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SAXS
Terms modified by SAXS Selected AbstractsBiomarker discovery in rat plasma for estrogen receptor-, actionELECTROPHORESIS, Issue 23 2005Tom G. Holt Dr. Abstract To support in vivo screening efforts for estrogen receptor (ER) subtype selective therapeutic agents, we initiated work to discover surrogate markers (biomarkers) in blood plasma that would change in response to ER subtype-specific action. We used a proteomic approach employing strong anion exchange chromatography (SAX), PAGE, and MS to identify potential plasma markers for selective ER-, action. The methodology was used to compare blood from vehicle-treated rats to blood from rats treated with either 17,-estradiol (an ER-,/ER-, agonist) or compound 1 (17,-ethynyl-[3,2-c]pyrazolo-19-nor-4-androstene-17,-ol, an ER-,-selective agonist). Blood samples were first fractionated by SAX to separate fractions containing dominant common plasma proteins from fractions enriched for less-abundant plasma proteins. 1-D PAGE analysis of fractions depleted of dominant plasma proteins revealed treatment-specific changes in protein profiles. Protein bands that changed reproducibly in response to ER-, action were excised from the gel, separated by capillary LC, and identified by microspray ESI-MS. Using this method, the plasma levels of two proteins, transthyretin and apolipoprotein E, were shown to decrease in response to ER-, agonism. The method lacked the sensitivity to identify the known, 1000-fold less-abundant, estrogenic marker prolactin (PRL). However, using a commercial RIA and immunoblots, we showed that PRL levels increase significantly in response to treatment with the ER-, selective agonist, compound 1. [source] Determination of avoparcin in animal tissues and milk using LC-ESI-MS/MS and tandem-SPEJOURNAL OF SEPARATION SCIENCE, JSS, Issue 22 2008Koichi Inoue Abstract A highly sensitive and selective method using LC-ESI-MS/MS and tandem-SPE was developed to detect trace amounts of avoparcin (AV) antibiotics in animal tissues and milk. Data acquisition using MS/MS was achieved by applying multiple reaction monitoring of the product ions of [M + 3H]3+ and the major product ions of AV-, and -, at m/z 637 , 86/113/130 and m/z 649 , 86/113/130 in ESI(+) mode. The calculated instrumental LODs were 3 ng/mL. The sample preparation was described that the extraction using 5% TFA and the tandem-SPE with an ion-exchange (SAX) and InertSep C18-A cartridge clean-up enable us to determine AV in samples. Ion suppression was decreased by concentration rates of each sample solution. These SPE concentration levels could be used to detect quantities of 5 ppb (milk), 10 ppb (beef), and 25 ppb (chicken muscle and liver). The matrix matching calibration graphs obtained for both AV-, (r >0.996) and -, (r >0.998) from animal tissues and milk were linear over the calibration ranges. AV recovery from samples was higher than 73.3% and the RSD was less than 12.0% (n = 5). [source] Large-scale phosphoproteome analysis of human liver tissue by enrichment and fractionation of phosphopeptides with strong anion exchange chromatographyPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 7 2008Guanghui Han Abstract The mixture of phosphopeptides enriched from proteome samples are very complex. To reduce the complexity it is necessary to fractionate the phosphopeptides. However, conventional enrichment methods typically only enrich phosphopeptides but not fractionate phosphopeptides. In this study, the application of strong anion exchange (SAX) chromatography for enrichment and fractionation of phosphopeptides was presented. It was found that phosphopeptides were highly enriched by SAX and majority of unmodified peptides did not bind onto SAX. Compared with Fe3+ immobilized metal affinity chromatography (Fe3+ -IMAC), almost double phosphopeptides were identified from the same sample when only one fraction was generated by SAX. SAX and Fe3+ -IMAC showed the complementarity in enrichment and identification of phosphopeptides. It was also demonstrated that SAX have the ability to fractionate phosphopeptides under gradient elution based on their different interaction with SAX adsorbent. SAX was further applied to enrich and fractionate phosphopeptides in tryptic digest of proteins extracted from human liver tissue adjacent to tumorous region for phosphoproteome profiling. This resulted in the highly confident identification of 274 phosphorylation sites from 305 unique phosphopeptides corresponding to 168 proteins at false discovery rate (FDR) of 0.96%. [source] Serum biomarker profiling by solid-phase extraction with particle-embedded micro tips and matrix-assisted laser desorption/ionization mass spectrometry,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2008Arti Navare One of the main challenges in high-throughput serum profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is the development of proteome fractionation approaches that allow the acquisition of reproducible profiles with a maximum number of spectral features and minimum interferences from biological matrices. This study evaluates a new class of solid-phase extraction (SPE) pipette tips embedded with different chromatographic media for fractionation of model protein digests and serum samples. The materials embedded include strong anion exchange (SAX), weak cation exchange (WCX), C18, C8, C4, immobilized metal affinity chromatography (IMAC) and zirconium dioxide particles. Simple and rapid serum proteome profiling protocols based on these SPE micro tips are described and tested using a variety of MALDI matrices. We show that different types of particle-embedded SPE micro tips provide complementary information in terms of the spectral features detected for , -casein digests and control human serum samples. The effect of different sample pretreatments, such as serum dilution and ultrafiltration using molecular weight cut-off membranes, and the reproducibility observed for replicate experiments, are also evaluated. The results demonstrate the usefulness of these simple SPE tips combined with offline MALDI-TOF MS for obtaining information-rich serum profiles, resulting in a robust, versatile and reproducible open-source platform for serum biomarker discovery. Copyright © 2008 John Wiley & Sons, Ltd. [source] Determination of the uronic acid composition of seaweed dietary ,bre by HPLCBIOMEDICAL CHROMATOGRAPHY, Issue 2 2004D. I. Sánchez-Machado Abstract A high-performance liquid chromatographic (HPLC) method is described for determination of the ratio of , - d -mannuronic acid to , - l -guluronic acid (M/G ratio) in dietary ,bre of edible seaweeds. Total dietary ,bre (TDF) content was determined gravimetrically. The TDF fraction was hydrolysed with 12 m and 1 m H2SO4, then neutralized with AG 4 × 4 resin. The uronic acids were separated in a Tracer Extrasil SAX 5 µm column (25 cm × 4 mm) at 35°C, with 2 mm KH2PO4 containing 5% methanol as mobile phase at a ,ow rate of 1.5 mL/min. The detection wavelength was UV 210 nm. The chromatographic identi,cations of , - d -mannuronic acid and , - l -guluronic acid were con,rmed by liquid chromatography,mass spectrometry (LC-MS). The method precision was 1.4% for , - d -mannuronic acid and 3.5% for , - l -guluronic acid. The method was used to determine M/G ratio in canned seaweeds (Saccorhiza polyschides and Himanthalia elongata) and in dried seaweeds (H. elongata, Laminaria ochroleuca, Undaria pinnati,da, Palmaria sp. and Porphyra sp.). Copyright © 2003 John Wiley & Sons, Ltd. [source] Direct Synthesis of Zr-Containing Hybrid Periodic Mesoporous Organosilicas with Tunable Zirconium ContentEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2007Shang-Ru Zhai Abstract Highly ordered Zr-containing periodic mesoporous organosilicas (ZrPMO) with different Zr/Si ratios were successfully synthesized, for the first time, by employing a ZrOCl2/NaCl combination as the promoting agent and by simply adjusting the molar ratio of the zirconium species to the organosilica precursor; no addition of mineral acids was necessary. The effect of preparation parameters on the structural and textural properties were carefully investigated by using different ratios of NaCl/Si and Zr/Si. It was found that both salts are essential for this system and highly ordered ZrPMOs can be prepared within fairly wide Si/Zr ratios (5,100) while keeping the NaCl/Si ratio constant. To prove the effectiveness of this synthetic pathway with a higher Zr incorporation, ZrPMO materials were also synthesized under strongly acidic conditions for the purpose of comparison. The synthesized ZrPMO materials were thoroughly characterized by ICP-AES, SAXS, N2 sorption, TEM, SEM, 13C CP/29Si MAS NMR spectroscopy, XPS, and TGA. Elemental analyses show that the amount of Zr incorporated into ZrPMO, which was synthesized under mild conditions, is greater than that obtained in a strongly acidic environment, and the Zr content, with a Si/Zr ratio up to 12, is close to that in the initial gel composition. A plausible assembly mechanism based on the synergistic effect of both "nonhydrolyzable" (NaCl) and "hydrolyzable" (ZrOCl2) inorganic salts was discussed in detail, where the "salting out" effect and self-generated acidity from both inorganic salts, respectively, are believed to be key factors for the formation of ordered SBA-15-type ZrPMO materials under the synthetic conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] In situ Investigation of Structural Changes during Deformation and Fracture of Polymers by Synchrotron SAXS and WAXS,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Konrad Schneider By simultaneous mechanical characterisation and synchrotron wide-angle x-ray scattering (WAXS) and small-angle x-ray scattering (SAXS), it is possible to characterise on-line local changes in a polymer's structure with a rather-high time and space resolution, together with the mechanical properties. In this contribution, we discuss the experimental requirements for such investigations as well as three examples. The evolution of structural features during tensile deformation of a polyethylene copolymer, as depicted by WAXS (top) and SAXS (bottom) are shown in the figure. The deformation leads to a martensitic transformation from the orthorhombic to monoclinic system and the formation of nanocavities. [source] Synthesis, Morphology, and Properties of Poly(3-hexylthiophene)- block -Poly(vinylphenyl oxadiazole) Donor,Acceptor Rod,Coil Block Copolymers and Their Memory Device ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Yi-Kai Fang Abstract Novel donor,acceptor rod,coil diblock copolymers of regioregular poly(3-hexylthiophene) (P3HT)- block -poly(2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiaz-ole) (POXD) are successfully synthesized by the combination of a modified Grignard metathesis reaction (GRIM) and atom transfer radical polymerization (ATRP). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low-lying highest occupied molecular orbital (HOMO) energy level (,6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT- b -POXD exhibits a non-volatile bistable memory or insulator behavior depending on the P3HT/POXD block ratio and the resulting morphology. The ITO/P3HT44 - b - POXD18/Al memory device shows a non-volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor-acceptor rod-coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications. [source] Supramolecular Soft Adhesive MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Jérémie Courtois Abstract The rheological and adhesive properties of bis-urea functionalized low-molecular-weight polyisobutylenes (PIBUT) are investigated. The polymers, which can interact through supramolecular hydrogen bonds, can self-organize over times of the order of days at room temperature. This organized structure has been identified by small angle X-ray scattering (SAXS) and its rheological properties indicate the behaviour of a soft viscoelastic gel. The ordered structure can be disrupted by temperature and shear so that at 80,°C, the material behaves as a highly viscoelastic fluid and no SAXS peak is observed. When cooled back at room temperature, the PIBUT retrieves its ordered structure and gel properties after 20 h of annealing. This very slow molecular dynamics gives PIBUT a highly dissipative nature upon deformation, which combined with strongly interacting moieties results in very interesting adhesive properties both on steel surfaces but more importantly on typical low adhesion surfaces such as silicone. A strategy based on the controlled incorporation of supramolecular bonds in a covalently crosslinked network appears promising for the development of a new generation of highly interacting and dissipative soft adhesives. [source] Structural basis for distinct roles of Lys63- and Lys48-linked polyubiquitin chainsGENES TO CELLS, Issue 10 2004Takeshi Tenno Ubiquitination, a modification in which single or multiple ubiquitin molecules are attached to a protein, serves as a signalling function that controls a wide variety of cellular processes. To date, two major forms of polyubiquitin chain have been functionally characterized, in which the isopeptide bond linkages involve Lys48 or Lys63. Lys48-linked polyubiquitin tagging is mostly used to target proteins for degradation by the proteasome, whereas Lys63-linked polyubiquitination has been linked to numerous cellular events that do not rely on degradative signalling via the proteasome. Apparently linkage-specific conformations of polyubiquitin chains are important for these cellular functions, but the structural bases distinguishing Lys48- and Lys63-linked chains remain elusive. Here, we report NMR and small-angle X-ray scattering (SAXS) studies on the intersubunit interfaces and conformations of Lys63- and Lys48-linked di- and tetraubiquitin chains. Our results indicate that, in marked contrast to Lys48-linked chains, Lys63-linked chains are elongated molecules with no stable non-covalent intersubunit interfaces and thus adopt a radically different conformation from that of Lys48-linked chains. [source] Plasmonic Enhancement or Energy Transfer?ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Its Potential for Light-Emitting Devices, Lanthanide-Doped Silicate Glasses, On the Luminescence of Gold-, Silver- Abstract With the technique of synchrotron X-ray activation, molecule-like, non-plasmonic gold and silver particles in soda-lime silicate glasses can be generated. The luminescence energy transfer between these species and lanthanide(III) ions is studied. As a result, a significant lanthanide luminescence enhancement by a factor of up to 250 under non-resonant UV excitation is observed. The absence of a distinct gold and silver plasmon resonance absorption, respectively, the missing nanoparticle signals in previous SAXS and TEM experiments, the unaltered luminescence lifetime of the lanthanide ions compared to the non-enhanced case, and an excitation maximum at 300,350,nm (equivalent to the absorption range of small noble metal particles) indicate unambiguously that the observed enhancement is due to a classical energy transfer between small noble metal particles and lanthanide ions, and not to a plasmonic field enhancement effect. It is proposed that very small, molecule-like noble metal particles (such as dimers, trimers, and tetramers) first absorb the excitation light, undergo a singlet-triplet intersystem crossing, and finally transfer the energy to an excited multiplet state of adjacent lanthanide(III) ions. X-ray lithographic microstructuring and excitation with a commercial UV LED show the potential of the activated glass samples as bright light-emitting devices with tunable emission colors. [source] Phase Reorganization in Self-Assembled Systems Through Interparticle Material Transfer,ADVANCED MATERIALS, Issue 10 2007C. Moitzi Transfer of material occurs when internally nanostructured emulsion droplets of different composition are mixed. This happens without droplet fusion. As the internal structure is dependent on the composition, the transfer can be followed by monitoring these changes using time-resolved small angle X-ray scattering (SAXS; see figure). [source] Dynamical scaling in fractal structures in the aggregation of tetraethoxysilane-derived sonogelsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5-1 2010Dimas R. Vollet Dynamical scaling properties in fractal structures were investigated from small-angle X-ray scattering (SAXS) data of the kinetics of aggregation in silica-based gelling systems. For lack of a maximum in the SAXS intensity curves, a characteristic correlation distance , was evaluated by fitting a particle scattering factor model valid for polydisperse coils of linear chains and f -functional branched polycondensates in solution, so the intensity at q = ,,1, I(,,1, t), was considered to probe dynamical scaling properties. The following properties have been found: (i) the SAXS intensities corresponding to different times t, I(q, t), are given by a time-independent function F(q,) = I(q, t),,D/Q, where the scattering invariant Q has been found to be time-independent; (ii) , exhibited a power-law behavior with time as ,,t,, the exponent , being close to 1 but diminishing with temperature; (iii) I(,,1, t) exhibited a time dependence given by I(,,1, t) ,t,, with the exponent , found to be around 2 but diminishing with temperature, following the same behavior as the exponent ,. In all cases, ,/, was quite close to the fractal dimension D at the end of the studied process. This set of findings is in notable agreement with the dynamical scaling properties. [source] Quality control of protein standards for molecular mass determinations by small-angle X-ray scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010Shuji Akiyama Small-angle X-ray scattering (SAXS) is a powerful technique with which to evaluate the size and shape of biological macromolecules in solution. Forward scattering intensity normalized relative to the particle concentration, I(0)/c, is useful as a good measure of molecular mass. A general method for deducing the molecular mass from SAXS data is to determine the ratio of I(0)/c of a target protein to that of a standard protein with known molecular mass. The accuracy of this interprotein calibration is affected considerably by the monodispersity of the prepared standard, as well as by the precision in estimating its concentration. In the present study, chromatographic fractionation followed by hydrodynamic characterization is proposed as an effective procedure by which to prepare a series of monodispersed protein standards. The estimation of molecular mass within an average deviation of 8% is demonstrated using monodispersed bovine serum albumin as a standard. The present results demonstrate the importance of protein standard quality control in order to take full advantage of interprotein calibration. [source] Determination of the molecular weight of proteins in solution from a single small-angle X-ray scattering measurement on a relative scaleJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2010H. Fischer This paper describes a new and simple method to determine the molecular weight of proteins in dilute solution, with an error smaller than ,10%, by using the experimental data of a single small-angle X-ray scattering (SAXS) curve measured on a relative scale. This procedure does not require the measurement of SAXS intensity on an absolute scale and does not involve a comparison with another SAXS curve determined from a known standard protein. The proposed procedure can be applied to monodisperse systems of proteins in dilute solution, either in monomeric or multimeric state, and it has been successfully tested on SAXS data experimentally determined for proteins with known molecular weights. It is shown here that the molecular weights determined by this procedure deviate from the known values by less than 10% in each case and the average error for the test set of 21 proteins was 5.3%. Importantly, this method allows for an unambiguous determination of the multimeric state of proteins with known molecular weights. [source] Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sitesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2009Xinguo Hong Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the program GASBOR at 5,Å resolution (qmax = 1.25,Å,1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8,Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2, level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax = 0.25,Å,1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination of FSEARCH and WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement. [source] Small-angle energy-dispersive X-ray scattering using a laboratory-based diffractometer with a conventional sourceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2007Giuseppe Portale The use of polychromatic Bremsstrahlung X-rays generated by commercial tubes for energy-dispersive small-angle scattering measurements has not been extensively discussed in the literature, mainly because of some difficulties associated with it. If a suitable experimental setup is chosen and concomitant phenomena are taken into account for correcting the observed X-ray patterns, energy-dispersive small-angle X-ray scattering (SAXS) may become an interesting alternative to conventional measurements based on monochromatic beams. Energy-dispersive SAXS experiments carried out on protein solutions, micelles, semicrystalline polymers and catalytic systems are discussed to illustrate the new opportunities offered by this technique as well as its limitations. [source] Structural characterization of N -lignoceroyl (C24:0) sphingomyelin bilayer membranes: a re-evaluationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Hiroshi Takahashi Sphingomyelin (SM) is a membrane lipid and plays important roles in signaling, protein trafficking, cell growth and death. The structure of the bilayer of a hydrated highly asymmetric SM, N -lignoceroyl (C24:0) SM, has been investigated with X-ray diffraction (XRD), simultaneous small-angle X-ray scattering (SAXS), wide-angle XRD and SAXS. At temperatures between two endothermic transitions of hydrated C24:0 SM bilayers, the C24:0 SM formed a ripple phase with the ripple periodicity of ~12,14,nm. At about three months incubation at 277,K, the formation of a stable phase with a short lamellar spacing of 5.62,nm was induced. Based upon the structures revealed by this study and the phase behavior, intermolecular interactions between C24:0 SM molecules in the bilayer membrane are discussed. [source] Iron K -edge anomalous small-angle X-ray scattering at 15-ID-D at the Advanced Photon SourceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Nigel Kirby Small-angle X-ray scattering (SAXS) is an ideal technique for characterizing inorganic nanoparticles in biological specimens large enough to be representative of tissues. As tissues consist of complex mixtures of structures, identifying particular structural features from single-wavelength scattering data can be problematic. Synchrotron SAXS can supply element-specific structural information in complex samples, using anomalous scattering close to absorption edges. Anomalous dispersion is a secondary effect that produces relatively subtle changes in scattering patterns. In order to utilize this effect for anomalous SAXS analysis, stringent control of instrument performance is required. This work outlines the development of high-quality data collection and processing strategies for Fe K -edge anomalous SAXS on the ChemMatCARS beamline at the Advanced Photon Source (APS), Chicago, with an emphasis on intensity normalization. The methods reported here were developed during a study of iron-loaded mammal tissues, but could equally well be applied to other complex specimens. [source] The application of distance distribution functions to structural analysis of core,shell particlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Oleksandr O. Mykhaylyk The structure of core,shell latex particles of polymethylmethacrylate (the core) and polyurethane (the shell) have been investigated by methods of small-angle X-ray scattering (SAXS) and atom-force microscopy. A set of SAXS patterns has been obtained using contrast variation method. Indirect methods have been used to follow the evolution of distance distribution functions from SAXS for lattices in various sucrose solutions over a range of solution density, yielding structural parameters of the particles such as core size, shell thickness and density of the polymers including density deviations within the particle's core and shell. A model for an ensemble of core,shell particles with a normal distribution of average electron density of both the core and the shell has been developed to fit the distance distribution functions using a random search algorithm. The effects of nanophase separation in the polyurethane is estimated using Monte Carlo simulations of the distance distribution functions where the phase-separated polyurethane is represented by spherical truncated cones in a shell simulating the location of hard and soft polyurethane blocks, respectively. [source] Focusing capillary optics for use in solution small-angle X-ray scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2007Jessica S. Lamb Measurements of the global conformation of macromolecules can be carried out using small-angle X-ray scattering (SAXS). Glass focusing capillaries, manufactured at the Cornell High Energy Synchrotron Source (CHESS), have been successfully employed for SAXS measurements on the heme protein cytochrome c. These capillaries provide high X-ray flux into a spot size of tens of micrometres, permitting short exposures of small-volume samples. Such a capability is ideal for use in conjunction with microfluidic mixers, where time resolution may be determined by beam size and sample volumes are kept small to facilitate mixing and conserve material. [source] Small-angle X-ray scattering measurements of helium-bubble formation in borosilicate glassJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006Alexander Y. Terekhov Small-angle X-ray scattering (SAXS) measurements have been performed to study helium-bubble formation in borosilicate glass. Helium was introduced by He+ implantation over an energy range of 1 to 2,MeV to give a uniform distribution over ,1,µm depth. The implanted dose was varied from 9 × 1013 to 2.8 × 1016,ions,cm,2, corresponding to a local concentration range of 40 to 11200 atomic parts per million (a.p.p.m.) averaged over the implantation depth. The SAXS response was fit with the Percus,Yevick hard-sphere interaction potential to account for interparticle interference. The fits yield helium-bubble radii and helium-bubble volume fractions that vary from 5 to 15,Å and from 10,3 to 10,1, respectively, as the dose increased from 9 × 1013 to 2.8 × 1016,cm,2. The SAXS data are also consistent with maximum helium solubility with respect to bubble formation between 40 and 200 a.p.p.m. in the borosilicate glass matrix. [source] Analysis of scattering from polydisperse structure using Mellin convolutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006Norbert Stribeck This study extends a mathematical concept for the description of heterogeneity and polydispersity in the structure of materials to multiple dimensions. In one dimension, the description of heterogeneity by means of Mellin convolution is well known. In several papers by the author, the method has been applied to the analysis of data from materials with one-dimensional structure (layer stacks or fibrils along their principal axis). According to this concept, heterogeneous structures built from polydisperse ensembles of structural units are advantageously described by the Mellin convolution of a representative template structure with the size distribution of the templates. Hence, the polydisperse ensemble of similar structural units is generated by superposition of dilated templates. This approach is particularly attractive considering the advantageous mathematical properties enjoyed by the Mellin convolution. Thus, average particle size, and width and skewness of the particle size distribution can be determined from scattering data without the need to model the size distributions themselves. The present theoretical treatment demonstrates that the concept is generally extensible to dilation in multiple dimensions. Moreover, in an analogous manner, a representative cluster of correlated particles (e.g. layer stacks or microfibrils) can be considered as a template on a higher level. Polydispersity of such clusters is, again, described by subjecting the template structure to the generalized Mellin convolution. The proposed theory leads to a simple pathway for the quantitative determination of polydispersity and heterogeneity parameters. Consistency with the established theoretical approach of polydispersity in scattering theory is demonstrated. The method is applied to the best advantage in the field of soft condensed matter when anisotropic nanostructured materials are to be characterized by means of small-angle scattering (SAXS, USAXS, SANS). [source] Small-angle neutron and X-ray scattering of dispersions of oleic-acid-coated magnetic iron particlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004Karen Butter This paper describes the characterization of dispersions of oleic-acid-coated magnetic iron particles by small-angle neutron and X-ray scattering (SANS and SAXS). Both oxidized and non-oxidized dilute samples were studied by SANS at different contrasts. The non-oxidized samples are found to consist of non-interacting superparamagnetic single dipolar particles, with a lognormal distribution of iron cores, surrounded by a surfactant shell, which is partially penetrated by solvent. This model is supported by SAXS measurements on the same dispersion. Small iron particles are expected to oxidize upon exposure to air. SANS was used to study the effect of this oxidation, both on single particles, as well as on interparticle interactions. It is found that on exposure to air, a non-magnetic oxide layer is formed around the iron cores, which causes an increase of particle size. In addition, particles are found to aggregate upon oxidation, presumably because the surfactant density on the particle surfaces is decreased. [source] PRINSAS, a Windows-based computer program for the processing and interpretation of small-angle scattering data tailored to the analysis of sedimentary rocksJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004Alan L. Hinde PRINSAS is a Windows program that takes as input raw (post-reduction) small-angle neutron and small-angle X-ray scattering (SANS and SAXS) data obtained from various worldwide facilities, displays the raw curves in interactive log,log plots, and allows processing of the raw curves. Separate raw SANS and ultra-small-angle neutron scattering (USANS) curves can be combined into complete scattering curves for an individual sample. The combined curves can be interpreted and information inferred about sample structure, using built-in functions. These have been tailored for geological samples and other porous media, and include the ability to obtain an arbitrary distribution of scatterer sizes, the corresponding specific surface area of scatterers, and porosity (when the scatterers are pores), assuming spherical scatterers. A fractal model may also be assumed and the fractal dimension obtained. A utility for calculating scattering length density from the component oxides is included in the program. [source] Particle size distributions from small-angle scattering using global scattering functionsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2004G. Beaucage Control and quantification of particle size distribution is of importance in the application of nanoscale particles. For this reason, polydispersity in particle size has been the focus of many simulations of particle growth, especially for nanoparticles synthesized from aerosols such as fumed silica, titania and alumina. Single-source aerosols typically result in close to a log-normal distribution in size and micrograph evidence generally supports close to spherical particles, making such particles ideal candidates for considerations of polydispersity. Small-angle X-ray scattering (SAXS) is often used to measure particle size in terms of the radius of gyration, Rg, using Guinier's law, as well as particle surface area, S/V, from the Porod constant B and the scattering invariant Q. In this paper, the unified function is used to obtain these parameters and various moments of the particle size distribution are calculated. The particle size obtained from BET analysis of gas adsorption data directly agrees with the moment calculated from S/V. Scattering results are also compared with TEM particle-counting results. The potential of scattering to distinguish between polydisperse single particles and polydisperse particles in aggregates is presented. A generalized index of polydispersity for symmetric particles, PDI = BRg4/(1.62G), where G is the Guinier prefactor, is introduced and compared with other approaches to describe particle size distributions in SAXS, specifically the maximum-entropy method. [source] Structural refinement by restrained molecular-dynamics algorithm with small-angle X-ray scattering constraints for a biomoleculeJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004Masaki Kojima A new algorithm to refine protein structures in solution from small-angle X-ray scattering (SAXS) data was developed based on restrained molecular dynamics (MD). In the method, the sum of squared differences between calculated and observed SAXS intensities was used as a constraint energy function, and the calculation was started from given atomic coordinates, such as those of the crystal. In order to reduce the contribution of the hydration effect to the deviation from the experimental (objective) curve during the dynamics, and purely as an estimate of the efficiency of the algorithm, the calculation was first performed assuming the SAXS curve corresponding to the crystal structure as the objective curve. Next, the calculation was carried out with `real' experimental data, which yielded a structure that satisfied the experimental SAXS curve well. The SAXS data for ribonuclease T1, a single-chain globular protein, were used for the calculation, along with its crystal structure. The results showed that the present algorithm was very effective in the refinement and adjustment of the initial structure so that it could satisfy the objective SAXS data. [source] Structure of magnetic poly(oxyethylene),siloxane nanohybrids doped with FeII and FeIIIJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2003N. J. O. Silva Hybrid organic,inorganic nanocomposites doped with FeII and FeIII ions and exhibiting interesting magnetic properties have been obtained by the sol,gel process. The hybrid matrix of these ormosils (organically modified silicates), classed as di-ureasils and termed U(2000), is composed of poly(oxyethylene) chains of variable length grafted to siloxane groups by means of urea crosslinkages. Iron perchlorate and iron nitrate were incorporated in the di-ureasil matrices, leading to compositions within the range 80 ,n, 10, n being the molar ratio of ether-type O atoms per cation. The structure of the doped di-ureasils was investigated by small-angle X-ray scattering (SAXS). For FeII -doped samples, SAXS results suggest the existence of a two-level hierarchical structure. The primary level is composed of spatially correlated siloxane clusters embedded in the polymeric matrix and the secondary, coarser level consists of domains where the siloxane clusters are segregated. The structure of FeIII -doped hybrids is different, revealing the existence of iron oxide based nanoclusters, identified as ferrihydrite by wide-angle X-ray diffraction, dispersed in the hybrid matrix. The magnetic susceptibility of these materials was determined by zero-field-cooling and field-cooling procedures as functions of both temperature and field. The different magnetic features between FeII - and FeIII -doped samples are consistent with the structural differences revealed by SAXS. While FeII -doped composites exhibit a paramagnetic Curie-type behaviour, hybrids containing FeIII ions show thermal and field irreversibilities. [source] Pole figure analysis of mineral nanoparticle orientation in individual trabecula of human vertebral boneJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003Daniel Jaschouz The spongious interior of human vertebral bone consists of interconnected trabecula with a thickness of about 0.2 mm. The texture of the bone material, a collagen-mineral nanocomposite, was studied within single trabecula by collecting two-dimensional small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) data exactly at the same specimen positions with an X-ray beam of 0.2 mm diameter. Three-dimensional information was reconstructed by combining measurements with different specimen orientations. The XRD data, and for the first time also the SAXS data, were subjected to a pole figure analysis. The method provides a quantitative description of the crystallographic orientation distribution as well as the morphological orientation distribution of the plate shaped nanoparticles, both with respect to the orientation of the investigated trabecula. As a main result it could be shown that a fibre-texture exists in the trabecula, and that the plate shaped nanoparticles are aligned with the lamellae within the trabecula. [source] Small-angle X-ray scattering studies on oxide layer thickness at the porous silicon interfaceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003M. Björkqvist We have determined the thickness of an oxide layer at the p+-type porous silicon interface as a function of oxidation time, by using a small angle X-ray scattering (SAXS). The scattering experiments were carried out using a Kratky camera with a step-scanning device. Oxidation was achieved by storing the porous silicon samples in various temperatures under high relative humidity. The negative deviations from Porod's law were observed from the scattering curves of oxidized samples. The oxide layer thickness was determined from the scattering curve using a sigmoidal-gradient approximation for the diffuse boundary. The oxide layer thickness values as a function of oxidation time, obtained using SAXS are compared to measured weight increase values, caused by the oxidation. [source] | |||||||||||||||||||||||||||||||||||||