Caffeine and Cationic Copolymers with Antimicrobial Properties

One of the primary global health concerns is the increase in antimicrobial resistance. Polymer chemistry enables the preparation of macromolecules with hydrophobic and cationic side chains that kill bacteria by destabilizing their membranes. In the current study, macromolecules are prepared by radical copolymerization of caffeine methacrylate as the hydrophobic monomer and cationic- or zwitterionic-methacrylate monomers. The synthesized copolymers bearing tert-butyl-protected carboxybetaine as cationic side chains showed antibacterial activity toward Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). By tuning the hydrophobic content, we prepared copolymers with optimal antibacterial activity against S. aureus, including methicillin-resistant clinical isolates. Moreover, the caffeine-cationic copolymers presented good biocompatibility in a mouse embryonic fibroblast cell line, NIH 3T3, and hemocompatibility with erythrocytes even at high hydrophobic monomer content (30-50%). Therefore, incorporating caffeine and introducing tert-butyl-protected carboxybetaine as a quaternary cation in polymers could be a novel strategy to combat bacteria.

Stimuli-responsive microgels with cationic moieties: characterization and interaction with E. coli cells

Stimuli-responsive microgel copolymer networks with ionizable functional groups have important applications for encapsulation of drugs, peptides, enzymes, proteins, or cells. Rational design of such networks can be based on characterization of stimuli-induced volume phase transition and spatial distribution of neutral and charged monomer units in crosslinked polymer chains. In this work we successfully synthesized poly(N-vinylcaprolactam-co-1-vinyl-3-methylimidazolium) (poly(VCL-VIM⁺)) microgels carrying permanent positive charges and demonstrate that ¹H high-resolution NMR spectroscopy in combination with transverse (T₂) magnetization relaxometry allows investigating separately the behavior of each functional group in the microgel network. The information about comonomer transition temperatures, width of transition, and change in transition entropy were reported and correlated with the concentration of charged functional groups and resulting electrophoretic mobility. A two-state approach was used to describe the temperature-induced volume phase transition separately for neutral and charged polymer segments. The core-corona architecture specific to each functional group was detected revealing that the charged methylated vinylimidazolium groups (VIM⁺) are concentrated mainly in the corona of the microgel. These biocompatible PVCL-based microgels functionalized with permanent positive charges are shown to serve as an antibacterial system against Gram-negative E. coli strains, due to the positive charge of the incorporated VIM⁺ comonomer in the polymer network.

Synthesis and stability of 1-aminoalkylphosphonic acid quaternary ammonium salts

An effective protocol for the quaternization of simple 1-aminoalkylphosphonic acids under basic conditions using Me2SO4 as a convenient alkylating agent is reported. During the course of the reaction, phosphonic acid quaternary ammonium derivatives, along with their corresponding monoesters are formed. Subsequent direct acidic hydrolysis of the crude reaction mixture leads to the desired novel N,N,N-trialkyl-N-(1-phosphonoalkyl)ammonium salts with overall yields of up to 88%. The developed protocol is general in scope and the products are purified by simple crystallization to give stable solids. Novel quaternary ammonium salts bearing a phosphonic group are generally unreactive in acidic and alkaline media. However, some of them undergo Hofmann elimination and substitution reactions in the presence of a base.

Selective Inhibition of Streptococci Biofilm Growth via a Hydroxylated Azobenzene Coating

Strategies to engineer surfaces that can enable the selective inhibition of bacterial pathogens while preserving beneficial microbes can serve as tools to precisely edit the microbiome. In the oral microbiome, this selectivity is crucial in preventing the proliferation of cariogenic species such as Streptococcus mutans (S. mutans). In this communication, coatings consisting of a covalently tethered hydroxylated azobenzene (OH-AAZO) on glassy acrylic resins are studied and characterized for their ability to selectively prevent the attachment and growth of oral Streptococci biofilms. The coating applied on the surface of glassy resins inhibits the growth and proliferation of cariogenic S. mutans and S. oralis biofilms while A. actinomycetemcomitans, S. aureus, and E. coli biofilms are unaffected by the coating . The antibacterial effect is characterized as a function of both the OH-AAZO concentration in the coatings (≥50 mg mL-1) and the structure of the monomer in the coating. Preliminary mechanistic results suggest that the targeted bactericidal effect against Streptococci species is caused by a disruption of membrane ion potential, inducing cell death.

Influence of the interfacial molecular structures of quaternary ammonium-type poly(ionic liquid) brushes on their antibacterial properties

Alkyl chains of C4 are more active in killing bacteria than C16 due to their orderly extension toward PBS solution.