Complexing and

Chelating Agents

By – Sahaya Asirvatham

What is Chelation???

Chelation (KEE-LAY-SHUN)

comes from the Greek word –

“chele”- which means CLAW

“the use of a chelating agent to

bind with a metal in the body to

form a chelate so that the metal

loses its toxic effect or

physiological activity”

CHELATION- CLAW-LIKE

FORMATION

Common Uses of Chelation

Therapy

Chelation therapy has primarily been used as agent to detoxify heavy metals such as calcium, iron, magnesium, lead and zinc.

Binds to these metal ions because of its strong affinity for cations.

The bound metal ions are then excreted in the urine.

LIGANDS

Ligand is an ion or molecule (functional group)

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.

MOA

• Heavy metals exert their toxic effects by combining with

and inactivating functional groups (ligands) of enzymes

and important biomolecules - sulfhydril, hydroxyl,

carboxyl etc. leading to inactivation

ME

TA

L

EN

ZY

ME

CO

MP

LE

XIN

G

AG

EN

T

NO TOXIC

EFFECT

Chelating agents compete with body ligands for the

heavy metal – also differ in affinity for different

metals

• Chelating agents have high affinity for such metals

and combine with them to form non toxic and water

soluble complexes for elimination

• Possesses: –ve charged groups to attract +ve

charged toxic metals

Ideal chelating agent

1. Ideal chelating agents have higher affinity for

toxic metals than for body Ca++ (readily

available in plasma and ECF)

2. Should also have higher affinity for toxic metals

than body ligands

3. Ideally should be water soluble

4. Interval of administration between exposure to

metals and chelating agents should be less

Chelating Agent

Classification

1. Penicillamine – Cu, Pb, Hg, Zn

2. Disodium edetate (EDTA) – lead poisoning

3. Dimercaprol (British antilewisite) or BAL –

As, Au, Bi, Ni, Sb and Hg poisoning

Penicillamine -------- Degraded product of Penicillin (beta

dimethylcysteine)

Prepared by alkaline hydrolysis of benzyl penicillin – d-

penicillamine

Strong Cu chelating property - useful in Cu poisoning

MOA is same as others – selective chelating of Cu, Hg, Pb and Zn

Absorbed orally - available as 250 mg capsules, metabolized in liver

and excreted in urine

Penicillamine

PenicillamineUses

Wilson`s disease: Hepatolenticular degeneration due

to genetic deficiency of ceruplasmin (Cu deposition in

body) – life long therapy (0.5-1 gm daily)

Cu and Hg (alternative) Poisoning

Chronic Pb poisoning (adjuvant to edetate)

Cystinuria and cystine stones

Scleroderma: benefits by increasing soluble

collagen

BAL or Dimercaprol

World War-II as British anti-Lewisite ---- Arsenical Gas

Oily , pungent smelling, viscous liquid, water soluble