Bioinspired Anchorable Thiol-Reactive Polymers: Synthesis and Applications Toward Surface Functionalization of Magnetic Nanoparticles

Functional magnetic nanoparticles for protein delivery applications: understanding protein-nanoparticle interactions

Iron oxide nanoparticles (IONPs) surface functionalised with thermo-responsive polymers can encapsulate therapeutic proteins and release them upon heating with an alternating magnetic field above the lower critical solution temperature (LCST). In order to make this delivery system clinically-relevant, we prepared IONPs coated with poly-N-isopropylmethacrylamide (PNIPMAM), a polymer with LCST above human body temperature. The optimal polymer chain length and nanoparticle size to achieve LCST of ca. 45 °C were 19 kDa PNIPMAM and 16 nm IONPs. The PNIPMAM-coated IONPs could encapsulate a range of proteins which were released upon heating above LCST in the presence of a competitor protein or serum. A small amount of encapsulated protein leakage was observed below LCST. The efficiency of protein encapsulation and release was correlated with molecular weight and glycosylation state of the proteins. Magnetic heating resulted in a faster protein release as compared to conventional heating without significant temperature increase of the bulk solution.

Photoswitchable dynamic conjugate addition-elimination reactions as a tool for light-mediated click and clip chemistry

Phototriggered click and clip reactions can endow chemical processes with high spatiotemporal resolution and sustainability, but are challenging with a limited scope. Herein we report photoswitchable reversible covalent conjugate addition-elimination reactions toward light-addressed modular covalent connection and disconnection. By coupling between photochromic dithienylethene switch and Michael acceptors, the reactivity of Michael reactions was tuned through closed-ring and open-ring forms of dithienylethene, allowing switching on and off dynamic exchange of a wide scope of thiol and amine nucleophiles. The breaking of antiaromaticity in transition states and enol intermediates of addition-elimination reactions provides the driving force for photoinduced change in kinetic barriers. To showcase the versatile application, light-mediated modification of solid surfaces, regulation of amphiphilic assemblies, and creation/degradation of covalent polymers on demand were achieved. The manipulation of dynamic click/clip reactions with light should set the stage for future endeavors, including responsive assemblies, biological delivery, and intelligent materials.

Synthesis, characterization and post-modification of aromatic (Co)polyesters possessing pendant maleimide groups

A new series of (co)polyesters possessing pendent maleimide groups was synthesized by low temperature solution polycondensation of 4, 4’-(5-maleimidopentane-2, 2-diyl) diphenol (BPA-MA) with isophthalic acid chloride (IPC), terephthalic acid chloride (TPC) and a mixture of TPC and IPC (50:50 mol %). Copolyesters were also synthesized by polycondensation of varying compositions of BPA-MA and bisphenol-A (BPA) with IPC. The chemical structures and compositions of (co)polyesters were confirmed by NMR spectroscopy. Inherent viscosity values and number-average molecular weights of (co)polyesters were in the range 0.50–0.76 dL/g and 17,700-32,100 g/mol, respectively, indicating the formation of reasonably high molecular weight polymers. (Co)polyesters were readily soluble in common organic solvents and could be cast into tough, transparent and flexible films from chloroform solutions. (Co)polyesters exhibited 10% weight loss and glass transition temperatures in the range 464–468 and 142–178°C, respectively. A representative copolyester possessing pendant maleimide groups was chemically modified via metal-free azide-maleimide 1,3-dipolar cycloaddition click reaction with two azido compounds, namely, (azidomethyl)benzene (Bz-N3) and 1-(azidomethyl)-pyrene (Py-N3) to yield corresponding modified copolyesters in a quantitative manner.

Fundamental Methods for the Phase Transfer of Nanoparticles

The utilization of nanoparticles for a variety of applications has raised much interest in recent years as new knowledge has emerged in nanochemistry. New and diverse methods for synthesis, characterization, and application of these particles have been discovered with differing degrees of ease and reproducibility. Post-synthetic modification of nanoparticles is often a required step to facilitate their use in applications. The reaction conditions and chemical environment for the nanoparticle synthesis may not support or may conflict with further reactions. For this reason, it is beneficial to have phase transfer methods for nanoparticles to allow for their dispersion in a variety of solvents. Phase transfer methods are often limited in the types and sizes of particles that can be effectively dispersed in an immiscible solvent. Currently, general transfer methods for a wide variety of nanoparticles have not been identified. New routes for phase transfer allow for utilization of a larger range of particles in applications which were previously limited by solubility and reactivity issues. In this work, we will describe the fundamental methods for the phase transfer of metallic nanoparticles. We will look at the major problems and pitfalls of these methods. The applications of phase transfer will also be reviewed, mainly focusing on catalysis and drug delivery.

Linear Coordination Polymer Synthesis from Bis-Catechol Functionalized RAFT Polymers

Catechol-Fe(III) complexes contain some of the strongest known metal-chelate coordination bonds. Despite this, they have until now not been utilized in (polymeric linker) linear coordination polymer (LCP) synthesis. With the view of generating catechol end-functional polymers, a new, symmetrical bis-catechol functionalized trithiocarbonate reversible addition fragmentation chain transfer (RAFT) agent is synthesized (CatDMAT). Acrylamide (AM) and dimethylacrylamide (DMA) polymerizations are conducted with CatDMAT using direct photoactivation RAFT polymerization to yield bis-catechol end-functionalized homo- and block-copolymers of molecular weight 10-15 kDa. Catechol-Fe(III) LCPs are successfully formed from the telechelic catechol polymers by bis-complexation to Fe(III). The tetrahedral bis-complex is detected by UV-vis spectroscopy (λ_max  = 570 nm), while increases in relative viscosity and M_n,GPC over their respective uncomplexed polymers confirm the occurrence of supramolecular polymerization. The catechol-LCPs are shown to undergo oxidation and crosslinking in aqueous solution after 24 h.

Multifunctional and Transformable 'Clickable' Hydrogel Coatings on Titanium Surfaces: From Protein Immobilization to Cellular Attachment

Multifunctionalizable hydrogel coatings on titanium interfaces are useful in a wide range of biomedical applications utilizing titanium-based materials. In this study, furan-protected maleimide groups containing multi-clickable biocompatible hydrogel layers are fabricated on a titanium surface. Upon thermal treatment, the masked maleimide groups within the hydrogel are converted to thiol-reactive maleimide groups. The thiol-reactive maleimide group allows facile functionalization of these hydrogels through the thiol-maleimide nucleophilic addition and Diels-Alder cycloaddition reactions, under mild conditions. Additionally, the strained alkene unit in the furan-protected maleimide moiety undergoes radical thiol-ene reaction, as well as the inverse-electron-demand Diels-Alder reaction with tetrazine containing molecules. Taking advantage of photo-initiated thiol-ene 'click' reactions, we demonstrate spatially controlled immobilization of the fluorescent dye thiol-containing boron dipyrromethene (BODIPY-SH). Lastly, we establish that the extent of functionalization on hydrogels can be controlled by attachment of biotin-benzyl-tetrazine, followed by immobilization of TRITC-labelled ExtrAvidin. Being versatile and practical, we believe that the described multifunctional and transformable 'clickable' hydrogels on titanium-based substrates described here can find applications in areas involving modification of the interface with bioactive entities.

Mussel-inspired coordination functional polymer brushes-decorated rGO-stabilized silver nanoparticles composite for antibacterial application

A catechol-terminated coordination functional polymer-modified rGO supported AgNPs composite was fabricated. Grafted polymer brushes improve the material's hydrophilicity and dispersion stability of AgNPs on rGO, enhancing antibacterial activity.

A modular and orthogonally reactive platform for fabrication of polymer–drug conjugates for targeted delivery

Increasing interest in utilization of polymeric systems in targeted drug delivery has necessitated fabrication of polymers that undergo facile functionalization with targeting groups and therapeutic agents in a modular and orthogonal fashion.

Thiol-reactive thiosulfonate group containing copolymers: facile entry to disulfide-mediated polymer conjugation and redox-responsive functionalizable networks

Herein, we report a synthetic approach to thiol-reactive polymers containing methanethiosulfonate groups as side chains, and demonstrate their application in post-polymerization functionalization through reversible disulfide linkages.

Magnetic glyconanoparticles for selective lectin separation and purification

A modular platform for the separation and purification of lectins using polymer coated iron oxide nanoparticles is developed.

The emerging applications of click chemistry reactions in the modification of industrial polymers

Click chemistry reactions have been applied to the modification of major industrial polymers by analysing the synthetic approaches and the resulting material properties.

The Taming of the Maleimide: Fabrication of Maleimide-Containing 'Clickable' Polymeric Materials

Functional polymers are widely employed in various areas of biomedical sciences. In order to tailor them for desired applications, facile and efficient functionalization of these polymeric materials under mild and benign conditions is important. Polymers containing reactive maleimide groups can be employed for such applications since they provide an excellent handle for conjugation of thiol- and diene-containing molecules and biomolecules. Until recently, fabrication of maleimide containing polymeric materials has been challenging due to the interference from the highly reactive double bond. A Diels-Alder/retro Diels-Alder reaction sequence based strategy to transiently mask the maleimide group provides access to such polymeric materials. In this personal account, we summarize contributions from our group towards the fabrication and functionalization of maleimide-containing polymeric materials over the past decade.

Polymer Nanocomposites via Click Chemistry Reactions

The emerging areas of polymer nanocomposites, as some are already in use in industrial applications and daily commodities, have the potential of offering new technologies with all manner of prominent capabilities. The incorporation of nanomaterials into polymeric matrix provides significant improvements, such as higher mechanical, thermal or electrical properties. In these materials, interface/interphase of components play a crucial role bringing additional features on the resulting nanocomposites. Among the various preparation strategies of such materials, an appealing strategy relies on the use of click chemistry concept as a multi-purpose toolbox for both fabrication and modulation of the material characteristics. This review aims to deliver new insights to the researchers of the field by noticing effective click chemistry-based methodologies on the preparation of polymer nanocomposites and their key applications such as optic, biomedical, coatings and sensor.

Functionalization of Reduced Graphene Oxide via Thiol-Maleimide "Click" Chemistry: Facile Fabrication of Targeted Drug Delivery Vehicles

Materials based on reduced graphene oxide (rGO) have shown to be amenable to noncovalent functionalization through hydrophobic interactions. The scaffold, however, does not provide sufficient covalent linkage given the low number of reactive carboxyl and alcohol groups typically available on the rGO. The integration of clickable groups, particularly the ones that can undergo efficient conjugation without any metal catalyst, would allow facile functionalization of these materials. This study reports on the noncovalent association of a maleimide-containing catechol (dopa-MAL) surface anchor onto the rGO. Thiol-maleimide chemistry allows thereafter the facile attachment of thiol-containing molecules under ambient metal-free conditions. Although the attachment of glutathione and 6-(ferrocenyl)hexanethiol was used as model thiols, the attachment of a cancer cell targeting cyclic peptide, c(RGDfC), opened the possibility of using the dopa-MAL-modified rGO as a targeted drug delivery system for doxorubicin (DOX). Although free DOX showed to be more effective at killing the human cervical cancer cells (HeLa) over human breast adenocarcinoma cancer cells (MDA-MB-231), the DOX-loaded rGO/dopa-MAL-c (RGDfC) nanostructure showed an opposite effect being notably more effective at targeting and killing the MDA-MB-231 cells. The effect is enhanced upon laser irradiation for 10 min at 2 W cm^-2. The facile fabrication and functionalization to readily obtain a functional material in a modular fashion make this clickable-rGO construct an attractive platform for various applications.

Surface-Anchored Thiol-Reactive Soft Interfaces: Engineering Effective Platforms for Biomolecular Immobilization and Sensing

Fabrication of antibiofouling, specifically reactive polymeric coatings that undergo facile functionalization with thiol-bearing small molecules and ligands, yields effective platforms for biomolecular immobilization and sensing. Poly(ethylene glycol) (PEG)-based copolymers containing alkoxysilyl groups to enable surface-anchoring and furan-protected maleimide groups as latent thiol-reactive moieties as side-chains were synthesized. Reactive interfaces were obtained by coating these copolymers onto Si/SiO₂ or glass surfaces and activating the maleimide groups to their thiol-reactive forms via thermal treatment. A series of surfaces modified with copolymers containing varying amounts of maleimide groups were synthesized. Effectiveness of surface modification was probed using Fourier transform infrared spectroscopy, contact angle goniometry, ellipsometry and X-ray photoelectron spectroscopy. Facile surface modification through thiol-maleimide conjugation was established by attachment of a thiol-containing fluorescent dye, namely BODIPY-SH. It was demonstrated that these surfaces allow spatially localized modification through microcontact printing. Importantly, the extent of surface modification could be tuned by varying the initial composition of the copolymer used for coating. Using fluorescence microscopy, it was observed that increasing amount of fluorescent dye was attached onto surfaces fabricated with copolymers with increasing amount of masked maleimide groups. Thereafter, the thiol-maleimide conjugation was utilized to decorate these surfaces with biotin, a protein-binding ligand. It was observed that though these biotinylated surfaces were able to bind Streptavidin effectively, some nonspecific binding was observed on places that were not in conformal contact with the stamp during microcontact printing. This nonspecific binding was eliminated upon neutralizing the residual maleimide units on the printed surface using thiol-containing PEG. Notably, fluorescence analysis of Streptavidin immobilized onto biotinylated surfaces fabricated using varying amounts of maleimide demonstrated that the amount of immobilized protein could be tuned by varying surface composition. It can be envisioned that facile fabrication of these maleimide-containing polymeric surfaces, their effective functionalization in a tunable manner to engineer interfaces for effective immobilization or sensing of biomolecules in a spatially controlled manner would make them attractive candidates for various biotechnological applications.

Synthesis of Peptide-Functionalized Poly(bis-sulfone) Copolymers Regulating HIV-1 Entry and Cancer Stem Cell Migration

Peptide-polymer conjugates have been regarded as primary stronghold in biohybrid nanomedicine, which has seen extensive development due to its intrinsic property to provide complementary functions of both the peptide material and the synthetic polymer platform. Here we present an advanced macromolecular therapeutic that targets two exclusive classes of important diseases (namely, the HIV and cancer) that are implicated by extremely different causative agents. Using a facile thiol-reactive monomer, the eventual polymer facilitates multivalent conjugation of an endogenous peptide WSC02 that targets the CXCR4 chemokine receptor. The biohybrid material demonstrated both potent antiviral effects against HIV-1 as well as inhibiting cancer stem cell migration thus establishing the foundation for multimodal nanotherapeutics that simultaneously target more than one class of disease implications.

Bio-Inspired Fluoro-polydopamine Meets Barium Titanate Nanowires: A Perfect Combination to Enhance Energy Storage Capability of Polymer Nanocomposites

Rapid evolution of energy storage devices expedites the development of high-energy-density materials with excellent flexibility and easy processing. The search for such materials has triggered the development of high-dielectric-constant (high-k) polymer nanocomposites. However, the enhancement of k usually suffers from sharp reduction of breakdown strength, which is detrimental to substantial increase of energy storage capability. Herein, the combination of bio-inspired fluoro-polydopamine functionalized BaTiO₃ nanowires (NWs) and a fluoropolymer matrix offers a new thought to prepare polymer nanocomposites. The elaborate functionalization of BaTiO₃ NWs with fluoro-polydopamine has guaranteed both the increase of k and the maintenance of breakdown strength, resulting in significantly enhanced energy storage capability. The nanocomposite with 5 vol % functionalized BaTiO₃ NWs discharges an ultrahigh energy density of 12.87 J cm^-3 at a relatively low electric field of 480 MV m^-1, more than three and a half times that of biaxial-oriented polypropylene (BOPP, 3.56 J cm^-3 at 600 MV m^-1). This superior energy storage capability seems to rival or exceed some reported advanced nanoceramics-based materials at 500 MV m^-1. This new strategy permits insights into the construction of polymer nanocomposites with high energy storage capability.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

Modular Fabrication of Polymer Brush Coated Magnetic Nanoparticles: Engineering the Interface for Targeted Cellular Imaging

Development of efficient and rapid protocols for diversification of functional magnetic nanoparticles (MNPs) would enable identification of promising candidates using high-throughput protocols for applications such as diagnostics and cure through early detection and localized delivery. Polymer brush coated magnetic nanoparticles find use in many such applications. A protocol that allows modular diversification of a pool of parent polymer coated nanoparticles will lead to a library of functional materials with improved uniformity. In the present study, polymer brush coated parent magnetic nanoparticles obtained using reversible addition-fragmentation chain transfer (RAFT) polymerization are modified to obtain nanoparticles with different "clickable" groups. In this design, trithiocarbonate group terminated polymer brushes are "grafted from" MNPs using a catechol group bearing initiator. A postpolymerization radical exchange reaction allows installation of "clickable" functional groups like azides and maleimides on the chain ends of the polymers. Thus, modified MNPs can be functionalized using alkyne-containing and thiol-containing moieties like peptides and dyes using the alkyne-azide cycloaddition and the thiol-ene conjugation, respectively. Using the approach outlined here, a cell surface receptor targeting cyclic peptide and a fluorescent dye are attached onto nanoparticle surface. This multifunctional construct allows selective recognition of cancer cells that overexpress integrin receptors. Furthermore, the approach outlined here is not limited to the installation of azide and maleimide functional groups but can be expanded to a variety of "clickable" groups to allow nanoparticle modification using a broad range of chemical conjugations.

Synthesis of magnetic microporous organic nanotube networks for adsorption application

Magnetic microporous organic nanotube networks (Fe₃O₄-MONNs) are successfully synthesized by an in situ hyper-cross-linking reaction between magnetic nanoparticles and core–shell bottlebrush copolymers.

Marrying mussel inspired chemistry with photoiniferters: a novel strategy for surface functionalization

We demonstrated a novel strategy of marrying mussel inspired chemistry with photoiniferters for surface functionalization.

Synthesis of well-defined catechol polymers for surface functionalization of magnetic nanoparticles

Well-defined fluorescent functional polymers with terminal catechol groups were synthesized by SET-LRP under aqueous conditions for “grafting to” modification of iron oxide nanoparticles.

Design and Synthesis of Water-Soluble Multifunctionalizable Thiol-Reactive Polymeric Supports for Cellular Targeting

Design and synthesis of novel water-soluble polymers bearing reactive side chains are actively pursued due to their increasing demand in areas such as bioconjugation and drug delivery. This study reports the fabrication of poly(ethylene glycol) methacrylate based thiol-reactive water-soluble polymeric supports that can serve as targeted drug delivery vehicles. Thiol-reactive maleimide units were incorporated into polymers as side chains by use of a furan-protected maleimide containing monomer. Atom transfer radical polymerization (ATRP) was employed to obtain a family of well-defined copolymers with narrow molecular weight distributions. After the polymerization, the maleimide groups were activated to their reactive form, ready for conjugation with thiol-containing molecules. Efficient functionalization of the maleimide moieties was demonstrated by conjugation of a tripeptide glutathione under mild and reagent-free aqueous conditions. Additionally, hydrophobic thiol-containing dye (Bodipy-SH) and a cyclic peptide-based targeting group (cRGDfC) were sequentially appended onto the maleimide bearing polymers to demonstrate their efficient multifunctionalization. The conjugates were utilized for in vitro experiments over both cancerous and healthy breast cell lines. Obtained results demonstrate that the conjugates were nontoxic, and displayed efficient cellular uptake. The presence of the peptide based targeting group had a clear effect on increasing the uptake of the dye-conjugated polymers into cells when compared to the construct devoid of the peptide. Overall, the facile synthesis and highly efficient multifunctionalization of maleimide-containing thiol-reactive copolymers offer a novel and attractive class of polyethylene glycol-based water-soluble supports for drug delivery.

Adhesive RAFT agents for controlled polymerization of acrylamide: effect of catechol-end R groups

Synthesizing polyacrylamide (PAM) inorganic nanocomposites with stable tethering and controlled polymer length has been elusive.

Solubilization, dispersion and stabilization of magnetic nanoparticles in water and non-aqueous solvents: recent trends

Solubilization and stabilization techniques for magnetic nanoparticles in water and in non-aqueous solvents are reviewed.