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.

Photo-Controllable Förster Resonance Energy Transfer Based on Dynamic Chiral Self-Assembly of Sequence-Defined Amphiphilic Alternating Azopeptoids

Endowing biomimetic sequence-controlled polymers with chiral functionality to construct stimuli-responsive chiral materials offers a promising approach for innovative chiroptical switch, but it remains challenging. Herein, it is reported that the self-assembly of sequence-defined chiral amphiphilic alternating azopeptoids to generate photo-responsive and ultrathin bilayer peptoidosomes with a vesicular thickness of ≈1.50 nm and a diameter of around ≈290 nm. The photoisomerization of azobenzene moiety facilitates a reversible structural transformation from isotropic peptoidosomes to anisotropic 1D helical nanoribbons (≈80 nm width) under the alternating irradiation with UV and visible lights, consequently leading to the chirality expression and transfer from chiral asymmetric center to achiral azobenzene units. As a biomimetic model with deformation-induced energy transfer, a non-invasive azobenzene-based Förster resonance energy transfer system is unprecedentedly constructed via the introduction of a fluorescent donor of pyrene derivatives and sequentially photo-regulated the donor/acceptor ratio, displaying a reversible gradient fluorescent color variation from blue to yellow (a broad Stokes shift of ≈200 nm) and a high-efficient energy transfer efficiency of 97.2%. The photo-controllable photoluminescence phenomenon endows these chiral aggregates with a proof-of-concept application on multi-colored information encryption. This work provides a prospective strategy to fabricate stimuli-responsive chiral biomimetic materials with a potential on the light-controllable switches.

Photosensitive Polymeric Janus Micromotor for Enzymatic Activity Protection and Enhanced Substrate Degradation

Immobilizing enzymes into microcarriers is a strategy to improve their long-term stability and reusability, hindered by (UV) light irradiation. However, in such approaches, enzyme-substrate interaction is mediated by diffusion, often at slow kinetics. In contrast, enzyme-linked self-propelled motors can accelerate this interaction, frequently mediated by the convection mechanism. This work reports on a new photosensitive polymeric Janus micromotor (JM) for UV-light protection of enzymatic activity and efficient degradation of substrates accelerated by the JMs. The JMs were assembled with UV-photosensitive modified chitosan, co-encapsulating fluorescent-labeled proteins and enzymes as models and magnetite and platinum nanoparticles for magnetic and catalytic motion. The JMs absorbed UV light, protecting the enzymatic activity and accelerating the enzyme-substrate degradation by magnetic/catalytic motion. Immobilizing proteins in photosensitive JMs is a promising strategy to improve the enzyme's stability and hasten the kinetics of substrate degradation, thereby enhancing the enzymatic process's efficiency.

Inducing enantioselective crystallization with and self-assembly of star-shaped hybrid polymers prepared via "grafting to" strategy

Helical polymers present some interesting and distinctive properties, and one of the most distinguished applications of them is the chiral recognition and resolution of enantiomers. In this work, star-shaped hybrid helical poly (phenyl isocyanide) (PPI) with polyhedral oligomeric silsesquioxanes (POSS) as the core was designed and synthesized by "grafting to" strategy. The homoarm star-shaped hybrid POSS-(PPI)₈ was first obtained by the click reaction between azide-modified POSS (POSS-(N₃ )₈ ) and alkynyl-modified PPI (PPI-Alkynyl). The hybrid POSS-(PPI)₈ was with predominated left-handed helical conformation and exhibited excellent ability in the enantioselective crystallization of racemic compounds. In the meantime, heteroarm star-shaped hybrid (PEG)₄ -POSS-(PPI)₄ was prepared by the click reaction of POSS-(N₃ )₈ with PPI-Alkynyl and alkynyl-modified poly (ethylene glycol) (PEG-Alkynyl). The hybrid (PEG)₄ -POSS-(PPI)₄ was amphiphilic, and it could self-assemble to form spherical micelles in aqueous solutions.

Fluorescent Azobenzene-Containing Compounds: From Structure to Mechanism

The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, inducing aggregation, and metal-enhancement, which make the materials ideal for application in fluorescence probes, light-emitting devices, molecular detection, etc. Herein, we review the recently reported progress in the development of various fluorescent azobenzenes and summarize the possible mechanism of their fluorescence emission. The potential applications of these materials are also discussed. Finally, in order to guide research in this field, the existing problems and future development prospects are discussed.

POSS-based starlike hybrid helical poly(phenyl isocyanide)s: their synthesis, self-assembly, and enantioselective crystallization ability

Well-defined starlike hybrid helical poly(phenyl isocyanide)s with POSS cores were designed and synthesized, and their self-assembly behaviour and enantioselective crystallization ability were investigated.