Bioinspired double-positively charged phosphodicholine-chitosan and zwitterionic phosphorylcholine-chitosan conjugates: The associated water structure, biocompatibility and antibacterial action

Bioinspired double-positively charged phosphodicholine (PdC)-chitosan conjugate was synthesized via Atherton-Todd reaction, which can hydrolyze to zwitterionic phosphorylcholine (PC)-chitosan in basic solutions, confirmed by 1H and 31P NMR spectra. Thermal analysis revealed that there existed the freezing bound water due to the introduction of PdC and PC groups for both PdC-chitosan and PC-chitosan, implying that double-positively charged PdC-chitosan may exhibit excellent biocompatibility as zwitterionic PC-chitosan. Cytotoxicity, hemolysis and antibacterial activity evidenced that PdC-chitosan displayed high antibacterial activity against Escherichia coli and Staphylococcus aureus under physiological conditions, and very low cytotoxicity and hemolytic activity, owing to its highly selective lysis of bacterial membranes over mammalian cell membranes mainly resulting from the competition of electrostatic interactions and shielding effect of the restrained water of PdC, while biocompatible PC-chitosan showed no antibacterial activity due to its non-fouling property. The results indicated that biocompatible double-positively charged PdC-containing bioinspired polymers may provide a promising approach for developing safe and effective antibacterial agents.