Chemistry
How Neutron Scattering Reveals Hydrogen Positions in Protein Structures
Quick fact
Even though hydrogen makes up about half of the atoms in a protein, it is almost completely invisible in X-ray crystal structures because X-rays scatter from electrons, and hydrogen has only one electron. Neutrons, however, scatter from the atomic nuclei, so hydrogen and its isotope deuterium have strong and distinct neutron signals, making them directly observable.
Why this is interesting
You've probably seen stunning 3D models of proteins that seem to show every atom—but they're actually missing the smallest and arguably most important ones. Why are hydrogen atoms 'invisible' in most protein structures, and how can they finally be seen?