Formation of a Chiral Center and Pyrimidal Inversion at the Single‐Molecule Level

One-at-a-time stereochemistry: AsS bond-making and bond-breaking reactions are important in pharmacology, toxicology, and cell biology. The aqueous covalent chemistry of individual AsIII molecules can be monitored inside a protein nanoreactor. The approach is used to follow the creation of a chiral center at AsIII, through the formation of a short-lived AsS bond, and to monitor inversion at that center (see picture).