Helical Polymers Research Articles

A Track-Based Molecular Synthesizer that Builds a Single-Sequence Oligomer through Iterative Carbon-Carbon Bond Formation

Summary We report an artificial molecular machine that moves along a track, iteratively joining building blocks to form an oligomer of single sequence with a continuous backbone of carbon-carbon bonds. The rotaxane features a macrocycle bearing an aldehyde-terminated chain and an axle containing different phosphonium ylides separated by rigid spacers. Each ylide is large enough to block the passage of the macrocycle, trapping the ring between the stopper at the terminus of original threading and the next ylide along the track. Once a building block is reachable, it is removed from the track through a Wittig reaction that adds it to the terminus of the growing chain. Operation on a four-barrier tetra(phosphonium salt) track produces a tetra(diphenylpropane) of single sequence linked through alkene bonds. The prototype extends the principle for molecular machines that build polymers by moving along tracks to the synthesis of sequence-encoded chains with continuous carbon backbones.

Trace Quantity Detection of H2PO4– by Fluorescent Metal–Organic Framework (F-MOF) and Bioimaging Study

Drinking water quality management and sustainable environment to water bodies are a major concern to Public Health Engineering departments. Inorganic Phosphate (Pi), one of the major inorganic pollutants, is addressed for the last two decades regarding trace quantity detection. Over the past few years, a large number of fluorescent metal-organic frameworks (F-MOFs) have been studied to explore the desirable method for selective water analysis. In this article, a Zn(II) 3D F-MOF, {[Zn2(PCDF-INH)(BDC)2].(H2O)}n (1) (H2BDC = 1,4-Benzenedicarboxylic acid, and PCDF–INH = N, Nʹ-diisonicotinoyl-2-hydroxy-5-methyl-isophthalaldehyde dihydrazone) is used for selective recognition of H2PO4− anion by ‘turn-off’ fluorescent sensing technique. Single-crystal X-ray analysis accounts that the asymmetric unit is constituted of two different Zn(II) centres by PCDF–INH and the bridging group, BDC2− ions are responsible for the generation of helical polymer and the biporous structures (14.807×13.096 A2 and 24.905×24.932 A2). The compound, 1, exhibits strong emission at 505 nm in CH3OH-H2O solution and is 'turn-off' upon the addition of H2PO4−. The selectivity and specificity for H2PO4− have been checked in the presence of fifteen different anions including different phosphates (PO43−, HPO42−, P2O74−). The entire sensing activity of 1 is examined by spectrofluorometric method, 1H–NMR titration, PXRD analysis, bio-imaging study, and the limit of detection is 3.903 μM. However, in vitro bio-sensing analysis confers that F-MOF (1) is sensible toward the H2PO4− ion at a trace level in the human lung fibroblast cells and human liver cancer cell line Hep G2.

Engineering Organization of DNA Nano-Chambers through Dimensionally Controlled and Multi-Sequence Encoded Differentiated Bonds.

Engineering the assembly of nanoscale objects into complex and prescribed structures requires control over their binding properties. Such control might benefit from a well-defined bond directionality, the ability to designate their engagements through specific encodings, and the capability to coordinate local orientations. Although much progress has been achieved in our ability to design complex nano-objects, the challenges in creating such nano-objects with fully controlled binding modes and understanding their fundamental properties are still outstanding. Here, we report a facile strategy for creating a DNA nanochamber (DNC), a hollow cuboid nano-object, whose bonds can be fully prescribed and complexly encoded along its three orthogonal axes, giving rise to addressable and differentiated bonds. The DNC can host nanoscale cargoes, which allows for the integration with functional nano-objects and their organization in larger-scale systems. We explore the relationship between the design of differentiated bonds and a formation of one-(1D), two-(2D), and three-(3D) dimensional organized arrays. Through the realization of different binding modes, we demonstrate sequence encoded nanoscale heteropolymers, helical polymers, 2D lattices, and mesoscale 3D nanostructures with internal order, and show that this assembly strategy can be applied for the organization of nanoparticles. We combine experimental investigations with computational simulation to understand the mechanism of structural formation for different types of ordered arrays, and to correlate the bonds design with assembly processes.

Recyclable Helical Poly(phenyl isocyanide)-Supported l-Proline Catalyst for Direct Asymmetric Aldol Reaction in Brine

A novel helical poly(phenyl isocyanide) bearing Boc protected l-proline pendants (poly-1m) was designed and synthesized. Removed the protecting Boc groups on the l-proline pendants led to the formation of helical polymer poly-2m, which showed high optical activity owing to the preferred right-handed helix of polyisocyanide main chain. Optically active helical poly-2m showed excellent catalytic ability on asymmetric aldol reaction. Helical polymer catalysts exhibited enhanced stereoselectivity in aldol reaction compared to small molecule l-proline. Under the optimized aldol reaction condition, the enantiomeric excess (ee) and diastereomeric ratio (dr) values of the aldol reaction product were respectively up to 90% and > 20/1. Moreover, the helical polyisocyanide catalyst Poly-2m can be easily recovered and reused in the aldol reaction for at least five cycles with maintained its activity and stereoselectivity. Enantioselective aldol reaction catalyzed by poly-2m.

Aggregation-Induced Emission-Active Chiral Helical Polymers Show Strong Circularly Polarized Luminescence in Thin Films

Circularly polarized luminescence (CPL) materials with aggregation-induced emission (AIE) performance have attracted extensive attention. In this study, we successfully achieve CPL emissions in chi...

Design and Construction of Cross-Linked PEO with the Integration of Helical Polyurethane as an Advanced All-Solid-State Polymer Electrolyte for Lithium Batteries

All-solid-state polymer electrolytes (SPEs) have been regarded as an advisible alternative for simultaneously overcoming the safety issues and high energy density demands presented in traditional lithium batteries, and they represent the development orientation of energy storage devices. This course describes the preparation of a cross-linked and helical polyurethane modified poly(ethylene oxide) (PEO@HPU) and its utilization as the SPE in lithium batteries, which can be used to teach upper-division undergraduates the principle of energy storage devices and the role of liquid-free electrolytes. Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopies are used to determine the structure of the polymers. The ionic conductivity, lithium ion transference number, and electrochemical window of PEO@HPU are measured through an electrochemical workstation. The lithium batteries assembled by students are evaluated via a battery testing system. The modification by the special helical polymer obviously improves the electrochemical and battery performance of the PEO-based SPE. Upon completion of the experiment, students will understand the structure–activity relationship in materials science and propose new suggestions for designing advanced SPEs. This experiment requires well-prepared laboratory chemicals as well as long-term processes, so it is suitable to be considered as a project. Meanwhile, it can be also used for senior projects and interdisciplinary projects between engineering and science.

Cryo-EM of Helical Polymers at Near-atomic Resolution Yields Many Surprises

Cryo-EM of Helical Polymers at Near-atomic Resolution Yields Many Surprises

Chiral PDTDH-based electrode modification material for L/D-tartaric acid electrochemical sensing

In this work, a kind of chiral helical polymer PDTDH of 9,9-dipropynylfluorene skeleton structure were prepared. The structure and chiral properties of the obtained polymer were characterized by Nuclear Magnetic Resonance (NMR) and Circular Dichroism (CD) Spectroscopy. These chiral PDTDH polymers were used to fabricate chiral sensors and to investigate the enantioselective recognition of D−/L- tartaric acid enatiomer. The results indicated that the (S)-PDTDH/GCE sensor showed obvious response toward the tested tartaric acid enantiomer, which was confirmed by two parameters: Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) tests. These findings expand the scope for the application of chiral polymer as electrode modification material in the electrochemical chiral recognition field.

Macromolecular Chiral Amplification through a Random Coil to One-Handed Helix Transformation Induced by Metal Ion Coordination in an Aqueous Solution

Many inspiring achievements have been made in inducing chiral amplification in helical polymers; however, the induction of helical chirality in random coil polymers by the intermolecular noncovalen...

Catalytic one-handed helix-induction and memory of amphiphilic poly(biphenylylacetylene)s in water

A series of amphiphilic biphenylylacetylene-based homo- and copolymers (PBPAs) carrying chiral and/or achiral oligo(ethylene glycol) pendants at the 4′-position of the biphenyl units were synthesized and the amplification of the macromolecular helicity through noncovalent and/or covalent chiral interactions followed by the memory of the helicity were investigated in both water and organic solvents. The macromolecular helicity was efficiently induced in the homopolymers of achiral monomers through specific encapsulation of a catalytic amount of hydrophobic chiral guests in water and their induced helicities were stably memorized in water after complete removal of the optically-active guests, while an excess helical sense was not biased at all in the homopolymers in toluene. One-handed macromolecular helicities were also efficiently induced in the chiral homopolymers through chiral information transfer from covalently linked optically-active pendants with a point chirality to biphenyl units with a dynamic axial chirality, whose helical senses were almost perfectly inverted in water and organic solvents. The achiral/chiral copolymers displayed a unique bidirectional (P and M) strong chiral amplification of the macromolecular helicity in water and toluene assisted by the solvent-induced helix-inversion, and their macromolecular helicities were further enhanced or inverted through encapsulation of a catalytic amount of enantiomeric alcohols in water, which could be further memorized in water after removing the encapsulated guests. We also demonstrated that the left- and right-handed circularly polarized lights could be generated through chirality transfer from the one-handed helical polymers with a macromolecular helicity memory, consisting entirely of achiral monomer units, to an achiral fluorescent dye in the blended films. Importantly, the resulting luminescence dissymmetry factors (ca. 2 × 10–3) were virtually the same as those of chiral homopolymers composed of the optically-pure repeating units.

Hybrid Helical Polymer Nanochannels Constructed by Combining Aromatic Amide and Pyridine‐Oxadiazole Structural Sequences

An effective method is reported to synthesize aromatic helical polymer nanochannels by combining both the well-studied aromatic amide helical codons with pyridine-oxadiazole helical codons into helical structure sequences. With this strategy, a type of helical polymer nanochannel that shows structure-directed transmembrane transport functions is synthesized. Although such nanochannels show relatively weak selectivity for the transportation of alkali metal ions, accessible chemical mutation of helical structure sequences will provide a great chance for the design of desired channel property. The straightforward preparation of well-established pyridine-oxadiazole helical structure will significantly promote the synthesis of this kind of aromatic helical polymer nanochannels. With the development of aromatic amide foldamers, moreover, a number of "monomers" will be available for the preparation of helical polymer nanochannels.

Helical Coordination Polymers Based on Keggin‐type POMs and N‐donor Ligand

Two new 1D helical coordination polymers based on polyoxometalate were synthesized by self‐assembly of Keggin‐type POMs and copper salts in the presence of triangular N‐heterocyclic derivatives or long‐chain N‐containing carboxylate ligand, that are, (H3O)[{Cu(H2tpim)2}{SiMo12O40}]·0.5H2O [Htpim = 2,4,5‐tri(4‐pyridyl)‐imidazole] (1) and [Cu2(Hcpp)3(cpp)(H2O)][PMo12O40]·2H2O [Hcpp = 1‐(4‐cyanobenzyl)‐3–2‐yl)pyrazole] (2). Their structures were determined by single‐crystal X‐ray diffraction and further characterized by elemental analyses and TG analyses. Compounds 1 and 2 exhibit (1D→2D) interdigitated architectures assembled from 1D helical chains. In compound 1, the achiral 2D interdigitated nets containing left‐ and right‐handed helixes are further interdigitated with each other to form a 3D supramolecular framework. In compound 2, adjacent 2D interdigitated layers with opposite chirality are further extended by supramolecular interactions into a 3D supramolecular network, in which non‐coordinating Keggin‐type POMs as guests are encapsulated.

Helical supramolecular polymers with rationally designed binding sites for chiral guest recognition

Since various helical supramolecular polymers became available, their application to molecular chirality recognition have been anticipated but not extensively studied. So far, only a few examples of chiral reactions have been reported, but none for chiral separation. Here, we report the application of a helical supramolecular polymer to the enantio-separation of chiral guest molecules. The monomer of this supramolecular polymer is the salt-pair of a dendritic carboxylic acid with an enantiopure amino alcohol. In an apolar solvent, this salt-pair stacks via hydrogen bonds to form a helical polymer. In conjunction with this carboxylic acid, various amino alcohols afford supramolecular polymers, whose helical handedness is determined by the stereochemistry of the amino alcohols. When two salts with the same chirality are mixed, they undergo copolymerization, while those with opposite chirality do not. Owing to this stereoselective copolymerizability, the helical supramolecular polymer could bias the enantiomeric composition of chiral amino alcohols.

Helical polymers for biological and medical applications.

Helices are the most prevalent secondary structure in biomolecules and play vital roles in their activity. Chemists have been fascinated with mimicking this molecular conformation with synthetic materials. Research has now been devoted to the synthesis and characterization of helical materials, and to understand the design principles behind this molecular architecture. In parallel, work has been done to develop synthetic polymers for biological and medical applications. We now have access to materials with controlled size, molecular conformation, multivalency or functionality. As a result, synthetic polymers are being investigated in areas such as drug and gene delivery, tissue engineering, imaging and sensing, or as polymer therapeutics. Here, we provide a critical view of where these two fields, helical polymers and polymers for biological and medical applications, overlap. We have selected relevant polymer families and examples to illustrate the range of applications that can be targeted and the impact of the helical conformation on the performance. For each family of polymers, we briefly describe how they can be prepared, what helical conformations are observed and what parameters control helicity. We close this Review with an outlook of the challenges ahead, including the characterization of helicity through the process and the identification of biocompatibility.

Highly Efficient Exclusion of Alkali Metal Ions via Electrostatic Repulsion Inside Positively Charged Channels.

Understanding of the structure-function relationships of natural protein channels remains a challenging task because of their unattainable physiological functions in terms of selectivity. To achieve this, a synthetic system of chemically modified channels has been constructed based on helical polymer scaffolds. Here, we report a type of positively charged channels in which multiple quaternary ammonium groups are covalently modified on the lumen surface of helical polymer while the helical conformation is intact. Compared to unmodified channels, the existence of multiple charged groups in the cavity not only makes the lumen size narrower but also essentially changes the channel properties without obstructing channel structure. Our study indicates that positively charged channels preferentially transport anions with size-dependent selectivity, whereas alkali metal ions are almost completely suppressed by electrostatic repulsion. As a consequence, a specific artificial channel with high Cl-/Na+ selectivity ratio of 41:1 is obtained.

Switching between Stacked Toroids and Helical Supramolecular Polymers in Aqueous Nanotubules.

Although significant advances have been made in supramolecular tubules, reversible polymerization in the tubular walls while maintaining their intact structure remains a great challenge. Here, reversible helical supramolecular polymerization of stacked toroids is reported, while maintaining tubular structures in aqueous solution. At room temperature, the tubules consist of discrete toroid stackings with hydrophobic interior. Upon heating, the tubules based on toroid stackings undergo a reversible helical supramolecular polymerization to transform into helical tubules by interconnecting between spirally open toroids. The helical polymerization arises from a tilting transition of the closed toroids that transform into spirally open toroids driven by the thermal dehydration of a hydrophilic oligoether dendron surrounding the toroid frameworks.

Polymeric Helical Structures à la Carte by Rational Design of Monomers

Preparation of helical structures a la carte by monomer design of dynamic helical polymers such as poly(phenylacetylene)s (PPAs) is a difficult task due to conformational freedom of the polyene bac...

Chiral Diketopyrrolopyrrole-Helicene Polymer With Efficient Red Circularly Polarized Luminescence.

Chiral diketopyrrolopyrrole (DPP)-helicene polymers were synthesized to develop efficient red circularly polarized (CP) light emitters. These original chiral dyes display intense electronic circular dichroism (ECD) and CP luminescence (CPL) in the far-red spectral region owing to the presence of excitonic coupling between achiral DPPs within the chiral environment of the polymeric structure. This work affords an interesting example illustrating the potential of π-conjugated helical polymers for chiral optoelectronic applications.

Raman Optical Activity (ROA) as a New Tool to Elucidate the Helical Structure of Poly(phenylacetylene)s

AbstractPoly(phenylacetylene)s are a family of helical polymers constituted by conjugated double bonds. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them good candidates to be studied by Raman optical activity (ROA). Four different well‐known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. Raman and ROA spectra were recorded and allowed to establish ROA‐spectrum/helical‐sense relationships: a left/right‐handed orientation of the polyene backbone (Mhelix/Phelix) produces a triplet of positive/negative ROA bands. Raman and ROA spectra of each polymer exhibited the same profile, and the sign of the ROA spectrum was opposite to the lowest‐energy electronic circular dichroism (ECD) band, indicating a resonance effect. Resonance ROA appears then as an indicator of the helical sense of poly(phenylacetylene)s, especially for those with an extra Cotton band in the ECD spectrum, where a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignment.

Raman Optical Activity (ROA) as a New Tool to Elucidate the Helical Structure of Poly(phenylacetylene)s

Poly(phenylacetylene)s is a family of helical polymers constituted by conjugated double bonds that are fixed into specific helical structures due to supramolecular and/or steric interactions among pendant groups. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them great candidates to study their helical structure by Raman Optical Activity (ROA). Four different well-known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. For all of these, Raman and ROA spectra were recorded which allows us to establish ROA spectrum/helical sense relationships: a right-handed orientation of the polyene backbone (P helix ) produces a triplet of negative ROA bands, whereas a M helix produces a positive triplet ROA pattern. Raman and ROA spectra of each polymer exhibited the same profile and the sign of the ROA spectrum was opposite to the lowest energy ECD band, thus indicating a resonance effect. Resonance ROA appears then as a useful selective indicator of the helical sense of poly(phenylacetylene)s, especially for those showing an extra Cotton band in the ECD spectrum. In these cases, a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignment.