Block Polypeptoids: Synthesis, Characterization, and Response Toward Irradiation with UV Light and Temperature

Self-Assembly Study of Block Copolypeptoids in Response to pH and Temperature Stimulation

Polypeptoids with well-designed structures have the ability to self-assemble into nanomaterials, which have wide potential applications. In this study, a series of diblock copolypeptoids were synthesized via ring-opening polymerization followed by click chemistry and exhibited both temperature and pH stimulation responsiveness. Under specific temperature and pH conditions, the responsive blocks in the copolypeptoids became hydrophobic and aggregated to form micelles. The self-assembly process was monitored using the UV-Vis and DLS methods, which suggested the reversible transition of free molecules to micelles and bigger aggregates upon instituting temperature and pH changes. By altering the length and proportion of each block, the copolypeptoids displayed varying self-assembly characteristics, and the transition temperature could be tuned. With good biocompatibility, stability, and no cytotoxicity, the polypeptoids reported in this study are expected to be applied as bionanomaterials in fields including drug delivery, tissue engineering, and intelligent biosensing.

Reversible transformation of peptide assembly between densified-polysarcosine-driven kinetically and helix-orientation-driven thermodynamically stable morphologies

Stimuli-responsive transformable biomaterials development can be manipulated practically by fine-tuning the built-in molecular design of their structural segments. Here, we demonstrate a peptide assembly by the bola-type amphiphilic polypeptide, glycolic acid-polysarcosine (PSar)13-b-(L-Leu-Aib)6-b-PSar13-glycolic acid (S13L12S13), which shows morphological transformations between hydrophilic chain-driven and hydrophobic unit-driven morphologies. The hydrophobic α-helical unit (L-Leu-Aib)6 precisely controls packing in the hydrophobic layer of the assembly and induces tubule formation. The densified, hydrophilic PSar chain on the assembly surface becomes slightly more hydrophobic as the temperature increases above 70 °C, starting to disturb the helix-helix interaction-driven formation of tubules. As a result, the S13L12S13 peptide assembly undergoes a reversible vesicle-nanotube transformation following a time course at room temperature and a heat treatment above 80 °C. Using membrane fluidity analysis with DPH and TMA-DPH and evaluating the environment surrounding the PSar side chain with NMR, we clarify that the vesicle was in a kinetically stable state driven by the dehydrated PSar chain, while the nanotube was in a thermodynamically stable state.

A Review on the Synthesis of Polypeptoids

Polyeptoids are a promising class of polypeptide mimetic biopolymers based on N-substituted glycine backbones. Because of the high designability of their side chains, polypeptoids have a wide range of applications in surface antifouling, biosensing, drug delivery, and stimuli-responsive materials. To better control the structures and properties of polypeptoids, it is necessary to understand different methods for polypeptoid synthesis. This review paper summarized and discussed the main synthesis methods of polypeptoids: the solid-phase submonomer synthesis method, ring-opening polymerization method and Ugi reaction method.

Research Progress in Polypeptoids Prepared by Controlled Ring-Opening Polymerizations

Polypeptoids, structural mimics of polypeptides, have attracted considerable attention due to their biocompatibility, proteolytic stability, thermal processability, good solubility, synthetic accessibility, and structural diversity. Polypeptoids have emerged as an interesting material in both polymer science and biological field. This review primarily discusses the research progress of polypeptoids prepared by controlled ring-opening polymerizations in the past decade, including synthetic strategies of monomers, polymerizations by different initiators, postfunctionalization, fundamental properties, crystallization-driven self-assembly, and potential biological applications.

Host defense peptide mimicking cyclic peptoid polymers exerting strong activity against drug-resistant bacteria

Extensive use of antibiotics accelerates the emergence of drug-resistant bacteria and related infections. Host defense peptides (HDPs) have been studied as promising and potential therapeutic candidates. However, their clinical applications of HDPs are limited due to their high cost of synthesis and low stability upon proteolysis. Therefore, HDP mimics have become a new approach to address the challenge of bacterial resistance. In this work, we design the amphiphilic peptoid polymers by mimicking the positively charged and hydrophobic structures of HDPs and synthesize a series of cyclic peptoid polymers efficiently via the polymerization on α-amino acid N-substituted glycine N-carboxyanhydrides (α-NNCAs) using 1,8-diazabicycloundec-7-ene (DBU) as the initiator. The optimal cyclic peptoid polymer, poly(Naeg_0.7Npfbg_0.3)₂₀, displays strong antibacterial activities against drug-resistant bacteria, but low hemolysis and cytotoxicity. In addition, the mode-of-action study indicates that the antibacterial mechanism is associated with bacterial membrane interaction. Our study implies that HDP mimicking cyclic peptoid polymers have potential application in treating drug-resistant bacterial infections.

An Inspection into Multifarious Ways to Synthesize Poly(Amino Acid)s

Poly(α-amino acid)s (PAAs) attract growing attention due to their essential role in the application as biomaterials. To synthesize PAAs with desired structures and properties, scientists have developed various synthetic techniques with respective advantages. Here, different approaches to preparing PAAs are inspected. Basic features and recent progresses of these methods are summarized, including polymerizations of amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), as well as other synthetic routes. NCA is the most classical monomer to prepare PAAs with high molecular weights (MWs). NTA polymerizations are promising alternative pathways to produce PAAs, which can tolerate nucleophiles including alcohols, mercaptans, carboxyl acids, and water. By various techniques including choosing appropriate solvents or using organic acids as promoters, NTAs polymerize to produce polypeptoids and polypeptides with narrow dispersities and designed MWs up to 55.0 and 57.0 kg mol^-1 , respectively. NPC polymerizations are phosgene-free ways to synthesize polypeptides and polypeptoids. For the future prospects, detail investigations into polymerization mechanisms of NTA and NPC are expected. The synthesis of PAAs with designed topologies and assembly structures is another intriguing topic. The advantages and unsettled problems in various synthetic ways are discussed for readers to choose appropriate approaches for PAAs.

Synthesis and self-assembly of photo-responsive polypeptoid-based copolymers containing azobenzene side chains

Photo-responsive polypeptoid-based copolymers containing azobenzene side chains have been well synthesized and they could self-assemble into tunable nanostructures with reversible light-switched behaviors.

Thermoresponsive Polypeptoids

Stimuli-responsive polymers have been widely studied in many applications such as biomedicine, nanotechnology, and catalysis. Temperature is one of the most commonly used external triggers, which can be highly controlled with excellent reversibility. Thermoresponsive polymers exhibiting a reversible phase transition in a controlled manner to temperature are a promising class of smart polymers that have been widely studied. The phase transition behavior can be tuned by polymer architectures, chain-end, and various functional groups. Particularly, thermoresponsive polypeptoid is a type of promising material that has drawn growing interest because of its excellent biocompatibility, biodegradability, and bioactivity. This paper summarizes the recent advances of thermoresponsive polypeptoids, including the synthetic methods and functional groups as well as their applications.