Figure 4. Summary of the metal-chelate complexes and their modes of conjugation to the Rev peptide (18). M = Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺. The sequence of the Rev peptide is shown above. The 7-coordinate geometries shown here for M-DOTA-Rev and M-DTPA-Rev are based on the X-ray crystal structures of [Fe-DOTA]^1- and [Fe-DTPA]^2- (51, 52). Note that Fe²⁺ complexes of GGH-Rev and KGHK-Rev were not observed and therefore were not used.