Spontaneous nanotube formation of an asymmetric glycolipid.

Over the past decades, advances in lipid nanotechnology have shown that self-assembled lipid structures providing ease of preparation, chemical stability, and biocompatibility represent a landmark on the development of multidisciplinary technologies. Lipid nanotubes (LNTs) are a unique class of lipid self-assembled structures, bearing unique properties such as high-aspect ratio, tunable diameter size, and precise molecular recognition. They can be obtained either by the action of external factors to already formed vesicles or spontaneously, the latter depending strongly on subtle molecular features. Here, we report on the spontaneous formation of supported lipid nanotubes of a particular type of glycolipid, ohmline, whose hydrophobic core displays remarkable asymmetry. The combination of bulk and surface-sensitive techniques indicates that below its main transition, ohmline displays an interdigitated gel phase, likely driven by the unique asymmetry in its hydrophobic core. Enhanced order packing by interdigitation favors the formation of ohmline nanotubes in agreement with chiral-based models of nanotube formation. The findings presented in this work call for additional studies to link lipid molecular structure-assembly relationships, whose understanding is relevant for the controlled design of lipid nanotubes networks in particular and controlled design of soft-matter nanomaterials in general.

Liposome Fusion Mediated by Hydrophobic Magnetic Nanoparticles Stabilized with Oleic Acid and Modulated by an External Magnetic Field.

Membrane fusion is considered relevant in countless scientific areas and biotechnological processes, ranging from vital life events to biomedicine, pharmaceuticals, and materials engineering, among others. In this study, we employed hydrophobic oleic acid (OA)-coated magnetite (Fe3O4) nanoparticles (MNP-OA) as a platform to induce the fusion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine liposomes [large unilamellar vesicles (LUVs)] in a colloidal dispersion. This fusion was monitored through dynamic light scattering, turbidimetry, and fluorescence assay using the well-known Tb/dipicolinic acid (DPA) complex formation assay. MNP-OA have shown to be able to induce fusion with the mixing of liposomal inner content with direct dependence on the nanoparticle concentration added to the LUVs. Moreover, changes in the permeability of the liposome bilayer, upon the addition of MNP-OA to liposomes, were evaluated by studying the leakage of carboxyfluorescein and of the co-encapsulated Tb/DPA complex. These assays allowed us to determine that MNP-OA did not significantly modify liposome permeability during the fusion process. Transmission electron microscopy and confocal microscopy revealed that MNP-OA remained embedded in the lipid bilayer without producing membrane rupture, liposome deformation, or destruction. In addition, we evaluated the effect of applying a low-intensity magnetic field to the LUVs/MNP-OA system and observed that the nanoparticles considerably increased their fusogenic activity under this external stimulus, as well as they are capable of responding to low magnetic fields of around 0.45 mT. These results revealed the potential of hydrophobic magnetic nanoparticles, stabilized with OA, to act as a fusogen, thus representing a valuable tool for biotechnological applications.

Hydrophobic silver nanoparticles interacting with phospholipids and stratum corneum mimic membranes in Langmuir monolayers.

The interaction of hydrophobic silver nanoparticles with different phospholipids and stratum corneum mimic (SCM) membranes is studied in Langmuir monolayers. Thus, silver nanoparticles coated with oleic acid (AgNP-OA) were synthesized, characterized and incorporated in Langmuir monolayers of single phospholipids -having different chain length, saturation degree and phase state- or of a SCM mixture. The incorporation of AgNP-OA to the lipid monolayers generated an expansion of the monolayers and a decrease of the surface compressional modulus compared to the pure lipid. X-ray photoelectron spectroscopy (XPS) suggested that the zwitterionic choline-phospholipids can be adsorbed onto the nanoparticles' surface, which is relevant considering that phospholipids are the major constituents of the cell membrane. We also studied the changes in the topography at the mesoscale level using Brewster angle microscopy. We found the most prominent changes in the lipids with liquid-condensed phase, such as SCM, showing segregation of their components. This could have major implications in the barrier function of the membrane, affecting for example the skin permeability towards hydrophobic nanoparticles. Finally, the capability of hydrophobic AgNP-OA for delivering Ag+ ions was studied in aqueous media in the absence and presence of phospholipids. In both conditions, AgNP-OA released Ag+ at reported-bactericidal concentrations, being double in the presence of phospholipids.

Alkyl esters of L-ascorbic acid: Stability, surface behaviour and interaction with phospholipid monolayers.

L-ascorbic acid alkyl esters (ASCn) are molecules of pharmaceutical interest for their amphiphilic nature and proposed antioxidant power. In contrast to L-ascorbic acid, ASC(n) with different acyl chain lengths behaved stably upon oxidation and a tautomeric isomerization was observed. In Langmuir films, when the ascorbic ring has a negative charge, ASC14 and ASC16 form stable monolayers, contrary to ASC10 and ASC12. ASC16 films showed transition from liquid-expanded (LE) to liquid-condensed phase, whereas ASC14 showed only an LE phase. When ASCn are mainly neutral, ASC14 showed phase transition from LE to a crystalline phase, as previously reported for ASC16. The two-dimensional domains displayed crystal-like shapes with anisotropic optical activity when interacting with the polarized light under Brewster angle microscopy. The compounds with the longer acyl chain (ASC16, ASC14 and ASC12) exhibited good surface activity, forming Gibbs monolayers. They also were able to penetrate into phospholipid monolayers up to a critical point of 45-50 mN/m. The 1-palmitoyl-2-oleoylphosphatidylcholine/ASCn films showed LC and/or crystalline domains only for ASC16. This study provides valuable evidence regarding the stability and surface properties of this drug family, and casts light into the differential interaction of these drugs with lipid membranes, which is important for understanding its differential pharmacological activity.