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Small Angle X-ray Scattering (small + angle_x-ray_scattering)
Selected AbstractsPolyphenylene 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] Structure of reactively extruded rigid PVC/PMMA blendsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2005Y. Haba Abstract A novel route for producing polymer blends by reactive extrusion is described, starting from poly (vinyl chloride)/methyl methacrylate (PVC/MMA) dry blend and successive polymerization of MMA in an extruder. Small angle X-ray scattering (SAXS) measurements were applied to study the monomer's mode of penetration into the PVC particles and to characterize the supermolecular structure of the reactive poly(vinyl chloride)/poly(methyl methacrylate) (PVC/PMMA) blends obtained, as compared to the corresponding physical blends of similar composition. These measurements indicate that the monomer molecules can easily penetrate into the PVC sub-primary particles, separating the PVC chains. Moreover, the increased mobility of the PVC chains enables formation of an ordered lamellar structure, with an average d -spacing of 4.1,nm. The same characteristic lamellar structure is further detected upon compression molding or extrusion of PVC and PVC/PMMA blends. In this case the mobility of the PVC chains is enabled through thermal energy. Dynamic mechanical thermal analysis (DMTA) and SAXS measurements of reactive and physical PVC/PMMA blends indicate that miscibility occurs between the PVC and PMMA chains. The studied reactive PVC/PMMA blends are found to be miscible, while the physical PVC/PMMA blends are only partially miscible. It can be suggested that the miscible PMMA chains weaken dipole,dipole interactions between the PVC chains, leading to high mobility and resulting in an increased PVC crystallinity degree and decreased PVC glass transition temperature (Tg). These phenomena are shown in the physical PVC/PMMA blends and further emphasized in the reactive PVC/PMMA blends. Copyright © 2005 John Wiley & Sons, Ltd. [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] 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] 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] Grazing incidence small-angle X-ray scattering studies of the synthesis and growth of CdS quantum dots from constituent atoms in SiO2 matrixJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003U.V. Desnica Grazing incidence small angle X-ray scattering was applied to study the synthesis and growth of CdS quantum dots (QDs) from Cd and S atoms implanted in SiO2. For a dose of 1017/cm2, the partial synthesis of CdS QDs occurred already during implantation, with only moderate size increase upon subsequent annealing up to Ta=1073 K. The dynamics of QD synthesis and growth were considerably different for just two times lower dose, where synthesis started only if the implanted samples were annealed at Ta = 773 K or higher, with a strong increase of the size of QDs upon annealing at higher Ta. The results suggest that high-dose implantation followed by low-temperature annealing could lead to better defined sizes and narrower size distributions of QDs. [source] Structural characterization of undoped and Sb-doped SnO2 thin films fired at different temperaturesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003Alessandro P. Rizzato SnO2 thin films were obtained by the sol-gel method starting from inorganic precursor solutions. In this work, we compare the structure of undoped and Sb-doped SnO2 films prepared by dip-coating. The films were deposited on quartz substrates and then fired at different temperatures ranging from 383 up to 1173 K. The density and the thickness of the films were determined by X-ray reflectivity (XRR) and their porous nanostructure was characterized by grazing-incidence small angle X-ray scattering (GISAXS). XRR results corresponding to undoped and Sb-doped samples indicate a monotonous decrease in film thickness when they are fired at increasing temperatures. At same time, the apparent density of undoped samples exhibits a progressive increase while for Sb-doped films it remains invariant up to 973 K and then increases for T = 1173 K. Anisotropic GISAXS patterns of both films, Sb-doped and undoped, fired above 573 K indicate the presence of elongated pores with their major axis perpendicular to the film surface. For all firing temperatures the nanopores in doped samples are larger than in undoped ones. This suggests that Sb-doping favours the pore growth hindering the film densification. At the highest firing temperature (1173 K) this effect is reversed. [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] Investigation of bone and cartilage by synchrotron scanning-SAXS and -WAXD with micrometer spatial resolutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000Biological materials such as bone or wood are hierarchically structured to optimize mechanical and other properties. Several methods and experimental techniques are usually needed to study these materials on different length scales. We developed a device for small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD), optimized for position resolved investigations of bone sections using synchrotron radiation. Thin samples can be scanned with 20 µm steps, acquiring two-dimensional SAXS or WAXD patterns at every point. The system was tested by performing one-dimensional scans across bone cartilage interfaces, revealing information about size, shape and orientation of nanometer sized mineral particles as well as about crystal type and texture of these particles. [source] Annealing effect of perfluorosulfonated ionomer membranes on proton conductivity and methanol permeabilityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Yinghao Luan Abstract Perfluorosulfonated ionomer (PFSI) was synthesized and PFSI membranes were prepared via a solution-cast method and annealed at different temperatures from 150 to 230°C. The annealing effect on water content, proton conductivity, and methanol permeability were reported and discussed. X-ray diffraction and small angle X-ray scattering were used to test the structure of the membranes. It was found that annealing increased the proton conductivity of the membranes because heat-treatment helped to free the sulfonic groups that were buried in the polymer segments and form more organized ionic clusters. Water content and methanol permeability of the annealed membranes decreased with increasing annealing temperature. Simultaneously, annealing induced more compact chain packing structure, which eventually affected the transport of the proton and methanol through these ionomer membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Aggregated structure of flocculated asphaltenesAICHE JOURNAL, Issue 1 2001Theophylaktos G. Savvidis Many petroleum processing problems are related to asphaltene flocculation. A detailed understanding of the colloidal structure of asphaltenes in oild can play a decisive role in improving processing facilities and/or operating conditions. The structure of the flocculated part of the asphaltenes of a crude oil far above the flocculation threshold was studied to understand its links with macroscopic phase separation. Asphaltene filtrations were performed using filter pore sizes from 0.025 to 10 ,m. According to small angle X-ray scattering (SAXS) spectra and density measurements, these extracted asphaltenes in toluene solutions did not have any physical differences. Measurements of nanometric sizes for the dispersed particles after dissolution in toluene show that micron-size flocculated asphaltenes are strongly aggregated structures. Therefore, filtration experiments separate asphaltenes corresponding powders show spherically shaped aggregates of micron size. SAXS and USAXS techniques were used to investigate the internal structure of the asphaltene powder. The aggregates are clearly a compact organization of asphaltenic material. This dense structure explains why flocculated asphaltenes are subject to sedimentation, which induces the visible macroscopic phase separation. [source] Molecularly defined (L)-lactic acid oligomers and polymers: Synthesis and characterizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Kenichi Takizawa Abstract The synthesis of (L)-lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t -butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3-dicyclohexylcarbodiimide or 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride were high (70,100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X-ray scattering demonstrated a close correlation between the molecular structure of the well-defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977,5990, 2008 [source] Block copolymer preparation by atom transfer radical polymerization under emulsion conditions using a nanoprecipitation techniqueJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2008Delphine Chan-Seng Abstract Living-radical polymerization of acrylates were performed under emulsion atom transfer radical polymerization (ATRP) conditions using latexes prepared by a nanoprecipitation technique previously employed and optimized for the polymerization of styrene. A macroinitiator of poly(n -butyl acrylate) prepared under bulk ATRP was dissolved in acetone and precipitated in an aqueous solution of Brij 98 to preform latex particles, which were then swollen with monomer and heated. Various monomers (i.e. n -butyl acrylate, styrene, and tert -butyl acrylate) were used to swell the particles to prepare homo- and block copolymers from the poly(n -butyl acrylate) macroinitiator. Under these conditions latexes with a relatively good colloidal stability were obtained. Furthermore, amphiphilic block copolymers were prepared by hydrolysis of the tert -butyl groups and the resulting block copolymers were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The bulk morphologies of the polystyrene- b -poly(n -butyl acrylate) and poly(n -butyl acrylate)- b -poly(acrylic acid) copolymers were investigated by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 625,635, 2008 [source] Crystallization of Poly(, -caprolactone)/Poly(vinyl chloride) Miscible Blends Under Strain: The Role of Molecular WeightMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2006Yubao Zhang Abstract Summary: The effect of poly(, -caprolactone) (PCL) molecular weight on the orientation of crystalline PCL in miscible poly(, -caprolactone)/poly(vinyl chloride) (PCL/PVC) blends, melt crystallized under strain, has been studied by a combination of wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) studies. An unusual crystal orientation with the b-axis parallel to the stretching direction was observed in miscible PCL/PVC blends with PCL of high molecular weight (>21,000). SAXS showed the presence of nanosize confined PCL in the PCL/PVC blends, which could be preserved at temperatures higher than the Tm of PCL but lower than the Tg of PVC. A mechanism based on the confinement of PCL crystal growth was proposed, which can explain the formation of b-axis orientation in PCL/PVC blends crystallized under strain. SAXS pattern of stretched PCL/PVC blend after annealing at 90,°C for 5 min. [source] Scaling behavior of plasmon coupling in Au and ReO3 nanoparticles incorporated in polymer matricesPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010Urmimala Maitra Abstract Polymer nanocomposites containing different concentrations of Au nanoparticles have been investigated by small angle X-ray scattering and electronic absorption spectroscopy. The variation in the surface plasmon resonance (SPR) band of Au nanoparticles with concentration is described by a scaling law. The variation in the plasmon band of ReO3 nanoparticles embedded in polymers also follows a similar scaling law. Distance dependence of plasmon coupling in polymer composites of metal nanoparticles. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanodomain growth in amorphous Si,C,NPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 2-3 2009W. Gruber Abstract Polymer-derived amorphous Si,C,N ceramics are phase separated into amorphous nanodomains after thermolysis. These nanodomains are expected to have a crucial importance for the extraordinary high temperature stability of these materials. We investigated nanodomain growth during isothermal annealing at 1400 °C using small angle X-ray scattering. The as-thermolyzed sample shows a domain radius of about 5 Å as determined from Guinier plots. During annealing, fast nanodomain growth up to 9 Å is observed for times up to 30 h while for longer annealing times up to 165 h the growth considerably slows down, resulting in a domain size of 11 Å. The experimental data can be fitted by a model based on diffusion controlled domain growth and simultaneous slow-down of diffusion due to structural relaxation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Order-disorder transitions in self-assembled polymers: A positron annihilation studyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Ramasubbu Ramani Abstract We report here the first results of order-disorder transition (ODT) in a self-assembled comb-like polymer-amphiphile supramolecular system as identified from the change in positron lifetime parameters. We have used poly(4-vinyl pyridine) hydrogen bonded with 3-pentadecyl phenol, which upon heating showed a stepwise reduction in o -Ps intensity at the ODT from lamellar self-assembled state to the disordered state. The ODT temperature was confirmed by differential scanning calorimetry and small angle X-ray scattering. The free volume "holes" in this polymer-amphiphile system are proposed to be near the chain ends of the polymer backbones. We suggest that positron lifetime spectroscopy can serve as a technique to identify ODTs in self-assembled lamellar structured supramolecular systems. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical properties of highly transparent polypropylene cast films: Influence of material structure, additives, and processing conditionsPOLYMER ENGINEERING & SCIENCE, Issue 4 2006Katharina Resch Polypropylene homopolymers and ethylene/propylene-random-copolymers formulated with and without anti-blocking additives were extruded to cast films with an industrial scale extruder equipped with a soft box, a specific air knife that expels a higher volume of air at lower velocity. The films were analyzed as to their optical properties haze and clarity. A comprehensive topographical characterization was performed using atomic force microscopy (AFM) and confocal microscopy. To obtain morphological information on a nanometer scale AFM phase imaging, micro-thermal analysis and small angle X-ray scattering (SAXS) were done. A significant effect of additives and processing conditions on the film topography and the optical properties was revealed. The films without anti-blocking and antacid aids showed the best optical properties and lowest vertical roughness fluctuations. In contrast, the addition of anti-blocking and antacid aids reduced the optical properties associated with an increase in surface roughness. While for films without anti-blocking aids an enhanced soft box condition resulted in lower vertical fluctuations of roughness and better optical properties, the behavior was in reverse for films with anti-blocking aid. By means of SAXS crystalline lamellae with a thickness of about 2.5 nm were detected. High-resolution phase imaging AFM yielded thicker crystal lamellae on the film surface. POLYM. ENG. SCI., 46:520,531, 2006. © 2006 Society of Plastics Engineers. [source] Domain structure and miscibility studies of blends of styrene,butadiene,styrene block copolymers (SBS) and styrene,glycidyl methacrylate statistical copolymers (PS-GMA) using SAXS and DMTAPOLYMER INTERNATIONAL, Issue 3 2007LB Canto Abstract The domain structure and miscibility in the solid state of a series of blends of styrene-butadiene-styrene (SBS) block copolymers and styrene-glycidyl methacrylate (PS-GMA) statistical copolymers with varying molecular weights and compositions were studied using small angle X-ray scattering and dynamic mechanical thermal analysis. Depending on the molecular characteristics of each component, different types and degrees of solubilization of PS-GMA in SBS were found which, in addition to the initially SBS phase morphology, lead to materials with multiphase domain morphologies with differences in size and structure. The degree of solubilization of PS-GMA into the PS domains of SBS was found to be higher for blends containing PS-GMA with lower molecular weight (Mw = 18 100 g mol,1) and lower GMA content (1 wt%) and/or for SBS with higher PS content (39 wt%) and longer PS blocks (Mw = 19 600 g mol,1). Localized solubilization of PS-GMA in the middle of PS domains of SBS was found to be the most probable to occur for the systems under study, causing swelling of PS domains. However, uniform solubilization was also observed for SBS/PS-GMA blends containing SBS with composition in the range of a morphological transition (PS block Mw = 19 600 g mol,1 and 39 wt% of PS) causing a morphological transition in the SBS copolymer (cylinder to lamella). Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd [source] Preparation and characterization of mesoporous materials based on silsesquioxane by block copolymer templating,POLYMER INTERNATIONAL, Issue 11 2002Byeong-Gyu Park Abstract Nanoporous materials were prepared by using silsesquioxane containing three alkoxy groups and a non-hydrolysable organic moiety. The influences of pH and precursor ratios of silsesquioxane and tetraethyl orthosilicate (TEOS) on the preparation of organo-modified periodic mesoporous materials were investigated. These materials were characterized using small angle X-ray scattering, infrared spectroscopy and thermogravimetric analysis. A non-ionic triblock copolymer was used as a structure-directing agent to provide large pores with a high density of silanol groups. It was found that silsesquioxanes could form ordered nanoporous materials in the presence of TEOS by controlling the pH and the co-precursors ratio, despite their structural irregularity. © 2002 Society of Chemical Industry [source] Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2004Sang Hyub Han Abstract Preparation of a polyimide nanofoam (PI-F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)-co-(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4,-oxydianiline (ODA). The precursor was then grafted with bromide-terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N -methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X-ray scattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The morphology showed nanophase-separated structures with uniformly distributed and non-interconnected pores of 20,40,nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd. [source] Grp94, the endoplasmic reticulum Hsp90, has a similar solution conformation to cytosolic Hsp90 in the absence of nucleotidePROTEIN SCIENCE, Issue 9 2009Kristin A. Krukenberg Abstract The molecular chaperone, Hsp90, is an essential eukaryotic protein that assists in the maturation and activation of client proteins. Hsp90 function depends upon the binding and hydrolysis of ATP, which causes large conformational rearrangements in the chaperone. Hsp90 is highly conserved from bacteria to eukaryotes, and similar nucleotide-dependent conformations have been demonstrated for the bacterial, yeast, and human proteins. There are, however, important species-specific differences in the ability of nucleotide to shift the conformation from one state to another. Although the role of nucleotide in conformation has been well studied for the cytosolic yeast and human proteins, the conformations found in the absence of nucleotide are less well understood. In contrast to cytosolic Hsp90, crystal structures of the endoplasmic reticulum homolog, Grp94, show the same conformation in the presence of both ADP and AMPPNP. This conformation differs from the yeast AMPPNP-bound crystal state, suggesting that Grp94 may have a different conformational cycle. In this study, we use small angle X-ray scattering and rigid body modeling to study the nucleotide free states of cytosolic yeast and human Hsp90s, as well as mouse Grp94. We show that all three proteins adopt an extended, chair-like conformation distinct from the extended conformation observed for the bacterial Hsp90. For Grp94, we also show that nucleotide causes a small shift toward the crystal state, although the extended state persists as the major population. These results provide the first evidence that Grp94 shares a conformational state with other Hsp90 homologs. [source] Expression, purification, and characterization of Thermotoga maritima membrane proteins for structure determinationPROTEIN SCIENCE, Issue 5 2006Linda Columbus Abstract Structural studies of integral membrane proteins typically rely upon detergent micelles as faithful mimics of the native lipid bilayer. Therefore, membrane protein structure determination would be greatly facilitated by biophysical techniques that are capable of evaluating and assessing the fold and oligomeric state of these proteins solubilized in detergent micelles. In this study, an approach to the characterization of detergent-solubilized integral membrane proteins is presented. Eight Thermotoga maritima membrane proteins were screened for solubility in 11 detergents, and the resulting soluble protein,detergent complexes were characterized with small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) spectroscopy, circular dichroism (CD) spectroscopy, and chemical cross-linking to evaluate the homogeneity, oligomeric state, radius of gyration, and overall fold. A new application of SAXS is presented, which does not require density matching, and NMR methods, typically used to evaluate soluble proteins, are successfully applied to detergent-solubilized membrane proteins. Although detergents with longer alkyl chains solubilized the most proteins, further characterization indicates that some of these protein,detergent complexes are not well suited for NMR structure determination due to conformational exchange and protein oligomerization. These results emphasize the need to screen several different detergents and to characterize the protein,detergent complex in order to pursue structural studies. Finally, the physical characterization of the protein,detergent complexes indicates optimal solution conditions for further structural studies for three of the eight overexpressed membrane proteins. [source] NMR and SAXS characterization of the denatured state of the chemotactic protein Che Y: Implications for protein folding initiationPROTEIN SCIENCE, Issue 6 2001Pascal Garcia Abstract The denatured state of a double mutant of the chemotactic protein CheY (F14N/V83T) has been analyzed in the presence of 5 M urea, using small angle X-ray scattering (SAXS) and heteronuclear magnetic resonance. SAXS studies show that the denatured protein follows a wormlike chain model. Its backbone can be described as a chain composed of rigid elements connected by flexible links. A comparison of the contour length obtained for the chain at 5 M urea with the one expected for a fully expanded chain suggests that ,25% of the residues are involved in residual structures. Conformational shifts of the ,-protons, heteronuclear 15N-{1H} NOEs and 15N relaxation properties have been used to identify some regions in the protein that deviate from a random coil behavior. According to these NMR data, the protein can be divided into two subdomains, which largely coincide with the two folding subunits identified in a previous kinetic study of the folding of the protein. The first of these subdomains, spanning residues 1,70, is shown here to exhibit a restricted mobility as compared to the rest of the protein. Two regions, one in each subdomain, were identified as deviating from the random coil chemical shifts. Peptides corresponding to these sequences were characterized by NMR and their backbone 1H chemical shifts were compared to those in the intact protein under identical denaturing conditions. For the region located in the first subdomain, this comparison shows that the observed deviation from random coil parameters is caused by interactions with the rest of the molecule. The restricted flexibility of the first subdomain and the transient collapse detected in that subunit are consistent with the conclusions obtained by applying the protein engineering method to the characterization of the folding reaction transition state. [source] The acid-induced folded state of Sac7d is the native statePROTEIN SCIENCE, Issue 10 2000Jennifer L. Bedell Abstract Sac7d unfolds at low pH in the absence of salt, with the greatest extent of unfolding obtained at pH 2. We have previously shown that the acid unfolded protein is induced to refold by decreasing the pH to 0 or by addition of salt (McCrary BS, Bedell J, Edmondson SP, Shriver JW, 1998, J Mol Biol 276:203,224). Both near-ultraviolet circular dichroism spectra and ANS fluorescence enhancements indicate that the acid- and salt-induced folded states have a native fold and are not molten globular. 1H, 15N heteronuclear single quantum coherence NMR spectra confirm that the native, acid-, and salt-induced folded states are essentially identical. The most significant differences in amide 1H and 15N chemical shifts are attributed to hydrogen bonding to titrating carboxyl side chains and through-bond inductive effects. The 1H NMR chemical shifts of protons affected by ring currents in the hydrophobic core of the acid- and salt-induced folded states are identical to those observed in the native. The radius of gyration of the acid-induced folded state at pH 0 is shown to be identical to that of the native state at pH 7 by small angle X-ray scattering. We conclude that acid-induced collapse of Sac7d does not lead to a molten globule but proceeds directly to the native state. The folding of Sac7d as a function of pH and anion concentration is summarized with a phase diagram that is similar to those observed for other proteins that undergo acid-induced folding except that the A-state is encompassed by the native state. These results demonstrate that formation of a molten globule is not a general property of proteins that are refolded by acid. [source] Proposal for molecular mechanism of thionins deduced from physico-chemical studies of plant toxinsCHEMICAL BIOLOGY & DRUG DESIGN, Issue 6 2004B. Stec Abstract:, We propose a molecular model for phospholipid membrane lysis by the ubiquitous plant toxins called thionins. Membrane lysis constitutes the first major effect exerted by these toxins that initiates a cascade of cytoplasmic events leading to cell death. X-ray crystallography, solution nuclear magnetic resonance (NMR) studies, small angle X-ray scattering and fluorescence spectroscopy provide evidence for the mechanism of membrane lysis. In the crystal structures of two thionins in the family, ,1 - and , -purothionins (MW: approximately 4.8 kDa), a phosphate ion and a glycerol molecule are modeled bound to the protein. 31P NMR experiments on the desalted toxins confirm phosphate-ion binding in solution. Evidence also comes from phospholipid partition experiments with radiolabeled toxins and with fluorescent phospholipids. This data permit a model of the phospholipid,protein complex to be built. Further, NMR experiments, one-dimensional (1D)- and two-dimensional (2D)-total correlation spectroscopy (TOCSY), carried out on the model compounds glycerol-3-phosphate (G3P) and short chain phospholipids, supported the predicted mode of phospholipid binding. The toxins' high positive charge, which renders them extremely soluble (>300 mg/mL), and the phospholipid-binding specificity suggest the toxin,membrane interaction is mediated by binding to patches of negatively charged phospholipids [phosphatidic acid (PA) or phosphatidyl serine (PS)] and their subsequent withdrawal. The formation of proteolipid complexes causes solubilization of the membrane and its lysis. The model suggests that the oligomerization may play a role in toxin's activation process and provides insight into the structural principles of protein,membrane interactions. [source] Self-Organisation in the Assembly of Gels from Mixtures of Different Dendritic Peptide Building BlocksCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007Andrew Abstract This paper investigates dendritic peptides capable of assembling into nanostructured gels, and explores the effect on self-assembly of mixing different molecular building blocks. Thermal measurements, small angle X-ray scattering (SAXS) and circular dichroism (CD) spectroscopy are used to probe these materials on macroscopic, nanoscopic and molecular length scales. The results from these investigations demonstrate that in this case, systems with different "size" and "chirality" factors can self-organise, whilst systems with different "shape" factors cannot. The "size" and "chirality" factors are directly connected with the molecular information programmed into the dendritic peptides, whilst the shape factor depends on the group linking these peptides together,this is consistent with molecular recognition hydrogen bond pathways between the peptidic building blocks controlling the ability of these systems to self-recognise. These results demonstrate that mixtures of relatively complex peptides, with only subtle differences on the molecular scale, can self-organise into nanoscale structures, an important step in the spontaneous assembly of ordered systems from complex mixtures. [source] | ||||||||||||||||||||||||||||