Chemistry in Everyday Life — Notes

Drugs: chemicals of low molecular mass (about 100–500 u) that interact with macromolecular targets to give a biological response. Medicines: drugs with a therapeutic effect, used for diagnosis, prevention or treatment; most are harmful in larger doses, so they are used only under medical supervision.

Classification: by pharmacological effect (analgesics, antiseptics), by drug action on a biochemical process (antihistamines), by chemical structure (sulphonamides), by molecular target (drugs acting on enzymes, receptors).

Enzymes as targets: drugs may block the active site (competitive inhibitors), bind at an allosteric site to change the active site’s shape, or bind covalently (irreversible inhibition).

Receptors as targets: membrane proteins that receive chemical messengers. Agonists mimic the messenger; antagonists block the receptor.

• Antacids: NaHCO₃, Mg(OH)₂, Al(OH)₃ neutralise excess acid ($\ce{Mg(OH)2 + 2HCl -> MgCl2 + 2H2O}$). Insoluble bases are preferred: excess soluble base makes the stomach alkaline and triggers more acid. H₂-receptor blockers (cimetidine, ranitidine) stop histamine from stimulating acid release.
• Antihistamines: brompheniramine, terfenadine — block histamine receptors in allergy (they do not affect acid secretion).
• Tranquilisers: for stress and mental illness — equanil (depression, hypertension); barbiturates (veronal, amytal, seconal, nembutal) as hypnotics.
• Analgesics: relieve pain without impairing consciousness. Non-narcotic: aspirin (also antipyretic, anti-inflammatory, prevents platelet clotting), paracetamol. Narcotic: morphine, codeine (severe pain; sleep and addiction).

Antimicrobials destroy or check microbes: antibacterials, antifungals, antivirals, antiparasitics. Early synthetic antimicrobials: salvarsan (arsenic compound, for syphilis), prontosil (converted in the body to sulphanilamide; led to the sulpha drugs).

Antibiotics: chemicals (originally from micro-organisms, now also synthesised) that kill or inhibit microbes.

• Bactericidal (kill): penicillin, aminoglycosides, ofloxacin. Bacteriostatic (stop growth): erythromycin, tetracycline, chloramphenicol.
• Broad-spectrum (many bacteria): ampicillin, amoxycillin, chloramphenicol, vancomycin, ofloxacin. Narrow-spectrum: penicillin G. Limited spectrum: one organism or disease.

Antiseptics (living tissue): Dettol (chloroxylenol + terpineol), bithionol, iodine tincture (2–3% I₂ in alcohol–water), iodoform, boric acid (eyes). Disinfectants (non-living objects): 1% phenol, chlorine (0.2–0.4 ppm in water), low concentrations of SO₂. 0.2% phenol is an antiseptic.

Antifertility drugs: synthetic progesterone derivatives with oestrogen derivatives, e.g. norethindrone, ethynylestradiol (novestrol).

Natural sweeteners (sucrose, fructose) add calories. Artificial sweeteners give sweetness with little or no energy — useful for diabetics and for weight control.

Mass needed for equal sweetness $=$ mass of sucrose $\div$ relative sweetness.

Food additives preserve food, improve appeal or add nutrients (colours, flavours, sweeteners, emulsifiers, flour improvers, antioxidants, preservatives, vitamins and minerals). Apart from nutritional supplements, they have no nutritive value.

Preservatives prevent microbial spoilage: table salt, sugar and vegetable oils (traditional); sodium benzoate (small amounts; metabolised to hippuric acid and excreted), salts of sorbic acid and propanoic acid.

Antioxidants slow oxidation (rancidity) of fats by reacting with oxygen or free radicals more readily than the food: BHT, BHA (often with ascorbic or citric acid); SO₂ and sulfites in wines, beers, sugar syrups and dried fruits.