Carbohydrate moieties of molluscan Rapana venosa hemocyanin

Using Zn2+ ions as new method, several FUs have been isolated from molluscan Hc Rapana venosa without formation of non-functional proteolytic side products. N-terminal sequences of these fragments in comparison with FUS from other gastropodan Hcs show a very high degree of structural identity. Four Fus, purified from enzyme-treated structural subunits RvH1 and RvH2 (RvH1-a, RvH1-f, RvH2-a and RvH2-e) show identical N-terminal sequences compared to fragments isolated after treatment with Zn2+ ions. However, in some cases trypsin cleaves RvH chains at different positions if compared to the Zn2+ treatment. To analyze the oligosaccharide composition of two FUS from the first structural subunit of Rapana Hc, RvH1-a and RvH1-f, several techniques were applied: capillary electrophoresis, MALDI-MS, ESI-MS in combination with glycosidase digestions. On basis of these results and the determined amino acid sequence two N-linkage sites were identified in the FU RvH1-a, but only one in the FU RvH1-f.     

X-ray scattering from a randomly rough surface

Abstract

On the basis of the method of reduced Rayleigh equations we present a simple and reciprocal theory of the coherent and incoherent scattering of x-rays from one- and two-dimensional randomly rough surfaces, that appears to be free from the limitations of earlier theories of such scattering based on the Born and distorted-wave Born approximations. In our approach, the reduced Rayleigh equation for the scattering amplitude(s) is solved perturbatively, with the small parameter of the theory η(ω) = 1 - ε(ω), where ε(ω) is the dielectric function of the scattering medium. The magnitude of η(ω) for x-rays is in the range from 10^?6 to 10^?3, depending on the wavelength of the x-rays. The contributions to the mean differential reflection coefficient from the coherent and incoherent components of the scattered x-rays are calculated through terms of second order in η(ω). The resulting expressions are valid to all orders in the surface profile function. The results for the incoherent scattering display a Yoneda peak when the scattering angle equals the critical angle for total internal reflection from the vacuum-scattering medium interface for a fixed angle of incidence, and when the angle of incidence equals the critical angle for total internal reflection for a fixed scattering angle. The approach used here may also be useful in theoretical studies of the scattering of electromagnetic waves from randomly rough dielectric-dielectric interfaces, when the difference between the dielectric constants on the two sides of the interface is small.     

Counterion distribution around DNA probed by solution X-ray scattering

Counterion atmospheres condensed onto charged biopolymers strongly affect their physical properties and biological functions, but have been difficult to quantify experimentally. Here, monovalent and divalent counterion atmospheres around DNA double helices in solution are probed using small-angle x-ray scattering techniques. Modulation of the ion scattering factors by anomalous (resonant) x-ray scattering and by interchanging ion identities yields direct measurements of the scattering signal due to the spatial correlation of surrounding ions to the DNA. The quality of the data permit, for the first time, quantitative tests of extended counterion distributions calculated from atomic-scale models of biologically relevant molecules.     

Biomolecular solution X-ray scattering at the National Synchrotron Light Source

In recent years there has been a growing interest in the application of X-ray scattering techniques to biomolecules in solution. At NSLS, a new undulator-based beamline, X9, has been constructed to address the oversubscribed user demand for X-ray scattering. Beamline X9 has the capability to perform small/wide-angle X-ray scattering (SAXS/WAXS) all in one single instrument. This is accomplished by utilizing a vacuum sample/detector chamber that is an integral part of the SAXS scattering flight path. This vacuum chamber allows a WAXS detector to be positioned at a close distance from the sample, while not interfering with scattered X-rays at small angles from reaching the SAXS detector. A regular training program, the X9 workbench, has also been established to allow users to become familiar with beamline X9 for solution X-ray scattering.     

X-ray diffuse scattering from incommensurable structures

X-Ray diffuse scattering from a series of examples where the reason for the existence of incommensurable features is fairly well understood, is described. They include in particular non stoichiometric compounds such as [DIPS Φ₄(l₃)0.76] and such as intercalated graphite RbC₂₄. and quasi one dimensional conductors. A particular emphasis is given on various 1 - D conductors and to the relation of the incommensurability to the characteristics of the electron conduction bands.     

X-ray scattering by a superlattice

X-ray scattering by a superlattice consisting of two types of alternating layers is considered, including both the statistical spread in the layer thicknesses and the phase slippage at inter-layer boundaries. The Bragg peak is not only smeared out, but it is also displaced by an amount proportional to the phase slippage.     

X-ray scattering from polymer nematic liquid crystals

X-ray scattering from main chain polymer nematics is discussed from the point of view of its use in studying the ordering and fluctuations of the polymer chains that make up the nematic phase. An example of data from poly-γ-benzyl glutamate is given, with a discussion of the important features of the data, in terms of the current understanding of the nature of nematic ordering in main chain polymer systems. This includes analyses of the angular distribution function for the polymer segments, long wavelength fluctuations dictated by elastic phenomena, the effects of finite chain lengths, and effects due to the short range interactions and packing of the chains.     

X-ray scattering from freely suspended smectic-A films

This work is devoted to a theoretical analysis of specular reflection and diffuse scattering of x-rays from a freely suspended smectic-A film, taking into account its spatial inhomogeneity and deviations of orientational and position ordering in smectic layers from ideal ordering. The results of the calculations are compared with the experimental data on small-angle scattering of x-rays from freely suspended films of 7 AB liquid crystals. It is found that the theoretical results agree with the experimental data.     

Small-angle X-ray scattering from styrene-butadiene-styrene block copolymers

Abstract

A new type of time-dependent and strain-history-dependent viscoelasticity was discovered in semidilute polymer solutions. Dynamic moduli G′ and G″ of 20% and 10% nitrile butadiene rubber (NBR) solutions were recorded as a function of time while oscillatory shear deformations were maintained. The moduli decrease with time was observed only at lower frequencies. The time dependence of G′ was more pronounced than that of G″. At a higher temperature, the time dependence was extended toward higher frequencies also, and the time dependence became stronger. Lowering the concentration of solution gave a similar effect as increasing temperature. After the cessation of oscillations, a slow recovery was observed. The recovery was somewhat faster at the higher temperature. The time-dependent moduli and their recovery were explained by the change and recovery of structures associated with long branches and gels in the NBR. The structure change occurred at higher frequencies also, but it was not observed during the application of oscillation. Only in subsequent measurements at lower frequencies could the structure change be detected. Thus, the change may be regarded as strain history dependent. The mechanism of the structural change was explained with either the entanglement or osmotic pressure models, depending on concentration.     

X-ray inelastic scattering from small particles of graphite

The spectrum of inelastically scattered X-ray radiation from small particles of graphite shows energy losses which are due to volume and surface plasmons, as in the foil case. Surface plasmons from spherical particles (SPS) have not been observed. It is shown that graphite is inappropriate in the study of SPS using X-ray scattering experiments.     

Small angle X-ray scattering studies on structures of alkylthiol stabilized-silver nanoparticles in solution

Silver nanoparticles (SNPs), which were stabilized with various alkylthiols, were studied in detail with synchrotron small angle X-ray scattering, UV-Vis spectroscopy and transmission electron microscopy (TEM). UV spectra of SNPs capped with various alkylthiols showed the characteristic surface plasmon bands at ∼ 450 nm. However, the spectral shapes of SNPs with relatively short butanethiols became weaker and asymmetrically broader in the longer wavelength region. Their nanostructures were deliberately characterized by small angle X-ray scattering analysis based on a hard sphere model and TEM results. PACS 61.05.cf; 61.46.Df; 81.07.Pr     

Anomalous small-angle X-ray scattering from charged soft matter

A review of recent applications of Anomalous Small-Angle X-ray Scattering (ASAXS) to charged soft matter systems is presented. Although the potential of ASAXS was realized in the eighties [1], applications to soft matter systems became feasible in recent years thanks to the technical developments at the synchrotron sources. Examples include both stiff chain and flexible polyelectrolytes, colloidal brush-like polyelectrolytes, DNA, RNA, and polysaccharides where the counterion profile could be determined with high precision and compared with theoretical models. In addition, ASAXS has also been found useful for microstructure characterization in soft materials. Finally, the present capability for ASAXS studies is illustrated by an example involving a surfactant micellar system.     

Diffuse X-ray scattering from several platinum chain compounds

Values of the Fermi wavevector for several platinum based one-dimensional conductors were determined from diffuse X-ray scattering measurements. The values were compared with those expected from the chemical compositions. The importance of conclusive values of this parameter is stressed and the coupling between Peierls instability and other structural instabilities is discussed.