Small-angle X-ray Measurements Research Articles

Hierarchical Porous SiO2 Cryogel via Sol-Gel Process.

The aim of this research work was to develop a new, low-cost and low-energy-consuming preparation route for highly porous silica systems. The precursor gel systems were synthesized by sol-gel chemistry. The starting materials were TEOS and water glass in the sol-gel syntheses. The effect of the chemical composition, the catalysis, the pH, and the additives were investigated on the structure and porosity of the cryogels. The gel systems were treated by freeze-drying process to obtain porous cryogel silica products. The cryogel systems possess hierarchical structures. The conditions of the freeze-drying process were also studied to increase the porosity. Small angle X-ray measurements, scanning electron microscope technique, and infrared spectroscopy were applied for the investigation of gel and cryogel systems.

Structural Insights into Cellulose-Coated Oil in Water Emulsions.

Cellulose is a renewable biopolymer, abundant on Earth, with a multi-level supramolecular structure. There has been significant interest and advancement in utilizing natural cellulose to stabilize emulsions. In our research, we develop and examine oil in water emulsions surrounded by unmodified cellulose as microreactors for the process of transformation of cellulose into valuable chemicals such as biodiesel. This study presents morphological characterization of cellulose-coated emulsions that can be used for such purposes. Cryogenic-scanning electron microscopy imaging along with light microscopy and light scattering reveals a multi-layer inner structure: an oil core surrounded by a porous cellulose hydrogel shell, coated by an outer shell of regenerated cellulose. Measurements of small-angle X-ray scattering provide quantification of the nano-scale structure within the porous cellulose hydrogel inner shell of the emulsion particle. These characteristics are relevant to utilization of cellulose-coated emulsions in various applications such as controlled release and as hosts for enzymatic biotechnological reactions.

Absolute measurements of anomalous small-angle X-ray scattering intensity using glassy carbon at the Mg K absorption edge

Absolute measurements of small-angle X-ray scattering (SAXS) intensities at the K absorption edge of Mg have been performed using glassy carbon as an intensity standard. Glassy carbon samples polished down to give appropriate transmission have been prepared as a secondary standard to be used at 1.3 keV. Al–Mg binary alloys were used to assess the metastable phase boundary for the Al3Mg metastable precipitation from the absolute scattering intensity. The assessed phase boundary agreed with the previous reports. Glassy carbon was concluded to be an appropriate candidate for an intensity standard sample for transmission measurements of SAXS in the tender X-ray regions.

Effect of thermal history on the structure and mechanical properties of a thermoplastic polyester elastomer

An appropriate processing protocol was proposed to improve the rubber elasticity of a thermoplastic polyester elastomer (TPEE). Rheology measurements at the processing temperature and thermal measurements determined the critical temperature at which small numbers of crystals exist. It was found from dynamic mechanical analyses, wide- and small-angle X-ray measurements, and electron microscope observations that cooling from the critical temperature markedly promoted the crystallization of hard segments. Moreover, tensile tests revealed that the modulus and yield stress increased. Most importantly, compared with films obtained by cooling from high temperatures, the residual strain at a fixed stress was low—i.e., the rubber elasticity was improved owing to its well-developed crystalline structure. These effects were accelerated by a more optimized process—i.e., subsequent heating at slightly below the critical temperature. The technique is noteworthy because a TPEE with high modulus generally shows poor elasticity.

Surfactant-Mediated Co-Existence of Single-Walled Carbon Nanotube Networks and Cellulose Nanocrystal Mesophases.

Hybrids comprising cellulose nanocrystals (CNCs) and percolated networks of single-walled carbon nanotubes (SWNTs) may serve for the casting of hybrid materials with improved optical, mechanical, electrical, and thermal properties. However, CNC-dispersed SWNTs are depleted from the chiral nematic (N*) phase and enrich the isotropic phase. Herein, we report that SWNTs dispersed by non-ionic surfactant or triblock copolymers are incorporated within the surfactant-mediated CNC mesophases. Small-angle X-ray measurements indicate that the nanostructure of the hybrid phases is only slightly modified by the presence of the surfactants, and the chiral nature of the N* phase is preserved. Cryo-TEM and Raman spectroscopy show that SWNTs networks with typical mesh size from hundreds of nanometers to microns are distributed equally between the two phases. We suggest that the adsorption of the surfactants or polymers mediates the interfacial interaction between the CNCs and SWNTs, enhancing the formation of co-existing meso-structures in the hybrid phases.

Simple carbon fiber graphitization device for in-situ measurement of small angle X-ray scattering (SAXS)

A small and simple device for the in-situ small angle X-ray scattering (SAXS) measurement of carbon fibers graphitization by direct electrical heating was developed. The graphitization process of polyacrylonitrile-based T700 carbon fibers from 1450 °C to 2100 °C with this device was followed in-situ by synchrotron radiation SAXS. The results show that there are needle-shaped voids oriented preferentially along the fibers axis with a surface fractal structure during graphitization of carbon fibers. The change in the fractal dimension as a function of temperature includes a dip with a minimum value at approximately 1700 °C. This short contribution briefly describes the device and analyzes the obtained experimental results.

Radial alignment of microtubules through tubulin polymerization in an evaporating droplet.

We report the formation of spherulites from droplets of highly concentrated tubulin solution via nucleation and subsequent polymerization to microtubules (MTs) under water evaporation by heating. Radial alignment of MTs in the spherulites was confirmed by the optical properties of the spherulites observed using polarized optical microscopy and fluorescence microscopy. Temperature and concentration of tubulins were found as important parameters to control the spherulite pattern formation of MTs where evaporation plays a significant role. The alignment of MTs was regulated reversibly by temperature induced polymerization and depolymerization of tubulins. The formation of the MTs patterns was also confirmed at the molecular level from the small angle X-ray measurements. This work provides a simple method for obtaining radially aligned arrays of MTs.

Structure of KCNH2 cyclic nucleotide-binding homology domain reveals a functionally vital salt-bridge.

Human KCNH2 channels (hKCNH2, ether-à-go-go [EAG]-related gene, hERG) are best known for their contribution to cardiac action potential repolarization and have key roles in various pathologies. Like other KCNH family members, hKCNH2 channels contain a unique intracellular complex, consisting of an N-terminal eag domain and a C-terminal cyclic nucleotide-binding homology domain (CNBHD), which is crucial for channel function. Previous studies demonstrated that the CNBHD is occupied by an intrinsic ligand motif, in a self-liganded conformation, providing a structural mechanism for the lack of KCNH channel regulation by cyclic nucleotides. While there have been significant advancements in the structural and functional characterization of the CNBHD of KCNH channels, a high-resolution structure of the hKCNH2 intracellular complex has been missing. Here, we report the 1.5 Å resolution structure of the hKCNH2 channel CNBHD. The structure reveals the canonical fold shared by other KCNH family members, where the spatial organization of the intrinsic ligand is preserved within the β-roll region. Moreover, measurements of small-angle x-ray scattering profile in solution, as well as comparison with a recent NMR analysis of hKCNH2, revealed high agreement with the crystallographic structure, indicating an overall low flexibility in solution. Importantly, we identified a novel salt-bridge (E807-R863) which was not previously resolved in the NMR and cryo-EM structures. Electrophysiological analysis of charge-reversal mutations revealed the bridge's crucial role in hKCNH2 function. Moreover, comparison with other KCNH members revealed the structural conservation of this salt-bridge, consistent with its functional significance. Together with the available structure of the mouse KCNH1 intracellular complex and previous electrophysiological and spectroscopic studies of KCNH family members, we propose that this salt-bridge serves as a strategically positioned linchpin to support both the spatial organization of the intrinsic ligand and the maintenance of the intracellular complex interface.

Structural Evolution Mechanism of Crystalline Polymers in the Isothermal Melt-Crystallization Process: A Proposition Based on Simultaneous WAXD/SAXS/FTIR Measurements.

Time-resolved simultaneous measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) (and FTIR spectra) were performed for various kinds of crystalline polymers in isothermal melt-crystallization processes, from which the common features of the structural evolution process as well as the different behaviors intrinsic to the individual polymer species were extracted. The polymers targeted here were polyethylene, isotactic polypropylene, polyoxymethylene, aliphatic nylon, vinylidene fluoride copolymer, trans-polyisoprene, and poly(alkylene terephthalate). A universal concept of the microscopically viewed structural evolution process in isothermal crystallization may be described as follows: (i) the small domains composed of locally regular but more or less disordered helical chain segments are created in the melt (this important information was obtained by the IR spectral data analysis); (ii) these domains grow larger as the length and number of more regular helical segments increase with time; (iii) the correlation among the domains becomes stronger and they approach each other; and (iv) they merge into the stacked lamellar structure consisting of the regularly arranged crystalline lattices. The inner structure of the domains is different depending on the polymer species, as known from the IR spectral data.

“Improving the impact strength of PLA and its blends with PHA in fused layer modelling ”

Abstract Poly-(lactic acid) (PLA) is one of the most popular thermoplastics for fused layer modelling (FLM). Due to its semi-crystalline nature, the influences of printing parameters on the properties of the printed part are more complicated than with amorphous thermoplastics like acrylonitrile-butadiene-styrene (ABS). In present study, the influence of the process parameters, such as temperature of the plate as well as printing angle used for the three-dimensional printing process was studied in the case of virgin PLA. In addition, PLA was mixed with an amorphous polyhydroxyalkanoate (PHA) copolymer with the aim to improve its impact properties. Mechanical performance of virgin PLA and its PLA/PHA blend prepared by 3D printing method was compared with the mechanical performance of the parts produced by injection moulding. Small and wide angle X-ray measurements were performed in order to study the influence of the crystal morphology on the mechanics of PLA and PLA/PHA 3D printed as well as injection moulded parts. The PLA/PHA parts produced by 3D printing showed higher impact strength and notched impact strength values than injection moulded parts.

Phase separation in solvent extraction of cobalt from acidic sulfate solution using synergistic mixture containing dinonylnaphthalene sulfonic acid and 2-ethylhexyl 4-pyridinecarboxylate ester

Abstract Phase separation rate is a critical character in determining the usefulness of a solvent extraction system in hydrometallurgy. A survey of the synergistic mixture containing dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexly 4-pyridinecarboxylate ester (4PC) for the extraction of cobalt from acidic single metal sulfate solution was carried out to suggest how the physicochemical properties and the morphology of the reverse micelles in the loaded organic phase affect the phase separation. The results show that effective parameters affecting the phase separation are the viscosity and the excess water uptake of the loaded organic phase. It is obvious that the specific settling rate (SSR) decreases with the apparent increase of these two parameters. The measurement of small angle X-ray scattering (SAXS) proves that the morphology of the reversed micelles in the loaded organic phase changes evidently with the change of the specific settling rate (SSR).

A small sample stretcher for in-situ small angle X-ray scattering measurement

A small sample stretcher for in-situ measurement of small angle X-ray scattering (SAXS) was developed, which consists of stretch, transmission, detection and control systems. The basic parameters of the stretcher are: tension ⩾ 400 N, 3 mm/min ⩽ stretching speed ⩽ 50 mm/min, sample length ⩽ 30 mm, stroke ⩾ 80 mm, and resolution = 50 μm. The stretcher is compact and has low stretching speed and convenient remote control. It is suitable for in-situ SAXS measurements on stretching of carbon fibers, polyethylene and other samples. Such measurement were carried out with high density polyethylene (HDPE) on the SAXS instrument at the 1W2A station of Beijing Synchrotron Radiation Facility (BSRF). The result verified the effectiveness of the stretcher.

Dual-modified bufalin loaded liposomes for enhanced tumor targeting

Bufalin, a traditional oriental medicine, has been incorporated into liposomes for better targeted drug delivery. Bufalin-loaded liposome (L-BF), bufalin-loaded PEGylated liposome (L-PEG-BF) and bufalin-loaded RGD targeted PEGylated liposome (L-RGD-PEG-BF) were successfully developed with homogeneous particle size and sufficient physical stability in 30 days. The entrapment efficiency (EE) and drug loading efficiency (DL) of bufalin in these liposomes were about 85.4–90.6% and 6.0–6.6%, respectively. The morphologies of these liposomes were determined as uniquely recognizable phospholipid bilayers of the vesicle membrane by the measurements of transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). L-BF, L-PEG-BF and L-RGD-PEG-BF exhibited improved anticancer efficacy compared to free bufalin. Moreover, L-RGD-PEG-BF showed higher inhibition on the proliferation of A549 cells than the other two non-targeted bufalin liposomes in cytotoxicity study, and the growth inhibition concentration (IC50) of L-RGD-PEG-BF (8.62 ± 0.74 ng/mL) was much lower than pure bufalin (20.37 ± 2.31 ng/mL). Both confocal and apoptosis assay indicated that L-RGD-PEG-BF was easier to be taken into cancer cells than non-targeted bufalin liposomes. Therefore, L-RGD-PEG-BF is expected to be an effective drug carrier for bufalin delivery in tumor treatment.

Combining Small-Angle X-ray Scattering and X-ray Powder Diffraction to Investigate Size, Shape and Crystallinity of Silver, Gold and Alloyed Silver-Gold Nanoparticles

The combination of simultaneous measurements of small and wide angle X-ray scattering (SAXS/WAXS–SWAXS) to investigate the overall size, shape, and crystallinity of silver nanoparticles and alloyed silver-gold nanoparticles in the size range of 8 to 80 nm is shown. The obtained results for overall size are in agreement with the particle size obtained by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). In addition to the overall size, SWAXS provided precise information about the crystallographic internal structure of the particles, providing a powerful multi-scale tool for structural characterization of the studied systems.

Twist-grain boundary phase induced by Au nanoparticles in a chiral liquid crystal host

ABSTRACTWe report on the stabilisation of the liquid-crystalline, twist-grain boundary A (TGBA) phase in mixtures of a chiral liquid crystal and surface-functionalised spherical Au nanoparticles (NPs) of 10 nm diameter. The results, obtained by calorimetric, optical, small-angle X-ray and plasmon resonance measurements, demonstrate that a TGBA phase, which is metastable for the pure liquid crystal host, can be effectively stabilised for a 3 K range in the presence of NPs. Moreover, the role of NPs size on the TGBA stabilisation is briefly discussed.

Structural and Thermodynamic Properties of Nanoparticle-Protein Complexes: A Combined SAXS and SANS Study.

We propose a novel method for determining the structural and thermodynamic properties of nanoparticle-protein complexes under physiological conditions. The method consists of collecting a full set of small-angle X-ray and neutron-scattering measurements in solutions with different concentrations of nanoparticles and protein. The nanoparticle-protein dissociation process is described in the framework of the Hill cooperative model, based on which the whole set of X-ray and neutron-scattering data is fitted simultaneously. This method is applied to water solutions of gold nanoparticles in the presence of human serum albumin without any previous manipulation and can be, in principle, extended to all systems. We demonstrate that the protein dissociation constant, the Hill coefficient, and the stoichiometry of the nanoparticle-protein complex are obtained with a high degree of confidence.

Scattering model for tetrapods with cylindrical arms

A scattering model for regular tetrapods, which are the endoskeleton structure of regular tetrahedrons, is presented. Since a tetrapod, unlike spheres and cylinders, is an anisotropic structure formed by four cylinders branching out from the centroid to the vertices of a tetrahedron, additional symmetry elements and random orientation must be accounted for to develop its scattering model. The scattering function of tetrapods was derived from the modification of the scattering model for cylinders and their structural regularity was simplified. Scattering intensity profiles and pair distance distribution functions were obtained by numerical calculation and compared with the experimental data from small angle X-ray measurements of CdSe tetrapod nanocrystals.

Anomalous structural response of nematic colloidal platelets subjected to large amplitude stress oscillations

Time-resolved small angle X-ray measurements are used to investigate the dynamic response to nonlinear oscillatory stresses and strains of a nematic dispersion of colloidal gibbsite platelets. We track the full 3D rotational motion of the director by employing plate-plate and concentric cylinder Couette geometries as well as a vertical X-ray beam. Under nonlinear oscillatory stress, we observe strong offsets in the rheological response as well as asymmetrical behavior in the microscopic structural response. This offset and asymmetry are connected to the yielding behavior of the platelets. By increasing the stress amplitude, we observed that the offset of the rheological response diminishes and the microscopic response becomes more symmetric; however, this strongly depends on the frequency of the stress input, and hence the time necessary for the system to yield.

Relation between higher-order structure and crystalline phase transition of oriented isotactic polybutene-1 investigated by temperature-dependent time-resolved simultaneous WAXD/SAXS measurements

Drawing of isotactic polybutene-1 sample near the melting point gives the oriented form II sample with the complicated higher-order structure or the stacked lamellar structure. The small-angle X-ray scattering (SAXS) measurement may give us a useful information about the higher order structure in principle. However, it is almost impossible to detect the higher-order structure from the SAXS data, since the electron density of form II crystal is almost the same as that of the amorphous phase. The 2-dimensional SAXS pattern has started to be detected gradually as the crystalline phase transition from form II to form I was proceeded, since the form I has the higher electron density than the form II and amorphous phase. In this paper, the simultaneous time-resolved measurement of wide-angle and small-angle X-ray scattering data has been performed for the first time to reveal the lamellar stacking structure created in the form II sample by monitoring the phase transition from form II to I crystal. The thus-visualized lamellar stacking structure has been found to be different depending on the preparation condition of the oriented form II sample. The phase transition rate was also found to differ for the various types of samples depending on the temperatures of the experiment: the maximal point was located at around 30 °C. The phenomenological equation of the phase transition behavior, derived by modifying a classical theory of nucleation and growth of crystals, has succeeded to reproduce the observed temperature dependence of the phase transition rate.

Multiphoton STED and FRET in Human Skin: Resolving the Skin Barrier

Understanding the penetration properties of substances across biological barriers and membranes is vital for many areas of research. In the case of human skin, the barrier is primarily found in the stratum corneum and consists of protein-enriched cells surrounded by a lipid membrane -enriched intercellular spaces. Characterization of the structural and dynamical processes occurring across the skin barrier is essential for understanding healthy and diseased skin and for designing successful transdermal drug delivery strategies. In this study we use Stimulated emission depletion (STED), two photon excited STED and Forster Resonance Energy Transfer (FRET) microscopy to probe the structure of human skin. Super resolution optical microscopy enables resolving structures in the skin below to 60 nm allowing visualization of the stratum corneum intercellular lipid matrix and individual proteins such as tight junction (TJ) proteins and corneodesmosomes. To further probe the nanoscopic structure of the intercellular lipids and the nanoscopic diffusion routes of hydrophilic and hydrophobic particles through the skin barrier we use FRET measurements of lipophilic and hydrophilic dye pairs. The measurements are carried out in artificial membranes of extracted human skin lipids and in skin tissue. They show FRET distance which agree with membrane models derived from small angle x-ray measurements of human skin lipids.