On the Supermolecular Structure of Fullerene C60 Solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C₆₀ solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of I_C with increase of scattering angle. The value of I_C depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C₆₀ in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C₆₀ by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C₆₀ solutions in good solvents are considered.     

X‐ray Raman spectroscopy of lithium‐ion battery electrolyte solutions in a flow cell

The effects of varying LiPF₆ salt concentration and the presence of lithium bis(oxalate)borate additive on the electronic structure of commonly used lithium‐ion battery electrolyte solvents (ethylene carbonate–dimethyl carbonate and propylene carbonate) have been investigated. X‐ray Raman scattering spectroscopy (a non‐resonant inelastic X‐ray scattering method) was utilized together with a closed‐circle flow cell. Carbon and oxygen K‐edges provide characteristic information on the electronic structure of the electrolyte solutions, which are sensitive to local chemistry. Higher Li⁺ ion concentration in the solvent manifests itself as a blue‐shift of both the π* feature in the carbon edge and the carbonyl π* feature in the oxygen edge. While these oxygen K‐edge results agree with previous soft X‐ray absorption studies on LiBF₄ salt concentration in propylene carbonate, carbon K‐edge spectra reveal a shift in energy, which can be explained with differing ionic conductivities of the electrolyte solutions.     

Thorough small‐angle X‐ray scattering analysis of the instability of liquid micro‐jets in air

Liquid jets are of interest, both for their industrial relevance and for scientific applications (more important, in particular for X‐rays, after the advent of free‐electron lasers that require liquid jets as sample carrier). Instability mechanisms have been described theoretically and by numerical simulation, but confirmed by few experimental techniques. In fact, these are mainly based on cameras, which is limited by the imaging resolution, and on light scattering, which is hindered by absorption, reflection, Mie scattering and multiple scattering due to complex air/liquid interfaces during jet break‐up. In this communication it is demonstrated that synchrotron small‐angle X‐ray scattering (SAXS) can give quantitative information on liquid jet dynamics at the nanoscale, by detecting time‐dependent morphology and break‐up length. Jets ejected from circular tubes of different diameters (100–450 µm) and speeds (0.7–21 m s^?1) have been explored to cover the Rayleigh and first wind‐induced regimes. Various solvents (water, ethanol, 2‐propanol) and their mixtures have been examined. The determination of the liquid jet behaviour becomes essential, as it provides background data in subsequent studies of chemical and biological reactions using SAXS or X‐ray diffraction based on synchrotron radiation and free‐electron lasers.     

Colloidal Crystals of NaYF4 Upconversion Nanocrystals Studied by Small‐Angle X‐Ray Scattering (SAXS)

Spherical NaYF₄ upconversion nanocrystals with mean radii of about 5 and 11 nm are observed to form colloidal crystals, i.e., 3D assemblies of the particles with long‐range order. The colloidal crystals of the larger particles form directly in solution when dispersions of the particles in toluene are stored at room temperature for several weeks. Crystallization of the smaller particles takes place when their dispersions in hexane are slowly dried at elevated temperatures. The formation and the structure of the colloidal crystals are studied by small‐angle X‐ray scattering (SAXS). SAXS measurements show that the smaller as well as the larger particles assemble into a face‐centered cubic lattice with unit cell dimensions of a = 18.7 nm and a = 35.5 nm, respectively. The SAXS data also show that the particles in the colloidal crystals still bear a layer of oleic acid on their surfaces. The thickness of this layer is 1.5–1.8 nm, as determined by comparing the unit cell dimensions of the colloidal crystals with the mean particle sizes. The latter could be very precisely determined from the distinct oscillations observed in the SAXS data of dilute colloidal dispersions of the nanocrystals.     

Small‐angle solution scattering using the mixed‐mode pixel array detector

Solution small‐angle X‐ray scattering (SAXS) measurements were obtained using a 128 × 128 pixel X‐ray mixed‐mode pixel array detector (MMPAD) with an 860 µs readout time. The MMPAD offers advantages for SAXS experiments: a pixel full‐well of >2 × 10⁷ 10 keV X‐rays, a maximum flux rate of 10⁸ X‐rays pixel^?1 s^?1, and a sub‐pixel point‐spread function. Data from the MMPAD were quantitatively compared with data from a charge‐coupled device (CCD) fiber‐optically coupled to a phosphor screen. MMPAD solution SAXS data from lysozyme solutions were of equal or better quality than data captured by the CCD. The read‐noise (normalized by pixel area) of the MMPAD was less than that of the CCD by an average factor of 3.0. Short sample‐to‐detector distances were required owing to the small MMPAD area (19.2 mm × 19.2 mm), and were revealed to be advantageous with respect to detector read‐noise. As predicted by the Shannon sampling theory and confirmed by the acquisition of lysozyme solution SAXS curves, the MMPAD at short distances is capable of sufficiently sampling a solution SAXS curve for protein shape analysis. The readout speed of the MMPAD was demonstrated by continuously monitoring lysozyme sample evolution as radiation damage accumulated. These experiments prove that a small suitably configured MMPAD is appropriate for time‐resolved solution scattering measurements.     

In situ study of nanotemplate‐induced growth of lysozyme microcrystals by submicrometer GISAXS

Ultrasmall lysozyme microcrystals are grown by classical hanging‐drop vapor diffusion and by its modification using a homologous protein thin‐film template displaying long‐range order. The nucleation and growth mechanisms of lysozyme microcrystals are studied at the thin lysozyme film surface using a new in situµGISAXS (microbeam grazing‐incidence small‐angle X‐ray scattering) technique recently developed at the microfocus beamline of the ESRF in Grenoble, France. New insight on the nucleation and crystallization processes appear to emerge.     

Precipitation kinetics of W2B5 in (Ti0.4W0.5Cr0.1)B2 solid solutions

The isothermal precipitation kinetics of W₂B₅ secondary phase from supersaturated polycrystalline (Ti_0.4W_0.5Cr_0.1)B₂ solid solutions were investigated with X-ray diffractometry and scanning electron microscopy in the temperature range between 1500 and 1700°C. The precipitate formation is described by a modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, where W₂B₅ particles nucleate preferentially at grain boundaries and subsequently grow into the volume by a two-dimensional process controlled by volume diffusion of the transition metals. Numerical calculations are used to describe quantitatively the time dependence of the precipitated fraction and to determine a differential JMAK exponent n _diff which gives information on the nucleation and growth modes. n _diff decreases during the precipitation process from 2 to about 0.8 for all temperatures investigated. The first limit corresponds to the classical JMAK model (two-dimensional diffusional growth and constant nucleation rate) and the decrease in n _diff is the consequence of an impingement of the nucleating and growing particles in the late stages of the process. Nucleation and growth rates are determined as functions of reciprocal temperature, where the first quantity shows a non-monotonic behaviour with a maximum at about 1650°C and the second quantity exhibits an Arrhenius behaviour with an activation enthalpy of 3.6?eV. From this it can be concluded that the overall precipitate formation is dominated by the kinetics of atomic motion at low temperatures and by the thermodynamics of nucleation at high temperatures.     

Performance of the micro‐PIC gaseous area detector in small‐angle X‐ray scattering experiments

The application of a two‐dimensional photon‐counting detector based on a micro‐pixel gas chamber (µ‐PIC) to high‐resolution small‐angle X‐ray scattering (SAXS), and its performance, are reported. The µ‐PIC is a micro‐pattern gaseous detector fabricated by printed circuit board technology. This article describes the performance of the µ‐PIC in SAXS experiments at SPring‐8. A dynamic range of >10⁵ was obtained for X‐ray scattering from a polystyrene sphere solution. A maximum counting rate of up to 5 MHz was observed with good linearity and without saturation. For a diffraction pattern of collagen, weak peaks were observed in the high‐angle region in one accumulation of photons.     

Time-resolved SAXS measurements facilitated by online HPLC buffer exchange

Small‐angle X‐ray scattering (SAXS) is a powerful technique to structurally characterize biological macromolecules in solution. Heterogeneous solutions are inherently challenging to study. However, since SAXS data from ideal solutions are additive, with careful computational analysis it may be possible to separate contributions from individual species present in solution. Hence, time‐resolved SAXS (TR‐SAXS) data of processes in development can be analyzed. Many reported TR‐SAXS results are initialized by a sudden change in buffer conditions facilitated by rapid mixing combined with either continuous or stopped flow. In this paper a method for obtaining TR‐SAXS data from systems where the reaction is triggered by removal of a species is presented. This method is based on fast buffer exchange over a short desalting column facilitated by an online HPLC (high‐performance liquid chromatography) connected to the SAXS sample cell. The sample is stopped in the sample cell and the evolving reaction is followed. In this specific system the removal of phenol initiates a self‐association process of long‐acting insulin analogues. For this experiment, data were collected in time series while varying concentrations. The method can be generally applied to other systems where removal of a species or other changes in experimental conditions trigger a process.     

Quality evaluation of quick‐frozen biological specimens by simultaneous microbeam SAXS/WAXS recordings

The quality of small‐angle X‐ray scattering (SAXS) patterns from quick‐frozen hydrated biological specimens was correlated with the extent of ice crystal formation by simultaneously recording wide‐angle X‐ray scattering (WAXS) of ice, at a micrometer‐order spatial resolution by using X‐ray microbeams. Flight muscle fibers from a giant waterbug, Lethocerus, known to generate well defined small‐angle reflection spots originating from the hexagonal lattices of myofilaments, were quick‐frozen in the presence or absence of various cryoprotectants. Freezing without a cryoprotectant resulted in massive ice‐crystal formation at almost all depths of the specimen, and the occurrence of reflection spots was limited to the region close to the specimen surface. Inclusion of 20% dimethyl sulfoxide or methylpentanediol ensured ideal vitreous ice formation and good diffraction qualities for up to 100 µm from the specimen surface. Glycerol and sucrose were found to be inferior at a 20% concentration, but left the reflection spots observable at depths of up to 100 µm. Thus, the microbeam SAXS/WAXS recording offers a high‐spatial‐resolution means of evaluating the extent of structure preservation of quick‐frozen biological specimens. The technique presented here may also provide useful information in cryoelectron microscopy.     

Crystallization in Microdomains of a Block Copolymer Comprising Semicrystalline Block Observed by Simultaneous Measurement of SAXS and WAXS with H v‐SALS or DSC

Abstract

Semicrystalline block copolymers provide us with a fascinating model for studying the kinetics of crystallization. We performed the simultaneous measurement of small‐ (SAXS) and wide‐angle (WAXS) x‐ray scattering (SWAXS) with differential scanning calorimetry (DSC), or SWAXS with small‐angle light scattering (H _v‐SALS). The specimen used was polyethylene‐b‐poly(ethylene propylene) (PE‐b‐PEP) with the molecular weight of 44,200. The PE block has the melting point (T _m) at 108°C. We observed the time evolution of crystallization in the lamellar microdomains of PE‐b‐PEP after a temperature drop from 180°C (?T _m) to a variety of temperatures slightly below T _m. The exothermic signal was observed by DSC right after the temperature drop, while the four‐leaf‐clover pattern of H _v‐SALS and the SAXS peaks due to the lamellar microdomains were observed several minutes after the temperature equilibration. The WAXS peaks of (110) and (200) reflection were almost simultaneously detected with the H _v‐SALS and the SAXS peaks at crystallization temperature of 100°C. With the crystallization temperature closer to T _m, the WAXS crystalline signals showed up with longer time lag after the H _v‐SALS and the SAXS peaks began to appear. Interestingly, these phenomena are interpreted as that long‐range order of density fluctuation up to the order of micrometers was generated prior to the formation of crystals with partially ordered phase rather than the instantaneous crystalline nucleation.     

Simultaneous small‐ and wide‐angle scattering at high X‐ray energies

Combined small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) is a powerful technique for the study of materials at length scales ranging from atomic/molecular sizes (a few angstroms) to the mesoscopic regime (～1 nm to ～1 µm). A set‐up to apply this technique at high X‐ray energies (E > 50 keV) has been developed. Hard X‐rays permit the execution of at least three classes of investigations that are significantly more difficult to perform at standard X‐ray energies (8–20 keV): (i) in situ strain analysis revealing anisotropic strain behaviour both at the atomic (WAXS) as well as at the mesoscopic (SAXS) length scales, (ii) acquisition of WAXS patterns to very large q (>20 Å^?1) thus allowing atomic pair distribution function analysis (SAXS/PDF) of micro‐ and nano‐structured materials, and (iii) utilization of complex sample environments involving thick X‐ray windows and/or samples that can be penetrated only by high‐energy X‐rays. Using the reported set‐up a time resolution of approximately two seconds was demonstrated. It is planned to further improve this time resolution in the near future.     

A portable ultrahigh‐vacuum system for advanced synchrotron radiation studies of thin films and nanostructures: EuSi2 nano‐islands

A portable ultrahigh‐vacuum system optimized for in situ variable‐temperature X‐ray scattering and spectroscopy experiments at synchrotron radiation beamlines was constructed and brought into operation at the synchrotron radiation facility ANKA of the Karlsruhe Institute of Technology, Germany. Here the main features of the new instrument are described and its capabilities demonstrated. The surface morphology, structure and stoichiometry of EuSi₂ nano‐islands are determined by in situ grazing‐incidence small‐angle X‐ray scattering and X‐ray absorption spectroscopy. A size reduction of about a factor of two of the nano‐islands due to silicide decomposition and Eu desorption is observed after sample annealing at 1270 K for 30 min.     

A new small‐angle X‐ray scattering set‐up on the crystallography beamline I711 at MAX‐lab

A small‐angle X‐ray scattering (SAXS) set‐up has recently been developed at beamline I711 at the MAX II storage ring in Lund (Sweden). An overview of the required modifications is presented here together with a number of application examples. The accessible q range in a SAXS experiment is 0.009–0.3 Å^?1 for the standard set‐up but depends on the sample‐to‐detector distance, detector offset, beamstop size and wavelength. The SAXS camera has been designed to have a low background and has three collinear slit sets for collimating the incident beam. The standard beam size is about 0.37 mm × 0.37 mm (full width at half‐maximum) at the sample position, with a flux of 4 × 10¹⁰ photons s^?1 and λ = 1.1 Å. The vacuum is of the order of 0.05 mbar in the unbroken beam path from the first slits until the exit window in front of the detector. A large sample chamber with a number of lead‐throughs allows different sample environments to be mounted. This station is used for measurements on weakly scattering proteins in solutions and also for colloids, polymers and other nanoscale structures. A special application supported by the beamline is the effort to establish a micro‐fluidic sample environment for structural analysis of samples that are only available in limited quantities. Overall, this work demonstrates how a cost‐effective SAXS station can be constructed on a multipurpose beamline.     

Performance on absolute scattering intensity calibration and protein molecular weight determination at BL16B1, a dedicated SAXS beamline at SSRF

The optical system and end‐station of bending‐magnet beamline BL16B1, dedicated to small‐angle X‐ray scattering (SAXS) at the Shanghai Synchrotron Radiation Facility, is described. Constructed in 2009 and upgraded in 2013, this beamline has been open to users since May 2009 and supports methodologies including SAXS, wide‐angle X‐ray scattering (WAXS), simultaneous SAXS/WAXS, grazing‐incidence small‐angle X‐ray scattering (GISAXS) and anomalous small‐angle X‐ray scattering (ASAXS). Considering that an increasing necessity for absolute calibration of SAXS intensity has been recognized in in‐depth investigations, SAXS intensity is re‐stated according to the extent of data processing, and the absolute intensity is suggested to be a unified presentation of SAXS data in this article. Theory with a practical procedure for absolute intensity calibration is established based on BL16B1, using glass carbon and water as primary and secondary standards, respectively. The calibration procedure can be completed in minutes and shows good reliability under different conditions. An empirical line of scale factor estimation is also established for any specific SAXS setup at the beamline. Beamline performance on molecular weight (MW) determination is provided as a straightforward application and verification of the absolute intensity calibration. Results show good accuracy with a deviation of less than 10% compared with the known value, which is also the best attainable accuracy in recent studies using SAXS to measure protein MW. Fast MW measurement following the demonstrated method also enables an instant check or pre‐diagnosis of the SAXS performance to improve the data acquisition.     

Classification of ab initio models of proteins restored from small‐angle X‐ray scattering

In structure analyses of proteins in solution by using small‐angle X‐ray scattering (SAXS), the molecular models are restored by using ab initio molecular modeling algorithms. There can be variation among restored models owing to the loss of phase information in the scattering profiles, averaging with regard to the orientation of proteins against the direction of the incident X‐ray beam, and also conformational fluctuations. In many cases, a representative molecular model is obtained by averaging models restored in a number of ab initio calculations, which possibly provide nonrealistic models inconsistent with the biological and structural information about the target protein. Here, a protocol for classifying predicted models by multivariate analysis to select probable and realistic models is proposed. In the protocol, each structure model is represented as a point in a hyper‐dimensional space describing the shape of the model. Principal component analysis followed by the clustering method is applied to visualize the distribution of the points in the hyper‐dimensional space. Then, the classification provides an opportunity to exclude nonrealistic models. The feasibility of the protocol was examined through the application to the SAXS profiles of four proteins.     

A dedicated small‐angle X‐ray scattering beamline with a superconducting wiggler source at the NSRRC

At the National Synchrotron Radiation Research Center (NSRRC), which operates a 1.5 GeV storage ring, a dedicated small‐angle X‐ray scattering (SAXS) beamline has been installed with an in‐achromat superconducting wiggler insertion device of peak magnetic field 3.1 T. The vertical beam divergence from the X‐ray source is reduced significantly by a collimating mirror. Subsequently the beam is selectively monochromated by a double Si(111) crystal monochromator with high energy resolution (ΔE/E? 2 × 10^?4) in the energy range 5–23 keV, or by a double Mo/B₄C multilayer monochromator for 10–30 times higher flux (～10¹¹ photons s^?1) in the 6–15 keV range. These two monochromators are incorporated into one rotating cradle for fast exchange. The monochromated beam is focused by a toroidal mirror with 1:1 focusing for a small beam divergence and a beam size of ～0.9 mm × 0.3 mm (horizontal × vertical) at the focus point located 26.5 m from the radiation source. A plane mirror installed after the toroidal mirror is selectively used to deflect the beam downwards for grazing‐incidence SAXS (GISAXS) from liquid surfaces. Two online beam‐position monitors separated by 8 m provide an efficient feedback control for an overall beam‐position stability in the 10 µm range. The beam features measured, including the flux density, energy resolution, size and divergence, are consistent with those calculated using the ray‐tracing program SHADOW. With the deflectable beam of relatively high energy resolution and high flux, the new beamline meets the requirements for a wide range of SAXS applications, including anomalous SAXS for multiphase nanoparticles (e.g. semiconductor core‐shell quantum dots) and GISAXS from liquid surfaces.     

The application of hybrid pixel detectors for in‐house SAXS instrumentation with a view to combined chromatographic operation

This study analyses the potential for laboratory‐based size‐exclusion chromatography (SEC) integrated small‐angle X‐ray scattering (SAXS) instrumentation to characterize protein complexes. Using a high‐brilliance home source in conjunction with a hybrid pixel X‐ray detector, the efficacy of SAXS data collection at pertinent protein concentrations and exposure times has been assessed. Scattering data from SOD1 and from the complex of SOD1 with its copper chaperone, using 10 min exposures, provided data quality in the range 0.03 < q < 0.25 Å^?1 that was sufficient to accurately assign radius of gyration, maximum dimension and molecular mass. These data demonstrate that a home source with integrated SEC–SAXS technology is feasible and would enable structural biologists studying systems containing transient protein complexes, or proteins prone to aggregation, to make advanced preparations in‐house for more effective use of limited synchrotron beam time.     

Phase transformations in CaCO3/iron oxide composite induced by thermal treatment and laser irradiation

Calcium carbonate (CaCO₃)/iron oxide composites were synthesized through a simple one‐step impregnation procedure by mixing iron oxide nanoparticles (γ‐Fe₂O₃ and Fe₃O₄) of about 6 nm in size and CaCO₃ microparticles (Φ = 2 µm–8 µm, vaterite phase). The morphology and structural properties of CaCO₃, iron oxide nanoparticles and CaCO₃/iron oxide composites were characterized as a function of low iron content (0 %w to 3.2 %w) by scanning electron microscopy and transmission electron microscopy, X‐ray diffraction and ⁵⁷Fe Mössbauer spectrometry. The phase transformations induced by thermal treatment and laser irradiation were investigated in situ by X‐ray thermodiffraction (XRTD) and Raman spectroscopy. We have shown that the phase transformations observed by XRTD are also observed under laser irradiation as a consequence of the absorption of the laser irradiation by iron oxide nanoparticles. Copyright © 2012 John Wiley & Sons, Ltd.     

我国同步辐射小角X光散射装置

小角X光散射是当X光照射到物质上时发生的在原光束附近小角度范围内的电子相干散射,凡是存在纳米尺度的电子密度不均匀区的物质均会产生小角X光散射现象,因此它是表征纳米、多孔材料结构的理想手段。普通X光源产生的X光强度弱,限制了小角X光散射的应用,采用同步辐射为X光源,则可以大大提高X光强度。目前我国已建立同步辐射小角X光散射站,本文对其装置进行了介绍。