Dibromomaleimide End Functional Polymers by RAFT Polymerization Without the Need of Protecting Groups

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Two Birds with One Stone: A Novel Dithiomaleimide-Based GalNAc-siRNA Conjugate Enabling Good siRNA Delivery and Traceability

For the first time, a novel dithiomaleimides (DTM) based tetra-antennary GalNAc conjugate was developed, which enable both efficient siRNA delivery and good traceability, without incorporating extra fluorophores. This conjugate can be readily constructed by three click-type reactions, that is, amidations, thiol-dibromomaleimide addition and copper catalyzed azide-alkyne cycloaddition (CuAAC). And it also has comparable siRNA delivery efficiency, with a GalNAc L96 standard to mTTR target. Additionally, due to the internal DTMs, a highly fluorescent emission was observed, which benefited delivery tracking and reduced the cost and side effects of the extra addition of hydrophobic dye molecules. In all, the simple incorporation of DTMs to the GalNAc conjugate structure has potential in gene therapy and tracking applications.

Cell-Derived Vesicles with Increased Stability and On-Demand Functionality by Equipping Their Membrane with a Cross-Linkable Copolymer

Cell-derived vesicles retain the cytoplasm and much of the native cell membrane composition. Therefore, they are attractive for investigations of membrane biophysics, drug delivery systems, and complex molecular factories. However, their fragility and aggregation limit their applications. Here, the mechanical properties and stability of giant plasma membrane vesicles (GPMVs) are enhanced by decorating them with a specifically designed diblock copolymer, cholesteryl-poly[2-aminoethyl methacrylate-b-poly(ethylene glycol) methyl ether acrylate]. When cross-linked, this polymer brush enhances the stability of the GPMVs. Furthermore, the pH-responsiveness of the copolymer layer allows for a controlled cargo loading/release, which may enable various bioapplications. Importantly, the cross-linked-copolymer GPMVs are not cytotoxic and preserve in vitro membrane integrity and functionality. This effective strategy to equip the cell-derived vesicles with stimuli-responsive cross-linkable copolymers is expected to open a new route to the stabilization of natural membrane systems and overcome barriers to biomedical applications.

Synthesis of Disulfide-Bridging Trehalose Polymers for Antibody and Fab Conjugation Using a Bis-Sulfone ATRP Initiator

Antibodies and antigen binding fragments (FABs) are widely used as therapeutics and conjugated polymers can enhance the properties of these important biomolecules. However, limitations to the selectivity and stability of current conjugation methodologies can inhibit the exploration of new antibody-polymer conjugates. Herein, we describe a new strategy for the synthesis of these conjugates that forms a stable thioether bond and can be directly incorporated into an atom transfer radical polymerization (ATRP) initiator. Specifically, a bis-sulfone alkyl bromide initiator was synthesized and utilized in the activators generated by electron transfer (AGET) ATRP of ethylene glycol methacrylate and trehalose methacrylate to form the respective polymers. The trehalose polymer was then irreversibly inserted into the disulfide bonds of Herceptin and Herceptin FAB after mild reduction to form the conjugates with quantitative conversions as verified by Western Blot and mass spectrometry after cleavage of the polymer. The binding of the Herceptin and Herceptin Fab conjugates to the receptor was investigated by indirect ELISA (enzyme-linked immunosorbent assay) and the EC50's were 0.90 and 2.74 nM, respectively, compared to Herceptin (0.26 nM) and the Fab (0.56 nM). The conjugates were subjected to heating studies at a constant 75 °C, the temperature determined in a heat ramp to be the threshold of stability for the antibody and FAB; the trehalose polymer was found to considerably increase the thermal stability of both Herceptin and Herceptin Fab. This work provides a new way to prepare polymer-antibody/Fab conjugates utilizing bis-sulfone end groups installed by atom transfer radical polymerization of the functionalized initiators and a way to stabilize these important molecules by conjugation to trehalose polymers.

Functional nanostructures by NiCCo-PISA of helical poly(aryl isocyanide) copolymers

Nickel-catalysed coordination polymerisation-induced self-assembly (NiCCo-PISA) as a straightforward and versatile methodology to achieve functional helix-containing polymeric nano-objects.

Preparation of Biomolecule-Polymer Conjugates by Grafting-From Using ATRP, RAFT, or ROMP

Biomolecule-polymer conjugates are constructs that take advantage of the functional or otherwise beneficial traits inherent to biomolecules and combine them with synthetic polymers possessing specially tailored properties. The rapid development of novel biomolecule-polymer conjugates based on proteins, peptides, or nucleic acids has ushered in a variety of unique materials, which exhibit functional attributes including thermo-responsiveness, exceptional stability, and specialized specificity. Key to the synthesis of new biomolecule-polymer hybrids is the use of controlled polymerization techniques coupled with either grafting-from, grafting-to, or grafting-through methodology, each of which exhibit distinct advantages and/or disadvantages. In this review, we present recent progress in the development of biomolecule-polymer conjugates with a focus on works that have detailed the use of grafting-from methods employing ATRP, RAFT, or ROMP.

Size-controlled clustering of iron oxide nanoparticles within fluorescent nanogels using LCST-driven self-assembly

Size-controlled clustering of iron oxide nanoparticles (IONPs) within the fluorescent polymer nanogels was achieved using the lower critical solution temperature (LCST) driven self-assembly and cross-linking of grafted polymer on the IONPs.

Photo-controlled one-pot strategy for the synthesis of asymmetric three-arm star polymers

A one-pot tandem strategy for the synthesis of asymmetric star polymers was developed. Two wavelengths of light were used to provide spatial and temporal control for the reactions. A series of stars were synthesised using this procedure giving well-defined structures.

Carborane RAFT agents as tunable and functional molecular probes for polymer materials

Carborane RAFT agents are introduced as tunable multi-purpose tools acting as ¹H NMR spectroscopic handles, Raman probes, and recognition units.

Bioconjugation and Fluorescence Labeling of Iron Oxide Nanoparticles Grafted with Bromomaleimide-Terminal Polymers

Iron oxide nanoparticles have been widely applied in biomedical applications for their unique physical properties. Despite the relatively mature synthetic approaches for iron oxide nanoparticles, surface modification strategies for obtaining particles with satisfactory biofunctionality are still urgently needed to meet the challenge of nanomedicine. Herein, we report a surface modification and biofunctionalization strategy for iron oxide-based magnetic nanoparticles based on a dibromomaleimide (DBM)-terminated polymer with brushed polyethylene glycol (PEG) chains. PEG acrylate and phosphonate monomers, serving as antibiofouling and surface anchoring compartments for iron oxide nanoparticles, were incorporated utilizing a novel DBM containing reversible addition-fragmentation chain transfer (RAFT) agent. The particles prepared through this new surface architecture possessed high colloidal stability in a physiological buffer and the capacity of covalent conjugation with biomolecules for targeting. Cell tracking of the molecular probes was achieved concomitantly by exploiting DBM conjugation-induced fluorescence of the nanoparticles.

Endo and Exo Diels-Alder Adducts: Temperature-Tunable Building Blocks for Selective Chemical Functionalization

The development and application of a novel endo furan-protected maleimide building block is reported. The endo isomer undergoes deprotection at temperatures ∼50 °C below the exo derivative. This enables a simple and powerful approach to quantitatively and selectively introduce functional maleimide groups via temperature modulation.

Dimeric Drug Polymeric Micelles with Acid-Active Tumor Targeting and FRET-Traceable Drug Release

Trans-activating transcriptional activator (TAT), a cell-penetrating peptide, is extensively used for facilitating cellular uptake and nuclear targeting of drug delivery systems. However, the positively charged TAT peptide strongly interacts with serum components and undergoes substantial phagocytosis by the reticuloendothelial system, causing a short blood circulation in vivo. In this work, an acid-active tumor targeting nanoplatform DA-TAT-PECL is developed to inhibit the nonspecific interactions of TAT in the bloodstream. 2,3-dimethylmaleic anhydride (DA) is used to convert the TAT's amines to carboxylic acid; the resulting DA-TAT is conjugated to poly(ethylene glycol)-poly(ε-caprolactone) (PEG-PCL, PECL) to get DA-TAT-PECL. After self-assembly into polymeric micelles, they are capable of circulating in the physiological condition for a long time and promoting cell penetration upon accumulation at the tumor site and deshielding the DA group. Moreover, camptothecin (CPT) is used as the anticancer drug and modified into a dimer (CPT)2 -ss-Mal, in which two CPT molecules are connected by a reduction-labile maleimide thioether bond. The Förster resonance energy transfer signal between CPT and maleimide thioether bond is monitored to visualize the drug release process, and effective targeted delivery of antitumor drugs is demonstrated. This pH/reduction dual-responsive micelle system provides a new platform for high fidelity cancer therapy.

A platform with connections in many directions - further remarkable facets to the multifaceted methylbiquinoxen dication

The N,N'-dimethyl-3,3'-biquinoxalinium "methylbiquinoxen" dicationic platform is revealed to have even more fascinating possibilities than we originally thought in terms of its chemical versatility. In addition to its rich redox chemistry and coordination abilities, we have now unveiled an unexpected Lewis acid/base chemistry linked with a tuneable switching of its luminescence properties. This, amongst other things, allows for the facile fluorescent covalent labelling of hydroxyl-terminated materials. This platform provides intriguing chemical prospects realised in molecular systems such as porphyrins as well as an easy alternative functionalisation methodology to that provided by click-chemistry.

Reduction-responsive dithiomaleimide-based polymeric micelles for controlled anti-cancer drug delivery and bioimaging

The biocompatible amphiphilic block copolymers and the CPT model drug were self-assembled into micelles with bright fluorescence and taken up by tumor cells. Then, the disulfide bonds in the micelles were cleaved to release CPT at a high GSH concentration.

Addressing the mid-point of polymer chains for multiple functionalization purposes through sequential thiol–epoxy ‘click’ and esterification reactions

A synthetic strategy is devised for the preparation of mid-chain multifunctional polymers.

Reversible Regulation of Thermoresponsive Property of Dithiomaleimide-Containing Copolymers via Sequential Thiol Exchange Reactions

The facile and efficient functionalization of thermoresponsive polymers based on sequential, reversible thiol-exchange reactions is reported. Well-defined dithiomaleimide-containing polymers have been synthesized via Cu(0)-mediated SET-LRP and characterized by ¹H NMR and size exclusion chromatography (SEC). The resulting thermosensitive copolymers were subsequently reacted with various thiols to demonstrate the applicability of the strategy, and the thiol-exchange reaction was found to be very fast and efficient. The cloud point of the prepared copolymers can be continually and reversibly tuned, and desirable functionality can be dynamically exchanged upon sequential addition of functional thiol reagents. Through the substitution by thioglucose, an ON-to-OFF switch for fluorescence of the copolymers along with the generation of a glycopolymer was achieved.

Reduction-responsive dithiomaleimide-based nanomedicine with high drug loading and FRET-indicated drug release

Dithiomaleimide-based camptothecin-containing nanoparticles are designed to have exceptionally high drug loading and are capable of reduction-responsive, FRET-indicated drug release.

Cu(0)-mediated living radical polymerisation in dimethyl lactamide (DML); an unusual green solvent with limited environmental impact

The synthesis of poly-acrylates, methacrylates and styrene derivatives by SET-LRP is reported in a user and environmentally friendly “green” solvent, dimethyl lactamide (DML).

Homopolymer bifunctionalization through sequential thiol–epoxy and esterification reactions: an optimization, quantification, and structural elucidation study

In this study, we probe various aspects of a post-polymerization double-modification strategy involving sequential thiol–epoxy and esterification reactions for the preparation of dual-functional homopolymers.

Polymer-protein conjugation via a ‘grafting to’ approach – a comparative study of the performance of protein-reactive RAFT chain transfer agents

The performances of various protein-reactive RAFT CTAs to afford polymer-protein conjugation via a grafting-to approach were compared.

Dual effect of thiol addition on fluorescent polymeric micelles: ON-to-OFF emissive switch and morphology transition

Reaction with a thiol causes solution-state self-assembled block copolymer nanoparticles to undergo a simultaneous morphology transition from micelles to vesicles coupled to an ON-to-OFF switch in particle fluorescence.

Synthesis and characterization of quaternary phosphonium-containing, trithiocarbonate RAFT agents

Quaternary phosphonium-containing RAFT agents were synthesized and used to prepare hemi-telechelic polystyrene ionomers with high end-group functionality by bulk, thermally-initiated polymerization.

Living Radical Polymerization by the RAFT Process – A Third Update

This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.