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Results for “Scattering, Small Angle”

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PubMed2005

Comparison of dewaterability and floc structure of synthetic sludge with activated sludge.

This work compared the appearance, dewaterability, floc size, fractal dimensions derived from free-settling test and light-scattering test, and detailed structural information of floc interior including porosity, Sierpinski carpet fractal dimension, and the fractal dimension of the pore boundaries of a synthetic sludge and an activated sludge. The present synthetic sludge could probe the change in filterability and in fractal dimensions extracted from small angle light scattering test and from free-settling test after conditioning, however, failed to reproduce the detailed structural information of sludge flocs. The use of specific synthetic sludge depends on the field of interest. For instance, the present synthetic sludge is not appropriate to simulate the intrafloc transport of solute owing to its incapability to reproduce the detailed floc structure or to its change after conditioning.

Flocculation↗

PubMed1990

Neutron scattering study of the (gamma-B) catalytic domains of complement proteases activated C1r and C1s.

The catalytic domains of activated C1r and C1s, comprising the C-terminal region of the A chain (gamma), disulphide-linked to the B chain, were obtained by limited proteolysis of the native proteases with chymotrypsin and plasmin, respectively, and studied by small angle neutron scattering. For activated C1s (gamma-B), a molar mass of 45,000 +/- 5000 g/mol, and a relatively large radius of gyration (Rg) of 28 +/- 1 A were determined, excluding a single globular domain. The corresponding values for activated C1r (gamma-B)2 (90,000 g/mol, Rg = 34 +/- 1 A) are consistent with a dimer involving the loose packing of two (gamma-B) subunits. Various models of the dimer are discussed in the light of neutron scattering and other data.

Chymotrypsin↗

PubMed2004

In vitro characterization of PEGylated phospholipid micelles for improved drug solubilization: effects of PEG chain length and PC incorporation.

Sterically stabilized micelles (SSM) composed of poly(ethylene glycol-2000)-grafted distearoylphosphatidylethanolamine (DSPE-PEG) and sterically stabilized mixed micelles (SSMM) composed of DSPE-PEG and egg-phosphatidyl choline (PC) have recently been introduced as novel lipid based carriers for water-insoluble drugs. However, factors that affect the solubilization behavior of these phospholipid micelles are not well understood. This study investigates the effect of PEG chain length and PC content on physical properties and solubilization potential of PEGylated phospholipid micelles. Critical micelle concentrations (CMC) determined for DSPE-PEG with different PEG chain lengths (2000, 3000, and 5000) using a fluorescent probe were in the micromolar range (0.5-1.5 microM) with higher CMC for longer PEG chain length. The size of micelles determined by quasi-elastic light scattering (QELS) showed that micellar systems became heterogeneous when PC was added at > or =25% for DSPE-PEG 2000 and > or = 40% for DSPE-PEG 5000, respectively. Above these critical PC ratios a significant increase in aggregation number and formation of rodlike particles were observed by small angle neutron scattering (SANS). Solubilization of diazepam was greater with DSPE-PEG 2000 than DSPE-PEG 5000 simple micelles as determined by RP-HPLC. However, DSPE-PEG 5000 micelles showed greater improvement in solubilization of the water-insoluble drug with an increase in PC content. In conclusion, phospholipid micelle size and solubilization potential varied with PEG chain length and PC content in the mixed micelle. Aggregation number and shape of the micelles did not significantly change until the critical PC concentrations.

Diazepam↗

PubMed2004

PNIPAM-co-polystyrene core-shell microgels: structure, swelling behavior, and crystallization.

The present contribution presents the single-step preparation and characterization of poly(N-isopropyl acrylamide)-co-polystyrene core-shell microgels with varying polystyrene content. The swelling behavior of the particles is investigated using dynamic light scattering and differs significantly from the swelling behavior of poly(N-isopropyl acrylamide) homopolymer particles. The lower critical solution temperature is found to be shifted to lower temperatures upon increasing the polystyrene content of the particles. The core-shell structure of the particles is revealed by means of small angle neutron scattering (SANS) using the method of contrast variation. Additionally, the formation of mesoscopic crystals of these particles is investigated by means of scanning electron microscopy and also by SANS. The particles seem to have preferable properties with respect to crystallization compared to homopolymer microgels.

Journal Article↗

PubMed1997

Collagen fiber architecture of a cultured dermal tissue.

Advances in tissue engineering have led to the development of artificially grown dermal tissues for use in burn and ulcer treatments. An example of such an engineered tissue is Dermagraft, which is grown using human neonatal fibroblasts on rectangular sheets of biodegradable mesh. Using small angle light scattering (SALS), we quantified the collagen fiber architecture of Dermagraft with the mesh scaffold contributions removed through the use of a structurally based optical model. Dermagraft collagen fibers were found to have a preferred direction nearly parallel to the long dimension of the kite-shaped mesh opening with small spatial variations over the mesh. This study demonstrated the utility of SALS as a rapid and inexpensive technique for the evaluation of gross collagen fiber architecture in engineered tissues.

Cells, Cultured↗

PubMedDate not supplied

Novel algorithm of processing optical coherence tomography images for differentiation of biological tissue pathologies.

A numerical algorithm based on a small-angle approximation of the radiative transfer equation (RTE) is developed to reconstruct scattering characteristics of biological tissues from optical coherence tomography (OCT) images. According to the algorithm, biological tissue is considered to be a layered random medium with a set of scattering parameters in each layer: total scattering coefficient, variance of a small-angle scattering phase function, and probability of backscattering, which fully describe the OCT signal behavior versus probing depth. The reconstruction of the scattering parameters is performed by their variation to fit the experimental OCT signal by the theoretical one using a time-saving genetic algorithm. The proposed reconstruction procedure is tested on model media with known scattering parameters. The possibility to estimate scattering parameters from OCT images is studied for various regimes of OCT signal decay. The developed algorithm is applied to reconstruct optical characteristics of epithelium and stroma for normal cervical tissue and its pathologies, and the potential to distinguish between the types of pathological changes in epithelial tissue by its OCT images is demonstrated.

Algorithms↗

PubMed1998

Structural Changes in the Isotropic Phase of the Ternary Surfactant System: Tetradecyldimethylamine Oxide/Benzyl Alcohol/Water.

The surfactant system tetradecyldimethylamine oxide (TDMAO)/benzyl alcohol/water has been studied. In the phase diagram of this ternary system a large isotropic region is encountered that connects the water corner to the benzyl alcohol corner. This isotropic phase has been investigated in some detail by means of electric conductivity, viscosity, electric birefringence, and small-angle neutron scattering (SANS) measurements. From these experiments it can be concluded that for roughly equal amounts of alcohol and water a bicontinuous structure is present, similar to that typically observed for bicontinuous microemulsions. The structural units present become continuously smaller with increasing alcohol content, and at very high alcohol content only small reverse aggregates are present. The formation of this bicontinuous phase can be understood by the fact that the presence of the benzyl alcohol reduces the stiffness of the surfactant film, and therefore such a "sponge"-type structure is favored. With increasing surfactant concentration the amphiphilic film becomes stiffer again, which leads to the formation of a lamellar phase. The corresponding phase boundary is exactly related to the amphiphilicity factor as it can be deduced from the scattering experiments. Copyright 1998 Academic Press.

Journal Article↗

PubMed2006

Self-assembly, structural, and retrostructural analysis of dendritic dipeptide pores undergoing reversible circular to elliptical shape change.

The synthesis of dendritic dipeptides (4-3,4-3,5-4)12G2-CH(2)-Boc-L-Tyr-L-Ala-OMe and (4-3, 4-3,5-4)12G2-CH(2)-Boc-D-Tyr-D-Ala-OMe is described. These dendritic dipeptides self-assemble into porous elliptical and circular columns that in turn self-organize into centered rectangular columnar and hexagonal columnar periodic arrays. The transition from porous elliptical to porous circular columns is mediated in a reversible or irreversible way by the thermal history of the sample. A method to determine the dimensions of hollow elliptical and circular columns by the reconstruction of the small-angle powder X-ray diffractograms of the centered rectangular or hexagonal columnar lattices was elaborated. This technique together with wide-angle X-ray experiments performed on aligned fibers provided access to the structural and retrostructural analysis of elliptical supramolecular pores. This procedure is general and can be adapted for the determination of the dimensions of pores of any columnar shape.

Calorimetry, Differential Scanning↗

PubMed2000

Measurements of the average thickness of material using scattered radiation

A method for determination of the average thickness of material placed between a gamma-ray source and a detector is presented. The method requires the measurement of the ratio between the number of gamma-rays scattered at small angles in the material and registered in the spectrum and the number of gamma-rays penetrating the material without interacting with it and registering in the full-energy peak. The relation describing that ratio in terms of the average gamma-ray path length in the sample, the energy interval where the scattered radiation is measured and the detector response to unscattered gamma-rays was verified by measurements of gamma-ray path lengths in material with known thicknesses at energies of 662 and 1115 keV. Differences between the measured and known thicknesses were less than 15% for thicknesses of copper between 2.5 and 17 g/cm2.

Journal Article↗

PubMed2003

Neutron-mapping polymer flow: scattering, flow visualization, and molecular theory.

Flows of complex fluids need to be understood at both macroscopic and molecular scales, because it is the macroscopic response that controls the fluid behavior, but the molecular scale that ultimately gives rise to rheological and solid-state properties. Here the flow field of an entangled polymer melt through an extended contraction, typical of many polymer processes, is imaged optically and by small-angle neutron scattering. The dual-probe technique samples both the macroscopic stress field in the flow and the microscopic configuration of the polymer molecules at selected points. The results are compared with a recent "tube model" molecular theory of entangled melt flow that is able to calculate both the stress and the single-chain structure factor from first principles. The combined action of the three fundamental entangled processes of reptation, contour length fluctuation, and convective constraint release is essential to account quantitatively for the rich rheological behavior. The multiscale approach unearths a new feature: Orientation at the length scale of the entire chain decays considerably more slowly than at the smaller entanglement length.

Journal Article↗

PubMed2002

A hybrid scatter correction for 3D PET based on an estimation of the distribution of unscattered coincidences: implementation on the ECAT EXACT HR+.

We implemented a hybrid scatter-correction method for 3D PET that combines two scatter-correction methods in a complementary way. The implemented scheme uses a method based on the discrimination of the energy of events (the estimation of trues method (ETM)) and an auxiliary method (the single scatter simulation method (SSSI) or the convolution-subtraction method (CONV)) in an attempt to increase the accuracy of the correction over a wider range of acquisitions. The ETM takes into account the scatter from outside the field-of-view (FOV), which is not estimated with the auxiliary method. On the other hand, the auxiliary method accounts for events that have scattered with small angles, which have an energy that cannot be discriminated from that of unscattered events using the ETM. The ETM uses the data acquired in an upper energy window above the photopeak (550-650 keV) to obtain a noisy estimate of the unscattered events in the standard window (350-650 keV). Our implementation uses the auxiliary method to correct the residual scatter in the upper window. After appropriate scaling, the upper window data are subtracted from the total coincidences acquired in the standard window, resulting in the final scatter estimate, after smoothing. In this work we compare the hybrid method with the corrections used by default in the 2D and 3D modes of the ECAT EXACT HR+ using phantom measurements. Generally, the contrast was better with the hybrid method, although the relative errors of quantification were similar. We conclude that hybrid techniques such as the one implemented in this work can provide an accurate, general-purpose and practical way to correct the scatter in 3D PET, taking into account the scatter from outside the FOV.

Brain↗

PubMedDate not supplied

A model for calculating the effects of small inhomogeneities on electron beam dose distributions.

Charged particles penetrating a medium are repeatedly deflected from their line of motion by coulomb interactions with target nuclei. This physical feature should be included in the calculation of dose distributions when the irradiated medium contains small inhomogeneities. We use the mean path taken by particles in homogeneous media to represent their motion through inhomogeneous materials. This procedure adapts wht small angle multiple scattering formalism to yield manageable, approximate solutions when a medium contains arbitrarily composed inhomogeneities. To promote the development of this procedure into an electron beam treatment planning program, we discuss the salient features which arise in connection with electron beam inhomogeneity calculations. We use a solid phantom containing an air cavity just below its surface as a particular example of a small inhomogeneity. We discuss qualitatively and quantitatively the dose distributions which result from their irradiation with an 11-MeV electron beam.

Humans↗

PubMed2003

Asphaltene nanoparticle aggregation in mixtures of incompatible crude oils.

We study the structure and phase behavior of asphaltenes comprised of large polyaromatic molecules in blends of naturally occurring crude oils using small angle neutron scattering (SANS). When two compatible oils are blended together, the asphaltenes remain dispersed as colloidal nanoparticles; however, when two incompatible oils are blended together, these asphaltene nanoparticles can aggregate to form microscale structures. We show that SANS directly probes asphaltene aggregation in unmodified (i.e., nondeuterated) crude oil mixtures due to a significant neutron scattering length density difference between the hydrogen-poor asphaltenes and the surrounding oil. Moreover, the small length scales probed by SANS are ideally suited for studying asphaltene aggregation: SANS simultaneously provides the average size and concentration of nanoscale asphaltene particles and also the volume fraction of microscale asphaltene aggregates. These discoveries yield a practical means for directly assessing the compatibility of crude oils and for diagnosing refinery fouling problems resulting from blending incompatible oils.

Journal Article↗

PubMed2006

Characterising the size and shape of polyamidoamines in solution as a function of pH using neutron scattering and pulsed-gradient spin-echo NMR.

Bioresponsive polymers are being developed as synthetic viral mimetics to enhance the intracellular delivery of macromolecular therapeutic agents such as genes, proteins and peptides. In this context we have designed pH-responsive, amphoteric polyamidoamines (PAAs) which change conformation on passing from a neutral pH (extracellular) to an acidic pH (endosomal and lysosomal) environments. PAAs have already demonstrated cytosolic delivery of genes and non-permeant toxins (e.g. gelonin and ricin A chain). The aim of this study was to use small-angle neutron scattering (SANS) to investigate the most likely shape of the hydrochloride salt form of one particular PAA (ISA23) in solution, under pH conditions that mimic those the polymer would be expected to encounter during endocytic internalisation (pH 7.4-3). It was shown that models based on a Gaussian coil representation of the polymer conformation described the SANS data better over this pH range than models based on a rod-like conformation. The conformation of ISA23 at 37 degrees C was expanded (radius of gyration approximately 80A) at pH approximately 3 but collapsed with an increase in pH (radius of gyration approximately 20A at pH 7.4), a conclusion also reached in a model-free analysis of the neutron data. Outside this pH range - at the extremes of high and low pH - the polymer coil collapsed and interpretation of the scattering was slightly complicated by the presence of a very weak structure factor indicating that the polymer coils are highly charged. The PAA concentration did not significantly affect the polymer size over the concentration range 10-50mg/ml. Characterisation of the dynamics of these polymer solutions - diffusion coefficients and viscosity -ostensibly suggest a very different conclusion with the polymer expanding as the pH is increased, but this arises due to weak aggregation of the amphoteric polymer coils.

Hydrogen-Ion Concentration↗

PubMed1991

The influence of heptane-1,2,3-triol on the size and shape of LDAO micelles. Implications for the crystallisation of membrane proteins.

The presence of small amphiphiles has been found to be necessary in the crystallization of several membrane-protein/surfactant complexes. It has been suggested that the role of the small amphiphile may be to reduce the size of the surfactant belt around the protein, making the formation of crystals easier. Thus far it was not known if this would involve changes in micellar size in general or whether the small amphiphile would merely replace LDAO during crystal growth. In the present study we have used small angle neutron scattering to study mixed micelles of lauryldimethyl amine oxide (LDAO; hydrogenated and deuterated) and heptane-1,2,3-triol (HP). Our results show that with increasing overall HP concentrations mixed LDAO/HP micelles of decreasing mass and radius are formed. The composition of these micelles has been determined. HP thus may decrease the size of the surfactant belt around a protein before crystallisation by insertion into a host micelle. As HP is a 'small amphiphile' compared to the surfactants used for solubilization of membrane proteins, the curvature of the host micelle will be increased by its insertion.

Dimethylamines↗

PubMed2003

Detection of ligand- and solvent-induced shape alterations of cell-growth-regulatory human lectin galectin-1 in solution by small angle neutron and x-ray scattering.

The bioactivity of galectin-1 in cell growth regulation and adhesion prompted us to answer the questions whether ligand presence and a shift to an aprotic solvent typical for bioaffinity chromatography might alter the shape of the homodimeric human lectin in solution. We used small angle neutron and synchrotron x-ray scattering studies for this purpose. Upon ligand accommodation, the radius of gyration of human galectin-1 decreased from 19.1 +/- 0.1 A in the absence of ligand to 18.2 +/- 0.1 A. In the aprotic solvent dimethyl sulfoxide, which did not impair binding capacity, galectin-1 formed dimers of a dimer, yielding tetramers with a cylindrical shape. Intriguingly, no dissociation into subunits occurred. In parallel, NMR monitoring was performed. The spectral resolution was in accord with these data. In contrast to the properties of the human protein, a nonhomologous agglutinin from mistletoe sharing galactose specificity was subject to a reduction in the radius of gyration from approximately 62 A in water to 48.7 A in dimethyl sulfoxide. Evidently, the solvent caused opposite responses in the two tested galactoside-binding lectins with different folding patterns. We have hereby proven that ligand presence and an aprotic solvent significantly affect the shape of galectin-1 in solution.

Computer Simulation↗

PubMed2004

Extraction of zirconium nitrate by TBP in n-octane: influence of cation type on third phase formation according to the "sticky spheres" model.

Small-angle neutron scattering (SANS) data for the tri-n-butyl phosphate (TBP)-n-octane, HNO(3)-Zr(NO(3))(4) solvent extraction system, obtained under a variety of experimental conditions, have been interpreted using the Baxter model for hard spheres with surface adhesion. The increase in scattering intensity in the low Q range observed when increasing amounts of Zr(NO(3))(4) were extracted into the organic phase was interpreted as arising from interactions between small reverse micelle-like particles containing two to three TBP molecules. Upon extraction of Zr(NO(3))(4), the particles interact through attractive forces between their polar cores with a potential energy that exceeds 2 k(B)T. The interparticle attraction, under suitable conditions, leads to third phase formation. A linear relationship exists between the derivative of the potential energy of attraction with respect to the concentration of nitrate ions in the organic phase and the ionization potential or the hydration enthalpy of the extracted metal cations.

Cations↗

PubMed1986

Distribution of protein and RNA in the 30S ribosomal subunit.

In Escherichia coli, the small ribosomal subunit has a sedimentation coefficient of 30S, and consists of a 16S RNA molecule of 1541 nucleotides complexed with 21 proteins. Over the last few years, a controversy has emerged regarding the spatial distribution of RNA and protein in the 30S subunit. Contrast variation with neutron scattering was used to suggest that the RNA was located in a central core of the subunit and the proteins mainly in the periphery, with virtually no separation between the centers of mass of protein and RNA. However, these findings are incompatible with the results of efforts to locate individual ribosomal proteins by immune electron microscopy and triangulation with interprotein distance measurements. The conflict between these two views is resolved in this report of small-angle neutron scattering measurements on 30S subunits with and without protein S1, and on subunits reconstituted from deuterated 16S RNA and unlabeled proteins. The results show that (i) the proteins and RNA are intermingled, with neither component dominating at the core or the periphery, and (ii) the spatial distribution of protein and RNA is asymmetrical, with a separation between their centers of mass of about 25 angstroms.

Escherichia coli↗