Grafting Short Peptides onto Polybutadiene-block-poly(ethylene oxide): A Platform for Self-Assembling Hybrid Amphiphiles

Conformational Changes of Poly(Maleic Anhydride-alt-styrene) Modified with Amino Acids in an Aqueous Medium and Their Effect on Cytocompatibility and Hemolytic Response

The conformational changes of poly(maleic anhydride-alt-styrene) (PSMA) modified with different amino acids (PSMA-Aa) were studied in an aqueous medium as a function of ionic strength and pH. The specific viscosity of PSMA-Aa decreased with increasing salt concentration due to a more compact conformation. There was a decrease in surface tension with increasing concentrations of the modified polyelectrolyte having a greater effect for the PSMA modified with l-phenylalanine at pH 7.0, demonstrating a greater surface-active character. The conformational changes were also confirmed by molecular dynamics studies, indicating that PSMA-Aa exhibits a compact structure at pH 4.0 and a more extended structure at pH 7.0. On the other hand, the conformational changes of PSMA-Aa were related to its biological response, where the higher surface-active character of the PSMA modified with l-phenylalanine correlates very well with the higher hemolytic activity observed in red blood cells, in which the surface-active capacity supports lytic potency in erythrocytes. The cytocompatibility assays indicated that there were no significant cytotoxic effects of the PSMA-Aa. Additionally, in solvent-accessible surface area studies, it was shown that the carboxylate groups of the PSMA modified with l-phenylalanine are more exposed to the solvent at pH 7.0 and high salt concentrations, which correlates with lower fluorescence intensity, reflecting a loss of mitochondrial membrane potential. It is concluded that the study of the conformational changes in PE modified with amino acids is essential for their use as biomaterials and relevant to understanding the possible effects of PE modified with amino acids in biological systems.

Enzymatic and Chemical Approaches for Post-Polymerization Modifications of Diene Rubbers: Current state and Perspectives

Diene rubbers are polymeric materials which present elastic properties and have double bonds in the macromolecular backbone after the polymerization process. Post-polymerization modifications of rubbers can be conducted by enzymatic or chemical methods. Enzymes are environmentally friendly catalysts and with the increasing demand for rubber waste management, biodegradation and biomodifications have become hot topics of research. Some rubbers are renewable materials and are a source of organic molecules, and biodegradation can be conducted to obtain either oligomers or monomers. On the other hand, chemical modifications of rubbers by click-chemistry are important strategies for the creation and combination of new materials. In a way to expand the scope of uses to other non-traditional applications, several and effective modifications can be conducted with diene rubbers. Two groups of efficient tools, enzymatic, and chemical modifications in diene rubbers, are summarized in this review. By analyzing stereochemical and reactivity aspects, the authors also point to some applications perspectives for biodegradation products and to rational modifications of diene rubbers by combining both methodologies.

BODIPY-based fluorescent polymeric probes for selective detection of Fe3+ ions in aqueous solution

It is of scientific and practical significance to sense and to remove heavy metal ions in the environment. In this work, four BODIPY-based fluorescent polymeric probes with the ability to sense and separate Fe3+ ions have been prepared via thiol-ene click reaction. The polymers have good thermal stability. Meanwhile, the results show that they have selective recognition capabilities only for Fe3+, which are mainly manifested as significant quenching of fluorescence and color modulation under visible light. The sensitivity is good, and the limit of detection reaches as low as 0.14 µM. They can also be used as reversible chemical probes to detect Fe3+. Therefore, the click reaction provides us with a facile method for preparing fluorescent polymer probes.

Control of Particle Size in the Self-Assembly of Amphiphilic Statistical Copolymers

A range of amphiphilic statistical copolymers is synthesized where the hydrophilic component is either methacrylic acid (MAA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic component comprises methyl, ethyl, butyl, hexyl, or 2-ethylhexyl methacrylate, which provide a broad range of partition coefficients (log P). Small-angle X-ray scattering studies confirm that these amphiphilic copolymers self-assemble to form well-defined spherical nanoparticles in an aqueous solution, with more hydrophobic copolymers forming larger nanoparticles. Varying the nature of the alkyl substituent also influenced self-assembly with more hydrophobic comonomers producing larger nanoparticles at a given copolymer composition. A model based on particle surface charge density (PSC model) is used to describe the relationship between copolymer composition and nanoparticle size. This model assumes that the hydrophilic monomer is preferentially located at the particle surface and provides a good fit to all of the experimental data. More specifically, a linear relationship is observed between the surface area fraction covered by the hydrophilic comonomer required to achieve stabilization and the log P value for the hydrophobic comonomer. Contrast variation small-angle neutron scattering is used to study the internal structure of these nanoparticles. This technique indicates partial phase separation within the nanoparticles, with about half of the available hydrophilic comonomer repeat units being located at the surface and hydrophobic comonomer-rich cores. This information enables a refined PSC model to be developed, which indicates the same relationship between the surface area fraction of the hydrophilic comonomer and the log P of the hydrophobic comonomer repeat units for the anionic (MAA) and cationic (DMAEMA) comonomer systems. This study demonstrates how nanoparticle size can be readily controlled and predicted using relatively ill-defined statistical copolymers, making such systems a viable attractive alternative to diblock copolymer nanoparticles for a range of industrial applications.

Thiol–ene coupling reaction achievement and monitoring by “in situ” UV irradiation NMR spectroscopy

In this study, the possibilities of a new “in situ” LED UV illumination NMR spectroscopic technique for performing an initiator-free thiol–ene “click” coupling reaction of an allyl-functionalized poly(allyl glycidyl ether) (PAGE) prepolymer with a number of mono- and di-oligo polyethylene glycol (PEG) thiols is demonstrated. The state-of-the-art setup constructed with LEDs as UV light sources that illuminate through optical fibers directly into an NMR testing tube at a fixed wavelength of 365 nm is appropriate for various polymeric materials and biologically active substances. The selected experimental protocol uses a series of periods of irradiation and dark periods, thus providing opportunities to conduct an effective thiol–ene “click” reaction and simultaneously study the kinetics of the photochemical reaction with the exposure time, as well as macromolecular association directly in a solution applying the whole types of NMR methods: from conventional ¹H or ¹³C NMR to diffusion NMR spectroscopy (DOSY). In addition, the molecular mass characteristics of the prepared copolymers were studied by gel-permeation chromatography (GPC). The observed differences in the reaction rates as well as in the size of species formed (the corresponding hydrodynamic radiuses R_h of aggregates) as a result of the coupling process of parent PAGE prepolymers and model PEG thiols were thoroughly discussed and the reaction pathway proposed.

An “In situ” LED UV illumination NMR setup for achievement of initiator-free coupling reactions of allyl-functionalized poly(allyl glycidyl ether) with polyethylene glycols thiols.

Fabrication of biocleavable crosslinked polyprodrug vesicles via reversible donor–acceptor interactions for enhanced anticancer drug delivery

Reversible donor–acceptor interactions were used to prepare biocleavable crosslinked polyprodrug vesicles toward enhanced anticancer drug delivery.

Thiol-Mediated Chemoselective Strategies for In Situ Formation of Hydrogels

Hydrogels are three-dimensional networks composed of hydrated polymer chains and have been a material of choice for many biomedical applications such as drug delivery, biosensing, and tissue engineering due to their unique biocompatibility, tunable physical characteristics, flexible methods of synthesis, and range of constituents. In many cases, methods for crosslinking polymer precursors to form hydrogels would benefit from being highly selective in order to avoid cross-reactivity with components of biological systems leading to adverse effects. Crosslinking reactions involving the thiol group (SH) offer unique opportunities to construct hydrogel materials of diverse properties under mild conditions. This article reviews and comments on thiol-mediated chemoselective and biocompatible strategies for crosslinking natural and synthetic macromolecules to form injectable hydrogels for applications in drug delivery and cell encapsulation.

pH-Sensitive Poly(histidine methacrylamide)

This research reports a synthetic amino acid based zwitterionic poly(histidine methacrylamide) (PHisMA), which possesses switchability among zwitterionic, anionic, and cationic states, pH-dependent antifouling properties, and chelation capability to multivalent metal ions. The PHisMA polymer brush surface shows good antifouling properties to resist protein adsorption and bacterial attachment in its zwitterionic state at pH 5. This study also demonstrates that the solution acidity significantly affects the mechanical properties of PHisMA hydrogels. PHisMA hydrogels show higher viscoelastic properties and lower swelling ratios in the zwitterionic state at pH 4 and pH 5, compared to higher or lower pH conditions. It was discovered that PHisMA can chelate multivalent metal ions, such as Ca(2+), Mg(2+), Cu(2+), Ni(2+) and Fe(3+). This study provides us a better understanding of structure-property relationships of switchable zwitterionic polymers. PHisMA can potentially be adapted for a broad range of applications including wound care, water treatment, bioseparation, coating, drug and gene delivery carriers, etc.

Disk-like micelles with cylindrical pores from amphiphilic polypeptide block copolymers

An unprecedented 2-dimensional disk-like micelle with cylindrical pores was achieved by self-assembly of amphiphilic block copolypeptides PEG-b-PBLG with an α-helical conformation of PBLG blocks.

Self-assembly concepts for multicompartment nanostructures

Compartmentalization is ubiquitous to many biological and artificial systems, be it for the separate storage of incompatible matter or to isolate transport processes. Advancements in the synthesis of sequential block copolymers offer a variety of tools to replicate natural design principles with tailor-made soft matter for the precise spatial separation of functionalities on multiple length scales. Here, we review recent trends in the self-assembly of amphiphilic block copolymers to multicompartment nanostructures (MCNs) under (semi-)dilute conditions, with special emphasis on ABC triblock terpolymers. The intrinsic immiscibility of connected blocks induces short-range repulsion into discrete nano-domains stabilized by a third, soluble block or molecular additive. Polymer blocks can be synthesized from an arsenal of functional monomers directing self-assembly through packing frustration or response to various fields. The mobility in solution further allows the manipulation of self-assembly processes into specific directions by clever choice of environmental conditions. This review focuses on practical concepts that direct self-assembly into predictable nanostructures, while narrowing particle dispersity with respect to size, shape and internal morphology. The growing understanding of underlying self-assembly mechanisms expands the number of experimental concepts providing the means to target and manipulate progressively complex superstructures.

Recycling tires? Reversible crosslinking of poly(butadiene)

Furan-modified poly(butadiene) prepared by the thiol-ene click reaction is crosslinked with bismaleimides through the Diels-Alder reaction, giving rise to a novel recyclable elastomer. This is possible because of the thermal reversibility of the adducts responsible for the formation of the network. The use of this strategy provides the possibility to produce recyclable tires.

Terpolymerization of propylene oxide and vinyl oxides with CO2: copolymer cross-linking and surface modification via thiol–ene click chemistry

Terpolymerization of epoxides containing vinyl pendant groups, propylene oxide, and carbon dioxide afforded polycarbonates which were cross-linked and surface modified via thiol–ene chemistry.

PEG-peptide conjugates

The remarkable diversity of the self-assembly behavior of PEG-peptides is reviewed, including self-assemblies formed by PEG-peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized.

Self-assembly and chemical processing of block copolymers: a roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures. Their assembly structures are influenced by their inherent structures, and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies. Some examples include self-assembly, directed assembly, coupling, as well as hierarchical assembly, which can yield assemblies having even higher structural order. These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching, the former technique leading to permanent structures, the latter towards sculpted and the combination of the two towards permanent sculpted structures. The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures. This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.

Controlled synthesis of amino acid-based pH-responsive chiral polymers and self-assembly of their block copolymers

Leucine/isoleucine side chain polymers are of interest due to their hydrophobicity and reported role in the formation of α-helical structures. The synthesis and reversible addition-fragmentation chain transfer (RAFT) polymerization of amino acid-based chiral monomers, namely Boc-L-leucine methacryloyloxyethyl ester (Boc-L-Leu-HEMA, 1a), Boc-L-leucine acryloyloxyethyl ester (Boc-L-Leu-HEA, 1b), Boc-L-isoleucine methacryloyloxyethyl ester (Boc-L-Ile-HEMA, 1c), and Boc-L-isoleucine acryloyloxyethyl ester (Boc-L-Ile-HEA, 1d), are reported. The controlled nature of the polymerization of the said chiral monomers in N, N-dimethylformamide (DMF) at 70 °C is evident from the formation of narrow polydisperse polymers, the molecular weight controlled by the monomer/chain transfer agent (CTA) molar ratio and the linear relationship between molecular weight and monomer conversion. The resulting well-defined polymers were used as macro-CTAs to prepare corresponding diblock copolymers by RAFT polymerization of methyl (meth)acrylate monomers. Deprotection of Boc groups in the homopolymers and block copolymers under acidic conditions produced cationic, pH-responsive polymers with primary amine moieties at the side chains. The optical activity of the homopolymers and block copolymers were studied using circular dichroism (CD) spectroscopy and specific rotation measurements. The self-assembling nature of the block copolymers to produce highly ordered structures was illustrated through dynamic light scattering (DLS) and atomic force microscopy (AFM) studies. The side chain amine functionality instills pH-responsive behavior, which makes these cationic polymers attractive candidates for drug delivery applications, as well as for conjugation of biomolecules.

Structural changes in block copolymer micelles induced by cosolvent mixtures

We investigated the influence of tetrahydrofuran (THF) addition on the structure of poly(1,2-butadiene-b-ethylene oxide) [PB-PEO] micelles in aqueous solution. Our studies showed that while the micelles remained starlike, the micelle core-corona interfacial tension and micelle size decreased upon THF addition. The detailed effects of the reduction in interfacial tension were probed using contrast variations in small angle neutron scattering (SANS) experiments. At low THF contents (high interfacial tensions), the SANS data were fit to a micelle form factor that incorporated a radial density distribution of corona chains to account for the starlike micelle profile. However, at higher THF contents (low interfacial tensions), the presence of free chains in solution affected the scattering at high q and required the implementation of a linear combination of micelle and Gaussian coil form factors. These SANS data fits indicated that the reduction in interfacial tension led to broadening of the core-corona interface, which increased the PB chain solvent accessibility at intermediate THF solvent fractions. We also noted that the micelle cores swelled with increasing THF addition, suggesting that previous assumptions of the micelle core solvent content in cosolvent mixtures may not be accurate. Control over the size, corona thickness, and extent of solvent accessible PB in these micelles can be a powerful tool in the development of targeting delivery vehicles.

From polymer to small organic molecules: a tight relationship between radical chemistry and solid-phase organic synthesis

Since Gomberg's discovery of radicals as chemical entities, the interest around them has increased through the years. Nowadays, radical chemistry is used in the synthesis of 75% of all polymers, inevitably establishing a close relationship with Solid-Phase Organic Synthesis. More recently, the interest of organic chemists has shifted towards the application of usual "in-solution" radical chemistry to the solid-phase, ranging from the use of supported reagents for radical reactions, to the development of methodologies for the synthesis of small molecules or potential libraries. The aim of this review is to put in perspective radical chemistry, moving it away from its origin as a synthetic means for solid supports, to becoming a useful tool for the synthesis of small molecules.

Vertically aligned multilayer films of monodispersed helical polypeptides with micrometer thickness via simple cast

Utilizing the zwitterionic alpha-helix peptide bearing a cationic and anionic group at the N- and C-terminus, respectively, we first demonstrated that the vertically aligned multilayer film can be prepared by a simple cast and slow evaporation. The tilt angle of the peptide remained unchanged with ca. 30 degrees in the range between submicrometer and several micrometers in thickness. The key designs allowing simple vertical alignment of the helical peptide multilayer films were (i) monodispersity of the peptide, (ii) electrostatic interaction between anionic substrate and the cationic group bearing at the N-terminus of the peptide, and (iii) interlayer electrostatic interaction among terminal groups of the peptide.

Chemoselective immobilization of peptides on abiotic and cell surfaces at controlled densities

We report herein a new and enabling approach for decorating both abiotic and cell surfaces with the extracellular matrix IKVAV peptide in a site-specific manner using strain promoted azide-alkyne cycloaddition. A cyclooctyne-derivatized IKVAV peptide was synthesized and immobilized on the surface of pancreatic islets through strain-promoted azide-alkyne cycloaddition with cell surface azides generated by the electrostatic adsorption of a cytocompatible poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) copolymer bearing azido groups (PP-N(3)). Both "one-pot" and sequential addition of PP-N(3) and a cyclooctyne-derivatized IKVAV peptide conjugate enabled efficient modification of the pancreatic islet surface in less than 60 min. The ability to bind peptides at controlled surface densities was demonstrated in a quantitative manner using microarrays. Additionally, the technique is remarkably rapid and highly efficient, opening new avenues for the molecular engineering of cellular interfaces and protein and peptide microarrays.