The development of novel nano-engineered materials poses important questions regarding the impact of these new materials on living systems. Possible adverse effects must be assessed in order to ...prevent risks for health and the environment. On the other hand, a thorough understanding of their interaction with biological systems might also result in the creation of novel biomedical applications. We present a study on the interaction of model lipid membranes with gold nanoparticles (AuNP) of different surface modifications. Neutron reflectometry experiments on zwitterionic lipid double bilayers were performed in the presence of AuNP functionalized with cationic and anionic head groups. Structural information was obtained that provided insight into the fate of the AuNPs with regard to the integrity of the model cell membranes. The AuNPs functionalized with cationic head groups penetrate into the hydrophobic moiety of the lipid bilayers and cause membrane disruption at an increased concentration. In contrast, the AuNPs functionalized with anionic head groups do not enter but seem to impede the destruction of the lipid bilayer at an alkaline pH. The information obtained might influence the strategy for a better nanoparticle risk assessment based on a surface charge evaluation and contribute to nano-safety considerations during their design.
Among all methods available for the preparation of multifunctional nanostructured composite materials with remarkable functional properties, Layer-by-Layer (LbL) assembly is currently one of the most ...widely used techniques due to its environmental friendliness, its ease of use and its versatility in combining a plethora of available colloids and macromolecules into finely tuned multicomponent architectures with nanometer scale control. Despite the importance of these systems in emerging technologies, their nanoscopic 3D structure, and thus the ability to predict and understand the device performance, is still largely unknown. In this article, we use neutron scattering to determine the average conformation of individual deuterated polyelectrolyte chains inside LbL assembled films. In particular, we determine that in LbL-films composed of poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) multilayers prepared from 2 M sodium chloride solutions the PSS chains exhibit a flattened coil conformation with an asymmetry factor of around seven. Albeit this highly non-equilibrium state of the polymer chain, its density profiles follow Gaussian distributions occupying roughly the same volume as in the bulk complex.
Abstract
SARS-CoV-2 spike proteins are responsible for the membrane fusion event, which allows the virus to enter the host cell and cause infection. This process starts with the binding of the spike ...extramembrane domain to the angiotensin-converting enzyme 2 (ACE2), a membrane receptor highly abundant in the lungs. In this study, the extramembrane domain of SARS-CoV-2 Spike (sSpike) was injected on model membranes formed by supported lipid bilayers in presence and absence of the soluble part of receptor ACE2 (sACE2), and the structural features were studied at sub-nanometer level by neutron reflection. In all cases the presence of the protein produced a remarkable degradation of the lipid bilayer. Indeed, both for membranes from synthetic and natural lipids, a significant reduction of the surface coverage was observed. Quartz crystal microbalance measurements showed that lipid extraction starts immediately after sSpike protein injection. All measurements indicate that the presence of proteins induces the removal of membrane lipids, both in the presence and in the absence of ACE2, suggesting that sSpike molecules strongly associate with lipids, and strip them away from the bilayer, via a non-specific interaction. A cooperative effect of sACE2 and sSpike on lipid extraction was also observed.
The properties of lipid monolayers at the interface between two immiscible electrolyte solutions (ITIES) have attracted much attention over the last 30 years. This is mainly because of the biological ...relevance of lipids and the possibility of controlling ion and electron transfer across one leaflet of a cellular membrane. In the last decade, the electrochemical characterization of phosphatidylcholine (PC) adsorbed monolayers at ITIES suggested that the transfer of aqueous cations across the interface is facilitated by the complexation of aqueous cations with the PC zwitterionic head groups, followed by the depletion of lipids from the interface. In this work, we present a study on the effects of applied electric fields and electrolyte concentration on the interfacial structure of the ITIES by combining neutron reflectometry (NR) and electrochemical characterization techniques including the effects of an adsorbed lipid layer. Our results confirm that lipid depletion occurs as cations are transferred. However, we found that the presence of lipids favors the intermixing of the two-liquid phases on a length scale of a few tens of nanometers. To our knowledge, this has been the first NR-electrochemistry study of the ITIES. We believe that our findings could open new possibilities for coupling bioelectrochemical characterization and scattering based techniques at the liquid-liquid interface.
Knowledge of the (supra)molecular structure of an interface that contains amphiphilic ligand molecules is necessary for a full understanding of ion transfer during solvent extraction. Even if ...molecular dynamics already yield some insight in the molecular configurations in solution, hardly any experimental data giving access to distributions of both extractant molecules and ions at the liquid–liquid interface exist. Here, the combined application of X‐ray and neutron reflectivity measurements represents a key milestone in the deduction of the interfacial structure and potential with respect to two different lipophilic ligands. Indeed, we show for the first time that hard trivalent cations can be repelled or attracted by the extractant‐enriched interface according to the nature of the ligand.
Liquid interfaces: For a full understanding of the ion transfer during solvent extraction, knowledge about the extractant and ion distributions across the water–oil interface is necessary. The extractant and ion distributions at the water–oil interface were studied by X‐ray and neutron reflectivity measurements for two different diamide extractants (see picture).
The plant plasma membrane (PM) is an essential barrier between the cell and the external environment, controlling signal perception and transmission. It consists of an asymmetrical lipid bilayer made ...up of three different lipid classes: sphingolipids, sterols, and phospholipids. The glycosyl inositol phosphoryl ceramides (GIPCs), representing up to 40% of total sphingolipids, are assumed to be almost exclusively in the outer leaflet of the PM. However, their biological role and properties are poorly defined. In this study, we investigated the role of GIPCs in membrane organization. Because GIPCs are not commercially available, we developed a protocol to extract and isolate GIPC-enriched fractions from eudicots (cauliflower and tobacco) and monocots (leek and rice). Lipidomic analysis confirmed the presence of trihydroxylated long chain bases and 2-hydroxylated very long-chain fatty acids up to 26 carbon atoms. The glycan head groups of the GIPCs from monocots and dicots were analyzed by gas chromatograph–mass spectrometry, revealing different sugar moieties. Multiple biophysics tools, namely Langmuir monolayer, ζ-Potential, light scattering, neutron reflectivity, solid state 2H-NMR, and molecular modeling, were used to investigate the physical properties of the GIPCs, as well as their interaction with free and conjugated phytosterols. We showed that GIPCs increase the thickness and electronegativity of model membranes, interact differentially with the different phytosterols species, and regulate the gel-to-fluid phase transition during temperature variations. These results unveil the multiple roles played by GIPCs in the plant PM.
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•Supported lipid bilayers (SLB) from the nucleolipid POP-Ade were prepared.•The SLBs were investigated with QCM-D and neutron reflectometry.•A specific affinity of POP-Ade SLB toward ...nucleic acids was found.
POP-Ade (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyladenosine) is a biocompatible anionic nucleolipid with the DNA nucleoside, Adenosine, in the polar headgroup. We have studied the affinity of nucleic acids of different contour length, composition and structure toward supported lipid bilayers (SLB) composed of POP-Ade mixed with the zwitterionic phospholipid POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) using quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR). In order to highlight the specificity of the nucleic acid interaction, the results were compared with data obtained for SLB containing the anionic phospholipid POPG (1-palmitoyl-2-oleoyl-sn-phosphatidyl-glycerol) replacing POP-Ade. Our results demonstrate that the presence of a nucleobase headgroup provides the bilayers with the ability to bind single stranded nucleic acids in a selective fashion, according to a Watson–Crick pattern. In addition the interaction with double stranded nucleic acids was strengthened. Overall, these findings represent fundamental information for the design of biocompatible DNA vectors with DNA–RNA-based amphiphiles.
The concentration profile of deuterated myoglobin (Mb) adsorbed onto polystyrene substrates displaying poly(ethylene glycol) (PEG) brushes is characterized by neutron reflectometry (NR). The method ...allows to directly distinguish among primary adsorption at the grafting surface, ternary adsorption within the brush, and secondary adsorption at the brush outer edge. It complements depth-insensitive standard techniques, such as ellipsometry, radioactive labeling, and quartz crystal microbalance. The study explores the effect of the PEG polymerization degree, N, and the grafting density, σ, on Mb adsorption. In the studied systems there is no indication of secondary or ternary adsorption, but there is evidence of primary adsorption involving a dense inner layer at the polystyrene surface. For sparsely grafted brushes the primary adsorption involves an additional dilute outer protein layer on top of the inner layer. The amount of protein adsorbed in the inner layer is independent of N but varies with σ, while for the outer layer it is correlated to the amount of grafted PEG and is thus sensitive to both N and σ. The use of deuterated proteins enhances the sensitivity of NR and enables monitoring exchange between deuterated and hydrogenated species.
Theoretical simulations have predicted that a lipid bilayer forms a stable superstructure when a sheet of graphene is inserted in its hydrophobic core. We experimentally produced for the first time a ...lipid–graphene–lipid assembly by combining the Langmuir–Blodgett and the Langmuir–Schaefer methods. Graphene is sandwiched and remains flat within the hydrophobic core of the lipid bilayer. Using infrared spectroscopy, ellipsometry, and neutron reflectometry, we characterized the superstructure at every fabrication step. The hybrid superstructure is mechanically stable and graphene does not disturb the natural lipid bilayer structure.
Neutron diffraction was used to study the behavior of water present in phospholipid multilamellar stacks from 1,2-dimyristoyl-
sn
-glycero-3-phosphatidylcholine (DMPC) at cryogenic temperatures. ...Evidence was found for the existence of a highly viscous phase of water that exists between 180 and 220 K based on the observation that water can leave the intermembrane space at these low temperatures. Similar measurements are described in the literature for purple membrane (PM) samples. From a comparison with results from this natural membrane by using the same flash-cooling protocol, it is found that in the case of pure lipid samples, less water is trapped and the water flows out at lower temperatures. This suggests that the water is less hindered in its movements than in the PM case. It is shown that at least the Lβ′-phase of DMPC can be trapped likely by flash cooling; upon heating to about 260 K, it transforms to another phase that was not fully characterized.
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