From living perception to abstract thought, and from this to practice.
By now, you have learnt the basic principles of chemistry and also realised that it influences every sphere of human life. The principles of chemistry have been used for the benefit of mankind. Think of cleanliness — the materials like soaps, detergents, household bleaches, tooth pastes, etc. will come to your mind. Look towards the beautiful clothes — immediately chemicals of the synthetic fibres used for making clothes and chemicals giving colours to them will come to your mind. Food materials — again a number of chemicals about which you have learnt in the previous Unit will appear in your mind. Of course, sickness and diseases remind us of medicines — again chemicals. Explosives, fuels, rocket propellents, building and electronic materials, etc., are all chemicals. Chemistry has influenced our life so much that we do not even realise that we come across chemicals at every moment; that we ourselves are beautiful chemical creations and all our activities are controlled by chemicals. In this Unit, we shall learn the application of Chemistry in three important and interesting areas, namely – medicines, food materials and cleansing agents.
16.1 Drugs and their Classification
Drugs are chemicals of low molecular masses (~100 – 500u). These interact with macromolecular targets and produce a biological response. When the biological 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 those recommended, most of the drugs used as medicines are potential poisons. Use of chemicals for therapeutic effect is called chemotherapy,
16.1.1 Classification of Drugs
Drugs can be classified mainly on criteria outlined as follows:
(a) On the basis of pharmacological effect
This classification is based on pharmacological effect of the drugs. It is useful for doctors because it provides them the whole range of drugs available for the treatment of a particular type of problem. For example, analgesics have pain killing effect, antiseptics kill or arrest the growth of microorganisms.
(b) On the basis of drug action
It is based on the action of a drug on a particular biochemical process. For example, all antihistamines inhibit the action of the compound, histamine which causes inflammation in the body. There are various ways in which action of histamines can be blocked. You will learn about this in Section 16.3.2.
(c) On the basis of chemical structure
It is based on the chemical structure of the drug. Drugs classified in this way share common structural features and often have similar pharmacological activity. For example, sulphonamides have common structural feature, given below.
(d) On the basis of molecular targets
Drugs usually interact with biomolecules such as carbohydrates, lipids,proteins and nucleic acids. These are called target molecules or drug targets. Drugs possessing some common structural features may have the same mechanism of action on targets. The classification based on molecular targets is the most useful classification for medicinal chemists.
16.2 Drug – target Interaction
Macromolecules of biological origin perform various functions in the body. For example, proteins which perform the role of biological catalysts Itrcin in the body are called enzymes, those which are crucial to neato communication system in the body are called receptors. Carrier proteins carry polar molecules across the cell membrane. Nucleic acids have coded genetic information for the cell. Lipids and carbohydrates are structural parts of the cell membrane. We shall explain the drug-target interaction with the examples of enzymes and receptors.
16.2.1 Enzymes as Drug Targets
(a) Catalytic action of enzymes
For understanding the interaction between a drug and an enzyme, it is important to know how enzymes catalyse the reaction (Section 5.2.4). In their catalytic activity, enzymes perform two major functions:
(i) The first function of an enzyme is to hold the substrate for a chemical reaction. Active sites of enzymes hold the substrate molecule in a suitable position, so that it can be attacked by the reagent effectively.
Substrates bind to the active site of the enzyme through a variety of interactions such as ionic bonding, hydrogen bonding, van der Waals interaction or dipole-dipole interaction (Fig. 16.1).
(ii) The second function of an enzyme is to provide functional groups that will attack the substrate and carry out chemical reaction.
(b) Drug-enzyme interaction
Drugs inhibit any of the above mentioned activities of enzymes. These can block the binding site of the enzyme and prevent the binding of substrate, or can inhibit the catalytic activity of the enzyme. Such drugs are called enzyme inhibitors. Drugs inhibit the attachment of substrate on active site of enzymes in two different ways;
(ii) Some drugs do not bind to the enzyme’s active site. These bind to a different site of enzyme which is called allosteric site. This binding of inhibitor at allosteric site (Fig.16.3) changes the shape of the active site in such a way that substrate can-not recognise it.
If the bond formed between an enzyme and an inhibitor is a strong covalent bond and cannot be broken easily, then the enzyme is blocked permanently. The body then degrades the enzyme-inhibitor complex and synthesises the new enzyme.
16.2.2 Receptors as Drug Targets
Receptors are proteins that are crucial to body’s communication process. Majority of these are embedded in cell membranes (Fig. 16.4). Receptor proteins are embedded in the cell membrane in such a way that their small part possessing active site projects out of the surface of the membrane and opens on the outside region of the cell membrane (Fig. 16.4).
In the body, message between two neurons and that between neurons to muscles is communicated through certain chemicals. These chemicals,known as chemical messengers are received at the binding sites of receptor proteins. To accommodate a messenger, shape of the receptor site changes. This brings about the transfer of message into the cell. Thus, chemical messenger gives message to the cell without entering the cell (Fig. 16.5).
There are a large number of different receptors in the body that interact with different chemical messengers. These receptors show selectivity for one chemical messenger over the other because their binding sites have different shape, structure and amino acid composition.
Drugs that bind to the receptor site and inhibit its natural function are called antagonists. These are useful when blocking of message is required. There are other types of drugs that mimic the natural messenger by switching on the receptor, these are called agonists. These are useful when there is lack of natural chemical messenger.
16.3 Theraputic Action of Different Classes of drugs
In this Section, we shall discuss the therapeutic action of a few important classes of drugs.
Over production of acid in the stomach causes irritation and pain. In severe cases, ulcers are developed in the stomach. Until 1970, only treatment for acidity was administration of antacids, such as sodium hydrogencarbonate or a mixture of aluminium and magnesium hydroxide. However, excessive hydrogencarbonate can make the stomach alkaline and trigger the production of even more acid. Metal hydroxides are better alternatives because of being insoluble, these do not increase the pH above neutrality. These treatments control only symptoms, and not the cause. Therefore, with these metal salts, the patients cannot be treated easily. In advanced stages, ulcers become life threatening and its only treatment is removal of the affected part of the stomach.
A major breakthrough in the treatment of hyperacidity came through the discovery according to which a chemical, histamine, stimulates the secretion of pepsin and hydrochloric acid in the stomach. The drug cimetidine (Tegamet), was designed to prevent the interaction of histamine with the receptors present in the stomach wall. This resulted in release of lesser amount of acid. The importance of the drug was so much that it remained the largest selling drug in the world until another drug, ranitidine (Zantac), was discovered.
Histamine is a potent vasodilator. It has various functions. It contracts the smooth muscles in the bronchi and gut and relaxes other muscles, such as those in the walls of fine blood vessels. Histamine is also responsible for the nasal congestion associated with common cold and allergic response to pollen.
Synthetic drugs, brompheniramine (Dimetapp) and terfenadine (Seldane), act as antihistamines. They interfere with the natural action of histamine by competing with histamine for binding sites of receptor where histamine exerts its effect.
16.3.3 Neurologically Active Drugs
Tranquilizers and analgesics are neurologically active drugs. These affect the message transfer mechanism from nerve to receptor. Tranquilizers are a class of chemical compounds used for the treatment of stress, and mild or even severe mental diseases. These relieve anxiety, stress, irritability or excitement by inducing a sense of well-being. They form an essential component of sleeping pills. There are various types of tranquilizers. They function by different mechanisms. For example, noradrenaline is one of the neurotransmitters that plays a role in mood changes. If the level of noradrenaline is low for some reason, then the signal-sending activity becomes low, and the person suffers from depression. In such situations, antidepressant drugs are required. These drugs inhibit the enzymes which catalyse the degradation of noradrenaline. If the enzyme is inhibited, this important neurotransmitter is slowly metabolised and can activate its receptor for longer periods of time, thus counteracting the effect of depression. Iproniazid and phenelzine are two such drugs.
Derivatives of barbituric acid viz., veronal, amytal, nembutal, luminal and seconal constitute an important class of tranquilizers. These derivatives are called barbiturates. Barbiturates are hypnotic, i.e., sleep producing agents. Some other substances used as tranquilizers are valium and serotonin.
Analgesics reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbances of nervous system. These are classified as follows:
(i) Non-narcotic (non-addictive) analgesics
(ii) Narcotic drugs
(i) Non-narcotic (non-addictive) analgesics: Aspirin and paracetamol belong to the class of non-narcotic analgesics. Aspirin is the most familiar example. Aspirin inhibits the synthesis of chemicals known as prostaglandins which stimulate inflammation in the tissue and cause pain. These drugs are effective
in relieving skeletal pain such as that due to arthritis. These drugs have many other effects such as reducing fever (antipyretic) and preventing platelet coagulation. Because of its anti blood clotting action, aspirin finds use in prevention of heart attacks.
(ii) Narcotic analgesics: Morphine and many of its homologues, when administered in medicinal doses, relieve pain and produce sleep. In poisonous doses, these produce stupor, coma, convulsions and ultimately death. Morphine narcotics are sometimes referred to as opiates, since they are obtained from the opium poppy. These analgesics are chiefly used for the relief of postoperative pain, cardiac pain and pains of terminal cancer, and in child birth.
Diseases in human beings and animals may be caused by a variety of microorganisms such as bacteria, virus, fungi and other pathogens. An antimicrobial tends to destroy/prevent development or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs), fungi (antifungal agents), virus (antiviral agents), or other parasites (antiparasitic drugs) selectively. Antibiotics, antiseptics and disinfectants are antimicrobial drugs.
Antibiotics are used as drugs to treat infections because of their low toxicity for humans and animals. Initially antibiotics were classified as chemical substances produced by microorganisms (bacteria, fungi and molds) that inhibit the growth or even destroy microorganisms. The development of synthetic methods has helped in synthesising some of the compounds that were originally discovered as products of microorganisms. Also, some purely synthetic compounds have antibacterial activity, and therefore, definition of antibiotic has been modified. An antibiotic now refers to a substance produced wholly or partly by chemical synthesis, which in low concentrations inhibits the growth or destroys microorganisms by intervening in their metabolic processes.
The search for chemicals that would adversely affect invading bacteria but not the host began in the nineteenth century. Paul Ehrlich, a German bacteriologist, conceived this idea. He investigated arsenic based structures in order to produce less toxic substances for the treatment of syphilis. He developed the medicine, arsphenamine, known as salvarsan. Paul Ehrlich got Nobel prize for Medicine in 1908 for this discovery. It was the first effective treatment discovered for syphilis. Although salvarsan is toxic to human beings, its effect on the bacteria, spirochete, which causes syphilis is much greater than on human beings. At the same time, Ehrlich was working on azodyes also. He noted that there is similarity in structures of salvarsan and azodyes. The –As = As– linkage present in arsphenamine resembles the –N = N – linkage present in azodyes in the sense that arsenic atom is present in place of nitrogen. He also noted tissues getting coloured by dyes selectively. Therefore, Ehrlich began to search for the compounds which resemble in structure to azodyes and selectively bind to bacteria. In 1932, he succeeded in preparing the first effective antibacterial agent, prontosil, which resembles in structure to the compound, salvarsan. Soon it was discovered that in the body prontosil is converted to a compound called sulphanilamide, which is the real active compound. Thus the sulpha drugs were discovered. A large range of sulphonamide analogues was synthesised. One of the most effective is sulphapyridine.
Despite the success of sulfonamides, the real revolution in antibacterial therapy began with the discovery of Alexander Fleming in 1929, of the antibacterial properties of a Penicillium fungus. Isolation and purification of active compound to accumulate sufficient material for clinical trials took thirteen years.
The range of bacteria or other microorganisms that are affected by a certain antibiotic is expressed as its spectrum of action. Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria are said to be broad spectrum antibiotics. Those effective mainly against Gram-positive or Gram-negative bacteria are narrow spectrum antibiotics. If effective against a single organism or disease, they are referred to as limited spectrum antibiotics. Penicillin G has a narrow spectrum. Ampicillin and Amoxycillin are synthetic modifications of penicillins. These have broad spectrum. It is absolutely essential to test the patients for sensitivity (allergy) to penicillin before it is administered. In India, penicillin is manufactured at the Hindustan Antibiotics in Pimpri and in private sector industry.
Chloramphenicol, isolated in 1947, is a broad spectrum antibiotic. It is rapidly absorbed from the gastrointestinal tract and hence can be given orally in case of typhoid, dysentery, acute fever, certain form of urinary infections, meningitis and pneumonia. Vancomycin and ofloxacin are the other important broad spectrum antibiotics. The antibiotic dysidazirine is supposed to be toxic towards certain strains of cancer cells.
(b) Antiseptics and disinfectants
Antiseptics and disinfectants are also the chemicals which either kill or prevent the growth of microorganisms. Antiseptics are applied to the living tissues such as wounds, cuts, ulcers and diseased skin surfaces. Examples are furacine, soframicine, etc. These are not ingested like antibiotics. Commonly used antiseptic, dettol is a mixture of chloroxylenol and terpineol. Bithionol (the compound is also called bithional) is added to soaps to impart antiseptic properties. Iodine is a powerful antiseptic. Its 2-3 per cent solution in alcohol- water mixture is known as tincture of iodine. It is applied on wounds. Iodoform is also used as an antiseptic for wounds. Boricacid in dilute aqueous solution is weak antiseptic for eyes.
Disinfectants are applied to inanimate objects such as floors, drainage system, instruments, etc. Same substances can act as an antiseptic as well as disinfectant by varying the concentration. For example, 0.2 per cent solution of phenol is an antiseptic while its one percent solution is disinfectant.
Chlorine in the concentration of 0.2 to 0.4 ppm in aqueous solution and sulphur dioxide in very low concentrations, are disinfectants.
16.3.5 Antifertility Drugs
Antibiotic revolution has provided long and healthy life to people. The life expectancy has almost doubled. The increased population has caused many social problems in terms of food resources, environmental issues, employment, etc. To control these problems, population is required to be controlled. This has lead to the concept of family planning. Antifertility drugs are of use in this direction. Birth control pills essentially contain a mixture of synthetic estrogen and progesterone derivatives. Both of these compounds are hormones. It is known that progesterone suppresses ovulation. Synthetic progesterone derivatives are more potent than progesterone. Norethindrone is an example of synthetic progesterone derivative most widely used as antifertility drug. The estrogen derivative which is used in combination with progesterone derivative is ethynylestradiol (novestrol).
16.1 Sleeping pills are recommended by doctors to the patients suffering from sleeplessness but it is not advisable to take its doses without consultation
with the doctor. Why ?
16.2 With reference to which classification has the statement, “ranitidine is an antacid” been given?
16.4 Chemicals in Food
Chemicals are added to food for (i) their preservation, (ii) enhancing their appeal, and (iii) adding nutritive value in them. Main categories of food additives are as follows:
(i) Food colours
(ii) Flavours and sweeteners
(iii) Fat emulsifiers and stabilising agents
(iv) Flour improvers – antistaling agents and bleaches
(vii) Nutritional supplements such as minerals, vitamins and amino acids.
Except for chemicals of category (vii), none of the above additives have nutritive value. These are added either to increase the shelf life of stored food or for cosmetic purposes. In this Section we will discuss only sweeteners and food preservatives.
16.4.1 Artificial Sweetening Agents
Natural sweeteners, e.g., sucrose add to calorie intake and therefore many people prefer to use artificial sweeteners. Ortho-sulphobenzimide, also called saccharin, is the first popular artificial sweetening agent. It has been used as a sweetening agent ever since it was discovered in 1879. It is about 550 times as sweet as cane sugar. It is excreted from the body in urine unchanged. It appears to be entirely inert and harmless when taken. Its use is of great value to diabetic persons and people who need to control intake of calories. Some other commonly marketed artificial sweeteners are given in Table 16.1.
|Artificial Sweetener||Structural formula||Sweetness value in comparison to cane sugar|
Aspartame is the most successful and widely used artificial sweetener. It is roughly 100 times as sweet as cane sugar. It is methyl ester of dipeptide formed from aspartic acid and phenylalanine. Use of aspartame is limited to cold foods and soft drinks because it is unstable at cooking temperature.
Alitame is high potency sweetener, although it is more stable than aspartame, the control of sweetness of food is difficult while using it. Sucrolose is trichloro derivative of sucrose. Its appearance and taste are like sugar. It is stable at cooking temperature. It does not provide calories.
Food preservatives prevent spoilage of food due to microbial growth. Preservatives The most commonly used preservatives include table salt, sugar, vegetable oils and sodium benzoate, C6H5COONa. Sodium benzoate is used in limited quantities and is metabolised in the body. Salts of sorbic acid and propanoic acid are also used as preservatives.
16.3 Why do we require artificial sweetening agents ?
16.5 Cleansing Agents
In this Section, we will learn about detergents. Two types of detergents are used as cleansing agents. These are soaps and synthetic detergents. These improve cleansing properties of water. These help in removal of fats which bind other materials to the fabric or skin.
Soaps are the detergents used since long. Soaps used for cleaning purpose are sodium or potassium salts of long chain fatty acids, e.g., stearic, oleic and palmitic acids. Soaps containing sodium salts are formed by heating fat (i.e., glyceryl ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is known as saponification.
In this reaction, esters of fatty acids are hydrolysed and the soap obtained remains in colloidal form. It is precipitated from the solution by adding sodium chloride. The solution left after removing the soap contains glycerol, which can be recovered by fractional distillation.Only sodium and potassium soaps are soluble in water and are used for cleaning purposes. Generally potassium soaps are soft to the skin than sodium soaps. These can be prepared by using potassium hydroxide solution in place of sodium hydroxide.
Types of soaps
Basically all soaps are made by boiling fats or oils with suitable soluble hydroxide. Variations are made by using different raw materials.
Toilet soaps are prepared by using better grades of fats and oils and care is taken to remove excess alkali. Colour and perfumes are added to make these more attractive.
Soaps that float in water are made by beating tiny air bubbles before their hardening. Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent.
In medicated soaps, substances of medicinal value are added. In some soaps, deodorants are added. Shaving soaps contain glycerol to prevent rapid drying. A gum called, rosin is added while making them. It forms sodium rosinate which lathers well. Laundry soaps contain fillers like sodium rosinate, sodium silicate, borax and sodium carbonate.
Soap chips are made by running a thin sheet of melted soap onto a cool cylinder and scraping off the soaps in small broken pieces. Soap granules are dried miniature soap bubbles. Soap powders and scouring soaps contain some soap, a scouring agent (abrasive) such as powdered pumice or finely divided sand, and builders like sodium carbonate and trisodium phosphate. Builders make the soaps act more rapidly. The cleansing action of soap has been discussed in Unit 5.
Why do soaps not work in hard water?
These insoluble soaps separate as scum in water and are useless as cleansing agent. In fact these are hinderance to good washing, because the precipitate adheres onto the fibre of the cloth as gummy mass. Hair washed with hard water looks dull because of this sticky precipitate. Dye does not absorb evenly on cloth washed with soap using hard water, because of this gummy mass.
16.5.2 Synthetic Detergents
Synthetic detergents are cleansing agents which have all the properties of soaps, but which actually do not contain any soap. These can be used both in soft and hard water as they give foam even in hard water. Some of the detergents give foam even in ice cold water.
Synthetic detergents are mainly classified into three categories:
(i) Anionic detergents (ii) Cationic detergents and (iii) Non-ionic detergents
(i) Anionic Detergents: Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. Alkyl hydrogensulphates formed by treating long chain alcohols with concentrated sulphuric acid are neutralised with alkali to form anionic detergents. Similarly alkyl benzene sulphonates are obtained by neutralising alkyl benzene sulphonic acids with alkali.
In anionic detergents, the anionic part of the molecule is involved in the cleansing action. Sodium salts of alkylbenzenesulphonates are an important class of anionic detergents.
They are mostly used for household work. Anionic detergents are also used in toothpastes.
(ii) Cationic Detergents: Cationic detergents are quarternary ammonium salts of amines with acetates, chlorides or bromides as anions. Cationic part possess a long hydrocarbon chain and a positive charge on nitrogen atom. Hence, these are called cationic detergents. Cetyltrimethylammonium bromide is a popular cationic Cetyltrimethyl ammonium bromide detergent and is used in hair conditioners. Cationic detergents have germicidal properties and are expensive, therefore, these are of limited use.
Liquid dishwashing detergents are non-ionic type. Mechanism of cleansing action of this type of detergents is the same as that of soaps. These also remove grease and oil by micelle formation.
Main problem that appears in the use of detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily. Slow degradation of detergents leads to their accumulation. Effluents containing such detergents reach the rivers, ponds, etc. These persist in water even after sewage treatment and cause foaming in rivers, ponds and streams and their water gets polluted.
These days the branching of the hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded more easily and hence pollution is prevented.
16.4 Write the chemical equation for preparing sodium soap from glyceryl oleate and glyceryl palmitate. Structural formulae of these compounds are given below.
(i) (C15H31COO)3C3H5 – Glyceryl palmitate
(ii) (C17H32COO)3C3H5 – Glyceryl oleate
16.5 Following type of non-ionic detergents are present in liquid detergents, emulsifying agents and wetting agents. Label the hydrophilic and hydrophobic parts in the molecule. Identify the functional group(s) present in the molecule.
Chemistry is essentially the study of materials and the development of new materials for the betterment of humanity. A drug is a chemical agent, which affects human metabolism and provides cure from ailment. If taken in doses higher than recommended, these may have poisonous effect. Use of chemicals for therapeutic effect is called chemotherapy. Drugs usually interact with biological macromolecules such as carbohydrates, proteins, lipids and nucleic acids. These are called target molecules. Drugs are designed to interact with specific targets so that these have the least chance of affecting other targets. This minimises the side effects and localises the action of the drug. Drug chemistry centres around arresting microbes/destroying microbes, preventing the body from various infectious diseases, releasing mental stress, etc. Thus, drugs like analgesics, antibiotics, antiseptics, disinfectants, antacids and tranquilizers are used for specific purpose. To check the population explosion, antifertility drugs have also become prominent in our life.
Food additives such as preservatives, sweetening agents, flavours, antioxidants, edible colours and nutritional supplements are added to the food to make it attractive, palatable and add nutritive value. Preservatives are added to the food to prevent spoilage due to microbial growth. Artificial sweeteners are used by those who need to check the calorie intake or are diabetic and want to avoid taking sucrose.
These days, detergents are much in vogue and get preference over soaps because they work even in hard water. Synthetic detergents are classified into three main categories, namely: anionic, cationic and non-ionic, and each category has its specific uses. Detergents with straight chain of hydrocarbons are preferred over branched chain as the latter are non-biodegradable and consequently cause environmental pollution.
16.1 Why do we need to classify drugs in different ways ?
16.2 Explain the term, target molecules or drug targets as used in medicinal chemistry.
16.3 Name the macromolecules that are chosen as drug targets.
16.4 Why should not medicines be taken without consulting doctors ?
16.5 Define the term chemotherapy.
16.6 Which forces are involved in holding the drugs to the active site of enzymes ?
16.7 While antacids and antiallergic drugs interfere with the function of histamines, why do these not interfere with the function of each other ?
16.8 Low level of noradrenaline is the cause of depression. What type of drugs are needed to cure this problem ? Name two drugs.
16.9 What is meant by the term ‘broad spectrum antibiotics’ ? Explain.
16.10 How do antiseptics differ from disinfectants ? Give one example of each.
16.11 Why are cimetidine and ranitidine better antacids than sodium hydrogencarbonate or magnesium or aluminium hydroxide ?
16.12 Name a substance which can be used as an antiseptic as well as disinfectant.
16.13 What are the main constituents of dettol ?
16.14 What is tincture of iodine ? What is its use ?
16.15 What are food preservatives ?
16.16 Why is use of aspartame limited to cold foods and drinks ?
16.17 What are artificial sweetening agents ? Give two examples.
16.18 Name the sweetening agent used in the preparation of sweets for a diabetic patient.
16.19 What problem arises in using alitame as artificial sweetener ?
16.20 How are synthetic detergents better than soaps ?
16.21 Explain the following terms with suitable examples
(i) cationic detergents
(ii) anionic detergents and
(iii) non-ionic detergents.
16.22 What are biodegradable and non-biodegradable detergents ? Give one example of each.
16.23 Why do soaps not work in hard water ?
16.24 Can you use soaps and synthetic detergents to check the hardness of water ?
16.25 Explain the cleansing action of soaps.
16.26 If water contains dissolved calcium hydrogencarbonate, out of soaps and synthetic detergents which one will you use for cleaning clothes ?
16.27 Label the hydrophilic and hydrophobic parts in the following compounds.
Answers to Some Intext Questions
16.1 Most of the drugs taken in doses higher than recommended may cause harmful effect and act as poison. Therefore, a doctor should always be consulted before taking medicine.
16.2 This statement refers to the classification according to pharmacological effect of the drug because any drug which will be used to counteract the effect of excess acid in the stomach will be called antacid.
I. Multiple Choice Questions (Type-I)
1. Which of the following statements is not correct.
(i) Some antiseptics can be added to soaps.
(ii) Dilute solutions of some disinfectants can be used as antiseptic.
(iii) Disinfectants are antimicrobial drugs.
(iv) Antiseptic medicines can be ingested.
2. Which is the correct statement about birth control pills?
(i) Contain estrogen only.
(ii) Contain progesterone only.
(iii) Contain a mixture of estrogen and progesterone derivatives.
(iv) Progesterone enhances ovulation.
3. Which statement about aspirin is not true
(i) Aspirin belongs to narcotic analgesics.
(ii) It is effective in relieving pain.
(iii) It has antiblood clotting action.
(iv) It is a neurologically active drug.
4. The most useful classification of drugs for medicinal chemists is _________.
(i) on the basis of chemical structure.
(ii) on the basis of drug action.
(iii) on the basis of molecular targets.
(iv) on the basis of pharmacological effect.
5. Which of the following statements is correct?
(i) Some tranquilisers function by inhibiting the enzymes which catalyse the degradation of noradrenaline.
(ii) Tranquilisers are narcotic drugs.
(iii) Transquilisers are chemical compounds that do not affect the message transfer from nerve to receptor.
(iv) Tranquilisers are chemical compounds that can relieve pain and fever.
6. Salvarsan is arsenic containing drug which was first used for the treatment of ____________.
7. A narrow spectrum antibiotic is active against _______________.
(i) gram positive or gram negative bacteria.
(ii) gram negative bacteria only.
(iii) single organism or one disease.
(iv) both gram positive and gram negative bacteria.
8. The compound that causes general antidepressant action on the central nervous system belongs to the class of _____________.
(iii) narcotic analgesics
9. Compound which is added to soap to impart antiseptic properties is __________.
(i) sodium laurylsulphate
(ii) sodium dodecylbenzenesulphonate
10. Equanil is __________.
(i) artificial sweetener
(iv) antifertility drug
11. Which of the following enhances leathering property of soap?
(i) Sodium carbonate
(ii) Sodium rosinate
(iii) Sodium stearate
(iv) Trisodium phosphate
12. Glycerol is added to soap. It functions ______________.
(i) as a filler.
(ii) to increase leathering.
(iii) to prevent rapid drying.
(iv) to make soap granules.
13. Which of the following is an example of liquid dishwashing detergent?
14. Polyethyleneglycols are used in the preparation of which type of detergents?
(i) Cationic detergents
(ii) Anionic detergents
(iii) Non-ionic detergents
15. Which of the following is not a target molecule for drug function in body?
16. Which of the following statements is not true about enzyme inhibitors?
(i) Inhibit the catalytic activity of the enzyme.
(ii) Prevent the binding of substrate.
(iii) Generally a strong covalent bond is formed between an inhibitor and an enzyme.
(iv) Inhibitors can be competitive or non-competitive.
17. Which of the following chemicals can be added for sweetening of food items at cooking temperature and does not provide calories?
18. Which of the following will not enhance nutritional value of food?
(ii) Artificial sweeteners
II. Multiple Choice Questions (Type-II)
Note : In the following questions two or more options may be correct.
19. Which of the following statements are incorrect about receptor proteins?
(i) Majority of receptor proteins are embedded in the cell membranes.
(ii) The active site of receptor proteins opens on the inside region of the cell.
(iii) Chemical messengers are received at the binding sites of receptor proteins.
(iv) Shape of receptor doesn’t change during attachment of messenger.
20. Which of the following are not used as food preservatives?
(i) Table salt
(ii) Sodium hydrogencarbonate
(iii) Cane sugar
(iv) Benzoic acid
21. Compounds with antiseptic properties are ______________.
(iii) Boric acid
(iv) 0.3 ppm aqueous solution of Cl2
22. Which of the following statements are correct about barbiturates?
(i) Hypnotics or sleep producing agents.
(ii) These are tranquilizers.
(iii) Non-narcotic analgesics.
(iv) Pain reducing without disturbing the nervous system.
23. Which of the following are sulpha drugs?
24. Which of the following are antidepressants?
25. Which of the following statements are incorrect about penicillin?
(i) An antibacterial fungus.
(ii) Ampicillin is its synthetic modification.
(iii) It has bacteriostatic effect.
(iv) It is a broad spectrum antibiotic.
26. Which of the following compounds are administered as antacids?
(i) Sodium carbonate
(ii) Sodium hydrogencarbonate
(iii) Aluminium carbonate
(iv) Magnesium hydroxide
27. Amongst the following antihistamines, which are antacids?
28. Veronal and luminal are derivatives of barbituric acid which are __________.
(ii) Non-narcotic analgesic
(iii) Antiallergic drugs
(iv) Neurologically active drugs
29. Which of the following are anionic detergents?
(i) Sodium salts of sulphonated long chain alcohol.
(ii) Ester of stearic acid and polyethylene glycol.
(iii) Quarternary ammonium salt of amine with acetate ion.
(iv) Sodium salts of sulphonated long chain hydrocarbons.
30. Which of the following statements are correct?
(i) Cationic detergents have germicidal properties
(ii) Bacteria can degrade the detergents containing highly branched chains.
(iii) Some synthetic detergents can give foam even in ice cold water.
(iv) Synthetic detergents are not soaps.
III. Short Answer Type
31. What is the average molecular mass of drugs?
32. Write the uses of medicines.
33. What are antiseptics?
34. Which type of drugs come under antimicrobial drugs?
35. Where are receptors located?
36. What is the harmful effect of hyperacidity?
37. Which site of an enzyme is called allosteric site?
38. What type of forces are involved in binding of substrate to the active site of enzyme?
39. What is the commonality between the antibiotic arsphenamine and azodye?
40. Which class of drugs is used in sleeping pills?
41. Aspirin is pain relieving antipyretic drug but can be used to prevent heart attack. Explain.
42. Both antacids and antiallergic drugs are antihistamines but they cannot replace each other. Explain why?
43. What is a soft soap?
44. If soap has high alkali content it irritates skin. How can the amount of excess alkali be determined? What can be the source of excess alkali?
45. Explain why some times foaming is seen in river water near the place where sewage water is poured after treatment?
46. Which category of the synthetic detergents is used in toothpaste?
47. Hair shampoos belong to which class of synthetic detergent?
48. Dishwashing soaps are synthetic detergents. What is their chemical nature?
49. Draw the diagram showing micelle formation by the following detergent.
50. How does the branching of hydrocarbon chain of synthetic detergents affect their biodegradability?
51. Why is it safer to use soap from the environmental point of view?
52. What are analgesics?
53. What is the scientific explanation for the feeling of depression?
54. What is the basic difference between antiseptics and disinfectants?
55. Between sodiumhydrogencarbonate and magnesium hydroxide which is a better antacid and why?
56. Which analgesics are called opiates?
57. What is the medicinal use of narcotic drugs?
58. What are antagonistic drugs?
59. What is the mode of action of antimicrobial drugs?
60. What is the side product of soap industry? Give reactions showing soap formation.
61. What is the difference between bathing soap and washing soaps?
62. How are transparent soaps manufactured?
63. What is the advantage of using antihistamines over antacids in the treatment of acidity?
64. What are the functions performed by histamine in the body?
65. With the help of an example explain how do tranquilizers control the feeling of depression?
66. Why are certain drugs called enzyme inhibitors?
67. What are fillers and what role these fillers play in soap?
68. Sugar is the main source of energy as it produces energy on metabolic decomposition. But these days low calorie drinks are more popular, why?
69. Pickles have a long shelf life and do not get spoiled for months, why?
70. What is the difference between saccharin and saccharic acid?
71. Name an artificial sweetener which is derivative of sucrose.
72. Name two α-amino acids which form a dipeptide which is 100 times more sweet than cane sugar?
73. Aspartame is unstable at cooking temperature, where would you suggest aspartame to be used for sweetening?
74. Sodium salts of some acids are very useful as food preservatives. Suggest a
few such acids.
75. Explain the role of allosteric site in enzyme inhibition?
76. How are receptor proteins located in the cell membrane?
77. What happens when the bond formed between an enzyme and an inhibitor is a strong covalent bond?
IV. Matching Type
Note : Match the items given in Column I with the items given in Column II.
78. Match the medicines given in Column I with their use given in Column II.
|Column I||Column II|
79. Match the soaps given in Column I with items given in Column II.
|Column I||Column II|
|(i)||Soap chips||(a)||dried miniature soap bubbles|
|(ii)||Soap granules||(b)||small broken pieces of soap formed from melted soaps|
|(iii)||Soap powder||(c)||soap powder + abrasives + builders (Na2CO3, Na3PO4)|
|(iv)||Scouring soap||(d)||soap powder + builders like Na2CO3 and Na3PO4|
80. Match structures given in Column I with the type of detergents given in Column II.
|Column I||Column II|
81. Match the detergents given in Column I with their uses given in Column II.
82. Match the class of compounds given in Column I with their functions given in Column II.
|Column I||Column II|
|(i)||Antagonists||(a)||Communicate message between two neurons and that between neurons to muscles|
|(ii)||Agonists||(b)||Bind to the receptor site and inhibit its natural function|
|(iii)||Chemical messenger||(c)||Crucial to body’s communication process|
|(iv)||Inhibitors||(d)||Mimic the natural messenger|
|(v)||Receptors||(e)||Inhibit activities of enzymes.|
83. Match the classes of drugs given in Column I with their action given in Column II.
|Column I||Column II|
|(i)||Analgesics||(a)||Inhibit the growth of microorganisms can be given orally.|
|(ii)||Antiseptics||(b)||Treatment of stress|
|(iii)||Antihistamines||(c)||Applied to inanimate objects|
|(iv)||Antacids||(d)||Prevents the interaction of histamine with its receptor|
|(v)||Tranquilisers||(e)||Pain killing effect|
|(vi)||Antibiotics||(f)||Applied to diseased skin surfaces|
|(vii)||Disinfectants||(g)||Treatment of acidity|
V. Assertion and Reason Type
Note : In the following questions a statement of assertion followed by a
statement of reason is given. Choose the correct answer out of the following
(i) Assertion and reason both are correct statement but reason does not explain assertion.
(ii) Assertion and reason both are correct and reason explains the assertion.
(iii) Both assertion and reason are wrong statement.
(iv) Assertion is correct statement reason is wrong statement.
(v) Assertion is wrong statement reason is correct statement.
84. Assertion : Penicillin (G) is an antihistamine
Reason : Penicillin (G) is effective against gram positive as well as gram negative bacteria.
85. Assertion : Sulpha drug contain sulphonamide group.
Reason : Salvarsan is a sulpha drug.
86. Assertion : Receptors are crucial to body’s communication process.
Reason : Receptors are proteins.
87. Assertion : Enzymes have active sites that hold substrate molecule for a chemical reaction.
Reason : Drugs compete with natural substrate by attaching covalently to the active site of enzyme.
88. Assertion : Chemical messengers are chemicals that enable communication of message between two neurons or between neurons and muscles.
Reason : Chemicals enter the cell through receptor.
89. Assertion : Transparent soaps are made by dissolving soaps in ethanol.
Reason : Ethanol makes things invisible.
90. Assertion : Sodium chloride is added to precipitate soap after saponification.
Reason : Hydrolysis of esters of long chain fatty acids by alkali produces soap in colloidal form.
91. Assertion : Competitive inhibitors compete with natural substrate for their attachment on the active sites of enzymes.
Reason : In competitive inhibition, inhibitor binds to the allosteric site of the enzyme.
92. Assertion : Non-competitive inhibitor inhibits the catalyic activity of enzyme by binding with its active site.
Reason : Non-competitive inhibitor changes the shape of the active site in such a way that substrate can’t recognise it.
93. Assertion : Chemical messenger gives message to the cell without entering the cell.
Reason : Chemical messenger is received at the binding site of receptor proteins.
94. Assertion : Receptor proteins show selectivity for one chemical messenger over the other.
Reason : Chemical messenger binds to the receptor site and inhibits its natural function.
95. Assertion : All chemicals added to food items are called food preservatives.
Reason : All these chemicals increase the nutritive value of the food.
96. Assertion : Preservative are added to food items.
Reason : Preservatives inhibit the growth of microorganisms.
97. Assertion : Artificial sweeteners are added to the food to control the intake of calories.
Reason : Most of the artificial sweeteners are inert and do not metabolise in the body.
VI. Long Answer Type
98. In what respect do prontosil and salvarsan resemble. Is there any resemblance between azo dye and prontsil? Explain.
99. How do enzymes catalyse a chemical reaction in the living system? Explain drug target interaction taking the example of enzyme as target.
100. Synthetic detergents have advantage over usual soaps as far as cleansing power is concerned. But use of synthetic detergents over a long time creates environmental pollution. How can the pollution caused by synthetic detergents
be minimised? Classify the detergents according to their chemical nature.
101. What are enzyme inhibitors? Classify them on the basis of their mode of attachments on the active site of enzymes. With the help of diagrams explain how do inhibitors inhibit the enzymatic activity.
I. Multiple Choice Questions (Type-I)
1. (iv) 2. (iii) 3. (i) 4. (iii) 5. (i) 6. (i) 7. (i) 8. (ii) 9. (iv) 10. (ii) 11. (ii) 12. (iii) 13. (ii) 14. (iii) 15. (iii) 16. (iii) 17. (iv) 18. (ii)
II. Multiple Choice Questions (Type-II)
19. (ii), (iv) 20. (i), (iii) 21.(ii), (iii) 22. (i), (ii) 23. (i), (ii) 24. (i), (ii), (iii) 25. (iii), (iv) 26. (ii), (iv) 27. (i), (iv) 28. (i), (iv) 29. (i), (iv) 30. (i), (iii), (iv)
III. Short Answer Type
32. Medicines are used in diagnosis, prevention and treatment of diseases.
33. Antiseptics are chemicals which either kill or prevent the growth of microorganisms and are applied to living tissues.
34. Antiseptics, antibiotics and disinfectants.
35. Receptors are embedded in cell membrane.
36. Ulcer development in stomach.
37. Sites different from active site of enzyme where a molecule can bind and affect the active site is called allosteric site. Some drugs may also bind at this site.
38. Ionic bonding, hydrogen bonding, van der Waals interaction, dipole-dipole interaction.
39. Arsphenamine possesses —As=== As— linkage that resembles —N=== N—linkages in azodyes.
41. Aspirin prevents platelet coagulation and thus has antiblood clotting action therefore can prevent blood clogging in heart.
42. See page no. 444 of NCERT textbook for Class XII.
43. These are potassium salts of fatty acids.
44. Acid-base titration can be used to determine the excess amount of alkali in soap. The excess alkali left after hydrolysis of oil can be the source of alkalinity in soap.
45. Detergents persist in water even after sewage treatment and cause foaming in river water.
46. Anionic detergent.
47. Cationic detergent.
48. Non-ionic detergents
50. Less branching leads to easy biodegradability.
51. Soaps are biodegradable while detergents are quite stable because of branching in hydrocarbon chain hence cause water pollution.
52. Analgesics are neurologically active pain killing drugs that reduce or abolish pain without causing impairment of consciousness, mental confusion, coordination or paralysis or some other disturbances of nervous system.
53. A person suffers from depression when he has low levels of noradrenaline. Noradrenaline is a neurotransmitter that plays a role in mood changes. Low levels of noradrenaline lower the signal-sending activity and make the person suffer from depression.
54. Antiseptics are applied to living tissues whereas disinfectants are applied to non living objects.
55. Magnesium hydroxide is a better antacid because being insoluble it does not allow the pH to increase above neutral. Hydrogencarbonate being soluble, its excess can make the stomach alkaline and trigger the production of even more acid.
56. Narcotic analgesics which are obtained from opium poppy are called opiates. Examples are morphine and its derivatives like heroin and codeine.
57. Since narcotic drugs relieve pain and produce sleep, these are chiefly used for the relief of postoperative pain, cardaic pain and pain of terminal cancer and in child birth.
58. Drugs that bind to the receptor site and inhibit its natural function are called antagonistic drugs.
59. Antimicrobial drugs can kill the microorganism such as bacteria, virus, fungi or other parasites. They can, alternatively, inhibit the pathogenic action of microbes.
60. [Hint : Glycerol.]
61. Bathing soaps are potassium salts of long chain fatty acids while washing soaps are sodium salts of long chain fatty acids.
62. Dissolving soap in ethanol followed by evaporating the excess solvent.
63. Antacids control only the symptoms and not the cause. They work by neutralising the acid produced in the stomach. They do not control the cause of production of more acid. Antihistamines are the drugs that suppress the action of histamine which is the chemical responsible for stimulation of secretion of pepsin and HCl in the stomach. Antihistamines influence and prevent the binding of histamine with the receptors present in the stomach wall resulting in lower acid production and therefore, better treatment.
64. Histamine is a potent vasodilator. It contracts muscles in the gut and bronchi. It relaxes some other muscles e.g. in the walls of blood vessels. Histamine is also responsible for congestion in the nose associated with
common cold and allergies. Also, histamine stimulates the release of pepsin and hydrochloric acid in the stomach.
65. See Class-XII NCERT, textbook page no. 444.
66. Enzymes have active sites that bind the substrate for effective and quick chemical reaction. The functional groups present at the active site of enzyme interact with functional groups of substrate via ionic bonding, hydrogen bonding, van der Waal interaction etc. Some drugs interfere with this interaction by blocking the binding site of enzyme and prevent the binding of actual substrate with enzyme. This inhibits the catalytic activity of the enzyme, therefore, these are called inhibitors.
67. Some substances are added to soap to affect the properties in order to make it useful for a particular application. Examples are sodium rosinate, sodium carbonate, etc. Sodium rosinate is added in laundry soaps, to increase lather and glycerol is added in shaving soaps, to prevent it from drying.
68. [Hint : In such drinks artificial sweetening agents are present which do not metabolise hence do not produce any energy.]
69. [Hint : Plenty of salt and cover of oil act as preservative. These do not allow bacteria to thrive on them.]
72. Aspartic acid and phenylalanine.
73. In cold foods and soft drinks.
74. Benzoic acid, sorbic acid, propanoic acid.
75. Hint : For answer see page no. 441 of NCERT textbook for Class XII.
76. Hint : For answer see page no. 442 of NCERT textbook for Class XII.
77. Hint : For answer see page no. 442 of NCERT textbook for Class XII.
IV. Matching Type
78. (i) → (c) (ii) → (d) (iii) → (a) (iv) → (b)
79. (i) → (b) (ii) → (a) (iii) → (d) (iv) → (c)
80. (i) → (c) (ii) → (d) (iii) → (b) (iv) → (a)
81. (i) → (c) (ii) → (d) (iii) → (b) (iv) → (a)
82. (i) → (b) (ii) → (d) (iii) → (a) (iv) → (e) (v) → (c)
83. (i) → (e) (ii) → (f) (iii) → (d) (iv) → (g) (v) → (b) (vi) → (a) (vii) → (c)
V. Assertion and Reason Type
84. (iii) 85. (iv) 86. (i) 87. (iv) 88. (iv) 89. (iv) 90. (ii) 91. (iv) 92. (v) 93. (ii) 94. (iv) 95. (iii) 96. (ii) 97. (ii)
VI. Long Answer Type
98. Hint: For answer see NCERT textbook for Class XII.
99. Hint: For answer see NCERT textbook for Class XII.
100. Hint: For answer see NCERT textbook for Class XII.
101. Hint: For answer see NCERT textbook for Class XII.