Types of Bonding

Question 1

Mention 5 drug targets.

Answer 1

1. Receptors
2. Enzymes
3. Biomembranes
4. Ion channels
5. Nucleic acids

REBIN

Question 2

Complementarities, such as ________ and _________ assure strong binding.

Answer 2

3-D characteristics
Physical and electrochemical properties

Question 3

Mention 8 bond types and their strengths (in Kcal/mol).

Answer 3

Covalent 40-140
Reinforced ionic 10
Ionic 5
Hydrogen 1-7
Ion-dipole 1-7
Dipole-dipole 1-7
Van der Waals 0.5-1
Hydrophobic 1

CRIHID Van Hydrophobe

Question 4

Classify bond types.

Answer 4

1. Irreversible bonds: Long lasting bonds. Applicable in antibacterial and anticancer drugs e.g. Covalent bonds
2. Reversible bonds: Majority of drugs. Drugs easily dissociate from binding site. e.g. Ionic bonds, hydrophobic bonds, van der Waals etc.

Question 5

Discuss covalent bonds with examples.

Answer 5

• Covalent bonds are irreversible and long-lasting.
• Ligand and receptor share a pair of electrons
• Bond strength 40-140 kcal/mol
• Leads to receptor destruction by endocytosis or chemical destruction
• Recovery involves synthesis of new receptors

Examples include:
i. Metalation
ii. Acylation
iii. Reactivation of Acetylcholinesterase
iv. Phosphorylation
v. Alkylation

MARPA
[Learn structures and reactions for Metalation and Acylation]

Question 6

Briefly discuss ionic bonding.

Answer 6

• Ionic bonding is a type of chemical bond where atoms transfer electrons to form oppositely charged ions that attract each other.
• Reversible bond
• Ionisable groups at physiological pH include:
  Carboxyl
  Aliphatic Amino
  Sulphonamide
  CAS
• Quaternary ammonium group are ionisable at any pH.

Question 7

Briefly discuss Dipole-dipole/Ion-dipole bonds.

Answer 7

• A dipole-dipole bond is an electrostatic interaction between polar molecules
• An ion-dipole bond is an electrostatic interaction that occurs between a charged particle and a polar molecule

Examples include interactions involving:
Carbonyl
Amide
Nitrile
Ether
Ester and related groups.

CANE2

Question 8

Briefly discuss Hydrogen bonds.

Answer 8

• A hydrogen bond is an electrostatic attraction that forms between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.
• Reversible bond
• Examples include interactions involving:
  Carbonyl
  Hydroxyl
  Imino
  Amino groups

CHIA

Question 9

Briefly discuss van der Waal Forces.

Answer 9

• van de Waals’ force is a distance-dependent interaction between atoms or molecules.
• Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond
  -They are comparatively weak and therefore more susceptible to disturbance.

Example: Benzene ring binds flat receptor areas via van der Waal force.

Question 10

Briefly discuss Hydrophobic bond.

Answer 10

• Hydrophobic bonds are interactions between nonpolar groups (e.g. Isopropyl) and water.
• No H bonds
• Not soluble in water
• Involves water displacement.
• There is a hydrophobic cleft on the receptor

Examples: Hydrocarbon side chains of the amino acids, valine, leucine and isoleucine.

Question 11

Briefly discuss Charge Transfer Complex.

Answer 11

A charge transfer complex (CT complex) is a molecular entity formed from the interaction between an electron donor and an electron acceptor.

Electron donors include: furan, pyrrole and thiopene.

Electron acceptors include: purine, pyrimidine