Designing antibacterial polymeric systems: (co)poly(2-oxazoline) conjugates with acyclic and macrocyclic polyamino polycarboxylic chelators†

In this work, we propose a new synthetic pathway to obtain conjugates of poly(2-oxazoline)s (POx) and chelating agents (CA) with antibacterial activity, applying a triazine-based coupling compound. The copolymers based on 2-ethyl-2-oxazoline (EtOx) and 2-(3-butenyl)-2-oxazoline (ButEnOx) were coupled with acyclic and macrocyclic chelating compounds, i.e., diethylenetriaminepentaacetic acid (DTPA) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). The obtained systems were named as POx-DTPA and POx-DOTA, respectively. This modification provided an opportunity to impart to the designed macromolecules the ability for complexation of ions, which stabilize the membrane of bacterial cell. We present, for the first time, studies on the uptake of various cations, including those stabilizing the membrane of Gram-negative bacteria at different environmental pH values for POx-DTPA and POx-DOTA macromolecules, where the increase in the efficiency of conjugate ion trapping is possible owing to the ionization of the functional groups of CA coupled to POx. The antibacterial properties of the designed systems were also confirmed by assessing their minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) with the use of Gram-negative strains of E. coli and P. aeruginosa. Using cytometric analysis, we further investigated the ability of the obtained systems to disrupt the bacterial cell membrane, demonstrating the permeability of the outer bacterial membrane (OM) after POx-DOTA treatment, and the disruption of the OM and the inner membrane (IM) after POx-DTPA treatment. The designed macromolecular systems also remained non-toxic to human skin fibroblasts in a wide range of concentrations, making them promising candidates for further studies on antibacterial biomaterials.