Small-angle X-ray Scattering Analysis Research Articles

Occurrence of intercalation of PCE superplasticizers in calcium aluminate cement under actual application conditions, as evidenced by SAXS analysis

Intercalation of polycarboxylate (PCE) superplasticizers in calcium aluminate cement (CAC) during early hydration under both idealized and actual application conditions was confirmed by small-angle X-ray scattering (SAXS) analysis. The CaAl-PCE-LDHs were characterized by XRD, TEM, SEM and elemental analysis, and exhibited interlayer distances (d-values) ranging from 5 to 24nm, owed to the polydispersity of the PCE samples. Intercalating ability of the PCEs was dependent on their grafting density and anionicity, but was independent of their molecular weights. When highly anionic PCEs were utilized, significant amounts of nanocrystalline, colloidal intercalates were recovered, while few intercalates were detected when less anionic PCEs possessing high graft density were employed. Thus, contrary to OPC, less anionic PCEs disperse CAC better as little amount is wasted via intercalation, whereas higher dosages are required for more anionic PCEs, owed to abundant formation of organo-mineral phases. Finally, recommendations for reliable analysis of PCE intercalates in cement are given.

Microstructure evolution and mechanical properties of Inconel 740H during aging at 750 °C

The microstructure evolution of Inconel 740H during aging at 750°C for up to 3000h was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), three-dimensional atom probe (3DAP) analysis and micro-phase analysis. The mechanical properties of samples after aging were also studied. The grain size increased substantially during the whole aging period. Two different types of grain boundary carbides were observed; block-shaped and needle-shaped. Both were identified to be M23C6 by selected area diffraction measurements. The grain boundary carbides did not coarsen significantly during aging, with the weight fraction increasing only from 0.20% to 0.28%. In contrast, a much higher coarsening rate of γ′ precipitates was observed, as evidenced from both TEM observations and SAXS analysis. 3DAP was used to study the elemental partitioning behavior between γ′ precipitates and γ matrix as well as the evolution in width of the γ/γ′ interface. A large increase in the width of γ/γ′ interfaces was seen between 1000h and 3000h aging. In addition, for the sample aged at 750°C for 3000h, Cr enrichment on the γ matrix side of the γ/γ′ interface was found. Tensile tests at 750°C of the aged samples showed a gradual decrease in elevated-temperature yield strength after 500h, when this alloy was over-aged. The critical precipitate size for the transition from precipitate cutting by weakly coupled dislocations to strongly coupled dislocations for Inconel 740H was calculated to be approximately 50nm, which agrees well with the experiment measurements of elevated-temperature yield strength. The room temperature impact toughness of all samples decreased during aging as the grain size kept growing.

Studying Ultradisperse Diamond Structure within Explosively Synthesized Samples via X-Ray Techniques

XRD (X-Ray Diffraction) and SAXS (Small-Angle X-Ray Scattering) data have been measured for a pair of samples produced with the help of explosives. XRD peaks have shown the both samples to contain crystal diamond components as well as graphite ones. Basing on SAXS analysis, possible presence of grains with radii up to 30–50 nm within all the samples has been shown. Structure components with fractal dimension between 1 and 2 in the sample have been detected, this fact being in agreement with the assumption of diamond grain coating similarity to onion shells. In order to broad rocking curves analysis, the standard SAXS treatment technique has been complemented by a Fourier filtering procedure. For the sample #1, rocking curve components corresponding to individual interplanar distances with magnitudes from 5 nm up to 15 nm have been separated. A hypothesis relating these values to the distances between concentric onion-like shells of diamond grains has been formulated.

Accurate SAXS Profile Computation and its Assessment by Contrast Variation Experiments

A major challenge in structural biology is to characterize structures of proteins and their assemblies in solution. At low resolution, such a characterization may be achieved by small angle x-ray scattering (SAXS). Because SAXS analyses often require comparing profiles calculated from many atomic models against those determined by experiment, rapid and accurate profile computation from molecular structures is needed. We developed fast open-source x-ray scattering (FoXS) for profile computation. To match the experimental profile within the experimental noise, FoXS explicitly computes all interatomic distances and implicitly models the first hydration layer of the molecule. For assessing the accuracy of the modeled hydration layer, we performed contrast variation experiments for glucose isomerase and lysozyme, and found that FoXS can accurately represent density changes of this layer. The hydration layer model was also compared with a SAXS profile calculated for the explicit water molecules in the high-resolution structures of glucose isomerase and lysozyme. We tested FoXS on eleven protein, one DNA, and two RNA structures, revealing superior accuracy and speed versus CRYSOL, AquaSAXS, the Zernike polynomials-based method, and Fast-SAXS-pro. In addition, we demonstrated a significant correlation of the SAXS score with the accuracy of a structural model. Moreover, FoXS utility for analyzing heterogeneous samples was demonstrated for intrinsically flexible XLF-XRCC4 filaments and Ligase III-DNA complex. FoXS is extensively used as a standalone web server as a component of integrative structure determination by programs IMP, Chimera, and BILBOMD, as well as in other applications that require rapidly and accurately calculated SAXS profiles.

Nanoporous layered silicate AMH-3/cellulose acetate nanocomposite membranes for gas separations

Nanoporous layered silicate/polymer composite membranes are of interest because they can exploit the high aspect ratio of exfoliated selective flakes/layers to enhance molecular sieving and create a highly tortuous transport path for the slower molecules. In this work, we combine membrane synthesis, detailed microstructural characterization, and mixed gas permeation measurements to demonstrate that nanoporous flake/polymer membranes allows significant improvement in gas permeability while maintaining selectivity. We begin with the primary-amine-intercalated porous layered silicate SAMH-3 and show that it can be exfoliated using a high shear rate generated by a high-speed mixer. The exfoliated SAMH-3 flakes were used to form SAMH-3/cellulose acetate (CA) membranes. Their microstructure was analyzed by small angle X-ray scattering (SAXS), revealing a high degree of exfoliation of AMH-3 layers in the CA membrane with a small number of layers (4–8) in the exfoliated flakes. TEM analysis visualized the thickness of the flakes as 15–30nm, and is consistent with the SAXS analysis. The CO2/CH4 gas separation performance of the CA membrane was significantly increased by incorporating only 2–6wt% of SAMH-3 flakes. There was a large increase in CO2 permeability with maintenance of selectivity. This cannot be explained by conventional models of transport in flake-containing membranes, and indicates complex transport paths in the membrane. It is also in contrast to the much higher loadings of isotropic particles required for similar enhancements. The present approach may allow avoidance of particle aggregation and poor interfacial adhesion associated with larger quantities of inorganic fillers.

Adhesion enhancement of 316L stainless steel to acrylic bone cement through nanocomposite sol–gel coating system

A nanocomposite hybrid coating was synthesised from tetraethylethoxysilane and 3-methacryloxypropyl trimethoxysilane in the presence of benzoyl peroxide as an initiator agent by sol–gel process. The AISI 316L stainless steel (SS) was coated with this coating at ambient temperature. The effect of the hybrid coating on the adhesion promotion of bone cement to SS substrate was investigated qualitatively as well as quantitatively. The adhesion tests indicated that the coated 316L SS compared with the uncoated samples induces increases of ∼450% in strength and 200% in strain by single lap joint shear test. The samples were also characterised using scanning electron microscopy, optical microscopy, Fourier transform infrared spectroscopy and small angle X-ray scattering (SAXS). The test results indicated that the coated surfaces were quite uniform and crack free. Silicon mapping and SAXS analysis of the coated samples indicated that the inorganic moieties of the hybrid (i.e. Si–O–Si) were uniformly distributed and had a particle size distribution of ∼1·5 nm. In addition, the haemocompatibility of the coated sample was investigated by clotting time test. The result of clotting time for the coated 316L SS showed an increase of 74% compared with the uncoated samples.

All-Atom Ensemble Modeling to Analyze Small-Angle X-Ray Scattering of Glycosylated Proteins

The flexible and heterogeneous nature of carbohydrate chains often renders glycoproteins refractory to traditional structure determination methods. Small-angle X-ray scattering (SAXS) can be a useful tool for obtaining structural information of these systems. All-atom modeling of glycoproteins with flexible glycan chains was applied to interpret the solution SAXS data for a set of glycoproteins. For simpler systems (single glycan, with a well-defined protein structure), all-atom modeling generates models in excellent agreement with the scattering pattern and reveals the approximate spatial occupancy of the glycan chain in solution. For more complex systems (several glycan chains, or unknown protein substructure), the approach can still provideinsightful models, though the orientations of glycans become poorly determined. Ab initio shape reconstructions appear to capture the global morphology of glycoproteins but in most cases offer littleinformation about glycan spatial occupancy. The all-atom modeling methodology is available as a web server at http://salilab.org/allosmod-foxs.

Small and Wide Angle X-Ray Scattering Studies of Biological Macromolecules in Solution

In this paper, Small and Wide Angle X-ray Scattering (SWAXS) analysis of macromolecules is demonstrated through experimentation. SWAXS is a technique where X-rays are elastically scattered by an inhomogeneous sample in the nm-range at small angles (typically 0.1 - 5°) and wide angles (typically > 5°). This technique provides information about the shape, size, and distribution of macromolecules, characteristic distances of partially ordered materials, pore sizes, and surface-to-volume ratio. Small Angle X-ray Scattering (SAXS) is capable of delivering structural information of macromolecules between 1 and 200 nm, whereas Wide Angle X-ray Scattering (WAXS) can resolve even smaller Bragg spacing of samples between 0.33 nm and 0.49 nm based on the specific system setup and detector. The spacing is determined from Bragg's law and is dependent on the wavelength and incident angle. In a SWAXS experiment, the materials can be solid or liquid and may contain solid, liquid or gaseous domains (so-called particles) of the same or another material in any combination. SWAXS applications are very broad and include colloids of all types: metals, composites, cement, oil, polymers, plastics, proteins, foods, and pharmaceuticals. For solid samples, the thickness is limited to approximately 5 mm. Usage of a lab-based SWAXS instrument is detailed in this paper. With the available software (e.g., GNOM-ATSAS 2.3 package by D. Svergun EMBL-Hamburg and EasySWAXS software) for the SWAXS system, an experiment can be conducted to determine certain parameters of interest for the given sample. One example of a biological macromolecule experiment is the analysis of 2 wt% lysozyme in a water-based aqueous buffer which can be chosen and prepared through numerous methods. The preparation of the sample follows the guidelines below in the Preparation of the Sample section. Through SWAXS experimentation, important structural parameters of lysozyme, e.g. the radius of gyration, can be analyzed.

Structural Studies of the Apo and Ca2+-Bound States of the Human BK (SLO1) Channel Gating Ring in Solution

The gating ring (GR) regulates the activity of large-conductance voltage- and Ca^(2+)-activated K^+ channels (BK) by interacting with intracellular signaling molecules. To understand the operation of this biological sensor under physiological conditions, we performed Small-Angle X-ray Scattering (SAXS) analysis, at beamline 4-2 at the Stanford Synchrotron Radiation laboratory. SAXS measurements of the purified GR were performed in the absence or in the presence of 35 μM free Ca^(2+), found to be a saturating concentration in previous work. The quality of the circularly-averaged scattering data was evaluated with Guinier analysis, while the ATSAS software suite was used to derive structural information. The radius of gyration (R_g) and maximum interparticle distance (D_(max)) of the apo GR were 48.65±1.372 A and 185 A, respectively. These values are comparable to data obtained from crystal structure of GR (3NAF), where the envelope R_g, calculated with CRYSOL, is 45.55 A, and its diameter 155.6 A. Ca^(2+)-bound GR shows a decrease in R_g to 42.77±1.058 A and D_(max) to 160 A, demonstrating the structural response of GR to Ca^(2+). Low-resolution structural models of the GR were generated from the experimental scattering pattern using DAMMIN. The Ca^(2+)-bound GR revealed notable changes in both flexible and assembly interfaces of the superstructure's constituent RCK1 (Regulator of Conductance for K^+) and RCK2 domains. Since the structural changes are resolved under physiologically-relevant conditions, we speculate that they represent the molecular transitions that initiate the Ca^(2+)-induced activation of human BK channels.

Adsorption of CO2 on chitosan modified CMK-3 at ambient temperature

An ordered mesoporous carbon CMK-3 was synthesized by the template method, and was used to adsorb CO2. The synthesized CMK-3 was modified by immersion with chitosan solution to introduce surface nitrogen-containing functional groups. The effect of CMK-3 surface modification on CO2 uptake capacity was investigated. The texture characteristics of the CMK-3s were determined by small angle X-ray scattering analysis (SAXS), transmission electron microscope (TEM) and nitrogen adsorption analysis. The surface functional groups of the CMK-3s before and after modification were determined by an X-ray photoelectron spectroscope (XPS). CO2 uptake capacity of the CMK-3s was obtained by a gravimetric adsorption apparatus at room temperature under atmospheric pressure. Experimental results revealed that both nitrogen functional groups (pyridine and pyrrole) and supermicropores (<1.0nm) of the chitosan modified CMK-3s after activation obviously increased. A remarkable enhancement of about 30% was obtained in CO2 adsorption at ambient temperature by the activated chitosan modified CMK-3 over the pristine one.

Self-association of zwitterionic polymer–lipid conjugates in water as examined by scattering measurements

As a model of lipopeptide, a zwitterionic polymer–lipid conjugate was prepared from carboxymethylbetaine monomer (CMB) using a lipophilic initiator having a cholesteryl or dihexadecylglyceryl end group for atom transfer radical polymerization (ATRP). The polymer–lipid conjugates (Lipid-PCMB) obtained could be dispersed in water, and self-association of the compounds could be characterized by both light scattering (dynamic light scattering, DLS; electrophoretic light scattering, ELS) and small-angle X-ray scattering (SAXS). DLS and ELS measurements showed no secondary aggregation of the self-associated Lipid-PCMB molecules in salt solutions, though their surfaces were almost charge-balanced. The hydrophilic PCMB layer of Lipid-PCMB aggregates gave rise to dispersions under ionic conditions. Furthermore, structural analyses by DLS, ELS and SAXS measurements suggested that Lipid-PCMB aggregates consisted of a hydrophobic lipid core and a hydrophilic PCMB layer, that is, a core–shell structure. To the best our knowledge, this is the first study in which SAXS analyses were performed for zwitterionic polymer–lipid conjugates.

High temperature phase transformation studies in magnetite nanoparticles doped with Co2+ ion

We investigate the effect of Co2+ ion doping in magnetite (Fe3O4) on its crystal structure, magnetic properties, and phase stability during air and vacuum annealing. The nanoparticles are prepared by co-precipitation method and the particles are characterized by XRD, small angle x-ray scattering (SAXS), themogravimetric and differential scanning calorimetry (DSC), and vibrating sample magnetometer. The SAXS analysis on the doped samples show the most probable size, shape, and the polydispersity of particles, synthesized with different fractions (0–0.6) of Co2+ ion doping remains almost the same. On increasing cobalt content ferrimagnetic to the antiferromagnetic hematite (α-Fe2O3) phase transformation temperature is found to increase dramatically. For 0.1 fraction of Co2+ metal ion doping, an enhancement of 100 °C in the γ-Fe2O3 to α-Fe2O3 phase transition temperature is observed in the air annealed samples, whereas magnetic nature remains stable up to 1000 °C in vacuum annealed samples. On increasing the cobalt fractions beyond 0.2, air annealed samples show no change in the phase transition temperature. The observed enhancement in the phase transition temperature is attributed to the increased activation energy for phase transformation in presence of Co2+. Further, the DSC results corroborate the finding of an increase in the maghemite to hematite phase transition temperature with increase in cobalt fraction (x). The decrease in enthalpy from 89.86 to 17.62 J g−1 with an increase in cobalt content indicates that the degree of conversion of maghemite to hematite decreases with the cobalt content, which is in good agreement with the Rietveld analysis. The decrease in the Ms value in air annealed sample is attributed to the re-distribution of cations in the tetrahedral and octahedral sites, as the Fe3+A-Fe3+B super-exchange interaction is different from the Co2+A-Fe3+B interaction. These results suggest that a very small percentage of Co2+ metal ion doping can dramatically enhance the thermal stability of magnetic nanoparticles, which will have important consequences on the phase stability of ferrite nanocrystals.

Microdomain expansion and transition behavior of PS-b-PMMA/PS homopolymers by SAXS analysis

We present the microdomain expansion and transition behavior of binary blends of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA)/PS homopolymers using small-angle X-ray scattering (SAXS) analysis, where the PS molecular weight (or chain length) was varied with chain length ratios (α) of 0.3, 1, and 2 with respect to the PS block length of the PS-b-PMMA. The d-spacing and order-to-disorder transition (ODT) by addition of PS homopolymers were significantly influenced by the PS molecular weight. In contrast to the typical decrease in d-spacing with increasing temperature in PS-b-PMMA, the d-spacing for PS-b-PMMA/PS homopolymers showed unusual behavior; specifically, it increased for shorter PS chains of α ≤ 1, but was independent of temperature for PS chains of α = 2. This variation can be attributed to a competing interaction between the thermal expansion effects of the microdomains with homopolymers and the decrease in the chain stretching between the two block components.

Esterification of lauric acid with butanol over mesoporous materials

Mesoporous silica (e.g. SBA-15) was evaluated in the esterification of lauric acid with butanol. ZnO/SBA-15 and MgO/SBA-15 were synthesized and characterized using N2 adsorption/desorption isotherms at 77 K, 29Si magic angle spinning solid state nuclear magnetic resonance (29Si MAS NMR), X-ray diffraction (XRD) and Small-Angle X-ray scattering (SAXS). The nanostructural parameters obtained from SAXS analysis were very similar for all samples revealing that the impregnation method for incorporation of Zn and Mg in mesoporous silica did not affect its structure. Both catalysts ZnO/SBA-15 and MgO/SBA-15 were able to promote the esterification reaction of lauric acid with 1-butanol at mild reactions conditions.

Correction to "Grazing Incidence Small-Angle X-ray Scattering Analysis of Initial Growth of Planar Organic Molecules Affected by Substrate Surface Energy".

Disc-type nano grains of copper(II) phthalocyanine (CuPc) were observed in an ultrathin CuPc layer (5 nm) evaporated on a hydrophilic Si surface showing the structure factor in grazing incidence sm...

Polystyrene/calcium carbonate nanocomposites prepared by in situ polymerization in the presence of maleic anhydride

AbstractPolystyrene (PS)/calcium carbonate (CaCO3) nanocomposites were prepared by in situ polymerization in the presence of maleic anhydride (MA). The composites were characterized by Fourier transform infrared spectra, gel permeation chromatography, differential scanning calorimetry, controlled stress rheometer, scanning electron microscope (SEM), small‐angle X‐ray scattering (SAXS), and mechanical test. Results show that the copolymer of styrene (St) and MA formed during the polymerization acts as a compatibilizer between PS and nanometer calcium carbonate (nano‐CaCO3) particles, resulting in an increase in the glass transition temperature of the composite. The complex modulus and the impact strength of the PS/nano‐CaCO3 composite show an increase with the addition of MA on account of the enhanced interfacial adhesion and the increased molecular weight. SEM and SAXS analyses indicate that a finer dispersion of nanoparticles and an increased homogeneity of the PS/nano‐CaCO3 composites are obtained with application of a small amount of MA. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013

Structural investigation of Poly(ethylene terephthalate)/Poly(trimethylene terephthalate) transesterificated blends

Wide-Angle X-ray Diffraction (WAXD) and Small-Angle X-ray Scattering analyses were carried out to evaluate the evolution of the crystalline and supermolecular structure of poly(ethylene terephthalate) (PET) blended with poly(trimethylene terephthalate) (PTT). The conditions adopted in preparing the PET/PTT 50/50 blend induce transesterification between the polyesters; these reactions produce a new molecular characteristics based on PET/PTT copolymer that exhibits its own WAXD profile. The PET/PTT 50/50 copolymers prepared by melt mixing of the homopolymers for increasing times evidence spherulitic morphology and an evolution of the crystalline structure in terms of crystallinity and crystal dimensions. The periodicity of the transesterificated samples is intermediate between the long periods observed for pure PET and pure PTT. For the PET/PTT 50/50 copolymers the value of periodicity and lamellar thickness increase with the increasing of the processing time.

Crystal Structures and Small-angle X-ray Scattering Analysis of UDP-galactopyranose Mutase from the Pathogenic Fungus Aspergillus fumigatus

UDP-galactopyranose mutase (UGM) is a flavoenzyme that catalyzes the conversion of UDP-galactopyranose to UDP-galactofuranose, which is a central reaction in galactofuranose biosynthesis. Galactofuranose has never been found in humans but is an essential building block of the cell wall and extracellular matrix of many bacteria, fungi, and protozoa. The importance of UGM for the viability of many pathogens and its absence in humans make UGM a potential drug target. Here we report the first crystal structures and small-angle x-ray scattering data for UGM from the fungus Aspergillus fumigatus, the causative agent of aspergillosis. The structures reveal that Aspergillus UGM has several extra secondary and tertiary structural elements that are not found in bacterial UGMs yet are important for substrate recognition and oligomerization. Small-angle x-ray scattering data show that Aspergillus UGM forms a tetramer in solution, which is unprecedented for UGMs. The binding of UDP or the substrate induces profound conformational changes in the enzyme. Two loops on opposite sides of the active site move toward each other by over 10 Å to cover the substrate and create a closed active site. The degree of substrate-induced conformational change exceeds that of bacterial UGMs and is a direct consequence of the unique quaternary structure of Aspergillus UGM. Galactopyranose binds at the re face of the FAD isoalloxazine with the anomeric carbon atom poised for nucleophilic attack by the FAD N5 atom. The structural data provide new insight into substrate recognition and the catalytic mechanism and thus will aid inhibitor design.

Reorganization Induced by Silver Salt Reduction Inside a Mesostructured Block Copolymer Silica Film

Block copolymer self-assembly can be used to get a noble metallic nanoparticle array. The silver nanoparticle array formation inside a mesostructured silica film with the triblock copolymer (PEO)106(PPO)70(PEO)106 (F127) has been studied using Grazing Incidence Small-Angle X-ray Scattering (GISAXS), TEM, and X-ray diffraction analyses. Mesostructure organization essentially occurs during the sodium borohydride reduction process used to form silver nanoparticles. The well-known orthorhombic order, Fmmm space group, appears with (020)orthorhombic plan parallel to the substrate. Such reorganization is explained by the silver ion diffusion occurring along preferential directions toward the film surface. These metallic nanostructures could be potentially used in surface-enhanced Raman scattering, catalysis, or optical devices.

Tandem RAFT-ATRP Synthesis of Polystyrene-Poly(Methyl Methacrylate) Bottlebrush Block Copolymers and Their Self-Assembly into Cylindrical Nanostructures.

A polystyrene-poly(methyl methacrylate) (PS-PMMA) bottlebrush block copolymer with asymmetric branches was synthesized by grafting from a symmetrical backbone containing a novel dual vinyl initiation system and characterized by atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The block copolymer backbone was prepared by sequential reversible addition-fragmentation chain transfer (RAFT) copolymerization of solketal methacrylate (SM) and 2-(bromoisobutyryl)ethyl methacrylate (BIEM). From the poly(BIEM) segment, PMMA branches of 26 units were grafted by atom transfer radical polymerization (ATRP). Solketal groups were then subjected to hydrolysis and functionalized with a RAFT agent. Subsequently, from RAFT sites of the poly(SM) segment, polystyrene branches of 45 units were grafted to yield the final bottlebrush block copolymer. The resulting polymer was found to have a vertically oriented cylindrical morphology by AFM with an average cylinder diameter of 45 nm; morphology was also confirmed by SAXS analysis.