POLYMERS　Vol.66　No.12
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COVER STORY
An Evolving Supramolecular Polymer
COVER STORY: Highlight Reviews
Precise Supramolecular Polymerization Daigo MIYAJIMA, Takuzo AIDA
<Abstract> This article describes the recent research progresses in precise supramolecular polymerization and its perspectives.
Keywords: Supramolecular Polymerization / Chain-growth Polymerization / Step-Growth Polymerization / Stereoselective Polymerization / Hydronge-Bond
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Supramolecular Materials Functionalized by Host-Guest Interactions Akira HARADA
<Abstract> Recently, many kinds of supramolecular polymers have been designed and constructed. Supramolecular polymers formed by host-guest interactions have made some progress toward design and constructions of supramolecular materials. In this article design and synthesis of new supramolecular materials formed by host-guest interactions are described. When a guest part was attached to a host molecule, supramolecular polymers were formed: linear, helical and cyclic polymers were formed. When host polymers and guest polymers were mixed in water, they formed supramolecular gels. When host monomers and guest monomers were mixed and polymerized in water, they formed gels as well. These gels show self-healing properties. When stimuli-responsive guests such as ferrocene and azobenzene were incorporated in tells, they formed stimuli-responsive gels. When daisy chains consisting of cyclodetrin and azobenzene were incorporated in a supramolecular gel, they formed a photo-responsive gel like muscle.
Keywords: Supramolecular Materials / Host-Guest Intaeraction / Cyclodextrin / Self-Healing / Artificial Muscle
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Supramolecular Hydrogels Toward Multi-Component Systems Itaru HAMACHI, Hajime SHIGEMITSU
<Abstract> Supramolecular hydrogels with unique dynamic properties (e.g. stimuli-responsiveness and reversibility) have been expected as novel smart biomaterials. Herein, we describe the recent progress of functional supramolecular hydrogels in artificial and natural multi-component systems. Rational hybridization of functional materials with supramolecular hydrogels, and double network supramolecular hydrogels afforded us novel materials with intriguing properties derived from each component. Additionaly, formation of supramolecular polymers in cell or in vivo have been achieved for biological applications. The recent examples clearly indicate tremendous potentials of supramolecular polymers in multi-component systems.
Keywords: Supramolecular Polymer / Hydrogel / Self-Assembly / Multi-Component / Biological Application
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COVER STORY: Topics and Products
Living Supramolecular Polymerization in One and Two Dimensions Kazunori SUGIYASU
<Abstract> We have recently identified a very unique dynamic behavior of a metastable supramolecular assembly consisting of a porphyrin derivative. The metastable assembly, which was nanoparticles, could transform into either nanofiber or nanosheet in time, as if it had a capacity of “differentiation”. We uncovered the energy landscape for this dynamic behavior, based on which we could control which way the nanoparticle would differentiate. Furthermore, we succeeded in “living polymerization” of both 1D and 2D nanostructures through seeded-growth approach.
Keywords: Supramolecular Polymers / Living Supramolecular Polymerization / Nucleation-Elongation / Porphyrins
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Supramolecular Polymers formed via Host-Guest Interaction Takeharu HAINO
<Abstract>A bisporphyrin molecular cleft captures an electron-deficient guest through a donor-acceptor interaction. A monomer, which possesses a bisporphyrin cleft and an electron-deficient guest, self-assembles to form supramolecular polymers that are cross-linked with coordination bonds. The resulting supramolecular polymers generate well-entangled solutions with associating and networking polymers. The free-standing films of the supramolecular polymer networks are fabricated with Young’s modulus of 1 GPa.
A self-assembled coordination capsule exists as a racemic mixture of the (P)- and (M)-enantiomeric forms. When a chiral guest is captured within the capsule, the chiral interior recognizes the shape of the guest, which results in the diastereomeric complex with high diastereoselectivity. The multiple guests, introduced onto a polymer main chain, are encapsulated within the coordination capsules, resulting in supramolecular graft copolymers. The steric communication among the graft sites results in the helical organization of the supramolecular graft polymers, and gives rise to the unique chiral amplifications known as the majority-rules effect.
Keywords: Supramolecular Polymer / Graft Polymer / Porphyrin / Self-Assembled Capsule / Chiral Recognition / Chiral Amplification
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Construction of a Hemoprotein Supramolecular Polymer Takashi HAYASHI
<Abstract> Hemoproteins such as myoglobin, hemoglobin, cytochrome P450 and horseradish peroxidase include protoheme (heme b) as a cofactor. This heme cofactor is removable from the proteins and the resulting apoproteins can be converted into reconstituted proteins upon addition of appropriate porphyrinoid cofactors. Our group has focused on the preparation of various supramolecular hemoprotein polymers using this process. For example, an external heme-linked apoprotein where the heme molecule is covalently bound to the protein surface is found to provide a linear hemoprotein polymer via the heme-heme pocket interaction. In addition, 2D and 3D hemoprotein assemblies, a branched polymer and cross-linked polymer, respectively, can also be generated using similar methodology. In other studies, our group has immobilized the hemoprotein polymer onto various surfaces such as gold and other metal-based particles and carbon materials to prepare functionalized electrodes. In the present article, supramolecular polymerization using a hemoprotein as a monomer will serve as a new strategy for generating functional materials and catalysts.
Keywords: Supramolecular Polymer / Hemoprotein / Artificial Cofactor / Reconstituted Protein
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Polymer Science and I: A Personal Account
Shifting from “What I Can Do” to “What I Should Do” Keita SAKAKIBARA
<Abstract> This essay is the short story of my life as a researcher, including why I decided to go on to a doctoral course, what I felt during post-doctoral research, and how I changed mind about “what I should do”.
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Front-Line Polymer Science
Cooperativity in Self-Assemblies and Dynamic Response to External Stimuli Takashi HIROSE, Kenji MATSUDA
<Abstract> Cooperative self-assembly is a key concept to create supramolecular systems that are highly responsive to external stimuli. Supramolecular structural change in solution can be usually detected using spectroscopic measurement—such as UV-Vis absorption, circular dichroism (CD) and NMR spectra—depending on concentration or temperature. The process of self-assembly can be quantitatively analyzed by applying appropriate thermodynamic models considering multistage open association of equilibrium polymers. When the process of self-assembly is highly cooperative, elongation of a supramolecular polymer has clear thresholds for concentration and temperature. Recently, we have developed a thermodynamic model for two-dimentional (2-D) self-assemblies formed at the liquid/solid interface. Concentration dependence of surface coverage of adsorbates on graphite substrate can be determined using scanning tunneling microscopy (STM). We found that surface coverage depending on concentration becomes prominently sharp when the system of 2-D self-assembly is highly cooperative. On the basis of this concept, highly photoresponsive 2-D self-assembly was achieved by using 2-D molecular ordering composed of photochromic diarylethene derivatives.
Keywords: Cooperative Self-Assembly / Nucleation–Elongation Model / Liquid–Solid Interface / External Stimuli
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