Macroscopic Biaxial Order in Multilayer Films of Bent-Core Liquid Crystals Deposited by Combined Langmuir-Blodgett/Langmuir-Schaefer Technique.

Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir-Blodgett and Langmuir-Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals.

Peptide Disc Mediated Control of Membrane Protein Orientation in Supported Lipid Bilayers for Surface-Sensitive Investigations.

In vitro characterization of membrane proteins requires experimental approaches providing mimics of the microenvironment that proteins encounter in native membranes. In this context, supported lipid bilayers provide a suitable platform to investigate membrane proteins by a broad range of surface-sensitive techniques such as neutron reflectometry (NR), quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), atomic force microscopy (AFM), and fluorescence microscopy. Nevertheless, the successful incorporation of membrane proteins in lipid bilayers with sufficiently high concentration and controlled orientation relative to the bilayer remains challenging. We propose the unconventional use of peptide discs made by phospholipids and amphipathic 18A peptides to mediate the formation of supported phospholipid bilayers with two different types of membrane proteins, CorA and tissue factor (TF). The membrane proteins are reconstituted in peptide discs, deposited on a solid surface, and the peptide molecules are then removed with extensive buffer washes. This leaves a lipid bilayer with a relatively high density of membrane proteins on the support surface. As a very important feature, the strategy allows membrane proteins with one large extramembrane domain to be oriented in the bilayer, thus mimicking the in vivo situation. The method is highly versatile, and we show its general applicability by characterizing with the above-mentioned surface-sensitive techniques two different membrane proteins, which were efficiently loaded in the supported bilayers with ∼0.6% mol/mol (protein/lipid) concentration corresponding to 35% v/v for CorA and 8% v/v for TF. Altogether, the peptide disc mediated formation of supported lipid bilayers with membrane proteins represents an attractive strategy for producing samples for structural and functional investigations of membrane proteins and for preparation of suitable platforms for drug testing or biosensor development.