Chemistry in Everyday Life

Drugs: Chemicals of low MW ($\sim 100$ to $\sim 500$ Da) that interact with biological targets to produce a therapeutic response. Used to treat, cure, or prevent disease.

Pharmacology: Study of drugs and their effects on living systems.

Chemotherapy: Use of chemicals to treat disease, especially infections and cancer.

Classification of Drugs:

A. Based on Pharmacological Effect:

B. Based on Drug Action:

• Agonist: Mimics natural messenger; binds receptor and activates it. (e.g., morphine mimics endorphins)
• Antagonist: Blocks receptor; doesn't activate. (e.g., naloxone blocks morphine receptors)

C. Based on Chemical Structure:

• Sulfa drugs, $\beta$-lactams, etc.

D. Based on Molecular Target:

• Enzyme inhibitors (e.g., aspirin inhibits cyclooxygenase, COX)
• Receptor binders (e.g., morphine binds opioid receptors)

Drug-Receptor Interaction:

Receptors: Proteins (mostly membrane proteins) that recognize specific chemical messengers (hormones, neurotransmitters).

Mechanism:

1. Drug binds to receptor site (often by hydrogen bonds, ionic, dipole, van der Waals).
2. Conformational change in receptor → signal transduction.
3. Cellular response (e.g., neurotransmitter release, enzyme activation).

Enzyme Inhibitors:

• Competitive: Drug structure resembles substrate; competes for active site (e.g., methotrexate competes with folate).
• Non-competitive: Binds elsewhere; changes enzyme shape (allosteric).
• Irreversible: Binds covalently; permanently inactivates enzyme (e.g., penicillin binds enzyme that makes bacterial cell wall).

Drug Design Strategy:

• Identify target (enzyme, receptor).
• Design drug to fit binding site precisely.
• Modify to enhance specificity, reduce side effects.

Antimicrobials: Substances that kill or inhibit microorganisms (bacteria, viruses, fungi, protozoa).

Categories:

1. Antiseptics:

• Applied to living tissue (skin, wounds).
• Examples: Dettol (mix of chloroxylenol + terpineol), tincture of iodine ($2-3\%\,I_2$ in alcohol/water), savlon, $H_2O_2$, KMnO₄ (mild), boric acid (eye wash).
• Furacin, soframycin (creams).

2. Disinfectants:

• Applied to non-living surfaces (floors, instruments).
• Examples: chlorine ($Cl_2$ in water), phenol ($1\%$ — antiseptic; concentrated — disinfectant), formaldehyde, hypochlorous acid (bleach), sulfur dioxide, bleaching powder.

Note: Same substance can be antiseptic or disinfectant depending on concentration:

• $0.2\%$ phenol: antiseptic
• $1\%$ phenol: disinfectant

3. Antibiotics:

Definition: Substances produced (in nature) by microorganisms that kill or inhibit growth of other microorganisms. Now also synthesized.

Classification by Spectrum:

• Broad spectrum: Effective against many types of bacteria (gram-positive and gram-negative). e.g., ampicillin, tetracycline, chloramphenicol.
• Narrow spectrum: Effective against only specific types. e.g., penicillin G (against gram-positive only).

Classification by Action:

• Bactericidal: Kill bacteria. e.g., penicillin, aminoglycosides.
• Bacteriostatic: Inhibit bacterial growth (let immune system clear infection). e.g., chloramphenicol, tetracycline, erythromycin.

Common Antibiotics:

Antibiotic Resistance: Repeated/improper use of antibiotics causes bacteria to evolve resistance (mutations, transfer of resistance genes via plasmids). Major public health issue.

4. Sulfa Drugs (Sulfonamides):

• Synthetic antibacterial drugs (pre-penicillin era).
• Sulfanilamide ($H_2N-C_6H_4-SO_2NH_2$) → many derivatives.
• Mechanism: Competitive inhibition of bacterial enzyme dihydropteroate synthase (mimics PABA — para-aminobenzoic acid).

5. Antifungal: Nystatin, ketoconazole, fluconazole. 6. Antiviral: Acyclovir, AZT (against HIV).

Common Analgesics:

Aspirin Properties:

• Acetylsalicylic acid
• Reduces fever, pain, inflammation
• Anti-platelet: prevents blood clotting → used for heart attack prevention
• Side effects: stomach ulcers, Reye's syndrome (in children)

Antacids:

Excess HCl in stomach → acidity, ulcers.

Common antacids:

• $Mg(OH)_2$ (milk of magnesia)
• $Al(OH)_3$
• $NaHCO_3$ (sodium bicarbonate, "soda")
• $CaCO_3$
• Modern: Ranitidine (Zantac), omeprazole (Prilosec) — inhibit histamine-2 receptors or proton pump (more targeted)

Antihistamines:

Histamine causes allergic reactions (runny nose, itching, hives).

Examples: Brompheniramine (Dimetapp), terfenadine (Seldane), cetirizine, loratadine, diphenhydramine. Mechanism: Block $H_1$ receptors.

Cleansing Agents: Substances that remove dirt and grease from surfaces by emulsifying them in water.

Two main types: soaps and synthetic detergents (syndets).

1. Soaps:

Definition: Sodium or potassium salts of long-chain fatty acids ($C_{12}$ to $C_{18}$).

Common examples:

• Sodium stearate: $CH_3(CH_2)_{16}COONa$
• Sodium palmitate: $CH_3(CH_2)_{14}COONa$
• Sodium oleate: $CH_3(CH_2)_7CH=CH(CH_2)_7COONa$ (unsaturated)

Manufacture (Saponification): $$\text{Fat/Oil (triglyceride)} + 3NaOH \to \text{Soap} + \text{Glycerol}$$

Triglyceride = triester of glycerol with three fatty acids. $$CH_2(OOCR)-CH(OOCR')-CH_2(OOCR'') + 3NaOH \to RCOONa + R'COONa + R''COONa + CH_2(OH)CH(OH)CH_2OH$$

Types of Soaps:

• Hard soap (sodium soap): From animal fat with NaOH. Soft, slightly soluble.
• Soft soap (potassium soap): From vegetable oils with KOH. Liquid, more soluble.
• Toilet soap: From high-quality fats; less alkali; with perfume.
• Medicated soap: Contains antiseptic.
• Transparent soap: Dissolved in alcohol.
• Shaving soap: Contains glycerol (prevents drying); stearic acid.

Cleansing Action of Soap:

Soap is a surfactant — has two parts:

• Hydrophilic head: $-COO^-Na^+$ (water-loving)
• Hydrophobic tail: Long alkyl chain (oil-loving)

In water above critical micelle concentration (CMC):

• Tails huddle together (avoid water); heads project outward.
• Form spherical aggregates: micelles.
• Heads on outside (in water); tails inside (in dirt/grease).

For washing:

1. Soap reduces surface tension of water.
2. Tails dissolve in grease/dirt; heads in water.
3. Micelles form around dirt, suspending it.
4. Rinsing washes micelles (with dirt inside) away.

Limitations of Soaps:

• Hard water: Contains Ca²⁺, Mg²⁺. These form insoluble Ca/Mg salts of fatty acids (scum):

$2C_{17}H_{35}COONa + Ca^{2+} \to (C_{17}H_{35}COO)_2Ca \downarrow + 2Na^+$

• Wastes soap; leaves residue on clothes.
• Doesn't work in acidic water (fatty acid precipitates out).

2. Synthetic Detergents (Syndets):

Designed to overcome hard water limitations.

Classification:

Sodium Dodecylbenzene Sulfonate (SDBS): $CH_3-(CH_2)_{11}-C_6H_4-SO_3^-Na^+$

Advantages over soap:

• Works in hard water (Ca/Mg salts of sulfonate are soluble — no scum)
• Works in acidic water
• Stronger cleansing
• Can be tailored for specific uses

Biodegradability:

• Straight chain: Biodegradable; broken down by microbes.
• Branched chain: Not biodegradable; persists in water; environmental pollution.
• Modern detergents are linear (linear alkyl benzenesulfonates, LAS) for environmental reasons.

Food Additives: Substances added to food to:

• Preserve (prevent spoilage)
• Enhance flavor, color, texture
• Replace nutrients

Types:

1. Preservatives: Prevent spoilage caused by microorganisms.

2. Antioxidants:

Prevent oxidation (rancidity) of fats/oils.

Mechanism: They donate hydrogen atom to free radicals; preferentially oxidized themselves, sparing the food.

3. Artificial Sweeteners:

Provide sweetness with little or no calories. Important for diabetics and weight management.

4. Food Colors:

• Natural: beta-carotene (orange), chlorophyll (green), curcumin (yellow), anthocyanin (purple/red).
• Synthetic: tartrazine (yellow), sunset yellow, erythrosine (red), brilliant blue.

5. Flavor Enhancers:

• Monosodium glutamate (MSG): umami flavor; debated health effects.
• 5'-nucleotides (GMP, IMP): synergize with MSG.

6. Emulsifiers/Stabilizers/Thickeners:

• Lecithin, mono-/diglycerides, gums (guar, xanthan, locust bean).
• Carrageenan, agar (from seaweed).
• Pectin, starches.

7. Anti-caking Agents:

• Silicon dioxide, calcium silicate, magnesium stearate.
• Prevent powders (salt, sugar) from clumping.

Spoilage of Food (How preservatives work):

Microbial spoilage: Bacteria, yeast, mold grow on food. Preservatives create unfavorable conditions:

• pH (acetic acid, lactic acid)
• Osmotic pressure (high salt/sugar)
• Direct toxicity (sulfites, benzoates)

Oxidative spoilage: Fats and oils undergo oxidation → rancidity. Antioxidants prevent.

Enzymatic spoilage: Natural enzymes in food cause browning (fruit cut). Antioxidants (Vitamin C) prevent.