Varying the Core Topology in All-Glycidol Hyperbranched Polyglycerols: Synthesis and Physical Characterization.

In the present study, low molecular weight cyclic polyglycidol is used as a macroinitiator for hypergrafting glycidol and producing cyclic graft hyperbranched polyglycerol (cPG-g-hbPG) in the molecular weight range of 10-10 g mol. Linear graft hyperbranched polyglycerol (linPG-g-hbPG) and hyperbranched polyglycerol (hbPG) are prepared as reference samples. This creates a family of hbPG structures with cyclic, linear, and star cores, allowing to evaluate their properties in solution and in bulk.

Softness matters: effects of compression on the behavior of adsorbed microgels at interfaces.

Deformable colloids and macromolecules adsorb at interfaces as they decrease the interfacial energy between the two media. The deformability, or softness, of these particles plays a pivotal role in the properties of the interface. In this study, we employ a comprehensive approach, combining neutron reflectometry with molecular dynamics simulations, to thoroughly examine the profound influence of softness on the structure of microgel Langmuir monolayers under compression.

Structure of graphene oxide-phospholipid monolayers: A grazing incidence X-ray diffraction and neutron and X-ray reflectivity study.

Hypothesis: Graphene oxide-based nanotechnology has aroused a great interest due to its applications in the biomedical and optoelectronic fields. The wide use of these materials makes it necessary to study its potential toxicity associated with the inhalation of Graphene Oxide (GO) nanoparticles and its interaction with the lung surfactant. Langmuir monolayers have proven to be an excellent tool for studying the properties of the lung surfactant and the effect of intercalation of nanoparticles on its structure and properties.

Effects of Charge Density on Spread Hyperbranched Polyelectrolyte/Surfactant Films at the Air/Water Interface.

The interfacial structure and morphology of films spread from hyperbranched polyethylene imine/sodium dodecyl sulfate (PEI/SDS) aggregates at the air/water interface have been resolved for the first time with respect to polyelectrolyte charged density. A recently developed method to form efficient films from the dissociation of aggregates using a minimal quantity of materials is exploited as a step forward in enhancing understanding of the film properties with a view to their future use in technological applications. Interfacial techniques that resolve different time and length scales, namely, ellipsometry, Brewster angle microscopy, and neutron reflectometry, are used.

Control of the structure and morphology of polypeptide/surfactant spread films by exploiting specific interactions.

We demonstrate control of the structure and morphology of polypeptide/surfactant films at the air/water interface as a function of the maximum compression ratio of the surface area, exploiting a recently developed film formation mechanism that requires minimal quantities of materials involving the dissociation of aggregates. The systems studied are poly(L-lysine) (PLL) or poly(L-arginine) (PLA) with sodium dodecyl sulfate (SDS), chosen because the surfactant (i) interacts more strongly with the latter polypeptide due to the formation of hydrogen bonds between the guanidinium group and its oxygen atoms, and (ii) induces bulk β-sheet and α-helix conformations of the respective polypeptides. The working hypothesis is that such different interactions may be used to tune the film properties when compressed to form extended structures (ESs).

Engineering phosphatidylinositol-4,5-bisphosphate model membranes enriched in endocytic cargo: A neutron reflectometry, AFM and QCM-D structural study.

The combination of in vitro models of biological membranes based on solid-supported lipid bilayers (SLBs) and of surface sensitive techniques, such as neutron reflectometry (NR), atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D), is well suited to provide quantitative information about molecular level interactions and lipid spatial distributions. In this work, cellular plasma membranes have been mimicked by designing complex SLB, containing phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P) lipids as well as incorporating synthetic lipo-peptides that simulate the cytoplasmic tails of transmembrane proteins. The QCM-D results revealed that the adsorption and fusion kinetics of PtdIns4,5P are highly dependent of Mg.

Association of oppositely charged polyelectrolyte and surfactant in solution: equilibrium and nonequilibrium features.

The association of polyelectrolytes and surfactants bearing charges of opposite signs has been for long time considered under an equilibrium framework. However, this is far to provide a true description of the physico-chemical rules of the association process when kinetically arrested nonequilibrium states are formed. This is the result of specific interaction pathways between the polyelectrolyte chains and the surfactant molecules determined by the mixing procedure and the mixture composition.

Developing advanced models of biological membranes with hydrogenous and deuterated natural glycerophospholipid mixtures.

Cellular membranes are complex systems that consist of hundreds of different lipid species. Their investigation often relies on simple bilayer models including few synthetic lipid species. Glycerophospholipids (GPLs) extracted from cells are a valuable resource to produce advanced models of biological membranes.

Probing the effect of the capping polyelectrolyte on the internal structure of Layer-by-Layer decorated nanoliposomes.

Hypothesis: The internal organization of polyelectrolyte layers deposited on colloidal templates plays a very important role for the potential applications of these systems as capsules for drug delivery purposes.

Experiments: The mutual arrangement of oppositely charged polyelectrolyte layers upon their deposition on positively charged liposomes has been studied by combining up three different scattering techniques and Electronic Spin Resonance, which has provided information about the inter-layer interactions and their effect on the final structure of the capsules.

Findings: The sequential deposition of oppositely charged polyelectrolytes on the external leaflet of positively charged liposomes allows modulating the organization of the obtained supramolecular structures, impacting the packing and rigidity of the obtained capsules due to the change of the ionic cross-linking of the multi-layered film as a result of the specific charge of the last deposited layer.

Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids.

Hypothesis: Unravelling the structural diversity of cellular membranes is a paramount challenge in life sciences. In particular, lipid composition affects the membrane collective behaviour, and its interactions with other biological molecules.

Experiments: Here, the relationship between membrane composition and resultant structural features was investigated by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry on in vitro membrane models of the mammalian plasma and endoplasmic-reticulum-Golgi intermediate compartment membranes in the form of Langmuir monolayers.

Unravelling the orientation of the inositol-biphosphate ring and its dependence on phosphatidylinositol 4,5-bisphosphate cluster formation in model membranes.

Hypothesis: Inositol phospholipids are well known to form clusters in the cytoplasmic leaflet of the plasma membrane that are responsible for the interaction and recruitment of proteins involved in key biological processes like endocytosis, ion channel activation and secondary messenger production. Although their phosphorylated inositol ring headgroup plays an important role in protein binding, its orientation with respect to the plane of the membrane and its lateral packing density has not been previously described experimentally.

Experiments: Here, we study phosphatidylinositol 4,5-bisphosphate (PIP) planar model membranes in the form of Langmuir monolayers by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry to elucidate the relation between lateral (in-plane) and perpendicular (out-of-plane) molecular organization of PIP.

Polyelectrolyte/surfactant films: from 2D to 3D structural control.

Reversible control of the 3D structure of polyelectrolyte/surfactant films at the air/water interface is showcased. A recently discovered mechanism is exploited to form highly efficient, stable and biocompatible films by spreading aggregates composed of poly-L-lysine and sodium dodecyl sulfate on the surface of water. Reversible control of: (1) the surface monolayer coverage, (2) the switching on or off discrete extended structures, and (3) the extended structure coverage is demonstrated for the first time.

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels.

The structural characterization of microgels at interfaces is fundamental to understand both their 2D phase behavior and their role as stabilizers that enable emulsions to be broken on demand. However, this characterization is usually limited by available experimental techniques, which do not allow a direct investigation at interfaces. To overcome this difficulty, here we employ neutron reflectometry, which allows us to probe the structure and responsiveness of the microgels in-situ at the air-water interface.

Soft Colloidal Particles at Fluid Interfaces.

The assembly of soft colloidal particles at fluid interfaces is reviewed in the present paper, with emphasis on the particular case of microgels formed by cross-linked polymer networks. The dual polymer/colloid character as well as the stimulus responsiveness of microgel particles pose a challenge in their experimental characterization and theoretical description when adsorbed to fluid interfaces. This has led to a controversial and, in some cases, contradictory picture that cannot be rationalized by considering microgels as simple colloids.

A broad perspective to particle-laden fluid interfaces systems: from chemically homogeneous particles to active colloids.

Particles adsorbed to fluid interfaces are ubiquitous in industry, nature or life. The wide range of properties arising from the assembly of particles at fluid interface has stimulated an intense research activity on shed light to the most fundamental physico-chemical aspects of these systems. These include the mechanisms driving the equilibration of the interfacial layers, trapping energy, specific inter-particle interactions and the response of the particle-laden interface to mechanical perturbations and flows.

Strikingly Different Roles of SARS-CoV-2 Fusion Peptides Uncovered by Neutron Scattering.

Coronavirus disease-2019 (COVID-19), a potentially lethal respiratory illness caused by the coronavirus SARS-CoV-2, emerged in the end of 2019 and has since spread aggressively across the globe. A thorough understanding of the molecular mechanisms of cellular infection by coronaviruses is therefore of utmost importance. A critical stage in infection is the fusion between viral and host membranes.

Strong synergistic interactions in zwitterionic-anionic surfactant mixtures at the air-water interface and in micelles: The role of steric and electrostatic interactions.

Hypothesis: The milder interaction with biosystems makes the zwitterionic surfactants an important class of surfactants, and they are widely used in biological applications and in personal care formulations. An important aspect of those applications is their strong synergistic interaction with anionic surfactants. It is anticipated that the strong interaction will significantly affect the adsorption and self-assembly properties.

How do chain lengths of acyl-l-carnitines affect their surface adsorption and solution aggregation?

Hypothesis: l-carnitines in our body systems can be readily converted into acyl-l-carnitines which have a prominent place in cellular energy generation by supporting the transport of long-chain fatty acids into mitochondria. As biocompatible surfactants, acyl-l-carnitines have potential to be useful in technical, personal care and healthcare applications. However, the lack of understanding of the effects of their molecular structures on their physical properties has constrained their potential use.

Particle-laden fluid/fluid interfaces: physico-chemical foundations.

Particle-laden fluid/fluid interfaces are ubiquitous in academia and industry, which has fostered extensive research efforts trying to disentangle the physico-chemical bases underlying the trapping of particles to fluid/fluid interfaces as well as the properties of the obtained layers. The understanding of such aspects is essential for exploiting the ability of particles on the stabilization of fluid/fluid interface for the fabrication of novel interface-dominated devices, ranging from traditional Pickering emulsions to more advanced reconfigurable devices. This review tries to provide a general perspective of the physico-chemical aspects associated with the stabilization of interfaces by colloidal particles, mainly chemical isotropic spherical colloids.

In situ determination of the structure and composition of Langmuir monolayers at the air/water interface by neutron and X-ray reflectivity and ellipsometry.

This review focuses on the description of the structure and composition of a variety of Langmuir monolayers (LMs) deposited at the air/water interface by using ellipsometry, Brewster Angle microscopy and scattering techniques, mainly neutron and X-ray reflectometry. Since the first experiment done by Angels Pockels with a homemade trough in her home kitchen until today, LMs of different materials have been extensively studied providing not only relevant model systems in biology, physics and chemistry but also precursors of novel materials via their deposition on solid substrates. There is a vast amount of surface-active materials that can form LMs and, therefore, far from a revision of the state-of-the-art, we will emphasize here: (i) some fundamental aspects to understand the physics behind the molecular deposition at the air/water interface; (ii) the advantages in using in situ techniques, such as reflectometry or ellipsometry, to resolve the interfacial architecture and conformation of molecular films; and, finally, (iii) a summary of several systems that have certain interest from the experimental or conceptual point of view.

Structural Disruptions of the Outer Membranes of Gram-Negative Bacteria by Rationally Designed Amphiphilic Antimicrobial Peptides.

Gram-negative bacteria are covered by both an inner cytoplasmic membrane (IM) and an outer membrane (OM). Antimicrobial peptides (AMPs) must first permeate through the OM and cell wall before attacking the IM to cause cytoplasmic leakage and kill the bacteria. The bacterial OM is an asymmetric bilayer with the outer leaflet primarily composed of lipopolysaccharides (LPSs) and the inner leaflet composed of phospholipids (PLs).

First quantitative assessment of the adsorption of a fluorocarbon gas on phospholipid monolayers at the air/water interface.

Hypothesis: Fluorocarbon gases introduced above monolayers of phospholipids at the air/water interface were recently found to promote the adsorption of diverse molecular compounds, with potential application in drug-loaded microbubble design. Quantitative determination of the fluorocarbon present in the monolayers is strongly needed for the development of such applications. We hypothesized that neutron reflectometry (NR) and ellipsometry experiments would allow quantification of the fluorocarbon trapped in the monolayers.

How do Self-Assembling Antimicrobial Lipopeptides Kill Bacteria?

Antimicrobial peptides are promising alternatives to traditional antibiotics. A group of self-assembling lipopeptides was formed by attaching an acyl chain to the N-terminus of α-helix-forming peptides with the sequence C-G(IIKK)I-NH (CG, = 4-12 and = 2). CG self-assemble into nanofibers above their critical aggregation concentrations (CACs).