SAXS analysis

The classical treatment of diffuse SAXS (analysis and elimination) is restricted to isotropic scattering. Separation of its components is frequently impossible or resting on additional assumptions. Anyway, curves have to be manipulated one-by-one in a cumbersome procedure. Discussion of diffuse background can sometimes be avoided if investigations are resorting to time-resolved measurements and subsequent discussion of observed variations of SAXS pattern features. A background elimination procedure that does not require user intervention is based on spatial frequency filtering (cf. p. 140). 

In an attempt to separate the domains from the cores, we used limited degradation with several proteases. CBH I (65 kda) and CBH II (58 kda) under native conditions could only be cleaved successfully with papain (15). The cores (56 and 45 kda) and terminal peptides (11 and 13 kda) were isolated by affinity chromatography (15,16) and the scission points were determined unequivocally. The effect on the activity of these enzymes was quite remarkable (Fig. 7). The cores remained perfectly active towards soluble substrates such as those described above. They exhibited, however, a considerably decreased activity towards native (microcrystalline) cellulose. These effects could be attributed to the loss of the terminal peptides, which were recognized as binding domains, whose role is to raise the relative concentration of the intact enzymes on the cellulose surface. This aspect is discussed further below. The tertiary structures of the intact CBH I and its core in solution were examined by small angle X-ray scattering (SAXS) analysis (17,18). The molecular parameters derived for the core (Rj = 2.09 mm, Dmax = 6.5 nm) and for the intact CBH I (R = 4.27 nm, Dmax = 18 nm) indicated very different shapes for both enzymes. Models constructed on the basis of these SAXS measurements showed a tadpole structure for the intact enzyme and an isotropic ellipsoid for the core (Fig. 8). The extended, flexible tail part of the tadpole should thus be identified with the C-terminal peptide of CBH I. 

Sakamoto N, Hashimoto T (1995) Order-disorder transition of low molecular weight polystyrene-block-polyisoprene. 1. SAXS analysis of two chracteristic temperatures. Macromolecules 28(20) 6825-6834... 

Table III. SAXS Analysis of PMMA-g-PDMS Films.

Results from SAXS analysis and GA (using COp gas) for the same coal samples are shown below in Table I. From the results of SAXS analysis it may be concluded that the investigated Victorian brown coal possesses an extensive micropore system containing between 10 to 10 pores per gram. Additionally, according to the shape hypothesis these pores may be either slit-like (thin discs with large diameters) or filament-like (long narrow cylinders) and are... 

Particle size distributions are important information for evaluating the synthesis, growth and kinetics of formation of nanoparticles and nanoparticle aggregates. The main contrasting techniques are imaging via TEM, and SAXS analysis. TEM analysis is independent of the type of aggregation, shape and size of nanoparticles, whereas SAXS interpretation requires assumptions about the nature of the sample. On the other hand, SAXS can be done on in situ systems, and often in real time during particle formation. 

Figure 35. Comparison of distribution functions extracted from SAXS data versus from TEM observations. There are some systematic errors in the TEM analysis. However some larger scale particles appear to be lost in the SAXS analysis. As TEM particle counting favors larger particles this could also be a systematic effect. After Rieker et al. (1999).

Both HA and FA have been shown to form micelles, but not at concentrations that are environmentally relevant. The inability of FA to solubilize pyrene at concentrations above its CMC, and the lower solubility enhance of DDT in FA micelles compared to HA suggests that the smaller size of the molecules which comprise FA, and consequently the micelles that form from it, affects the solubilization phenomena. The SAXS analysis of HA does not show an abrupt change in size or fractal dimension as the solution concentration increases beyond the CMC which suggests that only a portion of the molecules which comprise HA are involved in the micellization phenomena. 

For this electron microscopy examination, we used a dicarboxylic polystyrene neutralized with Ba, (PS-Ba) of FT = 60 000 and FT /FTp = 1.24. The end-to-end distance is about 198 A. Note that no SAXS analysis is possible for such a molecular weight because the "ionomer peak" is very weak (low ionic content) and its position is such that it is washed out by the small angle upturn observed in all ionomers. 

In order to get a better insight into the formed microstructures, SAXS analysis of thick films of all PBA-P AN copolymers listed in Table 2 was performed. Most of the materials revealed cylindrical morphologies and then-different compositions affected the cylinders fi -spacing in the micro-phase separated structures. Furthermore, the SAXS studies showed that annealing of the films for 2 hours at 150°C resulted in improved phase separation (42). 

There are no crystallites smaller than 1 nm in the low dispersion catalysts for hydrogen chemisorption on platinum particles (H/Pt) <0.5. In that case the MCP hydrogenolysis is selective, and the value of the ratio l hydrog. IS higher than 0.5. Above (H/Pt)>0.5, the MCP hydrogenolysis is non-selective, Rhydrog. is equal to 0.5, and crystallites smaller than 1 nm are present, as determined by electron spectroscopy and SAXS analysis. 

In the present article, we review recent SAXS-studies conducted on polymeric latexes. We will first give an exposition on the theory of SAKS including contrast variation based on references [56-60]. The main purpose of the theoretical exposition is a clear assessment of the structural information embodied in the SAXS-intensities. This discussion will also be helpful to delineate possible limitations of this method. It will reveal which parameters can be gained from a SAXS-analysis of latex particles and their relation to the structure of the particles. 

Polydispersity has a profound influence because it smears out the deep minima or zeros of the form factor. For standard deviations above 15% the SAXS-analysis of latex particles becomes very difficult because in these cases the minima of P(q) have nearly disappeared. The same holds true for the SANS-analysis of such systems, of course. 

Very often SAXS-measurements need to be conducted at rather high concentrations to obtain a good counting statistics. The considerations related to S(q) now demonstrate that the SAXS-analysis can indeed be done at a rather high concentration provided the q-value is not too small. 

First we shall discuss the SAXS-analysis of latex particles consisting of a homopolymer. This system serves as a check for the accuracy of the measurements and for a comparison with the general prediction of scattering theory as outlined in Sect. 2. 

Studies on the conformation of CD21 in the solution by small-angle X-ray scattering (SAXS) with molecular modeling simulations showed that this molecule as most likely adopted a circularized three-turn single helical structure with a radius of gyration of 11.5 A [ 1 ]. Other LR-CDs structures have not been reported, because their single crystals could not be prepared. However, several LR-CDs have been deduced from molecular dynamics simulations and SAXS analysis [1,7]. 

Figure 8.3 SAXS analysis of oriented lamellar former (b) d spacings and derived...

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