Investigating the molecular mechanism of action for antimicrobial polyelectrolytes on biomimetic Langmuir nanofilms using SFG spectroscopy

Abstract

The increasing microorganism resistance to antibiotics is a matter of global concern and it is evident that research on new antimicrobial molecules or strategies is crucial. In particular, the interaction studies of antimicrobial molecules in which act on the plasmatic membrane of bacteria are promising candidates. Among these, the cationic Conjugated Polyelectrolytes (CPEs) are noteworthy ones, because they are wide-spectrum bactericidal agents. These macromolecules have many advantages when compared to other small biocides: they have increased lifetimes, potency and specificity and lowered residual toxicity. Besides, the CPEs are amphiphiles (they self-assemble into nanoscale aggregates in liquids), they can be functionalized and some of them have good optical properties for photodynamic action. In other words, there is a great technological potential behind of CPEs - from the antimicrobial coating of solid surfaces to antimicrobial fibers for many scientific or biomedical applications such as sterile clothing and bandages. The present research has as a goal the investigation of the molecular mechanism in which a CPE interacts with a biomimetic plasmatic membrane model (Langmuir Film made of lipids). For that, the SFG Spectroscopy will be performed - the Surface Nonlinear Vibrational Spectroscopy by Sum-Frequency Generation, which is a intrinsically surface-specific technique, capable of acquiring the signal from the polyelectrolytes interacting with the film at the interface, without the signal contribution from the molecules in solution. SFG Spectroscopy allows us to obtain information about the orientation and the molecular conformation at the interface. For example, if the polyelectrolyte adsorbs without any preferential orientation (a disordered coiled conformation for example), no SFG signal would be detected. In the case of lipids, the technique can easily detect if their hydrophobic chains are extended or have gauche defects (a folding in the chain). In addition, by its vibrational spectrum, it could determine whether the lipid has been oxidized. Therefore, SFG Spectroscopy is perfect for analyzing the interaction between the lipid monolayer on the water (which simulates half of the bacterial plasmatic membrane) and the CPE, since it obtains information at the molecular level. The understanding of these interactions may elucidate the detailed mechanism of action of antimicrobial CPEs, permitting that new molecules could be planned in order to optimize their bactericidal activity or biocompatibility. (AU)