Development of hydrophilic imidazolium oligomers and comparison of their biocidal properties

Abstract

Observations from previously developed PIM 1 oligomer variants (OIM 1-8 NH2) suggest the formation of carbene at the C2 position may attribute to the overall bactericidal properties of PIM 1. As such, imidazolium oligomers resembling the hydrophilic PIM 5 variant polymer were developed to observe whether the same trends occur. PIM 5 oligomer variants of 10 repeating units (OIM 5–10 NH2) and 12 repeating units (OIM 5-12 NH2, C2 OIM 5-12 NH2 and C4 OIM 5-12 NH2) were synthesized in a stepwise fashion which ensures uniform chain length. Albeit with low yield, the oligomer products were afforded as pure uniform chains by the processing/purification process we developed, which couple dialysis and gel-filtration chromatography. This technique enables us to separate the oligomer products from the crude mixture despite moderate conversions. For the biological properties of the developed oligomers, the MIC assay showed OIM 5-12 NH2 to possess the most potent bactericidal activity, whilst OIM 5-10 NH2 only displayed moderate activity, indicating that 12 repeating unit is the effective chain length for the PIM 5 polymer to possess antimicrobial efficacy. Comparisons of the MIC values between the OIM 5-12 NH2 series of oligomers revealed that the difference in MIC values do not differ as significant as observed previously for OIM 1-8 NH2 oligomer series. Our conclusion is that the formation of carbene at the C2 position of the imidazolium ring might not contribute to the bactericidal properties of the PIM 5 polymer, which suggests other mechanisms of action for PIM 5 polymer. MTT assay showed that OIM 5-10 NH2 and OIM 5-12 NH2 displayed low cytotoxicity, whilst C2 OIM 5-12 NH2 and C4 OIM 5-12 NH2 displayed cytotoxic properties. Overall, OIM 5-12 NH2 was shown to display the most potent bactericidal activities whilst maintaining a low cytotoxicity profile. The developed oligomer chains will also be utilized for future mechanistic studies to better understand the interaction of the PIM 5 polymer and the bacteria components.