This journal is©The Royal Society of Chemistry 2015 Chem. Commun.
Cite this:DOI: 10.1039/c5cc01414j
Construction of giant branched nanotubes from cyclodextrin-based supramolecular amphiphiles†
Xiaotong Fan,a Liang Wang,b Quan Luo,b Linlu Zhao,b Jiayun Xu,b Junqiu Liu*b and
Giant branched nanotubes were successfully constructed using cyclodextrin-based amphiphiles. The ‘backbone’ of the nanotubes could branch out into two or multiple branches, fromwhich thinner branches grow out.
Molecular self-assembly, which is very common in nature, plays an important role in the formation process of many highly organized and functionalized biological macromolecules such as viruses and cytomembranes. Inspired by the wisdom of nature, a tremendous effort has been devoted to designing complicated nanostructures in the past decades. Supramolecular amphiphiles with the advantage of easy preparation attracted considerable attention. The amphiphilic supermolecules, which carry hydrophobic and hydrophilic segments within one complex structure, can self-assemble into a variety of configurations. For example, vesicles, nanorings, nanofibers and micelles.1 The exciting morphologies mainly depend on the architecture of the molecules and noncovalent driving forces, such as electrostatic attraction, hydrogen bonding, charge transfer interaction, metal–ligand coordination, host–guest recognition, and coiled–coil peptide interaction.2 However, it is still a great challenge to see how to utilize the driving forces discovered to construct more sophisticated nanostructures.
Herein, we successfully constructed a novel kind of nanostructure: branched giant nanotubes. The newly developed structure is triggered by direct self-assembly of superamphiphiles formed by cyclodextrin-based host–guest chemistry.
The ‘backbone’ of the giant nanotube could smartly branch out into two or more branches, from which thinner branches could grow out continually. 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 typical host–guest pair could form stable 1 : 1 complexes in aqueous solution, by directly mixing the host molecule b-CD and the guest molecule adamantanol moieties, it has been widely used in the construction of supramolecular assemblies. As an example,
Ravoo’s group prepared vesicles using amphiphilic cyclodextrins that could recognize adamantanol carboxylate via host–guest interaction.3 Shi et al. reported a pseudo block copolymer formed by adamantine-end poly(N-isopropylacrylamide) and b-CD-end poly(4-vinylpyridine) though b-CD–adamantane interaction.
Micelles formed by the pseudo block copolymer could transform into vesicles via changing the pH.4 Nanotubes based on cyclodextrins arouse considerable attention in these years, for example, Liu et al. prepared hollow tubular architectures as nanoreactors though host–guest interaction between the host molecule phthalocyanine-bridged b-cyclodextrins and the guest molecule carboxylated porphyrin.5 Kim’s group demonstrated that vesicles formed by dentron-like molecules could transform into nanotubes upon directly adding CDs into the solution of vesicles via host–guest interaction.6 Yuan and co-workers constructed lightresponsive nanotubes though a-CD–trans-azobenzene interaction between trans-azobenzene-end poly(acrylic acid) and a-CD-end poly(caprolactone).7
Our previous work has suggested that CD and adamantanol hydrophobic moieties can assemble into unusual giant nanotubes with the large diameter of 500 nm and length of about 20 mm.8 Inspired by this work, we wondered whether the nanotubes can be controlled to generate branched giant nanotubes.
The idea is very challenging, because except for steric straight organic nanotubes, fabricating more sophisticated tubular structures 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-1-3,4,5trihydroxybenzoicamide 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: email@example.com b State Key Laboratory of Supramolecular Structure and Materials,
College of Chemistry, Jilin University, Changchun 130012, China.
E-mail: firstname.lastname@example.org † Electronic supplementary information (ESI) available: Synthetic procedures and characterization of new compounds, and spectroscopic studies (UV, fluorescence,
DLS, NMR). See DOI: 10.1039/c5cc01414j
Received 15th February 2015,
Accepted 9th March 2015
DOI: 10.1039/c5cc01414j www.rsc.org/chemcomm
Pu bl ish ed o n 09
M ar ch 2 01 5.
D ow nl oa de d by
U ni ve rs ity o f M em ph is on 2 3/ 03 /2 01 5 07 :1 3: 11 .
View Article Online
Chem. Commun. This journal is©The Royal Society of Chemistry 2015 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) confirms 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. Themolecule packingmode 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.