Small-angle scattering experiments

Small angle scattering experiments are particularly well suited for in situ studies under realistic conditions [3], because they do not require quenching procedures of the reaction mixture, like TEM [4], NMR or EPR studies. 

Small-Angle Scattering Experiments Contrast Variation. 185... 

Small-Angle Scattering Experiments Influence of Concentration. . 188... 

High resolution multidimensional NMR experiments can provide the dendrimer chemist with a wealth of additional information extending far beyond the determination of the molecular structure. In the interpretation of (2D)-NOESY (NOESY=nuclear Overhauser enhancement spectroscopy) spectra, a knowledge of the spatial interrelationships between protons in different parts of the dendrimer scaffold can be acquired from proton-proton NOE interactions. At the same time, the prevailing conformation of the dendritic branches in the solvent used can be deduced from this information. Furthermore, studies of dendrimer/sol-vent interactions and the influence of solvent on the spatial structure of the dendrimer are also possible [22]. Thus the information content of such NMR experiments resembles that of small-angle scattering experiments on dissolved dendrimers (see Section 7.6). 

Glatter O (1979) The interpretation of real-space information from small angle scattering experiments. J Appl Crystallogr 12 166... 

Support for a concerted model for the yeast enzyme has come from X-ray small angle scattering experiments (162) as well as from hydro-dynamic and optical rotation studies (163, 164). A. volume contraction of about 5% occurs on binding of NAD to the apoenzyme, presumably related to tightening of the tetramer and expulsion of water mojecules. The relation between NAD bound (R) and change of volume (Y) was hyperbolic, in accord with the concerted model. It was lator shown (166) from buoyant density and preferential hydration studies that water is indeed excluded from the yeast enzyme on binding to NAD, such that a volume contraction of about 6% occurs. Furthermore, fluorimetric and calorimetric titrations over the range 6°-40° showed independence of... 

Small angle scattering experiments confirm that the polymer-bound micelles form distinct necklaces (12). Figure 4 shows the scattering curves of micelles bound to a FEO of M - 1.35E5. Here the shoulder corresponds to a separation between bridged micelles, with a low coordination number and a separation d 3 diameters. 

Animal FASs are functional dimers [76]. While /3-ketoacyl synthase requires dimer formation for activity [77], catalysis of the remaining FAS reactions is carried out by the monomeric enzyme. This behavior is reminiscent of yeast fatty acid synthase, where the -ketoacyl synthase and ACP from different subunits also contribute to the same active site. Electron microscopy and small angle scattering experiments have further defined the structure of the functional complex [34,78]. The overall shape of the molecule, as visualized by electron microscopy, is two side by side cylinders with dimensions of 160x146 x 73 A [34]. 

Only few small angle scattering experiments have been performed with this techniquehowever, which is due to the potential deterioration of organic material in the polychromatic beam and the count rate limitation of the detection system. Current applications of this method ly mainly in the area of special environment experiments, e.g. under high pressure and for small structures. 

Fig. 25. Schematic set-up for a small angle scattering experiment with a furnace incorporated into the beam line. The flux of the monochromatized beam is determined by an ionization chamber. A fraction of the primary beam is transmitted through a semitransparent beamstop and recorded together with the scattered photons with a linear position sensitive detector...

M words of information within 128 seconds. In many small angle scattering experiments carried out at EMBL, time frames as short as 1 millisecond are no exception. This is the case for instance in studies of the diffraction patterns of contracting muscle where up to a hundred repetitive measurements are accumulated. The total amount of data in such an experiment can be as high as 256x256x256 = 16Mwords. 

The above considerations make clear that, unless an elaborate data acquisition system is available, it is advisable to reduce the amount of data. In small angle scattering experiments, for instance, where the information is one-dimensional, the use of a circular detector, reduces the large amount of data to a onedimensional pattern. 

Monochromatic beams of 2, 5 or 10 pm in diameter can be used for small angle scattering experiments. 

This last result is known as the Guinier function and is the basis for determining the radius of gyration from small-angle scattering experiments for objects with unknown form factor. 

Figure 4. Characteristic curve obtained in a small angle scattering experiment showing both the peak and the zero order scattering increase.

Let us consider a small-angle scattering experiment. The radiation falls on molecules in a container at fixed pressure. Let us study the scattering in a volume V which is small with respect to the volume of the container but not microscopic (see Fig. 7.1). An elastic transfer wave vector q corresponds to each scattering angle 0 with q — 2k0 sin 0/2, (k0 being the incident wave vector) and the scattering is characterized by the differential cross-section... 

The possibility of controlling the contrast length b enables the experimentalist to deduce the partial structure functions of a mixture from small-angle scattering experiments. 

Asphaltenes can have a fixed capacity for complexing metals.This fact is demonstrated with washing cycles and with increments of scattering by small angle scattering experiments. These sites may be defect centers from the aromatization of S, N, and 0-containing hydrocarbon skeletons. ... 

Graczyk (1978) has investigated the short range order structure, microstructure and compositional fiuctuations of thin films (such as GdCoMoArO) prepared by bias sputter. From his small angle scattering experiments he reports the presence of one halo which shifts with the rotation angle and decreases in intensity as this parameter increases. This clearly shows the anisotropic scatter-... 

In principle, the dispersed phase size distribution can be determined from small-angle scattering experiments, using either X-rays or neutrons. Since a comparatively large volume is sampled by the incident beam, scattering... 

Fig. 14 Time sequence of a time-resolved small-angle scattering experiment Using a stopped-flow apparatus, the data acquisition time, can be synchronized with the mixing pulse time length, t, ...

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