Construction of giant branched nanotubes from cyclodextrin-based supramolecular amphiphiles

Article abstract of DOI:10.1039/c5cc01414j

Giant branched nanotubes were successfully constructed using cyclodextrin-based amphiphiles. The 'backbone' of the nanotubes could branch out into two or multiple branches, from which thinner branches grow out.

Full text of DOI:10.1039/c5cc01414j

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Construction of giant branched nanotubes from
cyclodextrin-based supramolecular amphiphiles†
Cite this:DOI: 10.1039/c5cc01414j
Xiaotong Fan,a Liang Wang,b Quan Luo,b Linlu Zhao,b Jiayun Xu,b Junqiu Liu*b and
Qingchuan Zheng*a
Received 15th February 2015,
Accepted 9th March 2015
DOI: 10.1039/c5cc01414j
www.rsc.org/chemcomm
Giant branched nanotubes were successfully constructed using into two or more branches, from which thinner branches could
cyclodextrin-based amphiphiles. The ‘backbone’ of the nanotubes grow out continually.
could branch out into two or multiple branches, from which thinner
branches grow out.
b-Cyclodextrin (b-CD), a macrocyclic cavitand consisting of
seven glucopyranose units, has a hydrophobic cavity that can
serve as a perfect receptor for an adamantanol group. Since this
Molecular self-assembly, which is very common in nature, plays typical host–guest pair could form stable 1 : 1 complexes in
an important role in the formation process of many highly aqueous solution, by directly mixing the host molecule b-CD and
organized and functionalized biological macromolecules such as the guest molecule adamantanol moieties, it has been widely used
viruses and cytomembranes. Inspired by the wisdom of nature, a in the construction of supramolecular assemblies. As an example,
tremendous effort has been devoted to designing complicated Ravoo’s group prepared vesicles using amphiphilic cyclodextrins
nanostructures in the past decades. Supramolecular amphiphiles that could recognize adamantanol carboxylate via host–guest
with the advantage of easy preparation attracted considerable interaction.3 Shi et al. reported a pseudo block copolymer formed
attention. The amphiphilic supermolecules, which carry hydro- by adamantine-end poly(N-isopropylacrylamide) and b-CD-end
phobic and hydrophilic segments within one complex structure, poly(4-vinylpyridine) though b-CD–adamantane interaction.
can self-assemble into a variety of configurations. For example, Micelles formed by the pseudo block copolymer could trans-
vesicles, nanorings, nanofibers and micelles.1 The exciting form into vesicles via changing the pH.4 Nanotubes based on
morphologies mainly depend on the architecture of the molecules cyclodextrins arouse considerable attention in these years, for
and noncovalent driving forces, such as electrostatic attraction, example, Liu et al. prepared hollow tubular architectures as
hydrogen bonding, charge transfer interaction, metal–ligand nanoreactors though host–guest interaction between the host
coordination, host–guest recognition, and coiled–coil peptide molecule phthalocyanine-bridged b-cyclodextrins and the guest
interaction.2 However, it is still a great challenge to see how to molecule carboxylated porphyrin.5 Kim’s group demonstrated that
utilize the driving forces discovered to construct more sophisti- vesicles formed by dentron-like molecules could transform into
cated nanostructures.
nanotubes upon directly adding CDs into the solution of vesicles
Herein, we successfully constructed a novel kind of nano- via host–guest interaction.6 Yuan and co-workers constructed light-
structure: branched giant nanotubes. The newly developed responsive nanotubes though a-CD–trans-azobenzene interaction
structure is triggered by direct self-assembly of super- between trans-azobenzene-end poly(acrylic acid) and a-CD-end
amphiphiles formed by cyclodextrin-based host–guest chemistry. poly(caprolactone).7
The ‘backbone’ of the giant nanotube could smartly branch out
Our previous work has suggested that CD and adamantanol
hydrophobic moieties can assemble into unusual giant nano-
tubes with the large diameter of 500 nm and length of about
20 mm.8 Inspired by this work, we wondered whether the nano-
tubes can be controlled to generate branched giant nanotubes.
The idea is very challenging, because except for steric straight
organic nanotubes, fabricating more sophisticated tubular struc-
tures is very difficult and has not yet been explored. To fulfill this
purpose, a disulfides linked b-CD dimer, as one of host molecules,
was introduced to the assemblies and adamantanol-1-3,4,5-
trihydroxybenzoicamide 1 was also used as the guest molecule,
a International Joint Research Laboratory of Nano-Micro Architecture Chemistry,
State Key Laboratory of Theoretical and Computational Chemistry,
Institute of Theoretical Chemistry, Jilin University, Changchun 130012, China.
E-mail: zhengqc@jlu.edu.cn
b State Key Laboratory of Supramolecular Structure and Materials,
College of Chemistry, Jilin University, Changchun 130012, China.
E-mail: junqiuliu@jlu.edu.cn
† Electronic supplementary information (ESI) available: Synthetic procedures and
characterization of new compounds, and spectroscopic studies (UV, fluorescence,
DLS, NMR). See DOI: 10.1039/c5cc01414j
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Fig. 1 Images of self-assembled giant nanotubes. Optical microscopy images:
(a) the assemblies of 3, (b) the assemblies of 3a and (c) the assemblies
of 3b. Transmission electron microscopy images: (d) the assemblies of 3,
(e) the assemblies of 3a and (f) the assemblies of 3b. The concentration of
b-cyclodextrin units is 5 ꢀ 10ꢁ5 mol Lꢁ1
.
Scheme 1 Structures of (A) guest molecule 1, host molecule b-CD 2, and
supramolecular amphiphile 3 formed by 1 and 2 and (B) 6-thio-b-CD 2a,
disulfide linked b-CD dimer 2b and supramolecular amphiphiles 3a, 3b
and 3b0. (C) Schematic representation of the self-assembly of the branched
nanotube and proposed self-assembled branched multilayers.
Fig. 2 XRD scan of (a) the nanotubes formed by 3a and (b) the branched
nanotubes formed by 3 with 3b at a ratio of 4 : 1.
as shown in Scheme 1. We hoped that the giant nanotubes would
generate branches when the disulfides linked b-CD dimer was
introduced in the self-assembly system.
The disulfide linked b-CD dimer (CD-S-S-CD) was obtained
by adding excess H2O2 to the aqueous solution of thiolated CD
(CD–SH). CD–SH was synthesized from 6-OTs-CD and thiourea
via refluxing for 50 hours.9 Details of the reaction procedure
and characterization data are outlined in ESI.†
We firstly prepared the amphiphiles using CD–SH and
adamantanol-1-3,4,5-trihydroxybenzoicamide. As expected, after
self-assembly, we get a straight giant tubular architecture with the
length of 20–30 mm observed by optical microscope (Fig. 1b).
Transmission electron microscopy (TEM) analysis (Fig. 1e) con-
firms the nanotube structure. Similarly to the nanostructure
formed by CD and adamantanol-1-3,4,5-trihydroxybenzoicamide
(Fig. 1a), the inner and outer diameters of these nanotubes here are
large, up to 400 nm and 460 nm, respectively, and the thickness of
the wall is about 30 nm. The molecule packing mode of these tubes
was further investigated by X-ray diffraction (XRD; Fig. 2a). Based
on the calculation result from the Bragg equation, we get the bilayer
thickness of 3.8 nm. We deduce that the unusual giant nanotubes
wall is made up of about eight bilayers of the superamphiphiles.
When CD-S-S-CD acts as the host molecule, we discovered that
giant branched aggregates with lengths of up to 100 mm emerged
(see Fig. 1c), surprisingly.
the unbranched nanotubes transform into branch-like aggregates
when the b-CD : CD-S-S-CD ratio equals 4 : 1 (Fig. 3c).
The preparation of branch-like aggregates is similar to that
of straight giant nanotubes.8 Typically, the host molecules b-CD
(2, 22.7 mg) and CD-S-S-CD (2b, 46 mg), and guest molecule
adamantanol-1-3,4,5-trihydroxybenzoicamide (1, 16.16 mg) were,
respectively, dissolved in 2 mL DMF. Then, 16 mL of 2, 4 mL of
2b and 24 mL of 1 were mixed together to prepare the complex.
Then, when the DMF solution of the amphiphile was diluted by
deionized water to a final concentration of 0.01 mM under the
Fig. 3 Optical microscopy images of the branched nanotubes with
b-CD : CD-S-S-CD, as the host molecules, at a molar ratio of (a) 10 : 1,
(b) 8 : 1 and (c) 4 : 1. (d–g) The magnified structures of the branched nano-
When the disulfides linked b-CD dimer, as one of the host
molecules of the amphiphiles, participates in self-assembly, tubes. The concentration of b-cyclodextrin units is 5 ꢀ 10ꢁ5 mol Lꢁ1
.
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condition of ultrasonication at 30 1C, a novel kind of architecture
In order to exploit the effect of the disulfides linked dimer on
emerged. Giant dendritic aggregates were observed by optical self-assembly, a series of complexes with different b-CD : CD-S-S-CD
microscope with a drop of the sample solution placed on a slide ratios were prepared. We discovered that the extent of nanotube
and air-dried. The optical microscopy image in Fig. 3c reveals branching was proportional to the amount of CD-S-S-CD in the host
that a great change is made in comparison with that observed in molecule. When the b-CD : CD-S-S-CD ratio was 10 : 1 (Fig. 3a), the
Fig. 1a. We could clearly see that the branch-like architecture assemblies presented the trend to branch out, but unbranched
emerged with the large length up to 100 mm. It should be noted nanotubes still accounted for the majority of the assemblies. As the
that the novel structure presents softness and flexibility, this CD-S-S-CD component increased, there became more and more
may be attributed to the wiggle of disulfide bonds.
branched structures. At a b-CD : CD-S-S-CD ratio of 8 : 1, obvious
Scanning electron microscopy (SEM) and transmission electron branched nanotubes emerge, but most nanotubes only show the
microscopy (TEM) were utilized to explore the morphology of these first branch (Fig. 3b). When the b-CD : CD-S-S-CD ratio reached 4 : 1,
branch-like architectures and provide direct characterization of the a large area of dentritic aggregates was obtained, and the nano-
‘branched nanotube’. The image of Fig. 3c clearly reveals that tubes could grow until the second branches (Fig. 3c). We can also
the two sides of the ‘backbone’, respectively, branch out into two observe the structure with multiple branches: the two sides of the
branches (named first branch), from which thinner branches ‘backbone’, respectively, branch out into two branches from which
(named second branch) grow out. The magnified image of the thinner branches grow out. These phenomenon imply that the
branched nanotubes (Fig. 3d–g) clearly shows the details of the disulfide bond is crucial for the formation of the branched
novel assemblies, the ‘backbone’ could grow out with two or structure, the nanotube branching out branches should be
multiple branches. The SEM analysis (Fig. S2, ESI†) shows that attributed to the disulphide linked dimer.
the diameter of the backbone is large, up to more than 1 mm, but
To summarize, for the first time, we fabricated giant dendritic
the diameter after the first branch is thinner, about 1 mm and nanotubes based on the cyclodextrin-based amphiphiles. The
500 nm, respectively. Though the two branches are not the same nanotube could generate two branches, from which thinner
size, they adopt a similar way to grow out the thinner branches. branches grow out. Meanwhile, this approach of constructing
It should be pointed out that the junction is very smooth, giant dendritic nanotubes is economical, simple, and environ-
indicating that the aggregate obtained is a whole structure. mentally benign. It is anticipated that this new finding will
From the TEM image in Fig. 1f we could clearly see the obvious provide a new strategy for constructing more diverse nano-
contrast between the periphery and the central part of the structures for material application.
junction, which is typical for the biforked hollow tube structure.
This work was supported by the Natural Science Foundation
Thus, we provide solid evidence that we obtained giant branched of China (No: 21234004, 21420102007, 21221063 and 21474038),
nanotubes. It should be noted that the wall thickness of the 111 project (B06009), the Chang Jiang Scholars Program of China.
‘backbone’ or the ‘branches’ is the same size. We deduce that
they may adopt the same molecule packing mode in the wall of the
nanotubes. The inner and outer diameters of the ‘backbone’ are
large, at 450 and 550 nm, respectively. The thickness of the wall is
about 50 nm. X-ray diffraction (XRD; Fig. 2b) was employed to
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