Discerning perturbed assembly of lipids in a model membrane in presence of violacein: Effects of membrane hydrophobicity

For the lack of effective antibiotics towards antibiotic resisting bacteria, it is required to discover new antibiotics and to understand their antimicrobial mechanism. Violacein is a violet pigment found in several gram-negative bacteria possessing antimicrobial properties to gram-positive bacteria. This present article investigates the insertion ability of this molecule into a model membrane composed of zwitterionic phospholipids. Thermodynamic characterization of lipid monolayers in the presence of violacein was carried out using a single lipid layer formed at air-water interface. The molecule inserts into the layer altering the area occupied by each lipid and the in-plane compressibility of the film. This insertion increases with the hydrophobic chain length of the lipid. The perturbed self-assembly of lipids in a bilayer is quantified using a lipid multilayer system applying the X-ray reflectivity technique. The electron density profile from the reflectivity data shows that the molecule inserts into the fluid phase creating a relatively ordered chain conformation. Further, the insertion into the gel phase is observed to increase with the increased thickness of the hydrophobic core of a bilayer.