Biocidal Activity and Mechanism Study of Unsymmetrical Oligo-Phenylene-Ethynylenes.

Bacterial contamination and the spread of antibiotic-resistant bacteria demand alternate methods to deal with bacterial infections. With particular advantages, photodynamic therapy (PDT) is a promising approach. As a kind of photosensitizer for PDT, light-induced antibacterial compounds like oligo-p-phenylene-ethynylenes (OPEs) have been widely investigated while these studies mainly focus on OPEs with quaternary ammonium salts. In our previous study, OPEs with tertiary amino groups (T-OPEs) were reported to exhibit a better antibacterial activity than the corresponding quaternary ammonium salts, which make it important to develop T-OPEs and further investigate their structure-activity relationship. Additionally, the terminal structure of the reported OPEs mainly consists of quaternary ammonium salts or tertiary amino groups, which could not be linked to other materials. Thus, to develop more effective and multifunctional antibacterial agents, we designed and synthesized four unsymmetrical OPEs having terminal amino groups, which could be linked to other functional units by covalent bonds. Their antibacterial activity against Gram-positive and Gram-negative bacteria and the mechanism have been investigated. The OPEs showed effective biocidal activity under fiber light irradiation, and no dark killing was observed. The mechanism study indicates that OPEs could penetrate and perturb the cell membrane and generate ROS under light irradiation, both of which could influence their antibacterial activity. The penetrating ability of OPEs is partly dependent on their lipophilicity and the structure and composition of the cell membrane.