Biocidal Potency of Polymers with Bulky Cations

The performance of antimicrobial polymers de-pends sensitively on the type of cationic species, charge density, and spatial arrangement of cations. Here we report antimicrobial polymers bearing unusually bulky tetraaminophosphonium groups as the source of highly delocalized cationic charge. The bulky cations drastically enhanced the biocidal activity of amphiphilic polymers, leading to remarkably potent activity in the submicro-molar range. The cationic polynorbornenes with pendent tetraaminophosphonium groups killed over 98% E. coli at a concentration of 0.1 mu g/mL and caused a 4-log reduction of E. coli within 2 h at a concentration of 2 mu g/mL, showing very rapid and potent bactericidal activity. The polymers are also highly hemolytic at similar concentrations, indicating a biocidal activity profile. Polymers of a similar chemical structure but with more flexible backbones were made to examine the effects of the flexibility of polymer chains on their activity, which turned out to be marginal. We also explore variants with different spacer arm groups separating the cations from the backbone main chain. The antibacterial activity was comparably potent in all cases, but the polymers with shorter spacer arm groups showed more rapid bactericidal kinetics. Interestingly, pronounced counterion effects were observed. Tightly bound PF6- counteranions showed poor activity at high concentrations due to gross aggregate formation and precipitation from the assay media, whereas loosely bound Cl- counterions resulted in very potent activity that monotonically increased with increasing concentration. In this paper, we reveal that bulky phosphonium cations are associated with markedly enhanced biocidal activity, which provides an innovative strategy to develop more effective self-disinfecting materials.

Automated summary

This study reports on a new type of antimicrobial polymer with unusually bulky tetraaminophosphonium groups, which act as highly delocalized cationic charges. These bulky cations significantly enhance the biocidal activity of amphiphilic polymers, resulting in potent antibacterial activity against E. coli. The flexibility of polymer chains and the spacer arm groups separating the cations from the backbone main chain have minimal effects on the activity. Counterion effects were observed, with tightly bound PF6- counteranions showing poor activity and loosely bound Cl- counterions exhibiting potent activity.