Helical Polymers Research Articles

Helical supramolecular polymer nanotubes with wide lumen for glucose transport: towards the development of functional membrane-spanning channels.

The manipulation of strong noncovalent interactions provides a concise and versatile strategy for constructing highly ordered supramolecular structures. By using a shape-persistent building block consisting of phenanthroline derivatives and two quadruply hydrogen-bonding AADD moieties, a type of precise helical supramolecular polymer (HSP) nanotube has been developed. The helical conformation of the supramolecular polymers has been proved via various techniques, showing significantly expanded topologies of supramolecular polymers. From the production of new topological structures of supramolecular polymers, predictable properties and functions have arisen. In this study, the helical folding of supramolecular polymers gave rise to the generation of specific wide lumen structures that can be directly visualized via TEM, and the resulting HSP nanotubes can puncture the lipid bilayer membrane to facilitate the transportation of glucose.

One-dimensional single-helix coordination polymer self-assembled by a crown-ether appended-N-heteroacene radical anion.

A crown-ether appended N-heteroacene 1 was reduced in the presence of NaBPh4 to the radical anion 2 by accepting one electron transferred from both the cathode and BPh4- as a reductant. The obtained radical anion 2 can function as a radical anion ligand to bridge two sodium ions to self-assemble into one-dimensional helical coordination polymers.

A homo-chiral helical coordination polymer constructed from an achiral ligand with excellent photo-physical properties and cell imaging application

Polymer 1 was prepared as nanoparticles and added to the culture media, and bright red fluorescence was observed in SH-SY5Y cells.

A series of helical coordination polymers based on two racemic bis(pyridylmethylene) propane-1,2-diamine ligands: relationship of conformations, structures and properties

The self-assembly of d10 metal salts and two racemic bis(pyridyl) diamine ligands generates ten complexes, showing diverse helical and wavelike chains, (4,4) layers, as well as 3D sqc and uog nets.

Molecular tectonics: from a rigid achiral organic tecton to 3D chiral Co and Fe coordination networks.

An achiral organic tecton bearing four coordinating sites of the pyridyl type leads to the formation of iso-structural 3D helical coordination polymers when combined with Co(SCN)2 and Fe(SCN)2 achiral neutral complexes. Their formation occurs during the self-assembly process in the solid state, which leads to crystals composed of homochiral coordination polymers.

Zn and Co redox active coordination polymers as efficient electrocatalysts.

New redox active 1D helical coordination polymers M(fcdHp) (M(ii) = Zn(1), Co(2)) have been obtained by utilizing the 1,1'-ferrocenylenbis(H-phosphinic) acid (H2fcdHp) ligand and Zn or Co nitrate salts. Complexes 1 and 2 are isomorphic, crystallizing in the chiral space groups P4122 and P4322, respectively. Their redox, electrocatalytic and other properties are described. These compounds incorporated into carbon paste electrodes and exhibited reversible redox reactions, arising from the ferrocenyl moiety. These coordination polymers are efficient as electrocatalysts for the reduction of protons to hydrogen. Using N,N-dimethylformamidium ([DMF(H)+]) as the acid in the acetonitrile solution, Co CP (2) displays a turnover frequency of 300 s-1, which is among the fastest rates reported for any CP electrocatalyst in CH3CN. This high rate of catalytic reaction comes at the cost of the 820-840 mV overpotential at the potential of catalysis. As the hydrogen evolution reaction (HER) catalysts, the CPs exhibited in 0.5 M H2SO4 the overpotential η10 of 340 or 450 mV, onset overpotential of 220 or 300 mV (vs. RHE), Tafel slope of 110 or 120 mV dec-1, correspondingly for 1 and 2, and considerable long-term stability for the HER.

Three helical chain-based 3D coordination polymers: solvent-induced syntheses, tunable structures and catalytic properties for the Strecker reaction

Three 3D Sc-CPs with different helical chains have been synthesized from isophthalic acid derivatives by solvent induced methods. Among them, 3 is optically active. Furthermore, 1 exhibits good catalytic activity for the Strecker reactions.

Synthesis of helical π-conjugated polymers bearing pyridine N-oxide pendants and asymmetric allylation of aldehydes in the helical cavity.

Catalytically active chiral π-conjugated polymers (poly-1(NO)r) bearing pyridine N-oxide pendants were synthesized by ternary copolymerization of a d-glucose-bound diethynyl compound with two types of thieno[3,4-b]thiophene comonomer, one of which contained a pyridine N-oxide group. When the pyridine N-oxide content in the copolymer was 10 mol% (poly-1(NO)0.10), the polymer backbone formed a one-handed helical structure in acetonitrile. Pyridine N-oxide pendants arranged inside the helical cavity of poly-1(NO)0.10 exhibited catalytic activity for the asymmetric allylation of benzaldehydes, producing the corresponding allyl alcohols with up to 43% ee.

Nonspherical chiral helical polymer particles with programmable morphology prepared by electrospraying.

Chirality and chiral materials demonstrate ever-growing importance. As a new type of chiral material, chiral polymer particles hold huge potential in both scientific research and practical applications. Meanwhile, nonspherical polymer particles (NPPs) have witnessed substantial progress in recent years because of their unique structures and especially the properties distinguishable from the corresponding spherical particles. We hypothesize that combining chirality with NPPs will open up an unprecedented category of advanced materials. The present contribution reports the first protocol for preparing electrosprayed nonspherical chiral particles constructed from chiral helical polymers, using helical substituted polyacetylenes as the model. SEM images demonstrate the successful fabrication of nonspherical chiral particles with tunable morphologies (bowl-, golf- and apple-like particles). Circular dichroism (CD) measurement proves the remarkable optical activity of the particles, which is observed in the predominantly one-handed helical polymer chains. The present work establishes a novel, versatile, and powerful platform for preparing nonspherical chiral polymer particles with controllable morphology.

Synthesis of a Heterotelechelic Helical Poly(methacrylamide) and its Incorporation into a Supramolecular Triblock Copolymer.

We report the first heterotelechelic helical poly(methacrylamide) (PMAc) bearing orthogonal supramolecular binding sites on its chain-ends synthesized through a combination of reversible addition-fragmentation chain-transfer (RAFT) polymerization and thiol-bromo "click" chemistry. The heterotelechelic PMAc was assembled with two monotelechelic polymers featuring different secondary structures, namely a coil-like poly(styrene) and a helical poly(isocyanide), resulting in the formation of a coil-helix-helix supramolecular triblock copolymer through orthogonal metal coordination and hydrogen bonding interactions. Triblock assembly was confirmed through 1H NMR spectroscopy, isothermal titration calorimetry (ITC) and viscometry. The individual polymer blocks retained their secondary structures in the final triblock copolymer, as evidenced by circular dichroism (CD) spectroscopy. Our synthetic strategy expands the toolbox of triblock copolymers featuring structural motifs similar to the ones found in proteins and provides the potential for the development of other complex multifunctional polymeric ensembles.

Chiral helical substituted polyacetylene grafted on hollow polymer particles: preparation and enantioselective adsorption towards cinchona alkaloids

Hollow polymer particles tethering chiral helical polymer chains and functional carboxyl groups were prepared and applied in enantioselective adsorption.

Combining Chiral Helical Polymer with Achiral Luminophores for Generating Full-Color, On–Off, and Switchable Circularly Polarized Luminescence

Circularly polarized luminescent (CPL) materials are currently drawing ever-increasing interest. This contribution reports the first success in simply combining chiral helical substituted polyacetylenes (HSPAs) with achiral luminophores to fabricate CPL materials demonstrating a high dissymmetry factor (glum) up to 10–1, despite neither covalent nor noncovalent interactions occurring between the two components. Circularly polarized scattering and fluorescence-selective absorption mechanisms are proposed for the generation of CPL, and a “matching rule” is further established for selecting chiral polymers and achiral luminophores for the purpose. Taking advantage of the circularly polarized scattering effect, full-color tunable CPL materials are prepared from the combination of achiral fluorescent dyes and chiral HSPAs. Following the fluorescence-selective absorption mechanism, functional composite films with on–off and switchable CPL performance are fabricated. Also, remarkably, the glum value in the prepa...

Clustering cryo-EM images of helical protein polymers for helical reconstructions

Helical protein polymers are often dynamic and complex assemblies, with many conformations and flexible domains possible within the helical assembly. During cryo-electron microscopy reconstruction, classification of the image data into homogeneous subsets is a critical step for achieving high resolution, resolving different conformations and elucidating functional mechanisms. Hence, methods aimed at improving the homogeneity of these datasets are becoming increasingly important. In this paper, we introduce a new algorithm that uses results from 2D image classification to sort 2D classes into groups of similar helical polymers. We show that our approach is able to distinguish helical polymers that differ in conformation, composition, and helical symmetry. Our results on test and experimental cases — actin filaments and amyloid fibrils — illustrate how our approach can be useful to improve the homogeneity of a data set. This method is exclusively applicable to helical polymers and other limitations are discussed.

Chiral Helical Polymer Nanomaterials with Tunable Morphology: Prepared with Chiral Solvent To Induce Helix-Sense-Selective Precipitation Polymerization

We report an unprecedented strategy for using achiral monomer to construct chiral helical polymer nanomaterials with tunable morphology—helix-sense-selective precipitation polymerization induced by a chiral solvent (HSSPP-CS). CHCl3, chiral α-pinene, and an alkanol were employed to constitute a solvent mixture for performing HSSPP-CS. (R)- or (S)-α-pinene worked as chiral source and transferred its chirality to the resulting helical polyacetylenes derived from achiral monomer in the course of polymerization, thereby forming chiral helical polymers and endowing the nanomaterials thereof with optical activity. Simply changing solvent composition provided chiral polymer products varying in morphology from fibrous to rod-like and finally to spherical morphology. This is the first report dealing with chirality transfer from chiral solvent to induce helix-sense-selective precipitation polymerizations. The study establishes a straightforward and effective alternative for making use of achiral monomers to constru...

Mechanostress resistance involving formin homology proteins: G- and F-actin homeostasis-driven filament nucleation and helical polymerization-mediated actin polymer stabilization

The actin cytoskeleton has two faces. One side provides the relatively stable scaffold to maintain the shape of cell cortex fit to the organs. The other side rapidly changes morphology in response to extracellular stimuli including chemical signal and physical strain. Our series of studies employing single-molecule speckle analysis of actin have revealed diverse F-actin lifetimes spanning a range of seconds to minutes in live cells. The dynamic part of the actin turnover is tightly coupled with actin nucleation activities of formin homology proteins (formins), which serve as rapid and efficient F-actin restoration mechanisms in cells under physical stress. More recently, our two studies revealed stabilization of F-actin either by actomyosin contractile force or by helical rotation of processively-actin polymerizing diaphanous-related formin mDia1. These findings quantitatively explain our proposed anti-mechanostress cascade in that G-actin released from F-actin upon loss of tension triggers frequent nucleation and subsequent fast elongation of F-actin by formins. This formin-restored F-actin may become specifically stabilized over long distance by helical polymerization-mediated filament untwisting. In this review, we discuss how and to what extent formins-mediated F-actin restoration might confer mechanostress resistance to the cell. We also give thought to the possible involvement of helical polymerization-mediated filament untwisting in the formation of diverse actin architectures including chirality control.

Molecular dynamics simulation of polymer-coupled ion transport in the crystalline polymer electrolyte poly(ethylene oxide)3:NaI

While solid polymer electrolytes (SPEs) possess a combination of the requisite properties to merit their use in all-solid-state rechargeable batteries, their low ionic conductivity (σ) at room temperature limits their widespread use in advanced commercial applications. To overcome this limitation, it is necessary to understand the crucial molecular factors that govern the energetics and transport of ions in SPEs. In this Article, all-atom molecular dynamics (MD) and adaptive biasing force (ABF) simulations are used to characterize the mechanism and energetics of polymer-coupled ion transport and to probe the nature of interactions of polymers and ions in a crystalline SPE (PEO3:NaI). In particular, the free energy profiles associated with the cation transport along the polymer helix, the activation energy for hopping of a cation between adjacent energetically favourable coordination sites, and crucial factors determining the features of the free energy profiles are examined. The calculated free energy profiles exhibit well-defined minima (correspond to favourable cation coordination sites) separated by relatively high energy barriers (12–14 kcal/mol) indicating that ion hopping is the likely mechanism of cation transport in PEO3:NaI crystals. The influence of the conformational flexibility of the polymer on the energetics of cation transport is also examined. The dissection of interaction of the cations provides insights into the interplay of ion-ion, ion-polymer, and polymer-polymer interactions in determining the activation barrier for cation transport in the crystalline PEO3:NaI.

Cryo-electron tomography reveals early steps of complement activation by IgM

Inflammasomes are high molecular weight protein complexes that play a crucial role in innate immunity by activating caspase-1. Inflammasome formation is initiated when molecules originating from invading microorganisms activate nucleotide-binding domain and leucine-rich repeat-containing receptors (NLRs) and induce NLR multimerization. Little is known about the conformational changes involved in NLR activation and the structural organization of NLR multimers. Here, we show by cryoelectron tomography that flagellin-induced NAIP5/NLRC4 multimers form right- and left-handed helical polymers with a diameter of 28 nm and a pitch of 6.5 nm. Subtomogram averaging produced an electron density map at 4 nm resolution, which was used for rigid body fitting of NLR subdomains derived from the crystal structure of dormant NLRC4. The resulting structural model of inflammasome-incorporated NLRC4 indicates that a prominent rotation of the LRR domain of NLRC4 is necessary for multimer formation, providing unprecedented insight into the conformational changes that accompany NLR activation.

Enhanced performances of enantioselective permeation through one-handed helical polymer membranes by enantioselective imine exchange reaction with permeants and by partially decomposed reaction of the membrane

Optical resolution by membrane permeation is a very effective continuous method compared with conventional batch methods. We previously reported some optical resolution by simple permeation through chiral poly(substituted acetylene) membranes. In this study, the performances have been improved by the following two methods. One is enantioselective imine exchange reaction of the side imino groups of the polymer membranes with a racemic chiral amine as permeants during permeation. The other is permeation through new composite membranes containing supramolecular polymers by partial in-situ decomposition reaction of the polymer membranes. As a result, permselectivity was enhanced up to 88.5%ee for (RS)-phenylethylamine (PEA).

Intense Circularly Polarized Luminescence Contributed by Helical Chirality of Monosubstituted Polyacetylenes

Introducing fluorescent chromophores to helical architectures can generate circularly polarized luminescence (CPL). Herein, a series of fluorescent chiral helical monosubstituted polyacetylenes showing both intense optical activity and CPL are prepared by copolymerizing achiral fluorescent acetylenic monomer and a chiral monomer. The luminescence dissymmetry factor (glum) values of the obtained copolymers can reach up to +0.136 and −0.264. The formation of predominantly one-handed helical structures in the copolymer backbones has proved to play crucial roles in achieving the intense CPL. The dynamic helical polymer chains further enable the CPL-active materials to exhibit both solvent sensitivity and temperature sensitivity. Moreover, the helical polymer structures can also helpfully restrain the aggregation-caused quenching (ACQ) effect of fluorescent groups. Therefore, the helical polymers play double roles: providing helical chirality for generating CPL and simultaneously circumventing ACQ effect of ch...

Chiral-to-Chiral Communication in Polymers: A Unique Approach To Control Both Helical Sense and Chirality at the Periphery.

A novel approach to the classical Sergeants and Soldiers effect, using chiral Sergeants and chiral Soldiers, allows control over both helical and external chirality in helical polymers. In the systems reported here, it is possible to induce the same helical sense ( M or P) from either of the two enantiomers of a chiral pendant group ["chiral Soldier", major component; i.e., ( R)- or ( S)-1] when it faces a single enantiomer of an appropriate "chiral Sergeant" [minor component; i.e., ( S)-2]. For instance, the copolymer series poly[( R)-1 r- co-( S)-2(1- r)], poly[( S)-1 r- co-( S)-2(1- r)], and poly[( rac)-1 r- co-( S)-2(1- r)] adopt the same P helix even though the major component shows the opposite absolute configuration. This chiral-to-chiral communication effect is transmitted by the stabilization of different conformations in each enantiomeric form of the Soldier. As a result, this groundbreaking approximation to the Sergeants and Soldiers effect allows the preparation of a single-handed helix-which depends only on the Sergeant's configuration-with different chiralities on the helix periphery. Thus, a P helix can be decorated with the R isomer, S isomer, or even a racemic mixture of the chiral Soldier. A change in the absolute configuration of the Sergeant affords the opposite M helix, which can also be decorated with the R isomer, S isomer, or racemic mixture of the chiral Soldier.