Angewandte
Chemie
Supramolecular Amphiphiles
Self-Assembly and Disassembly of Vesicles as Controlled by Anion–p
Interactions
Qing He, Yu-Fei Ao, Zhi-Tang Huang, and De-Xian Wang*
Abstract: Anion–p interactions have been widely studied as
new noncovalent driving forces in supramolecular chemistry.
However, self-assembly induced by anion–p interactions is still
largely unexplored. Herein we report the formation of
supramolecular amphiphiles through anion–p interactions,
and the subsequent formation of self-assembled vesicles in
water. With the p receptor 1 as the host and anionic amphi-
philes, such as sodium dodecylsulfate (SDS), sodium laurate
(SLA), and sodium methyl dodecylphosphonate (SDP), as
guests, the sequential formation of host–guest supramolecular
amphiphiles and self-assembled vesicles was demonstrated by
SEM, TEM, DLS, and XRD techniques. The intrinsic anion–p
interactions between 1 and the anionic amphiphiles were
confirmed by crystal diffraction, HRMS analysis, and DFT
motifs.[9] Since previous theoretical studies that predict such
noncovalent interactions,[10] experimental results both in the
solid state and in solution have exemplified the existence of
anion–p interactions.[11] As compared to well-studied cation–
p interactions, which have been successfully applied in
biological systems and chemistry,[12] the application of
anion–p interactions remains largely unexplored.[13] For
example, in living systems, functions of anion–p interactions
in enzymatic catalysis and protein structure have been
revealed by the groups of Frontera[13a] and Robertazzi,[13b]
respectively. In the field of supramolecular chemistry, Guha
and Saha[11k] reported anion sensing by the use of naphtha-
nediimides (NDIs) as p-electron-deficient receptors. Matile
and co-workers designed NDI-based and calixpyrrole-based
transporters that can transport anions across lipid bilayer
membranes.[13c,d] The Matile group also reported unprece-
dented catalytic reactions based on anion–p interactions.[13e,f]
Recently, we demonstrated that the size of vesicles formed
with tetraoxacalix[2]arene[2]triazine-derived covalent amphi-
philes can be regulated by anion–p interactions both in THF–
water and in water systems.[14] The further challenge is: could
anion–p interactions induce the formation of self-assembled
aggregates in water? Specifically, could the anion–p binding
motifs be used to build supramolecular amphiphiles? To
address this challenge, we report herein anion–p-controlled
self-assembly and disassembly. Our findings demonstrated
that tetraoxacalix[2]arene[2]triazine and anionic surfactants
can form supramolecular amphiphiles through anion–p
interactions. The resulting supramolecular amphiphiles fur-
ther self-assembled into vesicles with the help of hydrophobic
effects. Owing to the reversibility of anion–p interactions, the
controlled disassembly of vesicles can also be promoted by
adding competitive anions or decreasing the pH value.
calculations. Furthermore, the controlled disassembly of the
À
vesicles was promoted by competing anions, such as NO3
,
ClÀ, and BrÀ, or by changing the pH value of the medium.
S
elf-assembly by the use of amphiphiles as building blocks is
an important theme in supramolecular chemistry.[1] Besides
the vast amount of synthetic covalent amphiphiles, there has
been great interest in supramolecular amphiphiles formed by
noncovalent bonding.[1,2] The reversible nature of noncova-
lent bonding enables the straightforward construction of
diverse supramolecular amphiphiles, and their controllable
self-assembly and disassembly. The inclusion of versatile
functional groups in supramolecular amphiphilic entities also
enables the assembly of stimuli-responsive materials. Since
early examples based on multiple hydrogen bonding[3] and
electrostatic attraction,[4] noncovalent interactions such as
coordination,[5] charge transfer,[6] and p–p stacking[7] have
also been applied as driving forces to form supramolecular
amphiphiles. Macrocyclic host–guest motifs have also been
used to build supramolecular amphiphilic systems, and their
unique self-assemblies have attracted much attention.[8] Our
interest in anion–p interactions encouraged us to explore the
possibility of applying this novel type of noncovalent bond as
a driving force to induce the formation of supramolecular
amphiphiles.
We initiated our studies by using 1[15] as the host and
commercially available sodium dodecylsulfate (SDS) as the
guest to construct supramolecular amphiphiles (Scheme 1). In
principle, SDS forms micelles above the critical micelle
concentration (CMC; 8–10 mm) in water. Therefore, we chose
a concentration far below its CMC for the investigation, and
in such case SDSs are expected to exist as discrete molecules
in solution. The procedure was carried out by quickly
injecting water (1 mL) into a 1:1 mixture of 1 and SDS
(60 mL, 10 mm in THF/methanol (3:7)) to give a final
concentration of 6 10À4 m. Vortexing of the aqueous mixture
for 1 min produced an opalescent colloidal solution, thus
indicating the formation of self-assembled aggregates. The
critical aggregation concentration (CAC) was measured as
5.0 10À6 m by means of a fluorescence method with pyrene as
the probe (see Figure S38 in the Supporting Information).
The morphology of the aggregates was first investigated with
Anion–p interactions between electron-rich anions and
electron-deficient aromatic groups are emerging noncovalent
[*] Q. He, Dr. Y.-F. Ao, Prof. Z.-T. Huang, Prof. D.-X. Wang
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Molecular Recognition and Function
Institute of Chemistry, Chinese Academy of Sciences
Beijing, 100190 (China)
E-mail: dxwang@iccas.ac.cn
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2015, 54, 11785 –11790
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
11785