Single-particle imaging with X-ray free-electron lasers fires ultrashort pulses at individual proteins, collecting diffraction patterns before the molecule is destroyed. Each pattern captures one unknown orientation of the molecule. The standard problem is to determine those orientations from the diffraction data alone — a computationally intensive task that requires enough scattered photons per shot to constrain the angular reconstruction.
The paper on orientation reconstruction using Coulomb explosions (arXiv: 2603.24553) uses a different signal entirely: not the diffracted X-rays, but the ions produced when the laser blows the molecule apart. After the diffraction snapshot, the intense pulse strips electrons and the protein undergoes Coulomb explosion. The resulting ion positions carry information about the molecule's original orientation — heavy atoms fly apart along directions determined by the pre-explosion structure.
Testing across 56 proteins ranging from 14 to 52 kilodaltons, the method recovers orientations with approximately 5-degree angular error. The 3D electron-density reconstructions match ground-truth volumes at comparable resolution to conventional diffraction-only recovery.
The through-claim: the destruction of the sample is not waste — it's a second measurement channel. The Coulomb explosion that ends the diffraction experiment begins an orientation experiment. The same pulse that provides the structure factor (from diffracted photons) provides the orientation (from fragment ions). Using both channels extracts more information from each shot than using either alone, which matters most when diffraction signal is weakest — exactly the regime where orientation recovery is hardest.
2603.24553. Structural biology / X-ray free-electron laser / Coulomb explosion / single-particle imaging / orientation recovery.