Diethylenetriaminepentaacetic acid(CAS 67-43-6)

Molecular Structure

DTPA is an effective chelating agent, used in chelate fertilizers, used in Acrylic production 

as colour inhibitor, papermaking industry, water softener, as textile auxiliary agent, as 

complexing agent,etc..

Pentetic acid or diethylene triamine pentaacetic acid (DTPA) is an aminopolycarboxylic

acid consisting of a diethylenetriamine backbone with five carboxymethyl groups. The

molecule can be viewed as an expanded version of EDTA and is used similarly. It is a

white, water-soluble solid.

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 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.

Applications

Like the more common EDTA, DTPA is mainly used for sequestering metal ions that otherwise

decompose hydrogen peroxide, which is used to bleach pulp in paper making. Several million

kilograms are produced for this purpose annually.

Its chelating properties are useful in deactivating calcium and magnesium ions in hair products.

DTPA is used in over 150 cosmetic products. Additionally, DTPA is used in MRI contrasting

agents. DTPA improves MRI images by forming a complex with a gadolinium ion, which alters

the properties of nearby water molecules.

DTPA has been considered for treatment of radioactive materials such as plutonium, americium,

and other actinides. In theory, these complexes are more apt to be eliminated in urine. It is normally

administered as the calcium or zinc salt, since these ions are readily displaced by more highly

charged cations. DTPA forms complexes with thorium(IV), uranium(IV), neptunium(IV), and cerium(III/IV).

DTPA is also used as a chelate for aquarium plant fertilizer, specifically iron, an essential micronutrient

typically needed in substantial quantities by all plants. Chelates are dissolved organic substances that bind

to metals and prevent them from forming larger molecules through oxidation. FeDTPA is often sold under

the name iron chelate 10% or 11% when used for the purpose of aquarium plant fertilization. Iron typically

found in the aquarium water column has been converted into the ferric state (Fe+3) since it is in the presence

of dissolved oxygen. However plants require iron in the ferrous state (Fe+2), therefore additional energy must

be expended in order to extract the ferric iron from the water column and convert it to the ferrous form. When

used to chelate iron fertilizer DTPA ensures that the iron is kept in the ferrous state (Fe+2) over time so it

can be utilized by aquatic plants without expending valuable energy.