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At least 487 records · Page 27Linked to original sources
PubMed2000

Reconstruction from small-angle neutron scattering measurements of the real space magnetic field distribution in the mixed state of Sr2RuO4.

We have measured the diffracted neutron scattering intensities from the square magnetic flux lattice in the perovskite superconductor Sr2RuO4, which is thought to exhibit p-wave pairing with a two-component order parameter. The relative intensities of different flux lattice Bragg reflections over a wide range of field and temperature have been shown to be inconsistent with a single component Ginzburg-Landau theory but qualitatively agree with a two-component p-wave Ginzburg-Landau theory.

Journal Article↗
PubMed2003

Persistence length for a model semirigid polyelectrolyte as seen by small angle neutron scattering: a relevant variation of the lower bound with ionic strength.

In a SANS experiment, we have directly determined for the first time the conformation of hyaluronan, a model semirigid polyelectrolyte. At high ionic strength, this is completely possible, where the scattered intensity crosses over (when decreasing q) from a q(-1) rod variation to a q(-2) and, where fitting to the "wormlike" chain model gives the backbone, intrinsic, persistence length: L0 = 86.5 A. At low ionic strength, we can safely check that the measured persistence length appears increased by at least the amount predicted by Odijk for the electrostatic contribution, L(e) (approximately kappa(-2), square of the Debye screening length). However, the intensity at the lowest q is not only due to the single chain, since it crosses over from a q(-1) to a q(-4) variation, characteristic of polymer associations.

Journal Article↗
PubMed1978

Small-angle light scattering studies on xylose cataract formation in bovine lenses.

Using polarized light scattered in the I'' and I+ modes, we determined the relative contributions of density and orientation fluctuation to the opacity of bovine lenses. In both the cortex and the nucleus of bovine lenses cultured in xylose column, we found that the increase in hydration effects the optical anisotropy (birefringence) first, before the lake formation will contribute heavily to the density fluctuation.

Animals↗
PubMed2003

Trifluoperazine effects on anionic and zwitterionic micelles: a study by small angle X-ray scattering.

In this work small angle X-ray scattering (SAXS) studies on the interaction of the phenothiazine trifluoperazine (TFP, 2-10 mM), a cationic drug, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) and the anionic surfactant sodium dodecyl sulfate (SDS, 40 mM) at pH 4.0, 7.0, and 9.0 are reported. The data were analyzed through the modeling of the micellar form factor and interference function, as well as by means of the distance distribution function p(r). For anionic micelles (SDS), the results evidence a micellar shape transformation from prolate ellipsoid to cylinder accompanied by micellar growth and surface charge screening as the molar ratio TFP:SDS increases in the complex for all values of pH. Small ellipsoids with axial ratio nu=1.5+/-0.1 (long dimension of 60 A) grow and reassemble into cylinder-like aggregates upon 5 mM drug incorporation (1 TFP:8 SDS monomers) with a decrease of the micelle surface charge. At 10 mM TFP:40 mM SDS cylindrical micelles are totally screened with an axial ratio nu approximately 4 (long dimension approximately 140 A at pH 7.0 and 9.0). However, at pH 4.0, where the drug is partially diprotonated, 10 mM TFP incorporation gives rise to a huge increase in micellar size, resulting in micelles at least 400 A long, without altering the intramicellar core. For zwitterionic micelles (HPS), the results have shown that the aggregates also resemble small prolate ellipsoids with averaged axial ratio approximately nu=1.6+/-0.1. Under TFP addition, both the paraffinic radius and the micellar size show a slight decrease, giving evidence that the micellar hydrophobic core may be affected by phenothiazine incorporation rather than that observed for the SDS/TFP comicelle. Therefore, our results demonstrate that the axial ratio and shape evolution of the surfactant:TFP complex are both dependent on surfactant surface-charge and drug:surfactant molar ratio. The results are compared with those recently obtained for another phenothiazine drug, chlorpromazine (CPZ), in SDS and HPS micelles (Caetano, Gelamo, Tabak, and Itri, J. Colloid Interface Science 248 (2002) 149).

Antipsychotic Agents↗
PubMed2004

Interaction of proteins with spherical polyelectrolyte brushes in solution as studied by small-angle x-ray scattering.

We use small-angle x-ray scattering (SAXS) as a tool to study the binding of proteins to spherical polyelectrolyte brushes (SPB) in situ. The SPB consists of a solid core of approximately 100 nm diam onto which long polyelectrolyte chains [poly(styrene sulfonic acid, PSS) and poly(acrylic acid, PAA)] have been densely grafted. The proteins used in this investigation, Bovine Serum Albumine (BSA) and Bovine Pancreatic Ribonuclease A (RNase A), adsorb strongly to these SPB if the ionic strength is low despite their negative charge. Virtually no adsorption takes place at high ionic strength. SAXS demonstrates that both proteins are distributed within the brush. The findings reported here give further evidence that the strong adsorption of proteins to SPB is due to the "counterions release forces": The patches of positive charge on the surface of the proteins become multivalent counterions of the polyelectrolyte chains. Thus, a concomitant number of co- and counterions is thereby released and the entropy of the entire system is increased. The repulsive Coulombic interaction as well as the steric repulsion between the proteins and the brush layer are counterbalanced by this effect. The data discussed here demonstrate that the adsorption of proteins in SPB presents a new principle for the immobilization of proteins.

Adsorption↗
PubMed1991

Small angle X-ray scattering studies on myosin.

Small angle X-ray scattering (SAXS) is a potentially powerful method for obtaining structural information from biological molecules in solution. The use of this technique in the laboratory has hitherto been limited by the long exposures necessary to obtain patterns on photographic film. Multi-wire area detectors, due to their high efficiency and absence of noise, enable patterns to be collected much more rapidly, typically in 1-2 h for a typical protein using laboratory sources. This opens up the possibility of using the technique on a semi-routine basis for a wide variety of problems. We outline the use of SAXS to characterise a large conformational change of myosin.

Animals↗
PubMed1983

Structural studies of cytochrome P-450 using small angle x-ray scattering.

We have employed small angle x-ray scattering to examine the solution conformation of cytochrome P-450cam in the presence and absence of its substrate, camphor. The radius of gyration (Rg) of the protein is found to be 23.9 +/- 0.2 A in both states. Comparison of the radius of gyration with that expected for a spherical protein of the same molecular weight indicates that P-450 is an elongated molecule and that its shape may best be approximated by a cylinder about 30 A in diameter and 80 A in length.

Cytochrome P-450 Enzyme System↗
PubMed1995

Structures of fd gene 5 protein.nucleic acid complexes: a combined solution scattering and electron microscopy study.

Small-angle scattering and electron microscopy studies of fd gene 5 protein (g5p) and reconstituted g5p.nucleic acid complexes have been used to test models for the complexes and evaluate their uniqueness. In addition, we have obtained new information on the dependence of nucleotide type and protein/nucleotide (P/N) ratio on the structure of the complexes. Reconstituted complexes were made with single-stranded fd viral DNA (fd ssDNA), poly[d(A)] and poly[r(A)]. All complexes form similar left-handed, flexible superhelices having approximately the same diameter, but the pitch differs among these complexes. The g5p protein is a dimer in solution and the dimers associate to form a superhelical framework to which the polynucleotide is attached. The combined X-ray and neutron scattering data confirm the nucleic acid is inside the protein superhelix. A Monte Carlo integration modeling procedure applied to the scattering data was used to systematically test large numbers of possible models for each complex, and previously proposed models based on parameters obtained from electron microscopy were found to be essentially correct and unique. The data on the complexes with different P/N ratios showed that mass per unit length values decreased while the rise per dimer and pitch of the superhelix increased for g5p.fd-ssDNA complexes with decreasing P/N ratios.

DNA, Single-Stranded↗
PubMedDate not supplied

[Use of linear proportional chambers for small-angle synchrotron radiation scattering in solutions of biopolymers].

The results of applying linear position sensitive proportional counters to diffuse small-angle synchrotron radiation scattering to biopolymer solutions are presented. Synchrotron radiation of the VEPP-3 storage ring (Institute of Nuclear Physics, Novosibirsk) was used. On the basis of small-angle scattering curve obtained from protein pepsinogen it has been shown that the exposure is about 100 times less than with conventional X-ray technique.

X-Ray Diffraction↗
PubMed1993

Molten globule of cytochrome c studied by small angle X-ray scattering.

Recent advances in the small angle X-ray scattering technique have made it possible to obtain information on the spatial distribution of protein structure in solution, such as the radius of gyration and shape of the molecule, in a relatively short time. We have studied the various conformational states of horse ferricytochrome c by small angle X-ray scattering. Whereas Guinier plots showed that the radius of gyration of the molten globule state is slightly larger than that of the native state, Kratky plots indicated that their shape is globular. To clarify the mechanism of the formation of the molten globule state, we measured, by the small angle X-ray scattering, the equilibrium transition at pH 2 from the acid-unfolded state to the molten globule state, which was induced either by the addition of NaCl or the acetylation of lysyl amino groups. The Kratky plots at various stages of folding showed an isoscattering point, strongly suggesting a two-state mechanism. For both the NaCl and acetylation-induced transitions, the transition curve determined from Kratky plots agreed well with the transition curves from far-ultraviolet circular dichroism, tryptophan fluorescence, and Soret absorption, further supporting the two-state mechanism.

Acetylation↗