Chiral Recognition and Resolution Based on Helical Polymers

Controlled synthesis of β-cyclodextrin-based starlike helical poly(phenyl isocyanide) and its application in chiral resolution

In an effort to expand the diversity of helical polymers exhibiting intricate structures, a strategy for the precise fabrication of β-cyclodextrin-based star polymers adorned with helical poly(phenyl isocyanide) (PPI) arms has been successfully realized through the integration of isocyanide polymerization and atom transfer radical polymerization (ATRP). An elegant β-cyclodextrin embellished with 7 Pd(II) complexes on one side and 14 bromine groups on the other side, denoted as ((Pd(II))7-CD-(Br)14), was initially synthesized. Subsequently, the (PPI)7-CD-(Br)14 was synthesized through the polymerization of the phenyl isocyanide monomer initiated with (Pd(II))7-CD-(Br)14. Finally, starlike PPI was obtained by ATRP of 1,2-diacrylyl ethane initiated via the macro-initiator of (PPI)7-CD-(Br)14. Circular dichroism measurement analysis indicated that the obtained starlike PPI exhibited a consistent helical conformation with a preferred handedness, and it was revealed that the helical structure of starlike PPI originated from the PPI backbone, rather than intermolecular aggregation in solutions. Furthermore, the starlike PPI demonstrated excellent efficacy in the chiral resolution of racemic compounds, achieving an enantiomeric excess (e.e.) of 92 % for threonine racemates when used as a chiral resolution agent.

Helical Polymer-Containing Bottlebrush Polymers (BBPs): Design, Synthesis, and Perspectives

Helical polymer-containing bottlebrush polymers (BBPs) are a special and fascinating type of polymer. They possess bottlebrush topology and contain helical polymers as main chains (MCs) or side chains (SCs), thereby presenting interesting and fantastic properties, such as chiral amplification, circularly polarized luminescence, photonic crystal, and so on. This review mainly focuses on BBPs containing helical polymers of polypeptides, polyacetylenes (PAs), and polyisocyanides (PIs). Detailed summarizations are severally given to BBPs with helical polypeptides as MCs and SCs. Meanwhile, BBPs comprising helical PAs as MCs are fully discussed. What's more, BBPs consisted of helical PIs as MCs and SCs are described separately. In addition, BBPs with other helical polymers are briefly introduced, too. The authors hope this review will motivate more interest in developing helical polymers with complex topologies and fascinating properties, and encourage further progress in functional chiral materials.

Chiral Polymers Based on Vinyl[2.2]paracyclophane and Their Application as CPL Emitters

Chiral molecules are integral to various biological and artificial systems, influencing processes from chemical production to optical activities. In this study, we explore the potential of chiral vinyl[2.2]paracyclophane (vinyl-PCP) as a monomer for the synthesis of homopolymers and copolymers with styrene. We achieved polymerization through anionic, cationic, and radical methods. The resulting polymers demonstrated significant chiral properties, even in copolymers with small fractions of the chiral monomer. Further, we developed a polymerizable vinyl emitter from 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (DMAC-TRZ) through a two-step synthesis with an overall yield of 48%. Copolymerization with chiral vinyl-PCP resulted in emissive polymers that demonstrated circularly polarized luminescence (CPL) properties. The inclusion of the chiral PCP monomer, acting both as a host material and the source of chirality for CPL, enhanced the photoluminescence quantum yield (PLQY) to 47.2% in N2 at 5-10% emitter content, compared to 26.8% for the pure emitter polymer. CPL-active polymers show clear mirror-image Cotton effects at 240 nm and 267 nm and dissymmetry factors around +2 × 10-4 and -1 × 10-4. This self-hosting effect of PCP monomers underscores the potential of chiral vinyl-PCP for advanced functional materials in optical communication and bio-responsive imaging.

Stereoselective Crystallization of Chiral Pharmaceuticals Aided by Cellulose Derivatives through Helical Pattern Matching

Stereoselective inhibition aided by "tailor-made" polymeric additives is an efficient approach to obtain enantiopure compounds through conglomerate crystallization. The chemical and configurational match between the side groups of polymers and the molecules of undesired enantiomer is considered to be a necessary condition for successful stereoseparation. Whereas in this contribution, we present an effective resolution of chiral pharmaceuticals by using cellulose acetates as the additives, which stereoselectively reside on the specific crystal faces of one enantiomer and inhibit its crystal nucleation and growth through helical pattern and supramolecular interaction complementarity. An investigation of nimodipine serves as a case study to highlight the novelty of this strategy wherein R-crystals exhibiting an impressive enantiomeric excess value of 97 % can be attained by employing a mere 0.01 wt % cellulose acetate. Guaifenesin and phenyl lactic acid are also well-resolved by utilizing this methodology. Our work not only brings about a brand-new design strategy for "tailor-made" additives, but will also promote the further exploration of the endless potential for utilizing natural biomolecules in chiral recognition and resolution.

Chiral Acetal-Based Stereo-Controlled Degradable Polymer Synthesis

The precise synthesis of chiral polymers remains a significant challenge in polymer chemistry, particularly for applications in advanced biomedical and electronic materials. The development of degradable polymers is important for eco-friendly and advanced materials. Here, we introduce a stereo-controlled degradable polymer via cascade enyne metathesis polymerization and enantioselective acetal synthesis through Pd-catalyzed asymmetric hydroamination. This approach allows for the creation of chiral acetal-based polymers with controlled stereochemistry and degradability, highlighting their potential for use in drug delivery and electronic applications. This concept article reviews the background, development, and potential applications of these stereo-controlled degradable polymers.

Exploring enantioselective recognition of dTMP-Co-bpe coordination polymer for natural amino acids using molecular simulations and circular dichroism

The 1D homochiral coordination polymer (CP-1) {[Co(dTMP)(bpe)2(H2O)3]·9H2O}n was constructed by using 2'-deoxy thymidine 5'-monophosphate disodium salt (dTMP·2Na), and auxiliary ligand bpe (1,2-bis(4-pyridyl)ethene) and characterized by single-crystal XRD, PXRD, IR, UV-visible, CD and TGA analyses. Molecular simulations revealed the selective chiral behaviour of CP-1 towards phenylalanine and histidine, as indicated by their higher binding free energies compared to other amino acids. Theoretical parameters were also compared with experimental UV-visible verdicts. Notably, the D-enantiomers of phenylalanine and histidine demonstrated strong bonding abilities and optimal configurations for probing and distinguishing them from their L-counterparts. These findings led to propositions suggesting that the dissimilarities between these D and L amino acid forms and their binding orientations with CP-1 may contribute to alterations in the CD signal. CP-1 exhibited a robust inherent circular dichroism (CD) signal in aqueous solutions, modulated by the presence of specific amino acids, namely D/L phenylalanine and D/L histidine. Leveraging the measurement of CD signal intensity, a sensor capable of detecting unmodified amino acids has been developed. Unlike previously reported approaches that relied on complex chemical reactions between initially CD-silent molecules and probed amino acids, this new method offers a more straightforward means of amplifying the CD signal. Consequently, this change facilitates a more accurate differentiation between the enantiomers of these specific amino acids compared to others.

Polymers with Circularly Polarized Luminescent Properties: Design, Synthesis, and Prospects

Chiral materials with circularly polarized luminescence (CPL) have garnered significant attention owing to their distinctive luminescent properties and wide array of applications. CPL enables the selective emission of left and right circularly polarized light. The fluorescence quantum yield and dissymmetry factor play pivotal roles in the generation of CPL. Helical polymers exhibit immense promise as CPL materials due to their inherent chirality, structural versatility, modifiability, and capacity to incorporate diverse chromophores. This Review provides a brief review of the synthesis of CPL materials based on helical polymers. The CPL can be realized by aggregation-induced CPL of non-emissive helical polymers, and helices bearing chromophores on the pendants and on the chain end. Furthermore, future challenges and potential applications of CPL materials are summarized and discussed.

Homohelical Self-Assembly of Trimer of α-Cyclodextrin and Octamolybdate

The ability to conceptually mimic biomolecules to construct emergency-functional homospiral aggregates remains a long-standing challenge. Herein, we report artificial homohelical assembly by blending inorganic polyoxometalates (POMs) and organic cyclodextrin molecules. The chiral double-helical chains have been achieved by a left-hand arrangement of trimer-trimer. The trimer is formed by three {Mo8}@α-CD inclusive complexes as a Whittaker-style paddle wheel. During the process of assembly, chiral transfer and amplification from molecule to superstructure were observed. The enantioselective adsorption of the homohelical aggregate toward (R/S)-1,1'-binaphthyl-2,2'-diamine was further demonstrated. The interaction of {Mo8} and α-CD in solution was investigated. This work opens a wide scope for the design of a homohelix, enriching POM-based inorganic-organic materials.

Study on Asymmetric Vibrational Coherent Magnetic Transitions and Origin of Fluorescence in Symmetric Structures

In this work, the physical mechanisms of three highly efficient circularly polarized luminescent materials are introduced. The UV-vis spectra are plotted; the transition properties of their electrons at the excited states are investigated using a combination of the transition density matrix (TDM) and the charge difference density (CDD); combining the distribution of electron clouds, the essence of charge transfer excitation in three structures is explained. The resonance Raman spectrum of the three structures at the S1 and S2 excited states are calculated. The M, M-4 and M, M-5 structures are found to produce novel chirality by electronic circular dichroism (ECD) spectrum, and the reasons for the chirality of the M, M-4 and M, M-5 structures are discussed by analyzing the density of transition electric/magnetic dipole moments (TEDM/TMDMs) in different orientations. Finally, the Raman optical activity (ROA) of M, M-4, and M, M-5 are calculated, and the spectra are plotted. This study will provide guidance for the application of carbon-based nanomaterials in organic electronic devices, solar cells, and optoelectronics.

Recent advances of optically active helical polymers as adsorbents and chiral stationary phases for chiral resolution

Chiral resolution is very important and still a big challenge due to different biological activity and same physicochemical property of one pair (R)- and (S)-isomer. There is no doubt that chiral selectors are essentially needed for chiral resolution, which can stereoselectively interact with a pair of isomers. To date, a large amount of optically active helical polymers as chiral selectors have been synthesized via two strategies. First, the target helical polymers are derived from natural polysaccharide such as cellulose and amylose. Second, they can be synthesized by polymerization of chiral monomers. Alternatively, an achiral polymer is prepared first followed by static or dynamic chiral induction. Furthermore, a part of them is harnessed as chiral stationary phases for chromatographic chiral separation and as chiral adsorbents for enantioselective adsorption/crystallization, resulting in good enantioseparation efficiency. In summary, the present review will focus on recent progress of the polymers with optical activity for chiral resolution, especially the literature published in the past 10 years. In addition, development prospects and future challenges of optically active helical polymers will be discussed in detail.

Helical Crystals in Aliphatic Copolyesters: From Chiral Amplification to Mechanical Property Enhancement

We demonstrate herein a bottom-up strategy for achieving helical crystals via chiral amplification in copolyesters by incorporating a small amount of (d)-isosorbide into semicrystalline polyester, poly(ethylene brassylate) (PEB). During bulk crystallization of poly(ethylene-co-isosorbide brassylate)s, the molecular chirality of isosorbide in the amorphous region is transferred to PEB crystal chirality and amplified by the formation of right-handed helical crystals. Increasing isosorbide content or reducing crystallization temperature leads to thinner PEB lamellae crystals, strengthening chiral amplification by forming superhelices with a smaller helical pitch. Moreover, the superhelices with smaller helical pitch (larger chiral amplification) endow aliphatic copolyesters with enhanced modulus, strength, and toughness without sacrificing elongation-at-break. The principle outlined here could apply to the design of strong and tough materials.

Ultra-Fast Portable and Wearable Sensing Design for Continuous and Wide-Spectrum Molecular Analysis and Diagnostics

The design and characterization of spatiotemporal nano-/micro-structural arrangement that enable real-time and wide-spectrum molecular analysis is reported and demonestrated in new horizons of biomedical applications, such as wearable-spectrometry, ultra-fast and onsite biopsy-decision-making for intraoperative surgical oncology, chiral-drug identification, etc. The spatiotemporal sesning arrangement is achieved by scalable, binder-free, functionalized hybrid spin-sensitive (<↑| or <↓|) graphene-ink printed sensing layers on free-standing films made of porous, fibrous, and naturally helical cellulose networks in hierarchically stacked geometrical configuration (HSGC). The HSGC operates according to a time-space-resolved architecture that modulate the mass-transfer rate for separation, eluation and detection of each individual compound within a mixture of the like, hereby providing a mass spectrogram. The HSGC could be used for a wide range of applictions, including fast and real-time spectrogram generator of volatile organic compounds during liquid-biopsy, without the need of any immunochemistry-staining and complex power-hungry cryogenic machines; and wearable spectrometry that provide spectral signature of molecular profiles emiited from skin in the course of various dietry conditions.

Synthesis of Optically Active Helical Polycarbenes through Helix-Sense-Selective Polymerization Strategy and Their Application in Chiral Separation

In this work, helical polycarbenes with optical activity were designed and facilely synthesized through the helix-sense-selective polymerization (HSSP) of the diazoacetate monomer with a dimethylbenzyl ester pendant catalyzed by π-allylPdCl with chiral phosphine ligands at room temperature. The polymerization was carried out in a living and controlled style, and a range of helical polycarbenes with the desired number-average molecular weights and narrow molecular weight distributions were obtained. Circular dichroism and UV-vis analyses revealed that these polycarbenes exhibited a stable helical conformation with a preferred handedness, and their helical directions were dependent on the chirality of the chiral phosphine ligands. Further studies showed that the helical conformation of the obtained polycarbenes was from the polymeric backbone rather than the intermolecular aggregation in the solutions. Moreover, the prepared, optically active, helical polycarbenes possessed excellent enantioselective crystallization ability for threonine racemates. The enantiomeric excess (e.e.) of the induced crystals could be up to 83% via utilizing the prepared helical polycarbenes as a chiral separation agent.

Self-assembly of Helical Polymers and Oligomers to Create Liquid Crystalline Alignment for Anisotropic NMR Parameters

The measurement of anisotropic residual dipolar couplings (RDCs) parameters for the structure elucidation of organic molecules relies on suitable alignment media. Employment of self-assembled liquid crystalline systems to create anisotropic alignment can be an effective way to realize aligned samples and acquire RDCs. This Mini-review highlights the recent advances on amino acid-based helical polymers and supramolecular oligomers forming rigid, rod-like structures that aggregate into ordered liquid crystalline phases, including amino acid-based helical polyisocyanides, polyacetylenes, polypeptides, and oligopeptides assembled alignment media. The methodology for the determination of anisotropic liquid crystals was briefly discussed, and a summary of recent research progress in the enantiodifferentiation of helical polymers aligned media was followed. In addition, the self-assembled mechanism of oligopeptides and their RDCs structural analysis were also described. This article is protected by copyright. All rights reserved.

Thermotropic chirality enhancement of nanoparticles constructed from foldamer/bis(amino acid) complexes

Herein, chiral nanoparticles are constructed by mixing an artificial foldamer bearing aza-18-crown-6 pendants with l-homocystine perchlorate salt, showing a thermotropic chirality enhancement due to the binding mode changes in the heating process.

Synthesis and properties of helical polystyrene derivatives with amino acid side groups

A series of polystyrene derivatives with chiral amide groups with a controlled molecular weight and narrow molecular weight distribution were synthesized by reversible addition–fragmentation chain transfer (RAFT) radical polymerization.

Recent advances in asymmetric organocatalysis based on helical polymers

The significant research progress (from 2011 to 2021) in artificial helical polymers, such as polyacetylenes, polyisocyanides, polycarbenes, etc., in the fields of asymmetric organocatalysis is described.

Recent advances in helical polyacetylene derivatives used as coated chiral stationary phases for enantioseparation

The development of helical polyacetylene derivatives bearing different kinds of chiral pendants and the enantioseparation based on these helical polymers as coated CSPs for HPLC will be described.

Supramolecularly cross-linked nanoassemblies of self-immolative polyurethane from recycled plastic waste: high encapsulation stability and triggered release of guest molecules

Stabilizing noncovalently encapsulated guest molecules inside a nanoassembly constructed from amphiphilic polymers has become a very challenging effort in the area of targeted drug delivery of biomedical applications. The unwanted...

Visualisation of helical structures of poly(diphenylacetylene)s bearing chiral amide pendants by atomic force microscopy

The helical structures of poly(diphenylacetylene)s bearing optically active substituents linked through amide bonds and with a helicity memory have been visualised using atomic force microscopy. The polymers self-assembled into an ordered 2D monolayer on highly oriented pyrolytic graphite upon exposure to solvent vapour, whose helical pitch and handedness (right- and left-handed) were for the first time directly revealed at molecular resolution.