Passmore Spencer K, Sanders Alaric L, Martin Andrew V, Quiney Harry M
School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia.
School of Science, STEM College, RMIT University, Melbourne, Victoria 3000, Australia.
J Synchrotron Radiat. 2025 Sep 1;32(Pt 5):1124-1142. doi: 10.1107/S1600577525005934. Epub 2025 Aug 27.
Serial femtosecond X-ray crystallography (SFX) captures the structure and dynamics of biological macromolecules at high spatial and temporal resolutions. The ultrashort pulse produced by an X-ray free-electron laser (XFEL) outruns' much of the radiation damage that impairs conventional crystallography. However, the rapid onset of electronic damage' due to ionization limits this benefit. Here, we distinguish the influence of different atomic species on the ionization of protein crystals by employing a plasma code that tracks the unbound electrons as a continuous energy distribution. The simulations show that trace quantities of heavy atoms (Z > 10) contribute a substantial proportion of global radiation damage by rapidly seeding electron ionization cascades. In a typical protein crystal, sulfur atoms and solvated salts induce a substantial fraction of light-atom ionization. In further modeling of various targets, global ionization peaks at photon energies roughly 2 keV above inner-shell absorption edges, where sub-2 keV photoelectrons ejected from these shells initiate ionization cascades that are briefer than the XFEL pulse. These results indicate that relatively small quantities of heavy elements can substantially affect global radiation damage in XFEL experiments.
串行飞秒X射线晶体学（SFX）能够在高空间和时间分辨率下捕捉生物大分子的结构和动力学。X射线自由电子激光（XFEL）产生的超短脉冲能够“超越”许多会损害传统晶体学的辐射损伤。然而，由于电离导致的“电子损伤”迅速出现，限制了这一优势。在这里，我们通过使用一种将未束缚电子作为连续能量分布进行追踪的等离子体代码，来区分不同原子种类对蛋白质晶体电离的影响。模拟结果表明，痕量重原子（Z>10）通过迅速引发电子电离级联反应，对整体辐射损伤贡献了很大比例。在典型的蛋白质晶体中，硫原子和溶剂化盐会引发相当一部分轻原子的电离。在对各种靶标的进一步建模中，整体电离在光子能量比内壳层吸收边高约2 keV处达到峰值，从这些壳层中射出的能量低于2 keV的光电子引发的电离级联反应比XFEL脉冲更短。这些结果表明，相对少量的重元素会对XFEL实验中的整体辐射损伤产生重大影响。
