Controlled Radical Polymerization of an Acrylamide Containing l-Phenylalanine Moiety via RAFT

A Guideline for the Synthesis of Amino-Acid-Functionalized Monomers and Their Polymerizations

Amino acids have emerged as a sustainable source for the design of functional polymers. Besides their wide availability, especially their high degree of biocompatibility makes them appealing for a broad range of applications in the biomedical research field. In addition to these favorable characteristics, the versatility of reactive functional groups in amino acids (i.e., carboxylic acids, amines, thiols, and hydroxyl groups) makes them suitable starting materials for various polymerization approaches, which include step- and chain-growth reactions. This review aims to provide an overview of strategies to incorporate amino acids into polymers. To this end, it focuses on the preparation of polymerizable monomers from amino acids, which yield main chain or side chain-functionalized polymers. Furthermore, postpolymerization modification approaches for polymer side chain functionalization are discussed. Amino acids are presented as a versatile platform for the development of polymers with tailored properties.

Synthesis, Structure and Properties of the Grafted Peptidomimetic Polymer Brushes Based on Poly(N-methacryloyl-L-proline)

A new approach to synthesis at the aminated glass surface of novel biocompatible polymeric nanolayers consisting of poly(N-methacryloyl-L-proline) brushes has been developed. Formation of the polymer nanolayers has been realized in several stages. At the first stage, the glass surface has been modified by aminosilane (APTEC), afterwards monolayer of the peroxide-containing initiator (PI) based on pyromellitic acid has been tethered to this aminated surface. The immobilized PI has been used further for initiation of the grafting "from the surface" polymerization of N-methacryloyl-L-proline for obtaining of the peptidomimetic polymer brushes. Features of the reactions, as well as optimal conditions for performing the process are highlighted in this work. Presented here poly(N-methacryloyl-L-proline) grafted brush coatings are promising material for numerous applications in nanomedicine, especially for production of implants and systems of the controlled interaction with proteins and cells.

Poly(peptide): Synthesis, Structure, and Function of Peptide-Polymer Amphiphiles and Protein-like Polymers

In this Account, we describe the organization of functional peptides as densely arrayed side chains on polymer scaffolds which we introduce as a new class of material called poly(peptide). We describe two general classes of poly(peptide): (1) Peptide-Polymer Amphiphiles (PPAs), which consist of block copolymers with a dense grouping of peptides arrayed as the side chains of the hydrophilic block and connected to a hydrophobic block that drives micelle assembly, and (2) Protein-like Polymers (PLPs), wherein peptide-brush polymers are composed from monomers, each containing a peptide side chain. Peptides organized in this manner imbue polymers or polymeric nanoparticles with a range of functional qualities inherent to their specific sequence. Therefore, polymers or nanoparticles otherwise lacking bioactivity or responsiveness to stimuli, once linked to a peptide of choice, can now bind proteins, enter cells and tissues, have controlled and switchable biodistribution patterns, and be enzyme substrates (e.g., for kinases, phosphatases, proteases). Indeed, where peptide substrates are incorporated, kinetically or thermodynamically driven morphological transitions can be enzymatically induced in the polymeric material. Synergistically, the polymer enforces changes in peptide activity and function by virtue of packing and constraining the peptide. The scaffold can protect peptides from proteolysis, change the pharmacokinetic profile of an intravenously injected peptide, increase the cellular uptake of an otherwise cell impermeable therapeutic peptide, or change peptide substrate activity entirely. Moreover, in addition to the sequence-controlled peptides (generated by solid phase synthesis), the polymer can carry its own sequence-dependent information, especially through living polymerization strategies allowing well-defined blocks and terminal labels (e.g., dyes, contrast agents, charged moieties). Hence, the two elements, peptide and polymer, cooperate to yield materials with unique function and properties quite apart from each alone. Herein, we describe the development of synthetic strategies for accessing these classes of biomolecule polymer conjugates. We discuss the utility of poly(peptide)-based materials in a range of biomedical applications, including imaging of diseased tissues (myocardial infarction and cancer), delivering small molecule drugs to tumors with high specificity, imparting cell permeability to otherwise impermeable peptides, protecting bioactive peptides from proteolysis in harsh conditions (e.g., stomach acid and whole blood), and transporting proteins into traditionally difficult-to-transfect cell types, including stem cells. Poly(peptide) materials offer new properties to both the constituent peptides and to the polymers, which can be tuned by the design of the oligopeptide sequence, degree of polymerization, peptide arrangement on the polymer backbone, and polymer backbone chemistry. These properties establish this approach as valuable for the development of peptides as medicines and materials in a range of settings.

RAFT polymerization of a RGD peptide-based methacrylamide monomer for cell adhesion

The present study provides a robust method for the preparation of RGD peptide-based polymers that has important implications in the synthesized biomaterials that support cell adhesion.

Precise synthesis of poly(N-acryloyl amino acid) through photoinduced living polymerization

A library of N-acryloylamino acid polymers with controlled molecular weights and narrow molecular weight distributions (M_w/M_n < 1.20) was created by a universal and versatile photoinduced living radical polymerization technique.

Thermo-responsive polymer brushes on glass plate prepared from a new class of amino acid-derived vinyl monomers and their applications in cell-sheet engineering

In this study, we present a novel thermo-responsive polymer platform that is based on the alanine methyl ester-containing homopolymer (PNAAMe) and the copolymer with glycine methyl ester-based vinyl monomer (P(NAAMe-co-NAGMe)) brushes prepared via surface-initiated atom transfer radical polymerization. Water contact angles for these brushes measured at different temperatures reveal that the polymer brushes collapse and dehydrate around 13°C and 25°C (T_Ts), respectively, upon elevating the temperature. At 37°C, seeded fibroblasts (NIH/3T3) adhere to and spread well onto these brush surfaces although the copolymer brush of P(NAAMe-co-NAGMe) depresses the number of adherent cells less than half of that for the homopolymer of PNAAMe after 24h of cell culture due to increment in hydrophilicity. To prepare the cell-sheet, the cells are seeded on both polymer brushes and cultured at 37°C in the presence of serum. After 4days, the cells proliferated confluently on these brush surfaces. Lowering the temperature to 4°C and 20°C below T_T of each brush led to the cell-sheet detachment as a monolayer form from the polymer brushes accompanying with the switching of surface affinity.

Temperature-responsive molecular recognition chromatography using phenylalanine and tryptophan derived polymer modified silica beads

The separation system with dual temperature-response and molecular recognition characteristics leads to selective separation using only aqueous solution.

Influence of molecular weight on kinetics release of metronidazole from proline-based polymers prepared by RAFT polymerization

In the current study, the influence of polymer molecular weight on the release of metronidazole (MTZ) as a drug model from synthesized proline-based polymers was studied.

N-Ester-substituted polyacrylamides with a tunable lower critical solution temperature (LCST): the N-ester-substitute dependent thermoresponse

New thermoresponsive polymers ofN-ester-substituted polyacrylamides were discovered, and theN-ester-substitute exerting a great influence on the solution property was demonstrated.

Synthesis and characterization of poly(amino acid methacrylate)-stabilized diblock copolymer nano-objects

Two amino acid methacrylates prepared via Michael addition are used as building blocks to prepare novel diblock copolymer nano-objects via polymerisation-induced self-assembly.

Thermo-responsive amino acid-based vinyl polymers showing widely tunable LCST/UCST behavior in water

A thermo-responsive polymer system showing widely tunable UCST/LCST behaviors from amino acid-based vinyl polymers.

Side-chain amino-acid-based pH-responsive self-assembled block copolymers for drug delivery and gene transfer

Developing safe and effective nanocarriers for multitype of delivery system is advantageous for several kinds of successful biomedicinal therapy with the same carrier. In the present study, we have designed amino acid biomolecules derived hybrid block copolymers which can act as a promising vehicle for both drug delivery and gene transfer. Two representative natural chiral amino acid-containing (l-phenylalanine and l-alanine) vinyl monomers were polymerized via reversible addition-fragmentation chain transfer (RAFT) process in the presence of monomethoxy poly(ethylene glycol) based macro-chain transfer agents (mPEGn-CTA) for the synthesis of well-defined side-chain amino-acid-based amphiphilic block copolymers, monomethoxy poly(ethylene glycol)-b-poly(Boc-amino acid methacryloyloxyethyl ester) (mPEGn-b-P(Boc-AA-EMA)). The self-assembled micellar aggregation of these amphiphilic block copolymers were studied by fluorescence spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Potential applications of these hybrid polymers as drug carrier have been demonstrated in vitro by encapsulation of nile red dye or doxorubicin drug into the core of the micellar nanoaggregates. Deprotection of side-chain Boc- groups in the amphiphilic block copolymers subsequently transformed them into double hydrophilic pH-responsive cationic block copolymers having primary amino groups in the side-chain terminal. The DNA binding ability of these cationic block copolymers were further investigated by using agarose gel retardation assay and AFM. The in vitro cytotoxicity assay demonstrated their biocompatible nature and these polymers can serve as "smart" materials for promising bioapplications.

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.

Facile synthesis of multiamino vinyl poly(amino acid)s for promising bioapplications

We presented a general and facile strategy to prepare biocompatible multiamino polymers. Series of new monomers were synthesized by esterification of 2-hydroxyethyl methacrylate (HEMA) and Boc-amino acids, such as Boc-l-phenylalanine, Boc-glycine, Boc-l-alanine, Boc-l-valine, and Boc-l-lysine. Subsequent vinyl polymerization of monomers gave rise to vinyl poly(amino acid)s with a side primary amino group at each unit if deprotected. Both atom transfer radical polymerization (ATRP) and conventional free radical polymerization (FRP) were employed to prepare the multiamino polymers. A well controlled effect upon molecular weight with the standard first-order kinetics was achieved in cases of ATRP, and high molecular weight polymers were obtained via FRP. MTT assay showed that cell survival rates for the multiamino polymers were almost maintained above 90% and that their cytotoxicities were much lower than that of linear PEI (PEI 25000). Zeta potential measurements demonstrated that the vinyl poly(amino acid)s are electropositive, and AFM measurements showed that the vinyl poly(amino acid)s could tightly condense DNA into granular structures at a suitable concentration. The combination of facile availability, controlled productivity, low cytotoxicity and strong binding ability with DNA promises the great potential of the novel multiamino polymers in bioapplications.