Bioinspired nanoarchitectonics at the air-water interface to understand the interaction of lipids with a Europium-coordinated quinoline derivative

5SO3H-8-hydroxyquinoline coordinated to Europium (Eu-5SO3-HQ) was incorporated in biomembrane models using Langmuir monolayers. Dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylserine (DPPS) were employed, representing mammalian cells and dioctadecyldimethylammonium bromide (DODAB) as a positively charged lipid to study the contrast with negatively charged lipids. Tensiometric, rheological and spectroscopic techniques were employed to characterize Eu-5SO3-HQ- lipid monolayer interactions. The complex condenses all the monolayer indicating interactions with the lipids' polar heads, but with distinctive effects on the mechanical and rheological properties. While the complex decreases the compression and elastic moduli of DPPC and DPPS monolayers, it increases for DODAB, also decreasing its lateral viscosity. Infrared spectroscopy shows that the interaction of Eu-5-SO3-HQ alters the ordering of the lipids' alkyl chains, impacting the monolayer's molecular packing. These results show that the interaction of Eu-5SO3-HQ with lipid monolayers at the air-water is modulated by the composition of the polar head, which can be supportive in the preparation of nanodevices for molecular probing.

The antimicrobial peptide aurein 1.2 disrupts model membranes via the carpet mechanism

The membrane interactions of the antimicrobial peptide aurein 1.2 were studied using a range of biophysical techniques to determine the location and the mechanism of action in DMPC (dimyristoylphosphatidylcholine) and DMPC/DMPG (dimyristoylphosphatidylglycerol) model membranes that mimic characteristics of eukaryotic and prokaryotic membranes, respectively. Neutron reflectometry and solid-state NMR revealed subtle changes in membrane structure caused by the peptide. Quartz crystal microbalance with dissipation, vesicle dye leakage and atomic force microscopy measurements were used to investigate the global mode of peptide interaction. Aurein 1.2 displayed an enhanced interaction with the anionic DMPC/DMPG membrane while exhibiting primarily a surface interaction with both types of model membranes, which led to bilayer disruption and membrane lysis. The antimicrobial peptide interaction is consistent with the carpet mechanism for aurein 1.2 with discrete structural changes depending on the type of phospholipid membrane.

Phase separation of phospholipid multilayers incorporated with cell penetrating peptides

We used X-ray reflectivity to investigate the structures of phospholipid multilayers with transcription-activating-factor-derived peptide (TDP) as a function of the membrane charge density. Mixed phospholipid multilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl -sn-glycero-3-phosphoserine (DPPS) with different mixing ratios (C:S) were used to elucidate the various charge densities in a plasma membrane. We fixed the peptide/lipid molar ratio (P/L) and varied the DPPC/DPPS molar ratio in the mixed multilayer. In the pure DPPC multilayer, the incorporation of TDP had nearly no effect on the bilayer thickness of the mixed lipid multilayer. However, in the mixed DPPC/DPPS multilayer, the incorporation of TDP decreased the bilayer thickness, suggesting that the TDP peptide had a stronger interaction with DPPS than with DPPC and caused disorder in the lamellar structure. Combining this with the refined X-ray reflectivity (XR) data, we concluded that the TDP existed more in the headgroup region of the TDP-induced segregated DPPS in the mixed multilayer and caused significant membrane thinning.

Cholesterol mediates chitosan activity on phospholipid monolayers and Langmuir-Blodgett films

The polysaccharide chitosan has been largely used in many biological applications as a fat and cholesterol reducer, bactericide agent, and wound healing material. While the efficacy for some of such uses is proven, little is known about the molecular-level interactions involved in these applications. In this study, we employ mixed Langmuir and Langmuir-Blodgett (LB) films of negatively charged dimyristoyl phosphatidic acid (DMPA) and cholesterol as cell membrane models to investigate the role of cholesterol in the molecular-level action of chitosan. Chitosan does not remove cholesterol from the monolayer. The interaction with chitosan tends to expand the DMPA monolayer due to its interpenetration within the film. On the other hand, cholesterol induces condensation of the DMPA monolayer. The competing effects cause the surface pressure isotherms of mixed DMPA-cholesterol films on a chitosan subphase to be unaffected by the cholesterol mole fraction, due to distinct degrees of chitosan penetration into the film in the presence of cholesterol. By combining polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation spectroscopy (SFG), we showed that chitosan induces order into negatively charged phospholipid layers, whereas the opposite occurs for cholesterol. In conclusion, chitosan has its penetration in the film modulated by cholesterol, and electrostatic interactions with negatively charged phospholipids, such as DMPA, are crucial for the action of chitosan.

X-ray reflectivity study on the structure and phase stability of mixed phospholipid multilayers

Vertically oriented multilayers composed of two saturated phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS), were deposited on silicon. X-ray reflectivity was used to investigate the structures of the variously mixed phospholipid multilayers as a function of composition. Then, the phase stability was investigated at various annealing temperatures under humid conditions. The results indicated that the lipid spacing of the mixed phospholipid multilayers varied systematically as a function of the DPPC/DPPS ratio and that no macroscopic phase separation occurred during the annealing process under both dry and humid conditions.