| POLYMERS Vol.71 No.4 |
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COVER STORY
Progress in Macrocycles |
| COVER STORY: Highlight Reviews |
| π-Conjugated Giant Macrocycles | Tohru NISHINAGA, Masahiko IYODA |
| <Abstract> Giant macrocycles composed of aromatic rings such as benzene and thiophene and their π-expanded systems with acetylene and ethylene linkage have attracted growing interest, because they exhibit unique properties derived from the cyclic structures. In this article, we highlight the synthetic methodology of such giant macrocycles and their unique functions including complexation with C60, two-photon absorption, and global aromaticity of macrocycles in the oxidized states. In particular, the aromaticity caused a magnetically induced ring current that might have hidden potential for future applications. Keywords: π-Conjugation / Macrocycles / C60 Complex / Two-Phton Absorption / Aromaticity / Ring Current |
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| Creating Polycatenanes from Polymers | Atsushi ISOBE, Shiki YAGAI |
| <Abstract> Polycatenanes, which consist only of cyclic molecules, are next-generation polymers that many researchers are working on to synthesize efficiently because of their unique viscoelasticity. The use of larger and thicker polymers with a cyclic structure makes it possible to visualize the structure using probe microscopy and other techniques. In this section, we will discuss several polycatenanes consisting of ring polymers and introduce their preparation methods and characteristics. Keywords: Supramolecular Polymer / Self-Assembly / Toroid / Ring / Topology / Catenane |
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| COVER STORY: Topics and Products |
| Creation of One-Dimensional Tubular Structures Based on Pillar[5]arenes | Shunsuke OHTANI, Tomoki OGOSHI |
| <Abstract> Pillar[n]arenes, which were first reported by our group in 2008, are new macrocyclic compounds in supramolecular chemistry. Based on the highly symmetrical structures, one-dimensional (1D) tubular structures can be formed by connecting pillar[n]arenes via non-covalent interactions between the functional groups at the both rims. This article describes the formation and length control of self-assembled 1D tubular structures of pillar[5]arenes. Keywords: Macrocyclic Compound / Host-Guest Chemistry / Supramolecular Chemistry / One-Dimensional Tubular Structure |
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| Formation of Giant Cyclic Complexes Using a Flexible Tripeptide | Ryosuke MIYAKE |
| <Abstract> Herein, we describe the formation of giant cyclic complexes from a small, flexible tripeptide possessing three kinds of metal coordinating sites. Giant cavities (diameter: ca. 2 nm) was formed by connecting 14 artificial tripeptides and 14 Ni(Ⅱ) ions. A mesh-like structure should be important feature for the formation of the giant structures from the flexible tripeptide: three tripeptides connected to a octahedral Ni(Ⅱ) center by tridentate, bidentate, and monodentate binding sites to form the mesh-like structure. The structural and theoretical studies suggested that the metal coordination bonds at the tridentate binding site, which includes the O atoms of the amide groups in the peptide backbone, control the conformation of flexible tripeptides, supported by intramolecular hydrogen bonds. The design principle and possibility of metal complexes of short peptides to form giant structures is also discussed in this topic article. Keywords: Peptides / Formation of Giant Structures / Cyclic Metal Complexes / Flexible Tripeptide / Self-Assembly |
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| Creating Chiral Cyclic π-Conjugated Molecules by Aromatic Ring Construction | Juntaro NOGAMI, Ken TANAKA |
| <Abstract> Cyclic π-conjugated molecules have an interesting π-conjugated structure with no ends and are expected to be applied as light-emitting materials and semiconductor materials. However, their syntheses require overcoming the large distortion of the molecule, which has been a challenging target in synthetic organic chemistry. Following the synthesis of carbon nanorings and carbon nanobelts, Isobe succeeded in synthesizing a chiral cyclic π-conjugated molecule and exhibited its extraordinary circularly polarized luminescence property. However, this molecule was obtained as a mixture of diastereomers and enantiomers using multiple coupling reactions. Our research group discovered in 2003 that a cationic rhodium(Ⅰ)/biaryl bisphosphine complex exhibits extremely high activity and selectivity for the [2+2+2] cycloaddition reaction of alkynes. Then, we applied this reaction to the intramolecular [2+2+2] cycloaddition reactions of cyclic polyynes and achieved the asymmetric synthesis of various chiral cyclic π-conjugated molecules. Keywords: Alkynes / Aromatic Ring Construction / Asymmetric Catalysis / Chiral Cyclic π-Conjugated Molecules / Cycloparaphenylenes / Polyynes / Rhodium / [2+2+2] Cycloaddition |
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| Chiral Macrocycles Based on the Assembly of Phenylacetylenes as a Building Block | Ryo KATOONO |
| <Abstract> I describe herein chiral macrocycles in two parts, monocyclic and polycyclic. The first part shows chiral monomacrocycles based on a single ring that is helically folded in a molecule. Folding of a ring provides a diverse array of chiral fashions, while for linear molecules, folding is often associated with a helix as a representative. Through the cooperative transmission of external and internal chirality to a racemic pair of enantiomerically-folded macrocycles, a particular sense of (M)- or (P)-helicity can be preferred to show unique optical activities. In the second part, a variety of chiral polymacrocycles are demonstrated. There are several cases where a molecule possesses multiple rings or no rings, the stereochemistry is assured or not. Depending on the situations, several issues (new structure creation, unique helical-sense control with no use of stereogenic centers, and pluralistic transmission of chirality, etc.) are discussed. All macrocycles here are built up with phenylacetylene and terephthalamide units. Keywords: Terephthalamide / Macrocycle / Triple Bond (Phenylacetylene) / Chirality |
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| Precision Supramolecular Polymerization Using Secondary Nucleation | Norihiko SASAKI, Kazunori SUGIYASU |
| <Abstract> We have designed a porphyrin derivative that has fluorinated side chains. Interestingly, this molecule self-assembled into concentric toroids. AFM observation unveiled its growth mechanism in which secondary nucleation played an important role. Based on this understanding, we succeeded in controlling the size of the concentric toroid through seeded supramolecular polymerization. Keywords: Supramolecular Polymers / Living Supramolecular Polymerization / Secondary Nucleation / Porphyrins / Concentric Toroids |
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| Polymer Science and I: A Personal Account |
| Aiming for Freedom to Everything (or Quick Working) | Hiroshi INABA |
| <Abstract> My recent motto is “Aiming for freedom to everything”. Because of the previous experience, I became a cynical researcher who does not want to do trendy research. I want to enjoy research in a light-hearted way, without being particular about anything. |
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| Front-Line Polymer Science |
| Polymer Substrate Deformability as a Designing Parameter of Biomaterials for Cell Manipulation | Sayaka MASAIKE, Satoru KIDOAKI |
| <Abstract> Recent developments in cell manipulation technology on the biomaterials through designing the mechanical properties of polymer materials are reviewed. We focus on the deformability of a polymer matrix or a substrate as an essential parameter for cell manipulation such as on cell adhesion, proliferation, motility, and differentiation. Various modes of cell manipulation by a elastic or viscoelastic polymer matrix are summarized. In particular, the effect of microscopic deformation of a solid polymer substrate surface on cell manipulation is discussed from the views of cell-traction-force-induced microscopic stain on the biomaterials surface. Relating to the mechanism on those cell manipulations, recent developments in molecular clutch theory are outlined, which explain the kinetic behaviors of growth and reduction of cell adhesion machinery depending on the condition of deformation velocity of the polymer matrix. The emerging research field that integrates cell biology and polymer materials engineering are reviewed in terms of mechanical design of cell manipulation materials. Keywords: Cell Manipulation / Deformability / Elasticity / Viscoelasticity / Cell Adhesion / Molecular Clutch |
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