Chemistry in Everyday Life – Chemistry Study Notes

Chemicals in Medicines: Pharmacological Classification

Medicines are chemicals of low molecular masses that interact with macromolecular targets to produce a biological response. When this response is therapeutic and useful, these chemicals are called medicines and are used in diagnosis, prevention, and treatment of diseases. If taken in doses higher than recommended, most drugs act as poisons.

Medicinal chemistry categorizes drugs primarily by their pharmacological effect, drug action, chemical structure, or molecular target. Understanding the exact classification of drugs is vital for competitive exams. For instance, antipyretics are drugs used to reduce body temperature during high fever.

A classic example of an antipyretic is paracetamol (acetaminophen), which also possesses mild analgesic properties. Analgesics relieve pain without causing impairment of consciousness, mental confusion, or paralysis. They are broadly divided into two groups: narcotic analgesics and non-narcotic analgesics.

Narcotic analgesics include morphine and codeine, which are derived from opium poppies, addictive, and cause sleep. Non-narcotic analgesics include aspirin and ibuprofen, which reduce pain and inhibit platelet aggregation.

“Drugs are low molecular mass substances that interact with target macromolecules, altering their physiological function to produce a therapeutic outcome.”

Another major class of drugs is tranquilizers, which are chemical compounds used for the treatment of stress, anxiety, and mental diseases. They are essential components of sleeping pills. Tranquilizers act on the central nervous system by altering neurotransmitter levels.

Examples of tranquilizers include noradrenaline, a low level of which can cause depression. This is countered by antidepressant drugs like iproniazid and phenelzine. Other examples include equanil, used for controlling depression and hypertension, and valium (diazepam), which acts as a mild tranquilizer and muscle relaxant.

Antimicrobials, Antibiotics, and Antifertility Drugs

Diseases in human beings and animals are caused by a variety of microorganisms such as bacteria, fungi, viruses, or parasites. Antimicrobials are drugs that cure diseases by killing or inhibiting the growth of microorganisms. This broad category includes antibiotics, antiseptics, and disinfectants.

Antibiotics are chemical substances produced wholly or partly by chemical synthesis. In low concentrations, they inhibit the growth of or destroy microorganisms by intervening in their metabolic processes. Antibiotics can be bactericidal (cell-killing), such as penicillin, aminoglycosides, and ofloxacin. Alternatively, they can be bacteriostatic (growth-inhibiting), such as erythromycin, tetracycline, and chloramphenicol.

Furthermore, antibiotics are classified as broad-spectrum if they are effective against a wide range of gram-positive and gram-negative bacteria, such as chloramphenicol, ampicillin, and amoxicillin. They are classified as narrow-spectrum if effective mainly against either gram-positive or gram-negative bacteria, such as penicillin G. Limited-spectrum antibiotics are effective against a single organism or disease.

To distinguish between external and internal use, students must remember that antiseptics are applied to living tissues such as wounds, cuts, ulcers, and diseased skin surfaces. They destroy or prevent the growth of microorganisms. Common examples include furacine, soframycin, and a very dilute solution of iodine in alcohol-water mixtures known as tincture of iodine (2-3% iodine).

Conversely, disinfectants are applied to inanimate objects such as floors, drainage systems, and instruments because they are harmful to living tissues. Examples include a 0.2-0.4 ppm aqueous solution of chlorine and a 1% solution of phenol.

Antifertility drugs are synthetic hormonal compositions used to control population growth. These are birth control pills that typically contain a mixture of synthetic estrogen and progesterone derivatives. Both compounds are hormones that inhibit ovulation. A common example of a synthetic progesterone derivative is norethindrone, and an estrogen derivative is ethynylestradiol (novestrol).

Chemicals in Food: Preservatives and Artificial Sweeteners

Chemicals are added to food for various purposes: to impart flavor, texture, and color, to enhance nutritive value, and primarily to increase shelf life through preservation. Food preservatives prevent spoilage due to microbial growth. The most common preservative used worldwide is sodium benzoate ($\text{C}_6\text{H}_5\text{COONa}$).

Sodium benzoate is extensively utilized in soft drinks and acidic foods because it metabolizes safely and is converted to hippuric acid. Other important preservatives include salts of sorbic acid and propanoic acid. Natural sweeteners like sucrose add calories to the diet, creating a high demand for artificial sweeteners that provide sweetness without adding calories.

These are especially beneficial for diabetic patients and calorie-conscious individuals. Key artificial sweeteners frequently tested in exams include:

• Aspartame: Roughly 100 times as sweet as cane sugar. It is the methyl ester of a dipeptide formed from aspartic acid and phenylalanine. It is unstable at cooking temperatures and is thus restricted to cold foods and soft drinks.
• Saccharin: (O-sulfobenzimide) About 550 times as sweet as cane sugar. It is excreted from the body unchanged in urine and is non-caloric, though it has a bitter aftertaste at high concentrations.
• Sucralose: A trichloro derivative of sucrose. It is 600 times sweeter than sugar, stable at cooking temperatures, and does not provide calories.
• Alitame: Extremely potent, being about 2000 times sweeter than sucrose. Control of sweetness is difficult when using alitame due to its high potency.

Cleansing Agents: Soaps and Synthetic Detergents

Cleansing agents are substances used to remove dirt and grease; they improve the cleansing properties of water. The two primary types of cleansing agents are soaps and synthetic detergents. Soaps are sodium or potassium salts of long-chain fatty acids, such as palmitic, stearic, or oleic acid.

Soaps are sodium salts formed by the heating of fat or oil with aqueous sodium hydroxide, a process known as saponification.

A critical limitation of soaps is that they do not work well in hard water. Hard water contains soluble calcium and magnesium ions ($\text{Ca}^{2+}$ and $\text{Mg}^{2+}$), which react with soaps to form insoluble calcium and magnesium salts of fatty acids (scum). This scum precipitates out as a sticky grayish solid, wasting soap until all hard ions are removed.

Synthetic detergents overcome this limitation because they can be used in both soft and hard water; their calcium and magnesium salts are also soluble in water. Synthetic detergents are categorized into three main classes based on their electrical charge:

• Anionic Detergents: These are sodium salts of sulfonated long-chain alcohols or hydrocarbons. Examples include sodium alkyl sulfates (e.g., sodium lauryl sulfate) and sodium alkylbenzene sulfonates. They are primarily used in household dishwashing liquids and laundry detergents.
• Cationic Detergents: These are quaternary ammonium salts of amines with acetates, chlorides, or bromides. They possess germicidal properties and are relatively expensive. An example is cetyltrimethylammonium bromide, widely used in hair conditioners.
• Non-ionic Detergents: These do not contain any ions in their constitution. They are esters formed by the reaction of stearic acid with polyethylene glycol. Liquid dishwashing detergents frequently utilize non-ionic formulations.

Key Points to Remember

• Bithional is often added to soaps as an antiseptic to reduce the odor caused by bacterial decomposition of skin organic matter.
• Chloramphenicol is a broad-spectrum antibiotic isolated in 1947, highly effective against typhoid, dysentery, acute fevers, and certain urinary infections.
• Salvarsan (Arsphenamine) was discovered by Paul Ehrlich as an effective treatment for syphilis, representing an early milestone in chemotherapy.
• Antihistamines (such as brompheniramine and terfenadine) are drugs that block the action of histamine, a vasodilator responsible for nasal congestion and allergic responses.
• Omeprazole and lansoprazole are antacids that decrease the production of stomach acid by targeting proton pumps.
• Branched-chain synthetic detergents are non-biodegradable, leading to severe water pollution and river foaming; modern manufacturing focuses on linear, straight-chain biodegradable detergents.
• Tincture of Iodine is an antiseptic made of 2-3% iodine dissolved in an alcohol-water mixture.
• Equanil is a widely used tranquilizer prescribed for anxiety and hypertension.

Important Facts / Formulas

Previous Year Question Hints

• Question Type 1 (Matching Drugs to Categories): Aspirin, tranquilizers, antibiotics, and antifertility agents are often listed alongside their medical uses. Remember that aspirin acts both as an analgesic and an antipyretic with anti-blood-clotting properties.
• Question Type 2 (Soap vs. Detergent in Hard Water): Expect conceptual questions asking why synthetic detergents work in hard water while soaps fail. Focus on the solubility of calcium and magnesium salts of sulfonated detergents versus fatty acid soaps.
• Question Type 3 (Artificial Sweeteners stability): Questions frequently test which artificial sweetener is stable at cooking temperatures. Remember that sucralose and alitame remain stable at baking temperatures, whereas aspartame decomposes under heat.

Quick Revision Summary

• Medicines are low molecular mass chemicals that interact with macromolecular targets to produce therapeutic effects.
• Antipyretics reduce fever, while analgesics relieve pain (divided into narcotic and non-narcotic categories).
• Antibiotics can be bactericidal or bacteriostatic, and broad-spectrum or narrow-spectrum depending on their target spectrum.
• Antiseptics are safe for living tissues; disinfectants are meant strictly for non-living surfaces due to high toxicity.
• Artificial sweeteners like alitame, sucralose, aspartame, and saccharin offer high sweetness indexes with low or zero calorie intake.
• Sodium benzoate serves as a common food preservative, particularly in acidic foods and beverages.
• Soaps are sodium or potassium salts of long-chain fatty acids formed via saponification, rendering them ineffective in hard water.
• Synthetic detergents (anionic, cationic, and non-ionic) function effectively in both hard and soft water media.