Contrast variation method

More recently, Loppinet and co-workers have used both SAXS and SANS (with contrast variation methods) to characterize the morphology of dilute PFSI solutions having a volume fraction of polymer less... 

The contrast variation method gives the ability to highlight or blank out different phases of a multi-phase system and adds greatly to the power of SANS. 

Anomalous small angle X-ray scattering (ASAXS) exploits contrast variation methods to highlight the scattering from one elemental component in a multielement sample, such as one ion species in an ion-DNA system. The ASAXS... 

Anomalous SAXS (ASAXS) takes advantage of contrast variation methods to highlight the small angle scattering signal from a single elemental component correlated with a larger system (Stuhrmann, 1981), for example, one... 

Microemulsions consist of oil, water and an oil-water interfacial Him. DLS and SLS have been used to determine the translational diffusion coefficient and the interaction potential of microemulsions [45—47). The thickness of the inter-facial film and its curvature were measured by the contrast variation method in neutron scattering [48,491. This method is based on changing the scattering strength by changing the relative amount of light and heavy water in the microemulsion. 

Knoll WK, Ibel K, Sackmann E. Small-angle neutron scattering 48. study of lipid phase diagrams by the contrast variation method. Biochemistry 1981 20 6379-6383. 

The contrast Ap is the difference between the average particle density and the solvent, i.e. Pv-Ps- The step function pv(r) is 0 outside the particle and 1 within the particle boundaries, and corresponds to the volume that excludes solvent molecules. At high Ap, py(r) is dominant, and at low Ap, pp(r) is dominant. Contrast variation methods permit the separation of the Pv(r) and Ppir) terms by varying Ap. 

Several aspects of neutron scattering studies are particularly elegant and unique in terms of the contrast variation method to examine internal structures as well as the external morphology. Thus the protein positions within the 30S ribosomal subunit can be determined by triangulation of deuterated subunits [489,490] the shell-like spherical structures of protein, lipid and nucleic acid within viruses [546,555,566] and lipoproteins can be analysed the distinct disposition of carbohydrates within glycoproteins [197,198,214], membranes within membrane proteins [39], or proteins within protein-nucleic acid complexes [385,387,392] can be elucidated. Likewise X-ray scattering has been of value in protein-lipid systems since these two components can be readily distinguished from one another [75,76]... 

Application of Contrast Variation Methods to Core-Shell Latex Structures... 

Contrast variation methods can sometimes be used to remove a component of the scattering by matching its scattering power with that of the medium in which it is dispersed. This principle can be used in SANS experiments via isotopic solvent mixtures (e.g. H2O/D2O) to adjust the scattering power of the medium, as for example in studies of polymer latexes. Grancio and Williams [35] postulated a polymer-rich spherical core surrounded by a monomer-rich shell which serves as the major locus of polymerization, thus giving rise to core-shell morphology. Thus, the first formed... 

A small-angle X-ray scattering(SAXS) study of a model copolymer latex, based on styrene and pentabromobenzyl acrylate(PBBA, 40 wt %), was conducted. The contrast variation method used was shown to be a sensitive probe for inhomogeneity in the particles. The separation of the homogeneous function allowed direct calculation of the size distribution of the spherical particles. The SAXS analysis revealed a particle s inner structure which was a continuous copolymer phase, the composition of which was slightly richer in PBBA, within which domains of PS were randomly distributed. The volume fraction of the PS domains was estimated as 11 vol % and their characteristic length as 5.1 nm. 24 refs. 

Fig. 2. Contrast variation method for a core (Q — shell (S) particle immersed in a matrix (M). Scattering length densities as indicated...

This example further demonstrates the power of neutron scattering to extract structural information of individual components in a complex system by use of the contrast variation method. Contrast variation provides an additional sample preparation technique that allows the extraction of the scattering of a single component in a multicomponent mixture and broadens the utility of neutron scattering into fields such as the study of biological complexes and the structure of diblock copolymers (74). 

The contrast-variation methods which have found wide application in structural biology can sometimes be used to remove a component of the scattering by matching its scattering power with that of the medium in which it is dispersed, and thus... 

Abstract Sorbitol is a natural cryoprotectant for some organisms. In order to reveal the mechanism of a protection some organisms against low temperatures, we studied the interaction between sorbitol and phosphatidylcholine (PC) which is one of major component of cell membranes. Small-angle neutronscattering contrast variation method was used to characterize dihexanoyl-PC (dC(6)PC) micelles in the presence of sorbitol (2 M). As a result, the aggregation number for the dC(6)PC micelle and the volume per a single molecule in the micelle were estimated... 

Key words Sorbitol - cryoprotectant - phosphatidylcholine - micelle neutron scattering - contrast-variation method... 

Eq. (5) indicates that in the case of the system of aggregates with some hydration inside we can also determine the monomer volume directly by varying the solvent scattering density, namely, by using the solvent contrast variation method, in the same way of the cases of the large... 

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