Helical Superstructures from the Hierarchical Self-Assembly of Coil-Coil Block Copolymer Guided by Side Chain Amyloid-β(17-19) LVF Peptide

The rational design of precisely controlled hierarchical chiral nanostructures from synthetic polymers garnered inspiration from sophisticated biological materials. Since chiral peptide motifs induce helix formation in macromolecules, herein we report the synthesis of a novel type of hybrid polymer consisting of a β-sheet forming a LVF [L = leucine, V = valine, and F = phenylalanine] tripeptide pendant polymethacrylate block and a poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) block. The designed block copolymer self-organized into helical superstructures with a left-handed twisting sense, as visualized by field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. This intriguing hierarchical self-assembly is driven by the minimalistic peptide motif that itself has a high propensity to adopt an antiparallel β-sheet conformation. We also report the generation of a diverse array of nanostructures, including spherical micelles, spindle micelles, rod-like micelles, vesicles, helical supramolecular fibers, and helical toroids via self-assembly of the designed block copolymer in tetrahydrofuran/water mixed solvents. To realize the observable helical superstructure, a twisted two-dimensional core-shell tape is proposed as a structure model in which the peptide segments form an antiparallel β-sheet with a polymer shell. The findings contribute to the advancement of a helical polymer or the superhelical self-assembly of polymers, paving the way for diverse applications in materials science and related fields.

Block Copolymer Enabled Synthesis and Assembly of Chiral Metal Oxide Nanoparticle

Chiral metal oxide nanostructures have received tremendous attention in nanotechnological applications owing to their intriguing chiroptical and magnetic properties. Current synthetic methods mostly rely on the use of amino acids or peptides as chiral inducers. Here, we report a general approach to fabricate chiral metal oxide nanostructures with tunable magneto-chiral effects, using block copolymer (BCP) inverse micelle and R/S-mandelic acid (MA). Diverse chiral metal oxide nanostructures are prepared by the selective incorporation of precursors within micellar cores followed by the oxidation process, exhibiting intense chiroptical properties with a g-factor up to 7.0 × 10^-3 in the visible-NIR range for the Cr₂O₃ nanoparticle multilayer. The BCP inverse micelle is found to inhibit the racemization of MA, allowing MA to act as a chiral dopant that imparts chirality to nanostructures via hierarchical chirality transfer. Notably, for paramagnetic nanostructures, magneto-chiroptical modulation is realized by regulating the direction of the external magnetic field. This BCP-driven approach can be extended to the mass production of chiral nanostructures with tunable architectures and optical activities, which may provide insights into the development of chiroptical functional materials.

Full-Color and Switchable Circularly Polarized Light from a Macroscopic Chiral Dendritic Film through a Solid-State Supramolecular Assembly

Chiral materials displaying chirality across multiple length scales have attracted increasing interest due to their potential applications in diverse fields. Herein, we report an efficient approach for the construction of macroscopic crystal dendrites with hierarchical chirality based on an in situ solid assembly in a block copolymer film. Chiral fluorescent crystals are formed by enantiopure d-/l-dibenzoyl tartaric acid and pyrenecarboxylic acid in a poly(1,4-butadiene)-b-poly(ethylene oxide) film. The chiro-optical activity of the crystalline dendrites can be greatly amplified in the absorption and scattering regions and goes along with the dimension of dendrites. Notably, the chiral dendrites exhibited strong circularly polarized luminescence emission with a high dissymmetric factor (0.03). The enhancement of the quantum yield of the chiral film was up to 28%, which was 14 times higher that of the corresponding fluorescent molecules. The circularly polarized emission bands of the films can be fine-tuned by contriving the emissive bands of fluorescent molecules. More importantly, the chiral signals are able to be wiped when the fluorescent group photodimerizes under UV irradiation. This work provides an efficient way to develop functional materials through solid self-assembly.

One-Dimensional Helical Nanostructures from the Hierarchical Self-Assembly of an Achiral "Rod-Coil" Alternating Copolymer

The self-assembly of alternating copolymers (ACPs) has attracted considerable interest due to their unique alternating nature. However, compared with block copolymers, their self-assembly behavior has remained much less explored and their reported self-assembled structures are limited. Here, we report the formation of supramolecular helical structures by the self-assembly of an achiral rod-coil alternating copolymer, poly(quarter(3-hexylthiophene)-alt-poly(ethylene glycol)) (P(Q3HT-alt-PEG)). The copolymer exhibited an interesting hierarchical self-assembly process, driven by the π-π stacking of the Q3HT segments and the solvophobic interaction of the alkyl chains in tetrahydrofuran (THF)-isopropanol (iPrOH) mixed solvents. The copolymer first self-assembled into thin nanobelts with a uniform size, then grew to helical nanoribbons and eventually twisted into helical nanowires with an average diameter of 25 ± 9 nm and a mean pitch of 80 ± 10 nm. Dissipative particle dynamics (DPD) simulation supported the formation course of the helical nanowires. Furthermore, the addition of (S)-ethyl lactate and (R)-ethyl lactate in the self-assembly of P(Q3HT-alt-PEG) resulted in the formation of left-handed and right-handed chiral nanowires, respectively, demonstrating the tunability of the chirality of the helical wires. This study expands the library of ordered self-assembled structures of ACPs, and also brings a new strategy and mechanism to construct helical supramolecular structures. This article is protected by copyright. All rights reserved.

Template-assisted self-assembly of achiral plasmonic nanoparticles into chiral structures

The acquisition of strong chiroptical activity has revolutionized the field of plasmonics, granting access to novel light-matter interactions and revitalizing research on both the synthesis and application of nanostructures. Among the different mechanisms for the origin of chiroptical properties in colloidal plasmonic systems, the self-assembly of achiral nanoparticles into optically active materials offers a versatile route to control the structure-optical activity relationships of nanostructures, while simplifying the engineering of their chiral geometries. Such unconventional materials include helical structures with a precisely defined morphology, as well as large scale, deformable substrates that can leverage the potential of periodic patterns. Some promising templates with helical structural motifs like liquid crystal phases or confined block co-polymers still need efficient strategies to direct preferential handedness, whereas other templates such as silica nanohelices can be grown in an enantiomeric form. Both types of chiral structures are reviewed herein as platforms for chiral sensing: patterned substrates can readily incorporate analytes, while helical assemblies can form around structures of interest, like amyloid protein aggregates. Looking ahead, current knowledge and precedents point toward the incorporation of semiconductor emitters into plasmonic systems with chiral effects, which can lead to plasmonic-excitonic effects and the generation of circularly polarized photoluminescence.

Reversal of Handedness of Ionic liquid based Chiral Block Copolymers via Self-Assembly in Solution and Bulk Phase

Polymerized ionic liquid (PIL) based ionic chiral block copolymers (BCPs*) were synthesized by functionalization of poly(4-vinyl pyridine) segment in poly(styrene)-block-poly(4-vinyl pyridine) (PS-b-P4VP) block copolymer. Owing to the ease of ion...

Microphase separation in helix-coil block copolymer melts: computer simulation

By means of molecular dynamics simulation, the process of the microphase separation in the melts of diblock helix-coil copolymers comprising a flexible and a helical block was studied. The resulting microstructures were examined, and the spatial distribution of the blocks and molecular packing were investigated. The phase diagram was built in terms of the fraction of the helical block and the incompatibility parameter of the blocks. The comparison of the diagrams for helix-coil and the classic coil-coil copolymer blends was carried out. It was shown that the total region where the ordering into distinctive microstructures takes place is similar for both diagrams. But for the helix-coil copolymers the area of the cylinders splits into the region of those with circular and elliptical cross-sections; the bicontinuous phase area is much wider; in the lamellar phases, the helical blocks were oriented precisely perpendicular to the lamellar interface, forming a cohesive interlocked structure of densely packed helices.

Multidomain Helical Nanostructure by A1BA2C Tetrablock Terpolymer Self-Assembly

Among many possible nanostructures in block copolymer self-assembly, helical nanostructures are particularly important because of potential applications for heterogeneous catalysts and plasmonic materials. In this work, we investigated, via small-angle X-ray scattering and transmission electron microscopy, the morphology of a polystyrene-block-polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (S₁IS₂V) tetrablock terpolymer. Very interestingly, when the volume fraction of each block was 0.685, 0.125, 0.060, and 0.130, respectively, a multidomain double-stranded helical nanostructure (MH₂) was formed: P2VP chains became a core helix, and PI chains formed double-stranded helices surrounding the core helix. Core and double-stranded helices are connected by short PS₂ chains, and PS₁ chains become the matrix. The experimentally observed morphology is in good agreement with the prediction by self-consistent field theory. We believe that this multidomain helical structure will be pave the way to the creation of multifunctional helical structures for various applications such as metamaterials.

Reversible Micrometer-Scale Spiral Self-Assembly in Liquid Crystalline Block Copolymer Film with Controllable Chiral Response

The spiral is a fundamental structure in nature and spiral structures with controllable handedness are of increasing interest in the design of new chiroptical materials. In this study, micrometer-scale spiral structures with reversible chirality were fabricated based on the assembly of a liquid crystalline block copolymer film assisted by enantiopure tartaric acid. Mechanistic insight revealed that the formation of the spiral structures was closely related to the liquid crystalline properties of the major phase of block copolymer under the action of chiral tartaric acid. The chiral spiral structures with controllable handedness were easily erased under ultraviolet light irradiation and restored via thermal annealing. This facile thermal treatment method provides guidance for fabrication of chiral micrometer-scale spiral structures with adjustable chiral properties.

Controlling the chirality and number of strands of helices self-assembled from achiral block copolymers confined inside a nanopore: a simulation study

Achiral block copolymers can self-assemble into helical structures when confined inside a cylindrical nanopore. However, controlling the chirality and the number of strands of helices is challenging. We present our simulation results of the influence of a chiral patch added to the confining nanopore on the structures and chirality of helices self-assembled from achiral cylinder-forming diblock copolymers under the confinement. Our results indicate that, when the designed patch is of proper geometry, it can induce the formation of helical structures and exhibit good control over their chirality. The bottom surface of the patch can induce the formation of a characteristic local structure near and parallel to it. It is the characteristic local structure that directs the formation of helices and of their chirality consistent with that of the patch. A large patch angle or the top/bottom surface of a weakly selective pore promotes the formation of double-helices compared to single-helices by enlarging the pitch of the helices near the patch or through the entropic attraction of the top surface of the pore to the minority blocks.

Supramolecular Chirality Transfer toward Chiral Aggregation: Asymmetric Hierarchical Self-Assembly

Self-assembly, as a typical bottom-up strategy for the fabrication of functional materials, has been applied to fabricate chiral materials with subtle chiral nanostructures. The chiral nanostructures exhibit great potential in asymmetric catalysis, chiral sensing, chiral electronics, photonics, and even the realization of several biological functions. According to existing studies, the supramolecular chirality transfer process combined with hierarchical self-assembly plays a vital role in the fabrication of multiscale chiral structures. This progress report focuses on the hierarchical self-assembly of chiral or achiral molecules that aggregate with asymmetric spatial structures such as twisted bands, helices, and superhelices in different environments. Herein, recent studies on the chirality transfer induced self-assembly based on a variety of supramolecular interactions are summarized. In addition, the influence of different environments and the states of systems including solutions, condensed states, gel systems, interfaces on the asymmetric hierarchical self-assembly, and the expression of chirality are explored. Moreover, both the driving forces that facilitate chiral bias and the supramolecular interactions that play an important role in the expression, transfer, and amplification of the chiral sense are correspondingly discussed.

Handedness Inversion of Chiral 3-Aminophenol Formaldehyde Resin Nanotubes Mediated by Metal Coordination

Precise adjustment of microstructure and handedness of chiral nanomaterials is important to regulate their properties and performance. Herein, helical 3-aminophenol formaldehyde resin (APF) nanotubes and corresponding carbonaceous nanotubes with controllable handedness and optical activity were obtained via an external metal ion-mediated supramolecular co-templating method in an enantiomerically pure template system, in which an appropriate amount of Mn²⁺ (Co²⁺ or Ni²⁺ ) with moderate coordination abilities can reverse the spatial arrangement of the phenylglycine-based amphiphilic template molecules through metal coordination. Different stacking modes of coordination complexes in disparate metal ion systems lead to diverse helical senses (diameter and pitch) of the obtained helical APF. In addition, this coordination mode of metal intervention can be applied to other amine-based helical polymer synthesis systems, which paves the way for the design of high-quality chiral nanomaterials with satisfactory physical parameters and properties.

Constructing helical nanowires via polymerization-induced self-assembly

While reliable strategies for constructing block copolymer (BCP) nanowires have been developed, helical nanowires are rarely reported in polymerization-induced self-assembly (PISA). Herein, in this work, a new strategy for constructing helical nanowires was developed via PISA mediated by a fluorinated stabilizer block. Ultralong nanowires with helical structure can be readily produced in a wide range of block compositions. In addition, the generality of this strategy was well testified by expanding monomer types. The achiral BCP nano-objects underwent a morphology transition from spheres to helical nanowires during aging. We believe this work will provide a general strategy for producing helical nanowires through PISA of achiral BCPs.

Spiranthes sinensis-Inspired Circular Polarized Luminescence in a Solid Block Copolymer Film with a Controllable Helix

Chiral materials with circular polarized luminescence (CPL) have attracted much interest because of their extensive optical information and remarkable sensitivity. Inspired by the helical template in Spiranthes sinensis, we propose here a general and flexible method for fabricating solid CPL materials using a block copolymer-formed helix as a template. A chiral arrangement of various nonchiral fluorescent molecules was obtained in the block copolymer-based hybrid film. An excimer chiralty rule was found for the CPL emission of nonchiral fluorescent molecules: a right-handed helix induced left-handed CPL emission and a left-handed helix induced right-handed CPL emission. A dissipative particle dynamics simulation showed that such an antihelical effect is related to the length between the adjacent interacting points of nonchiral fluorescent molecules along the helical structure. Furthermore, the fluorescent films had a high dissymmetric factor for CPL emission, and thus, the films provide a general and flexible platform for designing and preparing advanced functional chiroptical materials.

Formation of homochiral helical nanostructures in diblock copolymers under the confinement of nanopores

The control of the homochirality of helical structures formed in achiral systems is of great interest as it is helpful for understanding the origin of homochirality in life.