No abstract

We synthesized cationic random amphiphilic copolymers by radical copolymerization of methacrylate monomers with cationic or hydrophobic groups and evaluated their antimicrobial and hemolytic activities. The nature of the hydrophobic groups, and polymer composition and length were systematically varied to investigate how structural parameters affect polymer activity. This allowed us to obtain the optimal composition of polymers suitable to act as non-toxic antimicrobials as well as non-selective polymeric biocides. The antimicrobial activity depends sigmoidally on the mole fraction of hydrophobic groups (fHB). The hemolytic activity increases as fHB increases and levels off at high values of fHB, especially for the high-molecular-weight polymers. Plots of HC50 values versus the number of hydrophobic side chains in a polymer chain for each polymer series showed a good correlation and linear relationship in the log–log plots. We also developed a theoretical model to analyze the hemolytic activity of polymers and demonstrated that the hemolytic activity can be described as a balance of membrane binding of polymers through partitioning of hydrophobic side chains into lipid layers and the hydrophobic collapsing of polymer chains. The study on the membrane binding of dye-labeled polymers to large, unilamellar vesicles showed that the hydrophobicity of polymers enhances their binding to lipid bilayers and induces collapse of the polymer chain in solution, reducing the apparent affinity of polymers for the membranes.

A library of amphiphilic random copolymers containing cationic and hydrophobic side chains were prepared by copolymerization of amine-functionalized methacrylate monomers with various ratios of an alkyl methacrylate. Primary or tertiary amine groups, or quaternary ammonium groups, were utilized as the source of cationic charge in each copolymer series. The antimicrobial and hemolytic activities of these copolymers are reported, enabling a systematic assessment of the effect different amine groups exert on the biological activity of the polymers. It was shown that the copolymer composition of amphiphilic copolymers containing primary or tertiary amine groups can be tuned to achieve potent antimicrobial activity while minimizing red blood cell lysis. On the other hand, the copolymers containing quaternary ammonium groups required a greater amount of hydrophobic comonomer to express activity and showed generally lower selectivity for E. coli versus human red blood cells. Potentiometric titration data revealed the fraction of the primary or tertiary amine groups in the polymers, which are deprotonated (basic) at physiological pH. Measurements of the bactericidal and hemolytic activities in buffers of pH varying from 6 to 8 showed the impact of polymer ionization on biological activity. A decrease in the fraction of amine groups that are cationic, from alpha = 1.0 to 0.7, caused an enhancement of antimicrobial and hemolytic activity. As this value was decreased further to alpha = 0.5, loss of activity was observed. The activities of polymers containing quaternary ammonium groups were shown to be pH-independent.