Small-angle X-ray Scattering Images Research Articles

Interaction between Gaomiaozi bentonite colloid and uranium

In a deep geological repository system, the presence of clay colloids in the geological disposal medium is considered to be a potential factor promoting nuclide migration. In this study, Gaomiaozi bentonite colloid (GMZC) was extracted using the gravity sedimentation method, and its interaction with U(VI) at neutral pH was studied. Small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), dynamic light scattering, and other characterizations methods were used to analyze and observe the microstructure and agglomeration morphology of the bentonite colloidal particles before and after the reaction with U(VI) at the macro-meso-microscopic level. The XPS results indicate that the U(VI) reacted with the Si–O and Al–O on the GMZC particle surfaces at room temperature, and the hydrolyzed product of the U(VI) covered the colloidal surfaces in the neutral water environment, resulting in a decrease in the absolute zeta potential (from ∼31 mV to ∼19 mV). The hydrodynamic diameter of the colloidal particles did not change significantly (∼336 nm–∼360 nm), but the small-angle scattering data revealed that the fractal dimension was larger after the reaction (∼2.8–∼3.1), indicating particle agglomeration. About 14% of the GMZC particles were precipitated after reacting with the U(VI). When the temperature was increased to 55 °C and 85 °C, the precipitation did not change significantly, but the fractal dimension of the mixed system increased (from ∼3.1 to ∼3.6), and the d001 peak was not observed in the SAXS results. When the temperature was decreased by 25 °C, the hydrodynamic diameter of the zeta potential and SAXS image both returned to the level before the temperature increase, indicating that the unstable change in the colloidal system caused by the temperature increase was reversible.

Clay platelet orientation inside self-standing beidellite clay films: Effect of silica nanospheres and link with macroscopic mechanical resistance

Clay minerals and silica are essential components of soil. Understanding the multi-scale structure of a simple model system formed of (negatively charged) beidellite clay nanoplatelets and silica nanospheres is a first step in understanding the complex structure of soil. Due to their strong shape anisotropy, clay nanoplatelets exhibit preferential orientation at the microscopic level, both in aqueous dispersions and in dry deposits. Adding spherical colloids into the system changes the clay platelet organization. These changes are studied here for the case of self-standing clay films, using a small angle X-ray scattering (SAXS) beamline, equipped with a goniometer and a rotating device. We investigated orientation of clay nanoplatelets as a function of the nanoplatelet and nanosphere sizes, their surface charge and sphere/platelet number ratio. Two methodologies are developed to calculate the nanoplatelet order parameter 〈P2〉: (a) background contribution is subtracted from the azimuthal profile curve at a given wavevector q and (b) isotropic contribution is subtracted directly at the level of the 2D SAXS images. Smaller clay nanoplatelets (∼200 nm in lateral size) exhibit a better orientation than larger platelets (> ∼300 nm). Adding small positively and negatively charged nanospheres (diameter ∼ 30 nm) destroys the high degree of orientation of small clay platelets. Large spheres (diameter similar to the nanoplatelet size, ∼300 nm) destroy orientation for both types of clay platelets. A simple tensile strength setup allows to measure the breaking stress of the self-standing films to make the link between microscopic and macroscopic structure. Films of small clay platelets without spheres were mechanically the most resistant. Films with added positively charged spheres were stiffer than films with negatively charged spheres. The methodology presented here opens perspectives for the study of structure and mechanical response of clay deposits.

BioSAXS on the SWING beamline at Synchrotron SOLEIL

Small-angle X-ray scattering (SAXS) of proteins in solution has become a key tool for biochemists and structural biologists, thanks especially to the availability of beamlines with high-throughput capabilities at synchrotron sources. Despite the large spectrum of scientific disciplines tackled on the SWING beamline since its opening in 2008, there has always been a strong commitment to offering state-of-the-art biological SAXS (BioSAXS) instrumentation and data reduction methods to the scientific community. The extremely reliable in-vacuum EigerX-4M detector allows collection of an unlimited number of frames without noise. A small beamstop including a diamond diode-based monitor enables measurements of the transmitted intensity with 0.1% precision as well as a q max/q min ratio as large as 140 at a single distance. The parasitic scattering has been strongly reduced by the installation of new hybrid blades. A new thermally controlled in-vacuum capillary holder including fibre-optics-based spectroscopic functionalities allows the simultaneous use of three spectroscopic techniques in addition to SAXS measurements. The addition of a second high-performance liquid chromatography (HPLC) circuit has virtually eliminated the waiting time associated with column equilibration. The easy in-line connection of a multi-angle light scattering spectrometer and a refractometer allows for an independent determination of the molecular mass and of the concentration of low-UV-absorption samples such as detergents and sugars, respectively. These instrumental improvements are combined with important software developments. The HPLC injection Agilent software is controlled by the SAXS beamline acquisition software, allowing a virtually unlimited series of automated SAXS measurements to be synchronized with the sample injections. All data-containing files and reports are automatically stored in the same folders, with names related to both the user and sample. In addition, all raw SAXS images are processed automatically on the fly, and the analysed data are stored in the ISPyB database and made accessible via a web page.

In-situ SAXS study on pore structure change of PAN-based carbon fiber during graphitization

Graphitization (1400 °C–2200 °C) of polyacrylonitrile (PAN)-based carbon fiber in a small furnace with direct electric heating by Joule effect was studied in situ by small angle X-ray scattering (SAXS) with X-ray synchrotron radiation. The two-dimensional SAXS images display an anisotropic shape indicating the existence of needle-like or elongated ellipsoid-shaped pores oriented along the fiber axis. The one-dimensional scattering curves display obvious positive deviation from Porod's law indicating the existence of micro-fluctuation of electron density in the skeleton of the fiber which give rise to additional scattering. After correcting the deviation from Porod's law, the pure pore scattering was derived, and the pore structure parameters were computed. The results show that with increasing temperature the orientation angle decreases whereas the orientation degree increases. The long axis decreases whereas the short axis increases leading to a lower axial ratio. The size distribution becomes broader and there is a maximum value of porosity and specific surface area at 1900 °C. The change of pore structure in the fiber with temperatures can be approximately divided into two stages corresponding to denitrification condensation (1400 °C–1900 °C) and structure rearrangement (1900 °C–2200 °C) during graphitization, respectively. The corresponding mechanism was analyzed. Reciprocal relationship between the orientation of the needle-like or elongated ellipsoid-shaped pores in carbon fiber and the scattering images (inspired from Macromolecules, 2000, 33, 1848–1852; Polymer, 2001, 42, 1601–1612; Journal of Light Scattering (In Chinese), 2021, 33, 328–334). The left is schematic diagram and the right is actual sample and SAXS images. Where φ is the orientation angle of pore, L is the long axis of pore, r is the short axis of pore, q 12 and q 3 are the components of the reciprocal space vector q (q = 4π·sinθ/λ, 2θ is the scattering angle, λ is the incident X-ray wavelength) in the directions perpendicular and parallel to the principal axis of the pore, respectively. • In-situ SAXS study on PAN-based carbon fiber during graphitization (1400 °C–2200 °C). • Obvious positive deviation from Porod's law for all measured SAXS curves. • Change of pore structure of fiber in two stages dividing by 1900 °C.

Feasibility of imaging amyloid in the brain using small-angle x-ray scattering

Small-angle x-ray scattering (SAXS) imaging may have the potential to image β-amyloid plaques in vivo in the brain without tracers for assessment of Alzheimer’s disease (AD). We use a laboratory SAXS system for planar imaging of AD model and control mouse brains slices to detect regions with high density of amyloid plaques. These regions were validated with histology methods. Using Monte Carlo techniques, we simulate SAXS computed tomography (SAXS-CT) system to study the potential of selectively differentiating amyloid targets in mouse and human head phantoms with detailed anatomy. We found contrast between amyloid and brain tissue at small q (below 0.8 nm−1) in the neocortex region of the transgenic brain slices as supported by histology. We observed similar behavior through planar SAXS imaging of an amyloid-like fibril deposit with a 0.8 mm diameter at a known location on a wild type mouse brain. In our SAXS-CT simulations, we found that 33-keV x rays provide increase plaque visibility in the mouse head for targets of at least 0.1 mm in diameter, while in the human head, 70-keV x rays were capable of detecting plaques as small as 2 mm. To increase radiation efficiency, we used a weighted-sum image visualization approach allowing the dose deposited by 70-keV x rays per SAXS-CT slice of the human head to be reduced by a factor of 10 to 71 mGy for gray matter and 63 mGy for white matter. The findings suggest that a dedicated SAXS-CT system for in vivo amyloid imaging in small animals and humans can be successfully developed with further system optimization to detect regions with amyloid plaques in the brain with a safe level of radiation dose.

Analysis of nanometer-sized aligned conical pores using small-angle x-ray scattering

Small angle X-ray scattering (SAXS) was used to quantitatively study the morphology of aligned, mono-disperse conical etched ion tracks in thin films of amorphous silicon dioxide with aspect ratios of around 6:1, and in polycarbonate foils with aspect ratios of around 1000:1. This paper presents the measurement procedure and methods developed for the analysis of the scattering images and shows results obtained for the two material systems. To enable accurate parameter extraction from the data collected from conical scattering objects a model fitting the 2-D detector images was developed. The analysis involved fitting images from a sequence of measurements with different sample tilts to minimise errors which may have been introduced due to the experimental set-up. The model was validated by the exploitation of the geometric relationship between the sample tilt angle and the cone opening angle, to an angle observed in the features of the SAXS images. We also demonstrate that a fitting procedure for 1-D data extracted from the scattering images using a hard cylinder model can also be used to extract the cone size. The application of these techniques enables us to reconstruct the cone morphologies with unprecedented precision.

Accelerated aging-induced variation of polypropylene (PP) structure studied by two-dimensional (2D) small-angle X-ray scattering (SAXS) correlation spectroscopy

Submolecular-level variation of polypropylene (PP) caused by aging treatment is studied by two-dimensional (2D) small-angle X-ray scattering (SAXS) in conjunction with 2D correlation spectroscopy. PP samples were prepared by a T-die extrusion method and then probed by 2D SAXS. Direction-depending SAXS profile data were obtained by extrusion the SAXS intensities along the direction from 90° (i.e. direction of extrusion) to 120° on the 2D SAXS image. 2D correlation spectra derived from the SAXS profiles of the PP samples revealed the detailed orientations of the lamellae in the polymer system. For example, the development of asynchronous correlation peaks indicates that significant portion of the lamellae in the initial PP sample aligns to the direction of the extrusion. These lamellae tend to go through subsequent crystallization to increase the thickness during the cooling process, while the polymer chain inclined to the direction of the extrusion does not undergo such sufficient level of crystallization. It was also revealed that the aging treatment based on the heating well above glass transition temperature of the PP (ca. 0 °C) essentially provides additional crystalline growth especially to the inclined lamellae.

Synchrotron radiation facility-based quantitative evaluation of pore structure heterogeneity and anisotropy in coal

Abstract In order to quantify coal pore structure heterogeneity and anisotropy, synchrotron radiation SAXS (Small Angle X-ray Scattering) was applied to obtain the SAXS images of two different rank coal samples. The surface fractal dimension (D1) and pore fractal dimension (D2) were obtained by processing the image data. The pore structure heterogeneity of two coal samples was quantified by pore fractal dimension (D2). Pore fractal dimension of Xinzhouyao coal is 2.74 and pore fractal dimension of Tangshan coal is 1.69. As a result, the pore structure heterogeneity of Xinzhouyao coal is stronger than that of Tangshan coal. 3D pore structure imaging was achieved by synchrotron radiation nano-CT. The selected Region of Interest (ROI) of coal sample was divided into a certain number of subvolumes. Pore structure heterogeneity was quantified by calculating the limit of the relative standard deviation of each subvolume's porosity. The heterogeneity value of Xinzhouyao coal pore structure is 3.21 and the heterogeneity value of Tangshan coal pore structure is 2.71. As a result, the pore structure heterogeneity of Xinzhouyao coal is also stronger than that of Tangshan coal, namely, pore structure heterogeneity from synchrotron radiation SAXS and synchrotron radiation nano-CT is consistent. Considering the corresponding relationship between the pore structure anisotropy and the permeability anisotropy, the quantification of pore structure anisotropy was realized by computing the permeability tensor of pore structure using the Lattice Boltzmann method (LBM), and the pore structure anisotropy was characterized by the eigenvalues and eigenvectors of the permeability tensor. The pore structure anisotropy obtained by the method proposed in this paper was validated by the pore structure geometrical morphology.

Convolutional neural networks for grazing incidence x-ray scattering patterns: thin film structure identification

Nano-structured thin films have a variety of applications from waveguides, gaseous sensors to piezoelectric devices. Grazing Incidence Small Angle x-ray Scattering images enable classification of such materials. One challenge is to determine structure information from scattering patterns alone. This paper highlights the design of multiple Convolutional Neural Networks (CNN) to classify nanoparticle orientation in a thin film by learning scattering patterns. The network was trained on several thin films with a success rate of 94%. We demonstrate CNN robustness under different noises as well as demonstrate the potential of our proposed approach as a strategy to decrease scattering pattern analysis time.

Improved small-angle x-ray scattering of nanoparticle self-assembly using a cell with a flat liquid surface

One important way of forming nanostructures entails the assembly of nanoparticle (NP) monolayers at a liquid surface. Probing this assembly of 11.8-nm-diameter iron oxide NPs by small-angle x-ray scattering (SAXS) is studied using cells with walls at angles designed to significantly reduce the size of the meniscus. This enables the collection of much larger signals in the SAXS images of ordered arrays of NPs at liquid/gas interfaces, as is needed for kinetics studies and x-ray exposure minimization, along with the observation of extremely high degrees of order. Meniscus flattening and improved signal collection are demonstrated for the assembly of ordered arrays of iron oxide NP monolayers at a diethylene glycol surface.

Small Angle X-Ray Scattering Imaging of Soft Tissue by Using Laue Diffraction Optical System

We performed a feasibility study of Small angle X-ray scattering imaging under the condition of X-ray bright field imaging by Laue crystal diffraction optics of X-ray dark-field imaging that works as an angular analysis. Collagen in chicken tibia containing abundant soft fibrous tissue was chosen as a specimen. In traditional Small angle X-ray scattering optical system, we can derive the structure information of sample by calculating q value which is available from a scattering pattern. Thus it is usually necessary to conduct a 2D scan in order to obtain scattering image. In this paper it is described by a method by which not only small angle X-ray scattering imaging is available directly but also bright-field imaging and dark-field imaging can be obtained at the same time. As the first step, the feasibility of the imaging method should be confirmed by taking pictures of the samples with known periodic length. The preliminary test showed that the collgan’s lattice spacing d is 65.1 nm that was also taken photos by scanning electron microscopy. By rotating Laue angular analyzer by 112 arcseconds small angle X-ray scattering image appeared in bright-field.

Small-angle X-ray scattering characteristics of mouse brain: Planar imaging measurements and tomographic imaging simulations.

Small-angle x-ray scattering (SAXS) imaging can differentiate tissue types based on their nanoscale molecular structure. However, characterization of the coherent scattering cross-section profile of relevant tissues is needed to optimally design SAXS imaging techniques for a variety of biomedical applications. Reported measured nervous tissue x-ray scattering cross sections under a synchrotron source have had limited agreement. We report a set of x-ray cross-section measurements obtained from planar SAXS imaging of 1 mm thick mouse brain (APP/PS1 wild-type) coronal slices using an 8 keV laboratory x-ray source. Two characteristic peaks were found at 0.96 and 1.60 nm−1 attributed to myelin. The peak intensities varied by location in the slice. We found that regions of gray matter, white matter, and corpus callosum could be segmented by their increasing intensities of myelin peaks respectively. Measured small-angle x-ray scattering cross sections were then used to define brain tissue scattering properties in a GPU-accelerated Monte Carlo simulation of SAXS computed tomography (CT) using a higher monochromatic x-ray energy (20 keV) to study design trade-offs for noninvasive in vivo SAXS imaging on a small-animal head including radiation dose, signal-to-noise ratio (SNR), and the effect of skull presence on the previous two metrics. Simulation results show the estimated total dose to the mouse head for a single SAXS-CT slice was 149.4 mGy. The pixel SNR was approximately 30.8 for white matter material whether or not a skull was present. In this early-stage proof-of-principle work, we have demonstrated our brain cross-section data and simulation tools can be used to assess optimal instrument parameters for dedicated small-animal SAXS-CT prototypes.

Planar small-angle x-ray scattering imaging of phantoms and biological samples

Coherent small-angle x-ray scattering (SAXS) provides molecular and nanometer-scale structural information. By capturing SAXS data at multiple locations across a sample, we obtained planar images and observed improved contrast given by the difference in the material scattering cross sections. We use phantoms made with 3D printing techniques, with tissue-mimicking plastic (PMMA), and with a highly scattering reference material (AgBe), which were chosen because of their well characterized scattering cross section to demonstrate and characterize the planar imaging of a laboratory SAXS system. We measure 1.07 and 2.14 nm−1 angular intensity maps for AgBe, 9.5 nm−1 for PMMA, and 12.3 nm−1 for Veroclear. The planar SAXS images show material discrimination based on their cross sectional features. The image signal-to-noise ratio (SNR) of each q image was dependent on exposure time and x-ray flux. We observed a lower SNR (91 ± 48) at q angles where no characteristic peaks for either material exist. To improve the visualization of the acquired data by utilizing all q-binned data, we describe a weighted-sum presentation method with a priori knowledge of relevant cross sections to improve the SNR (10 000 ± 6400) over the SNR from a single q-image at 1.07 nm−1 (1100 ± 620). In addition, we describe planar SAXS imaging of a mouse brain slice showing differentiation of tissue types as compared to a conventional absorption-based x-ray imaging technique.

Building-block architecture of botulinum toxin complex: Conformational changes provide insights into the hemagglutination ability of the complex

Clostridium botulinum produces the botulinum neurotoxin (BoNT). Previously, we provided evidence for the “building-block” model of botulinum toxin complex (TC). In this model, a single BoNT is associated with a single nontoxic nonhemagglutinin (NTNHA), yielding M-TC; three HA-70 molecules are attached and form M-TC/HA-70, and one to three “arms” of the HA-33/HA-17 trimer (two HA-33 and one HA-17) further bind to M-TC/HA-70 via HA-17 and HA-70 binding, yielding one-, two-, and three-arm L-TC. Of all TCs, only the three-arm L-TC caused hemagglutination. In this study, we determined the solution structures for the botulinum TCs using small-angle X-ray scattering (SAXS). The mature three-arm L-TC exhibited the shape of a “bird spreading its wings”, in contrast to the model having three “arms”, as revealed by transmission electron microscopy. SAXS images indicated that one of the three arms of the HA-33/HA-17 trimer bound to both HA-70 and BoNT. Taken together, these findings regarding the conformational changes in the building-block architecture of TC may explain why only three-arm L-TC exhibited hemagglutination.

Small-angle X-ray and light scattering analysis of multi-layered Curdlan gels prepared by a diffusion method

Curdlan, a microbial polysaccharide, forms a multi-layered gel consisting of four layers with different turbidity when its alkaline solution is dialyzed against aqueous solutions containing Ca2+ (diffusion-set gel). The present study clarified the microstructure of each layer of the diffusion-set Curdlan gel by small-angle X-ray scattering (SAXS) and small-angle light scattering (SALS). The SAXS data showed that Curdlan chains assume a helical ordered conformation in the gel and that the gel consists of the fibrils formed by the association of Curdlan chains and the aggregates of fibrils. The SAXS results also indicated that the gelation is induced by the formation of a network of Ca2+-cross-linked fibrils in the outer region of the gel, whereas by the network formation of the aggregation of fibrils in the neutralization process in the inner region of the gel. A structural anisotropy of the gel was investigated by analysis of two-dimensional SAXS images, showing that the fibril is oriented circumferentially in the outer region of the cylindrical gel, whereas it is oriented randomly in the inner region of the gel. The SALS data showed that a characteristic length of an inhomogeneous structure in the turbid layers is of the order of micrometers. The observed spatial variation of the microscopic structure is caused by the difference in the paths of pH and [Ca2+] traced in the gelation process.

回折格子を利用した小角X線散乱イメージング

回折格子を利用した小角X線散乱イメージング

Cellular Diffraction: Scanning X-Ray Nanodiffraction from Living Cells

Cellular diffraction, or scanning x-ray nanodiffraction applied to cells, is a new technique that promises insight into cellular organization at length scales of 1–200 nm, covering the features of molecules and organelles. Filling a niche between the length scales probed by optical and electron microscopy, cellular diffraction rasters a nanofocused x-ray beam across living cells in an aqueous medium and records a two-dimensional image of, for instance, the small-angle scattering signal at each position. This results in a real-space image of the cell where the contrast is based on the average intensity of the small-angle x-ray scattering (SAXS) signal (dark-field image), or phase contrast, or other modalities such as the x-ray fluorescence intensity, with spatial resolution determined by the step-size of the raster scan ranging from submicron to a few microns. But the individual diffraction patterns can also be analyzed, providing higher-resolution limited by the signal/noise of the scattering pattern, currently ∼6 nm. With the cells bound to a solid support, the SAXS patterns do not result from isotropic averaging of the scatterers, and no staining or labeling is required for the technique. The development of cellular diffraction is spearheaded by two groups from the Institute for X-Ray Physics at the University of Gottingen, led by Sarah Koster and Tim Salditt, who exploit recent advances in x-ray detectors, x-ray optics, and microfluidics in order to apply scanning SAXS imaging (1) to hydrated, living cells and address subcellular dimensions. In a collaborative first effort at beamline ID13 of the European Synchrotron Radiation Facility, they imaged freeze-dried epithelial cells and saw distinctive scattering from the network of keratin fibers in the cell (2). More recent work using a specially developed instrument and beamline P10 of PETRA III imaged both fixed and live cells. The Koster team, together with collaborators from the European Synchrotron Radiation Facility, HASYLAB, and Ghent University, observed that the azimuthally averaged SAXS signal from the cells follows a power-law decay, with different exponents for living and fixed cells (3). Moreover, the scattering decays more rapidly after repeated exposure, so the value of the exponent serves as a diagnostic for beam damage in the sample. This issue of the Biophysical Journal contains a report from the Salditt team and collaborators from the Max Planck Institute for Dynamics and Self-Organization about their studies on living and fixed amoeboid cells (4), one which provides the best realization yet of the full potential of this exciting new technique. Chemotaxis in amoeboids is accomplished by extending pseudopods with controlled polymerization of actin fibers and the retraction of receding edges by depolymerization of actin and contraction of myosin motor proteins, but the details of the actin networks remain unknown. The molecular signature of this mechanism is revealed by cellular diffraction, which shows highly anisotropic scattering streaks resulting from oriented fiber bundles in the periphery of the cell. Using an automated algorithm to convert this anisotropy to a contrast neatly outlines the advancing edges of the cell. Further modeling of the scattering streaks is necessary to characterize quantitatively the nature of the fiber bundles that give rise to the SAXS signal, but the richness of the data should allow the extraction of meaningful parameters such as the number of fibers in the bundle, their spacing, and the density of cross-links. The authors note that their data and instrument are both complementary to and compatible with x-ray coherent diffraction imaging, so that with suitable modifications, users could first apply coherent diffraction imaging to image the whole cell and then scanning nanodiffraction to examine particular regions in greater detail. Indeed, the team has already demonstrated this approach by examining freeze-dried bacterial cells with both ptychography and cellular diffraction at the coherent SAXS beamline of the Swiss Light Source (5). With the synchrotron community preparing for fourth-generation facilities that approach the diffraction limit, which will greatly improve the coherence of the x-ray beam and the ability to focus the beam (6), cellular diffraction will surely grow in application and impact.

Sugar-induced conformational change found in the HA-33/HA-17 trimer of the botulinum toxin complex

Large-sized botulinum toxin complex (L-TC) is formed by conjugation of neurotoxin, nontoxic nonhemagglutinin and hemagglutinin (HA) complex. The HA complex is formed by association of three HA-70 molecules and three HA-33/HA-17 trimers, comprised of a single HA-17 and two HA-33 proteins. The HA-33/HA-17 trimer isolated from serotype D L-TC has the ability to bind to and penetrate through the intestinal epithelial cell monolayer in a sialic acid-dependent manner, and thus it plays an important role in toxin delivery through the intestinal cell wall. In this study, we determined the solution structure of the HA-33/HA-17 trimer by using small-angle X-ray scattering (SAXS). The SAXS image of HA-33/HA-17 exhibited broadly similar appearance to the crystal image of the complex. On the other hand, in the presence of N-acetylneuraminic acid, glucose and galactose, the solution structure of the HA-33/HA-17 trimer was drastically altered compared to the structure in the absence of the sugars. Sugar-induced structural change of the HA-33/HA-17 trimer may contribute to cell binding and subsequent transport across the intestinal cell layer.

Small-angle X-ray scattering reveals structural dynamics of the botulinum neurotoxin associating protein, nontoxic nonhemagglutinin

In cell culture supernatants, the botulinum neurotoxin (BoNT) exists as part of a toxin complex (TC) in which nontoxic nonhemagglutinin (NTNHA) and/or hemagglutinins (HAs) are assembled onto the BoNT. A series of investigations indicated that formation of the TC is vital for delivery of the toxin to nerve cells through the digestive tract. In the assembly process, BoNT binds to NTNHA yielding M-TC, and it then matures into L-TC by further association with the HAs via NTNHA in the M-TC. Here, we report a crystal structure of the NTNHA from Clostridium botulinum serotype D strain 4947. Additionally, we performed small-angle X-ray scattering (SAXS) analysis of the NTNHA and the M-TC to elucidate the solution structure. The crystal structure of D-4947 NTNHA revealed that BoNT and NTNHA share a closely related structure consisting of three domains. The SAXS image indicated that, even though the N-terminal two-thirds of the NTNHA molecule had an apparently similar conformation in both the crystal and solution structures, the C-terminal third of the molecule showed a more extended structure in the SAXS image than that seen in the crystallographic image. The discrepancy between the crystal and solution structures implies a high flexibility of the C-terminal third domain of NTNHA, which is involved in binding to BoNT. Structural dynamics of the NTNHA molecule revealed by SAXS may explain its binding to BoNT to form the BoNT/NTNHA complex.

Guided self-assembly of nanostructured titanium oxide

A series of nanostructured titanium oxide particles were synthesized by a simple wet chemical method and characterized by means of small-angle x-ray scattering (SAXS)/wide-angle x-ray scattering (WAXS), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM), thermal analysis, and rheometry. Tetrabutyl titanate (TBT) and ethylene glycol (EG) can be combined to form either TiOx nanowires or smooth nanorods, and the molar ratio of TBT:EG determines which of these is obtained. Therefore, TiOx nanorods with a highly rough surface can be obtained by hydrolysis of TBT with the addition of cetyl-trimethyl-ammonium bromide (CTAB) as surfactant in an EG solution. Furthermore, TiOx nanorods with two sharp ends can be obtained by hydrolysis of TBT with the addition of salt (LiCl) in an EG solution. The AFM results show that the TiOx nanorods with rough surfaces are formed by the self-assembly of TiOx nanospheres. The electrorheological (ER) effect was investigated using a suspension of titanium oxide nanowires or nanorods dispersed in silicone oil. Oil suspensions of titanium oxide nanowires or nanorods exhibit a dramatic reorganization when submitted to a strong DC electric field and the particles aggregate to form chain-like structures along the direction of applied electric field. Two-dimensional SAXS images from chains of anisotropically shaped particles exhibit a marked asymmetry in the SAXS patterns, reflecting the preferential self-assembly of the particles in the field. The suspension of rough TiOx nanorods shows stronger ER properties than that of the other nanostructured TiOx particles. We find that the particle surface roughness plays an important role in modification of the dielectric properties and in the enhancement of the ER effect.