Dual electrical switching permeability of vesicles via redox-responsive self-assembly of amphiphilic block copolymers and polyoxometalates

Article abstract of DOI:10.1039/C8CC03749C

Electro-responsive vesicles were demonstrated based on an amphiphilic block copolymer PEO₁₁₄-b-P(DCH-Ru)_n and an inorganic nanoparticle polyoxometalate H₃PMo₁₂O₄₀ (PMo₁₂) via electrostatic

Full text of DOI:10.1039/C8CC03749C

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc
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DOI: 10.1039/C8CC03749C
Dual Electrical Switching Permeability of Vesicles via
Redox-Responsive Self-Assembly of Amphiphilic Block
Copolymers and Polyoxometalates
Dandan Chong, Junyan Tan, Jinlong Zhang, Yue Zhou, Xinhua Wan*, Jie Zhang*
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer
Chemistry and Physics of Ministry of Education, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, P. R. China.
E-mail: xhwan@pku.edu.cn；jz10@pku.edu.cn

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Dual Electrical Switching Permeability of Vesicles via Redox-
Responsive Self-Assembly of Amphiphilic Block Copolymers and
Polyoxometalates
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Eletro-responsive vesicles were demonstrated based on an simulating and understanding these life activities of cell
amphiphilic block copolymer PEO114-b-P(DCH-Ru) and an membranes under the membrane potentials.
inorganic nanoparticle polyoxometalate H PMo12 40 (PMo12) via The electro-responsive mode can simulate the opening and
n
3
O
electrostatic interactions. After undergoing electrochemical closing behavior of cell membrane channels under membrane
reactions, vesicle membranes allow the migration of electrolyte potential control, further to carry out more extensive
ions and release of loaded cargos.
biomimetic design. Compared with the traditional light and pH
stimuli, the voltage is clean and controllable, and leads to
smaller cell damage and more convenient implementation.
Albeit highly desirable, the electrically off-on switchable and
In living organisms, normal cellular activities and functions
depend on efficient and selective intra/extracellular
1
,2
1
4
communications.
Under the membrane potentials,
adjustable polymersomes have been far less explored. Yuan
permeation and fusion, assembly and disassembly,
transmembrane transport of ions and proteins are very typical
reported voltage-responsive reversible assembly and
disassembly behaviour of vesicles based on the terminal host-
guest interactions between poly(styrene)-β-cyclodextrin and
3
,4
5,6
life phenomena.
Polymer vesicles
(known as
1
5, 16
polymersomes) are good mimic of bilayer membrane owing to
their good structural stability, adjustable structural
parameters, and flexible functional integration. Their smart
poly(ethylene oxide)-ferrocene. Another vesicular system
that is switchable by electric potential was demonstrated using
redox-responsive self-assembly of an amphiphilic molecule
consisting of a tetraaniline and a poly(ethylene glycol) or
poly(N-isopropylacrylamide) block. To deeply understand and
simulate the transmembrane transport behaviour, an
alternative way that does not need to completely dissociate
the vesicles, is to simply adjust the membrane walls and
permeability of the vesicles.
7
performance in response to certain stimuli , such as chemical
redox, temperature, light, pH, electric potential, are finding
8
increasing applications in drug delivery , electrical therapy
,9
1
0,11
12,13
,
and energy storage
. In particular, development of the
electro-responsive polymer vesicles is very significant for
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J. Name., 2013, 00, 1-3 | 1
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Herein we present a new type of switchable vesicular
system with dual electro-responsive mode based on the
n
amphiphilic block copolymer PEO114-b-P(DCH-Ru) and the
inorganic Keggin polyoxometalate PMo12 via electrostatic
interaction (Figure 1). Electroactive moieties in the inner
membrane of supramolecular structure exhibit good
b-P(DCH-Ru) solution in CH CN at the charge ratio ~1:1 based
n
3
electrochemical performance. The coassemblies retain the on the electrostatic interaction between the cationic
vesicular structure before and after oxidation or reduction, but copolymers
PEO114-b-P(DCH-Ru)n and the anionic
the size and permeability change to “breath” in and out of polyoxometalates PMo . Both the dinuclear ruthenium
1
2
1
9
20,
21
22
different ions and controlled release of the loaded cargos.
The block copolymers containing dinuclear ruthenium electrochromic in the wide UV-vis-NIR region, and their
groups PEO114-b-P(DCH-Ru)n (polyethylene glycol-b- individual electrochemical activities are expected to be
compounds
and polyoxometalates
are
poly[benzoic acid N’-methylacryloylhydrazide dinuclear maintained in the thus-prepared coassemblies. The UV-vis-NIR
ruthenium complex]) were synthesized via combining spectroelectrochemistry method was used to track the
reversible addition-fragmentation (RAFT) chain transfer characteristic absorption bands of redox species at different
polymerization and subsequent ligand-exchange method. electrochemical state of these hybrid coassemblies (Figure 2).
Detailed synthetic procedures were described in Supporting In the presence of electrolytes, the original state of the
II
II
VI
VI
Information (Figure S1-S5). A series of diblock copolymer coassemblies were at the Ru /Ru and Mo /Mo state. By
precursors PEO -b-P(DCH) (m and n denote the degree of applying the +0.6 V potential, the absorption bands are
m
n
polymerization of EO and DCH, respectively) were prepared by typically at about 1600 nm assigned to the intramolecular
III
II
RAFT polymerization upon varying the feed ratio of the inter-valence charge transfer (IVCT) transitions of the Ru /Ru
1
monomer to the PEO114-DMP. H NMR measurements further species. Under the applied potential of -0.8 V, the absorption
confirm the chemical structures and compositions of PEO -b- bands are broad covering the visible and near-infrared region
m
P(DCH) (m = 114; n = 4, 10, 14). The copolymers PEO -b- of 700~1200 nm and assigned to the IVCT transitions of the
n
m
VI
P(DCH) have monodispersities of 1.2-1.3 indicated by GPC in Mo /Mo species.
V
n
DMF/0.1 M LiBr as an eluent. The corresponding complex
To identify the structures of coassemblies formed by
copolymers PEO -b-P(DCH-Ru) were synthesized through the cationic PEO114-b-P(DCH-Ru) with anionic PMo , we observed
ligand-exchange method with cis-Ru(bpy)
m
n
n
12
2 2 2
Cl ·H O (bpy = 2,2'- the samples oxidized or reduced at various voltages by using
bipyridine) according to the procedure described previously different microscopes. The statistical data were shown in Table
7,18
1
.
The complex ratio of Ru in diblock copolymers S1. For PEO114-b-P(DCH-Ru) /PMo (n = 10, 14) coassemblies,
n 12
determined by ICP analysis is about 50%. These characteristic TEM images, SEM images, and AFM images showed vesicular
data were summarized in Table S1.
The PEO114-b-P(DCH-Ru)
structures (Figure S6, Figure 3 and S7). Taking PEO114-b-P(DCH-
n
/PMo12
coassemblies were Ru) /PMo as an example, the initial average diameter of
12
1
4
prepared by the addition of PMo12 solution to a dilute PEO114
-
vesicles at 0 V state was about 103 ± 12 nm (Figure 3a). As we
2
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know, when the two partially fused vesicles diffused into and Table 1). At +0.6 V state, the coassemblies showed the
2
3
separate ones, an open-mouth-like pole and different types content of F increased by 6.58% and the content of N
of intermediates could be formed. The height ~20 nm in AFM decreased by 0.83% with Mo decreased by 0.21% compared
-
was much smaller than the horizontal size ~100 nm, further with those at the 0 V state, indicating that PF
6
came in and
+
indicating the vesicular structures. When the positive voltage Bu
0.6 V was applied, the vesicle size expanded to be 245 ± 26 system showed the content of N increased by 3.51% with Mo
nm (Figure 3b). A part of ruptured vesicles with the wall increased by 1.75% and the content of F decreased by 4.56%
4
N went out of the expansive vesicles. At -0.8 V state, the
+
+
4
thickness ~40 nm in TEM and the open-mouth vesicles in SEM compared with those at the 0 V state, indicating that Bu N
-
clearly confirmed the bilayer membrane structures. When the came in and PF
6
went out of the expansive vesicles. Both in
negative voltage -0.8 V was applied, the vesicle size increased positive and negative electrochemical stimuli, the variation
-
+
4
significantly to about 332 ± 40 nm (Figure 3c). Furthermore, trend of Mo contents indicated the PMo12 /Bu N symport and
-
the low height to diameter ratio 0.2-0.3 calculated from AFM PMo12 /PF
-
6
antiport.
indicated hollow structure of the vesicles. More TEM images of Based on the redox states in the spectroelectrochemical
the ruptured vesicles and intermediates were shown in Figure tests and the assembling structures, we proposed charge-
S8, and clearly confirmed the hollow structure of the vesicles. compensation mechanism to explain transmembrane
Besides, the elemental maps of Mo and Ru revealed that the transport process (Figure 1). In the case of vesicles, PEO acted
PMo12 and DCH-Ru moieties were dispersed on the vesicle as the stabilizing part in the core and shell of vesicles, and the
(
Figure S9). These results proved the hybrid assemblies in a skeleton membrane structures were the P(DCH-Ru)/PMo
12
II
II
bilayer pattern at the membrane interface for PEO114-b-P(DCH- part. At the original state, the coassemblies were at Ru /Ru
VI
Ru) /PMo (n = 10, 14). The amphiphilic block copolymer and Mo /Mo state and some small ions such as Bu N and
VI
+
n
12
4
-
PEO114-b-P(DCH-Ru) with shorter dinuclear ruthenium chain PF6 existed in the electrolyte solution. When the oxidation
4
II
can form spherical micelles when self-assembling with PMo12 potential +0.6 V was applied, the Ru /Ru component was
II
II
III
(Figure S10). All the hybrid coassemblies PEO114-b-P(DCH- oxidized to the mixed-valence state Ru /Ru ; and thus the
Ru) /PMo (n = 4, 10, 14) can be adjusted by corresponding internal P(DCH-Ru)/PMo12 complex became excessively
n
12
oxidation or reduction potentials. positively charged and mutually repulsed, so that the vesicle
-
To further identify the chemical composition and content expanded and the size increased to allow the negative ions PF6
variation before and after electrochemical stimulus, we into the system for charge compensation. The positive ions
+
measured the X-ray photoelectron spectroscopy (XPS) of the Bu N were excluded out from the membrane in company with
4
3
-
coassemblies. The contents of Ru, N, P, Mo, and other the counterions PMo12 . When the reduction potential -0.8 V
VI
representative elements in the coassemblies determined by was applied, the Mo /Mo component was reduced to the
VI
VI
the observed signal peaks in the full spectrum proved the mixed-valence state Mo /Mo ; the local excessive negative
V
-
structural integrity in the self-assembly structures (Figure S11 charges excluded out of other anions PF , and the vesicles
6
+
expanded with the entrance of cations Bu N for charge
4
compensation. Meanwhile, the reductive polyoxometalate
4
-/5-
nanoparticles PMo12
the overinflated
with higher charges easily entered into
vesicles. The above-mentioned
transmembrane transport process of different ions were
consistent with the XPS results. This phenomenon mimicking
the voltage-gated ion channels and selective intra/extracellular
communications in cell bilayer membranes, may help
understand these life activities of living organisms.
Table 1. Content analysis of characteristic elements in XPS full spectra of
PEO114-b-P(DCH-Ru)14/PMo12 at different state.
a
a
0
V
+0.6 V
74.06
5.43
△（%）
0.04
Ion
-0.8 V
73.96
9.77
△（%）
-0.06
Ion
C
74.02
6.26
/
/
+
+
N
-0.83
Bu
out)
4
N
3.51
Bu
4
N
(
(in)
PF
6
-
-
F
10.12
16.70
6.58
PF
6
5.56
-4.56
(in）
(out）
P
Mo
2.88
0.8
4.74
0.59
1.86
-0.21
/
2.40
2.55
-0.48
1.75
/
-
-
PMo12
PMo12
(
out)
/
(in)
/
Ru
5.92
5.92
0.00
5.92
0.00
a
The large copolymer structures constitute the stable framework of vesicles, so the
content of Ru was normalized in order to estimate the content variation of other small
ions.
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By using the feature of voltage response, these vesicles can supramolecular assembly can promote photoelectric
be used for drug loading and controlled release, as a simple properties, expanding the application in tailorable
optoelectronic materials.
This work was supported by the National Natural Science
Foundation of China (grant numbers 51673002 and 21322404).
We would like to thank Anchao Feng and Prof. Jinying Yuan at
Tsinghua University for helpful discussions in the controlled
release experiments.
Notes and references
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biomimetic model to simulate expansion movement of the
bilayer membrane of biological cells through membrane
potential to release the target molecules. In order to study the
potential application of the vesicles in controlled release
system, we used fluorescent Rhodamine B (RhB) as a model
drug molecule. The release process was carried out under
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electrolyte ions and the controlled release of loaded target
molecules. From the point view of stimulating sources, a new
dual-voltage response mode was developed to simulate and
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potentials. From the perspective of functionalities, the
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4
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