Data reduction and processing

Al Kikhney

The elastic scattering of randomly oriented particles in solution results in an isotropic scattering pattern which is usually recorded on a 2D detector. After scaling against the transmitted beam intensity and exposure time the normalized 2D scattering pattern is transformed into a 1D array of scattering intensities I(s) as a function of the modulus of the scattering vector s. The scattering pattern of the macromolecular solute is obtained by subtracting the scattering of the buffer that is measured separately in addition to the macromolecule solution. To monitor possible radiation damages two or more exposures of the same sample are recorded. The concentration of the macromolecular solute must be accurately determined to achieve correct normalization of the subtracted pattern. Several overall parameters (invariants) can be evaluated directly from the SAXS patterns of sufficient quality: molecular mass, radius of gyration (R_g) and hydrated volume. The shape of the distance distribution function p(r) provides information about the main features of the shape and size of the solute particles, including the maximum particle diameter D_max.

Date/time: Thursday, 18 October 2012, 11:30