<p>Nature Communications, Published online: 07 March 2026; <a href="https://www.nature.com/articles/s41467-026-69850-x">doi:10.1038/s41467-026-69850-x</a></p>Isotopic labeling of organic compounds is crucial for advancements in life sciences and is extensively utilized in drug discovery. Here, the authors report the development of an in situ prepared catalyst for hydrogen isotope exchange reactions with deuterium or tritium gas as the isotope source to selectively label peptides in aqueous solutions.