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Interfacial properties of surfactants are dependent on the conformation adopted by the hydrophilic headgroup or/and the hydrophobic tail at the boundary limit of two immiscible phases. Here, we demonstrate the impacts of the carbonyl group (-CO-) location of the ester bond of sugar-based surfactants by comparing some properties of two closely related esters, octyl glucuronate and glucose octanoate, at the air-water interface. The carbonyl group location influences the rate and extent of interfacial adsorption and the rheology properties of sugar esters at the air-water interface, which were evaluated by dynamic surface tension and complex surface viscoelastic measurements. Octyl glucuronate adsorbs the fastest at the air-water interface whereas glucose octanoate reduces the dynamic surface tension at the lowest value and exhibits the highest film viscoelasticity. Differences are attributed to molecular conformation constraints inducing relevant changes to the surface coverage kinetic capacity and the interaction strengths of the octyl sugar ester adsorbed films at the air-water interface. All of the results are supported by the minimum cross-sectional area values per molecule determined by both experimental and computational approaches.

Elucidation of the molecular mechanism leading to biomembrane fusion is a challenging issue in current biomedical research in view of its involvement in controlling cellular functions and in mediating various important diseases. According to the generally admitted stalk mechanism described for membrane fusion, negatively curved lipids may play a central role during the early steps of the process. In this study, we used atomic force microscopy (AFM) to address the crucial question of whether negatively curved lipids influence the interaction of the simian immunodeficiency virus (SIV) fusion peptide with model membranes. To this end, dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DOPC/DPPC) bilayers containing 0.5 mol % dioleoylphosphatidic acid (DOPA) were incubated with the SIV peptide and imaged in real time using AFM. After a short incubation time, we observed a 1.9 nm reduction in the thickness of the DPPC domains, reflecting either interdigitation or fluidization of lipids. After longer incubation times, these depressed DPPC domains evolved into elevated domains, composed of nanorod structures protruding several nanometers above the bilayer surface and attributed to cylindrical reverse micelles. Such DOPC/DPPC/DOPA bilayer modifications were never observed with nontilted peptides. Accordingly, this is the first time that AFM reveals the formation of cylindrical reverse micelles in lipid bilayers promoted by fusogenic peptides.