Progress on Catalytic Systems Used in Click Polymerization

Dual signal amplification based on polysaccharide-initiated ring-opening polymerization and click polymerization for exosomes detection

Exosomes, as a biomarker with enhancing tumor invasion and spread, play an essential role for lung cancer diagnosis, therapy, and prognosis. In this work, a novel electrochemical sensor was fabricated for detecting exosomes secreted by lung cancer cells based on polysaccharide-initiated ring-opening polymerization (ROP) and click polymerization. First, MPA formed a self-assembled monolayer on the gold electrode surface, and then anti-EGFR was immobilized on the electrode surface by amide bond. Subsequently, a lot of phosphate groups were introduced by the specific recognition between anti-EGFR and exosomes, then sodium alginate grafted Glycidyl propargyl ether (SA-g-GPE) prepared via ROP was attached to the exosomes through PO₄^3-Zr⁴⁺-COOH coordination bond. After that, click polymerization was initiated by alkyne groups on the SA-g-GPE polymerization chain to realize highly sensitive detection of A549 exosomes. Under the optimum conditions, the fabricated sensor showed a good linear relationship between the logarithm of exosomes concentration and peak current in the range of 5 × 10³ - 5 × 10⁹ particles/mL, and the limit of detection (LOD) was as low as 1.49 × 10² particles/mL. In addition, this method had the advantages of high specificity, anti-interference, high sensitivity, simplicity, rapidity and green economy, which proposed a novel avenue for the detection of exosomes, and also had potential applications in early cancer diagnosis and biomedicine.

Recent progress in the applications of amino–yne click chemistry

This mini-review summarizes the recent research studies on the application of the amino–yne click reaction in surface immobilization, construction of drug delivery systems, preparation of hydrogel materials and synthesis of functional polymers.

Metal-Free Catalysts for the Polymerization of Alkynyl-Based Monomers

Novel polymerizations based on alkyne monomers are becoming a powerful tool to construct polymers with unique structures and advanced functions in the areas of polymer and material sciences, and scientists have been attracted to develop a variety of novel polymerizations in recent decades. Therein, catalytic systems play an indispensable role in the influence of polymerization efficiencies and the performances of the resultant polymers. Concerning the shortcomings of metallic catalysts, much of the recent research focus has been on metal-free polymerization systems. In this paper, metal-free catalysts are classified and the corresponding polymerizations are reviewed, including organobase-catalyzed polymerizations, Lewis-acid-catalyzed polymerizations, as well as catalyst-free polymerizations. Moreover, the challenges and perspectives in this area are also briefly discussed.

Catalyst-Free Multicomponent Cyclopolymerizations of Diisocyanides, Activated Alkynes, and 1,4-Dibromo-2,3-Butanedione: a Facile Strategy toward Functional Polyiminofurans Containing Bromomethyl Groups

Polymers containing iminofuran (PIFs) are rarely reported due to the lack of simple and effective synthesis methods. In this work, a novel multicomponent cyclopolymerization (MCCP) of diisocyanides, activated alkynes, and 1,4-dibromo-2,3-butanedione using catalyst-free one-pot reactions under mild conditions to prepare PIFs containing bromomethyl groups is reported. PIFs with good solubility and thermal stability are obtained with high M_w s (up to 19 600) and good yields (up to 89.5%) under optimized polymerization conditions. The structure of the PIFs is characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography. The photophysical properties indicate that polymers P1a2b3 and P1c2b3 have cluster-triggered emission characteristics. Thin films made from PIFs quickly degrade under UV irradiation. Moreover, the obtained polymers are decorated with bromomethyl and carboxylate groups in the side chain, which can be postfunctionalized to prepare multifunctional materials, such as star branched polymers and biomedical carrier materials. Thus, this work not only enriches the field of polymerization based on isocyanates and activated alkynes but also provides a facile strategy toward functional iminofuran polymers.

Antibacterial properties of main-chain cationic polymers prepared through amine-epoxy 'Click' polymerization

Poly(β-hydroxyl amine)s are prepared through an amine-epoxy 'click' polymerization process in water under ambient conditions. These materials could be subjected to a post-polymerization protonation/alkylation reaction at the nitrogen atom to yield quaternary ammonium salts in the polymer backbone. The antimicrobial activities indicated that polymers carrying butyl chains at the nitrogen atom are effective towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), as only 10-20 μg mL-1 polymer concentrations are required to inhibit the bacterial growth by >90%. One of the candidates was also found to be effective towards Mycobacterium smegmatis (M. smegmatis) - a model organism to develop drugs against rapidly spreading tuberculosis (TB) infections. The hemolysis assay indicated that a majority of antimicrobial agents did not disrupt red blood cell membranes. The mechanistic studies suggested that cell wall disruption by the cationic polymers was the likely cause of bacterial death.

Construction of sequence-defined polytriazoles by IrAAC and CuAAC reactions

Here we report the first synthesis of sequence-defined polytriazoles, in which different side groups are sequentially anchored to the C-5 position of 1,2,3-triazole rings. By using efficient synthetic strategies based on IrAAC and CuAAC, different monodispersed polytriazoles with up to ∼5.3 kDa and 31-mer were constructed. Structural characterization via NMR, SEC, MALDI-TOF-MS, tandem MS and FTICR-MS evidenced the formation of polytriazoles with the desired specified sequences and exact chain lengths.

Metal-free polycycloaddition of aldehyde-activated internal diynes and diazides toward post-functionalizable poly(formyl-1,2,3-triazole)s

A metal-free polycycloaddition of aldehyde-activated internal diynes and diazides was successfully established and post-functionalizable poly(formyl-1,2,3-triazole)s were readily produced.

Thermoresponsive Poly(ß-hydroxyl amine)s: Synthesis of a New Stimuli Responsive Amphiphilic Homopolymer Family through Amine-Epoxy 'Click' Polymerization

A new synthesis of amphiphilic homopolymers is described. In this synthesis, commercially available and inexpensive primary amines and di-epoxide molecules are utilized as AA- and BB-types of monomers in an amine-epoxy ‘click’ polymerization process. This process can be carried out in water and at room temperature. It does not require a catalyst or inert conditions and forms no byproducts. Therefore, the polymer synthesis can be carried out in open-air and bench-top conditions and a post-synthesis purification step is not required. The modularity of the synthesis, on the other hand, allows for facile structural modulation and tuning of the thermally triggered aggregation process in the temperature range of 7 to 91 °C. Finally, the underlying principles can be translated from linear architectures to polymer networks (hydrogels).

Palladium/Benzoic Acid-Catalyzed Regio- and Stereoselective Polymerization of Internal Diynes and Diols through C(sp3)-H Activation

The C-H activation has been a hot research area in organic chemistry, and the most difficult one is the C(sp³)-H activation. Although the C-H activation has been introduced to the research of synthetic polymer chemistry, the polymerization developed based on C(sp³)-H activation is rarely reported, which will enrich the tools for the preparation of functional polymers. In this work, palladium/benzoic acid catalyzed polymerization of internal diynes and diols through C(sp³)-H activation was successfully established. Regio- and stereoregular functional poly(allylic ether)s with 100% E-isomers and high weight average molecular weights (M_w up to 33200) were prepared in excellent yield (98%). The reaction mechanism was unveiled with the assistance of density functional theory calculations. Furthermore, the thin films of polymers display high refractive indices and low optical dispersions. The polymer containing tetraphenylethene moiety displays the aggregation-enhanced emission feature and could be used to generate 2D fluorescent photopattern. Thus, this work not only establishes a powerful polymerization based on C(sp³)-H activation, but also furnishes functional polymers for diverse applications.

Polymer-Doxorubicin Prodrug with Biocompatibility, pH Response, and Main Chain Breakability Prepared by Catalyst-Free Click Reaction

Click chemistry has increasing applications of the development of polymer materials and modification of drug carriers. The amino-yne click polymerization reacts quickly at room temperature without catalyst, and the enamine bond (-ena-) gained from the reaction is sensitive to acid and can be used to prepare stimulus-responsive polymeric prodrugs. Herein, we report an alkynyl-terminated polymer containing alternately distributed low molecular weight polyethylene glycol (PEG) and hexamethylenediamino (HMDA) linked by enamine bonds, abbreviated as A-P(PEG-alt-HMDA)-A, which was synthesized within 3 h at 35 °C without catalyst. The polymer was verified to have good water solubility, biocompatibility, and acid-sensitive fracturing. Then, a pH-responsive polymeric prodrug (DOX-ena-PPEG-ena-DOX) was further prepared through the amino-yne click reaction between the alkynyl groups of A-P(PEG-alt-HMDA)-A and the amino group of doxorubicin hydrochloride (DOX·HCl). The resulting prodrug can self-assemble into nanoparticles (NPs) in aqueous solution. The pH responsiveness of the prodrug NPs was demonstrated by a stability experiment of NPs and in vitro drug release behavior measurement. The accumulative release of doxorubicin (DOX) was tested with different pH media, which confirmed that the prodrug NPs could effectively dissociate and release drug under a weak acid microenvironment of lysosome/endosome. Subsequently, we investigated cell cytotoxicity and intracellular uptake of the prodrug. It turned out that the prodrug nanoparticles could be internalized into HeLa cells, release original DOX, and efficiently inhibit the proliferation of cancer cells. These results show that the pH-responsive DOX-ena-PPEG-ena-DOX has the potential for use in cancer therapy.

Benzyne–azide polycycloaddition: a facile route toward functional polybenzotriazoles

An efficient benzyne–azide polycycloaddition is established and functional poly(benzotriazole)s are produced under mild reaction conditions.

Transition metal-free thiol–yne click polymerization toward Z-stereoregular poly(vinylene sulfide)s

An efficient K₃PO₄-mediated thiol–yne click polymerization was established, and regio- and stereoregular poly(vinylene sulfide)s with Z-isomers were produced.