Board exam focus — Chemistry in Everyday Life (CBSE & HBSE)

Drugs and medicines classification, drug-target interaction, chemicals in food (preservatives, sweeteners, antioxidants), and soaps and detergents.

Drugs: Classification and Drug-Target Interaction

Drugs and Medicines

Definition

A drug is a chemical substance used in prevention, diagnosis, and treatment of disease. A medicine is a drug used therapeutically.

Classification of Drugs

1. Based on Pharmacological Effect (Action on Body System):

2. Based on Chemical Structure: Drugs with similar chemical structures often have similar pharmacological effects (structure-activity relationship, SAR).

3. Based on Molecular Targets: Drugs interact with specific biological macromolecules (proteins, enzymes, receptors, DNA, lipids).

Drug-Target Interaction

Drugs exert their effect by binding to biological targets:

Enzymes as Drug Targets: Enzyme Inhibitors: Drugs that bind to enzyme active site or allosteric site to reduce/stop catalytic activity.

• Competitive inhibitors: Bind to active site (same as substrate); effect can be overcome by increasing substrate concentration.

Example: Sulphonamides compete with PABA (para-aminobenzoic acid) in bacterial folic acid synthesis → bacteriostatic.

• Non-competitive inhibitors: Bind to allosteric site; change enzyme shape so substrate cannot bind. Effect NOT overcome by increasing substrate.

Example: Aspirin irreversibly inhibits COX enzyme (cyclooxygenase) that synthesizes prostaglandins → anti-inflammatory effect.

Receptors as Drug Targets: Receptors are proteins embedded in cell membranes that receive chemical signals.

• Agonists: Drugs that mimic natural signal molecules and activate receptor.

Example: Morphine binds opioid receptors (mimics endorphins) → pain relief

• Antagonists: Drugs that block receptor without activating it; prevent natural signal from binding.

Example: Antihistamines block H1 histamine receptors → prevent allergic response

Structure-Activity Relationship (SAR)

Small structural changes in a drug can dramatically alter pharmacological activity:

• Adding -OH group to morphine → more soluble, different potency
• Replacing -COOH with -SO3H in sulfonamides → changes antibacterial spectrum
• Stereochemistry matters: L-DOPA (active in Parkinson's) vs D-DOPA (inactive)
• Thalidomide example: R-enantiomer (sedative) and S-enantiomer (teratogenic) → racemic mixture caused birth defects

Specific Drug Categories

Important Drug Categories

Analgesics (Painkillers)

Non-narcotic analgesics (non-addictive):

• Aspirin (Acetylsalicylic acid): Most widely used. COX inhibitor. Antipyretic, anti-inflammatory, antiplatelet. Cannot be used by children (Reye's syndrome risk). Gastric irritation side effect.
• Paracetamol (Acetaminophen): COX inhibitor in CNS. Antipyretic and analgesic but minimal anti-inflammatory. Safe for children. Overdose causes liver damage.
• Ibuprofen: NSAIDs (non-steroidal anti-inflammatory drug). COX inhibitor. Analgesic + anti-inflammatory + antipyretic. Fewer gastric side effects than aspirin.

Narcotic analgesics (addictive, for severe pain):

• Morphine: Opioid. Extracted from opium poppy. Binds opioid receptors. Used for severe pain (cancer, post-surgery). High addiction potential.
• Codeine: Weaker opioid. Cough suppressant, mild pain. Less addictive.
• Heroin (diacetylmorphine): Synthetic from morphine. Highly addictive. Illegal.

Tranquilizers

• Barbiturates (luminal, phenobarbital): GABA receptor agonists. Sedative, anticonvulsant. High addiction/overdose risk.
• Benzodiazepines (diazepam/Valium, chlordiazepoxide): GABA receptor agonists. Anxiolytic, muscle relaxant. Lower overdose risk than barbiturates.
• Meprobamate: Anxiety treatment
• Equanil: Mild depression and hypertension

Antibiotics

Classification:

• Bactericidal: Kill bacteria (penicillin, amoxicillin, streptomycin)
• Bacteriostatic: Inhibit bacterial growth (tetracyclines, erythromycin, sulfonamides)
• Broad spectrum: Active against both gram+ and gram- bacteria (ampicillin, amoxicillin, chloramphenicol, tetracyclines)
• Narrow spectrum: Active against limited bacteria (penicillin G - mainly gram+)

Penicillin: Beta-lactam ring structure. Discovered by Alexander Fleming (1928). Inhibits bacterial cell wall synthesis. First antibiotic for clinical use. Allergic reactions possible.

Sulfonamides: Bacteriostatic. Competitive inhibitors of PABA. Prontosil was first sulfonamide drug (Domagk, 1932).

Chloramphenicol: Broad spectrum but bone marrow toxicity risk.

Antacids

Excess HCl in stomach causes acidity/peptic ulcer. Antacids neutralize HCl:

Note: NaHCO3 generates CO2 (belching); Mg(OH)2 can cause diarrhea; Al(OH)3 causes constipation - often combined.

Antihistamines

Histamine triggers allergic response (sneezing, itching, hives, anaphylaxis). H1 receptor blockers: Block histamine H1 receptors

• First generation: Brompheniramine (Dimetapp), diphenhydramine (Benadryl) - cause drowsiness
• Second generation: Terfenadine, cetirizine (Zyrtec), loratadine (Claritin) - non-drowsy

Uses: Allergic rhinitis, hay fever, urticaria, anaphylaxis

H2 receptor blockers: Ranitidine - used for stomach acid (antacid function).

Soaps, Detergents and Food Chemicals

Soaps and Detergents

Soaps

Definition: Sodium or potassium salts of long-chain fatty acids (carboxylic acids). Formula: RCOONa where R = long hydrocarbon chain (C12-C18) Examples:

• Sodium stearate: CH3(CH2)16COONa (hard soap, Na salt)
• Potassium oleate: CH3(CH2)7CH=CH(CH2)7COOK (soft soap, K salt - shaving cream)

Saponification: Making soap from fat/oil + alkali Fat (triglyceride) + 3NaOH → 3RCOONa (soap) + glycerol

Structure of soap molecule:

• Hydrophilic (polar) head: -COO-Na+ (ionized carboxylate)
• Hydrophobic (non-polar) tail: long alkyl chain (-CH2-CH2-...)

Micelle formation and cleansing mechanism:

1. Soap molecules arrange in water with hydrophobic tails pointing inward, hydrophilic heads outward → micelle
2. When soap-water mixture contacts greasy dirt on fabric/skin:

• Hydrophobic tails insert into grease droplet
• Hydrophilic heads remain in water

1. Grease droplet is surrounded by soap molecules → emulsified
2. Charged COO- heads repel each other → keep grease droplets dispersed in water (cannot re-aggregate)
3. Water carries away emulsified grease → cleansing

Limitation in hard water: Hard water contains Ca2+ and Mg2+ ions. 2RCOONa + CaCl2 → (RCOO)2Ca (insoluble scum) + 2NaCl Insoluble calcium/magnesium salts form soap scum → soap wasted, poor lathering.

Synthetic Detergents

Advantage over soaps: Effective in hard water, acidic conditions, cold water. Types:

1. Anionic detergents:

• Sodium salts of sulphonic acids (R-SO3-Na+)
• Most common: sodium lauryl sulphate (SLS = CH3(CH2)11-OSO3Na), sodium alkylbenzenesulphonate
• Long hydrophobic chain + anionic head
• Used in shampoos, dishwashing liquids, laundry

2. Cationic detergents:

• Quaternary ammonium salts (R-N+(CH3)3 X-)
• Antimicrobial properties; used as antiseptics, hair conditioners, fabric softeners
• Expensive

3. Non-ionic detergents:

• No charge on the molecule
• Polyethylene glycol derivatives, esters
• Gentle; used for wool, silk, sensitive skin; dishwashers (don't foam)

Environmental issue with detergents: Old branched alkylbenzenesulphonate detergents NOT biodegradable → foam in rivers. Now replaced by linear alkylbenzenesulphonates (LAS) which ARE biodegradable.

Food Chemicals

Preservatives

Purpose: Prevent microbial spoilage of food.

Artificial Sweeteners

Antioxidants

Purpose: Prevent oxidative rancidity (fat oxidation) in foods.

Mechanism: BHA and BHT are phenolic compounds that scavenge free radicals (R• + BHA-H → RH + BHA•). The BHA radical is stable and doesn't propagate chain oxidation.

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Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Chemistry in Everyday Life.