Unexpected Order-Disorder Transition in Diacetylene Alcohol Langmuir Films

Opportunities and new developments for the study of surfaces and interfaces in soft condensed matter at the SIRIUS beamline of Synchrotron SOLEIL

The SIRIUS beamline of Synchrotron SOLEIL is dedicated to X-ray scattering and spectroscopy of surfaces and interfaces, covering the tender to mid-hard X-ray range (1.1-13 keV). The beamline has hosted a wide range of experiments in the field of soft interfaces and beyond, providing various grazing-incidence techniques such as diffraction and wide-angle scattering (GIXD/GIWAXS), small-angle scattering (GISAXS) and X-ray fluorescence in total reflection (TXRF). SIRIUS also offers specific sample environments tailored for in situ complementary experiments on solid and liquid surfaces. Recently, the beamline has added compound refractive lenses associated with a transfocator, allowing for the X-ray beam to be focused down to 10 µm × 10 µm while maintaining a reasonable flux on the sample. This new feature opens up new possibilities for faster GIXD measurements at the liquid-air interface and for measurements on samples with narrow geometries.

The composition of fusogenic lipid mixtures at the air-water modulates the physicochemical properties changes upon interaction with lysicamine

Knowing how a bioactive compound interacts with cell membranes is important to understand its effect at the molecular level. In this sense, this work aimed to study the interaction of lysicamine, an alkaloid with action against lung cancer cell lines, with lipid monolayers as cell membrane models. We employed two lipid mixtures: the first composed of 35% DOPC, 30% DOPE, 20% sphingomyelin, and 15% cholesterol as healthy cell membranes models (MM1), and the second replacing DOPC with DOPS as cancer cells models (MM2). The interaction of lysicamine with the monolayers was evaluated using tensiometry, Brewster angle microscopy (BAM), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). Lysicamine had interfacial effects in both membrane models. For MM 1, it expanded the lipid monolayer and changed the interfacial rheological properties, increasing the in-plane elasticity of the films. PM-IRRAS spectra suggested a higher conformational disorder of the alkyl chains of the lipids. For MM 2, lysicamine also shifted the isotherms to higher areas, expanding the monolayers, but with no significant alteration in their interfacial rheological properties. PM-IRRAS spectra also suggested higher disorder in the orientation of the lipid alkyl chains upon lysicamine incorporation. For both models, BAM did not show alteration in interfacial aggregation upon drug incorporation. In conclusion, changes in some interfacial properties of membrane models caused by lysicamine depend on the monolayer composition, which can be associated with its bioactivity in cellular membranes.

The Past and the Future of Langmuir and Langmuir-Blodgett Films

The Langmuir-Blodgett (LB) technique, through which monolayers are transferred from the air/water interface onto a solid substrate, was the first method to allow for the controlled assembly of organic molecules. With its almost 100 year history, it has been the inspiration for most methods to functionalize surfaces and produce nanocoatings, in addition to serving to explore concepts in molecular electronics and nanoarchitectonics. This paper provides an overview of the history of Langmuir monolayers and LB films, including the potential use in devices and a discussion on why LB films are seldom considered for practical applications today. Emphasis is then given to two areas where these films offer unique opportunities, namely, in mimicking cell membrane models and exploiting nanoarchitectonics concepts to produce sensors, investigate molecular recognitions, and assemble molecular machines. The most promising topics for the short- and long-term prospects of the LB technique are also highlighted.

Interfacial Behavior of Giant Amphiphiles Composed of Azobenzene and Polyhedral Oligomeric Silsesquioxane

Giant amphiphiles containing azobenzene and polyhedral oligomeric silsesquioxane (POSS) units are synthesized by linking 4,4'-azodianiline (ADA) and POSS derivatives by stepwise amidation and further modification. The synthesized giant amphiphiles are photoresponsive and show trans-cis isomerization under ultraviolet (UV) irradiation. These giant amphiphiles are spread on the air-water interface and compressed by the barrier without and under UV irradiation. By compression, the giant amphiphiles undergo a phase transition from gas (G), liquid expanded (LE), liquid condensed (LC), and solid (S) to a final collapse on the water surface. The giant amphiphiles are cis-isomer-rich under UV irradiation and are trans-isomer-rich without UV irradiation. The trans-isomers are straight-shaped, while the cis-isomers are bent, and hence, their phase transition behaviors on the water surface exhibit a distinct difference.