Pentetic Acid - Coordination Properties

Coordination Properties

The conjugate base of DTPA has a high affinity for metal cations. Thus, the penta-anion DTPA5- is potentially an octadentate ligand assuming that each nitrogen centre counts as a and each COO–-group counts as a centre for coordination. The formation constants for its complexes are about 100 greater than those for EDTA. As a chelating agent, DTPA wraps around a metal ion by forming up to eight bonds. Transition metals, however, usually form less than eight coordination bonds. So, after forming a complex with a metal, DTPA still has the ability to bind to other reagents, as is shown by its derivative pendetide. For example, in its complex with copper(II), DTPA binds in a hexadentate manner utilizing the three amine centres and three of the five carboxylates.