Synthesis of Guanidinium Functionalized Polycarbodiimides and Their Antibacterial Activities

Abstract

A family of guanidinium-side-chain functionalized polycarbodiimides has been synthesized by allowing an azido guanidinium salt to react with alkyne polycarbodiimides via the copper catalyzed [3 + 2] cycloaddition (Click) reaction. <b>Poly-2</b>(<b>a</b>-<b>d</b>) are cationic/amphiphilic polymers in which the global hydrophilic/hydrophobic balance has been tailored by local alteration of the length of alkyl side chain in the repeat unit of polymers prior to polymerization. The shorter alkyl chains yield water-soluble polymers, <b>Poly</b>-<b>2c</b>, -<b>2d</b>, and -<b>2e</b>. Antibacterial activities of these cationic polycarbodiimides have been investigated for Gram-positive and Gram-negative bacteria that include Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Acinetobacter baumannii. It was observed that the influence of hydrophobic-hydrophilic balance per repeat unit of these polymers have profound effects for both antimicrobial and hemolytic activities. In addition, these polycarbodiimide-guanidinium-triazole conjugates offered moderate to significant antibacterial activity and rapid interaction with red blood cells causing blood precipitation without significant hemolysis in case of <b>Poly</b>-<b>2</b>(<b>b</b>-<b>e</b>). This latter property has the potential to be exploited in the polymer coatings or wound protection.