PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Scattering, Small Angle”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60Linked to original sources
PubMedDate not supplied

Small-angle X-ray and light scattering studies on the influence of Mg2+ ions on the structure of the RNA from bacteriophage MS2.

The influence of Mg2+ ions on the secondary and tertiary structure of the RNA from bacteriophage MS2 was investigated by small-angle X-ray scattering and light scattering and by sedimentation experiments. The analysis of the outer part of the X-ray scattering curve obtained at low temperature in the absence of Mg2+ yielded a cross-section radius of gyration of 0.88 nm and a mass per unit length of 1720 g mol-1 nm-1. Very similar values for these parameters, which refer to the secondary structure of the RNA molecule, were also derived from the X-ray scattering curves obtained in the presence of different amounts of Mg2+ (0.07 to 1 ions per nucleotide). On the contrary, the inner part of the X-ray scattering curves turned out to be highly dependent on the Mg2+ concentration: the cross-section radius of gyration and the mass per unit length, which were determined from the scattering curves at small angles as parameters related to the tertiary structure of the RNA, amounted to 3.11 nm and 4000 g mol-1 nm-1, respectively, in the absence of Mg2+ and increased significantly upon raising the concentration of Mg2+. The increase of these structural parameters was found to be accompanied by a decrease of the overall radius of gyration (as revealed indirectly by X-ray scattering and directly by light scattering measurements) and by an increase of the sedimentation coefficient. The results from the investigations of the RNA at low temperature clearly establish the existence of double-stranded structures down to very low Mg2+ concentrations as well as the occurrence of Mg2+ induced changes of the tertiary structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriophages↗
PubMed2006

pH-responsive micelles and vesicles nanocapsules based on polypeptide diblock copolymers.

The self-assembly of well-defined polypeptide-based diblock copolymers into micelles and vesicles is presented. The stimuli-responsive behavior of polypeptides to pH and ionic strength is used to produce stimuli-responsive nanoparticles with controlled size and shape. Results focusing on micelles and vesicles obtained from polypeptide-based diblock copolymers that are particularly promising for biomedical applications are detailed by means of static and dynamic light scattering analysis, UV circular dichroism, NMR and small angle neutron scattering experiments. Also systems able to form vesicles with a narrow size distribution at basic and acid pH going through a single molecule intermediate state are presented. These nanoparticles are particularly interesting for encapsulation and delivery purpose at a controlled pH.

Capsules↗
PubMed2004

Micelle-vesicle transition of oleyldimethylamine oxide in water.

We studied the effects of the degree of ionization(alpha) and the surfactant concentration (C(d)) on the micelle-vesicle transition in salt-free oleyldimethylamine oxide (OlDMAO) aqueous solutions by the dynamic light scattering (DLS), the hydrogen ion titration, the small angle neutron scattering (SANS), the electrophoretic light scattering (ELS) and viscoelastic measurements. From the study of ionization effects, the micelle-vesicle transition was recognized as a change of aggregate size by the DLS measurement; however, the micelle-vesicle transition was not detected both in the ELS measurement and the hydrogen ion titration, suggesting that the electric properties of the worm-like micelles and the vesicles are very similar despite a large difference of shapes between them. From the results of the SANS, the DLS and the viscosity measurements, it was suggested that a concentration-dependent micelle-vesicle transition took place around C(p)=10 mmolkg-1 for the solutions at alpha=0.5. In the concentration-range 10 mmolkg-1<C(d)<150 mmolkg-1, the micelles and the vesicles coexisted. In the concentration region (C(d) = 10-50 mmolkg-1), the vesicle size increased with the surfactant concentration.

Electrophoresis↗
PubMed2000

Characterisation of a novel solid lipid nanoparticle carrier system based on binary mixtures of liquid and solid lipids.

A drug carrier of colloidal lipid particles with improved payloads and enhanced storage stability was investigated. Based on the experiences with hard fats nanoparticles, a new type of solid lipid nanoparticles (SLN) has been developed by incorporating triglyceride containing oils in the solid core of said particle. The structure and mixing behaviour of these particles were characterised and practical implications on controlled release properties tested. Nanoparticles were characterised by their melting and recrystallisation behaviour as recorded by differential scanning calorimetry (DSC). Polymorphic form and bilayer arrangement were assigned by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). Size distribution and storage stability were investigated by laser diffractometry (LD). Release properties were studied by drug release model according to Franz. A medium chain triglyceride oil was incorporated successfully in a matrix of a solid long chain glyceride. The crystal order was greatly disturbed, however, the carrier remained solid. The oil inside the particle remained in a liquid state and induced a slight shift form the beta' polymorph to the beta(i) form. Long spacings varied within 0.1 nm with increasing oil loads. Nanoparticles with low oil concentrations showed sustained release properties. Improved drug load levels were encapsulated by lipid particles supplemented with oily constituents. Thus, the presented carrier adds additional benefits to the well-known opportunities of conventional SLN and is suited for topical use.

Calorimetry, Differential Scanning↗
PubMed2001

Estimation of fractal dimension of colloidal gels in the presence of multiple scattering.

Colloidal dispersions of fluorinated polymer particles with a refractive index very close to that of water, have been used to investigate the effect of multiple scattering on the estimated fractal dimension of colloidal gels, at high-particle volume fractions. The extent of multiple scattering was varied by using cuvettes of different internal diameters, from 3 to 18 mm. Three gelation systems with different sizes and volume fractions of primary particles have been characterized by static light scattering SLS. The obtained results indicate that multiple scattering affects only the magnitude of the scattered radiation, but not the estimated fractal dimension of the gels. This result confirms the conclusion of the theoretical study reported by Chen et al. [Phys. Rev. B 37, 5232 (1988)]. As a further confirmation, the same gels have been formed in a specially designed cell, with only 0.1 mm thickness (where multiple scattering is negligible) and characterized using small-angle neutron scattering (SANS). It is found that the fractal dimension estimated from SANS measurements, without multiple scattering, is the same as that estimated from SLS measurements, in the presence of substantial multiple scattering.

Journal Article↗
PubMed2004

Influence of forward and multiple light scatter on the measurement of beam attenuation in highly scattering marine environments.

Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1 degrees) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered. Owing to forward-scattering error, a beam-attenuation meter (beam transmissometer) with a half-angle of receiver acceptance of 1.0 degrees and a path length of 0.1 m can underestimate the true beam attenuation within the bubble cloud by more than 50%. For bubble clouds with a beam attenuation of as much as 100 m(-1), the multiple-scattering error is no more than a few percent. These results are compared with simulations for some example phase functions that are representative of other scattering regimes found in natural waters. The forward-scattering error for the Petzold phase function of turbid waters is 16% for a typical instrument geometry, whereas for the Henyey-Greenstein phase function with the asymmetry parameter of 0.7 and 0.9 the error range is 8-28%.

Journal Article↗
PubMed1989

Structural change of the troponin C molecule upon Ca2+ binding measured in solution by the X-ray scattering technique.

The small-angle X-ray scattering technique was used to characterize the overall structural change as well as the state of aggregation of troponin C upon binding various amount of Ca2+ ions: in the Ca2+-free state and at pCa 6.5 and 4.0. Under these conditions, the forward scattering intensities of troponin C are not much different from each other: i.e., they coincide within 4%. From these intensities, the Ca2+-facilitated dimerization of troponin C was not verified, and no appreciable aggregation of troponin C molecules was detected below pCa 4.0. Thus, the small-angle X-ray scattering profiles from troponin C solutions were analyzed assuming a monomeric molecule. The radii of gyration of troponin C were 27.8 +/- 0.3 A, 23.8 +/- 0.2 A, and 22.6 +/- 0.1 A for the Ca2+-free state and at pCa 6.5 and 4.0, respectively. The maximum dimension of the molecule decreases from 111 to 98 A with increasing Ca2+ concentration. These results indicate that the troponin C molecule shrinks remarkably as Ca2+ ions bind to the high affinity sites of the molecule. Ca2+ binding to the low affinity sites, on the other hand, leads to a less pronounced change. Following the interpretation of scattering from the dumbbell-shaped structure (Fujisawa, T., Ueki, T., Inoko, Y., & Kataoka, M. [1987] J. Appl. Cryst. 20, 349-355), the two domains of the molecule move closer to each other. The distance between the centers of the two domains decreases from 46 to 35 A.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Application of percolation theory to the drainage of liquid nitrogen from mesoporous silica xerogel Gelsil 50.

Previous in situ small-angle neutron scattering studies of nitrogen adsorption and desorption at 78 K on the mesoporous silica xerogels Gelsil 50 and Gelsil 75 revealed the formation of ramified clusters of vapor-filled pores on desorption, which is characteristic for a percolation process. In the present work, we check whether the adsorption/desorption isotherm data for a monolithic sample of Gelsil 50 can be analyzed in terms of a bond-percolation model. Three powder samples were studied too. Percolation probability data are presented and the effects of heterogeneous nucleation, finite size, and surface clusters on drainage from Gelsil 50 are addressed. The mean coordination number was derived. The results of the analysis are discussed with respect to recent theoretical work for interactions of fluids with complex pore systems. The monolithic sample and a powder sample were characterized by small-angle neutron scattering data.

Journal Article↗
PubMed2000

Dimyristoylphosphatidylcholine/C16:0-ceramide binary liposomes studied by differential scanning calorimetry and wide- and small-angle x-ray scattering.

Ceramide has recently been established as a central messenger in the signaling cascades controlling cell behavior. Physicochemical studies have revealed a strong tendency of this lipid toward phase separation in mixtures with phosphatidylcholines. The thermal phase behavior and structure of fully hydrated binary membranes composed of dimyristoylphosphatidylcholine (DMPC) and N-palmitoyl-ceramide (C16:0-ceramide, up to a mole fraction X(cer) = 0.35) were resolved in further detail by high-sensitivity differential scanning calorimetry (DSC) and x-ray diffraction. Both methods reveal very strong hysteresis in the thermal phase behavior of ceramide-containing membranes. A partial phase diagram was constructed based on results from a combination of these two methods. DSC heating scans show that with increased X(cer) the pretransition temperature T(p) first increases, whereafter at X(cer) > 0.06 it can no longer be resolved. The main transition enthalpy DeltaH remains practically unaltered while its width increases significantly, and the upper phase boundary temperature of the mixture shifts to approximately 63 degrees C at X(cer) = 0.30. Upon cooling, profound phase separation is evident, and for all of the studied compositions there is an endotherm in the region close to the T(m) for DMPC. At X(cer) >/= 0.03 a second endotherm is evident at higher temperatures, starting at 32.1 degrees C and reaching 54.6 degrees C at X(cer) = 0.30. X-ray small-angle reflection heating scans reveal a lamellar phase within the temperature range of 15-60 degrees C, regardless of composition. The pretransition is observed up to X(cer) < 0.18, together with an increase in T(p). In the gel phase the lamellar repeat distance d increases from approximately 61 A at X(cer) = 0. 03, to 67 A at X(cer) = 0.35. In the fluid phase increasing X(cer) from 0.06 to 0.35 augments d from 61 A to 64 A. An L(beta')/L(alpha) (ripple/fluid) phase coexistence region is observed at high temperatures (from 31 to 56.5 degrees C) when X(cer) > 0.03. With cooling from temperatures above 50 degrees C we observe a slow increase in d as the coexistence region is entered. A sudden solidification into a metastable, modulated gel phase with high d values is observed for all compositions at approximately 24 degrees C. The anomalous swelling for up to X(cer) = 0.30 in the transition region is interpreted as an indication of bilayer softening and thermally reduced bending rigidity.

Biophysical Phenomena↗
PubMed2005

Roles of hydrophobic interaction in a volume phase transition of alkylacrylamide gel induced by the hydrogen-bond-driving alkylphenol binding.

It was found that a degree of the binding of alkylphenols to N-alkylacrylamide gel increased transitionally to induce the volume phase transition of gel. Binding isotherms of nonylphenol (n-Ph), propylphenol (p-Ph), ethylphenol (e-Ph), methylphenol (m-Ph), and phenol (Ph) to N-isopropylacrylamide (NIPA), N,N-diethylacrylamide (DEA), N,N-dimethylacrylamide (DMA), and acrylamide (AM) gels were examined. Two types of binding, the site binding at beta < 1 and the multimolecular binding at beta > 1, were observed, where beta was a degree of binding to a monomeric unit of the chain. The former binding was analyzed with the Hill equation applicable to the cooperative binding and the latter binding with the Brunauer-Emmett-Teller (BET) equation applicable to the multilayer adsorption. The binding constant, K, and the Hill coefficient, N, decreased and increased, respectively, in the order of DEA, NIPA, and DMA gels in the case where the binding alkylphenol was the same. The K value increased in the order of Ph, m-Ph, e-Ph, p-Ph, and n-Ph that bound to the same type of gel. The N value was found to change little with the type of binding alkylphenol. The complexes of N-alkylamide with alkylphenol were condensed to form the ordered nanostructures that were observed as broad scattering peaks in small-angle X-ray scattering experiments. The fluorescence excimer emission was observed for the phenol-binding DMA gel, which corresponded to the condensed state of phenol.

Acrylamides↗
PubMed2005

A small-angle neutron and static light scattering study of micelles formed in aqueous mixtures of a nonionic alkylglucoside and an anionic surfactant.

The size and shape of micelles formed in aqueous mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic sugar-based surfactant n-decyl beta-D-glucopyranoside (C(10)G) at different concentrations of added salt have been investigated with small-angle neutron and static light scattering. Rather small prolate ellipsoidal micelles form in the absence of added salt and at [NaCl] = 10 mM in D(2)O. The micelles grow considerably in length to large rods as the electrolyte concentration is raised to [NaCl] = 0.1 M. In excess of nonionic surfactant ([SDS]/[C(10)G] = 1:3) at [NaCl] = 0.1 M in D(2)O, several thousands of Angstroms long wormlike micelles are observed. Most interestingly, a conspicuously large isotope solvent effect was observed from static light scattering data according to which micelles formed at [SDS]/[C(10)G] = 1:3 and [NaCl] = 0.1 M in H(2)O are at least five times smaller than micelles formed in the corresponding samples in D(2)O.

Alkylation↗
PubMed1985

The shapes of biantennary and tri/tetraantennary alpha 1 acid glycoprotein by small-angle neutron and X-ray scattering.

Two forms of alpha 1 acid glycoprotein (orosomucoid) have been studied using small-angle neutron and X-ray scattering techniques; in one form all the five glycan chains were biantennary, while in the other they were either triantennary or tetraantennary. The radius of gyration RG was found to be sensitive to salt for the biantennary form, but to be unchanged up to an ionic strength of 3 M for the triantennary and tetraantennary forms. Conformational heterogeneity is thus associated with carbohydrate heterogeneity. Hydrodynamic frictional coefficients confirm these findings. Simple models of alpha 1 acid glycoprotein were developed to account for the RG and values. These show that the compact conformation is slightly more elongated than a globular protein and that the expanded biantennary conformation has a most extended carbohydrate structure. Up to half of the surface of the compact shape can be covered by carbohydrate residues.

Amino Acids↗
PubMed2004

Small angle x-ray scattering (SAXS) study of the extracellular Hemoglobin of Glossoscolex paulistus: effect of pH, iron oxidation state, and interaction with anionic SDS surfactant.

pH effects on the oligomeric structure of giant Glossoscolex paulistus extracellular hemoglobin in the oxyand met-forms have been studied as well as effects of the addition of anionic sodium dodecyl sulfate surfactant. A radius of gyration of 110 A is observed for a macromolecule. At 2 mm surfactant, the radius of gyration diminishes slightly for the oxy-form. However, the extrapolated initial scattering intensity (I0) decreases a factor of 2.5, indicating protein dissociation. At 20 mm surfactant, further I0 decrease is observed, with a reduction of radius of gyration to approximately 30 A consistent with dissociation into smaller subunits. At pH 9.0, the scattering curves are similar to that obtained for the protein in the presence of 20 mm surfactant at pH 7.0. A radius of gyration of approximately 35 A shows that the giant hemoglobin dissociation into small subunits also occurs at alkaline pH. From the I0 value, one can suggest that the tetramer is the main scatter at pH 9.0. At pH 7.0, the met-form dissociates to a larger extent at 2 mm surfactant as compared with the oxy-form, and the main scatters seem to be the 1/12 subunit. At pH 9.0, for the oxy-form, the addition of surfactant does not modify the scattering curve and a radius of gyration approximately 30 A is obtained, while for the met-form some kind of aggregation is observed. Our results give support to conclude that the iron oxidation state is an important factor modulating the oligomeric dissociation.

Animals↗
PubMed2003

Flow-induced enhancement of concentration fluctuations in polymer mixtures.

Many mixtures of high-molecular-weight polymers are partially miscible, separating into two co-existing phases in some ranges of temperature and concentration. Generally these binary blends exhibit lower critical solution temperature (LCST) behaviour, becoming phase separated as the temperature is raised. We have been undertaking a systematic study of the effect of simple shear flow on the miscibility limits of a number of high-molecular-weight binary polymer blends exhibiting lower critical-solution temperatures. Using a parallel-plate shear cell and light-scattering detection, we have observed large shifts in the cloud-point curves as blends are heated while shear is applied, and we have been able to show, using ancillary measurements of glass-transition temperatures on quenched samples, that these effects are the results of changes in the miscibility of the blends and not artefacts of the scattering techniques. Both shear-induced 'mixing' and 'demixing' have been observed-the latter in temperature ranges well below the quiescent cloud points. We have investigated the kinetics of the appearance of the two-phase structures, and this is very reminiscent of the spinodal decomposition processes observed in zero shear from these blends. Small-angle neutron scattering is very sensitive to the rather short wavelength concentration fluctuations (a few nanometres) in binary systems, both in the stable one-phase region and in the early stages of instability in the two-phase region. Small-angle neutron-scattering results on blends sheared and quenched at temperatures far below the spinodal temperature show the effects of the shear in modifying the blend's structure factors.

Light↗
PubMed1995

Small-angle X-ray solution scattering study on the dimerization of the FKBP25mem from Legionella pneumophila.

The dimerization of the FK506-binding peptidyl-prolyl cis/trans-isomerase (PPIase) FKBP25mem (Mip (macrophage infectivity potentiator) protein) from Legionella pneumophila was studied by small-angle X-ray solution scattering. A value of 44 kDa, independent on the protein concentration between 2 and 13 mg/ml, confirming that FKBP25mem is a dimer was found for the molecular mass of the protein. The radius of gyration of the protein is 3.3 nm and the Porod volume 87 nm3. A model of the shape of FKBP25mem was evaluated from the scattering curve. Each monomer consists of a proximal and a peripheral domain, which are perpendicular to each other. The envelope of the crystallographic model of human FKBP12 fits well into the peripheral domain. The contact regions between the two monomers in the dimeric protein are probably located between the N-terminal parts of the monomers.

Amino Acid Isomerases↗