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PubMed1988

Structure of tumour necrosis factor by X-ray solution scattering and preliminary studies by single crystal X-ray diffraction.

The structure of tumour necrosis factor has been investigated by X-ray small-angle scattering and X-ray diffraction using synchrotron radiation. The overall radius of gyration is 25.5 A. A plausible model accounting for the scattering curves consists of an elongated trimer with an axial ratio of 3 to 4 and a maximal chord with a lower limit of 80 A. Tumour necrosis factor has been crystallized in a trigonal space group. Our results are in favour of a single trimer in the asymmetric unit. The diffraction extends to 3.5 A.

Humans↗
PubMed2004

Adsorption of divalent cations on DNA.

The distribution of divalent ions in semidilute solutions of high-molecular-mass DNA containing both sodium chloride and strontium chloride in near-physiological conditions is studied by small-angle x-ray scattering and by small-angle neutron scattering. Both small-angle neutron scattering and small-angle x-ray scattering reveal a continuous increase in the scattering intensity at low q with increasing divalent ion concentration, while at high q the scattering curves converge. The best fit to the data is found for a configuration in which DNA strands of cross-sectional radius 10 angstroms are surrounded by a counterion sheath of outer radius approximately 13.8 angstroms, independent of the strontium chloride concentration. When the strontium chloride is replaced by calcium chloride, similar results are obtained, but the thickness of the sheath increases when the divalent salt concentration decreases. These results correspond in both cases to partial localization of the counterions within a layer that is thinner than the effective Debye screening length.

Adsorption↗
PubMed2003

Analysis of the structure of very large bacterial aggregates by small-angle multiple light scattering and confocal image analysis.

This work aims at developing a more accurate measurement of the physical parameters of fractal dimension and the size distribution of large fractal aggregates by small-angle light scattering. The theory of multiple scattering has been of particular interest in the case of fractal aggregates for which Rayleigh theory is no longer valid. The introduction of multiple scattering theory into the interpretation of scattering by large bacterial aggregates has been used to calculate the fractal dimension and size distribution. The fractal dimension is calculated from the form factor F(q) at large scattering angles. At large angles the fractal dimension can also be computed by considering only the influence of the very local environment on the optical contrast around a subunit. The fractal dimensions of E. coli strains flocculated with two different cationic polymers have been computed by two techniques: static light scattering and confocal image analysis. The fractal dimensions calculated with both techniques at different flocculation times are very similar: between 1.90 and 2.19. The comparison between two completely independent techniques confirms the theoretical approach of multiple scattering of large flocs using the Mie theory. Size distributions have been calculated from light-scattering data taking into account the linear independence of the structure factor S(q) relative to each size class and using the fractal dimension measured from F(q) in the large-angle range or from confocal image analysis. The results are very different from calculations made using hard-sphere particle models. The size distribution is displaced toward the larger sizes when multiple scattering is considered. Using this new approach to the analysis of very large fractal aggregates by static light multiple scattering, the fractal dimension and size distribution can be calculated using two independent parts of the scattering curve.

Bacteria↗
PubMed1985

Studies on hydroxyethyl starch. Part I: Molecular characterization by size exclusion chromatography coupled with low-angle laser light scattering.

Two commercially available hydroxyethyl starch (HES) preparations (in clinical use as plasma expanders) specified with Mw = 450,000/MS = 0.7 and Mw = 200,000/MS = 0.5, respectively, and three experimental HES-samples (supposingly similar to the commercial product with the specification 450,000/0.7, except of one with MS = 0.5) were studied. The latter were prepared via acid or enzymatic hydrolysis of waxy-maize starch. Each of the samples was characterized by its intrinsic viscosity and molar substitution, and was studied with low-angle laser light scattering (LALLS) and with size exclusion chromatography (SEC) coupled with LALLS. The weight-average molecular weight Mw of the commercial samples was found to be 60-80% higher than the value given in the product declaration. This discrepancy can be explained by the argument that previous measurements were not carried out at sufficiently small scattering angles to enable reliable extrapolation to zero angle. The calibration functions Mw(v) of the individual HES-samples measured by SEC/LALLS-coupling are identical over a broad range of the elution volume v and are used for calibration of conventional SEC in a subsequent paper. The small, but detectable differences in the Mw(v)-functions indicate interesting differences between these HES-preparations with respect to the effective hydrodynamic density of the branched HES-molecules.

Chromatography, Gel↗
PubMed1991

Acid denatured apo-cytochrome c is a random coil: evidence from small-angle X-ray scattering and dynamic light scattering.

The conformation of a denatured protein has been investigated, since the experimental data on the structure of denatured proteins have been incomplete until now. The Stokes' radius Rs and the radius of gyration Rg of apo-cytochrome c at pH 2.3 have been determined by dynamic light scattering and small-angle X-ray scattering, respectively. The values of these structure parameters, extrapolated to zero protein concentration, are Rs = 3.0 nm and Rg = 4.6 nm. The ratio Rg.Rs-1 is a sensitive indicator of the molecular conformation. The ratio of 1.55 obtained by us is typical for a random-coil polymer. The persistence length--the characteristic of the molecular flexibility--was determined to be a = 1.81 nm. From this results the root-mean-square average end-to-end distance of the molecules [h2] 1/2 = 11.2 nm and the characteristic ratio [h2]/npl2p = 8.43, where np = 104 is the number of amino acid residues and lp the distance between C alpha-atoms. We obtained a second virial coefficient A2 = 8.2.10(-3) mol cm3 g-2. The experimentally determined structure parameters are in approximate agreement with those predicted by Flory and others for an unperturbed, randomly coiled polypeptide. The expansion factor lies between 1.1 and 1.2. In conclusion, we have shown that apo-cytochrome c at pH 2.3 and at low concentrations has the conformation of a perturbed random coil with repulsive potentials between the chain segments.

Animals↗
PubMed2005

Optical properties of randomly distributed soot: improved polarimetric and intensity scattering functions.

Reference scattering curves for polarization and intensity produced by aggregates and agglomerates of ethylene and kerosene soot are obtained for scattering angles in the 10-170 degrees range. The polarization measurements were obtained with the Propriétés Optiques des Grains Astronomiques et Atmosphériques instrument for particles that levitate in microgravity during parabolic flights and on the ground by an air draught technique. The intensity measurements were obtained also on the ground with a Laboratoire de Metéorologie Physique nephelometer. The maximum polarization is of the order of 80% at a scattering angle of 80 degrees at lambda = 632.8 nm and approximately 75% at an angle of 90 degrees at lambda = 543.5 nm. The polarization increases by approximately 10% when the size of the agglomerate increases from 10 microm to a few hundred micrometers. The intensity curve exhibits a strong increase at small scattering angles. These reference curves will be used in the near future for the detection of stratospheric soot by remote-sensing measurement techniques.

Journal Article↗
PubMed2005

Porphyrin effects on zwitterionic HPS micelles as investigated by small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR).

In this work, small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) studies on the interaction of three anionic mesotetrakis (4-sulfonatophenyl) porphyrins, TPPS4, FeTPPS4, and ZnTPPS4, at concentrations in the 2-10 mM range, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) at pH 4.0 and 9.0 are reported. The SAXS results demonstrate that, upon addition of all species of porphyrins, the HPS micelle of prolate shape reduces its axial ratio from 1.8 +/- 0.2 (in the absence of porphyrin) to 1.5 +/- 0.1. Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.5 A to 18.0 +/- 0.2 A. This shows that the micellar hydrophobic core is affected by porphyrin incorporation, independent of the type of porphyrin and pH. Concurrently, EPR results demonstrate an increase in the micellar packing as noticed from the increase in motional restriction for both nitroxides. Furthermore, increase of the porphyrin concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of an interaction between surface-charged micelles. Such a finding gives strong evidence that the negatively charged porphyrin molecule must accommodate in the HPS micelle dipole layer close to the inner positive charges (near the hydrophobic core), inducing a surface charge (probably a negative one associated with the HPS sulfonate external groups) in the original zwitterionic (overall neutral) micelle. Such a porphyrin location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values that are quite large compared to the binding of cationic drugs to HPS micelles (Caetano, W.; Barbosa, L. R. S.; Itri, R.; Tabak, M. J. Coll. Int. Sci. 2003, 260, 414).

Electron Spin Resonance Spectroscopy↗
PubMed2003

SAXSANA: an interactive program for the analysis and monitoring of static and time-resolved small-angle X-ray solution scattering measurements.

An interactive analytical program, SAXSANA, for small-angle X-ray scattering measurements of solutions is described. The program processes scattered data without disciplined knowledge of small-angle scattering. SAXSANA also assists in finding the best experimental conditions, thus avoiding blind runs of experiments. SAXSANA consists of the following procedures: (i) determination of the centre of scattered X-rays and moment transfer Q (Q = 4pisintheta/lambda, where 2theta is the scattering angle and lambda is the wavelength) for each measured channel; (ii) conversion of the data format to the format of Q versus scattered intensities J(Q); (iii) truncation of unnecessary data and smoothing of scattering curves by cubic-spline function; (iv) correction of the absorption effect and subtraction of the scattered intensity of the buffer (solvent) solution from that of the sample solution; (v) creation of a data file for a three-dimensional representation of time-resolved scattering curves; (vi) determination of radii of gyration by Guinier plots; (vii) determination of persistent lengths by Kratky plots; (viii) extrapolation of the small-angle part by Guinier plots; (ix) extrapolation of the wide-angle part by Porod's & Luzzati's laws for the Hankel transformation in order to obtain the distance distribution function p(r); (x) calculation of p(r) and computation of the invariant, the chord length, the Volume, the spherical radius, the maximum dimension D(max) and the radius of gyration (Rg). SAXSANA also serves as an on-site monitor for the validity of an experimental result during the measurements.

Journal Article↗
PubMed2001

Brillouin scattering study of molten zinc chloride.

Polarized and depolarized Brillouin scattering experiments on molten ZnCl2 were performed between 300 and 600 degrees C in different geometries. VV spectra measured in backscattering and small angle scattering were analyzed with conventional viscoelastic theory using either a Debye or a Cole-Davidson model for the memory function. We also analyzed in the same way the temperature dependence of the transverse Brillouin lines detected in a 90 degrees VH geometry. We show that the Cole-Davidson memory function yields a consistent interpretation of all the spectra. The resulting shear and longitudinal relaxation times are equal within their error bars, and are about 2.5 times smaller than the alpha relaxation time previously determined. The static shear viscosity values deduced from the analysis of the propagating transverse waves agree, at all temperatures, with the measured viscosity values.

Journal Article↗
PubMedDate not supplied

An evaluation of NMR cryoporometry, density measurement and neutron scattering methods of pore characterisation.

Sol-gel silicas with nominal pore diameters ranging from 25A to 500A were studied by NMR cryoporometry, and by neutron diffraction and small angle scattering from dry silicas over the Q range 8. 10(-4)A(-1) < or = Q < or = 17A(-1). Density and imbibation experiments were also performed. Geometric models of porous systems were constructed and were studied by both analytic techniques and Monte-Carlo integration. These models, combined with the information from the above measurements, enabled the calculation of the fully density corrected solid-solid density correlation functions G(r) for the sol-gel silicas, deduction of the (voidless) silica matrix density, measurement of the silica fraction in the grain and of the packing fraction of the silica grains and an estimation of the water equivalent residual hydrogen on the dried silica surface. In addition, the pore diameter D, pore diameter to lattice spacing ratio D/a, and pore and lattice variance sigma could also be measured. While the NMR cryoporometry pore diameter measurements for the sol-gel silicas show excellent co-linearity with the nominal pore diameters as measured by gas adsorption, and the calculated pore diameters from the measured neutron scattering show surprisingly good agreement with these measurements at large pore diameters, there is a divergence between the calibrations for pore diameters below about 100A.

Magnetic Resonance Spectroscopy↗
PubMedDate not supplied

[Small-angle diffuse x-ray scattering on fine muscle filaments].

Theoretical small-angle diffuse scattering curves from muscle thin filament models have been calculated. The curves reveal a maximum at 115' scattering angle. It has been shown that the maximum is due to the pitch of F-actin helix. Theoretical curves are in good agreement with the earlier obtained curves of small-angle diffuse scattering from F-actin dilute solutions.

Actins↗
PubMed2002

Anomalous Rayleigh scatter in dilute media.

Anomalous Rayleigh scatter is examined for dilute concentrations of the biomedically relevant element iodine in aqueous media including measurements with monochromatic synchrotron radiation in the vicinity of the iodine K-edge. The measurements agree with anomalous scatter-factor corrections to the form-factor approximation which has been shown to have good agreement with higher precision S-matrix calculations for small angle scatter over a wide range of energies but has not been adequately tested at the edge. Monte Carlo modelling, including the modelling of polarized Compton and Rayleigh scattered x-rays, is used to determine the relative contributions of the scatter and fluorescent components at the detector as well as the modelling of self-absorption and relative dose in the determination of detection limits. A Rayleigh scatter minimum of 28 barns/sr was observed at an energy 10 +/- 5 eV below the K-edge of iodine at a position predicted from an evaluation of the dispersion integral that includes bound-bound resonance contributions. Minimum detectable concentrations for observation of the anomalous Rayleigh scatter feature at an exposure of 10 mSv, predicted for iodine and iron, are 1 mg ml(-1) and 10 mg ml(-1), respectively. Upper limits to detection of the feature imposed by degradation of the signal by self-absorption are 0.021 g cm(-2) and 0.0029 g cm(-2) radiation lengths, respectively.

Biophysical Phenomena↗
PubMed1999

Ab initio phasing using molecular envelope from solution X-ray scattering.

Solving the phase problem is the crucial and quite often the most difficult and time-consuming step in crystallographic structure determination. The traditional methods of isomorphous replacement (MIR or SIR) and molecular replacement require the availability of an isomorphous heavy-atom derivative or the structure of a homologous protein, respectively. Here, a method is presented which utilizes the low-resolution molecular shape determined from solution X-ray scattering data for the molecular search. The molecular shape of a protein is an important structural property and can be determined directly by the small-angle scattering technique. The idea of locating this molecular shape in the crystallographic unit cell has been tested with experimental diffraction data from nitrite reductase (NiR). The conventional Patterson search proved to be unsuccessful, as the intra-envelope vectors are uniformly distributed and do not match those of intra-molecular (atom-to-atom) vectors. A direct real-space search for orientation and translation was then performed. A self-rotation function using 2.8 A crystallographic data yielded the polar angles of the non-crystallographic threefold axis. Knowledge of the orientation of this axis reduces the potential six-dimensional search to four (Eulerian angle gamma and three translational parameters). The direct four-dimensional search within the unit cell produced a clear solution. The electron-density map based on this solution agrees well with the known structure, and the phase error calculated from the map was 61 degrees within 20 A resolution. It is anticipated that the low-resolution envelope can be used as a starting model for phase extension by the maximum-entropy and density-modification method.

Crystallography, X-Ray↗
PubMedDate not supplied

Refraction effects of diffraction-enhanced radiographic imaging: a new look at bone.

The objective of this study was to demonstrate the ability of a novel radiographic technology-diffraction-enhanced imaging-to detect contrast in bone tissue through absorption, refraction, and scatter rejection. Diffraction-enhanced imaging uses a synchrotron x-ray beam to produce images of high contrast by measuring the object's refraction and ultra-small angle scattering of x-rays in addition to the attenuation measured by conventional radiography. We present evidence that diffraction-enhanced imaging provides contrast enhancement at the edges of cortical and cancellous bone and a three-dimensional appearance of trabeculae.

Animals↗
PubMed1975

[Structure of animal ribosomes. VI. Adynamic model of ribosome structure].

A dynamic model for the structure of ribosomes is developed using X-ray small-angle scattering data and electron micrographs of ribosomes and polysomes. The large subunit has the shape of a conical frustum, and has a groove at its flat side. The small subunit consists of two semiparticles which are connected by a molecular strand; it may assume two conformations: a prolate P conformation and an oblate O conformation. Translocation of the ribosome along the mRNA in the elongation process of protein synthesis is accomplished by cyclic conformation transitions P-O-P-O in combination with the linking and rupturing of bonds. This mechanism is called "rack and roll" mechanism.

Animals↗
PubMed2004

The structure of metallomicelles.

The morphology of micelles formed by two novel metallosurfactants has been studied by small-angle neutron scattering (SANS) and small-angle-X-ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are Cu(II) complexes of monopendant alcohol derivatives of a) the face-capping macrocycle 1,4,7-triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10-tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X-ray scattering to locate the metal ions. For the 1,4,7,10-tetraazacyclododecane-based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7-triazacyclononane analogue. The X-ray scattering analysis shows that the metal ions are distributed throughout the polar head-group region, rather than at a well-defined radius; this is in good agreement with the SANS-derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.

Journal Article↗
PubMed1995

A comparison of structure and thermal behavior in human plasma lipoprotein(a) and low-density lipoprotein. Calorimetry and small-angle X-ray scattering.

Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) studies have been performed to investigate the structural properties of lipoprotein(a) [Lp(a)] and low-density lipoprotein (LDL) obtained from the same donor. In addition, a comparison was made between autologous LDL and the remnant particle Lp(a-) obtained by removal of apo(a) through chemical reduction. With Lp(a), three distinct thermal transitions have been observed: the first one around 20 degrees C, arising from the core-located apolar lipids, similar to LDL but with a significantly lower melting temperature as compared to LDL of the same donor. The second one, at 55.7 +/- 0.25 degrees C, can be attributed to apo(a), since it was found to be absent in Lp(a-) and LDL, whereas isolated apo(a) in aqueous solution exhibited a similar transition. The third transition, at 80.4 +/- 0.9 degrees C, corresponds to apo-B100 protein unfolding. The low melting temperature of the core lipids in Lp(a) is preserved in Lp(a-); this suggests that the apolar lipid interactions are unaffected by apo(a) binding, and that the difference in the core melting behavior between Lp(a) and LDL is due to a different stabilization through interaction between the apolar core and the surface monolayer lipids. SAXS curves exhibited qualitatively the same characteristic features for LDL, Lp(a), and Lp(a-). Thus, the SAXS results showed that no major deviations from spherical particle shape occur with Lp(a), indicating that apo(a) wraps around the particle surface without major globular protrusions into the aqueous surrounding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗