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.

Side-chain functionalized supramolecular helical brush copolymers

The construction of a supramolecular brush copolymer featuring a helical backbone is described. The pendant chains are grafted onto the backbone through metal coordination.

Fabrication of thermoresponsive magnetic micelles from amphiphilic poly(phenyl isocyanide) and Fe3O4 nanoparticles for controlled drug release and synergistic thermochemotherapy

The drug-loaded micelles self-assembled from co-poly(phenyl isocyanide), Fe₃O₄ and DOX demonstrated thermoresponsiveness and magnetic hyperthermia for synergistic thermochemotherapy.

Helical polymer self-assembly and chiral nanostructure formation

This review surveys recent progress towards robust chiral nanostructure fabrication techniques using synthetic helical polymers, the unique inferred properties that these materials possess, and their intricate connection to natural, biological chirality.

Semiflexible polymer scaffolds: an overview of conjugation strategies

Semiflexible polymers are excellent scaffolds for the presentation of a wide variety of (bio)molecules. This manuscript reviews advantages and challenges of the most common conjugation strategies for the major classes of semiflexible polymers.

Functional Isocyanide-Based Polymers

Research interest in the isocyanide-based reaction can be traced back to 1921 when the Passerini reaction was first reported. However, most of these research efforts did not lead to important progress in the synthesis of isocyanide-based polymers (IBPs). The major challenge resides in the lack of highly efficient polymerization methods, which limits large-scale preparation and applications. Modern organic chemistry provides efficient access to develop functional IBPs on the basis of isocyanide chemistry. However, it is still challenging to prepare the IBPs with small molecular isocyanide reaction. Our investigations into catalyst exploration and polymerization methodology have prompted the synthesis of a series of IBPs. Two classes of isocyanide monomers can be used for the construction of IBPs. The first class includes monomers with a single isocyanide. Novel catalysts for the synthetic chemistry of isocyanide allow the introduction of functional pendants into the linear polymer chains. This molecular functionalization endows the polymers with an array of new functional properties. For example, the incorporation of a chromophore on the polymeric side chain provides novel functional properties, such as aggregation-induced emission and optical activity. Diisocyanide monomers can be also utilized for the construction of heterocyclic, spiro-heterocyclic, and bispiro-heterocyclic polymers in the polymeric backbones. A new concept of "multi-component spiropolymerization" has been developed for the preparation of spiropolymers using the catalysis-free one-pot reaction. Proper structural design allows for the preparation of a heterocyclic polymeric chain with natural bioactivity and biological compatibility, generating new IBPs with biofunctionalities.In this Account, we discuss progress mainly made in our lab and related fields for the design of isocyanide monomers, exploration of new catalysts, and optimization of reaction conditions. The subsequent section discusses the characteristic properties and applications of selected examples of these functional polymers, mainly focusing on their optical applications. We have investigated the UV-sensitive IBPs that could potentially be used for lithography applications. One-pot highly efficient polymerization of diisocyanides and CO₂ under mild conditions can provide a new method for realizing the reuse of CO₂ and reducing the greenhouse effect. Through a combination of structural modifications, IBPs bearing dimethylbenzene moieties exhibit characteristics of black materials that can be potentially utilized as pyroelectric sensors, thermal detectors, and optical instruments. Most recently, our group synthesized a spiro-heterocyclic IBP with clusterization-triggered emission properties that can be used to discriminate cancer cells from normal cells and provides a new method for the treatment of cancer. The studies reviewed in this Account suggest that polymerization with isocyanide chemistry can be implemented in diverse functional macromolecules and materials.

Synthesis of Isocyanides by Reacting Primary Amines with Difluorocarbene

A general, convenient, and friendly route for preparing a versatile building block of isocyanides from primary amines is developed. Difluorocarbene, generated in situ from decarboxylation of chlorodifluoroacetate, reacts efficiently with primary amines to produce isocyanides. Various primary amines are well tolerated, including aryl, heteroaryl, benzyl, and alkyl amines, as well as amine residues in amino acids and peptides. Late-stage functionalization of biologically active amines is demonstrated, showing its practical capacity in drug design and peptide modification.

Recent Advances in Palladium-Catalyzed Isocyanide Insertions

Isocyanides have long been known as versatile chemical reagents in organic synthesis. Their ambivalent nature also allows them to function as a CO-substitute in palladium-catalyzed cross couplings. Over the past decades, isocyanides have emerged as practical and versatile C1 building blocks, whose inherent N-substitution allows for the rapid incorporation of nitrogeneous fragments in a wide variety of products. Recent developments in palladium catalyzed isocyanide insertion reactions have significantly expanded the scope and applicability of these imidoylative cross-couplings. This review highlights the advances made in this field over the past eight years.

Chiral information harvesting in helical poly(acetylene) derivatives using oligo(p-phenyleneethynylene)s as spacers

A chiral harvesting transmission mechanism is described in poly(acetylene)s bearing oligo(p-phenyleneethynylene)s (OPEs) used as rigid achiral spacers and derivatized with chiral pendant groups. The chiral moieties induce a positive or negative tilting degree in the stacking of OPE units along the polymer structure, which is further harvested by the polyene backbone adopting either a P or M helix.

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.

Chiral Overpass Induction in Dynamic Helical Polymers Bearing Pendant Groups with Two Chiral Centers

The dynamic behavior of helical polymers bearing pendant groups with two chiral centers was studied. Controlled conformational changes at the chiral units placed either closer to or further away from the main chain promote different helical structures. Although the first residue is usually responsible for determining a specific helicity (P or M), we now found that the second chiral center is also able to induce a preferred helical sense when it is located closer in space to the main chain, thereby cancelling the order from the first chiral moiety. This result was achieved through proper coordination with a metal cation. As proof of concept, poly(phenylacetylene)s (PPAs) that bear one and two chiral amino acid units of different sizes and configuration combinations (l/d-alanine and l/d-phenylalanine) as pendants were evaluated. In total, ten polymers were studied. This constitutes the first report of axial control from a remote stereocenter in polymers bearing complex chiral pendants.

Chiral gold-PPA nanocomposites with tunable helical sense and morphology

A novel type of stimuli-responsive dynamic helical polymer-metal nanoparticle nanocomposite formed by a helical poly(phenylacetylene) (PPA) combined with gold nanoparticles (AuNPs) is described. Thus, several PPA copolymers containing the ethynyl-4-benzamide of (S)-phenylglycine methyl ester (M1) to dictate the helical structure/sense of the copolymer, and the ethynyl-4-benzamide of the 11-((2-(2-(2-aminoethoxy)ethoxy)ethyl)amino)undecane-1-thiol (M2) to link the copolymer to the AuNPs are prepared. Different morphologies of these nanocomposites were obtained by considering the thiol ratio and the self-assembly properties of the PPA, which generates from dispersed AuNPs to fibre-like structures. All these nanocomposites show a dynamic chiral behaviour, it being possible to manipulate their helical sense by the action of external stimuli. Moreover, it is possible to control the aggregation of these nanocomposites into macroscopically chiral nanospheres with low polydispersity by using Ba2+ as a crosslinking agent.

Synthesis of Densely Functionalized Pyrimidouracils by Nickel(II)-Catalyzed Isocyanide Insertion

A robust nickel-catalyzed oxidative isocyanide insertion/C–H amination by reaction of readily available N-uracil-amidines with isocyanides affording polysubstituted pyrimidouracils has been reported. The reaction proceeds in moderate to quantitative yield, under mild conditions (i.e., green solvent, air atmosphere, moderate temperature). The broad range of structurally diverse isocyanides and N-uracil-amidines that are tolerated make this method an interesting alternative to the currently available procedures toward pyrimidouracils.

Silylium cation initiated sergeants-and-soldiers type chiral amplification of helical aryl isocyanide copolymers

Silylium cations act as new highly efficient metal-free single-component cationic initiators for the cationic polymerization and copolymerization of chiral or achiral aryl isocyanides, preparing optically active polymers and copolymers obeying “sergeants-and-soldiers” rule.

All-conjugated donor–acceptor block copolymers featuring a pentafulvenyl-polyisocyanide-acceptor

A fulvenyl-functionalized polyisocyanide (PIC2) with a high electron mobility of μ_e = 10⁻² cm² V⁻¹ s⁻¹ has been incorporated into donor–acceptor block copolymers. Their self-assembly and bulk-morphology have been studied, and potential device applications have been explored.

Self-assembly and fluorescence emission of UV-responsive azobenzene-containing helical poly(phenyl isocyanide) copolymers

UV-responsive azobenzene-containing helical copolymers were obtained, and their self-assembly and fluorescent properties were investigated.

Helical poly(phenyl isocyanide)s grafted selectively on C-6 of cellulose for improved chiral recognition ability

Cellulose graft copolymers are an effective way to endow new properties to cellulose substrate, as well the rigidity, regularity, and helicity of the cellulose backbone could induce the self-assembly of supramolecular structures. In this work, right-handed helical poly(phenyl isocyanide)s (PPI_n) were grafted selectively onto C-6-cellulose. Alkyne-terminated PPI_n was synthesized by living polymerization of right-handed phenyl isocyanide monomer using an alkyne-terminated palladium(II) complex as an initiator/catalyst, and were grafted onto the C-6 of the cellulose backbone (Cell-6-g-PPI_n) at various chain lengths using copper-catalyzed alkyne-azide cycloaddition (CuAAC) "click" chemistry. We confirmed the successful grafting by liquid ¹H NMR and ¹³C NMR, as well as solid ¹³C NMR, FTIR, and GPC. After grafting onto cellulose, the right-handed chirality of PPI_n was significantly increased by 111.2%. Additionally, the Cell-6-g-PPI_n exhibited better chiral recognition of L-Phe-DNSP than PPI_n alone. Therefore, the helical cellulose backbone has enhanced effect on preferred helix of PPI_n.

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.

One-Step Synthesis of One-Dimensional Supramolecular Assemblies Composed of Helical Macromolecular Building Blocks

Living systems achieve sophisticated functions using supramolecular protein assemblies, in which the protein building blocks possess a specific secondary structure and are noncovalently arranged in a preprogrammed manner. Herein, we demonstrate the one-step synthesis of one-dimensional macromolecular assemblies by simply mixing a glycine-based isocyanide with a nickel catalyst, in which helical constituent polymers are linked end-to-end through multiple hydrogen bonds. The applicable scope of this approach is not confined to a particular monomer bearing a specially designed pendant, but covers a wide range of glycine-based isocyanides with or without aromatic and other functional groups. Surprisingly, copolymerization with an analogous chiral isocyanide (1 mol %) afforded an almost perfect one-handed helical supramolecular fiber owing to intramolecular/intermolecular dual chiral amplifications. The simplicity and broad applicability of this approach, which can also afford exquisite chiral amplification, enable the creation of a wide variety of functional supramolecular assemblies and provide access to new supramolecular materials.

Synthesis and Light-Mediated Structural Disruption of an Azobenzene-Containing Helical Poly(isocyanide)

Helical poly(isocyanide)s are an important class of synthetic polymers possessing a static helical structure. Since their initial discovery, numerous examples of these helices have been fabricated. In this contribution, the synthesis of a chiral, azobenzene (azo)-containing isocyanide monomer is reported. Upon polymerization with nickel(II) catalysts, a well-defined circular dichroism (CD) trace is obtained, corresponding to the formation of a right-handed polymeric helix. The helical polymer, dissolved in chloroform and irradiated with UV light (365 nm), undergoes a cis to trans isomerization of the azobenzene side-chains. After the isomerization, a change in conformation of the helix occurs, as evidenced by CD spectroscopy. When the solution is irradiated with LED light, the polymer returns to a right-handed helical conformation. To open up the possibility for chain-end post-polymerization modification of this light-responsive system, an alkyne-functionalized nickel(II) catalyst is also used in the polymerization of the azobenzene monomer, resulting in a stimuli-responsive, terminal-alkyne-containing helical poly(isocyanide).

A Comparative Study on HCN Polymers Synthesized by Polymerization of NH4 CN or Diaminomaleonitrile in Aqueous Media: New Perspectives for Prebiotic Chemistry and Materials Science

HCN polymers are a group of complex and heterogeneous substances that are widely known in the fields of astrobiology and prebiotic chemistry. In addition, they have recently received considerable attention as potential functional material coatings. However, the real nature and pathways of formation of HCN polymers remain open questions. It is well established that the tuning of macromolecular structures determines the properties and practical applications of a polymeric material. Herein, different synthetic conditions were explored for the production of HCN polymers from NH₄ CN or diaminomaleonitrile in aqueous media with different concentrations of the starting reactants and several reaction times. By using a systematic methodology, both series of polymers were shown to exhibit similar, but not identical, spectroscopic and thermal fingerprints, which resulted in a clear differentiation of their morphological and electrochemical properties. New macrostructures are proposed for HCN polymers, and promising insights are discussed for prebiotic chemistry and materials science on the basis of the experimental results.

Extra hydrogen bonding interactions by peripheral indole groups stabilize benzene-1,3,5-tricarboxamide helical assemblies

Benzene-1,3,5-tricarboxamide monomers derived from alkyl esters of tryptophan (BTA Trp) self-assemble into helices with an inner threefold hydrogen bond network surrounded by a second network involving the indole N-H groups. As a consequence of this extra stabilization of its helical assemblies, BTA Trp forms more viscous solutions than a range of ester and alkyl BTAs.

Effect of the tactic structure on the chiroptical properties of helical vinylbiphenyl polymers

The effect of a tactic structure on the chiroptical properties of helical vinylbiphenyl polymers is systematically studied.

[Ph3 C][B(C6 F5 )4 ]: A Highly Efficient Metal-Free Single-Component Initiator for the Helical-Sense-Selective Cationic Copolymerization of Chiral Aryl Isocyanides and Achiral Aryl Isocyanides

Commercially available [Ph₃ C][B(C₆ F₅ )₄ ] served as a highly efficient metal-free and single-component initiator not only for the carbocationic polymerization of polar and bulky aryl isocyanides with extremely high activity up to 1.2×10⁷  g of polymer/(mol_cat.  h), but also for the helical-sense-selective polymerization of chiral aryl isocyanides and copolymerization with achiral aryl isocyanides to afford high-molecular-weight functional poly(aryl isocyanide)s with good solubility as well as AIE characteristics and/or a single-handed helical conformation.

Sequential Induction of Chirality in Helical Polymers: From the Stereocenter to the Achiral Solvent

Several steps of chiral induction have been detected in poly(phenylacetylene)s among their different hierarchical levels of chirality by vibrational circular dichroism, namely, (i) from the stereogenic centers to the innermost polyacetylene helical covalent backbone (helix_int), (ii) from this to the external helix (helix_ext) formed by the side phenyl pendants that form a complementary helix or counter-helix, and (iii) from this pendant helix to the helical solvation sphere (helix_solv.), the last one being observed along this work. The pendant to polyene backbone chiral induction determines the helical structure adopted by the polymer and therefore the solvation helix. This helical structure is promoted by two mechanisms: steric effects and hydrogen bonding. An important finding concerns the demonstration by VCD of how an achiral solvent becomes chirally organized owing to the template effect of the covalent polymer helices, an effect that is silent to other structural techniques such as ECD or AFM and that hence significantly broadens the scope of these previous analyses.

Elucidating the Solvent Effect on the Switch of the Helicity of Poly(quinoxaline-2,3-diyl)s: A Conformational Analysis by Small-Angle Neutron Scattering

Small-angle neutron scattering (SANS) was used to examine dilute solutions of a poly(quinoxaline-2,3-diyl) (PQX) with (R)-2-octyloxymethyl side chains in deuterated THF or a mixture of deuterated 1,1,2-TCE and THF (8/2, v/v), in which the PQX adopts pure P- and M-helical structures. The structures of the PQX that were obtained based on the SANS experiments in combination with theoretical calculations suggest that in THF, the chiral side chains of the P-helical PQX are extended, whereas in the 1,1,2-TCE/THF mixture, the side chains of the M-helical PQX are folded. Consequently, P-helical structures should be preferred in good solvents such as THF, which solvate the extended side chains, whereas M-helical structures should be preferred in poor solvents such as 1,1,2-TCE, wherein the side chains adopt shrunken conformations with maximized van der Waals interactions between the side chains. This study thus reveals the first example for fully determined nuanced conformations of the side chains of synthetic polymers in solution based on SANS experiments and theoretical calculations.