Chelation and biological action MCQs With Answer

Introduction:

Understanding chelation and biological action is essential for B. Pharm students preparing for pharmacology and medicinal chemistry exams. This concise guide covers chelation chemistry, ligand denticity, stability constants, common chelating agents (EDTA, DMSA, dimercaprol, deferoxamine, DTPA, DOTA), mechanisms of metal detoxification, drug–metal interactions, and clinical uses such as lead, arsenic, mercury and iron poisoning. Emphasis is placed on pharmacokinetics, adverse effects, selectivity, and therapeutic monitoring to build practical competency. These targeted concepts improve problem-solving in drug design, toxicology, and clinical pharmacotherapy. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is chelation?

• Formation of a ring-like complex between a multi-dentate ligand and a metal ion
• Simple ionic bond formation between a metal and a single donor atom
• Hydrophobic interaction between drugs and membrane lipids
• Enzymatic hydrolysis of metal complexes

Correct Answer: Formation of a ring-like complex between a multi-dentate ligand and a metal ion

Q2. The chelate effect primarily increases complex stability because of which thermodynamic factor?

• Decrease in enthalpy only
• Increase in entropy due to release of multiple solvent molecules
• Increase in pressure inside the coordination sphere
• Formation of ionic bonds exclusively

Correct Answer: Increase in entropy due to release of multiple solvent molecules

Q3. What does the term “denticity” refer to in chelation chemistry?

• Number of metal ions bound by a ligand
• Number of donor atoms in a ligand that bind to a single metal ion
• Overall charge of a chelate complex
• Rate of chelate formation

Correct Answer: Number of donor atoms in a ligand that bind to a single metal ion

Q4. What is the full name of EDTA commonly used in chelation and analytical chemistry?

• Ethylenediaminetetraacetic acid
• Ethylenetriaminepentaacetic acid
• Diethylenetriaminepentaacetic acid
• Triethylenetetraminehexaacetic acid

Correct Answer: Ethylenediaminetetraacetic acid

Q5. Which chelating agent is commonly used intravenously for severe lead poisoning?

• Calcium disodium EDTA (CaNa2EDTA)
• Deferoxamine
• Penicillamine
• Prussian blue

Correct Answer: Calcium disodium EDTA (CaNa2EDTA)

Q6. Which chelator is classically used for treating iron overload and acute iron poisoning?

• Deferoxamine (desferrioxamine)
• EDTA
• Dimercaprol
• Prussian blue

Correct Answer: Deferoxamine (desferrioxamine)

Q7. Which chelating agent is historically used for arsenic and mercury poisoning?

• Dimercaprol (British Anti-Lewisite, BAL)
• Deferasirox
• EDTA
• Prussian blue

Correct Answer: Dimercaprol (British Anti-Lewisite, BAL)

Q8. Which drug is commonly used to chelate copper in Wilson’s disease?

• Penicillamine
• EDTA
• Deferiprone
• Prussian blue

Correct Answer: Penicillamine

Q9. Which antibiotic class forms insoluble chelates with divalent cations and shows reduced oral absorption?

• Tetracyclines
• Beta-lactams
• Macrolides
• Aminoglycosides

Correct Answer: Tetracyclines

Q10. Which chelating agent is frequently used in pharmaceutical formulations as a preservative/antioxidant stabilizer?

• EDTA
• Dimercaprol
• Deferoxamine
• Prussian blue

Correct Answer: EDTA

Q11. What does the formation constant (Kf) of a chelate express?

• Rate at which the chelate dissociates
• Equilibrium constant for complex formation between ligand and metal
• Number of donor atoms in the ligand
• Solubility of the chelator in water

Correct Answer: Equilibrium constant for complex formation between ligand and metal

Q12. How are stepwise formation constants related to the overall formation constant of a complex?

• The product of the stepwise constants equals the overall formation constant
• The largest stepwise constant equals the overall constant
• Stepwise constants are always smaller than 1
• They are unrelated

Correct Answer: The product of the stepwise constants equals the overall formation constant

Q13. Which statement best distinguishes kinetic stability from thermodynamic stability of a chelate?

• Kinetic stability refers to equilibrium constant; thermodynamic stability refers to rate of dissociation
• Thermodynamic stability refers to equilibrium constant; kinetic stability refers to rate of dissociation
• They are identical concepts
• Only kinetic stability matters in vivo

Correct Answer: Thermodynamic stability refers to equilibrium constant; kinetic stability refers to rate of dissociation

Q14. According to HSAB (hard-soft acid-base) theory, sulfur donor ligands preferentially bind which type of metal ions?

• Soft metal ions (e.g., Hg2+, Pb2+)
• Hard metal ions (e.g., Ca2+, Mg2+)
• Only neutral metals
• Gaseous metal atoms

Correct Answer: Soft metal ions (e.g., Hg2+, Pb2+)

Q15. Which chelating agent is commonly used to stabilize gadolinium in MRI contrast agents?

• DTPA (diethylenetriaminepentaacetic acid)
• Penicillamine
• EDTA
• Dimercaprol

Correct Answer: DTPA (diethylenetriaminepentaacetic acid)

Q16. What is the stoichiometric ratio of EDTA binding to Ca2+ in a typical complex?

• 1:1 (one EDTA per Ca2+)
• 2:1 (two EDTA per Ca2+)
• 1:2 (one EDTA per two Ca2+)
• 3:1 (three EDTA per Ca2+)

Correct Answer: 1:1 (one EDTA per Ca2+)

Q17. How does pH generally affect chelation by ligands like EDTA?

• Lower pH (more acidic) protonates donor groups and decreases chelation
• pH has no effect on chelation
• More acidic pH always increases chelation
• Neutral pH destroys chelators

Correct Answer: Lower pH (more acidic) protonates donor groups and decreases chelation

Q18. Chelation can modify biological action by inhibiting metalloenzymes. Which mechanism explains this?

• Removal of essential metal cofactors from enzyme active sites
• Increasing enzyme synthesis at the transcriptional level
• Altering mRNA splicing of the enzyme
• Inducing protein phosphorylation

Correct Answer: Removal of essential metal cofactors from enzyme active sites

Q19. What is the primary route of excretion for most water-soluble chelate complexes formed during chelation therapy?

• Renal excretion (urine)
• Exhalation via lungs
• Excretion through hair
• Sequestration in adipose tissue

Correct Answer: Renal excretion (urine)

Q20. Which adverse effect is most associated with inappropriate EDTA therapy due to chelation of calcium?

• Hypocalcemia leading to tetany
• Hyperglycemia
• Bradycardia due to potassium overload
• Pancreatitis

Correct Answer: Hypocalcemia leading to tetany

Q21. Besides tetracyclines, which antibiotic class has reduced oral absorption when co-administered with multivalent cations due to chelation?

• Fluoroquinolones (quinolones)
• Macrolides
• Penicillins
• Aminoglycosides

Correct Answer: Fluoroquinolones (quinolones)

Q22. Which agent is used as a decorporation therapy for radioactive cesium and thallium by binding these ions in the gut?

• Prussian blue
• EDTA
• Deferoxamine
• Dimercaprol

Correct Answer: Prussian blue

Q23. Which analytical technique commonly uses EDTA for determination of divalent metal ions such as Ca2+ and Mg2+?

• Complexometric titration (EDTA titration)
• Gas chromatography
• NMR spectroscopy without chelators
• Polarography with mercury drop

Correct Answer: Complexometric titration (EDTA titration)

Q24. What is the denticity of EDTA when it binds to a metal ion using all available donor atoms?

• Hexadentate (six donor atoms)
• Bidentate (two donor atoms)
• Tetradentate (four donor atoms)
• Octadentate (eight donor atoms)

Correct Answer: Hexadentate (six donor atoms)

Q25. Which chelate ring sizes are generally most stable and commonly formed by multidentate ligands?

• Five- and six-membered rings
• Two- and three-membered rings
• Seven- and eight-membered rings exclusively
• Any ring is equally stable regardless of size

Correct Answer: Five- and six-membered rings

Q26. What is the key therapeutic mechanism by which chelating agents treat heavy metal poisoning?

• Formation of water-soluble complexes that enhance urinary excretion of metal ions
• Permanent sequestration of metals in bone
• Increasing gastrointestinal absorption of metals
• Converting metals into volatile forms for exhalation

Correct Answer: Formation of water-soluble complexes that enhance urinary excretion of metal ions

Q27. Which chelator is considered an alternative to penicillamine for copper removal in Wilson’s disease?

• Trientine
• EDTA
• DTPA
• Prussian blue

Correct Answer: Trientine

Q28. Which major organ toxicity is a concern with EDTA therapy and must be monitored?

• Nephrotoxicity (kidney damage)
• Pulmonary fibrosis
• Hepatic steatosis
• Cataract formation

Correct Answer: Nephrotoxicity (kidney damage)

Q29. Use of deferoxamine for iron chelation can predispose patients to infections with certain organisms because it can act like a siderophore. Which infection risk is increased?

• Infections by Yersinia and some fungi (e.g., Mucorales)
• Viral respiratory infections
• Prion diseases
• Protozoan malaria only

Correct Answer: Infections by Yersinia and some fungi (e.g., Mucorales)

Q30. Which chelator is a macrocyclic ligand noted for very high kinetic inertness and is used in radiopharmaceuticals (e.g., with Lu, Y, Ga)?

• DOTA (1,4,7,10-tetraazacyclododecane- N,N’,N”,N”’-tetraacetic acid)
• EDTA
• Dimercaprol
• Deferoxamine

Correct Answer: DOTA (1,4,7,10-tetraazacyclododecane- N,N’,N”,N”’-tetraacetic acid)

Q31. Which oral chelator is commonly used for arsenic and lead poisoning and is known as succimer?

• DMSA (dimercaptosuccinic acid, succimer)
• Deferasirox
• EDTA
• Penicillamine

Correct Answer: DMSA (dimercaptosuccinic acid, succimer)

Q32. For pediatric lead poisoning with moderate elevated blood lead levels, which agent is preferred due to oral administration and better tolerability?

• Succimer (DMSA)
• Dimercaprol
• Deferoxamine
• Prussian blue

Correct Answer: Succimer (DMSA)

Q33. How does chelation generally affect the distribution of metals in the body?

• Formation of polar complexes increases renal elimination and decreases tissue distribution
• It always increases metal deposition in fat
• It converts metals into gaseous forms for redistribution
• It has no effect on distribution

Correct Answer: Formation of polar complexes increases renal elimination and decreases tissue distribution

Q34. Which statement best differentiates chelation from general complexation?

• Chelation involves multidentate ligands forming ring structures; complexation can be any ligand–metal interaction
• Complexation always forms rings, chelation never does
• Chelation is weaker than complexation
• They are synonymous with no distinction

Correct Answer: Chelation involves multidentate ligands forming ring structures; complexation can be any ligand–metal interaction

Q35. Which body compartment is the most difficult source of lead to remove by chelation therapy?

• Bone (skeletal stores)
• Blood plasma
• Liver
• Kidney cortex

Correct Answer: Bone (skeletal stores)

Q36. Macrocyclic chelators typically show which advantage over acyclic chelators in vivo?

• Greater kinetic inertness (slower dissociation) leading to enhanced in vivo stability
• Faster renal clearance always
• Complete resistance to metabolic degradation
• Unlimited metal selectivity

Correct Answer: Greater kinetic inertness (slower dissociation) leading to enhanced in vivo stability

Q37. Which oral chelator is used for chronic iron overload (e.g., thalassemia) as a once-daily oral agent?

• Deferasirox
• Deferoxamine
• EDTA
• Dimercaprol

Correct Answer: Deferasirox

Q38. Which chelator contains two sulfhydryl (-SH) groups and is effective against arsenic poisoning?

• Dimercaprol (BAL)
• EDTA
• Penicillamine
• Deferasirox

Correct Answer: Dimercaprol (BAL)

Q39. How does increasing the positive charge on a metal ion generally affect its binding affinity to typical donor ligands?

• Increases binding affinity (stronger complexes)
• Decreases binding affinity
• Has no effect
• Always prevents chelation

Correct Answer: Increases binding affinity (stronger complexes)

Q40. Tetracycline-induced tooth discoloration occurs because tetracyclines chelate which essential component in developing teeth?

• Calcium in developing teeth
• Magnesium in enamel
• Iron in dentin
• Phosphate in saliva

Correct Answer: Calcium in developing teeth

Q41. Co-administration of which ions commonly reduces absorption of chelate-susceptible drugs?

• Multivalent cations such as Ca2+, Fe2+/Fe3+, Mg2+
• Monovalent anions like Cl- only
• Noble gases like argon
• Proteins in food exclusively

Correct Answer: Multivalent cations such as Ca2+, Fe2+/Fe3+, Mg2+

Q42. EDTA is used as an anticoagulant in blood collection tubes because it chelates which ion required for coagulation?

• Calcium (Ca2+)
• Sodium (Na+)
• Chloride (Cl-)
• Potassium (K+)

Correct Answer: Calcium (Ca2+)

Q43. Which parameter must be closely monitored during chelation therapy with renally excreted chelators such as EDTA?

• Renal function (serum creatinine, urine output)
• Serum bilirubin only
• Platelet aggregation exclusively
• Pulmonary function tests only

Correct Answer: Renal function (serum creatinine, urine output)

Q44. Which donor atom type would you select to design a ligand targeting mercury (a soft metal) for high affinity?

• Sulfur donor atoms (thiol/thiolate)
• Hard oxygen donors exclusively
• Only halide donors
• Aliphatic hydrocarbons with no heteroatoms

Correct Answer: Sulfur donor atoms (thiol/thiolate)

Q45. EDTA can inhibit metalloproteinases by chelating which essential metal ion from their active site?

• Zinc (Zn2+)
• Sodium (Na+)
• Potassium (K+)
• Helium (He)

Correct Answer: Zinc (Zn2+)

Q46. Which adverse effect is commonly associated with intramuscular dimercaprol therapy?

• Hypertension and tachycardia
• Severe hyperglycemia
• Painless injection site
• Permanent hearing loss

Correct Answer: Hypertension and tachycardia

Q47. After chelation therapy for a heavy metal, why might blood metal levels rebound days to weeks later?

• Mobilization of metal from deep stores such as bone back into blood
• Immediate complete removal of all metal from the body
• Transformation of the metal into inert forms
• Conversion of chelator to metallic form

Correct Answer: Mobilization of metal from deep stores such as bone back into blood

Q48. Which chelating agent is used to treat internal contamination with transuranic elements like plutonium and americium?

• DTPA (diethylenetriaminepentaacetic acid)
• EDTA
• Deferoxamine
• Prussian blue

Correct Answer: DTPA (diethylenetriaminepentaacetic acid)

Q49. What are phytochelatins?

• Peptides synthesized by plants that bind and detoxify heavy metals
• Synthetic chelators used in human medicine
• Inorganic salts that precipitate metals
• Plant hormones unrelated to metal binding

Correct Answer: Peptides synthesized by plants that bind and detoxify heavy metals

Q50. Which colorimetric indicator is commonly used in EDTA complexometric titrations for calcium and magnesium determination?

• Eriochrome Black T
• Methyl orange
• Phenolphthalein
• Litmus paper

Correct Answer: Eriochrome Black T

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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