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X-ray Scattering (x-ray + scattering)
Kinds of X-ray Scattering Terms modified by 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] Formation of diffusion-hindering interlayers in metals in contact by dedicated thermal treatmentCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005D. C. Meyer Abstract Thermal evolution of the structure of Fe/Al multilayers (MLs) with nominal composition 5*(5 nm Al / 5 nm Fe) prepared by crossed-beam pulsed laser deposition is studied by wide-angle X-ray scattering and X-ray reflectometry after different temperature-time procedures of thermal treatments under high-vacuum conditions. In comparison to direct thermal annealing at temperatures of 250 °C and 275 °C, respectively, which results in nearly complete mixing of the MLs and formation of the FeAl intermetallic compound, quite different behaviour was found after dedicated thermal pretreatment. Annealing at successive growing temperatures before final annealing at temperatures mentioned, resulted in conservation of pronounced multilayer structure. From the results it is generalised, that also in the case of ML systems, the tendency of mixing a dedicated tuning of interface characteristics by thermal treatment allows for formation of diffusion-hindering interlayers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [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] 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] Solution Processable Fluorenyl Hexa- peri -hexabenzocoronenes in Organic Field-Effect Transistors and Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Wallace W. H. Wong Abstract The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field-effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa- peri -hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide-angle X-ray scattering (2D WAXS) experiments that the sterically demanding 9,9-dioctylfluorene groups are preventing ,,, intermolecular contact in the hexakis-substituted FHBC 4. For bis-substituted FHBC compounds 5 and 6, ,,, intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field-effect mobility of FHBC 6, deposited by spin-casting, reached 2.8,×,10,3,cm2 V,1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC61BM. [source] Polyphenylene Dendrimer-Templated In Situ Construction of Inorganic,Organic Hybrid Rice-Shaped ArchitecturesADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Xiaoying Qi Abstract A novel dendrimer-templating method for the synthesis of CuO nanoparticles and the in situ construction of ordered inorganic,organic CuO,G2Td(COOH)16rice-shaped architectures (RSAs) with analogous monocrystalline structures are reported. The primary CuO nanoparticles are linked by the G2Td(COOH)16 dendrimer. This method provides a way to preserve the original properties of primary CuO nanoparticles in the ordered hybrid nanomaterials by using the 3D rigid polyphenylene dendrimer (G2Td(COOH)16) as a space isolation. The primary CuO nanoparticles with diameter of (6.3,±,0.4) nm are synthesized via four successive reaction steps starting from the rapid reduction of Cu(NO3)2 by using NaBH4 as reducer and G2Td(COOH)16 as surfactant. The obtained hybrid CuO,G2Td(COOH)16 RSA, formed in the last reaction step, possesses a crystal structure analogous to a monocrystal as observed by transmission electron microscopy(TEM). In particular, the formation process of the RSA is monitored by UV,vis, TEM, and X-ray diffraction. Small angle X-ray scattering and Fourier transform infrared spectroscopy are used to investigate the role of the dendrimer in the RSA formation process. The obtained results illuminate that Cu2+COO, coordination bonds play an indispensable role in bridging and dispersing the primary CuO nanoparticles to induce and maintain the hybrid RSA. More importantly, the RSA is retained through the Cu2+COO,coordination bonds even with HCl treatment, suggesting that the dendrimers and Cu2+ ions may form rice-shaped polymeric complexes which could template the assembly of CuO nanoparticles towards RSAs. This study highlights the feasibility and flexibility of employing the peculiar dendrimers to in-situ build up hybrid architectures which could further serve as templates, containers or nanoreactors for the synthesis of other nanomaterials. [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] Photocrosslinkable Polythiophenes for Efficient, Thermally Stable, Organic PhotovoltaicsADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Bumjoon J. Kim Abstract Photocrosslinkable bromine-functionalized poly(3-hexylthiophene) (P3HT-Br) copolymers designed for application in solution-processed organic photovoltaics are prepared by copolymerization of 2-bromo-3-(6-bromohexyl) thiophene and 2-bromo-3-hexylthiophene. The monomer ratio is carefully controlled to achieve a UV photocrosslinkable layer while retaining the ,,, stacking feature of the conjugated polymers. The new materials are used as electron donors in both bulk heterojunction (BHJ) and bilayer type photovoltaic devices. Unlike devices prepared from either P3HT:PCBM blend or P3HT-Br:PCBM blend without UV treatment, photocrosslinked P3HT-Br:PCBM devices are stable even when annealed for two days at the elevated temperature of 150,°C as the nanophase separated morphology of the bulk heterojunction is stabilized as confirmed by optical microscopy and grazing incidence wide angle X-ray scattering (GIWAXS). When applied to solution-processed bilayer devices, the photocrosslinkable materials show high power conversion efficiencies (,2%) and excellent thermal stability (3 days at 150,°C). Such performance, one of the highest obtained for a bilayer device fabricated by solution processing, is achieved as crosslinking does not disturb the ,,, stacking of the polymer as confirmed by GIWAXS measurements. These novel photocrosslinkable materials provide ready access to efficient bilayer devices thus enabling the fundamental study of photophysical characteristics, charge generation, and transport across a well-defined interface. [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] 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] Cyclic Enones as Substrates in the Morita,Baylis,Hillman Reaction: Surfactant Interactions, Scope and Scalability with an Emphasis on FormaldehydeADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Brett Abstract Traditionally, cyclic enones and formalin are reactants notorious for displaying problematic behaviour (i.e., poor solubility and low yields) under Morita,Baylis,Hillman (MBH) reaction conditions. The body of research presented herein focuses on the use of surfactants in water as a solvent medium that offers a resolution to many of the issues associated with the MBH reaction. Reaction scope, scalability and small angle X-ray scattering have been studied to assist with the understanding of the reaction mechanism and industrial application. A comparison against known literature methods for reaction scale-up is also discussed. [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] Ultra-small-angle X-ray scattering at the Advanced Photon SourceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2009Jan Ilavsky The design and operation of a versatile ultra-small-angle X-ray scattering (USAXS) instrument at the Advanced Photon Source (APS) at Argonne National Laboratory are presented. The instrument is optimized for the high brilliance and low emittance of an APS undulator source. It has angular and energy resolutions of the order of 10,4, accurate and repeatable X-ray energy tunability over its operational energy range from 8 to 18,keV, and a dynamic intensity range of 108 to 109, depending on the configuration. It further offers quantitative primary calibration of X-ray scattering cross sections, a scattering vector range from 0.0001 to 1,Å,1, and stability and reliability over extended running periods. Its operational configurations include one-dimensional collimated (slit-smeared) USAXS, two-dimensional collimated USAXS and USAXS imaging. A robust data reduction and data analysis package, which was developed in parallel with the instrument, is available and supported at the APS. [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] 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] 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] Crystal truncation rod X-ray scattering: exact dynamical calculationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2008Václav Holý A new method is presented for a calculation of the reciprocal-space distribution of X-ray diffracted intensity along a crystal truncation rod. In contrast to usual kinematical or dynamical approaches, the method is correct both in the reciprocal-lattice points and between them. In the method, the crystal is divided into a sequence of very thin slabs parallel to the surface; in contrast to the well known Darwin dynamical theory, the electron density in the slabs is constant along the surface normal. The diffracted intensity is calculated by a matrix formalism based on the Fresnel reflection and transmission coefficients. The method is applicable for any polarization of the primary beam and also in a non-coplanar scattering geometry. [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] | ||||||||||||||||||||||||||||||||||