals is primarily in selecting the appropriate pH value of
the solution, so the influence of pH on 1@CFMCN/GCE ECS
6
4
successfully.
was investigated in 0.10 M NaH PO −Na HPO solution with
Scheme 1. Electrochemical Oxidation and Reduction
Processes of DPA and PCM
2
4
2
4
DPA and PCM (Figure S10). As shown in Figure S10a,b, the
reduction and oxidation peak potentials have blue shifts with
the decrease in the pH value. Within the whole scope of pH
values, the current signals of DPA and PCM could be
accurately distinguished, so the current peak values can be used
as the selection criteria for searching the optimum pH value.
When the pH value is increased from 1.0 to 6.0 (Figure 4d),
the oxidation peak current of DPA gradually declines and rises
a little at pH 7.0, and then it continues to decline in an alkaline
environment. The oxidation peak current of PCM increases at
first and then decreases with an increase in the pH value. After
a comprehensive consideration, the optimum pH scope is 3.0−
4.0. Nevertheless, it is necessary to investigate the structural
stability of the POA skeleton of 1 in this pH scope. Therefore,
the stability of the POA skeleton of 1 was probed by UV−vis
spectra, and the results reveal that the POA skeleton of 1 is
stable in the pH range of 3.0−8.0 (Figure S11). Considering
the above-mentioned analysis, the optimum pH value is 3.0,
and the following measurements were all obtained in pH 3.0
NaH PO −Na HPO solution. Under this condition, the
The electrochemical activities of the bare GCE and modified
GCEs were examined via cyclic voltammetry (CV). Figure 4a
depicts the CV curves of bare GCE, CFMCN/GCE, and 1@
4
−
3−
CFMCN/GCE in a 5.00 mM [Fe(CN) ] /[Fe(CN) ]
6
6
solution. The CV curve of the bare GCE displays a peak
separation (ΔE ) of 0.093 V, indicating the good reversibility
P
of the bare GCE. Moreover, modified CFMCN/GCE and 1@
CFMCN/GCE also have good reversibility. It can also be
observed that the anode peak current rises from 0.118 to 0.164
mA after CFMCN is used to cover the bare GCE surface. After
the GCE surface is coated with 1@CFMCN, the peak current
2
4
2
4
electrochemical stability of the 1@CFMCN/GCE ECS was
surveyed via CV for 100 cycles (Figure 4e, Figure S12). It is
obvious that almost all of the CV curves overlap with each
other and the slight damping of DPA and PCM peak currents
can be ignored. It can be concluded that the 1@CFMCN/
GCE ECS possesses high stability, which can completely meet
the experimental requirement.
The influence of the scan rate on the redox peak currents of
DPA and PCM for the 1@CFMCN/GCE ECS was also
examined (Figure 4f, Figure S13). On one hand, when the scan
rate increases from 20 to 180 mV/s, the cathodic peak
increases to 0.180 mA. Meanwhile, the ΔE values of these
P
electrodes are almost invariant. Overall, it is illustrated that the
1
@CFMCN material promotes electron transport from
4
−
3−
[Fe(CN) ] /[Fe(CN) ] to the electrode surface. The
6 6
results described above also demonstrate that 1, after being
loaded onto CFMCN, could promote electron transport and
improve the electrochemical responses. This role of POMs as
66−68
electrode materials was also proven previously.
To determine whether the 1@CFMCN electrode material
can be utilized to detect DPA and PCM, 1@CFMCN/GCE
E
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4
−
3−
Figure 4. (a) CV curves of bare/GCE, CFMCN/GCE, and 1@CFMCN/GCE in 5 mM [Fe(CN) ] /[Fe(CN) ] solution at a scan rate of 100
6
6
mV/s. (b) Comparison of the CVs of 1@CFMCN/GCE in 0.10 M NaH PO −Na HPO solution (pH 3.00) with both DPA (500 μM) and PCM
2
4
2
4
(
500 μM) and without DPA and PCM. (c) DPV curves of bare/GCE, CFMCN/GCE, and 1@CFMCN/GCE in a 0.10 M NaH PO −Na HPO
2
4
2
4
solution (pH 3.00) with 500 μM DPA and 500 μM PCM. (d) Anodic peak currents from CVs on 1@CFMCN/GCE in different pH values of 0.10
M NaH PO −Na HPO solution with 500 μM DPA and 500 μM PCM (scan rate: 100 mV/s). (e) Anodic peak currents of CVs on 1@CFMCN/
2
4
2
4
GCE ECS from the 1st to the 100th cycle in 0.10 M NaH PO −Na HPO solution with 500 μM DA and 500 μM PA (scan rate: 100 mV/s). (f)
2
4
2
4
CVs of 1@CFMCN/GCE at different scan rates (from 20 to 180 mV/s) in 0.10 M NaH PO −Na HPO solution (pH 3.00) with 500 μM DPA
2
4
2
4
and 500 μM PCM.
Figure 5. Variations of the DPV peak current intensity for 1@CFMCN/GCE ECS in 0.1 M NaH PO −Na HPO solution (pH 3.0) containing
2
4
2
4
different concentrations of (a) DPA (from 1 to 200 μM), (c) PCM (from 2 to 1000 μM), and (e) both DPA (from 1 to 800 μM) and PCM (from
to 1000 μM). The relations of the DPV peak current for the 1@CFMCN/GCE ECS versus the logarithm of different concentrations of (b) DPA
4−100 μM), (d) PCM (8−600 μM), and (f) both DPA (4−100 μM) and PCM (8−600 μM).
2
(
potentials move slightly in the negative direction while the
anodic peak potentials move slightly in the positive direction,
and this phenomenon states a reversible but nonideal redox
process. On the other hand, the oxidation and reduction peak
currents of DPA and PCM simultaneously increase with
increases in the scan rate, and the good linear relationship
between the peak currents and the scan rate implies that the
electrochemical redox processes of DPA and PCM for the 1@
62,69
CFMCN/GCE ECS are surface-controlled.
Compared with the CV method, DPV is often considered to
be a more sensitive method for detecting small molecules
because intensive signals could be gained by banishing the
F
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Inorganic Chemistry
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Article
6
4
non-Faradaic currents that exist in the CV method. Hence,
DPV was also chosen to explore the relationship between the
concentration of DPA and PCM and the peak current (Figure
CONCLUSIONS
■
An organic−inorganic cerium-encapsulated SeT hybrid 1
comprising three POM subunits was acquired in the acetic
acid and aqueous mixed solution. Its POA is made up of Ce−
W−Se heterometal cluster {Ce Se W } connecting four
5
). In the individual dectction of DPA and PCM, the DPV
peak potentials of DPA or PCM for the 1@CFMCN/GCE
ECS in 0.1 M NaH PO −Na HPO (pH 3.0) solution appear
6
2
15
8−
2
4
2
4
trilacunary [B-α-SeW O ] segments. The rare {Se W }
9
33
2
7
at 0.380 and 0.560 V, respectively. As presented in Figure 5a,
when the DPA concentration changes from 1 to 200 μM, the
DPV peak current intensity increases gradually. The linear
relationship between the peak current and the logarithm of the
DPA concentration (4−100 μM) can be fitted by the
subunit was observed, in which the central W atom together
with two triangular triads formed by three edge-sharing {WO
octahedra are aligned in the dumbbell-shaped motif, and two
}
6
IV
Se atoms cap two sides of the W plane in the asymmetrical
7
mode. Moreover, the 1@CFMCN composite was manufac-
tured by simply using ultrasound on 1 and CFMCN, which
was used as the electrode material for constructing the 1@
CFMCN/GCE ECS. The experiments have proven that this
ECS exhibits an enhanced current response for DPA and PCM.
In the simultaneous detection of DPA and PCM, the broad
linear range of concentration of 4−100 μM had an LOD of
regression equation of I
(mA) = 0.112 × log c (μM) +
DPA
2
0
.054 (R = 0.995) (Figure 5b). The limit of detection (LOD)
is 0.038 μM, which is acquired from 3s (s: standard deviation)
divided by the slope of the linear part (k). The s value is
calculated from three blank current measurements without
DPA. In the same way, the variation of the DPV peak current
intensity with the PCM concentration (2−1000 μM) was also
recorded, and a similar tendency can be observed in which the
PCM peak current increases with the enhancement of
concentration (Figure 5c). The calibration plot shows a linear
relationship between the DPV peak current and the
concentration of PCM ranging from 8 to 600 μM (Figure
0
6
.053 μM for DPA and a linear range of concentration of 8−
00 μM with an LOD of 2.03 μM for PCM. In conclusion, this
work not only enriches the structural types of organic−
inorganic hybrid SeTs with several kinds of POM building
blocks and also provides an inspiration to construct
complicated Ln-incorporated POMs by innovative synthesis
methods but also can exploit and expand electrochemical
biosensing applications of POM-based composite materials.
5
d). The linear regression equation is IPCM (mA) = 0.069 × log
2
c (μM) + 0.067 (R = 0.995), and the LOD is 1.74 μM. The
results above demonstrate that the 1@CFMCN/GCE ECS
could potentially be applied as a promising sensor to detect
DPA or PCM and further provides a possibility that DPA and
PCM could be simultaneously detected in their mixed solution.
The peak current changes in DPA and PCM with
simultaneously increasing concentrations of two analytes
were studied (Figure 5e). It is clear that two separated
oxidation signals arise with the concentrations increasing from
ASSOCIATED CONTENT
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c02318.
■
*
Crystal data, experiments, PXRD, TG, IR, CV, and DPV
relevant figures (PDF)
Accession Codes
CCDC 2021004 contains the supplementary crystallographic
data for this article. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
to 800 μM for DPA and 2 to 1000 μM for PCM. The peak
currents exhibit the linear correlation to the concentration in
the range of 4−100 μM for DPA and 8−600 μM for PCM, and
their corresponding regression equations are I
(mA) =
(mA) =
DPA
2
0
.080 × log c (μM) + 0.066 (R = 0.997) and I
PCM
2
0
.059 × log c (μM) + 0.064 (R = 0.982) with LODs of 0.053
and 2.03 μM for DPA and PCM (Figure 5f). Besides the
detecting scope and the LOD, the oxidation potentials and
peak currents of DPA and PCM in the simultaneous detection
are similar to those in the individual detection, which provides
evidence that the coexistence of DPA and PCM does not
influence the sensing performance. Therefore, the 1@
CFMCN/GCE ECS could be effectively utilized as an ECS
to simultaneously detect DPA and PCM.
AUTHOR INFORMATION
Corresponding Authors
■
Lijuan Chen − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic of
China; orcid.org/0000-0001-5894-2082; Email: ljchen@
henu.edu.cn
Junwei Zhao − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic of
China; orcid.org/0000-0002-7685-1309;
Additionally, the time-dependent stability and the reprodu-
cibility of the 1@CFMCN/GCE ECS were also examined by
means of DPV tests in 0.1 M NaH PO −Na HPO (pH 3.0)
2
4
2
4
Email: zhaojunwei@henu.edu.cn
containing 50 μM DPA and 50 μM PCM (Figures S14 and
S15). As illustrated in Figure S14, the DPV peak currents are
barely changed for 7 days, which reveal that the 1@CFMCN/
GCE ECS has good stability in detect DPA and PCM. In order
to investigate the reproducibility, five independent 1@
CFMCN/GCE ECSs were fabricated to test the concentration
of DPA and PCM (Figure S15). The DPV peak currents for
these five tests are very close, and the relative standard
deviations of DPA and PCM are 2.92 and 1.21%, which exhibit
acceptable reproducibility of the 1@CFMCN/GCE ECS.
Authors
Jun Jiang − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic
of China
Lulu Liu − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic
of China
G
https://dx.doi.org/10.1021/acs.inorgchem.0c02318
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Article
Guoping Liu − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic
of China
Dan Wang − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic
of China
Yan Zhang − Henan Key Laboratory of Polyoxometalate
Chemistry, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng, Henan 475004, People’s Republic
of China
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Notes
The authors declare no competing financial interest.
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3
ACKNOWLEDGMENTS
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Technology in Universities of Henan Province
20IRTSTHN004), and the First-Class Discipline Cultivation
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