Information retrieval from X-ray small-angle scattering with polychromatic (`white') synchrotron radiation

Abstract

The possibilities of obtaining structural information from X-ray small-angle scattering experiments with 'white' polychromatic synchrotron radiation using line collimation are investigated by numerical simulation. Theoretical scattering curves of geometrical models were smeared with the appropriate wavelength distributions and slit-length functions, afflicted by statistical noise, and then evaluated by identical methods as normally used for experimental data, as described previously [program ITP;Glatter (1977). J. Appl. Cryst. 10, 415-421-1. It is shown that even for a wavelength distribution of 50% half width, the information content is not limited to the parameters derived from the central part of the scattering curves, i.e. the radius of gyration and the zero-angle intensity, but also allows qualitative information on particle shape via the distance distribution function p(r). By a 'hinge-bending model' consisting of two cylinders linked together at different angles it is demonstrated that changes in the radius of gyration amounting to less than 5% can be detected and quantified, and the qualitative changes in particle shape be reproduced.

A Wide-Bandpass Multilayer Monochromator for Biological Small-Angle Scattering and Fiber Diffraction Studies

“…The increased¯ux would then more effectively allow time-resolved experiments with smaller amounts of often dif®cult-to-obtain biological samples. It is also very important to obtain solution scattering data at higher Q values with good statistics, primarily for three reasons: (i) some proteins (mostly oligomeric) exhibit subsidiary scattering peaks that are sensitive to the changes in subunit arrangements, which are often linked to biological functions; (ii) higher-angle data are needed to make accurate indirect Fourier transforms to obtain additional structural information such as distance distribution functions of a protein; and (iii) the Kratky plot at relatively high angles is often used to distinguish folded protein structures from unfolded ones (Kataoka et al, 1993). Solution scattering intensity falls very quickly with angle, resulting in very weak signal levels being observed at higher angles.…”

“…The latter is true for small-angle scattering studies on noncrystalline biological systems; here, one would like to increase the monochromator bandpass to a few percent or more (as is common in neutron scattering) in order to obtain a signi®cant gain in beam¯ux. Glatter & Laggner (1983) demonstrated that one could still retrieve a reasonable amount of structural information from small-angle scattering patterns using a polychromatic (i.e. white) synchrotron radiation beam.…”