Membrane activity of antimicrobial phenylene ethynylene based polymers and oligomers

Poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and cationic phenylene ethynylene oligomers (OPEs) exhibit broad-spectrum antimicrobial activity and one of their main targets is believed to be the bacterial cell wall and membrane. This review focuses on recent progress made in elucidating the membrane perturbation mechanism of these antimicrobial molecules. We first review the membrane action models proposed for naturally occurring antimicrobial peptides (AMPs) because the membrane activities of CPEs and OPEs and AMPs are believed to be mediated by the same physical and chemical driving forces. An overview of the current research progress on the interactions between CPE and OPE compounds and model membranes is then presented, including main parameters controlling the membrane activity of these synthetic antimicrobial compounds. Combined with direct visualization of CPE and OPE induced changes in bacterial cell morphology, evidence to date points to a carpet or detergent-like pathway by which these compounds perturb the lipid membrane. Lastly, general trends between the membrane activity and dark antimicrobial activity of the CPEs and OPEs are reviewed to shed light on the structure-function relationship of this novel class of biocidal compounds.