Chelation and complexation

1. Chelation and Complexation
SABEER KANDEL

2. We will be learning about:
 Chelation:
 Routes of administration
 Examples
 Factors affecting
 Pharmaceutical uses
 Side effects
 Complexation:
 Complex formation
 Types
 More about topic

3. Chelation
 Chelating agent: Organic/ inorganic compounds capable of
binding metal ions to form complex ring-like structure
“chelates”.
 Chelation therapy: Medical procedure that involves
administration of chelating agents to remove heavy metals
from body.

4. More about chelation
 Route of administration:
 Intravenous
 Intramuscular
 Oral
 Depending on agents and type of poisoning
 Common chelating agents:
1. EDTA Ethylenediaminetetraacetic acid= Pb
2. DMSA Dimercaptosuccinic acid= Pb, As, Hg
3. Deferoxamine and Deferasirox= Fe poisoning and overload
4. Dimercaprol (british anti-Lewisite:BAL)= Pb, Hg, As
5. Penicillamine=Cu, Ar, Pb

5. Factors affecting stability and
formation
 Endogenous factors: Hemoglobin, cytochromes
 pH
 Net ionic charge of chelator: Determines its AD and ability
to reach site of binding
 Possible Side effects:
 Dehydration
 Hypocalcaemia
 Allergic reaction

6. Pharmaceutical uses
 Antidote for metal poisoning : heavy metals and toxic metals
 Removing trace metals from pharmaceutical preparations
 EDTA removes calcium ion from hard water
 Also prevents oxidative degradation of ascorbic acid
 However,
 Essential metals are also lost from body and vitamin C and E are
also lost
 Poor clinical recovery
 May be hepatotoxic and neurotoxic

7. Complexation
 Process of Complex formation. Complex consists of:
central metallic atom/ion
Surrounded by ligands
 It occurs via:
 Hydrophobic interaction: involves vander waal’s force
 Charge transfer system: interaction between electron donor
and acceptor

8. Classification
 Are of three types:
1. Metal ion complex: metal + electron donor
2. Organic molecular complex: donor and acceptor held by
weak force
3. Inclusion or occlusion ion complex: one component of
complex is trapped in cage like structure of another
 It is to be noted that chelation is a kind of complexation

9. More about topic
 Urine test to be done before chelation
 Vitamin E and C also removed so must be supplemented
 In vivo and in vitro effects vary due to endogenous factors
 Newer strategy: Combination therapy
 Uses two structurally different chelators
 Lipophilic (intracellular) and lyophobic (extracellular)
 Enhanced effect

10. References
 Ansel et al, Pharmaceutical Dosage Forms And Drug
Delivery System (7th Ed.) Lippincott Wilhams and Wilkins
227 East Washington Square, Philadelphia pp.266-267
 Florence AT, Attwood D, Physiochemical Principle of
Pharmacy, 4th Ed