Radiation damage to biological samples: still a pertinent issue.

An understanding of radiation damage effects suffered by biological samples during structural analysis using both X‐rays and electrons is pivotal to obtain reliable molecular models of imaged molecules. This special issue on radiation damage contains six papers reporting analyses of damage from a range of biophysical imaging techniques. For X‐ray diffraction, an in‐depth study of multi‐crystal small‐wedge data collection single‐wavelength anomalous dispersion phasing protocols is presented, concluding that an absorbed dose of 5 MGy per crystal was optimal to allow reliable phasing. For small‐angle X‐ray scattering, experiments are reported that evaluate the efficacy of three radical scavengers using a protein designed to give a clear signature of damage in the form of a large conformational change upon the breakage of a disulfide bond. The use of X‐rays to induce OH radicals from the radiolysis of water for X‐ray footprinting are covered in two papers. In the first, new developments and the data collection pipeline at the NSLS‐II high‐throughput dedicated synchrotron beamline are described, and, in the second, the X‐ray induced changes in three different proteins under aerobic and low‐oxygen conditions are investigated and correlated with the absorbed dose. Studies in XFEL science are represented by a report on simulations of ultrafast dynamics in protic ionic liquids, and, lastly, a broad coverage of possible methods for dose efficiency improvement in modalities using electrons is presented. These papers, as well as a brief synopsis of some other relevant literature published since the last Journal of Synchrotron Radiation Special Issue on Radiation Damage in 2019, are summarized below. [ABSTRACT FROM AUTHOR]