Such As Small-angle X-ray Scattering Research Articles

Characterization of complex micellar systems by Scattering techniques (SAXS and SANS) and wet-scanning transmission electron microscopy (wet-STEM)

The morphology of complex micellar assemblies is generally described using indirect methods such as small-angle X-ray scattering (SAXS) or small angle neutron scattering (SANS) that can yield to ambiguous descriptions of the nano-objects when the sample contains multiple structures or completely unknown structures. We herein propose to directly observe the nano-objects formed in P123 pluronic solutions (with and without rare-earth element - REE) using wet-Scanning Transmission Electron Microscopy (wet-STEM) and to compare the results with sample descriptions derived from SAXS and SANS measurements. The results obtained by the different analytical techniques are consistent. Each analytical method provides complementary information that allows the internal structure of the objects, their compositions and their mutual interactions to be described precisely. The main contributions of wet-STEM microscopy are to describe the nano-objects individually and, in particular, to show that the REE content can vary from 1 to 10 from one micelle to another, to observe the dynamics of the nano-objects in the liquid and to prove the co-existence of nano-objects with very different morphologies in the same system.

Dispersion Performances and Fluorescent Behaviors of Naphthalic Anhydride Doped in Poly(acrylic acid) Frameworks for pH-Sensitive Ibuprofen Delivery via Fractal Evolution.

The pH-responsive fluorescent P(1,8-naphthalic anhydride (NA)-acrylic acid (AA)) matrix was successfully prepared by a doping method using poly(acrylic acid) (PAA) as a pH-sensitive polymer and NA as a fluorescent tracer. The fluorescent behaviors of the used NA dispersed in PAA frameworks were demonstrated based on fractal features combined with various characterizations, such as small-angle X-ray scattering (SAXS) patterns, photoluminescence (PL) spectra, scanning electron microscope (SEM) images, thermogravimetry (TG) profiles, Fourier transform infrared (FT-IR) spectroscopy, and time-resolved decays. The effects of NA-doping on the representative fluorescent P(NA-AA) were investigated, in which the fluorescent performance of the doped NA was emphasized. The results indicated that aggregated clusters of the doped NA were gradually serious with an increase in NA doping amount or extension of NA doping time, accompanied by an increase in mass fractal dimension (Dm) values. Meanwhile, the doped NA presented stable fluorescent properties during the swelling-shrinking process of PAA. Ibuprofen (IBU) was used as a model drug, and fractal evolutions of the obtained P(NA-AA) along with the drug loading and releasing behaviors were evaluated via SAXS patterns, in which the drug-loaded P(NA-AA) presented surface fractal (Ds) characteristics, while the Dm value varied from 2.94 to 2.58 during sustained drug-release in pH 2.0, indicating occurrences of its structural transformation from dense to loose with extension of IBU-releasing time. Finally, the cytotoxicity and cellular uptake behaviors of the obtained P(NA-AA) were preliminarily explored. These demonstrations revealed that the resultant P(NA-AA) should be a potential intelligent-responsive drug carrier for targeted delivery.

Automation of liquid crystal phase analysis for SAXS, including the rapid production of novel phase diagrams for SDS-water-PIL systems.

Lyotropic liquid crystal phases (LCPs) are widely studied for diverse applications, including protein crystallization and drug delivery. The structure and properties of LCPs vary widely depending on the composition, concentration, temperature, pH, and pressure. High-throughput structural characterization approaches, such as small-angle x-ray scattering (SAXS), are important to cover meaningfully large compositional spaces. However, high-throughput LCP phase analysis for SAXS data is currently lacking, particularly for patterns of multiphase mixtures. In this paper, we develop semi-automated software for high throughput LCP phase identification from SAXS data. We validate the accuracy and time-savings of this software on a total of 668 SAXS patterns for the LCPs of the amphiphile hexadecyltrimethylammonium bromide (CTAB) in 53 acidic or basic ionic liquid derived solvents, within a temperature range of 25-75 °C. The solvents were derived from stoichiometric ethylammonium nitrate (EAN) or ethanolammonium nitrate (EtAN) by adding water to vary the ionicity, and adding precursor ions of ethylamine, ethanolamine, and nitric acid to vary the pH. The thermal stability ranges and lattice parameters for CTAB-based LCPs obtained from the semi-automated analysis showed equivalent accuracy to manual analysis, the results of which were previously published. A time comparison of 40 CTAB systems demonstrated that the automated phase identification procedure was more than 20 times faster than manual analysis. Moreover, the high throughput identification procedure was also applied to 300 unpublished scattering patterns of sodium dodecyl-sulfate in the same EAN and EtAN based solvents in this study, to construct phase diagrams that exhibit phase transitions from micellar, to hexagonal, cubic, and lamellar LCPs. The accuracy and significantly low analysis time of the high throughput identification procedure validates a new, rapid, unrestricted analytical method for the determination of LCPs.

Tailoring pore structures and morphologies of highly ordered cubic mesoporous silica prepared in mild conditions: the effects of reaction parameters

In this study, we report on a novel and reactive synthesis of highly ordered cubic mesoporous silica that is able to tailor different symmetries of pores and morphologies through a two-step procedure carried out in relatively low temperatures (20–60 °C) using a single type of surfactant. We systematically examined the effects of reaction parameters such as pH, times of hydrolysis and condensation, concentration of Pluronic F-127 surfactant, and aging temperature, by using characterization techniques such as small-angle X-ray scattering (SAXS), analysis of surface area and porosity by adsorption of N2 (BET isotherms), and scanning and transmission electron microscopy (SEM and TEM). Our investigations found that, at 20 °C, the shape of particles is sensitive to changes in surfactant concentration which means that it is possible to tune spherical to polyhedral particles by simply increasing the amount of surfactant. In addition, at low concentrations of F-127, the size of the particles is temperature-dependent, with an inversely proportional pattern of behavior. The protocol also enables the production of well-ordered pores, particularly with 3D-cubic symmetries Fm3m and Im3m, and some hexagonal, as well as to control the sizes of the pores.

Probing Thermoresponsive Polymerization-Induced Self-Assembly with Variable-Temperature Liquid-Cell Transmission Electron Microscopy

Summary We directly initiate and visualize the formation of polymeric nanomaterials via variable-temperature liquid-cell transmission electron microscopy (VT-LCTEM). With temperature control in the liquid cell, reversible addition-fragmentation chain transfer polymerization was thermally initiated, leading to the formation of amphiphilic block copolymers that assemble upon dispersion polymerization-induced self-assembly (PISA). In combination with traditional ex situ analyses, VT-LCTEM enabled not only the characterization of the nanoparticles in situ but also the observation of a thermal phase transition. Critically, because these assemblies form from thermoresponsive components, any temperature changes during sample preparation and analysis can alter morphologies, necessitating direct in situ characterization of reaction progression. We believe that the findings and the technique described herein will lead to unprecedented possibilities for the development and characterization of self-organizing soft matter.

Curbed of molybdenum oxido-diperoxido complex on ionic liquid body of mesoporous Bipy-PMO-IL as a promising catalyst for selective sulfide oxidation

In this work, we introduce a novel bipyridinium ionic liquid bridged periodic mesoporous organosilicas (Bipy-PMOs-IL) which is used as the support to immobilize oxygen-rich Molybdenum (VI)-based oxido-peroxido complex (MoO(O2)2@Bipy-PMO-IL). Several techniques such as Small-angle X-ray scattering (SAXS), low angle XRD, FE-SEM (field emission scanning electron microscope), TEM (transmission electron microscope), N2 adsorption-desorption analyses (BET), atomic absorption spectroscopy (AAS), Fourier-transform infrared spectroscopy (FT-IR) and Energy Dispersive X-Ray (EDS or EDX) were used to characterize this nanomaterial. Also, the catalytic activities of the MoO(O2)2@Bipy-PMO-IL as a hybrid catalyst is tested in the selective oxidation of sulfides in water by using H2O2 (30%) as an eco-friendly and green co-oxidant. The as-prepared novel catalyst shows high to excellent performance under optimum reaction conditions at ambient room temperature. The obtained results in this work show several outstanding advantages, such as green conditions, high product yields, easy work-up, easy preparation and acceptable reusability of the catalyst for at least 5 runs. To study the IL effect in immobilization of Mo-complex, in a comparison study, the MoO(O2)2@Bipy-PMO-IL materials and MoO(O2)2@SBA-15 (with simple SiO2 body, no IL) body were employed for sulfide oxidation. After the treatment, the Mo@Bipy-PMO-IL with IL body in channels was reused for subsequent experiments (5 runs), but in Mo@SBA-15 after second run the yield was decreased dramatically.

Structural Characterization of Protein-Protein Interactions with pyDockSAXS.

Structural characterization of protein-protein interactions can provide essential details to understand biological functions at the molecular level and to facilitate their manipulation for biotechnological and biomedical purposes. Unfortunately, the 3D structure is available for only a small fraction of all possible protein-protein interactions, due to the technical limitations of high-resolution structural determination methods. In this context, low-resolution structural techniques, such as small-angle X-ray scattering (SAXS), can be combined with computational docking to provide structural models of protein-protein interactions at large scale. In this chapter, we describe the pyDockSAXS web server ( https://life.bsc.es/pid/pydocksaxs ), which uses pyDock docking and scoring to provide structural models that optimally satisfy the input SAXS data. This server, which is freely available to the scientific community, provides an automatic pipeline to model the structure of a protein-protein complex from SAXS data.

On the Calculation of SAXS Profiles of Folded and Intrinsically Disordered Proteins from Computer Simulations

Solution techniques such as small-angle X-ray scattering (SAXS) play a central role in structural studies of intrinsically disordered proteins (IDPs); yet, due to low resolution, it is generally necessary to combine SAXS with additional experimental sources of data and to use molecular simulations. Computational methods for the calculation of theoretical SAXS intensity profiles can be separated into two groups, depending on whether the solvent is modeled implicitly as continuous electron density or considered explicitly. The former offers reduced computational cost but requires the definition of a number of free parameters to account for, for example, the excess density of the solvation layer. Overfitting can thus be an issue, particularly when the structural ensemble is unknown. Here, we investigate and show how small variations of the contrast of the hydration shell, δρ, severely affect the outcome, analysis and interpretation of computed SAXS profiles for folded and disordered proteins. For both the folded and disordered proteins studied here, using a default δρ may, in some cases, result in the calculation of non-representative SAXS profiles, leading to an overestimation of their size and a misinterpretation of their structural nature. The solvation layer of the different IDP simulations also impacts their size estimates differently, depending on the protein force field used. The same is not true for the folded protein simulations, suggesting differences in the solvation of the two classes of proteins, and indicating that different force fields optimized for IDPs may cause expansion of the polypeptide chain through different physical mechanisms.

Dependence of Electrochemical Properties on Structure and Deeper Understanding of Sodium Insertion in Hard Carbons Used As Anode for Sodium-Ion Batteries

Nowadays, Lithium ion (Li-ion) batteries are present in many applications such as mobile phones, computers, power tools, hybrid electric (HEV) and electric (EV) vehicles. However abundance, cost and especially accessibility of lithium will be able to bring some issues for Li-ion development in the future [1]. This leads the scientist community to go back to sodium ion battery research, which decreased significantly after Li ion battery success in the 90’s. Sodium seems to be an interesting alternative to lithium because of its abundance and availability. However, in order to be competitive against other technologies, capacity, rate capability and cycle life should be improved [2]. Carbon for Na-ion battery applications has been extensively studied in the literature [3,4] whatever its form: hard carbon, carbon black, carbon nanospheres or nanotubes, carbon fibers and graphene. Especially for hard carbons the main problems reported in literature are a high first irreversible capacity and a poor cyclability. For example, Ding et al.[5] tested carbon made from peat (organic matter) pyrolysis and they obtained a reversible capacity of 255 mAh.g-1 after 200 cycles with a current density equal to 50 mA.g-1 and an initial coulombic efficiency reaching 60%. Recently Sun et al.[6] have synthesized hard carbon from shaddock peel pyrolysis. The pyrolysis temperature was varied from 800 to 1400°C and the best performances were obtained for the temperature 1200°C: the material exhibited a very high reversible capacity of around 400 mAh.g-1 with a good stability over 200 cycles and a first coulombic efficiency of 68%. Even though hard carbon structure and sodium ion insertion into these materials were studied, especially by Dahn’s group in 2000 [7,8,9], insertion mechanisms are still in debate in the literature. Dahn and coworkers developed a card-house model with two different mechanisms: in the galvanostatic curve, the sloppy part corresponds to sodium intercalation between graphene sheets and the low voltage plateau is related to the sodium insertion in micropores. Lately Bommier et al. [10] have proposed another point of view concerning this model based on ab initio calculations: the low voltage plateau is due to intercalation into sites around the defective carbon surface. In this presentation we proposed to develop two parts. The first part exhibits the dependence of electrochemical performances on hard carbon structure. All hard carbon samples are made from the same organic precursor, cellulose. The final pyrolysis temperature is varied from 700°C to 1600°C. The samples are fully characterized with both usual techniques such as X-ray diffraction, scanning electron microcopy and N2 adsorption and more advanced tools such as small-angle X-ray scattering (SAXS) and transmission electron microscopy. The different parameters obtained from all these characterization methods (d002, specific surface area, radius of gyration and crystallite size) can be linked to the electrochemical performances as indicated in the figure. Samples pyrolysed from 1300°C to 1600°C showed a reversible capacity equal to 300 mAh.g-1 at C/10 rate (where C=372 mA.g-1) with an excellent stability in cycling and a very good initial coulombic efficiency reaching 84%. The second part of the presentation aims to deeper understand sodium insertion mechanisms in these disordered structures. To distinguish the different mechanisms hard carbons are discharged at different potentials and analyzed with SAXS and impedance spectroscopy.

The application of thermal analysis to the study of epoxy–clay nanocomposites

The development of polymer layered silicate (PLS) nanocomposites goes back over 20 years now, and yet they still have not achieved their full potential. A principal reason for this is the difficulty of obtaining a truly exfoliated nanostructure. The fabrication procedure for such PLS nanocomposites based upon epoxy resin includes several stages, including dispersion of the clay in the resin, intercalation of the resin into the clay galleries, and finally curing of the nanocomposite system. Many attempts have been made to improve the degree of exfoliation in the final nanostructure by modifying the procedures involved in these fabrication stages, and the usual approach is to examine the nanostructure, by techniques such as small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), as a function of the fabrication procedure. We show here, however, that thermal analytical techniques, and in particular differential scanning calorimetry, can complement the techniques of SAXS and TEM in the search for ways in which to achieve improved degrees of exfoliation in PLS nanocomposites based upon epoxy resin.

Characterization methods of polymer core–shell particles

The design and synthesis of various polymer core–shell particles result from their distinct characteristics, which combine the properties of two or more components into one material. Many accessible synthetic strategies for obtaining polymer core–shell particles lead to the formation of particles for which the internal morphology differs from the ideal core–shell structure. Understanding the precise morphology characteristics is important for mechanistic studies of particle formation, which ultimately results in the design of particles for specific structures and properties. The detailed characteristics of complex polymer particle structures are complicated and require more than one method. This review focuses on imaging methods such as transmission electron microscopy (TEM), cryo-TEM, scanning transmission electron microscopy (STEM) and confocal fluorescence microscopy that reveal the radial redistribution of the components and methods for the quantitative analysis of individual phases (core, shell and interfacial layer), such as small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). Methods that can determine the surface composition and makeup of the character of interfacial layer (gradient or containing small domains, etc.) were also reviewed.

PyDockSAXS: protein-protein complex structure by SAXS and computational docking.

Structural characterization of protein–protein interactions at molecular level is essential to understand biological processes and identify new therapeutic opportunities. However, atomic resolution structural techniques cannot keep pace with current advances in interactomics. Low-resolution structural techniques, such as small-angle X-ray scattering (SAXS), can be applied at larger scale, but they miss atomic details. For efficient application to protein–protein complexes, low-resolution information can be combined with theoretical methods that provide energetic description and atomic details of the interactions. Here we present the pyDockSAXS web server (http://life.bsc.es/pid/pydocksaxs) that provides an automatic pipeline for modeling the structure of a protein–protein complex from SAXS data. The method uses FTDOCK to generate rigid-body docking models that are subsequently evaluated by a combination of pyDock energy-based scoring function and their capacity to describe SAXS data. The only required input files are structural models for the interacting partners and a SAXS curve. The server automatically provides a series of structural models for the complex, sorted by the pyDockSAXS scoring function. The user can also upload a previously computed set of docking poses, which opens the possibility to filter the docking solutions by potential interface residues or symmetry restraints. The server is freely available to all users without restriction.

Synthesis, Characterization, and Epoxidation Activity of Tungsten-Incorporated SBA-16 (W-SBA-16)

Tungsten, in varying amounts, was incorporated into a SBA-16 structure via a one-pot direct synthesis method under an acidic medium using Pluronic F127 triblock co-polymer as a template and n-butanol as a co-surfactant. Tetraethyl orthosilicate (TEOS) and sodium tungstate were used as the Si and W sources, respectively. The resulting materials (denoted as W-SBA-16) are characterized for structural ordering, textural properties, and types of tungsten incorporation by techniques such as small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), N2 sorption, high-resolution transmission electron microscopy (HR-TEM), diffuse-reflectance ultraviolet–visible light (DR-UV-vis) microscopy, temperature-programmed reduction in a hydrogen atmosphere (H2-TPR), and temperature-programmed desorption of ammonia (NH3-TPD). The surface area (823–354 m2/g) and pore volume (0.71–0.44 cm3/g) of the W-SBA-16 materials are found to decrease with an increase in tungsten loading (from 2.7 wt % to 30.4 wt % of the total sample...

Towards traceable size determination of extracellular vesicles

BackgroundExtracellular vesicles (EVs) have clinical importance due to their roles in a wide range of biological processes. The detection and characterization of EVs are challenging because of their small size, low refractive index, and heterogeneity.MethodsIn this manuscript, the size distribution of an erythrocyte-derived EV sample is determined using state-of-the-art techniques such as nanoparticle tracking analysis, resistive pulse sensing, and electron microscopy, and novel techniques in the field, such as small-angle X-ray scattering (SAXS) and size exclusion chromatography coupled with dynamic light scattering detection.ResultsThe mode values of the size distributions of the studied erythrocyte EVs reported by the different methods show only small deviations around 130 nm, but there are differences in the widths of the size distributions.ConclusionSAXS is a promising technique with respect to traceability, as this technique was already applied for traceable size determination of solid nanoparticles in suspension. To reach the traceable measurement of EVs, monodisperse and highly concentrated samples are required.

Mesoporous Block Copolymer Morphology Studied by Contrast-Matched Resonant Soft X-ray Scattering

We demonstrate the use of contrast-matched resonant soft X-ray scattering (RSoXS) for studying the morphology of mesoporous polystyrene-block-polyethylene-block-polystyrene (SES) copolymer membranes. The mesoporous membranes were obtained by blending the SES copolymer and polystyrene (PS) homopolymer to obtain a nonporous membrane, followed by selective dissolution of the PS. If the PS homopolymer chains are initially located within the PS microphase of the SES copolymer, then one obtains a porous film wherein the pores are lined with PS. We refer to this as the templated morphology. The membranes are thus composed of three phases: voids, PS, and PE. Conventional techniques such as small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) only distinguish between the polymer and the voids. The main advance in this paper is to show that microphase separation between PS and PE can be studied by contrast-matched RSoXS in spite of the presence of voids. Under certain circumstances, we obtain ...

Structural Characterization of Protein–Protein Complexes by Integrating Computational Docking with Small-angle Scattering Data

X-ray crystallography and NMR can provide detailed structural information of protein–protein complexes, but technical problems make their application challenging in the high-throughput regime. Other methods such as small-angle X-ray scattering (SAXS) are more promising for large-scale application, but at the cost of lower resolution, which is a problem that can be solved by complementing SAXS data with theoretical simulations. Here, we propose a novel strategy that combines SAXS data and accurate protein–protein docking simulations. The approach has been benchmarked on a large pool of known structures with synthetic SAXS data, and on three experimental examples. The combined approach (pyDockSAXS) provided a significantly better success rate (43% for the top 10 predictions) than either of the two methods alone. Further analysis of the influence of different docking parameters made it possible to increase the success rates for specific cases, and to define guidelines for improving the data-driven protein–protein docking protocols.

The Ig Doublet Z1Z2: A Model System for the Hybrid Analysis of Conformational Dynamics in Ig Tandems from Titin

Titin is a gigantic elastic filament that determines sarcomere ultrastructure and stretch response in vertebrate muscle. It folds into numerous Ig and FnIII domains connected in tandem. Data on interdomain arrangements and dynamics are essential for understanding the function of this filament. Here, we report a mechanistic analysis of the conformational dynamics of two Ig domains from the N terminus of titin, Z1Z2, by using X-ray crystallography, SAXS, NMR relaxation data, and residual dipolar couplings in combination. Z1Z2 preferentially adopts semiextended conformations in solution, with close-hinge arrangements representing low-probability states. Although interdomain contacts are not observed, the linker appears to acquire moderate rigidity via small, local hydrophobic interactions. Thus, Z1Z2 constitutes an adaptable modular system with restricted dynamics. We speculate that its preexistent conformation contributes to the selective recruitment of the binding partner telethonin onto the repetitive surface of the filament. The structural interconversion of four Z1Z2 conformers is analyzed.