DTPA
Encyclopedia
Pentetic acid or diethylene triamine pentaacetic acid (DTPA) is a polyamino carboxylic acid
consisting of a diethylenetriamine backbone with five carboxymethyl groups. The molecule can be viewed as an expanded version of EDTA and it is used similarly.
of DTPA has a high affinity for metal cations. Thus, the penta-anion DTPA5- is potentially an octadentate ligand
. In contrast, EDTA possesses 6 centres to form coordination bonds with metals. 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 have a limited coordination capacity and can form less than eight coordination bonds with ligand
s. 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. Like many other chelating agents, DTPA has been considered for treatment of internal contamination from radioactive materials such as plutonium
, americium
and other actinide
s. In theory, these complexes are more apt to be eliminated in urine. It is normally administered as the calcium
or zinc
salt.
, which is used to bleach pulp
in paper making. Several million kilograms are produced for this purpose annually.
Polyamino carboxylic acid
thumb|left|120px|a metal complex with the [[EDTA]] anionthumb|120px|the [[glycine|glycinate]] ion can form a chelate complex with a metal ionthumb|120px| β [[alanine]]...
consisting of a diethylenetriamine backbone with five carboxymethyl groups. The molecule can be viewed as an expanded version of EDTA and it is used similarly.
Coordination properties
The conjugate baseConjugate acid
Within the Brønsted–Lowry acid-base theory , a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward chemical...
of DTPA has a high affinity for metal cations. Thus, the penta-anion DTPA5- is potentially an octadentate ligand
Denticity
Denticity refers to the number of atoms in a single ligand that bind to a central atom in a coordination complex. In many cases, only one atom in the ligand binds to the metal, so the denticity equals one, and the ligand is said to be monodentate...
. In contrast, EDTA possesses 6 centres to form coordination bonds with metals. The formation constants
Stability constants of complexes
A stability constant is an equilibrium constant for the formation of a complex in solution. It is a measure of the strength of the interaction between the reagents that come together to form the complex...
for its complexes are about 100 greater than those for EDTA.
As a chelating agent
Chelation
Chelation is the formation or presence of two or more separate coordinate bonds between apolydentate ligand and a single central atom....
, DTPA wraps around a metal ion by forming up to eight bonds. Transition metals, however, usually have a limited coordination capacity and can form less than eight coordination bonds with ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s. 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
Pendetide
Pendetide is a chelating agent. It consists of pentetic acid linked to the tripeptide glycine – L-tyrosine – L-lysine .-Use:The following monoclonal antibodies are linked to pendetide to chelate a radionuclide, indium-111...
. 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. Like many other chelating agents, DTPA has been considered for treatment of internal contamination from radioactive materials such as plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
, americium
Americium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...
and other actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...
s. In theory, these complexes are more apt to be eliminated in urine. It is normally administered as the calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
or zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
salt.
Applications
Like the more common EDTA, DTPA is mainly used for sequestering metal ions that otherwise decompose hydrogen peroxideHydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
, which is used to bleach pulp
Bleaching of wood pulp
Bleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...
in paper making. Several million kilograms are produced for this purpose annually.
Related compounds
Compounds that are structurally related to DTPA are used in medicine, taking advantage of the high affinity of the triaminopentacarboxylate scaffold for metal ions.- In ibritumomab tiuxetanIbritumomab tiuxetanIbritumomab tiuxetan, sold under the trade name Zevalin, is a monoclonal antibody radioimmunotherapy treatment for some forms of B cell non-Hodgkin's lymphoma, a lymphoproliferative disorder and thus affects the lymphatic system...
, the chelator tiuxetan is a modified version of DTPA whose carbon backbone contains an isothiocyanatobenzyl and a methyl group. - In capromab pendetide and satumomab pendetide, the chelator pendetidePendetidePendetide is a chelating agent. It consists of pentetic acid linked to the tripeptide glycine – L-tyrosine – L-lysine .-Use:The following monoclonal antibodies are linked to pendetide to chelate a radionuclide, indium-111...
(GYK-DTPA) is a modified DTPA containing a peptidePeptidePeptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
linker used to connect the chelate to an antibodyAntibodyAn antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
. - Pentetreotide is a modified DTPA attached to a peptide segments.
- DTPA and derivatives are used to chelate gadoliniumGadoliniumGadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...
to form a MRIMagnetic resonance imagingMagnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
contrast agent, such as Magnevist. - Technetium is chelated with DTPA for ventilation perfusion scan (V/Q scan) and renal scan.