After studying this Unit you will be

able to

• visualise the importance of

Chemistry in daily life;

• explain the term ‘chemotherapy’;

• describe the basis of classification

of drugs;

• explain drug-target interaction of

enzymes and receptors;

• explain how various types of

drugs function in the body;

• know about artificial sweetening

agents and food preservatives;

• discuss the chemistry of cleansing

agents.

Objectives

From living perception to abstract thought, and from this to practice.

V.I. Lenin.

Unit

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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.

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. Most of the drugs used as medicines are potential

poisons, if taken in doses higher than those recommended. Use of

chemicals for therapeutic effect is called chemotherapy.

16.116.1

16.1

Drugs andDrugs and

Drugs and

their

theirtheir

their

ClassificationClassification

Classification

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448Chemistry

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.

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.

Structural features of sulphonamides

(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.

Macromolecules of biological origin perform various functions in the

body. For example, proteins which perform the role of biological catalysts

in the body are called enzymes, those which are crucial to

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.

(a) Catalytic action of enzymes

For understanding the interaction between a drug and an enzyme,

it is important to know how do 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.

16.1.1

Classification of

Drugs

16.216.2

16.2

Drug-TargetDrug-Target

Drug-Target

InteractionInteraction

Interaction

16.2.1 Enzymes

as Drug

Targets

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449 Chemistry in Everyday Life

Fig. 16.2

Drug and substrate

competing for active

site

(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;

(i) Drugs compete with the natural substrate for their attachment

on the active sites of enzymes. Such drugs are called competitive

inhibitors (Fig. 16.2).

Fig. 16.1

(a) Active site of an

enzyme (b) Substrate

active site of the

enzyme

(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

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).

Fig. 16.3: Non-competitive inhibitor changes the active

site of enzyme after binding at allosteric site.

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450Chemistry

cannot be broken easily, then the enzyme is blocked permanently.

The body then degrades the enzyme-inhibitor complex and

synthesises the new enzyme.

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).

16.2.2 Receptors

as Drug

Targets

Fig. 16.4

Receptor protein

embedded in the cell

membrane, the

active site of the

receptor opens on

the outside region of

the cell.

Fig. 16.5: (a) Receptor receiving chemical messenger

(b) Shape of the receptor changed after attachment of messenger

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.

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).

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451 Chemistry in Everyday Life

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.

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.

16.316.3

16.3

Therapeutic Action ofTherapeutic Action of

Therapeutic Action of

Different Classes of DrugsDifferent Classes of Drugs

Different Classes of Drugs

16.3.1 Antacids

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

16.3.2

Antihistamines

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452Chemistry

of histamine by competing

with histamine for binding

sites of receptor where

histamine exerts its effect.

Now the question that

arises is, “Why do above

mentioned antihistamines not

affect the secretion of acid in

stomach?” The reason is that

antiallergic and antacid drugs

work on different receptors.

16.3.3

Neurologically

Active Drugs

(a) Tranquilizers

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.

Some tranquilizers namely, chlordiazepoxide and meprobamate,

are relatively mild tranquilizers suitable for relieving tension. Equanil

is used in controlling depression and hypertension.

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453 Chemistry in Everyday Life

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.

(b) Analgesics

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.

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454Chemistry

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.

(a) Antibiotics

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

16.3.4

Antimicrobials

The structures of salvarsan, prontosil azodye and sulphapyridine showing structural

similarity.

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455 Chemistry in Everyday Life

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.

Antibiotics have either cidal (killing) effect or a static (inhibitory) effect

on microbes. A few examples of the two types of antibiotics are as follows:

Bactericidal Bacteriostatic

Penicillin Erythromycin

Aminoglycosides Tetracycline

Ofloxacin Chloramphenicol

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.

H.W. Florey and

Alexander Fleming

shared the Nobel prize

for Medicine in 1945 for

their independent

contributions to the

development of

penicillin.

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456Chemistry

(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. Boric

acid 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.

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).

16.3.5

Antifertility Drugs

Intext QuestionsIntext Questions

Intext Questions

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?

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457 Chemistry in Everyday Life

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

(v) Antioxidants

(vi) Preservatives

(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.

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.

16.416.4

16.4

ChemicalsChemicals

Chemicals

in Foodin Food

in Food

16.4.1 Artificial

Sweetening

Agents

Table 16.1: Artificial Sweeteners

Artificial Structural formula Sweetness value in

sweetener comparison to cane sugar

Aspartame 100

Saccharin 550

Sucralose 600

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458Chemistry

16.4.2 Food

Preservatives

Alitame 2000

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.

Sucralose 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.

The most commonly used preservatives include table salt, sugar,

vegetable oils and sodium benzoate, C

COONa. 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.

These are important and necessary food additives. These help in food

preservation by retarding the action of oxygen on food. These are more

reactive towards oxygen than the food material which they are

protecting. The two most familiar antioxidants are butylated hydroxy

toluene (BHT) and butylated hydroxy anisole (BHA). The addition of

BHA to butter increases its shelf life from months to years.

Sometimes BHT and BHA along with citric acid are added to

produce more effect. Sulphur dioxide and sulphite are useful

antioxidants for wine and beer, sugar syrups and cut, peeled or dried

fruits and vegetables.

Intext QuestionIntext Question

Intext Question

16.3 Why do we require artificial sweetening agents ?

16.4.3 Antioxidants

in Food

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.

16.5.1 Soaps

16.516.5

16.5

CleansingCleansing

Cleansing

AgentsAgents

Agents

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459 Chemistry in Everyday Life

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?

Hard water contains calcium and magnesium ions. These ions form

insoluble calcium and magnesium soaps respectively when sodium or

potassium soaps are dissolved 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.

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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.

16.5.2 Synthetic

Detergents

CH (CH )

3 2 11

H SO

2 4

CH (CH )

3 2 11

SO H

NaOH(aq)

CH (CH )

3 2 11

SO Na

Dodecylbenzene

Dodecylbenzenesulphonic acid Sodium dodecylbenzenesulphonate

CH (CH )

3 2 15

Cetyltrimethyl ammonium bromide

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

detergent and is used in hair

conditioners.

Cationic detergents have germicidal properties and are expensive,

therefore, these are of limited use.

(iii) Non-ionic Detergents: Non-ionic detergents do not contain any ion

in their constitution. One such detergent is formed when stearic

acid reacts with polyethyleneglycol.

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.

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461 Chemistry in Everyday Life

Intext QuestionsIntext Questions

Intext Questions

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) (C

COO)

– Glyceryl palmitate

(ii) (C

COO)

– 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.

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.

SummarySummary

Summary

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

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462Chemistry

Exercises

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.

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.

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463 Chemistry in Everyday Life

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.

16.5

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.

(i)

(ii)

(iii)

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