The nanostructure of the fibrin fibers in fibrin clots is investigated by using spectrometry and small angle x-ray scattering measurements. First, an autocoherent analysis of the visible light spectra transmitted through formed clots is demonstrated to provide robust measurements of both the radius and density of the fibrin fibers. This method is validated via comparison with existing small-angle and dynamic light-scattering data. The complementary use of small angle x-ray scattering spectra and light spectrometry unambiguously shows the disjointed nature of the fibrin fibers. Indeed, under quasiphysiological conditions, the fibers are approximately one-half as dense as their crystalline fiber counterparts. Further, although the fibers are locally crystalline, they appear to possess a lateral fractal structure.

The genus Orthobunyavirus within the family Bunyaviridae constitutes an expanding group of emerging viruses, which threaten human and animal health. Despite the medical importance, little is known about orthobunyavirus structure, a prerequisite for understanding virus assembly and entry. Here, using electron cryo-tomography, we report the ultrastructure of Bunyamwera virus, the prototypic member of this genus. Whilst Bunyamwera virions are pleomorphic in shape, they display a locally ordered lattice of glycoprotein spikes. Each spike protrudes 18 nm from the viral membrane and becomes disordered upon introduction to an acidic environment. Using sub-tomogram averaging, we derived a three-dimensional model of the trimeric pre-fusion glycoprotein spike to 3-nm resolution. The glycoprotein spike consists mainly of the putative class-II fusion glycoprotein and exhibits a unique tripod-like arrangement. Protein–protein contacts between neighbouring spikes occur at membrane-proximal regions and intra-spike contacts at membrane-distal regions. This trimeric assembly deviates from previously observed fusion glycoprotein arrangements, suggesting a greater than anticipated repertoire of viral fusion glycoprotein oligomerization. Our study provides evidence of a pH-dependent conformational change that occurs during orthobunyaviral entry into host cells and a blueprint for the structure of this group of emerging pathogens.

Protein adsorption on surfaces is used in analytical tools as an immobilization mean to trap the analyte to be detected. However, protein adsorption can lead to a conformational change in the protein structure, resulting in a loss of bioactivity. Here, we study the adsorption of the Streptavidin -Biotin complex on amorphous SiO 2 surfaces functionalized with five different silane selfassembled monolayers by all-atom Molecular Dynamics simulations. We find that the Streptavidin global conformational change increases linearly with the adsorption energy, which depends, as well as the nature of residues with high mobility, on the alkyl chain length and head group charge of silane molecules. Effects on interactions with Biotin are further investigated by Steered Molecular Dynamics (SMD) simulations, which mimics Atomic Force Microscope (AFM) spectroscopy with the Biotin attached on the tip. We show the combined effects of adsorptioninduced global conformational changes and of the position of residues with high mobility on the force of Biotin detachment. By comparing our results to experimental and SMD detachment forces obtained in water, without any surface, we conclude that silane with uncharged and short alkyl chains allow Streptavidin immobilization, with high adsorption energy, while keeping Biotin interactions better than silanes with long alkyl chains or charged head-groups.

Objective— Because of the widespread clinical use of heparins, their effects on the enzymatic cascade are very well known. In contrast, little is known about the direct effect of heparins on the nanostructure of fibrin fibers, even though this nanostructure plays a major role in the mechanical strength and lysis of clots. This lack of reliable data can be correlated with the lack of a nonintrusive, quantitative method to determine this structure. We recently developed such a method that allows the simultaneous determination of the average fiber radius and the protein content using spectrometric data. In this study, we assessed the nanostructure of fibrin in a system composed of human thrombin and fibrinogen. Methods and Results— We provide quantitative evidence showing that both unfractionated heparin and low molecular weight heparin directly alter the nanostructure of fibrin fibers independent of their other actions on the coagulation cascade; as expected, the pentasaccharide fondaparinux has no effect. Conclusion— Our results show that in addition to the effect of heparin on the coagulation cascade, modifications of the fibrin nanostructure may also contribute to improved fibrinolysis.

Surface chemical functionalization is used in analytical tools to immobilize biomolecules that will capture a specific analyte and also to reduce the nonspecific adsorption. Silane monolayers are widely used to functionalize silica surfaces. Their interfacial properties are linked to the silane organization. Here, we study, by molecular dynamics simulations, the effects of silane molecule headgroup charge, alkyl chain length, and surface coverage on the structure of silane monolayers. Four molecules are investigated: 3aminopropyldimethylethoxysilane, n-propyldimethylmethoxysilane, octadecyldimethylmethoxysilane, and tert-butyl-11-(dimethylamino-(dimethyl)silyl)undecanoate. The results suggest that, while long alkyl chains straighten out and adopt a more organized structure as surface coverage increases, the tilt angle of short chains is independent of surface coverage. Furthermore, in the case of long alkyl chains, a charged head-group seems to reduce the tilt angle to surface coverage dependence. The simulated alkyl chain tilt angles were qualitatively validated by infrared spectroscopy and X-ray photoelectron spectroscopy. Also, a hexagonal packing is observed in all of the monolayers but is more defined as surface coverage increases. The nematic order parameter suggests that this packing is governed by the parallel orientation of the first C−C bonds near the surface. So, even short alkyl chains, with a large tilt angle distribution, present a hexagonal packing.

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Hybrid nanoparticles composed of an efficient nonlinear optical core and a gold shell can enhance and tune the nonlinear optical emission thanks to the plasmonic effect. However the influence of an incomplete gold shell, i.e., isolated gold nano-islands, is still not well studied. Here LiNbO3 (LN) core nanoparticles of 45 nm were coated with various densities of gold nano-seeds (AuSeeds). As both LN and AuSeeds bear negative surface charge, a positively-charged polymer was first coated onto LN. The number of polymer chains per LN was evaluated at 1210 by XPS and confirmed by fluorescence titration. Then, the surface coverage percentage of AuSeeds onto LN was estimated to a maximum of 30% using ICP-AES. The addition of AuSeeds was also accompanied with surface charge reversal, the negative charge increasing with the higher amount of AuSeeds. Finally, the first hyperpolarizability decreased with the increase of AuSeeds density while depolarization values for Au-seeded LN were close to the one of bare LN, showing a predominance of the second harmonic volumic contribution.

200 nm thick films of titanium tungsten (TiW) were cleaned by oxygen plasma and the resulting oxidized surfaces were functionalized by 3-aminopropylphosphonic acid (APPA), 3-ethoxydimethylsilylpropylamine (APDMES) or dopamine (DA) to form three different organolayers. The three resulting organolayers were characterized by X-ray photoelectron spectroscopy (XPS), Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. Stability of each organolayer was investigated. Our results suggested that the Si-O-Ti or Si-O-W bonds issued from the reactions of APDMES with surface oxidize TiW were rather labile whereas the catechol layer was less labile. The APPA layer was the most stable of all tested surface modifications.