Functioning via host–guest interactions

Abstract

Molecular recognition is essential for realizing functional supramolecular materials. Non-covalent host–guest interactions are an effective tool to introduce switching and functional properties into materials. This review focuses on the achievement of selective molecular adhesion, self-healing, toughness, and actuation properties. These functions have been achieved by reversible bond formation with cyclodextrins (CDs). Self-healing materials with host–guest interactions involving CDs have been used to achieve redox-responsive healing properties and healing efficiency. Furthermore, the materials, which undergo self-healing by chemical and physical mechanisms, exhibit rapid and efficient self-healing properties under semi-dry conditions. To prepare a supramolecular actuator using host–guest complexes, two approaches have been introduced. The first is the functionalization of a supramolecular gel actuator by changing the cross-linking density, and the second is the functionalization of a topological gel actuator by changing distances between the cross-linking points. Both actuators exhibit contractive bending behavior. This review summarizes advancements within the past ten years in supramolecular materials that function via the chemical mechanism of host–guest interactions and the physical mechanism of the sliding motion of ring molecules.

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J Incl Phenom Macrocycl Chem (2017) 87:313–330
DOI 10.1007/s10847-017-0702-z
ORIGINAL ARTICLE
Functioning viahost–guest interactions
YoshinoriTakashima1· AkiraHarada1
Received: 8 February 2017 / Accepted: 10 February 2017 / Published online: 9 March 2017
© Springer Science+Business Media Dordrecht 2017
Keywords Host–guest interactions· Cyclodextrin·
Supramolecular materials· Topological materials· Stimuli-
responsive materials
Introduction
Molecular recognition of small molecules and macromol-
ecules is important in many functions in biological sys-
tems [1–6]. Herein, we focus on muscle motion [7–10],
self-healing properties, and cell adhesion [11, 12] via
dynamic movement and selectivity through molecular rec-
ognition properties. Myosin, kinesin, and dynein convert
energy from ATP hydrolysis to mechanical work. In muscle
fibrils, myosin and actin filaments exist as a complex with
an alternating layered structure, whose components slide
over one another, thus leading to contraction and expansion
behaviors [7–9]. The sliding motion of myosin and actin
filaments has inspired the development of artificial linear
motors. Self-healing and cell adhesion properties are simi-
lar functions based on molecular recognition between cell
surfaces. Cellular adhesion, through which cells may form
clumps, is essential for maintaining multicellular structures.
These cell clumps eventually form organs through cell sort-
ing. These behaviors are accurately controlled through
molecular recognition. Inspired by the ideas of mechanical
movement and selective assembly formation, we have cre-
ated stimuli-responsive supramolecular materials that act
through molecular recognition.
Molecular recognition chemistry [13–15] and supramo-
lecular chemistry [16, 17] have received much attention,
owing to their effects on structure, catalytic activity, pho-
tochemical properties, molecular switches, and materials.
Macrocyclic molecules (crown ethers [13], cyclophanes
[14], cryptands [16], and cucurbiturils [18]) are typical host
Abstract Molecular recognition is essential for real-
izing functional supramolecular materials. Non-covalent
host–guest interactions are an effective tool to introduce
switching and functional properties into materials. This
review focuses on the achievement of selective molecular
adhesion, self-healing, toughness, and actuation proper-
ties. These functions have been achieved by reversible bond
formation with cyclodextrins (CDs). Self-healing materials
with host–guest interactions involving CDs have been used
to achieve redox-responsive healing properties and heal-
ing efficiency. Furthermore, the materials, which undergo
self-healing by chemical and physical mechanisms, exhibit
rapid and efficient self-healing properties under semi-dry
conditions. To prepare a supramolecular actuator using
host–guest complexes, two approaches have been intro-
duced. The first is the functionalization of a supramolecular
gel actuator by changing the cross-linking density, and the
second is the functionalization of a topological gel actua-
tor by changing distances betweenthe cross-linking points.
Both actuators exhibit contractive bending behavior. This
review summarizes advancements within the past ten years
in supramolecular materials that function via the chemi-
cal mechanism of host–guest interactions and the physical
mechanism of the sliding motion of ring molecules.
This is a paper selected for the “HGCS Japan Award of
Excellence 2016”.
* Yoshinori Takashima
takasima@chem.sci.osaka-u.ac.jp
* Akira Harada
harada@chem.sci.osaka-u.ac.jp
1 Department ofMacromolecular Science, Graduate School
ofScience, Osaka University, 1-1 Machikaneyama-cho,
Toyonaka, Osaka560-0043, Japan
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