Nature of radiation defects in synthetic quartz according to the small-angle neutron scattering data

The supraatomic structure of single crystals of synthetic quartz in the initial state with a dislocation density of 570 cm^?2 and after irradiation in the VVR-M reactor at the Petersburg Nuclear Physics Institute with fast neutrons having the energy E _n > 1 MeV in the range of fluences F _n = 7.7 × 10¹⁷ ?2.1 × 10²⁰ neutrons/cm² has been studied by small-angle scattering of thermal neutrons. It is established that fast neutrons form point, linear, and volume lattice defects throughout the entire sample volume. Large-volume structures (nuclei of the amorphous phase) in quartz, reaching ～100 nm in size, occupy a small total volume (～1.5%) even at the maximum fluence 2.1 × 10²⁰ neutrons/cm². The majority of damage is related to the point defects with the radius of gyration of 1–2 nm and linear defects, which give comparable contributions up to several percent.     

Structure of unilamellar vesicles: Numerical analysis based on small-angle neutron scattering data

The structure of polydispersed populations of unilamellar vesicles is studied by small-angle neutron scattering for three types of lipid systems, namely, single-, two-and four-component vesicular systems. Results of the numerical analysis based on the separated-form-factor model are reported.     

Choice of potential in the analysis of small-angle neutron scattering

The small-angle scattering of thermal neutrons from large-scale inhomogeneities of a material is considered. It is shown that the neutron-optical potential must be taken as the inhomogeneity potential both in the Born and eikonal approximations. The neutron-optical potential is the Fermi pseudopotential averaged over a volume containing many nuclei but with linear sizes much smaller than the sizes of the inhomogeneities measured.     

Investigation of the tripoli porous structure by small-angle neutron scattering

The characteristics of the tripoli porous structure have been investigated by small-angle neutron scattering (SANS). Tripoli is a finely porous sedimentary rock formed by small spherical opal particles. Its main component is aqueous silica SiO₂ · nH₂O (80–90%). Tripoli is widely used in practice as a working medium for sorption filters and in some other commercial and construction technologies. The shape of the experimental SANS curves indicates the presence of small and large pores in tripoli. The small-pore size was estimated to be ～100 Å. The size of large pores turned out to be beyond the range of neutron wave vector transfers Q that are available for the instrument used; however, their size was indirectly estimated to be ～(2000–2500) Å. The pores of both groups behave as surfacetype fractal scatterers with the fractal dimension D ～ 2.2‐2.6. The densities of pores of these two groups differ by approximately three orders of magnitude (～10¹⁶ and ～10¹³ cm^?3 for small and large pores, respectively); the fraction of large pores amounts to 70–80% of the total pore volume. The found pore characteristics (their densities, sizes, and relative volumes) are in satisfactory agreement (when a comparison is possible) with the absorption data.     

Structural studies of amorphous solids by small-angle neutron scattering

Sophisticated new methods of preparation developed over the last decade have considerably extended the range and nature of amorphous materials, many of which have a microstructure on a scale of 10–1000 Å. Whilst in some cases this is due to the composition, in others it is a direct result of the preparation technique. This paper reviews the present state of small-angle scattering as a tool to study the microstructure in the four main classes of amorphous materials: bulk glass, metal ribbons, thin films and inorganic gels. The techniques specific to neutron scattering, which have been developed to separate the various components of the scattering curves, are reviewed.     

Database for rapid protein classification based on small-angle X-ray scattering data

A method was developed for rapid protein classification based on comparison of the experimental small-angle X-ray scattering data with scattering curves calculated for proteins with known structures. For this purpose, a database was compiled from about 1500 theoretical scattering curves for proteins with known structures. The potential of this method was illustrated by its application to analysis of the experimental scattering data from sperm whale myoglobin.     

Study of three-dimensionally ordered structures of intact mitochondria by small-angle neutron scattering

The ultrastructure of cristae of intact mitochondria, in which the activity of the oxidative phosphorylation system was retained, was investigated by small-angle neutron scattering. Osmotic swelling of organelles was found to cause ultrastructural rearrangements of the inner mitochondrial membrane in rat liver and heart mitochondria. This process was accompanied by the appearance of diffraction peaks indicative of the formation of ordered structures. The lamellar packing of the membranes in heart mitochondria, which is observed under normal conditions, was found to undergo a transition to a nonlamellar hexagonal packing, whose scattering curve shows two peaks with the scattering vectors characterized by a spacing ratio of 1:√3. The electron-microscopy results confirm the possibility of the formation of a hexagonal packing of the inner membrane in heart mitochondria.     

Investigation of the interaction of dimethyl sulfoxide with lipid membranes by small-angle neutron scattering

The influence of dimethyl sulfoxide (CH₃)₂SO (DMSO) on the structure of membranes of 1,2-dimiristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in an excess of a water-DMSO solvent is investigated over a wide range of DMSO molar concentrations 0.0 ≤ X _DMSO ≤ 1.0 at temperatures T = 12.5 and 55°C. The dependences of the repeat distance d of multilamellar membranes and the thickness d _b of single vesicles on the molar concentration X _DMSO in the L _β’ gel and L _α liquid-crystalline phases are determined by small-angle neutron scattering. The intermembrane distance d _s is determined from the repeat distance d and the membrane thickness d _b. It is shown that an increase in the molar concentration X _DMSO leads to a considerable decrease in the intermembrane distance and that, at X _DMSO = 0.4, the neighboring membranes are virtually in steric contact with each other. The use of the deuterated phospholipid (DMSO-D6) and the contrast variation method makes it possible, for the first time, to determine the number of DMSO molecules strongly bound to the membrane.     

Characterization of oligomerization of a peptide from the ebola virus glycoprotein by small-angle neutron scattering

Transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) studies showed that model peptides QNALVCGLRQ (G33) and QNALVCGLRG (G31) corresponding to region 551–560 of the GP protein of the Sudan Ebola virus are prone to oligomerization in solution. Both peptides can form amyloid-like fibrills. The G33 peptide forms fibrils within one day of incubation, whereas the fibrillogenesis of the G31 peptide is observed only after incubation for several months. The possible role of the observed processes in the pathogenesis and the possibility of applying a combination of the TEM and SANS techniques to search for new compounds that are able to influence the protein oligomerization are discussed.     

Effect of surfactant excess on the stability of low-polarity ferrofluids probed by small-angle neutron scattering

The structures of ferrofluids (FFs) based on nonpolar solvent decahydronaphthalene, stabilized by saturated monocarboxylic acids with hydrocarbon chains of different lengths, C16 (palmitic acid) and ?12 (lauric acid), with an excess of acid molecules, have been studied by small-angle neutron scattering. It is found that the addition of acid to an initially stable system with optimal composition leads to more significant structural changes (related to aggregation) than those observed previously for this class of FFs. A comparison of the influence of monocarboxylic acids on the stability of nonpolar FFs suggests that the enhancement of aggregation is much more pronounced in the case of palmitic acid excess. This fact confirms the conclusion of previous studies, according to which an increase in the hydrocarbon chain length in a saturated acid reduces the efficiency of the corresponding FF stabilization.     

Structural hierarchy of chromatin in chicken erythrocyte nuclei based on small-angle neutron scattering: Fractal nature of the large-scale chromatin organization

The chromatin organization in chicken erythrocyte nuclei was studied by small-angle neutron scattering in the scattering-vector range from 1.5 × 10^?1 to 10^?4 Å^?1 with the use of the contrast-variation technique. This scattering-vector range corresponds to linear dimensions from 4 nm to 6 μm and covers the whole hierarchy of chromatin structures, from the nucleosomal structure to the entire nucleus. The results of the present study allowed the following conclusions to be drawn: (1) both the chromatin-protein structure and the structure of the nucleic acid component in chicken erythrocyte nuclei have mass-fractal properties, (2) the structure of the protein component of chromatin exhibits a fractal behavior on scales extending over two orders of magnitude, from the nucleosomal size to the size of an entire nucleus, and (3) the structure of the nucleic acid component of chromatin in chicken erythrocyte nuclei is likewise of a fractal nature and has two levels of organization or two phases with the crossover point at about 300–400 nm.     

Porosity and structural parameters of Karelian shungites according to the data of small-angle synchrotron radiation scattering and microscopy

The nanoporosity and structure of natural carbons has been investigated on the example of Karelian carbon-rich shungites by comparing the data of small-angle synchrotron radiation scattering and highresolution microscopy. The analysis of small-angle scattering data is based on the model of scattering spheres with lognormal size distribution. It is found that the structure of samples from the Maksovo and Zazhogino deposits subjected to high temperatures in the geological medium and (also to a lesser extent) a sample from the Shunga deposit can be described as an aggregation of polydisperse scattering spheres with lognormal size distribution; the characteristic scatterer size is determined for them. A comparison with microscopy data shows that these scatterers are mainly associated with pores, and the character of their size distribution is similar to that previously established for nanoglobules in schungites.     

Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C₆₀ in carbon disulfide CS₂ have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 Å in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.     

Effect of the age of the C60/N-methyl-2-pyrrolidone solution on the structure of clusters in the C60/N-methyl-2-pyrrolidone/water system according to the small-angle neutron scattering data

Fullerene clusters in the C₆₀/N-methyl-2-pyrrolidone (NMP)/water system have been investigated by small-angle neutron scattering. It is shown that the scattering cross section corresponding to the size range 10–100 nm depends on the water content in the mixture. Addition of water to a C₆₀/NMP solution in an amount exceeding 40% leads to a sharp increase in the average scattering cross section. This effect depends on the interval between the times of preparation of a C₆₀/NMP solution and its dilution with water: the size of the clusters formed as a result of adding water increases with increasing the age of the initial solution. The reasons for this effect are discussed.     

Anomalous small-angle scattering as a way to solve the Babinet principle problem

X-ray absorption spectra (XAS) have been used to determine the absorption edges of atoms present in a sample under study. A series of small-angle X-ray scattering (SAXS) measurements using different monochromatic X-ray beams at different wavelengths near the absorption edges is performed to solve the Babinet principle problem. The sizes of clusters containing atoms determined by the method of XAS were defined in SAXS experiments. In contrast to differential X-ray porosimetry, anomalous SAXS makes it possible to determine sizes of clusters of different atomic compositions.     

Algorithms for solving atomic structures of nanodimensional clusters in single crystals based on X-ray and neutron diffuse scattering data

New algorithms for solving the atomic structure of equivalent nanodimensional clusters of the same orientations randomly distributed over the initial single crystal (crystal matrix) have been suggested. A cluster is a compact group of substitutional, interstitial or other atoms displaced from their positions in the crystal matrix. The structure is solved based on X-ray or neutron diffuse scattering data obtained from such objects. The use of the mathematical apparatus of Fourier transformations of finite functions showed that the appropriate sampling of the intensities of continuous diffuse scattering allows one to synthesize multiperiodic difference Patterson functions that reveal the systems of the interatomic vectors of an individual cluster. The suggested algorithms are tested on a model one-dimensional structure.     

A study of the structure of mixed micellar solutions based on heptaethylene glycol monotetradecyl ether and sodium (lithium) dodecyl sulfate by the small-angle neutron scattering method

The micellization in mixed aqueous systems based on a new nonionic surfactant, namely, heptaethylene glycol monotetradecyl ether (C₁₄E₇), and an anionic surfactant, namely, sodium dodecyl sulfate, sodium decyl sulfate, or lithium dodecyl sulfate, is studied by small-angle neutron scattering. Preliminary results of the investigation into the behavior of C₁₄E₇ aqueous solutions (at two concentrations, 0.17 and 0.50%) upon addition of small amounts of three different classical anionic surfactants are reported.