Chemistry in everyday life (Chapter 16) Class XII

Chemistry in everyday life

Drugs – are the chemicals of low molecular mass (100-500u) which interact with macromolecular targets and produce a biological response i.e. can act as medicines or as poisons.

Chemotherapy - Branch in medicine where we use chemicals to cure the diseases or reduce suffering from pains (for therapeutic effect).

Classification of drugs: a) On the basis of pharmacological effect – analgesics for pain killing effect, antiseptics for killing or arresting the growth of micro-organisms.

b) On the basis of drug action – It is based on the action of a drug on a particular biochemical process. E.g. all antihistamines inhibit the action of the compound, histamine which causes inflammation in the body.

c) On the basis of chemical structure – on the basis of common structural features and similar pharmacological activity. E.g. sulphonamides have common structure:

d) On the basis of molecular targets – Drugs possessing some common structural features may have the same mechanism of action on targets. (most useful classification).

Consideration of drug designing – Two considerations are essential: (i) Choice of drug target – Drugs usually interact with biological macromolecules known as targets, (ii) Drug metabolism – A drug travels through the body in order to reach the target. So, its design should be such that it reaches the target without being metabolised in between and also, after its action, it should be excreted without causing harm to the body.

Drugs are designed by lead compounds (Sources = plants, trees, bushes, metabolites of microorganisms)

Q. How do drugs interact with targets?

Drugs interact with biological macromolecules like proteins, carbohydrates, lipids and nucleic acids. E.g. Enzymes are the proteins which perform the role of biological catalysts. They hold the substrate for a chemical reaction and they provide functional group (-OH, -NH₂, -COOH) that will attack the substrate and carry out chemical reaction (by H-bonding, ionic bonds, Vander Waal’s forces, dipole-dipole interactions). Drugs are designed to inhibit any of the above activities of enzymes and are known as enzymes inhibitors which can block the binding site and prevent the binding of substrate with enzyme.

Drugs compete with the natural substrate for active site. Such drugs are called as competitive inhibitors. Some drugs do not bind to the active site but bind to the different site of enzyme known as allosteric site. This changes the shape of active site such that substrate cannot recognize it.

Receptors – are the proteins that are crucial to the body’s communication process which are embedded in cell membrane (made up of phospholipid bilayer). Two chemical messengers which help the receptor to transfer message into the cell are:

a) Hormones – are released from endocrine glands. These enter into the blood stream and travel in the body, activating all the receptors which recognize them for message transfer (that helps in the growth and development of the body). E.g. Adrenaline (epinephrine) is a hormone released from adrenal medulla in the situation of stress or danger.

b) Neurotransmitters – like acetylcholine, dopamine and serotonin. Nerves transfer message through them.

Drugs are categorised as – a) Antagonists : drugs that bind to receptors site and inhibits its natural function by blocking the active site.

b) Agonists : Drugs that mimic the natural messenger by switching on the receptor. These are useful when there is lack of natural chemical messenger in the body.

Side effects are caused when drugs bind to more than one type of receptor or are taken in excess.

Therapeutic action of different classes of drugs:

 a) Antacids – Chemical substances which can reduce or neutralise the acidity of stomach which occurs due to release of excess of gastric acid (HCl) in stomach. E.g. Ranitidine (Zantac), Cimetidine. They are better than NaHCO₃ and Mg(OH)₂ as they prevent interaction of histamine with receptors (or anti-allergic action) in stomach and helps in quick healing of ulcers as they  are mild bases.

b) Antihistamines (or anti-allergic drugs)- Drugs which combat or prevent the effects of histamine, a chemical released by certain cells of body (mast cells) during an allergic reaction. E.g. Dimetapp and seldane.

Histamine is a potent vasodilator. It contracts smooth muscles in bronchi and gut and relaxes other muscles of blood vessels. It is also responsible for nasal congestion associated with common colds and allergic response to pollen grains. 

Antihistamines do not affect the secretion of acid in stomach because antiallergic and antacid drugs work on different receptors.

c) Neurologically active drugs –

(i) Tranquilizers or sedatives – drugs given to patients suffering from anxiety and tension. These relieve anxiety, stress, irritability or excitement. Antipsychotic tranquilizers are the major tranquilizers while sedative tranquilizers are used during intense anxiety or panic. These are used for making sleeping pills like Barbituric acid, lyminal and seconal. Non-adrenaline is a neurotransmitter that plays role in mood changes. If level of non-adrenaline is low, the person suffers from depression. So, anti-depressant drugs are required like Iproniazid, Nardil (phenelzine).

(ii) Analgesics – Chemical substances which are used for relieving pains in the body. Two types of analgesics are: Non-narcotic drugs (non-addictive) – Salicylates (for e.g. aspirin and paracetamol) belong to this class. Aspirin inhibits the synthesis of chemicals known as prostaglandins which stimulate inflammation in tissue and cause pain. These drugs are effective in reducing fever (antipyretic) and preventing platelet coagulation. Because of its anti-blood clotting action, aspirin finds its use in prevention of heart attacks.(Aspirin = 2-Acetoxy benzoic acid).                                                                  Narcotic analgesic drugs – such as morphine and many of its homologous, when administered in medicinal doses, relieve pain and produce sleep and cause addiction. Morphine narcotics are sometimes referred to as opiates, since they are obtained from the opium poppy.  

d) Antibiotics – Chemical substances produced by micro-organisms (bacteria, fungi, moulds) that inhibit the growth or even destroy other micro-organisms. First antibiotic was discovered by Alexander Fleming and it was penicillin (for malaria). The complete range of micro-organisms which can be killed by a particular antibiotic is called its spectrum. There are two types of antibiotics-: Broad – spectrum antibiotics: antibiotics which can kill different types of micro-organisms. They can cause several infections. E.g. Tetracyclines, chloramphenicol. Narrow – spectrum antibiotics: antibiotics which can kill only few micro-organisms. E.g. Penicillin, streptomycin, chloromycetin.

Two major classes of antibiotics: Bactericidal is an antibiotic which kills the micro-organisms in the body. E.g. Penicillin, ofloxacin. Bacteriostatic is an antibiotic which inhibit or control the growth of micro-organisms. E.g. tetracycline, chloramphenicol.

e) Antiseptics – can kill or prevent the growth of micro-organisms. They do not harm the living tissue and can be applied to the skin. They are used for dressing wounds, ulcers and in treatment of diseased skin. E.g. Dettol (a mixture of chloroxylenol and terpineol), Tincture of iodine (2-3% iodine solution of alcohol-water)

Disinfectants – can kill micro-organisms. They are toxic to living tissues. So, it cannot be applied to the skin. These are used for disinfecting floors, toilet drains, instruments, etc. E.g. DDT (Dichloro Diphenyl Trichloroethane), BHC (Benzene hexachloride).

Phenol 1-2% solution is used as disinfectant while 0.2% solution of phenol is used as antiseptic.

f) Antifertility drugs – are hormonal contraceptives and are available for females only. Birth control pills are derivatives of synthetic oestrogen and progesterone. E.g. Norethindrone (progesterone derivative), novestrol (oestrogen derivative).

Chemicals in food: a) Artificial sweetners – Natural sweetners sucrose adds to calorie intake and therefore many people prefer to use artificial sweetners. Its use is of great value to diabetic persons. E.g. Aspartame (unstable at cooking temperature as it contains peptide linkages), Saccharine(low quality), Sucrulose, Alitame (high potency sweetner).  

b) Preservatives – They prevent the spoilage of food due to microbial growth. They are classified into two groups: Class 1 preservatives contain table salts, sugars and vegetable oils and Class 2 preservatives contain sodium benzoate (C_6­H₅COONa).

c) Antioxidants – Substances which when added to the fats and fat containing food prevents their  oxidation (rancidity) and thus prolong their life. Example : Butylated  Hydroxy Anisole (BHA), Butylated Hydroxy Toluene (BHT), Vitamin C.

 Chemistry of Cleansing agents :

SOAPS  ::  are sodium and potassium salts of long chain fatty acids. Soaps are formed  by treating NaOH with fatty acids. This process is known as saponification.

The soap obtained is in colloidal form which is precipitated by adding NaCl and is obtained by fractional distillation. Cleansing action of soaps –

Hydrophobic tail and Hydrophilic head forming micilles.

Soaps do not work in hard water (disadvantage): Hard water contains calcium and magnesium ions which form insoluble salts with soaps as scum which are useless as cleansing agent.

2C₁₇H₃₅COONa  +  CaCl₂ (in hard water)     è     2NaCl  +  (C₁₇H₃₅COO)₂Ca    (insoluble)

Soaps can be biodegraded.

Advantage of detergents :  They do not form scum with hard water.

 Disadvantage of detergent: They are non-biodegradable.

STRUCTURE :

Sodium palmitate :  C₁₅H₃₁COONa

Sodium oleate : C₁₇H₃₁COONa

Types of synthetic detergents:

a) Anionic detergents – are sodium salts of sulphonated long chain alcohols. They are effective in acidic solutions. Their larger part of molecule is anion. E.g. ABS (alkyl benzene sulphonate) CH₃(CH₂)₁₆OSO₃Na and Sodium lauryl sulphonate  CH₃(CH₂)₁₀CH₂OSO₃Na.

b) Cationic detergents – are chlorides or bromides of quarternary amines. Cationic part possesses a long hydrocarbon chain and a positive charge. E.g. Cetylmethylammonium bromide(non-biodegradable). They have germicidal properties but have high cost.

c) Non-ionic detergents – Liquid dishwashing detergents are of non-ionic type. They have same mechanism of cleansing action as of soaps.

HO-CH₂-CH₂-OH   +   n  CH₂-CH₂     →     HO(CH₂CH₂O)_nCH₂CH₂OH (polyethylene glycol)

Q. Why medicines or sleeping pills should not be taken without consulting doctors?

Ans. Because most drugs are potential poisons if taken in doses higher than the dose recommended.

Q. What is biothionol? Give its use.

Ans. Biothionol is an aromatic compound containing sulphur and it is added to soaps to impart antiseptic  properties.

Q. What are hypnotics? Give an e.g.

Ans. Hypnotics are drugs which produce sleep. They are habit forming. E.g. Luminal, Seconal.

Q. What kind of medicines are given to agitated and violent patient?

Ans. Tranquilizers or sedatives or anti-depressant drugs.

Q. Low level of non-adrenaline is the cause of depression. What type of drugs are needed to cure this problem? Name two drugs.

Ans. Psychotherapeutic drugs or tranquilizers. E.g. Luminal, Equanil.

Q. Why aspirin should not be taken empty stomach?

Ans. It decreases pH and causes ulcer.