DOI: 10.1002/chem.201402612
Communication
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Nanoreactors
A Supramolecular Tubular Nanoreactor
Zhi-Qiang Li, Ying-Ming Zhang, Yong Chen, and Yu Liu*[a]
between permethylated b-cyclodextrin (PMCD) dimers with
rigid silicon(IV) phthalocyanine cores (1) and carboxylated por-
phyrin bearing long hydrophobic tails (2), followed by the
supramolecular assembly of 1/2 couples (Scheme 1). In this
nanostructure, the rigid-core-tethered host (1) of silicon(IV)
phthalocyanine axially bridged with two permethylated b-cy-
clodextrins (PMCD) can adjust the curvature of organic nano-
tubes to avoid any undesirable formation of micelles or vesi-
cles,[8] whereas carboxylated porphyrin 2 not only provides the
anchoring sites for catalytic centers, but also offer a hydropho-
bic microenvironment to readily accommodate the active bind-
ing domains. As a result, the tubular nanostructure can pro-
mote highly efficient catalytic reactions under environmentally
benign conditions.
Abstract: The extremely strong noncovalent complexation
between the rigid host of phthalocyanine-bridged b-cyclo-
dextrins and the amphiphilic guest carboxylated porphyrin
is employed to construct a hollow tubular structure as
a supramolecular nanoreactor. A representative coupling
reaction occurs in the hydrophobic interlayers of the tubu-
lar walls in pure water at room temperature, leading to an
enhancement of ten times higher reaction rate without
any adverse effect on catalytic activity and conversion.
In the last two decades, nanometer-scaled hollow structures
have attracted growing interest owing to their fascinating
properties in material conversion and delivery,[1] and construc-
tion protocols for various self-assembled hollow nanostruc-
tures with cage-like, cavity-like, vesicle-like, tube-like, and
porous topology have been successfully established.[2] Among
them, tubular nanostructures possess several considerable ad-
vantages compared with nanostructures with other topolo-
gies.[3] Firstly, the tubular structures may have reduced weight,
better mechanic stability, and larger surface-to-volume area.
Secondly, the open-ended feature of tubular arrays enables
not only the simultaneous interactions of cylindrical internal
and external surfaces with substrates, but also the delivery of
exogenous products, which jointly maximize the catalytic per-
formance.[4] These advantages are also used by natural systems
such as in the coating protein of the tobacco mosaic virus, cy-
toplasmic microtubules, and endoplasmic reticulum.[5] Typically,
the enveloping membrane of chloroplast in some plants can
form vesicle or tubular structures, and the biosynthesis of
lipids takes place under the catalysis of enzymes attached to
the surface of these hollow structures.[6] However, the potential
of artificial tubular nanostructures as reactors has barely been
uncovered, despite the fact that these tubular nanostructures,
which have tunable diameters ranging from the micro- down
to nano-scale, can provide spatially confined reaction cham-
bers and channels for materials synthesis and substance ex-
change. Herein, we report a hollow tubular nanostructure con-
structed through reasonably strong host–guest associations[7]
The dimeric host, 1, possessing a silicon(IV) phthalocyanine
core, was prepared according to the reported method,[9] and
the amphiphilic guest, 2, with hydrophobic tail was synthe-
sized by the reaction of phenolic hydroxyl-substituted porphy-
rin with a benzyl bromide derivative bearing alkyl chains under
basic conditions (Figures S1–S3, see the Supporting Informa-
tion). Subsequently, UV/Vis spectroscopic experiments were
performed to quantitatively investigate the host–guest binding
behaviors in aqueous solution. As shown in Figure 1, the incor-
poration of 1 with 2 underwent a clear complexation-induced
bathochromic shift from 680 to 689 nm, accompanied by
a clear isosbestic point at 685 nm. Similarly, the absorbance
changes of 1 became steady in the presence of 1 equivalent of
2, indicating 1:1 host–guest binding stoichiometry between
1 and 2 (Figure 1, inset).[10] In addition, the complex stability
constant (KS) was calculated to be 1.3ꢀ107 mÀ1 by analyzing
the sequential changes in absorbance intensity (DA) of 1 at
varying concentrations of 2 by using a nonlinear least-squares
curve-fitting method.[11] Moreover, the peak at m/z 1619.4413
in the mass spectrum was assigned to [1+2À3K+]3À (Fig-
ure S4, see the Supporting Information). These results jointly
reveal that the porphyrin backbone of 2 was concurrently as-
sociated with two PMCD cavities of 1 to form a highly stable
inclusion complex in water, and more importantly, this ex-
tremely strong binding would facilitate the eventual formation
of supramolecular tubules as described below (Scheme 2).
Direct morphological information of the tubular nanostruc-
ture based on the host–guest complexation of 1 with 2 was
provided by scanning electron microscopy (SEM) and transmis-
sion electron microscopy (TEM). As can be discerned from
Figure 2A, SEM images of an air-dried equimolar solution of
1 and 2 exclusively display cylindrical tubules with an open-
ended hollow space. Moreover, TEM images gave detailed
structural information, in which the aggregates constructed
from complex 1·2 clearly show hollow tubular structures with
[a] Z.-Q. Li, Dr. Y.-M. Zhang, Prof. Dr. Y. Chen, Prof. Dr. Y. Liu
Department of Chemistry, State Key Laboratory of
Elemento-Organic Chemistry, Nankai University
Collaborative Innovation Center of Chemical Science and Engineering
Tianjin 300071 (P.R. China)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402612.
Chem. Eur. J. 2014, 20, 1 – 6
1
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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