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Colloids and Surfaces A: Physicochem. Eng. Aspects 409 (2012) 98–104
Contents lists available at SciVerse ScienceDirect
Colloids and Surfaces A: Physicochemical and
Engineering Aspects
journal homepage: www.elsevier.com/locate/colsurfa
Construction and transformation of stimuli-responsive vesicles from the
ferrocene derivative supramolecular amphiphiles
Qiuhong Li a,b , Xiao Chen a,∗ , Xiu Yue a , Dandan Huang a , Xudong Wang a
a
b
Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100, China
School of Material Science and Engineering, Shandong University of Technology, Zibo 255049, China
h i g h l i g h t s
g r a p h i c a l
a b s t r a c t
The tough stimuli-responsive vesicles were prepared via electrochemical oxidation.
The vesicles obtained by electrooxidation possess redox responsive
properties.
The stimuli-responsive vesicles can
be formed from the ␤-CD inclusion
complex.
The vesicles formed from the complex can be transformed into nanotubes with time.
a r t i c l e
i n f o
Article history:
Received 15 February 2012
Received in revised form 22 May 2012
Accepted 28 May 2012
Available online 17 June 2012
Keywords:
Ferrocene
Electrochemical oxidation
Vesicles
Cyclodextrins
Stimuli-responsive
a b s t r a c t
The tough stimuli-responsive vesicles were prepared via electrochemical oxidation on the mixture
solution of ferrocenylmethyl-trimethylammonium iodide (FcMI) and sodium deoxycholate (NaDC). The
vesicle structure and morphology are characterized respectively by transmission electron microscopy
(TEM), dynamic light scattering (DLS) and atomic force microscopy (AFM). The vesicle shells can be clearly
observed by TEM with the thickness ranging from several to several tens of nanometers and their outer
diameters at the range of 50–200 nm. The formation of vesicular structures is also supported via AFM
measurements. Such tough vesicles made up of ferrocene and deoxycholate blocks are redox-responsive,
and their assembly or disassembly behaviors may be controlled by electrochemical methods through
the change of ferrocene states between the neutral hydrophobic and the hydrophilic ferrocenium cation.
In addition, the stimuli-responsive vesicles can also be formed from the supramolecular inclusion complex between the ferrocene blocks and the ␤-cyclodextrin hosts, which can then be transformed into
nanotubes with time. The obtained results are significant for the preparation of smart supramolecular
aggregates.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Self-assembly and structural transformation of molecules with
stimuli-responsive properties are crucial subjects for the achievement of functional supramolecules at the molecular level [1–4].
As a type of intelligent assembly, they can undergo physical or
∗ Corresponding author. Tel.: +86 531 88365420; fax: +86 531 88564464.
E-mail address: [email protected] (X. Chen).
0927-7757/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.colsurfa.2012.05.043
chemical changes and adjust their aggregated nanostructures in
response to external stimuli such as pH [5,6], electron-transfer
[7–9], light [4,10], and temperature [11,12]. By employing suitable
physical modulation, those stimuli-responsive groups may change
their polarity and hence the morphology formed by supramolecular
complexes.
Among the possible modulation methods, the redox stimulus
has recently drawn much research interests since it can effectively influence or trigger a range of physicochemical property
changes in a molecular system [13,14]. In such studied systems,
Author's personal copy
Q. Li et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 409 (2012) 98–104
103
Acknowledgements
We are thankful for the financial support from the National
Natural Science Foundation of China (20973104, 21033005) and
Shandong Provincial Science Fund (2009ZRB01147).
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.colsurfa.2012.05.043.
References
Fig. 8. Proposed mechanism on the formation of nanotubes by ␤-CD–FcM–DC in
aqueous solution. (a) Vesicles, (b) necklaces, (c) tubules, and (d) nanotubes.
larger diameter could take place by a lateral association of the
tubules. After 30 days, nanotubes with larger diameter are observed
(Fig. 7d). The dark walls of the nanotubes appear parallel along their
long axis, evidencing that they have a constant diameter along this
axis and they are apparently rigid structures.
In view of the similar formation process of tubes as reported by
Tato et al. [34], the same scheme is adopted here. Fig. 8 presents
the scheme of the observed process as reported by Tato et al. The
observed first step of the tube formation, i.e., the formation of
the necklaces from spherical vesicles, is similar to the mechanism
proposed by Lauf et al. on the formation of tubular vesicles by 1,2dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) [35]. They
have proposed that the tube formation is based on a stepwise fusion
of small vesicles, which relaxes local defects and allows ripple formation. In our studied system, the steroidal and hydroxyl groups of
NaDC molecules could associate with their neighbors, which contribute to the assembly of ␤-CD–FcM–DC. At the same time, the
presence of lateral H-bonds between CDs is possible because it was
proven by single-crystal XRD for many CD complexes [36]. Therefore, the H-bonds between ␤-CD molecules (including the direct
ones and those bridged by water) are responsible for the formation
of the tubes.
It should be noted that the change of the redox states of FcMI also
influences the stability of the inclusion complex because the oxidized form of ferrocene does not bind to ␤-CD [37]. Therefore, the
oxidation of FcMI leads to the dissociation of the inclusion complex,
which will induce the transformation of aggregates. Further efforts
are underway to find an electrochemical control of the interaction
among FcMI, NaDC, and ␤-CD.
4. Conclusions
To summarize, we have prepared the tough vesicles by electrochemically oxidizing FcMI and NaDC mixture solution. Such
vesicles are stable at the ambient environment and possess redox
responsive properties. What is more, ␤-CD could include Fc
blocks and form stable supramolecular inclusion complexes. These
pseudo-amphiphiles can also self-assemble into vesicles in the
water. With the increase of the keeping time, the vesicles will
be transformed into nanotubes. Herein, the association of their
hydrophobic steroidal backbones and the formation of hydrogen
bonding networks via their hydroxyl groups of NaDC molecules
and CDs are responsible for the formation and transformation of
the vesicles. It is anticipated that the topic of multi-stimuli responsive vesicles will be an active area of research that will result
in the development of novel systems with possible commercial
applications.
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