Calculated Fo−Fc omit maps for the modified Cys209 of Ag85C and respective ebselen derivatives. Both maps are contoured at 3σ in blue mesh. Atom color: carbon is beige in panel a, orange in panel b, nitrogen blue, oxygen red, sulfur yellow, and selenium light orange. (a) Ag85C covalently modified by azido ebselen and (b) Ag85C covalently modified by adamantyl ebselen.