Figure 6.

Coordination of IMAC ligands (IDA, NTA, and TED) to a divalent metal for binding histidine residues in proteins. Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ have predominantly been utilized in this application. IDA (iminodiacetic acid) is a tridentate ligand (coordination number = 3), with the remaining three coordination sites in the metal available to bind two histidine residues and a water molecule. NTA (nitrilotriacetic acid) is a tetradentate ligand (coordination number = 4) with two coordination sites for histidine residue binding. TED (tris(carboxymethyl)ethylene diamine) is a pentadentate ligand (coordination number = 5) with one remaining coordination site for protein binding.