Guanidinylated Amphiphilic Polycarbonates with Enhanced Antimicrobial Activity by Extending the Length of the Spacer Arm and Micelle Self-Assembly.

Nine guanidinylated amphiphilic polycarbonates are rationally designed and synthesized. Each polymer has the same biodegradable backbone but different side groups. The influence of the hydrophobic/hydrophilic effect on antimicrobial activities and cytotoxicity is systematically investigated. The results verify that tuning the length of the spacer arm between the cationic guanidine group and the polycarbonate backbone is an efficient design strategy to alter the hydrophobic/hydrophilic balance without changing the cationic charge density. A spacer arm of six methylene units (CH2 )6 shows the best antimicrobial activity (minimum inhibitory concentration, MIC = 40 µg mL-1 against Escherichia coli, MIC = 20 µg mL-1 against Staphylococcus aureus, MIC = 40 µg mL-1 against Candida albicans) with low hemolytic activity (HC50 > 2560 µg mL-1 ). Furthermore, the guanidinylated polycarbonates exhibit the ability to self-assemble and present micelle-like nanostructure due to their intrinsic amphiphilic macromolecular structure. Transmission electron microscopy and dynamic light scattering measurements confirm polymer micelle formation in aqueous solution with sizes ranging from 82 to 288 nm.