Synchrotron Small-angle X-ray Scattering Research Articles

SAXS study on the morphology of etched and un-etched ion tracks in apatite

Natural apatite samples were irradiated with 185 MeV Au and 2.3 GeV Bi ions to simulate fission tracks. The resulting track morphology was investigated using synchrotron small angle x-ray scattering (SAXS) measurements before and after chemical etching. We present preliminary results from the SAXS measurement showing the etching process is highly anisotropic yielding faceted etch pits with a 6-fold symmetry. The measurements are a first step in gaining new insights into the correlation between etched and unetched fission tracks and the use of SAXS as a tool for studying etched tracks.

Rapid mixing stopped-flow small-angle X-ray scattering study of lipoplex formation at beamline ID02@ESRF

Rapid mixing stoppedflow experiments, coupl ed with synchrotron smallangle Xray scattering (SAXS) on the subsecond timescale, produce a vast amount of experimental structural data. The purpose of this work is to present the key steps of the SAXS data treatment for the case of selfassembly and complexation of cationic lipid particles (vesicles or cubosomes) with plasmid DNA in the course of a rapid mixing stopped� flow process. This approach is significant for the structural analysis of rapidly forming softmatter biomacro� molecular delivery systems.

Self-assembly of block copolymer-based ionic supramolecules based upon multi-tail amphiphiles

Using synchrotron small angle X-ray scattering (SAXS), self-assembly of ionic supramolecules based upon diblock copolymers of poly(styrene)-b-poly(methacrylic acid) and multi-tail (2- or 4-tail) alkyl quaternary ammonium amphiphiles is investigated.

Spontaneous Reconstitution of Bovine Rhodopsin into Artificial Membranes

Rhodopsin is a canonical G-protein-coupled receptor (GPCR) that is responsible for vision in dim light. It has the potential to serve as a high-fidelity, light-sensing molecular switch for a broad range of nanotechnologies. Previous studies revealed that the photoactivity of rhodopsin depends critically on the native lipid bilayer environment surrounding this membrane protein [1-3]. It is not yet clear how artificial membranes in synthetic systems would affect the activity of rhodopsin [4], and recent study suggests that membrane moduli may play important roles [4, 5]. Partially this uncertainty is due to the fact that it is experimentally challenging to prepare rhodopsin-supporting artificial proteomembranes with systematically varied membrane chemistry and physical properties. Here we show that bovine rhodopsin can be spontaneously reconstituted into a series of well-defined artificial membranes, including both lipid-based (i.e., liposome) and polymer-based (i.e., polymersome) membranes, via a charge-interaction-directed reconstitution (CIDR) mechanism [5, 6]. Using synchrotron small-angle X-ray scattering (SAXS), we show that n-dodecyl-β-D-maltoside solubilized bovine rhodopsin is reconstituted spontaneously to form 2-D proteomembrane arrays, which in turn are coupled along the trans-membrane direction to form a 3-D multilamellar structure. The lamellar periodicity is ∼5.7 nm, which matches closely the transmembrane dimension of rhodopsin. Using time-resolved UV-visible spectroscopy, we are currently examining the photoactivity of embedded bovine rhodopsin, and its dependency on the surface charge states and membrane moduli of the artificial membrane. [1] M. F. Brown (1997) Curr. Top. Membr. 44, 285-356. [2] A.V. Botelho et al. (2006) Biophys. J. 91, 4464-4477. [3] A.V. Struts et al. (2014) Meth. Mol. Biol. (in press). [4] V. Subramaniam et al. (2005) JACS 127, 5320-5321. [5] L.J. Kuang et al. (2014) ACS Nano 8, 537-545. [6] D.B. Hua et al. (2011) JACS 133, 2354-2357.

Microphase Separation and Crystallization in All-Conjugated Poly(3-alkylthiophene) Diblock Copolymers

The microphase separation and crystallization of all-conjugated poly(3-butylthiophene)-b-poly(3-dodecylthiophene) (P3BDDT) diblock copolymers were systematically investigated by temperature-resolved wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), and synchrotron small-angle X-ray scattering (SAXS) in a step-by-step cooling process. The WAXD, FTIR, and SAXS results revealed that the crystallization of poly(3-butylthiophene) (P3BT) blocks with shorter alkyl side-chains in high temperature region led to the formation of microphase-separated lamellar structure consisting of P3BT crystalline domains and P3BT/poly(3-dodecylthiophene) (P3DDT) amorphous domains, followed by a rapid crystallization of P3DDT blocks in relatively low temperature region, which occurred in the amorphous domains between P3BT crystalline domains. Analysis of the one-dimensional (1D) correlation function derived from SAXS data suggested that the previously crystallized P3BT segments could confine the size of P3DDT crystalline subdomains and possibly contribute to the rapid increase in the P3DDT crystallinity.

A synchrotron small-angle X-ray scattering study on structures of 1,3:2,4-dibenzylidene sorbitol gels

Abstract Synchrotron small-angle X-ray scattering (SAXS) and polarized optical microscopy were used to investigate structures of 1,3:2,4-dibenzylidene sorbitol (DBS) gels in various solvents at temperatures above and below the sol–gel transition temperatures. DBS formed a transparent gel in acetophenone, while it formed a turbid gel in ionic liquids such as 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide [BMIm][TFSI] and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIm][TFSI]. Synchrotron SAXS analysis reveals that the transparent gel in acetophenone forms fibrillar aggregates composed of circular cross-section with a radius ranging from 34 to 43 A depending upon temperature, while the turbid gels in the ionic liquids form thicker nanofibrils in comparison with the transparent gel. As temperature approached the sol–gel transition temperature, the fibrillar aggregates in both gels gradually melted. As a consequence, the cross-sectional size of the fibrillar aggregates for the transparent gel became more homogeneous due to melting of thermodynamically unstable thinner fibrils, while the spatial inhomogeneities of the aggregates for the turbid gel became remarkable near the sol–gel transition temperature.

Nematic director reorientation at solid and liquid interfaces under flow: SAXS studies in a microfluidic device.

In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane is measured using a 2D detector. At moderate-to-high flow rates, the nematic director is predominantly aligned in the flow direction, but with a small tilt angle of ∼±11° in the velocity gradient direction. The director tilt angle is constant throughout most of the channel width but switches sign when crossing the center of the channel, in agreement with the Ericksen–Leslie–Parodi (ELP) theory. At low flow rates, boundary conditions begin to dominate, and a flow profile resembling the escaped radial director configuration is observed, where the director is seen to vary more smoothly from the edges (with homeotropic alignment) to the center of the channel. In the second experiment, hydrodynamic focusing is employed to confine the nematic phase into a sheet of liquid sandwiched between two layers of Triton X-100 aqueous solutions. The average nematic director orientation shifts to some extent from the flow direction toward the liquid boundaries, although it remains unclear if one tilt angle is dominant through most of the nematic sheet (with abrupt jumps near the boundaries) or if the tilt angle varies smoothly between two extreme values (∼90 and 0°). The technique presented here could be applied to perform high-throughput measurements for assessing the influence of different surfactants on the orientation of nematic phases and may lead to further improvements in areas such as boundary lubrication and clarifying the nature of defect structures in LC displays.

Uptake of the butyrate receptors, GPR41 and GPR43, in lipidic bicontinuous cubic phases suitable for in meso crystallization

The butyrate G-protein coupled receptors (GPCRs), GPR41 and GPR43, have been implicated in colorectal cancer and leptin production. To date their function has not been elucidated as low levels of protein expression and difficulties in producing diffraction quality crystals have hindered their structural determination. In meso crystallization, which uses an artificial lipid membrane matrix to facilitate crystal growth, is becoming an increasingly successful crystallization technique, particularly for GPCRs. We report herein the lipid membrane matrix structural characterization for GPR41 and GPR43 within two lipid self-assembly systems (monoolein and phytantriol) commonly used for in meso crystallization and comment on their suitability for crystallizing these GPCRs. Synchrotron small angle X-ray scattering (SAXS) studies were used to determine the initial phase and uptake of these receptors within the lipid matrix and investigate the role of cholesterol in this process. The self-assembled lipid nanostructure was retained in the presence of GPR43 for both lipids but was destabilized for GPR41 in the phytantriol lipid system. The structural changes to the lipid matrix upon protein incorporation were greater for cholesterol-doped systems, potentially indicative of increased receptor uptake.

Advanced glycation end-products reduce collagen molecular sliding to affect collagen fibril damage mechanisms but not stiffness.

Advanced glycation end-products (AGE) contribute to age-related connective tissue damage and functional deficit. The documented association between AGE formation on collagens and the correlated progressive stiffening of tissues has widely been presumed causative, despite the lack of mechanistic understanding. The present study investigates precisely how AGEs affect mechanical function of the collagen fibril – the supramolecular functional load-bearing unit within most tissues. We employed synchrotron small-angle X-ray scattering (SAXS) and carefully controlled mechanical testing after introducing AGEs in explants of rat-tail tendon using the metabolite methylglyoxal (MGO). Mass spectrometry and collagen fluorescence verified substantial formation of AGEs by the treatment. Associated mechanical changes of the tissue (increased stiffness and failure strength, decreased stress relaxation) were consistent with reports from the literature. SAXS analysis revealed clear changes in molecular deformation within MGO treated fibrils. Underlying the associated increase in tissue strength, we infer from the data that MGO modified collagen fibrils supported higher loads to failure by maintaining an intact quarter-staggered conformation to nearly twice the level of fibril strain in controls. This apparent increase in fibril failure resistance was characterized by reduced side-by-side sliding of collagen molecules within fibrils, reflecting lateral molecular interconnectivity by AGEs. Surprisingly, no change in maximum fibril modulus (2.5 GPa) accompanied the changes in fibril failure behavior, strongly contradicting the widespread assumption that tissue stiffening in ageing and diabetes is directly related to AGE increased fibril stiffness. We conclude that AGEs can alter physiologically relevant failure behavior of collagen fibrils, but that tissue level changes in stiffness likely occur at higher levels of tissue architecture.

Endophilin-A1 BAR domain interaction with arachidonyl CoA.

Endophilin-A1 belongs to the family of BAR domain containing proteins that catalyze membrane remodeling processes via sensing, inducing and stabilizing membrane curvature. We show that the BAR domain of endophilin-A1 binds arachidonic acid and molds its coenzyme A (CoA) activated form, arachidonyl-CoA into a defined structure. We studied low resolution structures of endophilin-A1-BAR and its complex with arachidonyl-CoA in solution using synchrotron small-angle X-ray scattering (SAXS). The free endophilin-A1-BAR domain is shown to be dimeric at lower concentrations but builds tetramers and higher order complexes with increasing concentrations. Extensive titration SAXS studies revealed that the BAR domain produces a homogenous complex with the lipid micelles. The structural model of the complexes revealed two arachidonyl-CoA micelles bound to the distal arms of an endophilin-A1-BAR dimer. Intriguingly, the radius of the bound micelles significantly decreases compared to that of the free micelles, and this structural result may provide hints on the potential biological relevance of the endophilin-A1-BAR interaction with arachidonyl CoA.

Self-assembly of biaxial discorectangular lead carbonate nanosheets into stacked ribbons studied by SAXS and HAADF-STEM tomographic tilt series.

The self-assembling behaviour of 2.6 nm thin PbCO3 nanoplatelets with discorectangular shape and uniform width and thickness occurring after their formation in nonionic water-in-oil microemulsions has been investigated using synchrotron small angle X-ray scattering (SAXS) and (scanning) transmission electron microscopy ((S)TEM). The presence of attractive depletion forces originating from the ubiquitous microemulsion droplets triggers a new type of superstructure at low particle concentration. Instead of the universally observed formation of face-to-face assembled lamellar mesostructures, the nanosheets self-organise into extended ribbon structures, whereby each on top lying sheet is displaced by a constant shift in the length and width directions leading to a so far unprecedented staggered zigzag-type stack assembly with restricted height. This type of stacking gives rise to a complex interference pattern in the isotropic small angle scattering of the stacked ribbon assemblies (SRAs) in reverse micellar solution. Different to the, for lamellar-structured nanosheets typical, diffraction peaks at multiples of the wave vector corresponding to one particular repeat distance, the scattering peaks measured in this study are asymmetric, displaying a shoulder on their low wave vector side. The asymmetric shape of the observed face-to-face correlation peaks indicates that the SRAs do not extend in one direction only. Their scattering behaviour is analysed by expanding the Kratky-Porod structure factor for stacking plates into three dimensions. High-angle annular dark-field (HAADF)-STEM tilt series have complementary been acquired to retrieve three-dimensional structural information on the SRAs in the dry state and to confirm the model used for the refinement of the SAXS data.

Relationship between helical aggregates and polymorphs in a 12-hydroxystearic acid gel: their thermal stability and formation kinetics

Structures of 12-hydroxystearic acid (12-HSA)/phenyl methyl silicone gel and the gelation process were investigated by means of synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and polarized optical microscopy (POM). Spherulite structures were formed at low temperatures, while helical aggregates without branching were observed at high temperatures. The morphological transformation from spherulites into helical aggregates occurred during a heating process but not vice versa. Combined synchrotron SAXS and POM studies reveal that the morphological transformation is associated with polymorphs of 12-HSA crystal. Thermal stability and formation kinetics of the aggregates and the polymorphs are discussed in the text.

SAXS Analysis of Catalyst Degradation in High Temperature PEM Fuel Cells Subjected to Accelerated Ageing Tests

AbstractThe loss in performance during fuel cell operation is one of the critical factors that hamper fuel cells commercialization. This paper presents a research activity related to high temperature polymer electrode membrane fuel cell (HT‐PEMFC) degradation. The aim of the study is to investigate catalyst degradation of membrane electrode assemblies (MEAs) subjected to load cycles. Two HT‐PEM MEAs have been subjected to accelerated ageing tests based on load cycling. The cycles profile has been chosen in order to enhance catalyst degradation. Both the tests show a fuel cell performance loss lower than 30 mV after 100,000 cycles at 600 mA cm−2. In order to analyze the catalyst evolution, synchrotron small angle X‐ray scattering (SAXS) has been employed. The catalyst degradation of the two conditioned samples has been compared with the data obtained from a new MEA that has been used as reference sample. The SAXS results showed a mean size increase of the platinum nanoparticles up to the 100%.

Phase Behavior of Poly(4-hydroxystyrene-block-styrene) Synthesized by Living Anionic Polymerization of an Acetal Protected Monomer

We have synthesized a series of poly(4-(2-tetrahydropyranyloxy)styrene) [P(OTHPSt)] homopolymers by living anionic polymerization of the protected monomer (OTHPSt) in tetrahydrofuran at −78 °C, with excellent control over molecular weight and dispersity. The high Tg of P(OTHPSt) led to facile purification and isolation of the polymer as a powder. Characterization of the POTHPSt homopolymer by nuclear Overhauser effect spectroscopy confirms the strong preference for the axial position of the relatively sterically demanding alkoxy phenyl group. By sequential monomer addition, a series of low to high molecular weight P(OTHPSt-b-styrene) BCPs with narrow dispersities were synthesized. Quantitative deprotection of the THP groups yielded poly(4-hydroxystyrene-b-styrene) with tunable molecular weights and compositions. The solid-state and melt-phase self-assembly of these diblocks was investigated using synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Mean-field theory analysis of the temperature-dependent correlation-hole scattering for a disordered diblock was used to determine the interaction parameter as χHS/S(T) = (4.39 ± 0.83)/T + (0.109 ± 0.002), which is approximately 4 times larger than that of poly(styrene-b-methyl methacrylate) with the same disproportionately high contribution of entropy to the free energy of mixing.

Investigations in annealing effects on structure and properties of β-isotactic polypropylene with X-ray synchrotron experiments

The influence of annealing on the microstructure and mechanical properties of β-form isotactic polypropylene (iPP) was investigated via in situ synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). Transition of β-iPP to α-iPP was investigated via recrystallization at high annealing temperatures (Ta > 120 °C). And crystallinity, crystal sizes, and long period of ordered structure increased with increasing annealing temperature. Abrupt changes were found in both mechanical properties and structural features at the same Ta range (∼120 °C). The in situ synchrotron SAXS and WAXD shows that the destruction of b phase at yielding and after yielding should account for the ductility of β-iPP. The thermodynamics and kinetics of annealing were investigated with DSC and X-ray synchrotron experiments. A characteristic annealing time was investigated, which measures the rate of phase evolution in annealing of β-iPP. Eventually, a hypothesized model can be used to describe the property/structure relations during this process.

Melting and β to α transition behavior of β-PBA and the β-PBA/PVPh blend investigated by synchrotron SAXS and WAXD

Synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) are used to monitor the melting and βα transition behavior of β-PBA and the β-PBA/PVPh blend during the heating process. After melt recrystallized at 10 °C, the β crystals are obtained. The lamellar thickness of β crystals in the neat PBA is similar to that in its PBA/PVPh blend and the long period for the former one is shorter than the latter one. At lower heating rate, α crystals start to appear at 39 °C suggesting the βα phase transition occurs. Compared with the neat PBA, the β-PBA in the blend transits to α crystals at a higher rate. At a higher heating rate, β crystals melt directly. Both at the lower and higher heating rate, the crystal structure along the a-axis is much more stable than that along b-axis in the β crystals. Moreover, the heating rate does not play a role in the melting mechanism of the β crystals. The melting of the β crystals in the neat PBA and its PBA/PVPh blend chose different mechanisms. The melting mechanism of the β crystals in the PBA/PVPh blend is attributed to the sequential melting. On the contrary, the melting of the β phase in the neat PBA is complex. Besides the peak of q = 0.54 nm−1, a new peak appears at q = 0.32 nm−1 in the SAXS profiles in the heating process suggesting the appearance of a population with a larger long period. The presence of two peaks is caused by the coexistence of two kinds of lamellar stacks. And the partial melting of thinner β-PBA lamellae occurs firstly in one kind of lamellar stacks.

Labeling phospholipid membranes with lipid mimetic luminescent metal complexes

Lipid-mimetic metallosurfactant based luminophores are promising candidates for labeling phospholipid membranes without altering their biophysical characteristics. The metallosurfactants studied exhibit high structural and physicochemical similarity to phospholipid molecules, designed to incorporate into the membrane structure without the need for covalent attachment to a lipid molecule. In this work, two lipid-mimetic phosphorescent metal complexes are described: [Ru(bpy)2(dn-bpy)]2+ and [Ir(ppy)2(dn-bpy)]+ where bpy is 2,2′-bipyridine, dn-bpy is 4,4′-dinonyl-2,2′-bipyridine and ppy is 2-phenylpyridine. Apart from being lipid-mimetic in size, shape and physical properties, both complexes exhibit intense photoluminescence and enhanced photostability compared with conventional organic fluorophores, allowing for prolonged observation. Moreover, the large Stokes shift and long luminescence lifetime associated with these complexes make them more suitable for spectroscopic studies. The complexes are easily incorporated into dimyristoil-phosphatidyl-choline (DMPC) liposomes by mixing in the organic solvent phase. DLS reveals the labeled membranes form liposomes of similar size to that of neat DMPC membrane. Synchrotron Small-Angle X-ray Scattering (SAXS) measurements confirmed that up to 5% of either complex could be incorporated into DMPC membranes without producing any structural changes in the membrane. Fluorescence microscopy reveals that 0.5% label content is sufficient for imaging. Atomic Force Microscopic imaging confirms that liposomes of the labeled bilayers on a mica surface can fuse into a flat lamellar membrane that is morphologically identical to neat lipid membranes. These results demonstrate the potential of such lipid-mimetic luminescent metal complexes as a new class of labels for imaging lipid membranes.

Crystal size shrinking in radiation-induced crosslinking of polytetrafluoroethylene: Synchrotron small angle X-ray scattering and scanning electron microscopy analysis

The crystal structure of crosslinked polytetrafluoroethylene (XPTFE) and its morphological variations as compared with pure PTFE were investigated using differential scanning calorimetry, synchrotron small angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The XPTFE samples were obtained by irradiating PTFE at the melt state using different radiation doses. Results showed that the melting temperature of the XPTFE decreases with the increase in radiation dose. The crystal melting enthalpy increases under low-dose irradiation. The scattering intensity decreases with the increase in radiation dose, which indicates the decrease in crystal size. Based on the SAXS patterns, the XPTFE crystallite size is smaller than the PTFE crystallite size. The difference in crystal sizes is more pronounced for XPTFE obtained under high radiation doses. This finding is confirmed by the SEM images of the XPTFE fractured surfaces. These results provide a reasonable explanation for the improved transparency and the relatively low crystallinity and high wear resistance of XPTFE compared with PTFE.

Preparation of Ag nanospheres filled with Cu

Surface properties of Ag nanoparticles may not be perturbed when they are filled with the relatively cheap Cu. To better understand how Ag can be coated on Cu, growth of the Cu and Ag bimetal during the temperature-programmed carbonisation (TPC) of Ag+- and Cu2+-β-cyclodextrin (CD) complexes having the Cu/Ag ratios of 0.5, 1 and 2 was studied by in situ synchrotron small angle X-ray scattering (SAXS) spectroscopy. The SAXS spectra provide the detailed structural changes corresponding to the growth of Ag and Cu nanoparticles as the Ag+- and Cu2+-CD complexes are carbonised at the temperature range of 363–513 K. It seems that Cu having a relatively high surface free energy is enriched in the core of the cherry-like Cu@Ag bimetal nanoparticles. The Cu@Ag bimetals are encapsulated in the carbon-shell formed from carbon unconsumed in the oxidation of CD during TPC. A rapid growth of the bimetal nanoparticles occurs at 393–423 K. As Ag+ and Cu2+ are reduced during the CD oxidation, the Ag nanospheres are filled with Cu, and eventually encapsulated in the carbon-shell. Note that the carbon-shell coated on Cu@Ag can be removed by steam reforming at 573 K.

Understanding Solvothermal Crystallization of Mesoporous Anatase Beads by In Situ Synchrotron PXRD and SAXS

Submicrometer-sized mesoporous anatase (TiO2) beads have shown high efficiency as electrodes for dye-sensitized solar cells and are recoverable photocatalysts for the degradation of organic pollutants. The detailed mechanism for crystallization of the amorphous TiO2/hexadecylamine (HDA) hybrid beads occurring during the solvothermal process needs to be understood so that reaction parameters can be rationally refined for optimizing the synthesis. In this work, the solvothermal crystallization was monitored by in situ synchrotron powder X-ray diffraction (PXRD) and synchrotron small-angle X-ray scattering (SAXS) techniques. In situ PXRD provided crystallization curves, as well as the time evolution of anatase crystallite mean size and size distribution, and in situ SAXS provided complementary information regarding the evolution of the internal bead structure and the formation of pores during the course of the solvothermal process. By exploring the effects of temperature (140–180 °C), bead diameter (300 and ...