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PubMed1991

Detection of structural defects in phosphatidylcholine membranes by small-angle neutron scattering. The cluster model of a lipid bilayer.

The oriented DPPC multilayers hydrated by D2O have been studied by a small-angle neutron scattering method in the Guinier range, and the gyration radius of the structural inhomogeneities has been estimated at about 29 A. They are interpreted as the annular defects between adjacent clusters uniting the all-trans chain 'segments' adjacent to the polar head group regions. The angle of the 'segment' tilt is determined by the hydrated polar group area (59.2 A2 for DPPC bilayers) and has been estimated to be about 44 degrees under the given experimental conditions. The hydrocarbon interior of a bilayer can be suggested as a 'sandwich' that is formed by two clustered layers (approx. 7 A of the thickness) and the central disordered (liquid) layer. The average cluster size along the bilayer surface is estimated to be approx. 24 A which correlates with the estimations of the short order region dimensions from the halfwidth of the X-ray 'packing' reflex (4.6 A)-1. The average interchain separation of approx. 5 A and the average cross-section area of a chain in a cluster (21.4 A2) were estimated from the reflex position and the chain cross-section geometry. The total volume of defects and the fraction of a bilayer surface occupied by them were estimated too.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1985

Methionyl-tRNA synthetase from E. coli: direct evidence for exchange of protomers in the dimeric enzyme by using deuteration and small-angle neutron scattering.

Direct demonstration of the reversible dissociation of native dimeric methionyl-tRNA synthetase from E. coli has been obtained using small angle neutron scattering and deuterated enzyme. Structural parameters of the fully deuterated dimer are very similar to the hydrogenated one. Analysis of the variations of the intensity and of the radius of gyration of a stoichiometric mixture of the two types of dimer (hydrogenated and deuterated), as a function of D2O content in the solvent, enabled us to characterize an hybrid dimer, having both hydrogenated and deuterated protomers. By separating the contribution of each protomer to the scattering, the radius of gyration of the protomer in situ and the distance between the centers of mass of each protomer in the dimer are determined.

Amino Acyl-tRNA Synthetases↗

PubMed2006

Investigation of sol-gel transition in pluronic F127/D2O solutions using a combination of small-angle neutron scattering and monte carlo simulation.

Physical gelation in the concentrated Pluronic F127/D2O solution has been studied by a combination of small-angle neutron scattering (SANS) and Monte Carlo simulation. A 15% F127/D2O solution exhibits a sol-gel transition at low temperature and a gel-sol transition at the higher temperature, as evidenced by SANS and Monte Carlo simulation studies. Our SANS and simulation results also suggest that the sol-gel transition is dominated by the formation of a percolated polymer network, while the gel-sol transition is determined by the loss of bound solvent. Furthermore, different diffusion behaviors of different bound solvents and free solvent are observed. We expect that this approach can be further extended to study phase behaviors of other systems with similar sol-gel phase diagrams.

Journal Article↗

PubMed2006

Autoxidized phospholipids in hexane: nano-self-assemblies studied by synchrotron small-angle X-ray scattering.

Synchrotron small-angle X-ray scattering (SAXS) was used to analyze the structure of self-assembled autoxidized phospholipids in a very dilute solution of hexane. In addition, it was used to build a self-consistent model of the aggregates, taking into account their inner heterogeneities and polydispersity. The scattering intensity from a dilute mixture of different types of noninteracting components of the phospholipid system was represented as a linear combination of partial intensities from the components weighted by their volume fractions. Applying this approach the final model of the system was described as a mixture of polydisperse reverse micelles and aggregates with spherical and cylindrical shapes. Spherical aggregates were represented as hollow spheres with inner radius 0.7 nm (occupied by water or hexane) and outer radius 1.5 nm. Geometrical parameters of the aggregates did not change much during the oxidation process, while the ratio of reverse micelles and aggregates in solution varied. The amount of the reverse micelles increased from very low to about 80%, whereas the content of other aggregates constantly reduced. The analysis performed in this study helps one to better understand the processes of phospholipid oxidation, which may occur in biological membranes.

Hexanes↗

PubMed2006

Water-Tween 40/Imwitor 308-isopropyl myristate microemulsions as delivery systems for ketoprofen: small-angle X-ray scattering study.

Small-angle X-ray scattering technique has been used to study the structural properties of the quaternary microemulsion Tween 40/Imwitor 308/isopropyl myristate/water and of five-component system obtained by the addition of the drug ketoprofen to the original quaternary system. The results enlighten the structuration of the studied systems and represent new complementary findings to the previous study [Podlogar, F., Bester-Rogac, M., Gasperlin, M., 2005. The effect of internal structure of selected water-Tween 40 (R)-Imwitor 308 (R)-IPM microemulsions on ketoprofene release. Int. J. Pharm. 302, 68-77] on the correlation between the structuration of these systems and the release rates of the ketoprofen. The present results indicate that in the samples with the moderate to high concentration of water where the latter is a continuous phase the addition of smaller amounts of the ketoprofen does not change their inner structuration significantly. The quaternary sample containing 46.2wt.% of water seems to be very near the composition where the transition from the bicontinuous to the lamellar structure of the microemulsion occurs. In the samples containing from 46.2 to 62.7wt.% of water the swelling of lamellar phases with constant thickness of double-layer can be characterized. At approximately the latter composition another noticeable transition in the inner structuration of the microemulsion has been observed. Interestingly, all these changes in the inner structuration of the studied systems did not affect the trend of the drug release rates in this regime of water concentrations.

Caprylates↗

PubMed2006

Water density in the electric double layer at the insulator/electrolyte solution interface.

I studied the spatial structure of the thick transition region between n-hexane and a colloidal solution of 7-nm silica particles by X-ray reflectivity and grazing incidence small-angle scattering. The interfacial structure is discussed in terms of a semiquantitative interface model wherein the potential gradient at the n-hexane/sol interface reflects the difference in the potentials of "image forces" between the cationic Na(+) and anions (nanoparticles) and the specific adsorption of surface charge at the interface between the adsorbed layer and the solution, as well as at the interface between the adsorbed layer and n-hexane. The X-ray scattering data revealed that the average density of water in the field approximately 10(9)-10(10) V/m of the electrical double layer at the hexane/silica sol interface is the same as, or only few percent higher (1-7%) than, its density under normal conditions.

Colloids↗

PubMed2006

Solution structure of human von Willebrand factor studied using small angle neutron scattering.

von Willebrand factor (VWF) binding to platelets under high fluid shear is an important step regulating atherothrombosis. We applied light and small angle neutron scattering to study the solution structure of human VWF multimers and protomer. Results suggest that these proteins resemble prolate ellipsoids with radius of gyration (R(g)) of approximately 75 and approximately 30 nm for multimer and protomer, respectively. The ellipsoid dimensions/radii are 175 x 28 nm for multimers and 70 x 9.1 nm for protomers. Substructural repeat domains are evident within multimeric VWF that are indicative of elements of the protomer quarternary structure (16 nm) and individual functional domains (4.5 nm). Amino acids occupy only approximately 2% of the multimer and protomer volume, compared with 98% for serum albumin and 35% for fibrinogen. VWF treatment with guanidine.HCl, which increases VWF susceptibility to proteolysis by ADAMTS-13, causes local structural changes at length scales <10 nm without altering protein R(g). Treatment of multimer but not protomer VWF with random homobifunctional linker BS(3) prior to reduction of intermonomer disulfide linkages and Western blotting reveals a pattern of dimer and trimer units that indicate the presence of stable intermonomer non-covalent interactions within the multimer. Overall, multimeric VWF appears to be a loosely packed ellipsoidal protein with non-covalent interactions between different monomer units stabilizing its solution structure. Local, and not large scale, changes in multimer conformation are sufficient for ADAMTS-13-mediated proteolysis.

Animals↗

PubMed1999

Quantitative measurements of Ostwald ripening using time-resolved small-angle neutron scattering.

Using a unique method we present accurate quantitative measurements of the Ostwald ripening of an emulsion system. Time-resolved small-angle neutron scattering monitors the time evolution of the average radius and number density of the emulsion drops. The results qualitatively agree with the current theory of Ostwald ripening but there is a quantitative, experimentally significant, discrepancy of a factor of 1.7. We argue that these accurate experiments, performed on a well characterized system, provide a most useful basis for testing further refinements of the theory.

Journal Article↗

PubMed1982

Small angle neutron scattering studies of the structure of nucleosome cores at low ionic strength.

Nucleosome core particles from chicken erythrocytes have been studied by small angle neutron scattering over the range from 10 to 0.04 mM Na+ at 65 and 100% D2O, and the radii of gyration of the particle were determined. A single transition in the radius of gyration was observed at either D2O concentration. With decreasing the ionic strength from 10 mM, the radius of gyration of the histones obtained at 65% D2O increased from 35 to 40A at about 1 mM ionic strength, whereas at 100% D2O the radius of gyration decreased from 39 to 36A also near 1 mM ionic strength. No loss of the secondary structure of the histones was observed by circular dichroism over the range of the ionic strength examined. These results suggest that at low ionic strength (less than or equal to 1 mM) the histones may locate outside of the nucleosome core particle accompanied by an alteration of the tertiary and/or the quaternary structure of the histone octamer.

Animals↗

PubMed1984

The morphology of bone mineral as revealed by small-angle X-ray scattering.

Diffuse small-angle X-ray scattering of oriented bone from bovine femur and canine femur was described in terms of an ideal isotropic two-dimensional two-phase system which consists of mineral phase and organic phase. The microstructure of powdered, randomly-oriented bone from bovine femur was found to be affected by grinding. An analysis of small-angle scattering from oriented bone showed that bone mineral was to a large extent in the form of needle-like particles with a 50-60 A the diameter, and the dimension of organic phase transverse to the longitudinal axis of long bone was in the range 45-55 A. The intersect distribution function was directly calculated from the scattering intensities, and the results strongly suggested the presence of needle-like mineral with sharp edges.

Animals↗

PubMed2005

Interactions of Humicola insolens cutinase with an anionic surfactant studied by small-angle neutron scattering and isothermal titration calorimetry.

The interaction of cutinase from Humicula insolens (HiC) and sodium dodecyl sulfate (SDS) has been investigated by small-angle neutron scattering (SANS) and isothermal titration calorimetry (ITC). The concerted interpretation of structural and thermodynamic information for identical systems proved valuable in attempts to elucidate the complex modes of protein-detergent interaction. Particularly so at the experimental temperature 22 degrees C, where the formation of SDS micelles is athermal (deltaH = 0), and the effects of protein-detergent interactions stand out clearly in the thermograms. It was found that the effect of SDS on cutinase depended strongly on the sample composition. Thus, addition of SDS corresponding to a molar ratio, n(s) = n(SDS)/n(HiC) of about 10, was associated with the formation of HiC/SDS aggregates, which include more than one protein molecule. The SANS results suggested that on the average such adducts contained two HiC, and the ITC traces showed that they form and break down slowly. At slightly higher SDS concentrations (n(s) = 10-25) these "dimers" dissociated, and the protein denatured. The denaturation showed the characteristic positive enthalpy change, but the SDS denatured state of HiC was unusually compact with a radius of gyration close to that of the native conformation. Further titration with SDS was associated with exothermic binding to the denatured protein until the saturation point at about n(s) = 90. At this point, the free monomer concentration was 2.2 mM and the binding number was approximately 40 SDS/HiC. Interestingly, this degree of SDS binding (approximately 0.5 g of SDS/g of HiC) is less than half the amount bound to typical water-soluble proteins.

Ascomycota↗

PubMed2004

Are thermoresponsive microgels model systems for concentrated colloidal suspensions? A rheology and small-angle neutron scattering study.

The structure of concentrated temperature-sensitive poly(N-isopropylacrylamide) (PNiPAM) microgel suspensions has been investigated employing rheology and small-angle neutron scattering (SANS). A previously described model expression for the particle form factor P(inho)(q) is extended by a model hard sphere structure factor S(q), and the average radial density profiles phi(r) are calculated from the amplitude of the form factor A(q) and the structure factor S(q). By this procedure, a direct real space description of the spatial ordering in the neighborhood of a single particle is obtained. The overall particle size and the correlation length xi of the concentration fluctuations of the internal polymer network decrease with concentration, revealing the increasing compression of the spheres. Thus, the particle form factor P(inho)(q) of the swollen PNiPAM microgels depends on concentration. The particle-particle interaction potential does not change significantly between 25 and 32 degrees C. Even approximately 1 K below the lower critical solution temperature (LCST), the experimental scattering intensity distributions I(q)/c are described very well by the hard sphere structure factor when an equivalent hard sphere particle size R(HS) and volume fraction eta(HS) are used. Microgels with different degrees of cross-linking and particle size resemble true hard sphere behavior up to effective volume fractions of phi(eff) < 0.35. At higher effective volume fractions phi(eff) > 0.35 strong deviations from true hard spheres are observed. Interpenetration of the outer, less cross-linked regions of the soft spheres as well as particle compression occurred at higher concentrations. In agreement with this, the equilibrium colloidal phase behavior and rheology also has some features of soft sphere systems. At temperatures well above the LCST, the interaction potential becomes strongly attractive and the collapsed microgel spheres form aggregates consisting of flocculated particles without significant long-range order. Hence, an attractive interaction potential in concentrated suspensions of PNiPAM microgels leads to distinctively different structures as compared to attractive hard sphere colloids. When the peculiar structural properties of the PNiPAM microgels are considered, they can be used as model systems in colloidal science.

Journal Article↗

PubMed1999

Two concentric protein shell structure with spikes of silkworm Bombyx mori cytoplasmic polyhedrosis virus revealed by small-angle neutron scattering using the contrast variation method.

The overall and internal structures of the silkworm Bombyx mori cytoplasmic polyhedrosis virus was investigated by small-angle neutron scattering using the contrast variation method. Data were collected in aqueous buffer solutions containing 0, 50, 75, and 100% D2O in the q range of 0.002 to 0.0774 A-1 at 5 degrees C. The radius of gyration at infinite contrast was estimated to be 336 A. The contrast matching point of the virus was determined to correspond to about 50% D2O level, evidence that the virus is composed of protein and nucleic acid. The virus was basically spherical and had a diameter of about 700 A. The main feature of its structure is the clustering of protein into two concentric shells separated by about 100 A. Most of the RNA moieties are located in the central core and between these two protein shells. However, the distance distribution function P(r) showed a minor distribution beyond a distance of r = 700 A, with a maximum particle distance of the virus of 1350 A. This is indicative of an external structure region with very low scattering density, in addition to the basic spherical structure. This external region is thought to correspond to twelve pyramidal protruding spikes shown by electron microscopic studies.

Animals↗

PubMedDate not supplied

[Efficacy of purine nucleotides on purinergic P2 platelet receptors by small angle light scattering].

The effect of purines on the activation and aggregation of thrombocytes in rats and rabbits was studied by the method of small-angle light scattering. The EC50 values of ADP, inducing the activation and aggregation of thrombocytes, reflect the sequence of the agonist action on various receptors: P2X1, 20-40 nM; P2Y1, 90-110 nM; P2YADP, 120-240 nM. It was demonstrated that ADP behaves as partial agonist not only with respect to P2X1 receptors, but with respect to P2Y1 receptors as well. Thrombocytes activated by 20 nM ADP or 100-nM ATP pass into a refracter state in the absence of further stimulation. The reaction halftime is tau 1/2 = 6.0 +/- 0.2 min for the cells activated with ADP and tau 1/2 = 16.5 +/- 0.2 min for ADP.

Adenosine Diphosphate↗

PubMed1991

Conformation of one- and two-chain high molecular weight urokinase analyzed by small-angle neutron scattering and vacuum ultraviolet circular dichroism.

The structures of one- and two-chain high molecular weight human urokinase were analyzed by small-angle neutron scattering and vacuum ultraviolet circular dichroism. Both one- and two-chain high molecular weight urokinases exhibited a radius of gyration of 31 A and a maximum dimension of 90 A. Neither parameter was affected by the presence of lysine sufficient to saturate all the lysine-binding sites in human plasminogen. These physical parameters are consistent with the sedimentation coefficient of high molecular weight urokinase and indicate that both proteins are highly asymmetric. Neither protein contained much alpha-helix or parallel beta-sheet. Most of the secondary structure was in the form of antiparallel beta-sheet and beta-turns, very similar to the secondary structure of plasminogen. The macroscopic kinetic constants, Km and kcat, for the hydrolysis of (pyroGlu-Gly-Arg-NH)2-rhodamine by two-chain high molecular weight urokinase and low molecular weight urokinase which lacks the epidermal growth factor and kringle domains were similar. These structural and kinetic data are consistent with the domains in both forms of urokinase being independent structural and functional units.

Circular Dichroism↗

PubMed2003

Small-angle neutron scattering with contrast variation reveals spatial relationships between the three subunits in the ternary cardiac troponin complex and the effects of troponin I phosphorylation.

Small-angle neutron scattering with contrast variation has been used to determine the shapes and dispositions of the three subunits of cardiac troponin and to study the influence of phosphorylation on the structure. Three contrast variation series were collected on three different isotopically labeled variants of the cTnC/cTnI/cTnT(198-298) complex, one of which contained deuterated and bisphosphorylated cTnI. Analysis of the scattering data shows cTnT(198-298) interacting with a single lobe of a somewhat compacted cTnC that sits at one end of an elongated rodlike cTnI, covering about one-third of its length. The cTnT(198-298) sits near the center of the long cTnI axis. The components undergo significant conformational changes and reorientations in response to protein kinase A phosphorylation of cTnI. The rodlike cTnI bends sharply at the end interacting with the cTnC/cTnT(198-298) component, which reorients so as to maintain its contacts with cTnI while undergoing only a relatively small change in shape.

Animals↗

PubMed2002

Interactions between a nonionic gemini surfactant and cyclodextrins investigated by small-angle neutron scattering.

The microstructure of complexes between hydroxypropyl-cyclodextrins (HPCDs) (alpha, beta, and gamma) and a novel gemini surfactant has been investigated by small-angle neutron scattering (SANS). This nonionic hetero-gemini surfactant (denoted NIHG750) contains two hydrophobic groups and two hydrophilic groups. One is a methyl-capped polyoxyethylene chain with 16 oxyethylene units and the other is a secondary hydroxyl group. Various form factor models have been considered for fitting the SANS data. Spherical aggregates (25 to 40 A) with a size slightly larger than that of NIHG750 micelles (about 23 A) appear in mixed systems. These could be micellar aggregates partly covered with a few cyclodextrin molecules. In addition, the results indicate rod formation (r approximately 8 A, L approximately 70 A) for the NIHG-HPCD complexes. This result is consistent with the threading of HPCDs onto NIHG750 to such an extent that the surfactant molecule takes an extended conformation at high levels of HPCD. Also, the results indicate that HPCDs may interact with the oxyethylene groups of the spherical micellar aggregates leading to an increase in micelle size and a gradual transformation to rod-shaped aggregates. The tendency to form rods increases in the order gamma-CD<alpha-CD<beta-CD. An increase in HPCD concentration results in an increased amount of rods in the system. All spherical aggregates disappear at relative amounts of HPbetaCD above 4 to 5 (molar ratio). However, for HPalphaCD and HPgammaCD spherical aggregates coexist with rod shaped aggregates in the whole range of concentrations investigated here.

Cyclodextrins↗

PubMed2003

Small-angle neutron scattering study of particle coalescence and SDS desorption during film formation from carboxylated acrylic latices.

Four monodisperse core-shell latices were synthesized for small-angle neutron scattering (SANS) studies, differing by the acrylic acid content in the particle shell (1 or 4 wt%) and the T(g) of the acrylic core (around -40 or 10 degrees C). In a first part, the coalescence kinetics of the surfactant-free latices were studied. It was shown that coalescence was hindered by an increase in the acrylic acid content of the shell, pH of the latex, and Tg of the core. These results could be interpreted in terms of chain mobility in the shell and in the core. Upon coalescence, the hydrophilic phase was segregated in spherical, polydisperse domains with an average diameter of 110 nm. In a second part, labeled SDS was used to follow desorption of the surfactant during film formation. It was shown that desorption occurred early in the film formation process when the latex still contained around 20% of water. A small fraction of the surfactant remained irreversibly adsorbed at the particle surface.

Journal Article↗