To combat the escalating threat of drug-resistant bacteria, the development of novel antimicrobial agents is essential for replacing increasingly ineffective conventional antibiotics. Antimicrobial Peptides (AMPs) are promising alternatives, but their inherent toxicity to mammalian cells and instability limit widespread application. To overcome these limitations, an attractive strategy is to conjugate AMPs to neutral, hydrophilic polymers, such as PEG. Our lab recently found comb-like AMP-PEG conjugates to eradicate bacteria, while not causing hemolysis. However, PEG's potential to trigger anti-PEG antibodies necessitates the exploration of non-immunogenic alternatives. Sulfobetaine (SB), a highly hydrophilic, zwitterionic polymer, is a promising replacement well poised to improve solubility and therein, allow more AMP per chain without compromising aqueous solubility. Comparing PEG- and SB-based AMP-polymer conjugates necessitates the synthesis of copolymers that are otherwise similar in molecular weight, AMP content, etc. Yet, in reversible addition-fragmentation chain transfer (RAFT) polymerization, the larger 22-amino acid AMP monomer incorporates into the polymer much slower than PEG, generating a gradient in AMP content along the polymer chain. Thus, understanding the kinetics of the copolymerizations of each neutral, hydrophilic monomer with the AMP monomer is essential to comparing the properties and performance of PEG- and SB-based AMP-polymer conjugates. Initial photoinitiation conditions proved problematic for reproducible kinetics: we observed the conversion in a given amount of time to vary with spatial orientation relative to the bulb and even run-to-run when a polymerization was conducted in the same position. Thus, we moved to thermal initiation to accurately measure the significant difference in SB and PEG polymerization rates. This presentation will showcase the role of initiator decomposition temperature and polymerization temperature on the kinetics of sulfobetaine polymerization and copolymerization with the AMP monomer. By understanding the kinetics and comparing PEG- and SB-based AMP-polymer conjugates, we will gain insight into how the type of hydrophilic monomer impacts solubility, surface charge, supramolecular assembly, proteolytic stability, and antimicrobial performance, ultimately informing the design of next-generation antimicrobial therapeutics.
