Helical Structure of Oligo- and Poly(m-substituted phenyl isocyanate)s Bearing an Optically Active End-Group

Maeda, Katsuhiro

doi:10.1295/polymj.30.100

Cited by 39 publications

(35 citation statements)

References 16 publications

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“…This phenomenon was called the ™non-covalent domino effect∫. [32] Chiral solvation, while its chiral bias seems to be very weak, can also be used to induce a helical conformation with a preferential screw-sense in the achiral poly(n-hexyl isocyanate) (17) [33] and a polysilane (18). [34] The helicity induction was detected by the appearance of CD in the UVvisible region of the polymer backbone.…”

Section: Chirality Sensing By Supramolecular Systemsmentioning

confidence: 99%

Detection and Amplification of Chirality by Helical Polymers

Yashima

Maeda

Nishimura

2003

Chemistry A European J

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534

302

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A unique feature of synthetic helical polymers for the detection and amplification of chirality is briefly described in this article. In sharp contrast to host-guest and supramolecular systems that use small synthetic receptor molecules, chirality can be significantly amplified in a helical polymer, such as poly(phenylacetylene)s with functional pendants, which enable the detection of a tiny imbalance in biologically important chiral molecules through a noncovalent bonding interaction with high cooperativity. The rational design of polymeric receptors can be possible by using chromophoric helical polymers combined with functional groups as the pendants, which target particular chiral guest molecules for developing a highly efficient chirality-sensing system. The chirality sensing of other small molecular and supramolecular systems is also briefly described for comparison.

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Section: Chirality Sensing By Supramolecular Systemsmentioning

confidence: 99%

Detection and Amplification of Chirality by Helical Polymers

Yashima

Maeda

Nishimura

2003

Chemistry A European J

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534

302

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“…As a consequence, they consist of interconvertible right-and lefthanded helical segments separated by rarely occurring helical reversals, as demonstrated by Green et al, 6,20,21 so that a preferred-handed helical conformation can be induced in the presence of a small amount of chiral residues at the pendant 6 or terminal ends 22,23 or a noncovalently interacting stimulant, 24 with their helical senses being determined under thermodynamic control. Either static or dynamic helical polymers with an excess one-handedness, such as poly(quinoxaline-2,3-diyl)s (4), 25,26 polyguanidines (5), 27,28 poly(phenyl isocyanide)s (6) 29,30 and polyacetylenes (7), [8][9][10][11][12][31][32][33][34] have also been prepared by the polymerization of analogous monomers bearing different chiral or achiral substituents, that is, the boundary between static and dynamic helical conformations is totally dependent on the helix inversion barrier.…”

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confidence: 99%

Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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During the last decade, remarkable progress in developing synthetic helical polymers with a controlled helical sense has been achieved. However, the exact helical structures of most of the already prepared synthetic helical polymers remain unsolved. In this review, the recent progress in the synthesis of helical polymers and their structural determination, including helical pitch and handedness based on X-ray diffraction and spectroscopic measurements, together with high-resolution atomic force microscopy, is described. Polymer Journal (2010) 42, 3-16; doi:10.1038/pj.2009 Keywords: atomic force microscopy; circular dichroism; helical polymer; helical structure; X-ray diffractionThe helix is a unique structure as observed in nature from microscopic to macroscopic levels and is inherently chiral. Inspired by biological helices, such as DNA and proteins, chemists have been challenged to synthesize helical polymers with a controlled helical sense that aims not only to mimic biological helical structures but also to develop chiral materials for the separation of enantiomers and asymmetric catalysis. [1][2][3][4][5][6][7][8][9][10][11][12] The history of synthetic helical polymers with optical activity extends back to the 1960s when Pino and Lorenzi 13 investigated the structural and chiroptical properties of isotactic vinyl polymers prepared by the polymerization of a-olefins bearing optically active substituents. Although helical polyolefins are totally dynamic in nature and consist of short helical segments separated by frequently occurring helical reversals among disordered, random coil conformations, 14 this study was significant in the field of synthetic helical polymers, from which a number of helical polymers have been synthesized.On the basis of the pioneering studies by Nolte et al., 15 Okamoto et al. 16 and Green et al., 17 the existing synthetic helical polymers that exhibit an optical activity solely because of their macromolecular helicity can be classified into two categories with respect to their helix inversion barriers, that is, static and dynamic helical polymers (Figure 1). 9,12 Optically active helical polymers, such as poly(triphenylmethyl methacrylate) (1), 16 poly(t-butyl isocyanide) (2) 15 and polychloral (3), 18 have a sufficiently high helix inversion barrier and belong to the family of static helical polymers. Therefore, these helical polymers with either a right-or left-handed helix can be prepared by the helix-sense-selective polymerization of the corresponding achiral monomers using chiral catalysts or initiators under kinetic control. On the other hand, dynamic helical polymers, such as polyisocyanates (8) 17 and polysilanes (9), 19 possess a very low helix inversion barrier.As a consequence, they consist of interconvertible right-and lefthanded helical segments separated by rarely occurring helical reversals, as demonstrated by Green et al.,6,20,21 so that a preferred-handed helical conformation can be induced in the presence of a small amount of chiral residues at the pendant 6 or ter...

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“…The CD intensity of 2 depended on the molecular weight, and the polymer prepared in run 2 exhibited the largest intensity. Previously, Okamoto and coworkers52–55 reported similar observations for polymers prepared by the asymmetric polymerization of phenylisocyanate derivatives; they clarified that the persistence length of the helical structure was relatively short for the poly(phenyl isocyanate) bearing the chiral initiator residue in the terminal end and that the one‐handed helical sequences decreased with an increasing degree of polymerization. Therefore, polymer 2 should partially form a one‐handed helical structure, which was preserved by the chirality of MMP bonding to the terminal end in 2 .…”

Section: Resultsmentioning

confidence: 60%

“…The asymmetric polymerization using a chiral initiating system is extensively known as an effective approach to producing a one‐handed helical polymer, and this strategy has been applied to the preparations of a number of helical polymers 42–51. In fact, Okamoto and coworkers52–55 achieved the synthesis of a one‐handed helical polyisocyanate by means of this synthetic procedure. Thus, the asymmetric polymerization of phenylisocyanate bearing crown ether should be a suitable candidate for producing the one‐handed helical arrays of crown ether.…”

Section: Introductionmentioning

confidence: 99%

Chiral discrimination of a helically organized crown ether array parallel to the helix axis of polyisocyanate

Sakai

Otsuka

Satoh

et al. 2005

J. Polym. Sci. A Polym. Chem.

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The asymmetric polymerization of 4′‐isocyanatobenzo‐18‐crown‐6 with the lithium amide of (S)‐(2‐methoxymethyl)pyrrolidine successfully proceeded to afford end‐functionalized poly(4′‐isocyanatobenzo‐18‐crown‐6) with (S)‐(2‐methoxymethyl)pyrrolidine (polymer 2). In the circular dichroism (CD) spectrum of 2, a clear positive Cotton effect was observed in the range of 240–350 nm corresponding to the absorption of the polymer backbone, indicating that 2 partially formed a one‐handed helical structure, which was preserved by the chirality of (S)‐(2‐methoxymethyl)pyrrolidine bonding to the terminal end in 2. In the titration experiments for the CD intensity of 2 in the presence of D‐ and L‐Phe·HClO4 (where Phe is phenylalanine), a small but remarkable difference was observed in the amount of the chiral guest needed for saturation of the CD intensity and in the saturated CD intensity, indicating that the extremely stable, one‐handed helical part should exist in the main chain of 2, which was not inverted even when the unfavorable chiral guest for the predominant helical sense, L‐Phe·HClO4, was added. In addition, helical polymer 2 exhibited a chiral discrimination ability toward racemic guests; that is, the guests were extracted from the aqueous phase into the organic phase with enantiomeric excess. The driving force of the chiral discrimination ability of 2 should certainly be attributed to the one‐handed helical structure in 2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 325–334, 2006

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Helical Structure of Oligo- and Poly(m-substituted phenyl isocyanate)s Bearing an Optically Active End-Group

Cited by 39 publications

References 16 publications

Detection and Amplification of Chirality by Helical Polymers

Detection and Amplification of Chirality by Helical Polymers

Synthesis and structure determination of helical polymers

Chiral discrimination of a helically organized crown ether array parallel to the helix axis of polyisocyanate

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