Limitations in macromolecular crystallography due to radiation damage

Intense synchrotron radiation from insertion devices can cause rapid decay of macromolecular crystals. Flash-cooling the sample and holding it at around 100K during the experiment extends the lifetime significantly but often not sufficiently. Radiation damage can severely compromise data quality by changing oxidation states, disrupting covalent bonds or by simply causing the crystal lattice to disintegrate. A significant increase in beam intensity, as accomplished with SPEAR3 and other 3rd generation light sources, does not only open new scientific opportunities but also makes the study and understanding of sample decay a pressing requirement. A detailed understanding of the physical processes involved and in particular a delineation of radiation specific and sample specific parameters is needed to, if possible, prolong crystal lifetimes by changing experimental parameters. The present state of our understanding of radiation damage to crystalline samples was discussed at a recent workshop hosted by the ESRF and a summary will be presented. A basic set of experiments will be described, which have been designed to further understand decay. Much of our current knowledge about effects of, for example, crystal surface/volume ratio, sample temperature, cryogen flow rate past the sample, duty cycle of crystal irradiation, and incident X-ray wavelength, are anecdotal and initial attempts at a systematic study will be presented