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Small-angle X-ray Scattering (small-angle + x-ray_scattering)
Kinds of Small-angle X-ray Scattering Terms modified by Small-angle X-ray Scattering Selected AbstractsMulti-scale Microstructure Characterization of Solid Oxide Fuel Cell Assemblies With Ultra Small-Angle X-Ray Scattering,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Andrew J. Allen Ultra small angle X-ray scattering with synchrotron radiation is applied to assess the pore space of a highly complex solid oxide fuel cell assembly. The instrument permits to record scattering curves covering a size range from 1,nm to several ,m in a fine step width of 15,,m. [source] Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small-Angle X-Ray ScatteringMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006Arben Jusufi Abstract Summary: We performed molecular dynamics simulation of a charged colloidal particle with explicit counterions. Our work provides a direct comparison between simulations and ASAXS-experiments, offering insight into the counterion distribution of charged colloidal suspensions. We give a detailed constitution of the appearing scattering terms with their physical meaning. It is shown that the cross-correlation between a macroion and its counterions gives the meanfield approximation of the counterion density even if the counterion system is highly fluctuating. Furthermore, it is shown that cross-correlations can be negative due to oscillations of the density amplitudes of the macroion and counterions and, therefore, must be distinguished from other scattering contributions. These oscillations become more pronounced if the counterions exhibit a fixed shape and if the size of the macroion and that of the counterion system are different. Simulation sanpshot of a charged colloid (big central sphere) with counterions (small spheres). [source] Structural Studies of Bleached Melanin by Synchrotron Small-angle X-ray Scattering,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2003Kenneth C. Littrell ABSTRACT Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 Å with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 Å at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules. [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] Modifications in the correlation function in poly(vinyl alcohol)/silica hybrid wet gelsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2009Dimas R. Vollet Small-angle X-ray scattering was used to study structural modifications in tetraethoxysilane-derived poly(vinyl alcohol) (PVA)/silica hybrids. The basic structure of the wet gels can be described as a mass-fractal structure with fractal dimension D equal to 2 and characteristic length ,, which increases with addition of PVA. Wet gels with high PVA content exhibit a positive deviation from the mass-fractal power-law scattering at low q; this deviation is associated with additional scattering due to a second large correlation distance ,, reinforced by the addition of PVA. The fraction of both contributions to the total correlation function was estimated; this is the first time that such a study has been carried out for mass-fractal structures. [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] 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] In situ SAXS studies of the morphological changes of an alumina,zirconia,silicate ceramic during its formationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2006Rudolf Winter Small-angle X-ray scattering is used at two energies, one either side of the zirconium K -edge, to probe the in situ formation of an alumina,zirconia,silicate ceramic. The use of energies either side of the edge allows the decomposition of information regarding the scattering from the zirconia particles from that of the glass matrix. Porod slope data show how the nanoparticles progress from being relatively isolated particles to becoming agglomerates as the pore network in the glass collapses. The shape of the agglomerates resembles the pore network of the glass at low temperature. The Guinier radii of the particles show the growth of the agglomerates past the Littleton softening point, whilst still resolving the primary particles. [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] Polyurethane/acrylate hybrids: Effects of the acrylic content and thermal treatment on the polymer propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Pablo J. Peruzzo Abstract Polyurethane (PU)/acrylate hybrids with different acrylic contents (10, 30, 50, 70, and 90 wt %) were prepared by the polymerization of acrylic monomers in the presence of preformed PU chains with polymerizable terminal vinyl groups. Films obtained by the casting of polymer dispersions before and after thermal annealing were characterized by dynamic light scattering, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), TEM electron energy-loss spectroscopy, differential scanning calorimetry, and gel fraction determination. Small-angle X-ray scattering (SAXS), wide-angle X-ray scattering, mechanical properties testing, atomic force microscopy, water contact angle testing, Buchholz hardness testing, and roughness testing of the films were also performed. The effects of the acrylic content and thermal treatment on the structure and properties were determined. TEM showed that a core,shell morphology was formed during polymerization. When the acrylic content increased, smaller particles without core,shell morphologies were observed. TEM energy-loss spectroscopy studies confirmed this observation. Systems with up to 50 wt % acrylic component were homogeneous, as determined by SAXS, before and after thermal annealing. An attempt to incorporate a higher amount of acrylic component led to phase-separated materials with a different morphology and, therefore, different properties. The relationship between the acrylic content and properties did not follow linear behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Structural Studies of Bleached Melanin by Synchrotron Small-angle X-ray Scattering,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2003Kenneth C. Littrell ABSTRACT Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 Å with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 Å at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules. [source] Contact Angle, WAXS, and SAXS Analysis of Poly(,-hydroxybutyrate) and Poly(ethylene glycol) Block Copolymers Obtained via Azotobacter vinelandii UWDBIOTECHNOLOGY PROGRESS, Issue 3 2005Kerry J. Townsend This study investigated and correlated physical properties and cell interactions of copolymers obtained by a poly(ethylene glycol) (PEG)-modulated fermentation of Azotobacter vinelandii UWD. PEGs with molecular weights of 400 and 3400 Da and di(ethylene glycol) (DEG) were used to modulate the bacterial synthesis of poly(,-hydroxybutyrate) (PHB). The PHB crystallinity was determined by wide-angle X-ray scattering (WAXS). Small-angle X-ray scattering (SAXS) showed that lamellar distances decreased between the PHB and the PHB modulated with PEG or DEG. Furthermore, the contact angle of water on the PHB/PEG polymer surfaces decreased when compared to that of PHB. The significant decrease of the contact angle and corresponding increase in surface tension, as well as significant decrease in cell adhesion, suggest the presence of hydrophilic PEG and DEG within the hydrophobic surface. [source] The Molecular Basis of Self-Assembly of Dendron,Rod,Coils into One-Dimensional NanostructuresCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2006Eugene R. Zubarev Prof. Abstract We describe here a comprehensive study of solution and solid-state properties of self-assembling triblock molecules composed of a hydrophilic dendron covalently linked to an aromatic rigid rod segment, which is in turn connected to a hydrophobic flexible coil. These dendron,rod,coil (DRC) molecules form well-defined supramolecular structures that possess a ribbonlike morphology as revealed by transmission-electron and atomic-force microscopy. In a large variety of aprotic solvents, the DRC ribbons create stable networks that form gels at concentrations as low as 0.2,% by weight DRC. The gels are thermally irreversible and do not melt at elevated temperatures, indicating high stability as a result of strong noncovalent interactions among DRC molecules. NMR experiments show that the strong interactions leading to aggregation involve mainly the dendron and rodlike blocks, whereas oligoisoprene coil segments remain solvated after gelation. Small-angle X-ray scattering (SAXS) profiles of different DRC molecules demonstrate an excellent correlation between the degree-of-order in the solid-state and the stability of gels. Studies on two series of analogous molecules suggest that self-assembly is very sensitive to subtle structural changes and requires the presence of at least four hydroxyl groups in the dendron, two biphenyl units in the rod, and a coil segment with a size comparable to that of the rodlike block. A detailed analysis of crystal structures of model compounds revealed the formation of stable one-dimensional structures that involve two types of noncovalent interactions, aromatic ,,, stacking and hydrogen bonding. Most importantly, the crystal structure of the rod,dendron compound shows that hydrogen bonding not only drives the formation of head-to-head cyclic structures, but also generates multiple linkages between them along the stacking direction. The cyclic structures are tetrameric in nature and stack into ribbonlike objects. We believe that DRC molecules utilize the same arrangement of hydrogen bonds and stacking of aromatic blocks observed in the crystals, explaining the exceptional stability of the nanostructures in extremely dilute solutions as well the thermal stability of the gels they form. This study provides mechanistic insights on self-assembly of triblock molecules, and unveils general strategies to create well-defined one-dimensional supramolecular objects. [source] Nanostructured copolymer gels for dsDNA separation by CEELECTROPHORESIS, Issue 23 2008Fen Wan Abstract Pluronics are triblock copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) that are able to form many different ordered nanostructures at appropriate polymer concentrations and temperatures in selective solvents. These nanostructured "gels" showed desirable criteria when used as DNA separation media, especially in microchip electrophoresis, including dynamic coating and viscosity switching. A ternary system of F127 (E99P69E99)/TBE buffer/1-butanol was selected as a model system to test the sieving performance of different nanostructures in separating dsDNA by CE. The nanostructures and their lattice constants were determined by small-angle X-ray scattering. Viscosity measurements showed the sol,gel transition phenomena. In addition to the cubic structure, successful electrophoretic separation of dsDNA in 2-D hexagonally packed cylinders was achieved. Results showed that without further optimization, ,X174 DNA,Hae III digest was well separated within 15,min in a 7-cm separation channel, by using F127/TBE/1-butanol gel with a 2-D hexagonal structure. A mechanism for DNA separations by those gels with both hydrophilic and hydrophobic domains is discussed. [source] Insights into the structure of plant ,-type phospholipase DFEBS JOURNAL, Issue 10 2007Susanne Stumpe Phospholipases D play an important role in the regulation of cellular processes in plants and mammals. Moreover, they are an essential tool in the synthesis of phospholipids and phospholipid analogs. Knowledge of phospholipase D structures, however, is widely restricted to sequence data. The only known tertiary structure of a microbial phospholipase D cannot be generalized to eukaryotic phospholipases D. In this study, the isoenzyme form of phospholipase D from white cabbage (PLD,2), which is the most widely used plant phospholipase D in biocatalytic applications, has been characterized by small-angle X-ray scattering, UV-absorption, CD and fluorescence spectroscopy to yield the first insights into its secondary and tertiary structure. The structural model derived from small-angle X-ray scattering measurements reveals a barrel-shaped monomer with loosely structured tops. The far-UV CD-spectroscopic data indicate the presence of ,-helical as well as ,-structural elements, with the latter being dominant. The fluorescence and near-UV CD spectra point to tight packing of the aromatic residues in the core of the protein. From the near-UV CD signals and activity data as a function of the calcium ion concentration, two binding events characterized by dissociation constants in the ranges of 0.1 mm and 10,20 mm can be confirmed. The stability of PLD,2 proved to be substantially reduced in the presence of calcium ions, with salt-induced aggregation being the main reason for irreversible inactivation. [source] Electropolymerization of a Bifunctional Ionic Liquid Monomer Yields an Electroactive Liquid-Crystalline PolymerADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Sungwon Lee Abstract The preparation and polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer that incorporates both a vinyl group and a thiophene moiety is reported. Potentiodynamic electropolymerization of the monomer produces an optically birefringent polymer film that strongly adheres to the electrode surface. Fourier transform IR spectroscopy shows that polymerization occurs through both the vinyl and thienyl groups. Cylic voltammetry (CV) is used to determine the polymer oxidation potential (1.66,V) and electrochemical bandgap, Eg, of 2.45,eV. The polymer exhibits electrochromism, converting from yellow in the neutral form (,max,=,380,nm) to blue in the polaronic state at 0.6,V (,max,=,672,nm) and to blue-grey in the bipolaronic state at 1.2,V (,max,>,800,nm). Topographic atomic force microscopy (AFM) images reveal isolated (separated) fibrils. Grazing-incidence small-angle X-ray scattering (GISAXS) studies indicate a lamellar structure with a lattice spacing of 3.2,nm. Wide-angle X-ray diffraction (WAXD) studies further suggest that the polymerized thiophene sheets are oriented perpendicular to the polymerized vinylimidazolium. The electrical conductivity, as determined by four-probe dc conductivity measurements was found to be 0.53,S cm,1 in the neutral form and 2.36,S cm,1 in the iodine-doped state, values higher than typically observed for polyalkylthiophenes. The structural ordering is believed to contribute to the observed enhancement of the electrical conductivity. [source] Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer BlendsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Christopher R. McNeill Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,°C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,°C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,°C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,°C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [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] Self-Assembly of Nanoparticle,Copolymer Mixtures: A Kinetic Point of View,ADVANCED MATERIALS, Issue 3 2007J. He The prediction of synergistic effects between two self-organizing systems is tested. In,situ grazing-incidence small-angle X-ray scattering (see figure) is used during thermal annealing of a nanoparticle,copolymer mixture, and shows that the orientation of the microdomains begins at the free surface and propagates in the film towards the substrate. This synergistic interaction is shown to apply to both cylindrical and lamellar block-copolymer morphologies. [source] Monodisperse Bile-Salt Nanotubes in Water: Kinetics of Formation,ADVANCED MATERIALS, Issue 6 2005B. Jean Sodium lithocholate forms stabilized cylindrical nanotubes with thin monomolecular walls (see Figure) through fast and complex morphological evolutions. The kinetics of formation can be followed by small-angle X-ray scattering using a brilliant synchrotron source, and are corroborated by cryo-transmission electron microscopy. Coaxial cylinders, helical ribbons, fibrils, and single-walled tubes are found to coexist in the first few minutes of the supramolecular organization process. [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] Structure of PbTe(SiO2)/SiO2 multilayers deposited on Si(111)JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2010Guinther Kellermann The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO2, named as PbTe(SiO2), between homogeneous layers of amorphous SiO2 deposited on a single-crystal Si(111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO2)/SiO2 multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers. [source] Simulating and evaluating small-angle X-ray scattering of micro-voids in polypropylene during mechanical deformationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2010Stefan Fischer Micro-voids that evolve during mechanical deformation in polypropylene have been characterized by small-angle X-ray scattering. Such voids can be modelled as randomly distributed cylinders which are oriented along the stretching direction, showing a log-normal size distribution. The model and simulation results are presented here. Advantages and disadvantages of the approach, the validity of the model, and important considerations for data evaluation are discussed. Data analysis of two-dimensional scattering images has been performed using a fully automated MATLAB routine by direct model fitting to scattering images. [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] Critical opalescence points to thermodynamic instability: relevance to small-angle X-ray scattering of resorcinol,formaldehyde gel formation at low pHJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2008Cedric J. Gommes During the formation at low pH of resorcinol,formaldehyde gels with a structure in the micrometre range, small-angle X-ray scattering exhibits a non-monotonic intensity variation as a function of reaction time. The data are analyzed in terms of scattering by statistical fluctuations of polymer concentration, the amplitude of which is maximal close to the critical point for phase separation between polymer and solvent. The data do not carry any morphological information, but they unambiguously show that the driving force of the gel formation is a thermodynamic instability of the polymerizing solution. [source] Two-dimensional small-angle X-ray scattering of self-assembled nanocomposite films with oriented arrays of spheres: determination of lattice type, preferred orientation, deformation and imperfectionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007Bernd M. Smarsly Mesostructured oxide films were prepared by dip-coating from colloidal solutions on ultrathin Si wafers and solidified by heating at various temperatures. Two-dimensional small-angle X-ray scattering measurements were carried out in transmission under selected tilt angles and evaluated by comparison with analytical expressions. The films are composed of oriented mesophases, the structures of which are defined in terms of lattice type, preferred orientation, deformation and imperfection, notably stacking faults. [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] Structure of nanoporous zirconia-based powders synthesized by different gel-combustion routesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Jorge R. Casanova Zirconia-based ceramics that retain their metastable tetragonal phase at room temperature are widely studied due to their excellent mechanical and electrical properties. When these materials are prepared from precursor nanopowders with high specific surface areas, this phase is retained in dense ceramic bodies. In this work, we present a morphological study of nanocrystalline ZrO2,2.8 mol% Y2O3 powders synthesized by the gel-combustion method, using different organic fuels , alanine, glycine, lysine and citric acid , and calcined at temperatures ranging from 873 to 1173,K. The nanopore structures were investigated by small-angle X-ray scattering. The experimental results indicate that nanopores in samples prepared with alanine, glycine and lysine have an essentially single-mode volume distribution for calcination temperatures up to 1073,K, while those calcined at 1173,K exhibit a more complex and wider volume distribution. The volume-weighted average of the nanopore radii monotonically increases with increasing calcination temperature. The samples prepared with citric acid exhibit a size distribution much wider than the others. The Brunauer,Emmett,Teller technique was used to determine specific surface area and X-ray diffraction, environmental scanning electron microscopy and transmission electron microscopy were also employed for a complete characterization of the samples. [source] | ||||||||||||||||||||||||||||||||||