Radiation Damage

Overview

Small-angle X-ray scattering (SAXS) provides a low resolution structural probe for biological macromolecules in solution. SAXS measurements generally require a homogeneous, monodisperse, aggregate-free solution, and that these conditions be maintained throughout data collection. X-ray induced radiation damage can cause macromolecule aggregation, fragmentation, conformation changes, and unfolding, all of which can be detected by SAXS. Radiation damage is therefore a major obstacle for SAXS, and descriptions of dedicated biological SAXS beamlines acknowledge the need to check for and avoid radiation damage. Minimizing radiation induced changes in SAXS places limits on minimum sample volumes (~10 μL) and maximum X-ray exposure times.

To minimize radiation damage, three strategies are commonly employed. First, exposure times for a test sample can be reduced until subsequent exposures of the test sample show no change in the scattering profile. Second, the total sample volume irradiated can be increased, typically by flowing/oscillating the sample or defocusing the beam at the sample, to minimize dose. Third, small-molecule compounds such as glycerol can be added to reduce changes in the SAXS profile (e.g. by competitively binding with free radicals or by inhibiting aggregation). These approaches can be employed in parallel and result in the limitations on sample volume and exposure time given above. Cryocooling samples to 100 K has been shown to reduce radiation damage rates in SAXS, but substantial methodological development is required before cryocooling can be accepted for routine use.

With recent and planned upgrades to already bright third-generation sources and construction of high-brightness fourth-generation sources, understanding, quantifying and ultimately minimizing radiation damage in biological SAXS will be essential to efficient use and full exploitation of these sources. The last few years has seen an uptick in interest and publications about radiation damage in SAXS, showing that the community in general is aware that this is an important topic to understand.

My work has focused on ways to quantify and prevent radiation damage in samples, and trying to better understand the fundamental physical and chemical mechanisms of the damage process.

My work