Peptide block copolymers by N -carboxyanhydride ring-opening polymerization and atom transfer radical polymerization: The effect of amide macroinitiators

Influence of the block copolypeptide surfactant structure on the size of polypeptide nanoparticles obtained by mini emulsion polymerisation

Polypetide nanoparticles obtained by miniemulsion polymerisation of amino acid N-carboxyanhydrides (NCA) are a novel class of tuneable bio-derived functional nano materials for potential applications in nutraceutics, agriculture, and medicine. This...

Amphiphilic Star Polypept(o)ides as Nanomeric Vectors in Mucosal Drug Delivery

Mucosal delivery across the gastrointestinal (GI) tract, airways, and buccal epithelia is an attractive mode of therapeutic administration, but the challenge is to overcome the mucus and epithelial barriers. Here, we present degradable star polypept(o)ides capable of permeating both barriers as a promising biomaterial platform for mucosal delivery. Star polypept(o)ides were obtained by the initiation of benzyl-l-glutamate N-carboxyanhydride (NCA) from an 8-arm poly(propyleneimine) (PPI) dendrimer, with subsequent chain extension with sarcosine NCA. The hydrophobic poly(benzyl-l-glutamate) (PBLG) block length was maintained at 20 monomers, while the length of the hydrophilic poly(sarcosine) (PSar) block ranged from 20-640 monomers to produce star polypept(o)ides with increasing hydrophilic: hydrophobic ratios. Transmission electron microscopy (TEM) images revealed elongated particles of ∼120 nm length, while dynamic light scattering (DLS) provided evidence of a decrease in the size of polymer aggregates in water with increasing poly(sarcosine) block length, with the smallest size obtained for the star PBLG₂₀-b-PSar₆₄₀. Fluorescein isothiocyanate (FITC)-conjugated PBLG₂₀-b-PSar₆₄₀ permeated artificial mucus and isolated rat mucus, as well as rat intestinal jejunal tissue mounted in Franz diffusion chambers. An apparent permeability coefficient (P_app) of 15.4 ± 3.1 ×10^-6 cm/s for FITC-PBLG₂₀-b-PSar₆₄₀ was calculated from the transepithelial flux obtained with the apical-side addition of 7.5 mg polypept(o)ide to jejunal tissue over 2 h. This P_app could not be accounted for by flux of unconjugated FITC. Resistance to trypsin demonstrated the stability of FITC-labeled polypept(o)ide over 2 h, but enzymatic degradation at the mucus-epithelial interface or during flux could not be ruled out as contributing to the P_app. The absence of any histological damage to the jejunal tissue during the 2 h exposure suggests that the flux was not associated with overt toxicity.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Strategies from nature: polycaprolactone-based mimetic antimicrobial peptide block copolymers with low cytotoxicity and excellent antibacterial efficiency

PCL₁₆-b-K_n diblock copolymers exhibit excellent antibacterial activities and low cytotoxicity. Meanwhile, they act by the pore-forming bactericidal mechanism without inducement of drug resistance.

Synthesis of block copolymers using end-functionalized polyacetylenes as macroinitiators

A block copolymer consisting of helically twisted polyacetylene and α-helical peptide was successfully synthesized for the first time.

Strategies to Fabricate Polypeptide-Based Structures via Ring-Opening Polymerization of N-Carboxyanhydrides

In this review, we provide a general and clear overview about the different alternatives reported to fabricate a myriad of polypeptide architectures based on the ring-opening polymerization of N-carbonyanhydrides (ROP NCAs). First of all, the strategies for the preparation of NCA monomers directly from natural occurring or from modified amino acids are analyzed. The synthetic alternatives to prepare non-functionalized and functionalized NCAs are presented. Protection/deprotection protocols, as well as other functionalization chemistries are discussed in this section. Later on, the mechanisms involved in the ROP NCA polymerization, as well as the strategies developed to reduce the eventually occurring side reactions are presented. Finally, a general overview of the synthetic strategies described in the literature to fabricate different polypeptide architectures is provided. This part of the review is organized depending on the complexity of the macromolecular topology prepared. Therefore, linear homopolypeptides, random and block copolypeptides are described first. The next sections include cyclic and branched polymers such as star polypeptides, polymer brushes and highly branched structures including arborescent or dendrigraft structures.

Orthogonally reactive amino acids and end groups in NCA polymerization

We summarize recent strategies for the synthesis of orthogonally reactive polypeptides and polypeptoids by direct and post-polymerization approaches.

Polypeptide–poly(ethylene glycol) miktoarm star copolymers with a fluorescently labeled core: synthesis, delivery and imaging of siRNA

Polypeptide–PEG miktoarm star copolymers with a fluorescently labeled core have been synthesized and exhibit dual functions of gene delivery and bioimaging.

A vegetable oil-based organogel for use in pH-mediated drug delivery

Organogels prepared with vegetable oils as the liquid organic phase present an excellent platform for the controlled delivery of hydrophobic guest molecules. We disclose a graft copolymer comprised of a poly(L-serine) backbone linked to alkane side-chains by hydrolytically susceptible ester bonds, that is capable of gelating edible safflower oil. The thermoresponsive organogel formed, which is non-cytotoxic, is capable of withholding guest molecules before undergoing targeted disassembly upon incubation in solutions of acidic pH, permitting the directed release of payload molecules. The presented material offers an extremely promising candidate for the controlled delivery of hydrophobic agents within acidic environments, such as cancer tumour sites.

Amorphous and crystalline blends from polytyrosine and pyridine-functionalized anthracene: hydrogen-bond interactions, conformations, intramolecular charge transfer and aggregation-induced emission

A new pyridine-terminated fluorophore of (E)-4-(2-(anthracen-9-yl)vinyl)pyridine (AnPy) with intramolecular charge transfer and aggregation-induced emission properties was synthesized and was blended with polytyrosine (PTyr) through hydrogen-bond interactions.

Molecular weight and architectural dependence of well-defined star-shaped poly(lysine) as a gene delivery vector

A series of well-defined star-shaped polypeptides were successfully synthesised by the ring opening polymerisation (ROP) of the N-carboxyanhydride (NCA) of ε-carbobenzyloxy-l-lysine (ZLL) using a range of generations of polypropylene imine (PPI) dendrimers as multifunctional initiators. The monomer feed ratio and dendrimer generation were varied to afford a series of polypeptide dendrimer hybrids with superior structural versatility and functionality. Subsequent protecting group removal yielded star-shaped poly(lysine) of controlled variation in polypeptide chain length and arm multiplicity. Star-shaped PLL polymers were used to prepare pDNA and siRNA to form "polyplexes" to determine their ability to complex different nucleic acid cargoes and were compared with linear PLL polyplex controls. Significant differences in size and surface charge were seen between star-shaped PLL polyplexes and linear PLL polyplexes for both cargoes. The star-shaped polypeptides were capable of more effective complexation of both nucleic acids at low N/P ratios compared to linear PLL as evidenced by zeta potential and electrophoretic data. This was particularly evident in siRNA polyplexes as linear PLL failed to completely complex siRNA into nanocomplexes of appropriate size for cell transfection i.e. <200 nm in size, while star poly(lysine) formed siRNA polyplexes <100 nm at certain N/P ratios, albeit strongly dependent on the particular molecular weight and architecture, as analysed by dynamic light scattering (DLS). Atomic force microscopy (AFM) identified discrete spherically shaped polyplexes for all star-shaped polypeptide-based polyplexes while linear PLL formed elongated irregular shaped complexes. This difference in morphology may go some way towards explaining the 300-fold increase in luciferase expression seen for star-shaped PLL polyplexes G5(64)-PLL₄₀ compared to linear PLL pGLuc polyplexes in epithelial cells. Each of the PPI-PLL polymers appeared to be capable of protecting the nucleic acid cargoes from degradation by the relevant nuclease enzyme as effectively as the positive control polyethyleneimine (PEI) polyplexes. Overall the promising nucleic acid complexation, sizing, morphology and protection capacity of two different genetic "cargoes" highlight the potential of polypeptide dendrimer hybrids as gene delivery vectors.

Protein immobilization onto poly(acrylic acid) functional macroporous polyHIPE obtained by surface-initiated ARGET ATRP

Amino-functional macroporous monoliths from polymerized high internal phase emulsion (polyHIPE) were surface modified with initiators for atom transfer radical polymerization (ATRP). The ATRP initiator groups on the polyHIPE surface were successfully used to initiate activator regeneration by electron transfer (ARGET) ATRP of (meth)acrylic monomers, such as methyl methacrylate (MMA) or tert-butyl acrylate (tBA) resulting in a dense coating of polymers on the polyHIPE surface. Addition of sacrificial initiator permitted control of the amount of polymer grafted onto the monolith surface. Subsequent removal of the tert-butyl protecting groups yielded highly functional polyHIPE-g-poly(acrylic acid). The versatility to use the high density of carboxylic acid groups for secondary reactions was demonstrated by the successful conjugation of enhanced green fluorescent protein (eGFP) and coral derived red fluorescent protein (DsRed) using EDC/sulfo-NHS chemistry, on the polymer 3D-scaffold surface. The materials and methodologies presented here are simple and robust, thus, opening new possibilities for the bioconjugation of highly porous polyHIPE for bioseparation applications.

Aggregation behaviour of peptide-polymer conjugates containing linear peptide backbones and multiple polymer side chains prepared by nitroxide-mediated radical polymerization

A series of peptides with an alternating sequence of alkoxyamine conjugated lysine and glycine residues were synthesized by classical solution phase peptide coupling. The resulting peptides containing up to eight alkoxyamine moieties were used as initiators in nitroxide-mediated polymerization (NMP) to obtain peptide-polymer conjugates with well defined linear peptide backbones and a defined number of polymeric side chains. Polymerization of styrene and N-isopropylacrylamide (NIPAM) occurred in a highly controlled fashion. Molecular weight and polydispersity index (PDI) were determined by gel permeation chromatography (GPC). Aggregation behaviour of these hybrid materials was investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). Depending on composition, number and length of the polymer side chains, the conjugates aggregate to different topologies. Whereas peptide-polystyrene conjugates may aggregate to so called honeycomb structures, peptide-poly-N-isopropylacrylamide conjugates show differentiated aggregation behaviour.

How controlled and versatile is N-carboxy anhydride (NCA) polymerization at 0 °C? Effect of temperature on homo-, block- and graft (co)polymerization

The polymerization of N-carboxyanhydride (NCA) at low temperatures is controlled and allows the synthesis of a variety of well-defined polypetides.