No abstract

Construction of predominantly one-handed helical polyacetylenes with a desired helix sense utilizing noncovalent chiral interactions with nonracemic chiral guest compounds based on a supramolecular approach is described. As with the conventional dynamic helical polymers possessing optically active pendant groups covalently bonded to the polymer chains, this noncovalent helicity induction system can show significant chiral amplification phenomena, in which the chiral information of the nonracemic guests can transfer with high cooperativity through noncovalent bonding interactions to induce an almost single-handed helical conformation in the polymer backbone. An intriguing ''memory effect'' of the induced macromolecular helicity is observed for some polyacetylenes, which means that the helical conformations induced in dynamic helical polyacetylene can be transformed into metastable static ones by tuning their helix-inversion barriers. Potential applications of helical polyacetylenes with controlled helix sense constructed by the ''noncovalent helicity induction and/or memory effect'' as chiral materials are also described.

A series of cis-poly(biphenylylacetylene) (PBPA) derivatives bearing chiral and achiral pendant groups at the 4’-position of the biphenyl units through an amide (–NHCO–) or carbamate (–NHCOO–) linker were synthesized by polymerization of the corresponding biphenylylacetylene (BPA) monomers that can be readily prepared in one step from a novel amino-functionalized BPA. An excess one-handed helix induction in the PBPAs through covalent and noncovalent chiral interactions and their chiral recognition abilities when used as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were investigated. PBPAs bearing optically-pure L-amino acid residues showed unique two-state helical conformational changes between the extended and contracted helices regulated by the solvent-mediated on/off switching of the intramolecular hydrogen-bonding formations between the pendants or at each pendant. The chiral recognition abilities of the helical PBPAs were significantly influenced by the kinds of the pendant L-amino acid residues. The preferred-handed contracted helical PBPA carrying an L-leucine derived pendant showed an excellent chiral resolving power toward various racemic compounds including axially and point chiral compounds and chiral metal complexes. The elution orders of some racemates were completely reversed when its helical conformation was changed to the extended helix. On the other hand, the trans-enriched nonhelical L-leucine-bound PBPA derived from its preferred-handed cis-helical PBPA and achiral pendant-bound cis-helical PBPAs induced by noncovalent chiral interactions and subsequent static memory of the helicity showed a poor and no chiral recognition, respectively.

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Catalytic ultra‐fast helix induction and its static helicity memory in a poly(biphenylylacetylene) were achieved by using chiral ammonium salts, as reported by Katsuhiro Maeda, Eiji Yashima, and co‐workers in their Research Article (e202217020). The remarkable acceleration of the helix‐induction rate accompanied by strong chiral amplification relies on crown‐ether‐like specific intermolecular complex formation of the two methoxymethoxy groups of the biphenyl pendants with chiral ammonium species.