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.
Photodynamic therapy (PDT) is a potential approach to resolve antibiotic resistance, and phenylene/thiophene-ethynylene oligomers have been widely studied as effective antibacterial reagents. Oligomers with thiophene moieties usually exhibit good antibacterial activity under light irradiation and dark conditions. In the previous study, we verified that neutral oligo-p-phenylene-ethynylenes (OPEs) exhibit better antibacterial activity than the corresponding cationic ones; however, whether this regular pattern also operates in other kinds of oligomers such as oligo-thiophene-ethynylene (OTE) is unknown. Also, the antibacterial activity comparison of OTEs bearing cyclic and acyclic amino groups will offer useful information to further understand the role of amino groups in the antibacterial process and guide the antibacterial reagent design as amino groups affect the antibacterial activity a lot. We synthesized four OTEs bearing neutral or cationic, cyclic, or acyclic amino groups and studied their antibacterial activity in detail. The experimental results indicated that the OTEs exhibited better antibacterial activity than the OPEs, the neutral OTEs exhibited better antibacterial activity in most cases, and OTEs bearing cyclic amino groups exhibited better antibacterial activity than those bearing acyclic ones in most cases. This study provides useful guidelines for further antibacterial reagent design and investigations.
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