Structural changes in cellular membranes induced by ionic liquids: From model to bacterial membranes.

Area of Science:

• Biochemistry
• Materials Science
• Microbiology

Background:

• Ionic liquids (ILs) are investigated for their antibacterial properties and potential as antibiotics.
• The precise mechanism by which ILs induce cytotoxicity, particularly their interaction with cell membranes, remains unclear.
• Imidazolium-based ILs, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), are examined for their antibacterial effects.

Purpose of the Study:

• To investigate the antibacterial activities of two specific imidazolium-based ILs: [BMIM][BF4] and [EMIM][BF4].
• To elucidate the mechanism of IL-induced cell membrane damage by studying their effects on model cellular membrane structures.
• To correlate the observed antibacterial activity with the structural changes induced in lipid bilayers.

Main Methods:

• Antibacterial activity assays were performed, comparing the efficacy of [BMIM][BF4] and [EMIM][BF4] against Gram-negative bacteria, E. coli.
• Surface tension and in-plane elasticity measurements were conducted on lipid monolayers (DPPC) at the air-water interface in the presence of ILs.
• X-ray reflectivity studies were employed to analyze the structural alterations (thickness, electron density) of polymer-supported lipid bilayers exposed to ILs.

Main Results:

• The IL [BMIM][BF4] demonstrated stronger antibacterial activity against E. coli compared to the shorter-chain IL [EMIM][BF4].
• The presence of both ILs reduced the in-plane elasticity of DPPC lipid monolayers.
• X-ray reflectivity data revealed that ILs cause lipid bilayers to shrink and increase in electron density.
• Incorporating negatively charged lipids (DPPS) into DPPC monolayers and bilayers significantly amplified the effects of the ILs.

Conclusions:

• The study provides insights into the mechanism of IL-induced bacterial membrane damage, linking it to alterations in lipid bilayer structure and elasticity.
• [BMIM][BF4]'s enhanced antibacterial activity is potentially related to its greater impact on membrane properties compared to [EMIM][BF4].
• The findings suggest that ILs interact with and perturb lipid bilayers, with charge interactions playing a crucial role, which could be leveraged for antibiotic development.