Synthesis and Properties of Mono- or Diamine-Initiated Imidazolium-Based Cationic Polypeptides

Facile Preparation of Polysaccharide-Polypeptide Conjugates via a Biphasic Solution Ring-Opening Polymerization

Polysaccharide-polypeptide conjugates have gained a broad interest in mimicking the structure and bioactivity of peptidoglycans or proteoglycans for biomedical applications. Efficient and precise preparation of the conjugates is challenging and unresolved, mainly because of the mismatched solubility between polysaccharide initiators and N-carboxyanhydrides (NCAs), which frequently results in competing side reactions and oligomeric polypeptide chain. Herein, we report a facile and efficient strategy to prepare the conjugates with well-controlled polypeptide chain length (l_p) directly from unmodified polysaccharides via a biphasic solution ring-opening polymerization. The effect of l_p on surface antibacterial properties has been investigated. Elongating the l_p can significantly potentiate the antibiofilm property of the conjugate coatings. Our results may provide opportunities to develop various polypeptide-based conjugates with well-defined structures toward versatile uses.

Imidazolium-Based Polypeptide Coating with a Synergistic Antibacterial Effect and a Biofilm-Responsive Property

Surface modification with cationic polymer coatings represented an important strategy to address the medical device-related infection issues. However, limited antibacterial activities and high cytotoxicity have hampered their development. Herein, we report a facile method to enhance the surface antibacterial activity by construction of an imidazolium-based polypeptide with fosfomycin counteranions (i.e., S₄-PIL-FS). The polypeptide coating displayed a synergistic antibacterial effect from the combination of membrane disruption and inhibition of initial cell wall synthesis, leading to higher in vitro and in vivo surface antibacterial activities than cationic polypeptide or fosfomycin sodium alone. S₄-PIL-FS also showed a decrease in the hemolytic ratio and cytotoxicity toward different mammalian cells. Moreover, we observed an interesting biofilm-responsive property of S₄-PIL-FS originating from the esterase-induced cleavages of side-chain ester bonds that enabled an antibiofilm property of the cationic polypeptide coating.

Organocatalytic Copolymerization of Cyclic Lysine Derivative and ε-Caprolactam toward Antibacterial Nylon-6 Polymers

Functional polymers of nylon-6, particularly those with sustained antibacterial functions, have many practical applications. However, the development of functional ε-caprolactam monomers for the subsequent ring-opening copolymerization (ROCOP) formation of these materials remains a challenge. Here we report a t-BuP₄-mediated ROCOP of dimethyl-protected cyclic lysine with ε-caprolactam, followed by quaternization, affording antibacterial nylon-6 polymers bearing quaternary ammonium functionality with high molecular weight (up to 77.4 kDa). The antibacterial nylon-6 polymers exhibited good physical and mechanical properties and strong antimicrobial activities. At 25 mol % quaternary ammonium group incorporation, the nylon-6 polymer demonstrated complete killing of Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). The results from this study may provide a strategy for the facile preparation of antibacterial nylon-6 polymers to addressing the public health and safety challenges.

PiPo: random copolymers of C- with N-substituted glycines

This letter introduces a method to obtain PiPo by the copolymerization of N-phenyloxycarbonyl-amino acids initiated by primary amine. The obtained PiPo have adjustable solubility in water and organic solvents to assemble into nanoparticles.

Versatile fully-substituted triazole-functionalized polypeptides with a stable α-helical conformation for gene delivery

A library of polypeptides bearing fully-substituted triazoles (FT) was developed via a Cu-catalyzed multicomponent reaction (MCR), which avoided the undesired hydrogen bonding and stabilized the α-helix in a broad pH range.

Single-Chain Nanoparticle-Based Coatings with Improved Bactericidal Activity and Antifouling Properties

Dual-function antibacterial surfaces have exhibited promising potential in addressing implant-associated infections. However, both bactericidal and antifouling properties need to be further improved prior to practical uses. Herein, we report the preparation and properties of a linear block copolymer coating (LP-KF) and a single-chain nanoparticle coating (NP-KF) with poly(ethylene glycol) (PEG) and cationic polypeptide segments. NP-KF with cyclic PEG segments and densely charged polypeptide segments was expected to display improved bactericidal and antifouling properties. LP-KF was prepared by the combination of ring-opening polymerization of N-carboxyanhydride (NCA) monomers and subsequent deprotection. NP-KF was prepared by intramolecular cross-linking of LP-KF in diluted solutions. Both LP-KF- and NP-KF-coated PDMS surfaces were prepared by dipping with polydopamine-coated surfaces. They showed superior in vitro bactericidal activity against both Staphylococcus aureus and Escherichia coli with >99.9% killing efficacy, excellent protein adsorption resistance, antibacterial adhesion, and low cytotoxicity. The NP-KF coating showed higher bactericidal activity and antifouling properties than its linear counterpart. It also showed significant anti-infective property and histocompatibility in vivo, which makes it a good candidate for implants and biomedical device applications.

Facile Synthesis of Imidazolium-Based Block Copolypeptides with Excellent Antimicrobial Activity

Antimicrobial polypeptides are promising mimics of antimicrobial peptides (AMPs) with low risks of antimicrobial resistance (AMR). Polypeptides with facile and efficient production, high antimicrobial activity, and low toxicity toward mammalian cells are highly desirable for practical applications. Herein, triblock copolypeptides with chloro groups (PPG_n-PCPBLG_m) and different main-chain lengths were synthesized via an ultrafast ring-opening polymerization (ROP) using a macroinitiator, namely poly(propylene glycol) bis(2-aminopropyl ether), and purified or nonpurified monomer (i.e., CPBLG-NCA). PPG_n-PCPBLG_m with 90 amino acid residues can be readily prepared within 300 s. Imidazolium-based block copolypeptides (PPG_n-PIL_m) were facilely prepared via nucleophilic substitution of PPG_n-PCPBLG_m with NaN₃ and subsequent "click" chemistry. α-Helical PPG_n-PIL_m can self-assemble into nanostructured and cationic micelles which displayed highly potent antimicrobial activity and low hemolysis. The top-performing material, namely PPG₃₄-PIL₇₀, showed low minimum inhibitory concentration (MIC) against both Gram-positive S. aureus and Gram-negative E. coli (25 μg mL^-1). It also displayed low toxicity against mouse embryonic fibroblast (NIH 3T3) and human embryonic kidney (293T) cells at 2× MIC.

Efficient synthesis and excellent antimicrobial activity of star-shaped cationic polypeptides with improved biocompatibility

Antimicrobial peptides (AMPs) have been considered as a promising new tool to combat the antimicrobial resistance (AMR) crisis. However, the high toxicity and high cost of AMPs hampered their further development. Herein, a series of star poly(_L-lysine) (PLL) homo- and copolymers with excellent antimicrobial activity and improved biocompatibility were prepared by the combination of ultra-fast ring opening polymerization (ROP) and side-chain modification. The amine-terminated polyamidoamine dendrimer (Gx-PAMAM) mediated ROP of Nε-tert-butyloxycarbonyl-_L-lysine N-carboxyanhydride (Boc-_L-Lys-NCA) and γ-benzyl-_L-glutamic acid-based N-carboxyanhydride (PBLG-NCA) was able to prepare star PLL homo- and copolymers with 400 residues within 50 min. While the star PLL homopolymers exhibited low minimum inhibitory concentration (MIC = 50-200 μg mL^-1) against both Gram-positive and Gram-negative bacteria (i.e., S. aureus and E. coli), they showed high toxicity against various mammalian cell lines. The star PLL copolymers with low contents of hydrophobic and hydroxyl groups showed enhanced antimicrobial activity (MIC = 25-50 μg mL^-1) and improved mammalian cell viability. Both SEM and CLSM results indicated the antimicrobial mechanism of membrane disruption.

Transition of Conformation and Solubility in β-Sheet-Structured Poly(l-cysteine)s with Methylthio or Sulfonium Pendants

Poly(l-cysteine)s with methylthio pendants (PMTLCs) were synthesized by ring-opening polymerization of a new l-cysteine-based N-carboxyanhydride. The thioether bonds of PMTLC can be readily oxidized by H₂O₂ yielding water-soluble PMTLC^OX. The methylthio groups can undergo an alkylation reaction using methyl iodide and a subsequent ion-exchange reaction yielding sulfonium-based polypeptides (PPLC-DMS-X, where X = I, BF₄). PPLC-DMS-X showed upper critical solution temperature-type thermo- and oxidation-responsive properties in aqueous solutions. Both PMTLC and PPLC-DMS-X showed oxidation-induced β-sheet to α-helix transitions. The absorbance of PPLC-DMS-I and methyl orange aqueous solution displayed a significant linear correlation with temperature, which makes the sulfonium-based polypeptides good candidates in the field of temperature sensors.